432   Figure 7 – Contact pressures on qualification test unit roller for cases of misaligned and aligned  rollers. The pressures shown are at the midpoint of the Hertz contact in the direction of rolling. 

The lab apparatus can be operated with the misalignment angle at a maximum value of about 1.5  degrees. The influence of the misalignment angle on the contact conditions depends on overall system stiffness and the contact dimensions. The sliding distance in such a condition can be approximately quantified as proportional to the product of the misalignment angle and the length of the contact patch in the rolling direction. Using this concept the misalignment angle of the lab test apparatus times a factor of 1.7 provides the approximate simulated misalignment angle of the qualification test unit. The lab test was conducted for misalignment angles up to 1.5 degrees that would simulate a misalignment angle of about 2.5 degrees for the qualification unit.  A summary of the test conditions is provided in Table 1. The tests are listed sequentially in the order of testing. In general one would prefer to have a randomly chosen testing order, but in this work roller availability dictated the testing sequence. In some cases the same roller pair was tested at more than one misalignment angle. In those cases the angles were tested sequencing from smallest to largest.  Post-test documentation of the rollers included recording of the mass of each roller, profilometry, and photographs. Some rollers were inspected via scanning electron microscope. Debris was collected. In some cases the debris was swept from the debris tray, collected to a glass vial, and total mass of debris determined. In some cases debris was collected using a square piece of tacky material that could be placed onto the tray and lifted to collect the debris. The collected debris could then be subjected to automated analysis of debris particle counts and sizes. At completion of one test there was no debris readily visible on the brass-hued debris tray, but a swiping of the tray with a cotton-gloved finger revealed debris. The glove fingertip was saved to retain the debris. For later tests a dark grey anodized plate was used for the debris tray. The darker and matte-finished plate allowed to more easily see the small particles. 

Test Results 

Roller wear.  Photographs of the test rollers were recorded through a view port during test operations at regular intervals. Figure 8 provides a set of photographs documenting the progression of wear during tests with test ID 3, 4 and 8 (test ID per Table 1). These photos show the difference in wear resulting from material condition. The first two rows of Figure 8 can be used to compare and contrast the wear when using annealed 440F rollers (first row) to the wear when using hardened 440C (second row). In these photos the upper roller is the one made from steel alloy and the lower roller is the titanium alloy. The steel rollers took on a relatively uniform appearance of wear while the titanium rollers had patches of irregular appearance. The wear rate can be qualitatively judged by the width of the wear track of the upper roller location along roller (mm)-1.0 -0.5 0.0 0.5 1.0 pressure (MPa) 0100200300400500misaligned aligned