Chain conveyor thru a heater.. Holding tension

[EspElement]

Hello guys, I am new to this forum and I am currently working on my engineering degree.. I work as a designer now for a palletizing company.. i have a very unique application that i would like to share with some others and get their thoughts

A company that is very close to our facility is buying a chain conveyor that is running thru a heater.. They produce chemicals.. and they send barrals of them into the heater to liquify them.. They currently run gravity conveyor thru it and they a stick to push and pull them thru.. They would like a powered application and due to our limited space, cant use live driven roller.. We offered using chain conveyor for the application.. Heres what i am doing

Using double 100 pitch chain.. 2 driven chains.. barrals 550 lbs each.. up to 9 on it at a time.. They would like to run the conveyor in forward and reverse.. so a center driven application is required.. Conveyors are about 12' long.. temp gets up to 200 degrees F.. I am able to drive the conveyor outside of the heater on the tail end of the normal running direction.. my solution is to use 2 custom chain tensioners with 2 different springs.. one taking up about 200 lb of load (tsubaki recommends only using 150 lb max of tension on the chain without prematurely stretching it.. they claimed we could use a little more, due to high safty factors.. im not sure where they get this when i calculate the working load to be 5000lb per chain) and the 2nd spring take up about 500 lb of load.. (due to the coefficent of friction on the 550 lb pails, my max load is 1980 lb(550*9*.4), so about 1000 lb on each chain) since i am pulling down on the tightener 90 degrees, i figure the tightener will take half and the mount for the tightener will take half

i would wrap the chain 90 degrees on each idler sprocket that is attached to the tensioner.. below it a 180 degree wrap on the drive.. the tensioners will push in toward each other over the driven section.. I invision when the chain is ran forward the leading tensioner will compress its 200lb load, and as its pulling the larger load, compress into the 500lb spring (if chain has expanded, spring will take up the difference).. on the tail end, it will work in reverse, as the chain will become loose it will pull it tight against the drive.. so no matter what direction i run, or how much the chain expands.. it will stay tight on the drive.. what would your guys opinion on this application be?

I appreciate anyone who is interested in reading my issue.. just want to get another oppinion on my situation.. i plan on getting involved in these forums to help me learn more about fellow engineers applications

thanks again!

 

[zekeman]

Need a drawing .

 

[EspElement]

I thought about that.. its very hard to discribe.. I quick drew a very bad sketch (with my laptop mouse) of the application in paint.. Just showing how my drive and tighteners function.. I could get some better autocad drwings when i get to work monday as well

 

[EspElement]

Oh and thanks for the post and interest

 

[dvd]

You can drive the take-up end of a "standard" conveyor by using a shaft mounted reducer, or a u-joint drive and eliminate some of your take-up complication. Your conveyor would just have "head" and "tail" sprockets with the take-up sprocket being the driven sprocket. The chain needs to be sized to accommodate higher chain pull.

The take-up needs to be sized to tension the chain with load on it plus what would be the return strand of chain on a more traditional conveyor arrangement. So take-up forces and chain forces are higher but the system is not complicated.

 

[EspElement]

I planned on using a hollow shaft gearmotor so i can directly drive each chain.. so are you saying that using the weight of the reducer to pull downward (and additional load) on the chain at all times so that it holds tension on the chain?

Are you saying that my chain might not be strong enough?

Standard 100 pitch chain tensile strength is 24000 lb's double would be 48000 lb's per strand.. I am calcualting the working load of 5333.33 lb's (48000*1/9).. If im putting 1100 lbs max on each chain wouldnt the chain that i selected be adequate? Is there something i am missing? I will be ramping on a motor starter from 0 to 46 fpm.. i calculate the additional load to do that by.. (m/g)a = (4950/32.14)(46fpm/60s) = 118.08 lbs.. with the overall sum of things that still gives me a sf of 5.. please help me if i have this incorrect

I like the idea i wasnt thinking of it in that way and its definitly something to think about.. I wont be at work til tomorrow and when i do i will determine how much room i have to the floor to possibly do something like that.. it deffinitly simplifys the system for sure

thanks for the post! let me know if i got my numbers straight

 

[dvd]

I can't tell by your wording if you plan on separately driving each chain with its own gearmotor. I would not do it that way.

Your tension will be probably be higher than the weight of the gearmotor. You will need a separate tensioning device, which, in my world, would be a pair of air cylinders interconnected through spur gears, an equalizer shaft and gear racks. I am not going to do any calculations for you, so I can't say whether your chain is overloaded and I can't say what the take-up forces will be. But you can figure it out, you appear conscientious and enthusiastic. Check out the publications that CEMA has to offer if you are unsure about conveyor design.

Don't forget to allow for chain stretch, wear and thermal growth when deciding how much stroke you need on the take-up cylinders. A word of caution, if you use springs and the chains grow due to thermal expansion, you won't have the tensioning that you thought you might.

Don't get too far into the design without checking with some of the more experienced people that you work with. This may include mechanics and craftsmen.

 

[IRstuff]

Just how much stretch are you expecting? Commercial conveyor pizza ovens don't appear to have any tensioning on the belt itself:

http://www.blodgett.com/Literature/Parts Lists/Conveyor/S1820E-parts.pdf.

Other systems that I've seen have tensioning built into the freewheeling sprocket assembly, while the other end sprocket is either directly driven or belt-driven.

TTFN

FAQ731-376

 

[PeterCharles]

200 deg F is no great temperature. I don't like springs on chain conveyors, if you really want automatic tensioning just use a gravity weight.

