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Plugging Hole in Pressure vessel via Staked in Ball
2

Plugging Hole in Pressure vessel via Staked in Ball

Plugging Hole in Pressure vessel via Staked in Ball

(OP)
Not sure where to post this so I am putting it here.

I am looking for design advice for plugging a hole in a hydraulic brake master cylinder by staking in a steel ball.
The hole I am plugging is shown in the image below:



The cylinder is filled with brake fluid at pressures up to 150bar.  The hole that has to be plugged is approximately 6.1mm.  The hole diameter can be varied as needed, but I want to us a 6.35mm ball for the plug.  The cylinder is made out of extruded aluminum (6061).  Currently we are using an Advil high pressure plug to fill the hole, but for manufacturing reasons and cost we want to change to a staked ball.  The staked in ball would look like this image:



I need to determine the diameter of the hole, the shape of the staking tool, the required staking depth, the staking force, etc.  Is there a way to determine these parameters through calculation or is the only way via experimination in the lab?



 

RE: Plugging Hole in Pressure vessel via Staked in Ball

FYI: Your images didn't come through on my computer (consider using the file upload on engineering.com).

 

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

RE: Plugging Hole in Pressure vessel via Staked in Ball

How thick is the sidewall of your extrusion?

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read FAQ731-376: Eng-Tips.com Forum Policies to make the be

RE: Plugging Hole in Pressure vessel via Staked in Ball

I agree with MadMango.  We used Koenig plugs in aluminum to seal to 3000 psi.  Easy to install.  Easy to inspect for correct installation.

Ted

RE: Plugging Hole in Pressure vessel via Staked in Ball

(OP)
We have looked at these.  Before we used the Avdel plugs, we used a different type of plug also by Sherex(same company that makes the Koeing plug).  In all cases cost is the driving factor. Staking a ball always costs less than any standard plug that I can purchase.

RE: Plugging Hole in Pressure vessel via Staked in Ball

What about the legal aspects of using just the ball instead a qualified solution as Lee Plugs or Keonig Plugs. You should check the code you are designing the pressure system.

RE: Plugging Hole in Pressure vessel via Staked in Ball

Consider these costs.  Development to determine correct, repeatable hole production.  Development to determine correct, repeatable staking.  Testing to prove your process to the satisfaction of withstanding product liability pressure, not just product application pressure.

Direct your cost control effort to more productive activities.

Ted

RE: Plugging Hole in Pressure vessel via Staked in Ball

What israelkk and hydtools said.  You are apparently making an automotive brake manifold; the liability on those parts is enough to put your company out of business many times over should your product be linked to automobile accidents, injuries, or fatalities.

RE: Plugging Hole in Pressure vessel via Staked in Ball

(OP)
Thanks for all of the advice, but I fully am aware of all legal/code/liability issues that may result from ball staking.  These types of situations always occur within automotive products and it is up to the product engineers to ensure that all such risks are handles to ensure that no issues occur in the field.  
I think you would find that the manufacturers of these standard pugs would assume very little liability responsibility in the event of any failure that might happen in the field.
As for the costs, I agree that all costs need to be considered, but we will be making approx. 1 million of these cylinders each year each with 5 of these holes that need to be plugged per cylinder. Therefore with, the cost savings of staking 5 million balls per year vs. buying 5 million standard plugs can be significant , and this costs savings will justify the engineering development necessary to determine the proper bal staking design.   Also, manufacturing has difficulty feeding and installing any sort of standard plug that needs to be oriented (balls can be easily fed into the assembly line).  So... back to my original question.  Does anyone have any idea of how to design the hole & staking tool parameters without excessive trial-and-error in the lab?  The lab work will still be necessary to confirm the design, but I want to get the design close before I start in the lab.  Thanks for any help that can be provided.
 

RE: Plugging Hole in Pressure vessel via Staked in Ball

I've seen something grossly similar done with lead ball plugs in zinc (or maybe aluminum) carburetor bodies... but they only had to withstand a few inches of head... and they didn't always do that.

I'm not saying it's impossible, but it's so obvious that someone must have tried it already... and designed it out, since we don't see it in practice.

To answer your question, most any mechanical engineering graduate should be able to analytically evaluate your starting design, without even using any fancy tools.  I suggest you rent such an engineer for a while.

