Injection Molded Bearing 3

[MECH8T4]

Our engineers are working on design a two part bearing which will act to support a top box and allow it to rotate and self locate by lifting up via the bearing and dropping down via the bearing. The box would weight about 70lbs and the bearing would have a diameter of approx. 4 inches

We have run proto units in delrin which seem to work well but will be producing injection mold tools to run production with. We have some areas as thin as 3/16" or so and wanted to know what material we should run for producion that would ensure we wouldn't have failure of the part due to impact and cold wheather conditions.

If you had to recommend the strongest possibly material option, would it be some grade of Nylon, Delrin, or Polycarbonate? We cannot have failure.

Any help or advise would be greatly appreciated.

We would mold samples off the tool and run some testing to confirm the durability, but would like to strt with the right possible materila spec.

 

[MikeHalloran]

>>>We cannot have failure.<<<

Then don't make the part. Go out of business and forget it.


The Unobtainium store is closed, and won't reopen until my Time Machine gets back from the shop.


Where's the other part? How do they interact?
What loads and speeds are involved?
What's the environment like? "Cold" is not sufficient.
I don't personally care, but you'd need to answer all those questions and more in order to propose a suitable material. .... and you want us to do it, blind, without even a single dimension?

We're not _that_ good.

You've done some unspecified testing in machined billet Delrin and didn't have a failure. You'd know more about your problem if you did have a failure. Test it until it fails, then figure out how it failed. That will tell you what to do next.



Mike Halloran
Pembroke Pines, FL, USA

 

[asimpson]

Have a look at IGUS bearings.

 

[MECH8T4]

Thanks for the emails Mike/Simpson
The mating part to the half shown is virtually a mirror image to the part.
The parts rotate on each other 180 degrees to the right with a stop and then 180 degrees back.
I didn't think I would need to get the details to the table on the part itself to the point of supply of some of the dims etc but was looking more for possible suggestions on materials based on previous deisgn knowledge from someone maiking parts for outdoor use.

We have worked with nylon sheet to prodcue test parts for a similar application and find it to be unbreakable(yes Mike), but have some concerns possibly with water absorbtion.

We will probably prodcue tooling and run parts in several materials and come up with field and internal testing to confirm strength ourselves, but just thought I would put this put there for feedback. The IGUS bearing suggesting is good as it will give us an indication of what has worked for them.

 

[MikeHalloran]

Now I get it. The part is mostly self-conjugate. Which means that the functional feature of interest is a cam ramp. With a little inside-out thinking, you could probably make the part completely self-conjugate, so you'd only have to buy one mold. The key to that is that the radial bearing doesn't really have to be continuous; it could be replaced by two half-cylinders of different radii.

Self-conjugate parts in turn impose a material limitation; the cam ramp slides on the same material of which it is made. Not all materials behave nicely under that circumstance. Be sure to mention this limitation to any potential material suppliers.





Mike Halloran
Pembroke Pines, FL, USA

 

[MECH8T4]

Hi Mike-thanks for the reply.
We looked at one part for both, but have limitations on mounting them in place which requires the two halves.
Looking to run the parts probably in polycarb or polycarb/ABS blend.

The friction between the parts with the rotation isn't as big a problem for us in this case, though we have run into this in the past where it became an issue.

Thanks for your help

 

[MikeHalloran]

I don't think you'll get the results you want running polycarbonate on polycarbonate.

If you must buy two molds anyway, you could use two different materials.



Mike Halloran
Pembroke Pines, FL, USA

 

[MECH8T4]

The parts we have in delrin work fine, not sue if the poly would be different.
Concern on running one part in one and the other in another would be shrinkage possibly, unless planned for from the start.

 

[dgallup]

If your machined parts work in Delrin why not stay with it? There are some nylons that are pretty dimensionally stable and stronger than Delrin. If you really need stronger parts and dimensional stability PPS is a good material. Don't know about it's frictional properties. It's what we usually go to as one step above nylons. You don't say anything about loads, life expectancy, cost, quantities, etc. so like Mike said in his first post, don't expect miracle solutions, we are not mind readers.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[MECH8T4]

Thanks for the reply Gallup.
We have the machined delrin parts in the field in an actual unit.
We want to proceed to produce the tools in order to make more parts to allow us to test and verify the design/strenght etc.

I can get you more info on the parts themselves and how it is used if it would help. It sounds like delrin might be a good option and so might nylon.

You also reference PPS, which I don't know what this is.

As far as costs go, not an issues her for us as this would actually save us money to an alternative design in place.

Our goal is to get the tooling made, ideally to maybe run several differnt material optiosn to confirm a selection via testing of run parts. Just thought getting someones expert advise beyond ours might help confimr to go with delrin or poly or nylon etc.

 

[MikeHalloran]

>>>more info on the parts themselves and how it is used if it would help<<<

<sarcasm>
No, we'd rather guess in the dark.
... or play twenty damn questions.
</sarcasm>


Mike Halloran
Pembroke Pines, FL, USA

 

[MECH8T4]

Thanks Mike
I will be able to upload some drawings of the part tomorrow and explain more about the application as well.

 

[sreid]

You might consider UHMWPE.

 

[MECH8T4]

Thanks sreid-will look into it as well.

 

[ornerynorsk]

The only thing to watch out for with UHMW is that it cold flows under load. In fact, it is commonly cold pressed, ala compression molding.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[MECH8T4]

Thanks for the responses
We are leaning towards running the part in delrin as was sampled. Have not run destructive tests on the unit, but was thinking we would go ahead and produce tooling and then do so with actual parts.

These are going outside and will be exposed to temps form -40C to 70C and really act as a bearing and need to be able to take some impact when the parts rotate.