 

[EspElement]

Thanks dvd for the input.. I like having a different view on the application to help improve my final design.. You are right, a cylinder would allow me to have constant pressure on the chain no matter how much stretch.. i will definitly look into using that kind of design

thanks for the thought of the pizza oven design but i think with that application and it moving so slow and driving in one direction.. u can sag the chain/belt to allow it stretch and use the weight of the chain to hold tension on its drive

I dont have anyone to go to at work actually, its a small company and ironicly.. no one this company has an engineering degree.. me being the only one going for it.. but as you said, i am enthusiastic about this and im excited about joining here and keeping up with other peoples designs and opening my thoughts.

thanks again guys! its been very helpful

 

[EspElement]

Thanks Peter, i thought about that too.. I used intralox belting on a conveyor that was very short with a nose roller deisgn in front so i had to drive on the underside.. i used a roller on an arm to hold the tension on the belt.. thought about that, and the suggestion by DVD maybe it can be put together with that thought

 

[unclesyd]

You need to look up the application of "Dancer Rolls" on your conveying system. We used dancer rolls on everything from synthetic fiber tow line to a process making non-woven fabric. If I recall correctly most of our dancer roll applied tension was controlled using air cylinder or pistons.

 

[EspElement]

Thats a pretty good idea.. Definitly something i wasnt thinking about using.. another thing that i could look into using... thanks uncles!

 

[Ross0684]

Hi EspElement
Old saying-keep it simple.
I feel you are way over-designing this application.
You have already worked out the required chain pull of about 2000 lbs (1000 per chain) so why use 24000 lb chain when 6000/7500 lb would suffice or even just 1" pitch transmission chain.
Using such large chain just adds to the bulk of the thing with bigger sprockets/bearings/ shafts etc when it is not necessary.
As you say the conveyors are 12'long I would not even worry about auto take up designs-just use basic mechanical takeup at either the drive position or on one of the end shafts.
The ammount of thermal expansion is miniscule and not worth the worry or cost to implement an auto take up system-just normal design to accomodate wear/ stretch is all that is required.
Just remember on the idler shaft positions to only key one sprocket per shaft and allow the other to float between collars or some other means to contain the side ways movement.
Good luck
Ross

 

[MintJulep]

There are thousands of conveyor ovens and driers that use a spring tensioned take-up at the tail shaft. They run hotter, longer, heavier and faster then your case.

I don't see the need to have the third shaft for the drive.

Just drive the fixed shaft and use a spring tension tail. It'll be fine.

 

[Compositepro]

Walking-beam conveyors also work in tunnel-ovens for heavy loads.

 

[EspElement]

Thanks for your posts..
Ross, it is a project i got involved with in the middle of the game.. the guy who started this project suggested 100 pitch double (1 1/4") for the application.. which is obviously over kill as i stated with the SF.. the customer expects it and is part of what is sold.. unfortunitly even if i wanted to go back its a tough one to sell "why" to the customer at this point

The tsubaki engineer (again, my fellow co worker talked with him about it) said the chain stretch over that distance and that temp change could but as much as a 1/2".. Now it appears many of you are suggesting that isnt enough to disrupt the system.. i suppose you could look at it since the pitch is 1 1/4" thats not even half of the pitch of one link.. This being said, you guys could be right about me over engineering this design

Note: This got me wondering how the tsubaki guy got his numbers.. i researched about thermal expansion in chain but couldnt find anything.. however the expainsion of steel in meters per C is 0.000016.. with a delta C of 72 degrees if i were to have a solid plate 24' (7.31m) long (12' top, 12' return chain) then the expansion of that plate would be (72 C)(0.000016 m/m C)(7.31m) = 0.0084m which is .03315" a 1/32" of differance.. With that calculation there it appears that either tsubaki has a different formula from the construction or i dont got my numbers right.. in reality, with me doing the calc on a solid plate rather then a bunch of small links.. it would actually be LESS then what i just calculated

Also, picking up on what you guys have said too, these chains can handle brutal temps, up to 400 C at times.. and im running it at around 200 F or 93 C which is nothing compared to its max

I do appreciate everyones comments as i continue to work on this project.. Not only is it helping me learn but it is helping me keep my thoguhts "simple" and sometimes as we all do, we get to complicated and think to far outside the box.. and clearly i think that is what i have done..

Does anyone know how i can prove that calcuation i did? I have looked for ANSI Roller chain expansion numbers and came up empty

thanks again guys!

 

[MintJulep]

Your solid bar approximation for thermal expansion is ok, the alternate would be to calculate expansion for each link and add them all up, but you would find that it results in the same number.

I very much doubt the Tsubaki guy bothered to do any calculations. His number is probably at best a swag and more likely a wag.

 

[PeterCharles]

Another thought is that you are assuming the drive and tail shafts are fixed in position. If they are fixed to the outer part of the oven might they not expand a bit as the oven expands??
My reference is 0.013 mm / m per deg C for steel.
With delta C = 72 and length of 8 m then the elongation is 7.5 mm (a bit more than 1/4") or 3.75 mm change in tension shaft position. So I don't think I'd bother with automatic tensioning.

 

[EspElement]

I just quicked checked a site and it appears that number was incorrect.. I also found an inch one that puts me right where you say.. 7.3 x 10^-6 .. (.0000073in/in F)(130F)(288in) = .273 also you stated it would be half of that which is a good observation as well.. a little over an 1/8"

Thanks Peter.. I think this is very close to beable to be solved on my end.. and i appreciate everyones efforts in helping me