You also might talk to some vibratory feeder suppliers; they have decades of experience orienting parts that are nearly but not quite symmetrical.  I don't see expanding plugs as being particularly difficult to feed and orient.

The term of the financial balance equation that you seem intent on ignoring, and which the other members keep trying to highlight, is that you could easily lose five million dollars in a judgment resulting from a failure of any one of those five million cheap balls.  Better hope you don't lose two.



 

Mike Halloran
Pembroke Pines, FL, USA

RE: Plugging Hole in Pressure vessel via Staked in Ball

hi there all
I've been involved in quite alot of hydraulic manufacture and maintenance ,and ball staking is a common and accepted practice for sealing manufacturing holes in componentry with system pressures up to 10000psi... force is calculated on psi to surface area so the force against the ball is fairly minimal,all we used was a pin punch to pop the ball in and a 3/8 ball in the end of a punch to pein the hole over(these were only small production runs how you do this on a large scale would obviously differ.. oh on the legality side of things all hydraulics have peoples lifes in the balance every application the potential for failure is allways there be it a crane or a car!!      

RE: Plugging Hole in Pressure vessel via Staked in Ball

(OP)
Thanks Seano51450!  You are the first poster who has attempted to address my original question.  I must say I am disappointed by most of the replies.  Everyone here appears to be implying I am an idiot for even considering this idea.  However, as Seano5150 mentions, it is very common in the auto industry as a way to seal hydraulic cylinders.  If you don't believe this, just open the hood of your car and look at the ABS hydraulic unit as an example of where this is commonly done.  As to some of the other comments posted:
     1.    I am a graduate mechanical engineer so I don't need to "rent one".
     2.    The calculations would appear to be straight forward, but it comes down to the fact that the force holding the ball in place is the normal force due to the interference between the ball and the hole and the friction level between the ball and the aluminum housing. So what is the simple calculation that tells me what the normal force is for a steel ball in an aluminum housing for 0.05mm interference?  What about for 0.1mm interference?  If I knew how to calculate this force, I wouldn't have asked the question in the first place.
     3.    The manufacturing engineers I am working with have over 30 years experience with assembling similar products, including the types of plugs that have been mentioned, using various feeder devices (including vibratory ones), and they would prefer using staked in balls.

Just because we have a solution that works (plugs), doesn't mean we are not constantly looking to find a better solution (balls) based upon cost, ease of assembly, etc.  In fact in the auto industry, 90% of the design work is not inventing something new, it is optimizing/refining existing designs.
    So I guess my point is, I realize there many ways to seal a hole in a hydraulic vessel, but I am looking for tips on how to do it using a ball from someone who has experience with this common approach.  I am disappointed that of the many replies, only one addressed the question.  Although I appreciate these other suggestions, I find it a little insulting that when I try to politely redirect the topic back to the original question, I am told I am an idiot for even wanting to do it this way in the first place!  The whole reason for my post in the first place was that this is a very common practice and I was just looking for some advice from someone who has done this before on what I should be looking for in my design.  
Thanks to everyone for all of the replies (good and bad).  All comments/ideas/suggestiosn are always appreciated!
 

RE: Plugging Hole in Pressure vessel via Staked in Ball

Look at press fit equations.  I am not near my references to quote equations.  It looks like you have to resist about 100 lbs(440 N) of blowout force due to hydraulic pressure.

There are rotary staking tools available that could be set up to do the staking.  Or simply a push tool to do the staking.

Drill a stepped hole to provide a step against which the inserted ball would stop.

Ted

RE: Plugging Hole in Pressure vessel via Staked in Ball

It isn't very common among the experience _here_.

Seano just wandered through the door; he could be a high schooler for all you or we know.

The simple calculation is in Machinery's Handbook.

It gets less simple when you peen after pressing, and Mr. Poisson gets involved.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Plugging Hole in Pressure vessel via Staked in Ball

Quote:

Seano just wandered through the door; he could be a high schooler for all you or we know.
or a co-worker that's supporting your opinion (as has happened before.)
Nevertheless, you get what you pay for.  Since this is free advice, you have to take the bad (in your mind) with the good.

Quote:

I am a graduate mechanical engineer so I don't need to "rent one"...If I knew how to calculate this force, I wouldn't have asked the question in the first place.

But you're asking strangers on a free internet site to do the engineering with no idea of whether they're giving you good advice or not. ...which led to the recommendation that you hire someone.  No one's questioning your competence, and you admit a few sentences later, that you don't have expertise in this area.  And as several posts have pointed out, failure to properly design this part could have unpleasant repercussions.

