1. Most manufacturers do not test their idlers as a standard course of action. The client must specifiy such a test or the manufacturer may have some QC program which in not typical.

2. There are many methods to measure the rotational resistance of idler rolls. Most have procedures that color the result. The tests need to be dynamic

3. You need to know what you are testing for and have the right method to rotate the roll that will not introduce undesirable noise into the data. Things such as speed, temperature, lubricants, seal desgn response to age, temperature, rotating speed, as well as synthesis of material loading, need to be defined in the procedure so they can be independently factored for their contributions. Do you grab the shaft and rotate the shell or grab the shell and rotate the shaft. How do you apply a loading factor? You cannot use any belt or rubber device. You must make sure how the load distorts the seal system as well and bearings. You need to test for changes in resistance behavior with time and temperature.

4. Are you going to measure breakaway resistance?

These are some of the points you will need to research in your quest.

You cannot make such a theorectical calculation and expect any degree of accuracy. First, it is extremely complex in its detail. Second, you will invariably forget some major factors or have to assume so much as to trivialize the result and make it meaningless.

Ask the idler manufacturers how easy it is and if they get good agreement and get agreement with the universities or other laboratories. Ask them if there is a well defined standard, that is bulletproof. Some will tell you yes and some will tell you no. Now what? TO a large degree it depends on your definition of accuracy. So what accuracy do you need? ■

Breakaway is the initial, non-dynamic resistance to motion. It is relevant for colder operation where the grease settles to the bottom of the bearing race and must be churned during starting.

Also you did not ask about the grabbing of shaft or shell. If you grab the shell you will not see the error in shell balance and changes in its geometry that will reflect in the measurements.

There are other factors which we will leave for another time or person to respond. ■

Anothe rpoint: How long will it take to bring the rolling resistance down from new to a well used state? What do you espect this change will be? Will it differ between manufacturers and greases, etc. ■