Deleted gearcase thread issue
Deleted gearcase thread issue
(OP)
On Mike's suggestion, I have asked admin of the forum to delete the thread. But we can discuss that here
Desert forx post
"What grade of bolt is it ie whats its proof load? img511 and 514 don't work.
I assume the bolts are in tapped holes?
Could be a number of things like you have already mentioned
vibration;cyclic loading.
If the bolt pre-load is not high enough the bolts can loosen
off under vibration and subsquently fail in fatigue.
Have you any of the failed screws? if so post a pic.
In addition if your truely getting 80% - 90% of proof load on all bolts it doesn't give you much room for increasing
bolt tension unless you use a higher strength material.
Finally the bolts will not see equal tension , shear etc
for a given engine position: but depending on engine position and external force position at a particular point in time the bolts will share the load unequally.
"
Yes the bolts are in tapped holes and the holes are blind. Bolts dont break, they just come loose or missing.
6 Bolts,joint and proof load info
4 perimeter bolts (Bolt 1-4) – 3/8-16 (1.75 in) unc-2A stainless steel plated(tq spec – 27 ft-lb target)-min proof load - 8370 lbs
1 bolt in center- 3/8-16 (3.5 in) unc-2A stainless steel(tq spec – 27 ft-lb target)-min proof load -8716
1 bolt in center– 7/16-14 (3.5 in) unc-2A stainless steel(tq spec – 47 ft-lb target)-min proof load - 9567
Desertfox you saw one of the pic which is been deleted now right.Did that give u an idea about the joint?
Desert forx post
"What grade of bolt is it ie whats its proof load? img511 and 514 don't work.
I assume the bolts are in tapped holes?
Could be a number of things like you have already mentioned
vibration;cyclic loading.
If the bolt pre-load is not high enough the bolts can loosen
off under vibration and subsquently fail in fatigue.
Have you any of the failed screws? if so post a pic.
In addition if your truely getting 80% - 90% of proof load on all bolts it doesn't give you much room for increasing
bolt tension unless you use a higher strength material.
Finally the bolts will not see equal tension , shear etc
for a given engine position: but depending on engine position and external force position at a particular point in time the bolts will share the load unequally.
"
Yes the bolts are in tapped holes and the holes are blind. Bolts dont break, they just come loose or missing.
6 Bolts,joint and proof load info
4 perimeter bolts (Bolt 1-4) – 3/8-16 (1.75 in) unc-2A stainless steel plated(tq spec – 27 ft-lb target)-min proof load - 8370 lbs
1 bolt in center- 3/8-16 (3.5 in) unc-2A stainless steel(tq spec – 27 ft-lb target)-min proof load -8716
1 bolt in center– 7/16-14 (3.5 in) unc-2A stainless steel(tq spec – 47 ft-lb target)-min proof load - 9567
Desertfox you saw one of the pic which is been deleted now right.Did that give u an idea about the joint?





RE: Deleted gearcase thread issue
"First thing that came to mind is Spiralok taps, which are alleged to produce (modified form) threads that are extremely vibration resistant.
Second thing that came to mind is, I wonder if the grease on the threads in interfering with the operation of the locking patch. I'm interpreting "... wool greased and also low strength (pink color) no metallic lock patch " to mean "well greased threads with nonmetallic lock patch".
Third thing that came to mind is Loctite PST instead of grease. Belt, suspenders, and more suspenders...
"
Thanks for the suggestion on the issue and also about posting on public forums. I will be more carefull hereafter
Mintjulep post
"I agree with Mike that there are probably some nasty cyclic loads imposed by running with only one blade in the water.
I would suspect loss of preload due to embedment (I assume the case is cast aluminum, yes?)"
Yes cast aluminum case
RE: Deleted gearcase thread issue
For example we are using low srength loctite, I can go to high strength as it is lil cost, but I cant change the bolt and use loct fasteners.It will cost us more and our dept will not buy off.
Initiall I thought the failure is because of low preload in the joint.. But what if I found out (we will be checking the joint preload tomm) that we are actually having 90% of proof load in the joint and still we find loose bolts? what might be the other reasons other than low preload for loose or missing bolts?
RE: Deleted gearcase thread issue
If your setting the bolts by torque then your tensile load in fastener is quite open +/- 25% as I posted in the other thread about engine bolts yielding.
So you can be up or down by 25% before it even see's an external load.
When a joint is designed the pre-load is usually worked out on the basis of the various material strengths and the external loads the joint will see in service which is why we keep telling you to pester engineering dept.
It appears to me that your eng dept is just specifying 80% or 90% of the proof load for the bolt without consideration of anything else which is why your having so many problems
in the field.
To solve this problem somebody needs to do so serious stress
modeling or better still fit some strain gauges to the engine and run it like you say its being used and get some
practical data that can be used to calculate an accurate pre-load for the bolts.
Loss of pre-load as previously stated can be due to vibration, using torque to set pre-load, embedding of the head during tightening or in service, friction etc.
You say the material is Aluminium or do you mean the Alumium/Copper alloy as in the previous post?
Taking the 3/8" bolt and a regular plain washer form B I calculate the pressure under the washer 13288lbs/in^2 I have
no idea whether that would cause embedding unless you can tell us the yield stress for the connecting materials.
Finally as your using conventional washers the pre-load in the bolt can be affected greatly be relative lateral movement between bolt and washer ID which can change the friction surfaces from bolt head to washer, to washer and
joint surface; subsquently affecting the torque-tension relationship and hence the pre-load.
The bottom line is your engineering department have to take responsibility you cannot just do knee jerk quick fixes as you will find they have a habit of biting you in the bum.
regards
desertfox
RE: Deleted gearcase thread issue
Have you seen this?
http://www.nord-lock.com/video/nl_uk.wmv
Can you give us the material, grade etc. of
the stainless steel bolts. Have you tested
these?
RE: Deleted gearcase thread issue
Look at this video
ht
desertfox
RE: Deleted gearcase thread issue
I agree with you 100% about pestering the engg dept.But the problem is there I will have no answer from them and as a quality guy from plant , its ultimately my work to do that.But I will get some help from eng like strain gauging the bolts in field and letting me know the possible service loads. I already asked them to do this and they will be working on it.
the joint materials here are die cast Aluminum only.
I will try to find out the yeild stress of material.
I am looking forward for our preliminary clamp load study on the joint on monday.I will let u guys know the values.I am eager to see if we are installing them at 80-90% of clampload or not.
RE: Deleted gearcase thread issue
Have a look at this site it will give you some idea of whats involved doing an analsys for bolt fatigue.
http://
http://w
regards
desertfox
RE: Deleted gearcase thread issue
I.e., it's conceivable that the gearcase flange is stretching the bolts while trying to bend and/or separate itself from the exhaust housing.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deleted gearcase thread issue
High vibration. High temperature swings due to exhaust. Relatively soft joint material with a relatively high coefficient of thermal expansion. Blind tapped holes (that very probably are contaminated with cutting oil).
My SWAG at what is going on:
The surface finish of the mating surfaces of the joint, and any spotfaces or whatever for the fastener heads is relatively rough (and of a soft material).
The finish of the (cut?) threads in the blind tapped holes is rough.
The cutting lube used when tapping the holes is not being throughly cleaned out, rendering the Loctite ineffictive.
The soft and rough surfaces result in significant relaxation shortly after assembly, and continue to allow further embedment in service due to loading from thermal expansion and vibration.
Very soon all bolt preload is gone and the bolts fall out because of vibration.
Although I generally detest them, properly selected and applied Belleville springs might help in this situation.
Or perhaps even easier is to advise your "special needs" customers to scrap the stock fasteners and install self-locking fasteners per MIL-DTL-18240, Type L, along with daily retorque.
RE: Deleted gearcase thread issue
RE: Deleted gearcase thread issue
Thanks for the links.
Mike,
Yup, I requested them to run the field testwith worst conditions possible (single blade surfacing)
Mintjulep,
yes temperatures will be there in the exaust housing, but shoud be minimal, because it will get continous cooling in water. both housing and gearcase are die cast aluminum so theyare relatively soft. I am not sure about the un clean tapped threads and bolt underhead rough surfaces,but we use flat stainless steel washers under the bolt head. does it matter? But I will check for rough and unclean surfaces and letyou guys know.
when u say "The cutting lube used when tapping the holes is not being throughly cleaned out, rendering the Loctite ineffictive"
when loctite is ineffective,will loctite form as a gasket and comes off eventually and the boltgets loose?
Unclesyd,
we dontuse anyy sealing material between the two joint surfaces.
RE: Deleted gearcase thread issue
What size are the washers ie-outer and inner dia?