Finally, making snide comments doesn't endear you to those who willingly provide free engineering expetise here.  People are more likely to help those who are willing to help others rather than those that complain about the lack of free answers.

 

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

RE: Plugging Hole in Pressure vessel via Staked in Ball

Have you looked at the ballizing process parameters for sizing a hole. A lot of ball suppliers are also in the ballizing business and there have the know how to keep from ruining the hole or getting the ball stuck. You might buy a few balls and get a lot of information.
  
Things like if you are pushing a ball through a hole too slowly you generate waves in the wall of the hole, especially true of Al. In your case this would be good because it would tend to trap the ball. By selecting the right size ball and insertion speed you could possibly generated an extremely tight fit in the part.  

RE: Plugging Hole in Pressure vessel via Staked in Ball

(OP)
First, somehow this string got too personal.  That was not my intent.  Sorry if I upset anyone.  Second, everyone has provided lots of good info.  Let me try to reply back to some of the comments posted.  I have researched and found the equations for determining the force to press fit a cylinder (pin) into a hole and think I understand these equations, however I am not sure they apply to a ball pressed into a hole.  As I understand it, the force to press in a pin is F = friction coefficient * contact area * contact pressure. The contact pressure is a function of the pin/hole diameters, the modulus & Poisson's of the materials and the interference. If I assume the contact pressure equation is the same for a pin in a hole as for a ball in a hole (which it probably isn't exactly the same), I still have a problem in calculating the contact area. For a cylinder it is pi * Length * Diameter.  For a ball, the theoretical contact is a line so L = 0, therefore contact area = 0, therefore force = 0.  So what I am trying to find is force equation for a ball press fit into a hole.  MikeHalloran, you mention this is the Machinery's Handbook, but I can't find anything about a ball pressed into a hole.  Could you give a page number or index entry as a reference?  hydtools, you mention to look at press fit equations.  That is where I found the equations I mentioned above for a pin in a hole. Do you know of a good reference that discusses a ball in a hole?  That is the crux of my problem.  I have found good examples of a pin in a hole, but nothing on a ball in a hole.   If anyone knows where I can find this reference, it would help me out tremendously

As far as the ballizing, I had not considered that before.  Although, as I understand ballizing it is not used to plug holes, rather it is used to resize holes and improve the surface finish.  However, the companies that manufacture the balls and ballizing equipment might be a good resource of information for my problem.  I will try to contact one of them to see if they can help out.  Thanks for the idea.  
 

RE: Plugging Hole in Pressure vessel via Staked in Ball

Sorry to rake you over the coal, Mr. Roach, but we need to have all the legal disclaimers up front.  You seem to be ready to spend a lot of development money and test time up-front for this project, and to understand the risks, which is what we were asking.

"For a ball, the theoretical contact is a line so L = 0, therefore contact area = 0, therefore force = 0."

No, look at Roark's Formulas for Stress and Strain for Hertzian contact.  For your situation, the hole will expand, the ball will contract, and you will get a funny pressure distribution over a somewhat cylindrical section of the ball's surface.  Not a simple problem, but if you dig into the references in Roarks, and go to the source (Timoshenko may be a good place to start) you may find some classical analysis that will help you predict better.

As far as the staking/peening operation on the backside of the ball, you are dealing with a plastic deformation process.  Classical analysis is pretty limited, but Slater's Engineering Plasticity has some pretty good descriptions of the mechanics and some of the old-style solution methods (method of characteristics) that can give you a place to start.  Past that, you will want to look into FEA codes that can handle material and geometric non-linearites (large plastic deformations), these were fairly cutting edge stuff 10-15 years ago, but are becoming somewhat common today.  What is not common are material parameter handbooks to tell you what the various elastic/plastic material model coefficients should be for your particular material(s), nor far less what the likely 3-sigma distributions of those parameters may be; you will likely need to pay to have a reputable lab develop a large number of stress/strain curves, under various loading conditons, to get to where you ought to be.

