Molded Urethane Covered Bearings - Formula to calculate failure under load

[NickJenks]

Hi Guys,
I'm new to the forum and I appreciate anyone who can help.

I am working on a covered bearing product line and need help on defining some allowable loads for urethane covered bearings (over-molded). For example, the most common load this cover will see is when the bearing is mounted onto a shaft and the roller is forced against a load either riding on the covered bearing or the covered bearing is being pressed against the load while rotating.

I know this is a very dynamic situation and there are a lot of forces at work here. This is what I have found for similar types of loads and would like to see if anyone can offer guidance if this is even in the ball park conceptually.

U= [(.075*W*(b-a))/(E*S*(8b)^1/2)]^2/3

U=Deflection in inches
W=Load in pounds
a=inside radius of cover material
b=outside radius of covered material
E=Compression Modulus of cover material
S=cover width in inches

My thought is, if the calculation shows greater than 5-10% deflection then there is risk of the urethane material coming off of the bearing. That is the benchmark we have set so far, thoughts?


Below is an example of a competitor's website that shows allowable load values for this product....Can anyone tell me how they are coming up with these values?

 

[hendersdc]

I don't think any calculation will work for this.

I would start by defining failure (separation of overmold from bearing is one, also consider how much wear is acceptable) and defining the desired life of the product (in terms of rpm and distance). After that, you will need to perform testing to determine at what load you meet your desired product life with an acceptable amount of failures. Be sure to test at the worst case operating temperature and humidity conditions.

 

[3DDave]

Almost certainly they created a test rig and did a lot of testing, both to confirm the basic mechanics and to confirm their production process to understand how to control failure modes.

 

[NickJenks]

Thank you for the replies. This is what I thought as there are just too many factors with temperature, rpm, load, urethane make up, etc. Too many things that could be application specific and I agree the failure point or what is allowable could be very grey here... I really appreciate your help!


Nick