With this joint flanged hex heads or flat washer hex head bolts maybe better provided that the above have heads big enough not to cause embedding.
Flat washers can cause variation in pre-load for the reasons I gave in yesterdays post.
regards
desertfox
RE: Deleted gearcase thread issue
Yes the tapped holes are not really clean and we have a smooth finish under the bolt head surface of the joint.
Desertfox,
For 3/8 bolt washer ID is 0.391 +0.015/-0.005 and OD is 0.75 +0.015/-0.007
For 7/16 bolt washer ID is 0.453 +0.015/-0.005 and OD is 0.75 +0.015/-0.007
I don’t know if I can get you the yield stress of the die cast Aluminum, but will try.
RE: Deleted gearcase thread issue
Thanks for the response, can you not get the material grade for the aluminium of a drawing?
Also how can a quality department ensure the materials are
correct if you can't get material specifications.
Washer sizes noted.
regards
desertfox
RE: Deleted gearcase thread issue
RE: Deleted gearcase thread issue
Without knowing the results of your study on the clamping load produced by your assembly procedures/tools and any issues with dimensional or material specifications, I would venture a guess you are dealing with an application that exceeds the intent and/or capabilities of the design.
If materials, pre-load, and dimensions are to spec I would tend to think you have done your part as QA. Maybe if you can confirm that everything meets spec this will give you (or your boss) enough ammo to send the problem on to the design department or at least get assistance from them?
Seems like you are stuck trouble shooting a lot of design issues without the assistance of the design department. Sorry to hear that, it sucks getting stuck in a situation like that.
RE: Deleted gearcase thread issue
the lock patch we are using is a hard plastic kind of metallic/mechanical lock patch (yellow color)
RE: Deleted gearcase thread issue
The lock patch material can accumulate between the mating surfaces in the joint, almost like a gasket. After some time this build-up of patch material goes away and now you have a loose joint
do u guys think if the above cause is possible????
I as said the lock patch we are using is like a hard plastic lock patch (not liquid loctite)and they call it as mechanical lock patch
RE: Deleted gearcase thread issue
You could check the accumulation/ false gasket assertion by disassembling and inspecting a few units on the line.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deleted gearcase thread issue
yield stress of joint materials is 19ksi and tensile strength is 42ksi
RE: Deleted gearcase thread issue
Could you please explain how does a hard plastic mechanical lock patch will be ineffective if the cutting lube oil in the tapped hole is not cleaned?
and also could you please help me understand how wool grease effects this lock patch?
RE: Deleted gearcase thread issue
Loctite forms a chemical bond, on clean parts. On oily parts, it forms a weak bond, or none.
The plastic lock patch wedges the male threads to one side of the female threads, relying on friction between the threads (and some retention of strain energy in the plastic) to prevent loosening. Anything greasy, e.g. lanolin, is going to interfere with that locking to an even greater extent than the leftover cutting oil would.
I'm guessing the engineering dept. specified the lanolin because of excessive torque levels required to deform the plastic inserts without it. It's not sounding like a winner of an idea right now.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deleted gearcase thread issue
Great explanation. Thanks a lot.The hard plastic kind of lock patch we are using is called epoxy-lock.
Anyway, the other way of decribing this kind of behaviour is " There isn't enough friction in the joint to make the joint immune to vibration loosening" right????
so how low of a friction coefficient or K value should be minimum for a joint to not to loose under vibration?
RE: Deleted gearcase thread issue
I think that ND brand "epoxy-lock" smears epoxy on the bolt during assembly, in hope of forming a chemical bond. I can't see that happening in a greased joint, unless the lanolin has some special property such that it doesn't interfere with an epoxy bond.
I couldn't get into the ND website, which doesn't seem to have a non "Flash!" entry point.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deleted gearcase thread issue
ND epoxy-lock is a pre-applied adhesive thread locker.
(non-flash PDF of the sales sheet here mike: http://ww
Adhesives do not adhere to lanolin, cutting oil, grease or other lubricants.
I still think a proper plastic lock patch (MIL-DTL-18240, Type L) would be effective here. The plastic tends to work as a squeegee to clean out any lubricant from the female threads.
RE: Deleted gearcase thread issue
The epoxy-lock looks like it would work great, _if_ you clean out the cutting oil and don't grease the bolts, or limit the grease to the shanks and under the head.
I agree with Mint that the friction type plastic locks would probably hold the bolts well enough; my only concern with them is that they do nothing to exclude corrodents, e.g. seawater. Maybe _that's_ what the lanolin was intended to do. I'm real curious about the design intent, and any history the stuff may have at your outfit.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deleted gearcase thread issue
One of our lube doc says,
All IFI124 (non-metallic lock patch fasteners) shall be coated with wool grease heated to 200 F. But the mating parts, holes, nuts should be oil and residue free.
All IFI125 (chemical lock fasteners) shall be free of oil and residue and wool grease.
If epoxy lock is a non-metallic lock patch, it says we can use wool grease, is this wrong?
RE: Deleted gearcase thread issue
Epoxy-lock is a chemical adhesive lock, not a mechanical lock.
The patch that you see contains tiny capsules of liquid epoxy harder and resin. These capsules are embedded in the patch that you see.
When the fastener is threaded into a mating thread, the capsules are broken, the epoxy parts get mixed and are supposed to form a chemical expoxy bond between the male and female threads.
Epoxy does not adhere to oil, wax, lanolin and the like.
RE: Deleted gearcase thread issue
Thanks for explanation. Just for my knowledge, In case if the lock patch is not chemical patch and if it is a non-metallic mechanical lock patch, then does the wool grease effects the patch effectiveness? if yes why and how?
Thanks in advance
RE: Deleted gearcase thread issue
min proof load for this bolt is 8370 lbs. Other two bolts has the same avg.
So, this shows we are following our 80-90% of proof load.
for vibration looseining the extrenal loads should be more than our avg clamp load in the joint right?
I requested for field test and gotta see how much time its gonna take.
RE: Deleted gearcase thread issue
Take a look at the Handbook available for download here:
http://www.longlok.com/
You can also download the MIL-DTL-18240 spec there.
RE: Deleted gearcase thread issue
RE: Deleted gearcase thread issue
Your clamp load figures off 3 joints show a scatter of 4300lbs which is only about 51% of proof load and 9400lbs
which is 112% of proof load so if your tolerance is 80%-90%
of proof load your outside the spec.
In the thread where you pasted a torque fastening spec which you asked people to comment on there was mention of a formula for the constant K (friction constant) can you tell us what that formula is and what friction constant you are using in this case.
regards
desertfox
RE: Deleted gearcase thread issue
No the loads don't have too exceed your clamping force to come loose just the friction force between the two clamped joint surfaces.
regards
desertfox
RE: Deleted gearcase thread issue
http:
M – Assembly torque - 333 in-lbs
Fv – 90% of the proof load
P = pitch
d2 = PITCH DIA
DKM = DW+DH divided by 2
When I calculated K for our application, using our torque and collected clamp load data, It came up to 0.11 (this low friction is because of cad plating and also wool grease on the bolt)
Regarding vibration loosening theory, I thought if the external load exceeds the preload in the joint, then the joint comes loose. So am I wrong?
And also I wanna let you guys know that I observed the l/d ratio of the bolts is les than 8. It is actually 4.6. I read some where that of the l/d ratio is less than 8 then the bolt is susceptible for vibration looseining.
RE: Deleted gearcase thread issue
I can't see the file you have posted till friday evening.
Imagine two plates clamped together the bolt axis vertical,now if you try and push the plates at 90 degrees to the bolt axis relative to each other you only need to exceed the friction force generated by the bolt pre-load.
Roughly speaking lets say your clamp load is 100lbs now to slide one plate over the other you only need:-
mu * 100lb = .25*100lb = 25lb
mu= coefficient of friction and not to be confused with K the friction factor for bolt torque calcs.
Not sure about your l/d ratio I have never heard of that.
regards
desertfox
RE: Deleted gearcase thread issue
l/d ratio = 3.50/.375 = 9.333 ?????
or
l/d ratio = (3.50 - .81)/.375 = 7.173 ?????
RE: Deleted gearcase thread issue
Over all friction Mu = numerator/denominator
Numerator = M/F – 0.159 * Pitch
Denominator = 0.578 * pitch dia + (Dkm/2)
Where DKM = DW+DH divided by 2 = effective bearing dia of bolt
RE: Deleted gearcase thread issue
Numerator = [0.16* Pitch + O.58*Pitch dia* Mu + (Dkm*Mu/2)]
Denominator = D = nominal dia of bolt
RE: Deleted gearcase thread issue
But when I referred to a bolted joint book, it says unless the external service load is more than the joint clamp loads, the joint wont come loose. It says, for example if the joint clamp load is 12000 lbs and the external service loads acting on the joint is 10,000 lbs then the joint wont come loose. Is this principle only good for vibrations?
