Plastic v bronze bushes/bearings

[Bob Brown 1Participant @bobbrown1]

Has anyone considered or used plastic bushes/bearings in things like wheel bearings or linkages. I am thinking of using Igus bushes (good to 250C working temp) in place of bronze ones on a 3.5" scale 2-6-2 loco I'm building.

Some will probably say it would not be in keeping with the design but my view is things have moved forward and the use of modern materials should be incorporated.

Any views and opinions welcome good or bad.

Bob

[Bob Brown 1Participant @bobbrown1]

[jason udallParticipant @jasonudall57142]

Igus plastic is superb.
Note the housing sizes are designed to “squease” the plastic a little. .
So selection of shaft bearing housing sizes is specific to the material .
Igus also favour s low surface speeds ( phenomenonal endurance but low speed)..so as wheel bearings ..maybe not..see data sheets…
…also performance under pressure( say again wheels support loads) is much lower than bronze….the shaft will tend to press through in the direction of the load. …again not poor but not bronze….

As to realism. ..well you are building a model of a steam locomotive ….maybe authenticity is more important than function. ….but it is your model.

[jason udallParticipant @jasonudall57142]

Btw as to keeping with the design…ball bearing races would be an excellent functional replacement. .but authentic …?….

[Bob Brown 1Participant @bobbrown1]

Jason,

I'm thinking function over form or at least up to a point.

The bearings would not be that visible so should still retain the "look", I'm thinking H370 which they can supply in imperial sizes down to 1/8" ID.

Hole size in the housing allowing for fitting the bush is usually the OD specified so 3/16" OD is 0.1875 +/- .0002 e.g. in this example ream 3/16" should do the trick.

I am also looking to change some of the material specification from BMS to stainless steel to reduce the problem of corrosion. Shafts and rods seem the most likely as they are exposed to the elements, I have worked with stainless steel in the past and understand which alloys are easier to machine, cut, file etc. and which are a real pain to work.

[jason udallParticipant @jasonudall57142]

Just so…
Igus used to recommend ground hard anodised ( not certain from memory?weather ground then anodised or ground after anodising) ali shafts…for longevity and friction. .but ss idealy ground would be good ( and not unconventional)
Are you talking turned from bar or moulded bushes. .again years ago igus weren’t keen on one
Machining your own.. ( they used to be very “protective” of their products reputation)..
Good luck..

[Bob Brown 1Participant @bobbrown1]

I was thinking standard bushes all be it the lengths may need modified rather than mess about machining them running on 304 stainless shafts/pins. I think wear is more down to surface finish which should not be a problem to get something reasonable on 304 ss.

[Russ BParticipant @russb]

I've been keeping Oilon rod in mind for such a purpose but I've not had chance to use it yet.

It's only a couple of quid for a 250mm Ø20mm bar from DirectPlastics

[Bob Brown 1Participant @bobbrown1]

My concern with Oilon would be it's service temperature which is relatively low at 110 C and it's melting point being only 220 C.

iglidur® H370 as an example has a max long term application temperature of 200 C

plus you have to consider water absorption which can cause problems

[Howard LewisParticipant @howardlewis46836]

Be aware of the corrosion problems that happen if a hygroscopic material is used with a shaft made from almost any material. A steel shaft in a nylon bush is guaranteed to rust if assembled dry. With lubrication, (I favour grease during assembly) life is much better, and friction is reduced.

Ideally, make provision to supply lubrication into the bush, whether grease or oil.

Also, if grit ,of any size, gets into the bearings, the bush being softer than the shaft will hold the grit, and act as a lap to grind away the shaft.  "Plastic" bushes do not withstand shock loads too well, and will extrude.

On Leyland Leopard buses, the Glacier DU shackle pin bushes were good, with auto chassis lubrication, but the flanges extruded with the lateral loads, and had to be replaced to prevent horrendous wheel wobble and steering shake. 

If in doubt, over engineer, as has been said on other threads, to "Fit and Forget"; unless you like replacing parts!

Howard

Edited By Howard Lewis on 01/04/2014 18:34:28

[Russ BParticipant @russb]

Posted by Bob Brown 1 on 31/03/2014 15:28:47:

My concern with Oilon would be it's service temperature which is relatively low at 110 C and it's melting point being only 220 C.

iglidur® H370 as an example has a max long term application temperature of 200 C

plus you have to consider water absorption which can cause problems

I didn't realise the difference was so huge, I'll keep that in mind too thanks

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