Delrin: ability to accept pressed bronze bushings?
Delrin: ability to accept pressed bronze bushings?
(OP)
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 immediately. (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? A better, commonly-available plastic we should look at?
Any observations, suggestions that help toward the goal of getting these rollers rolling again would be greatly appreciated.
Thanks.
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 immediately. (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? A better, commonly-available plastic we should look at?
Any observations, suggestions that help toward the goal of getting these rollers rolling again would be greatly appreciated.
Thanks.





RE: Delrin: ability to accept pressed bronze bushings?
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Alternatively, have you looked a plastic plain bearing instead of sintered bronze? There are a number of products from GGB that may be suitable.
http://www.ggbearings.com/products.php
RE: Delrin: ability to accept pressed bronze bushings?
Do you think the issue could be not the properties of material but the age of the nylon? Would the delrin (simply because it's new) be better suited to receiving the bronze than old nylon will?
I guess the question is: do these plastic brittle with age?
Thanks again.
RE: Delrin: ability to accept pressed bronze bushings?
James Spisich
Design Engineer, CSWP
RE: Delrin: ability to accept pressed bronze bushings?
i would give someone like Alro a call for a specific recommendation.
http://www
RE: Delrin: ability to accept pressed bronze bushings?
Yes, plastics can become embrittled over time, due to exposure to UV radiation, as well absorption of oil and other organic fluids.
RE: Delrin: ability to accept pressed bronze bushings?
What you are facing is an issue where plastic elongate undger stress. Unfilled nylons and acetals can elongate 80% or more before rupturing.
If you use glass or other special reinforcements in the acetal or nylon, the elongation to break may drop to the 2-4% range.
I suspect that you just dont have enough of an interference fit for your design to work.
See the following link
http://pl
Another possibility to help with wear is to change the rollers to a high molecular weight nylon. For example - DuPont Zytel E51HSB would be a good choice. The higher molecular weight material has better toughness than the standard nylon 6.6 materials.
A 3rd possibility is to insert mold over the metal inserts with the plastic materials
RE: Delrin: ability to accept pressed bronze bushings?
Another trick that I use is to leave a small "internal" ridge in the bore of the nylon at the start of the bore(that is the internal bore of the ridge is slightly smaller than the bore of the nylon)-hope that makes sense,
a groove is then machined in the outside of the bronze bush which corresponds in size with the "internal" ridge.
When the bronze bush is pressed into the nylon, the nylon expands at the ridge, but then snaps back into the groove of the bronze bush, thus applying a crude type of circlip arrangement which conteracts any end thrust which causes the bronze bush to move outwards.
Trust that you can follow my example.
I also do similar to hold precision roller/ball bearings into nylon/delrin/ UHMW components, in these cases the bearings are pushed completely passed the ridge and to date have not had any problems with this method.
Ross
RE: Delrin: ability to accept pressed bronze bushings?
James Spisich
Design Engineer, CSWP
RE: Delrin: ability to accept pressed bronze bushings?
Russell Giuliano
RE: Delrin: ability to accept pressed bronze bushings?