And when there is transverse loading(transverse slip), even smaller loads than clamp load would make the joint loose?
RE: Deleted gearcase thread issue
from your earlier posting,
9300lb/0.0775 = 120000 psi the 0.0775 square inches is the stress area for your bolt.
For steels up to 100000 psi .0775 square inches is correct. As = pi/4 (D - .9743/n)^2
For steels over 100000 psi .0678 square inches is correct. As = pi (Dpe/2 - .162/n)^2
Dpe = Min. Pitch Dia. n = No. of threads per inch. Yields 8136lb/0.0678 = 120000 psi.
if we are now talking (4500lb pre-load) with the infomation we now have, I calculate that to achieve this pre-load you would need to stretch a 3.5 inch length bolt 0.0047534”
Going back to the earlier calculations which I uploaded, I now calculate that to achieve a 4500lb pre-load you will need about 21ft-lbs of torque with an assumed K of 0.1497
which is unlubricated.
?*L/E = x (deflection)
where ?=stress= F/A approx (4500*4)/(3.142*0.375^2) = 40744 psi
L= bolt length 3.500
E = modulus elasticity Bolt= 30*10^6 psi
E = modulus elasticity Casting= 10.3*10^6 psi
Punching this through the calc gives: x= 0.0047534" assumes steel & steel.
Should x be almost triple that value to agree with the
different modulus values or are experiments necessary
to confirm those values?
RE: Deleted gearcase thread issue
One thing got cleared to me now ,
If an external load is tensile or axial load, then the external load should be more than clamp load to make the joint loose.
But if the external load is transverse vibration load, then to make the joint loose, the external load need not be more than clamp load of the joint
If I understand the whole thing right, then
If I have a clamp force of 1000 lb in the joint and my frictional force in joint is for example 0.25*1000 = 250 lbs.
A transverse load of anything more than 250 lbs can make my joint loose, even though I have a 1000 lb of clamp force in the joint.
Am I right???????
RE: Deleted gearcase thread issue
Our production clamp load studies says K = 0.11 and torque is 27 ft-lb.The length of bolt is 1.75 in.
not to get confused, though we have
3/8 x 1.75 in - 4 bolts used in assembly
3/8 x 3.5 in - 1 bolt used in assembly in the center
we are here talking about 3/8 x 1.75 in bolt because these bolts are used on perimter of the joint and are the weakest link in the joint.
RE: Deleted gearcase thread issue
Sorry, looks like I jumped threads.
RE: Deleted gearcase thread issue
Yes your right with your post ref J.bickford.
Hi dimjim will respond later just starting work now.
desertfox
RE: Deleted gearcase thread issue
According is Bickford (chapter 20 page 735, an intro to the design and behavior of bolted joints) joint slip can be prevented if
F is greater than or equal to Mu * L
F= clamp force in joint
Mu – friction coef
L – external "transverse" load (not the whole external load)
Now if we go by an example,
External transverse loads = 7500 lbs
Mu = 0.2
Then clamp force should be greater than or equal to 1500 lbs
How come external loads are more than joint clamp load?
RE: Deleted gearcase thread issue
I haven't reference to Bickford I only mentioned it earlier so you could see which of your posts I was refering too.
I think you have your numbers in your last post the wrong way round ie:-
F/N =mu
N= normal reaction (clamp load)= 1500lbs
F= sliding force or transverse force
mu= coeff of friction = 0.25
F= N*mu using your figures = 0.25*1500 = 375lb
therefore a transverse force of 375lb or greater will cause slip of a joint.
The idea of a designed joint is that you know what your external loads are at the beginning, you then calculate the correct size and number to ensure the joint doesn't fail in service.
regards
desertfox
RE: Deleted gearcase thread issue
So now I need to know my transverse service loads. But if I strain guage the bolts and do some field testing and get the service loads figured out, how will I know how much of that service load is coming from transverse loads?
RE: Deleted gearcase thread issue
I am not sure how you would measure the transverse load, its not an area I am familiar with to be fair, however I think it maybe difficult for you to do in practice as you need to know the vibrations the engine is subject to during service ie:-
the tilting of the engine as you described previously which
eventually causes failure.
I thought the engineering team were going to do an dynamic analysis for you according to one of your earlier posts.
Have a look at the site and video I posted earlier
junkers test video at the bolt science site.
regards
desertfox
RE: Deleted gearcase thread issue
The deflections within the bolted joint would be different
for the bolt and casting material and these will depend on the relative stiffness of each part.
By way of example consider a 20mm bolt passing through a copper tube having a 25mm bore and 45mm o.d. and a length of 0.75m.
assume a nut is wound onto the bolt and just touches the tube end ie no stress induced in tube.
Now tighten the nut by half a turn and assume pitch of thread is 2.5mm.
therefore F*Lb/(Eb*Ab) + F*Lc/(Ec*Ac) = 2.5mm/2
WHERE Lb= BOLT LENGTH
Eb= MOD ELASTIC OF BOLT
Ab= AREA OF BOLT
The other symbols are the same but represent the copper tube. Working through this assuming 210GN/m^2 = Eb and
100GN/m^2=Ec
F= 68723N
defl for copper tube is 4.6875*10^-4m
defl for bolt is 7.81257*10^-4m
In this case the tube is stiffer than the bolt and adding the two deflections together roughly gives 1.25mm the half pitch of thread.
regards
desertfox
RE: Deleted gearcase thread issue
Yes engineering will do my testing. I got to ask them if they have any other way to find transverse forces on the joint exclusively.
Yes I loked at your link about junkers test. I think junkers test is for experimental set up with small vibration loads and here in my case will be larger loads and also I need to find those loads to check if our joint is designed properly or not.
RE: Deleted gearcase thread issue
whatever you've been doing on the floor is sort of covered by your documentation:
<<<<One of our lube doc says,
All IFI124 (non-metallic lock patch fasteners) shall be coated with wool grease heated to 200 F. But the mating parts, holes, nuts should be oil and residue free.
All IFI125 (chemical lock fasteners) shall be free of oil and residue and wool grease.>>>>
It appears that the root cause of bolts loosening in extreme service is that the "lube doc" does not specifically identify epoxy-lock as a chemical locker, or refer to a document that does, but leaves it up to the production floor to guess which part of the spec covers it, and they guessed wrong.
In addition to cleaning the tapped holes and not greasing the epoxy-lock bolts, you need to get the spec fixed, to prevent recurrence.
You have a data point, sort of. It seems that normal customer applied loads are not large enough to dislodge the joint, but the loads associated with running the o/b as a surface piercing prop, are large enough to do it. So you need to get the epoxy-lock functioning correctly.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deleted gearcase thread issue
The info I got from the dept about the lock patch is wrong. It is not a epoxy lock, they minsunderstood a non-metallic hard plastic lock patch as epoxy lock.
I then found out with my loctite expert that a non-metallic lock patch is like amechanical lock patch and woll greasing of bolts wouldn't effect them.But wool grease will effect a chemcal lock patch as you guys already said.
so now we shorted listed the possible root causes to
1) transverse loads more than frictional forces in the joint and joint slip is occuring, which makes the bolt loose
2)very low friction in the joint because of cad plate+wool grease
RE: Deleted gearcase thread issue
I have a couple of questions:-
Are you using a locking patch (mechanical) on the
fasteners you are using? if so why are you lubricating
them before assembly?
Looking at MintJulep's link to longlok and reading the installation data there is no suggestion of lubricating the
fasteners prior to assembly,they clearly state that the bolts have to be installed correctly and the technical data
provided is for dry threads with no special cleaning.
Taking a step back here my final question before go off on another tangent is "are you installing the fasteners correctly"?
Oops its not my final question I would like to refer back to the clamp loads you posted the other day ie:- 4300lb-9400lb how have these figures been derived? and what is the tolerance your tightening specification allows for this application? as previously pointed out you are outside the
80% to 90% of proof load.
regards
desertfox
RE: Deleted gearcase thread issue
Your last post states two possible causes of failure:-
"so now we shorted listed the possible root causes to
1) transverse loads more than frictional forces in the joint and joint slip is occuring, which makes the bolt loose
2)very low friction in the joint because of cad plate+wool grease"
Can you expand on the second one and why you think that is the cause.
regards
desertfox
RE: Deleted gearcase thread issue
Regarding why we are using wool grease? the answer is the lock patch we are using is mechanical non metallic lock patch which will not interact with the grease at the time of assembly.But before applying lock pach to bolt, the bolt should be free of oil or grease and we are doing that.
longlok link u got is a chemical based lock and wool grease interacts with this kinda lock patches.
for your question "are you installing the fasteners correctly?" . after the installation process we check the torques again with clicker wrench seat at target installation torque at the end of the line to make sure all fasteners reached the torque specification.
