I would be glad to get quality answers from skillful and experience engineers researchers and scientist concerning how to determine the PV limit for polymers used in automotive bearings applications.
I have researched a lot about this topic, however I am not satisfied with the answers currently at my disposal.
I am not referring to the formular used for calculating PV; this is straightforward. But the criteria for setting the PV limit.
1. One popular criterion i see mentioned in literature commonly is that PV limit is the PV at which the wear of the polymer increase excessively. This I think could be subjective to individuals. It will also depend on the quality of the polymer developed by specific person. I mean are there references that illustrate this in terms of number whereby subjectivity is minimized.
2. Are there various wear rates for various automotive polymer bearings application regarded as critical limits which can be used to determine the PV limit of these polymers?
kindly answer by explaining and possibly providing references.
Thank you in advance.
While I can hardly tell you something about assessing 'wear' or 'wear limts', I can at least guide you regarding your 2nd question:
Automotive OEMs do not specifiy 'wear limits' or alike - they specify "drive cycles", calendar years and alike of component 'life'.
These requirements are to translated into the component specifications. Regarding your question about PV limits: as PV can be reduced by enlarging the bearing, a multitude of polymers with as many individual PV limits result is a lot of potential solutions. The final choice typically depends on cost and size (the space available is restricted) and has to be qualified to 'survive' the lifetime specification given.
Thus, PV limits are not quite as important as you seem to presume ...
@Dreher.
Thank you very much for taking your time to contribute to my question and learning process.
Regarding what you mentioned that OEMs specify time rather than PV, I feel that when a PV limit is stated with corresponding wear rate you can estimate the time as well. Hence I will ask you here, if OEMs specify time for a bearing without specifying pressure and velocity, if the bearing is used at much higher pressure don't you think it will fail much earlier than the specified time?
Now concerning the use of enlarged bearing, is the enlargement in terms of area or thickness? whichever one, I think PV limit can still be obtained for the new enlarged bearing.
With respect to cost, I am currently not looking at that factor, because generally, better things are costlier. for space, once you have space limitation you would likely go for a bearing material with better limits if you can afford them.
Now concerning the importance of PV limit. I am not sure if you consider polymer bearing application or experience. Almost all the commercial polymer bearing sellers catalogue that i have seen contain PV limits for each product. Although they do say that it is just a guide, because application condition may not be exact as the testing condition that gave rise to the PV limits.
Once again thank you for contributing.
@Dreher
these are few examples of the PV limits mentioned in commercial documents.
in the second link, it was mentioned that PV is a prime factor in material selection
https://www.google.com.sa/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwiKusCLjK_OAhVFWRoKHVHJAvYQFgglMAE&url=http%3A%2F%2Fwww.gtweed.com%2Fdocs%2Febrochures%2FPlasticBearingDesignGuide-0901.pdf&usg=AFQjCNFP28Xpxx6ZXvia64HEh8GcpTmf_g&sig2=Cv4nMR9wBcG_Th0j4_COrw
https://www.google.com.sa/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0ahUKEwjzhtXljK_OAhUJVRoKHbhDAscQFggpMAI&url=http%3A%2F%2Fwww.dupont.com%2Fcontent%2Fdam%2Fdupont%2Fproducts-and-services%2Fplastics-polymers-and-resins%2Fparts-and-shapes%2Fvespel%2Fdocuments%2FE61500.pdf&usg=AFQjCNH7awPKqiANgfhAiVq8FRSPSj7YPg&sig2=bERv9SPAtpMJQ-tB5ZYuug
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