Delrin: pressing bronze bushings into?

Idle rollers (1" dia. x 1.25" length) on a small 20-year old conveyer system are made of nylon running on steel shoulder bolts turning < 100 rpm. The
nylon rollers wear over a year or 2 such that the bearing clearance is no longer acceptable and the belts that run over these rollers start to wander.
Replacement rollers made from delrin don't last much longer.
So we've decided to try inserting sintered bronze bushings into the rollers. When drilled, the nylon bushings are not holding the bushings. They press in (-0.003 interference fit) but then loosen. (The machinist says the nylon is cracking, but I can't see evidence; it looks to me like scoring, not cracking.)
Does delrin have better properties such that it will be better at maintaining the pressed bushings?
Any observations, suggestions that help toward the goal of getting these rollers rolling again would be greatly appreciated.
Thanks.
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On 26/02/2010 17:30, Paul Conners wrote:

Try UHMWPE (Ultra high molecular weight polyethylene) http://en.wikipedia.org/wiki/Ultra_high_molecular_weight_polyethylene
The issue with the forced insertion of bushings in Nylon or plastics in general is the creep. Those materials slowly deform under strenth. Better to bound or use other anti-rotation assembly with no interference fit.
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Would the use of nylon containing molybdenum disulphide, (Nylatron) be a possible solution? Best wishes, Reundant Roger
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