But the numbers 4300-9400 lbs are collected before checking them with clicker wrench and this shows that friction is not consistent in our case.tightening tolerance is 26-28 ft-lb, 27 ft-lb being target.
reg your last post,
Acc to Bickford,low friction coefficient in the joint is one of the major cause for vibration loosesning. He suggested no use of lubrication to avoid self loosening
RE: Deleted gearcase thread issue
Not the answers I was looking for what I really wanted to know was how you measured those clamping loads of 4300lb etc. Your tolerance on torque equates to +/- 3.7% if you expect the clamping load to fall within that region you need
to change your method of tightening control ie:-
Hydraulic Bolt pretension +/- (1% to 10%)
Strain Gauges / Ultrasonics +/- 1%
The locking patches covered in the longlok site covers
plastic mechanical patches too and again it does not refer to lubrication in the installation info.
Regarding friction on the threads the higher the K factor
the less pre-load or clamp force you obtain for a given torque and the converse is true for a lower K factor.
Low friction in the joint would probably refer to joint face
with bolt head or nut and the joint mating faces themselves
and not neccesarily the threads.
I think you need to look at the installation method your using, your bolt pre-loads are all over the place, if it only takes one bolt to come loose and the rest follow then you need to get the pre-load consistant, or more consistant
then you currently have.
In addition the longlok locking fasteners claim they prevent the joint coming apart even when the intial pre-load
is lost, see page 3 of there handbook but to achieve this they need to be installed correctly hence my question in my last post. What info have the engineering dept come up with so far for this problem and for that matter what about the
other engine bolt failures that the designer promised clamping loads for about 4 weeks ago.
Let me put this installation matter to you another way if
all the bolts in the engine for this particular problem achieved a pre-load of 9400lbs would this failure still occur? now if only all but one bolt had 9400lbs pre-load
would the failure occur and finally what happens if all the bolts in the joint only have 4300lbs pre-load?
regards
desertfox
RE: Deleted gearcase thread issue
Not the answers I was looking for what I really wanted to know was how you measured those clamping loads of 4300lb etc.\\\
we used ultrasonics to measure the clamp load.
\\Your tolerance on torque equates to +/- 3.7% if you expect the clamping load to fall within that region you need
to change your method of tightening control ie:-
Hydraulic Bolt pretension +/- (1% to 10%)
Strain Gauges / Ultrasonics +/- 1% \\
if lubrication is not in control, then even if we use precise tightening stategies for a given torque, clamp load can be different right? so I need to make sure the lube is consistent.
\\The locking patches covered in the longlok site covers
plastic mechanical patches too and again it does not refer to lubrication in the installation info.\\
Then I got to recheck with our loc patch expert. he assure me that wool grease wont interact with mechanical lock patches. Any way I will confirm about this again.
\\Low friction in the joint would probably refer to joint face with bolt head or nut and the joint mating faces themselves and not neccesarily the threads.\\
so when we say F=N*mu, is Mu = frictional coeff of bolt under head surface + joints mating face?
\\
if all the bolts in the engine for this particular problem achieved a pre-load of 9400lbs would this failure still occur? \\
This is what I gotta find out doing field test. To answer this question, I need to know my external loads in the worst possible condition.
RE: Deleted gearcase thread issue
I take back my previous post
"if lubrication is not in control, then even if we use precise tightening stategies for a given torque, clamp load can be different right? so I need to make sure the lube is consistent."
I agree if we go to precise control, then lube will not effect as we are controlling the bolt tightening with stretch.
RE: Deleted gearcase thread issue
What are the installation torque's or pre-loads given by
the locking bolt supplier and do they mention any lubrication or not? thats the important thing, if they give you a reccomended torque figure without lube the clamping force will be a lot smaller than the same torque figure with lube.
In addition I have just ran a calculation for the stress
under the washer of a 3/8" bolt on the aluminium casting ie:-
force req
to reach yield = area of washer * 19000lbs/in^2
in aluminium
= (.75^2-.391^2)*3.142 * 19000
--------------------
4
= 6113lbs force
It would appear that your exceeding the yield stress for the aluminium with any clamp load over 6000lbs which would lead to loss of bolt pre-load due to embedding of the fastener on assembly.
Your engineering department really need to start coming up
with design info for these joints.
regards
desertfox
RE: Deleted gearcase thread issue
the 7/16 bolts is even worse.
In what sequence are these bolts tightened?
Are the center bolts tightened first and then
the perimeter bolts tightened afterwards?
6 Bolts,joint and proof load info
4 perimeter bolts (Bolt 1-4) – 3/8-16 (1.75 in) unc-2A
stainless steel plated(tq spec – 27 ft-lb target)-min proof load - 8370 lbs
Washer ID is 0.391 +0.015/-0.005 and OD is 0.75 +0.015/-0.007
l/d ratio 4.667
1 bolt in center- 3/8-16 (3.5 in) unc-2A
stainless steel(tq spec – 27 ft-lb target)-min proof load -8716
Washer ID is 0.391 +0.015/-0.005 and OD is 0.75 +0.015/-0.007
l/d ratio 9.333
1 bolt in center– 7/16-14 (3.5 in) unc-2A
stainless steel(tq spec – 47 ft-lb target)-min proof load - 9567
washer ID is 0.453 +0.015/-0.005 and OD is 0.75 +0.015/-0.007
l/d ratio 8.000
Very complex system.
RE: Deleted gearcase thread issue
Great find. Thank you. So we are basically yielding the joint material (embedment issue). Our lock bolt supplier dosent mention any torque values. Our engineering dept mentioned the torque value as 26-18 ft-lb and clamp load should be 80-90% proof load. That is the whole info from our dept. Other than this they can help me in solving this issue.Now I am gonna take this embedment issue to them.
Dimjim,
Yes you are right, 7/16 is even worse, It can yield the cast aluminum for 5300 lb of force.
regarding the tightening sequence, we first do center boolts then do perimeter bolts.
RE: Deleted gearcase thread issue
Just looking at the washers again if you changed the plain washers your using under the 3/8" bolts to type 'A' plain washer series W this would reduce the stress under the washer to 14,835 psi which is below the 19000psi you quoted
earlier.
The 7/16" bolt would need a similar washer again to reduce
the stress below 19000psi and as dimjim pointed out the material under this bolt is suffering more than the 3/8" bolts.
I was also thinking along the lines of the transverse loading would it be possible to fit dowels to take the transverse loading instead of the bolts but I am not sure
how often you need the joint to come apart.
Incidently the blind tapped holes in the joint are they fitted with threaded inserts?
regards
desertfox
RE: Deleted gearcase thread issue
we use dowel pins on some of the other model gearcases. But I gotta find out if we are using dowel pins on these models.I will let you know on tuesday.
No the tapped holes are not fitted with threaded inserts.
RE: Deleted gearcase thread issue
Yes the OD and ID are bigger but the main difference is the OD as this increases the surface area to dissipate the load.
Some more info if you can what grade is the stainless fastener and how much thread engagement have you got?
Whats the clearance hole in the component the bolts pass
through?
Are you saying from your last post the design department cannot give you any more technical info about the joint?
You need the dynamic analysis from them and also the original design info, if they can't give you this then somebody needs sort out your design dept as there's something terribly wrong.
regards
desertfox
RE: Deleted gearcase thread issue
I have long wondered why they have not used
helicoil inserts on these but assumed since
no threads were breaking they had at least
2 times the diameter length of engagement.
If no dowels, would a loctite product at the
mating surfaces help reduce the vibration
movement side to side? What are the hole
sizes in the castings?
RE: Deleted gearcase thread issue
Yeah I thought they would have used inserts too but nevermind lets see what tuesday brings.
preload you quoted a K value of 0.11 for your bolts with cadmium plate my machinery's handbook says 0.12 for cadmium plate without lubrication your value seems high espcially as
the 0.12 is subject to +/- 20%.
regards
desertfox
RE: Deleted gearcase thread issue
the K value I quoted is calculated from our clamp load values. I will get you new set of clamp load values on tuesday(we are doing a 30 pc samle). we can see what is the K value. I bet as you said, my K values will be less than 0.09, because we use cad + wool grease.
how do inserts help in my situation?
RE: Deleted gearcase thread issue
Very often when materials like alumium and copper are tapped it is common to use threaded inserts as it improves
the strength of the tapped hole by increasing the shear area
and distributing the axial load more evenly in the female threads and finally helps to prevent galling.