At some point in the analysis, you may find that plastic staking from the backside of the ball may not reliably maintain a compressive load to hold the ball against the bottom of its hole, and the ball can in some cases slip backwards, however slightly, ruining the sealing line.  The expansion plugs can have this problem as well, and (some plugs) use an elastomeric coating or other seal element (e.g. multiple ridges to create multiple seal lines) to help increase the friction coefficient and development of the seal line by plastic displacement of the elastomer.  Maybe you could put a stepped hole for the ball to bottom against, and put an O-ring into the corner between teh ball and the step, would seem like a more reliable way to seal something than just pressing in a plug.

Sorry, that rambled a bit, but as somebody said, you are getting this for free.

RE: Plugging Hole in Pressure vessel via Staked in Ball

MH covers the shaft in hub case, which is a starting point.  I did not mean to imply that it covers the ball case; it doesn't.

As btb points out, you need the housing to behave elastically in order to retain some radial pressure at the sealing surface... and when you induce plastic behavior nearby, e.g. by staking, you may inadvertently relieve some of the elastic stress you need... and then it gets complicated.

How about an autogenous EB weld of a simple aluminum plug?



 

Mike Halloran
Pembroke Pines, FL, USA

RE: Plugging Hole in Pressure vessel via Staked in Ball

(OP)
Sorry for my late reply, I was out of the office.  The welding is and intresting idea that I had not considered.  I discussed this approach with my manufacturing engineers and they don't want to try and tackle welding at this time.  I think I will have to stick with ball staking for now.  I have been doing extensive literature searches on the engineering theories for plugs pressed into holes and am hoping I can find something there that will give me some hints on how to proceed.  Unfortunately most of the examples are for cylinder plugs (haven't found one for a ball yet). It will take me some time to try and modify the equations from a cylinder to a ball.  I guess that's why they pay me the big bucks. (ha ha)   

Thanks to everyone for all of the input.  It helped to guide me in the right direction!

RE: Plugging Hole in Pressure vessel via Staked in Ball

Staking will be similar to riveting. You must yield material from the side of the hole into the center. The ball will be trying to yield this material back as pressure pushed it out. Using a cylindrical plug will be less costly and require less material to be deformed than a ball.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: Plugging Hole in Pressure vessel via Staked in Ball

Ah someone with the same problem that I have.  I'm trying to plug a brass housing but my problem is more complicated because of galvanic corrosion so I'm thinking of using a brass ball or 316 which are drastically softer than say 440C or 52100.  I also have to withstand 3250 PSI and seal against gas leakage.  Now that's exciting.
There is no way I'm going to solve it without testing and I guess you are in the same boat but looking for a starting point.   Well I did some googling for ballizing,  ball burnishing etc.  and didn't get too far.  But I think there is a lot to be learned from those guys.  If anyone comes across any good resources on bollixing or ball burnishing please let me know.
As for my starting point .  I plan to use a press fit for 0.0005" to 0.002" interference.  Since Aluminum has a lower modulus you can probably go higher.
 

RE: Plugging Hole in Pressure vessel via Staked in Ball

Why are you trying to reinvent the wheel. Lee Plugs from the Lee Company are cheap and reliable and have proven for many years.  

RE: Plugging Hole in Pressure vessel via Staked in Ball

Unclesyd:  Those guys are bad, ass thanks.  http://www.precisionballs.com/Ball_Sizing.htm

Israelkk:  I'll look into those Lee plugs but I work in corporate American on a product sold to Americans. I'm re-inventing the wheel for the same reason everyone is outsourcing to the country with the lowest labor costs.  Must be nice to be in Aerospace :)

RE: Plugging Hole in Pressure vessel via Staked in Ball

see United States Patent 6679953

Basically, they nitride the steel housing to cause the steel to expand, and better seal the ball after press fit.  Perhaps a similar process (anodizing?) could work in your case.

Still think you'd be better off incorporating $0.0003 per unit of some elastomeric element under the ball to ensure a seal.

RE: Plugging Hole in Pressure vessel via Staked in Ball

Israelkk:  I took at look at the lee plugs, and I quote from the website "It is slipped into a reamed counterbore in the product"  at this point sounds like a backup plan if I can't get the ball to work.  Thanks

RE: Plugging Hole in Pressure vessel via Staked in Ball

debun

This is what nice about the Lee Plug which is freely inserted into a reamed hole and then a coned small cylinder is pushed/hammered into the plug pressing it radially. The plug also has a series of round slots that to my opinion serve as a labyrinth to avoid leaks. So basically the plug is in contact over a cylinder while a ball will be in contact with the body only across a round circle/line.

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