Synthetic material used for very high load rollers?

[Adam HarrisParticipant @adamharris13683]

I have a 2MT gantry hoist trolley where one of the rollers has chipped badly albeit still functions. These rollers are 82mm diameter x 80mm wide x 20mm bore and are rated to 1000kgs each. The material is a very hard synthetic material that is too hard to be nylon. PU equivalent type for pallet trucks are not available for loads above 700kgs. The bearings are fine and I would like to buy an 82mm+ diameter bar of the material and machine it to fit the existing salvageable bearings.  Anyone know what the likely material this should be?? Please do not bombard me with Health and Safety warnings.

[Adam HarrisParticipant @adamharris13683]

[David George 1Participant @davidgeorge1]

Acetal is what I would use.

David

[Roderick JenkinsParticipant @roderickjenkins93242]

I’m wondering whether the rollers were originally as hard as they are now.  Nylon can harden with age which may be why they have fractured.

Rod

[Adam HarrisParticipant @adamharris13683]

Thank you David. Is Acetal easy to machine?

[Adam HarrisParticipant @adamharris13683]

Rod the trolley is not terribly old at 2010 so I think unlikely. Does PU harden much over 15 years?

[Dick HParticipant @dickh]

From the look of the roller I would guess UHMWPE (ultra high molecular weight polyethylene).

[Adam HarrisParticipant @adamharris13683]

UHWMPE sounds quite exotic and seems difficult to buy short lengths (100mm) so works out more expensive than Acetal. Googling says UHWMPE favoured for its impact resistance but clearly this roller has not performed well on impact so I think Acetal may be the better way forward? A 90mm x 100mm Acetal is £30 which is cheapest I can find

[Adam HarrisParticipant @adamharris13683]

Acetal seems to machine very nicely compared to UHWMPE

[peak4Participant @peak4]

Have you had a word with Direct Plastics?
https://www.directplastics.co.uk/uhmwpe-rod

UHMWPE seems a bit cheaper than this; though I would think they would be able to advise on the most appropriate material, but it might be something even dearer.
https://www.directplastics.co.uk/acetal-rod

Bill

[David SeniorParticipant @davidsenior29320]

directplastics.co.uk offer both with acetal being more expensive than UHMWPE

Acetal is certainly easy to machine. I’ve never needed to machine UHMWPE myself so can’t comment on that.

Dave

[Adam HarrisParticipant @adamharris13683]

Thanks.Direct Plastics warns on website downsides of UHMWPE “Maybe not suitable for high load applications”

[Adam HarrisParticipant @adamharris13683]

I was making some top hat washers from a nylon or maybe UHMWPE (I’m not good in keeping my materials well labelled!) rod for use on bathroom basin supports and I do remember being appalled at my lack of ability to turn smooth surfaces and the binding up with sticky strings. I think I will stick with Acetal unless any other types are proposed. Many thanks

[Ian PParticipant @ianp]

Why are the rollers so wide?

Sort of rhetorical question really but I wonder why the designer chose to use a large chunk of plastic and profile it in such a manner that in use it was subject to bending loads. My initial thought was (when making replacements) to bore the bearing recesses deeper into the roller so that they are directly between the axle bolt and the track surface.

In fact no need to make brand new rollers, just modify the existing ones (and re-arrange the spacers on the caphead bolt)

Hopefully not relevant now but Acetal is a dream to machine, especially with polished carbide inserts.
Starting from scratch the ballraces would not really be needed as Acetal is a low friction material and would happily run for many years on a bolt shank (your looks about M12)

IanP

 

[bernard towersParticipant @bernardtowers37738]

PCD inserts will transform your turning of all plastics.

[Adam HarrisParticipant @adamharris13683]

Yes Ian, well that modification makes sense but the roller’s bore for the shaft is 20mm,  as is also the bore for the bearing (5204 ZC3), so I reckon the shaft is a 20mm shaft that has M16 threads either end, therefore the inner plastic bore will be supported by the steel shaft, in addition to  the outer diameter of the steel bearings both ends. I have not yet disassembled as the all the bolts clamping the 2 outer plates together require a 14mm allen key which is missing from my untidy tool drawers. I think the rollers are wide because the material lifted by the hoist can swing a bit and so rock the trolley, just as pallet truck rollers are wide because the load the legs lift can sway about as you go over ground that is not perfectly flat. It is only these 2 rollers supporting the hoist which is rated to lift 2 MT. I think it is easy to replicate the original design so I will be sticking to that

[Adam HarrisParticipant @adamharris13683]

Well Bernard I have never used or even seen PCD inserts. I am hoping fresh CMT inserts at high speeds will get suitable results

[cedric 1Participant @cedric]

<p style=”text-align: left;”>Does the roller have to be plastic? Would common mild steel do the job?</p>

[DiogenesParticipant @diogenes]

Are you sure they are not standard off-the-shelf industrial ‘load wheels’ – something like this 1000kg rated nylon roller

https://www.technicawheels.co.uk/p1730-80-93-47×14-nylon-roller-no-bearings.html

should fit a 6204 bearing

There are other sizes I’ll leave you to do the scrolling 😁

..not much acetal on offer, maybe that tells you something..?

[FatgadgiParticipant @fatgadgi]

Nylon would definitely be my preference.

Higher impact and generally tougher than acetal.  It’s not as hard as acetal, but I think the risk of breakage is more important.

There are idiot’s ways of finding out which plastic the current one is; you burn a small bit of the plastic (like a shaving off the edge), set it alight, then blow the flame out.  Nylon, from memory, smells like burning wool, acetal is acrid and nasty. Probably comes with a health warning these days.

Cheers Will

[BazyleParticipant @bazyle]

They may well have been intended to be a little soft so that they don’t stop dead on a small bit of grit on the floor.

[noel shelleyParticipant @noelshelley55608]

One interesting point that was drawn to my attention was the moisture absorbing properties of nylon, quite a surprise. I used acetal to avoid this issue and it machines very well.  Noel..

[Adam HarrisParticipant @adamharris13683]

Thanks Will, I like Acetal because it machines much better. Interestingly directplastics.co.uk suspect from the photo of the chip-type fracture that it might be Acetal because apparently Acetal can indeed go hard and brittle from very heavy loading, however they actually suggest Nylon 6 as better for the job.

[Adam HarrisParticipant @adamharris13683]

Thanks Diogenes for that link to technicawheels.co.uk – I did not find that in my googling but will look at it now. I have not found a roller of 80mm length that goes above 700 kgs

[Dick HParticipant @dickh]

Just out of curiosity, before you toss the old roller away, see what the density is, the roller looks unfilled, Nylon and Acetal are similar in density at about 1.14 g/cm3, PE should be about 1 or lower, i.e should float in water.

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