Have a look at this site and play the video :-
http:/
regards
desertfox
RE: Deleted gearcase thread issue
From the internet.
The assembled HeliCoil offers:
High tensile Stainless Steel threads
Flank hardness of 43-50 R.C.
Surface finish of 2 to 4 Microns.
Dimensional accuracy to extreme limits.
Reduce friction between bolt and female thread flanks.
Greater loading for an applied torque.
Minimal torsional strain in the bolt
Even distribution of load over ALL threads
Greater loading capacity
Maintains pre-load stretch in bolt.
Characteristics
Screw-Lock Inserts positively secure threaded members
against loosening caused by vibration and shock.
They have a high reusable factor due to the exclusive
HELI-COIL Resilient Screw-Lock which permits frequent
removal and reassembly of bolt without appreciable, loss of torque.
Positive self-locking torque, complying with MIL-I-8846 & MIL-N-25027.
Savings in space, weight and money, through the elimination of lock wiring, lock nuts, lock washers, chemical compounds,plastic pellets/patches and other locking mechanisms.
RE: Deleted gearcase thread issue
Before you go rushing off to buy inserts there's a price to
pay in terms of installation, I obtained this passage from
this site:-http://www.hillcliff-tools.com/helicoil.html
"To obtain the best performance from HeliCoil Screw-Lock
inserts it is recommended that only good quality close
limit fit, rolled thread, oil lubricated screws or bolts
are used. On no account should sub standard or "Black"
bolts (with heat treatment scale) be used with HeliCoil
Screw-Lock inserts.
"When using Unplated, Heat Treated or Stainless Steel
screws with HeliCoil Screw-Lock inserts and Anti Seize
Compound (such as Molibdenum Disulphide) should be applied
(preferably to the screw) to minimise galling and maximise
cycle life".
regards
desertfox
RE: Deleted gearcase thread issue
Mike Halloran
Pembroke Pines, FL, USA
RE: Deleted gearcase thread issue
I agree helicoils won't solve the problem.
Still to be resolved are the dynamic loads the unit is subject too, although it appears that it is only when the unit is abused this failure occurs.
The fastener pre-loads appear to be completely inconsistant
which surprises me that more failures have not occurred and
in addition if the bolts do manage to reach the figures quoted then there is a good chance of embedding.
In fact preloads biggest problem is getting any sense out the design dept.
regards
desertfox
RE: Deleted gearcase thread issue
Anybody know the mechanical properties of paint?
Mike Halloran
Pembroke Pines, FL, USA
RE: Deleted gearcase thread issue
Thanks for the info Mike.
RE: Deleted gearcase thread issue
Is there any chance you can give a sketch of the outboard
showing the rough angle you think it is held in the water at and some dimesions overall to where it enters the water
and the bolts in question.
regards
desertfox
RE: Deleted gearcase thread issue
Epoxy systems on Aluminium have typically ~2000 PSI bond strength.
RE: Deleted gearcase thread issue
No we don’t use dowel pins.but we use alignment pins which we remove them after bolt tightening. So the answer is no, we don’t use dowel pins.
All are stainless steel A2 (304) grade strain hardened bolts per ASTM F593
For 4 perimeter holes, 2 holes dia 0.406 in (+0.002,-0.002), 2 other holes 0.441 (+.036,-.013). 2 holes dia is smaller than other 2 holes because we use alignment pins for better alignment.
Thread engagement, I can get you this info in 2 hrs from now
Regarding the sketch, I can provide that to you, but my only concern is according to Mike Halloran, its not advisable to copy images here. But I will try to draw a rough sketch and up load
Dimjim yes, first we tighten center ones then go to perimeter ones. how does this effect?
Mike,
"Speaking of embedding, these units are typically coated with a very thick paint system. How does paint effect?"
Does thick paint coating helps me from embedment or does it worsens embedment? The only painted surface in this joint is under the bolt/washer head.
RE: Deleted gearcase thread issue
If the paint yields in compression, there goes some of your hard-won preload.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deleted gearcase thread issue
As Desertfox mentioned, any force over 6113 lbs on our perimeter bolts will yield the joint material, then aren’t we yielding the paint too?
Any way I will try to post the pics then.
Desertfox here are the thread engagement lengths for all bolts
3/8 center bolt -0.596"
Perimeter 3/8 bolts - 0.707"
7/16 center bolt - 0.794"
RE: Deleted gearcase thread issue
RE: Deleted gearcase thread issue
how do I know if my clamp force is exceeding the bond strength of the paint system?
so are you saying that even if my clamp force is good enough to yield the die cast aluminum, but less than the bond strength of paint system, then I will not have embedding problem?
RE: Deleted gearcase thread issue
Thanks for the info I will get back to you.
Regarding the sketch I was meaning just a hand drawn sketch with some dimensions on would suffice.
regards
desertfox
RE: Deleted gearcase thread issue
and also in military tank bearings.
Why are they not used here as a benefit.
They are used on the hummer machine gun
bearing mounts. These also have low
l/d ratios and see heavy vibration
as you can imagine.
How many mils is the paint thickness that
you are loosing by embedment. We had special
washers that we used around holes on the mounting
surface sides to keep the paint off these surfaces.
Are the aluminum surfaces anodized and then sealed
before painting?
RE: Deleted gearcase thread issue
We don’t do any anodizing and sealing before paint.
And how do I know how many mills of paint we are losing? By microscopic testing in the lab?
RE: Deleted gearcase thread issue
paint. Are there two coats? First a primer, then
the topcoat?
RE: Deleted gearcase thread issue
yes first a primer and then topcoat. I can get you the paint thickness value
Thanks
RE: Deleted gearcase thread issue
Will do calcs shortly however I was looking at your thread engagement which doesn't seem an awful lot, the failures your having you said doesn't break the bolt but what about the internal thread is there any damage to that area?
Have you got any of the failed parts? have you actually got
any of the bolts which have come from one of these failures
I assume you must have otherwise you wouldn't know whether the bolts are breaking or not.
regards
desertfox
RE: Deleted gearcase thread issue
as to:
Dimjim yes, first we tighten center ones then go to perimeter ones. how does this effect?
I assume you are tightening the 7/16, then the
3/8 in the center, then the 3/8 perimeter bolts.
Each bolt would lessen the clamp load of the
previous bolt clamp load. Sounds like you
are ok.
RE: Deleted gearcase thread issue
No I dont have any failed parts.But the warranty document says they dont see any signs of damged threads. Yes I agree thread engagement length is not really good.This is what I meant by L/D ratio is very less on especially those 3/8 perimeter bolts.
RE: Deleted gearcase thread issue
Paint thickness (paint+primer+top coat) = 0.0037 in
By the time we put the fastener it's only half cured. We can loose 0.001-0.002 in of paint thickness in between the fastener installation and the paint is fully cured.
RE: Deleted gearcase thread issue
I did some calculations on thread engagement for the 3/8" bolt with the 0.596" and found that the thread engagement
should actually be about 2.6 x bolt dia,calculations were based on the Aluminium tensile strength of 42000 psi and I couldn't find exactly your bolt spec but assumed a tensile strength of 100000 psi, perhaps you can let me know the actual bolt value.This means that the internal thread is the weakest part of the joint and internal thread failure
would occur before the bolt breaks, so I wondered under service conditions if the internal thread failed that it might render the locking patch useless and ultimately the bolt disappears.
If you have no failed parts, what as happened to them have the bolts been replaced?, gear case scrapped?
http://w
http://
The above sites I looked at for fastener info the first site
mentions grade A4 for marine use and A2 for light industrial use are you using the right grade?
The second site lists A2 (304) as being 700N/mm^2 as the tensile strength which is close to 100000psi.
I would say that with such short engagement lengths then helicoil inserts would have helped if only from the point of view of increasing the shear stress area.
We really need some more info now to be of any further help
eg:- dynamic loading, evidence of failed parts,sketch of gear case etc..
What is happening in respect of your 30pc clamping loads
and working a new K value.
One last question whats happened with the other failed bolts
in the engine as the problem been resolved?
regards
desertfox
RE: Deleted gearcase thread issue
What did engineering dept say about embedding issue?
regards
desertfox
RE: Deleted gearcase thread issue
1)Thanks for the calculations. Yes I agree the thread engagement is less.But could u explain how does it help if the thread engagement is more?
2)we are using A2 grade bolt, not A4.I will confirm the tensine strength numbers of the bolt on monday for sure.
3)when u say u need dynamic loading, do u mean the dynamic loads the joint sees in the service? id yes , I am in process of doing the field test, I will let you guys know the loads as soon as I am done with the testing.The documented failures occured 3 yrs back, so we dont have those bolts now, but the docunemtation says bolts missing/loose almost all. one case bolts broken.And on the loose bolts they dint see any thread damage.regarding the sketch I will get the sketch link too on monday for sure.
