AGMA 07FTM15-2007 pdf download.Experience with a Disc Rig Micropitting Test.
Typically, the test roller was examined after 1 hour, 4 hours, 10 hours, 20 hours and 30 hours. Only occasionally were tests continued for longer than 30 hours. The following monitoring techniques were investigated, with varying degrees of success:
Ootical Examination: Images of the damage were recorded at four positions around the circumference of the roller. This allows the progress of the damage to be assessed during the course of a test. In addition, the stored images can be processed to determine the area of micropitting (see below).
Area of Microoitting: A PC-based image processing program was used to quantify the area of micropitting. This type of technique seems to have potential for monitoring low levels of micropitting damage (i.e., micropitting that is not severe enough to cause significant profile loss).
Profile Loss Using Surface Protilometrv: By superimposing surface profiles taken on the track at various stages during the test onto a profile of the original surface, the track profile loss was measured and monitored. This technique is suitable for monitoring moderate and severe micropitting in the disc rig but is not as suitable for monitoring in conditions where low levels of micropitting are produced and there is very little profile loss.
Roller Track Ra: Surface profilometry was used to monitor the axial roughness (Ra) of the contact track and this provided a useful measure of the development of the damage to the roller track. In tests where the track becomes well p01- ished during the early stages of the test, relatively little micropitting develops during the later stages. In tests where the track does not polish quickly, however, moderate or severe micropitting usually develops later on in the test. Some typical track roughness results are shown in Table 1.
Mass Loss: The mass loss associated with micropitting of the test roller is typically 1 mg or less after 30 hours of testing. Mass loss thus does not seem to be a practical method of monitoring micropitting in the disc rig.
In order to monitor the development of micropitting damage, it was necessary to return to the same regions of the roller track at various times during the test to carry out the optical examinations, area measurements and surface profiles. To facilitate this, a special jig was designed and manufactured which consistently presented exactly the same four regions around the circumference for assessment.
The results of previous gear-based micropitting tests have shown that sometimes the micropitting damage produced by an oil is relatively deep but does not cover a large area. This means that a different oil ranking can be obtained if area is used as the measure of micropitting instead of profile loss. In commercial gears, loss of profile due to micropitting often leads to increased contact stresses (which can lead to further damage) and noisy operation. Consequently, for the current studies, track profile loss, measured at the four reference positions, has been used as the main monitoring technique.AGMA 07FTM15 pdf download.