4)when u say helicoils would help, how does ncreasing shear stress area help in my case?
5) 30 pc sample testing is not done yet.It should be done next week for sure.
6)regarding embedment issue, I dint hear anything from them , but I got a meeting on this issue on monday. I will let you know thier views.
7)reg other failed bolts in engine- I thought of updating that thread today.I think I got the minimum clamp load spec u were asking.the nest thing is to develop angle strategy.I will let you know the minimm clamp load number ASAP.
RE: Deleted gearcase thread issue
Basically the shear area is increased if either the thread engagement is increased or a bigger thread diameter is used.
Remember stress equals force/area, then if I increase the area I decrease the stress for a given load.
Now if you fit an insert to take a 3/8" bolt then the shear area of the internal thread increases because you have to tap a larger thread in the Alumium to fit the insert.
Now also the insert according to the list given in dimjim's
post gives other advantages such as spreading the load more evenly etc.Further when a joint is designed it should be designed so that the bolt fails in preference to the internal thread as the bolt is easier to replace than the tapped component. This is not to say that the insert will solve the problem, in order to do that the joint needs to be designed correctly in terms of its pre-load to keep the joint together in service and a correct installation method that ensures the pre-load is achieved within sensible tolerances.
If you wish to understand more about thread strength have a look in the Machinery's Handbook.
Interesting you say one bolt broke was it the 7/16" bolt or a 3/8" bolt?
regards
desertfox
RE: Deleted gearcase thread issue
I too am going to check out the length of engagement.
I have never seen a factor greater than 2.
Which formula are you using. I have seen one in
Machineries Handbook under the bolts and nuts section.
It starts out by defining a J factor as
J= As x tensile strength of external thread divided by
An x tensile strength of internal thread.
They then define As and An. Is that the basic formula
that you are using?
RE: Deleted gearcase thread issue
Yes thats the formula I used, bearing in mind I used 100000psi for the bolt.
Glad your working it out too, let me know if I have made a mistake.
regards
desertfox
RE: Deleted gearcase thread issue
Since the strength is just a tad over 100000, I would use
the At value for steels over 100000 psi just to be conservative. It will be good to see the actual value of
these bolts that preload will eventually define.
I have seen proof loads equal to 125000 psi from one source that had a value for strained hardening. Interesting.
RE: Deleted gearcase thread issue
I calculated 1.689D. I used 102000 and 42000 psi
for the tensile strengths. I also assumed 2A and
2B threads for the calculation.
Since pi x n x Le is in both As and An formulas,
I simply removed them from my calculations as we
are only looking for a ratio.
I ended up having .69552 x 102000/42000 yielding the
1.689D value.
This was for the 3/8-16unc bolts.
I assume the 7/16-14unc will have a similar ratio.
RE: Deleted gearcase thread issue
Thanks I see my error now I got J =1.656 but I then multiplied the actual engagement length instead of the engagement length obtained from the formula with equal strength materials.
Looks like the engagement lengths aren't to bad then except for the 3/8" centre bolt, I'll check the 7/16" bolt later.
regards
desertfox
RE: Deleted gearcase thread issue
Your assumption of 2A and 2B fit for external and internal is right.
RE: Deleted gearcase thread issue
There seems to be an error in the maths in machinery's,
we both agree that J is around 1.6xxx depending on whether
you use 100000 for the bolt or 102000.
Now the machinery's goes onto say that if the materials are different strength's then to calculate J as we have done and if this exceeds 1 then the engagement required is J multiplied by the value of Le obtained by formula (1) which is for thread materials of equal strength.
I have checked this several times now and if the threads were of equal strength then for the 3/8" bolt I need only 0.269" of engagement. Now multiply this figure by J and you get a figure for engaged length of 0.454" using 1.689 and using 1.656 we need 0.445", but we know that the engagement
of the 3/8" bolt is 0.596" so it doesn't add up.
I notice that you assume its 1.689*D which assumes that you need at least 1D of engagement to start with.
http://www.boltplanet.com/un/errata.htm
This site talks about some of the errors with the bolt strength calcs, scroll down the site till you see the title
"more errors in machinery's handbook"
interesting is it not?
regards
desertfox
RE: Deleted gearcase thread issue
----------------------------------------
That is interesting. You are correct in that I assumed
Le for steel on steel would be 1.00D. When I use the calculation for Le provided earlier in the Handbook I get
a value about .744D or .72D depending on which At calculation you use. If I multiply 1.689 times these
values I get 1.2566D and 1.216D. That is interesting
as I have seen values in bearing catalogue for low carbon
steel to require values of 1.25D to 1.5D for length of
engagement depending on the bolt grade. It is also interesting that the normal range of heli-coils are
either 1.00D or 1.50D for lengths and even provide
2.00D in special cases. Thanks for pointing out my
incorrect assumption. Something that looks suspect
is that in the Le calculation .50 plus .57735n() is used
whereas in the As calculation .50/n and .57735() is used.
Has this been changed in the 25th edition? I only have the
17th edition of Machinery's Handbook. Seems like an error.
I also like to use the equations for the At values as
follows:
At = .7854 (D - .9743/n)^2 and
At = .7854 (Esmin - .32476/n)^2 or see these as
At = Pi (D/2 - .9743/2n)^2
At = Pi (Esmin/2 - .16238/n)^2
just for visualizing or comparing these two formulas.
I guess since this is an Area and we tend to think of a
circular area as Pi r^2 or Pi (D^2)/4 either makes sense.
RE: Deleted gearcase thread issue
Thanks for the response, I wasn't questioning your assumption which is I feel a valid, one for materials of the same strength.
What concerns me more is that we work out J and it leads us to believe there is not enough thread engagement however when you follow it through and multiply the thread engagement obtained from formula (1) (equal strength materials) you obtain in this case a shorter thread engagement required than what we have actually got ie 0.445"
as compared with 0.596" in practice.
regards
desertfox
RE: Deleted gearcase thread issue
I meant to add that the same formula are shown in 17th and 25th editions no modifications at all.
regards
desertfox
RE: Deleted gearcase thread issue
Have a look at this site I found some more formula for thread engagement:-
http://ww
Its late here and I may of made mistake however I used the
formula and got a thread engagement of 1.974" and its seems
quite a lot.
regards
desertfox
RE: Deleted gearcase thread issue
Thanks. Will print it out and go thru the
calcs.
RE: Deleted gearcase thread issue
Ultimate Tensile strength of the bolts is 120-160 Ksi.
RE: Deleted gearcase thread issue
Thanks for the info
regards
desertfox
RE: Deleted gearcase thread issue
The picture is here.
http://si
the middle picture is the trimmed out position (our bolts failed in this position). The middle pic shows only trimed out position of gear case, but in or application we even have lift of the gear case till just one prop blade is in water.
Regarding embedment issue, yes the dept agreed that we are embedding the joint . We will be doing some lab test to see how much embedding is caused.
PS
The plan is to strain gauge some fasteners and do field study to see whats the dynamic loads the joint is seeing. If I strain guage the bolts, the dynamic loads I get after experiment is combination of shear+tension right? But I want to know the tensile loads and shear laods separately. How do I need to set the test to get these two loads seperately.
RE: Deleted gearcase thread issue
this is another picture which shows the engine in normal condition and the engine when it is trimmed at an angle.
RE: Deleted gearcase thread issue
Thanks I will see the pics on friday.
In the meantime I am still looking at the joint.
regards
desertfox
RE: Deleted gearcase thread issue
Regards,
Cory
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Deleted gearcase thread issue
I think you meant J factor equal to 1.97
rather than inches. I do feel that the value
from the Le equation is the one to use in
the other calculations as entering an actual
value of length in the Q equation would be
wrong. I think it should read Le required
Q = Le(required) times J.
I got J = 1.987 which is a ratio.
I would like to see others respond to these
equations in Machinery's Handbook under the
Bolt and Nuts section. Remember too that they
are using 2 as a safety factor against stripping
vs min cross section of the screw or bolt area.
I think the really critical issue is embedment
of the washers into the mounting surfaces as well
as the painted surfaces.
RE: Deleted gearcase thread issue
Thanks a lot for the response. That was really helpful.
You said "you can see preload response to applied forces (checking for things like embedment, loosening, etc.)" Could you please explain me more how determining applied forces can help me understand embedment?
Dimjim,Desertfox,
Every one agreed theoretically that embedment might be one of the main causes, but how can I prove that? What kind of lab test proves embedment on my joint?
For example" measure the bearing joint hole depth and install screws at specified torque and back off the screws and re measure the hole depth precisely, and if there is change in length then embedment occurred?????" or is there any other sophisticated lab way??
RE: Deleted gearcase thread issue
Regards,
Cory
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Deleted gearcase thread issue
Yes dimjim I agree the 1.987 should be the factor to multiply the diameter with.
So if we work on a factor of 2 then for all the 3/8" bolts
they should have a thread engagement of 0.75" which gives a small margin of safety.
Haven't checked the 7/16" screw yet will do that later assuming its the same material spec as the other fixings.
Preload it looks like your thread engagement could be marginally short for all the 3/8" bolts this should also be considered in the joint failure.
Dimjim I am ignoring the formula in the machinery's now and using them I found in that link.
I agree also that the paint and embedding issue is probably paramount.
regards
desertfox
RE: Deleted gearcase thread issue
for the perimeter 3/8 bolts we have thread engagement length of 0.707 in
for center 3/8 bolt we have 0.79 in
if 0.75 inch is the required LE then I am good except for the perimeter 3/8 right?
RE: Deleted gearcase thread issue
For steels up to 100000 psi .0775 square inches is correct. As = pi/4 (D - .9743/n)^2
For steels over 100000 psi .0747 square inches is correct. As = pi (Dpe/2 - .162/n)^2
Dpe = Min. Pitch Dia. n = No. of threads per inch.
Yields 8976lb/0.0747 = 120000 psi max clamping force.
In order to help lessen the embedment, you might
want to consider using larger diameter washers to
reduce the bearing stresses below the washers.
You also might want to incorporate helical serrated
washers. This may have been mentioned before.
9300/(.7854*(0.72^2 - 0.441^2))= 36555.7 psi
9300/(.7854*(0.72^2 - 0.406^2))= 33490.7 psi
I also wonder if after 24 hours, if you retighten
the bolts, if that would help. I remember seeing
in the literature where someone was recommending
going to 3 tightening cycles. I should keep better
documentation when I am reading thru the literature.
RE: Deleted gearcase thread issue
here are the thread engagement lengths for all bolts
3/8 center bolt - 0.596"
Perimeter 3/8 bolts - 0.707"
7/16 center bolt - 0.794"
then you said:
for the perimeter 3/8 bolts we have thread engagement length of 0.707 in
for center 3/8 bolt we have 0.79 in
if 0.75 inch is the required LE then I am good except for the perimeter 3/8 right?
So which values are correct?
RE: Deleted gearcase thread issue
Thnaks for correcting me.
"for the perimeter 3/8 bolts we have thread engagement length of 0.707 in
for center 3/8 bolt we have 0.79 in"
this is correct. I am sorry about that confusion.
RE: Deleted gearcase thread issue
dimjim beat me to that one.
I get just over 0.8" for 7/16" screw engagement.
so your still short on engagement, which means that the thread will fall before bolt thread ultimately
RE: Deleted gearcase thread issue
the early equations came from and get a better explanation.
If you can get a copy, I think you will agree that
the equations are over conservative.
It looks like .75D would be the normal Le length
for steel on steel and somewhere it says that even
this could be reduced to somewhat like 17 percent.
So I think the value of J times .75D would be realistic.
You could have 2.00D in the joint and it may be a false
assumption that you can ever get that many threads sharing
the load. So I feel very confident that 1.5D lengths of
thread is sufficient assuming these all share the load
which again is probably not happening. Remember that
this has a factor of 2 built in to assure that the bolt
fails before stripping of the threads. I would like to
see the root diameter of the bolt be used for the
min. bolt cross section for high strength bolts ie those
having a tensile greater than 100000psi. I did find a
source of the H28 handbook but it is a pdf file and
some of the equations are hard to read.
RE: Deleted gearcase thread issue
Dimjim and Desertfox,
You guys are talking about the formula in the link below right?
http:
RE: Deleted gearcase thread issue
What is different is that they define Le = Length
of thread engagement required to develop strength.
This is absent in my Machinery's Handbook.
Le can be interpreted to be the actual Length of
engagement in the clamped parts.
Thanks.
Another source uses the Nut example that the normal
nut thickness is .8xD and suggests using .75D as
the value of Le.
RE: Deleted gearcase thread issue
So what do you think from your calculations? We are short of Le on 7/16th bolt and perimeter 3/8 th bolts? If so how much Le do I need on both of them?
By any chance could you please upload your calculation because I wanna see the numbers you guys used for minimum OD of bolt threads and maximum PD for nut and basic (minimum) PD for the nut? I couldn't find them on net.
RE: Deleted gearcase thread issue
1) embedment issue
2) insufficient LE issue
These two "might" be the causes for my loose/missing bolts.How can I prove embedment in our lab? Any easy and quick method?
I think after our dynamic testing and getting the service loads we can get more info which should guide us in right direction of solving the issue.
P.S: on this issue, we cannot validate the joint after making any changes because failure rate is very low. The only thing I can do is make some changes to the design and process which I believe might be the causes and that’s it I am done.
RE: Deleted gearcase thread issue
Ds Major Dia. Min .3643 .4258
Ds Major Dia. Max .3743 .4361
Es Pitch Dia. Min .3287 .3850
Es Pitch Dia. Max .3331 .3897
Minor Dia. .2970 .3485
Kn Minor Dia. Min .307 .360
Kn Minor Dia. Max .321 .376
En Pitch Dia. Min .3344 .3911
En Pitch Dia. Max .3401 .3972
from Machinery's Handbook 17th Edition
Where did your page come from for future
reference?
RE: Deleted gearcase thread issue
What did you take for tensile strength of the bolt material? Ultimate tensile strength of bolt is 120-160 ksi
And tensile area for bolt is 0.0747 in^2 or 0.0775 in^2?
RE: Deleted gearcase thread issue
42000psi for the casting
RE: Deleted gearcase thread issue
RE: Deleted gearcase thread issue
My calclulations using the formula in the link I posted gave
Le = 0.515 in for 3/8
Le = 0.621 in for 7/16
I used
tensile strength of bolt = 120ksi for both bolts
tensile strength of nut = 42ksi for both
n = 16 for 3/8, n = 14 for 7/16
minimum OD of bolt threads = 0.3643 in for 3/8
minimum OD of bolt threads = 0.4258 in for 7/16
maximum PD of nut = 0.3401 for 3/8
maximum PD of nut = 0.3972 for 7/16
tensile stress area of bolt = 0.0747 in^2 for 3/8
tensile stress area of bolt = 0.1063 in^2 for 7/16
RE: Deleted gearcase thread issue
You need to use 160000 for the bolts to give you worst case.
If you have embedding you should see a witness mark were the washer was situated.
In an earlier post I said if you change the washers you can
eliminate embedding ie use plain washer's series W.
regards
desertfox
RE: Deleted gearcase thread issue
You are right about the 160000psi.
I missed that. I did get Preload's
values using the 120000psi value.
Have we lost Cory and Mike?
Have not heard from them for awhile.
It would have been nice to have gotten
all of the correct data required at the
beginning.
Ultimate Tensile strength of the bolts is 120-160 Ksi
That is quite a range. I wonder if they have been
tested?
RE: Deleted gearcase thread issue
Yes they are tested, but I need to rquest our supplier for the data.
but even with 160ksi for a 3/8 bolt we are safe. I got LE of 0.68 in for 160ksi which is still less than our current le values for 3/8 bolts
the problem is only with the 7/16 bolt regarding the LE
RE: Deleted gearcase thread issue
if you refer to my posting of 5 june i calculated, using the 160psi bolt strength, that you need 0.75in thread engagements. the thread engagement given by you was 0.707 which means, according to my figures, you are marginally short on thread engagement.
referring to my earlier post today, the thread engagement for the 7/16 bolt should be over 0.8, therefore again the thread engagement is slightly short.
i will re-check my calculations, can you re-check yours and post again?
regards,
desertfox
RE: Deleted gearcase thread issue
I am following this thread on a part-time basis. Trading 100+ posts on detail engineering is not really within the scope of this site. It is Eng-Tips, not Eng-Solutions. Also, it has been hard to follow some of these threads due to missing information, lack of images, etc.
Regards,
Cory
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Deleted gearcase thread issue
I like doing this kind of stuff, but I like getting paid for doing it, too.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deleted gearcase thread issue
The issue of thread engagement will go away if you fit helicoil inserts.
regards
desertfox
RE: Deleted gearcase thread issue
RE: Deleted gearcase thread issue
I am really sorry for long threads.As I mentioned earlier I am brand new to this fasteneing field (for short term projects) and was seeking help.I hate to be new. Thanks for understanding and helping.
RE: Deleted gearcase thread issue
This forum is not for us to provide you with free
engineering but to give you guidance. The calculations
are your responsibility. I know the literature is
huge as to try to understand fasteners and their
applications. I think it is quite frustrating that
you come with a problem without having all of the
information. You have Bickford's book and it is a
good reference. There are always questions even with
having text information and examples of how to solve
some of the problems in a clamping situation. There
are even assumptions built into some of the equations
that expect your bearing surface areas be equal to at
least three times the area of the bolts. That comes
from the cross section of (2D^2 - D^2). We have not
even asked about your cross sectional area where the
parts interface. For a new guy, you seem to be able
to quickly pick up the thrust of the problems.
RE: Deleted gearcase thread issue
Thanks and reg the insufficient info, yes I agree it will be frustating for some one who is trying to help.
Here are the pics of assembly for better understanding. I can get different angle pics if you need.
ht
http://img524.imageshack.us/img524/402/assypc9.jpg
I doubt if we have bearing area 3 times the bolt area on perimeter bolts (u can see it in pics-bolt 1,2)
RE: Deleted gearcase thread issue
putting compressive forces on some of these bolts
and tension forces on the others when the propeller
is driving. The pictures help a lot, but I would
like to see both the upper and lower surfaces before
they are assembled together to see the bearing surfaces
at the interfaces.
RE: Deleted gearcase thread issue
http
this is exhuast housing (tapped holes)
RE: Deleted gearcase thread issue
Thanks Dimjim
RE: Deleted gearcase thread issue
painting. It is very difficult to see
after these are painted.
RE: Deleted gearcase thread issue
RE: Deleted gearcase thread issue
More pix before paint
http
http:/
http:/
http:/
RE: Deleted gearcase thread issue
Thanks for the pic's they do help.
I'll study them a bit more and post later.
regards
desertfox
RE: Deleted gearcase thread issue
Can't they be spot faces to ensure parallel tightening?
Have not seen this mentioned before. Are the upper and
lower casting surface ground before painting and assembly?
How flat are they? It appears that you have a raised or
c'sunk surface area at the 3/8 perimeter bolt tapped holes.
What is this for?
RE: Deleted gearcase thread issue
Dimjim,
All the surfaces(exhaust housing tapped holed surface, gear case bottom surface) are really flat (no raise) except for the 3/8 perimeter 4 bolts on the top side of gear case where the bolt head/washer lands. That surface is little raised and has a draft angle of less than 2 deg, u can see that in this picture http:/
We thought a draft angle of less than 2deg is allowable and will not be a big problem. So I dint mention that before.
This raise is one of the reason I cannot introduce big washer to solve my embedment issue. If you see the pic again, there is no room to introduce a big OD washer to reduce the stress underhead.
RE: Deleted gearcase thread issue
I agree it is pretty but ultimately acting as a
thin gasket. Something else to consider. I do not
know the acceptable allowable out of parallel surfaces
that is allowed. It only compounds the torque value
readings for the perimeter bolts. Need more input from
others about this. The unpainted surface pictures helped alot. It would be interesting to see a moment force diagram of the clamping bolts about whatever neutral axis you think opposes the thrust of the propellers.
RE: Deleted gearcase thread issue
I can catch up a bit now I am at home, firstly I can see why we got different engagements lengths in our calcs, I used the 0.0775" area whereas you used 0.0747" for the 3/8"
bolts in my opinion the 0.0775" should be used as this gives worst case for engaged length, other than that I see no difference in our respective formula.
Looking at your pic's and assuming I am looking at them correctly I would say that the 3/8" bolts furthest away from the prop will see the most external tensile load and
those nearest the prop the least tensile load as the boat moves along. To clarify I am saying that bolt2 in this link
ht
and its opposite one on the side we can't see carry most of the external load imposed as the boat moves forward; followed by the next pair ie bolt1 + opp bolt which will carry less and subsequent bolts carrying even less as we approach the prop. This is a vey simplified view of course assuming that the bolted flanges are rigid (which I very much doubt in practice) I am saying that the gearbox cover tips about the back edge ie:- pivots behind bolt6 given in this link:-http://img524.imageshack.us/img524/402/assypc9.jpg
A good example of what I am saying can be seen in the link
below where an offset load on a right angle bracket is resisted by a line of bolts who's axis is 90 degrees to the plane of the offset load.
http://w
Of course in practice the gearbox cover gets pivoted to the right and left, up and down etc which will dramatically vary the forces on the bolts not to mention acceleration. So my view is only valid for the boat moving in a straight
line but I feel it gives an idea of how the bolts maybe loaded.
My view also leads me to think that pre-load in the bolts
particularly those furthest away from the prop are extremely
important as those bolts are working the hardest to resist slip and seperation of the joint faces.
Fatigue is another issue in any of the bolts if the joint
can seperate due to lack of pre-load.
On the 3/8" perimeter bolts do the bolt heads and washers sit on a tapered face so that only a portion of the washer
or bolt head are in contact with the case?
regards
desertfox
RE: Deleted gearcase thread issue
Yet Stress = F/A
so if the force is constant like 9300 lbs and as A
decreases, S gets larger.
RE: Deleted gearcase thread issue
when u said bolt 2 and other side bolt would take the max external tensile load, are u sure about tensile load? I thought it would be more shear loading because the water flow or the water pressure is acting perpendicular to the bolts axis here right?
regarding the tapered face, if you look into this picture
http:/
the bolts underhead sit on this raised areas.you can clearly see the raised holes.those holes have a draft angle of 1.5 - deg. so they are not really parallel.but dooes a less than 2 deg tapered surface make much difference? but I agree we loose some clamp there because of that draft angle.
RE: Deleted gearcase thread issue
There are shear forces acting too; in addition to the tensile loads, I was merely trying to convey that I see
the gear case as trying to pivot away from its mating face
like that bracket example from the site I posted.
You have a combination of shear and tension forces acting
together however the main point I am saying is that most
of the load is being taken by the first pair of bolts as the
gear case tries to seperate from its mating face.
The tapered faces can't be helping that bolt joint my feelings are it should be clamped square onto the joint face; by having that taper your bearing stress under the washer will certainly not be evenly distributed.
Regarding embedding is there any chance you can make some joints up ensuring that you obtain the proof load you were looking for by using ultrasonics;then stripping down the assembly and examing for witness marks on the joint surface?
regards
desertfox
RE: Deleted gearcase thread issue
Looking at 3pf9 picture for the 7/16 bolt hole.
How large is that diameter hole? I looks like
about 5/8 diameter at the interface surface.
The tapped hole surface looks great on the mating
part. How deep does this 5/8 diameter hole go
into the casting? It looks like about an inch
deep. Does this 7/16 bolt seem to be deflecting
the casting when you tighten it? Because that hole
is so large, you have very little surface area
mating between the parts for this bolt hole.
What is the od of that general area around the hole?
RE: Deleted gearcase thread issue
Yes I can do some testing to see any embedding witness marks. I will do that on monday.
Dimjim,
I will get you the dimensions of that hole on monday for sure. Thanks a lot.
RE: Deleted gearcase thread issue
Yes the hole diameter increases uniformly from under head of the 7/16 bolt to the bottom.
Under the head ID is 0.48 in and the ID of other side of the hole in the picture(3pf9) is 0.58 in. OD is 0.88 in. The depth of the hole in the gear case is 2.71 inch
RE: Deleted gearcase thread issue
here is the link for the embedment test snaps.
http:
Top 2 snaps are the 3/8 perimeter took to proof load
bottom 1 is the 7/16 taken to proof load
does these pics show any signs of embedment? sure we lost paint under the washer which is normal.
RE: Deleted gearcase thread issue
I can't see the file till friday I will post then.
regards
desertfox
RE: Deleted gearcase thread issue
If you clear the paint away can you feel a step or see a step in the metal surface?
regards
desertfox
RE: Deleted gearcase thread issue
I looked at the joint and did not find any step or signs of embedment other than the paint scratching off which is normal.
RE: Deleted gearcase thread issue
I will look on friday at your picture.
If the paint is getting destroyed during tightening then
the fixing is embedding into the paint work at least.
How did you determine the clamp load by ultrasonic's?
regards
desertfox
RE: Deleted gearcase thread issue
Looking at the pics it looks to me that the washer as embedded itself into the material I can see a witness ring
were the washer is on each photo.
But your telling me thats its just the paint work damaged,
well your closer to the component than me, maybe you could try making some joints without paint and see if you get a witness ring under the washer then.
regards
desertfox
RE: Deleted gearcase thread issue
For some reason my handle "preload" is not working. It says some registrations problems. So I created a new handle.
Anyway, the witness ring you are seeing is just the washer taking the paint away on the surface. I dint feel or see and step under the washer.
But yes It would be a good idea to run some un-painted parts.