Pitting on the Hardest Surfaces

Are there corrosive substances in the environment?

No. these are components of Ball-Way Bearing. During the test trails, no water is allowed to contact the surfaces of concern. these components are applied with Grease. even the humidity is controlled and the area of test is cordoned off sufficiently from the outside environ.

some substantial delay has happened in applying corrosion preventive coating on the nitrided case. shall it be a concern? please guide.

Is there any constant vibration, even low levels could cause fretting erosion/corrosion. This was a problem shipping military machinery on railroad flat cars, to roller and ball bearings.

a good exemplification. but these bearings were manufactured assembled and tested at same place. there was hardly any transit before the testing.

the pressure is applied through hydraulic means. the supports are considered to be very rigid. the power pack which supplies the fluid to the test cylinders is distant away from the test setup. no electrical connection is attached to the moving parts. there are limit switches to stroke limit the travel, which are held in place stationary.

as shown in the photographs both the surfaces are affected badly.could you suggest any book on tribology that could give info on material selection and their metallurgical condition and also the wear rate and life expectancy from the subject assemblage.

Send me all data as ball diam, complete drawing of guide and load for test, traveling speed and I shall make an estimation (use for confidentiality the private direct channel). It is on my humble opinion not only pitting but also marks of hard particles pressed on the guide. Since there is no separator between balls (at least I have the feeling it is the case) you have as well a friction between 2 balls at 2x the speed (if they roll) and according to it wear. Under circumstances this friction could have an impact on rolling itself and justify the guides wear.

For such applications in general there are special high carbon steels used as in the ball or roller bearings. If you are confronted with corrosion then a very fine computation has to be made for the whole design of the nearing since other steels do not have same through hardness.

The fact that the moving guide is supported on rollers (concentrated loads) could lead to problems best to test 2 devices at same times the load distribution would be better.

As for the book you may use any book about contact stresses but in the books some specific details are NOT mentioned only experience allows you to get them.

ball is of one inch diameter. load for the test is 50000N. trevel speed is 600 mm/min. the stroke is 750 mm in order to ensure each ball touch the guide ones. You have rightly pointed that there is no separator between the balls. are you trying to say the test setup with more roller supports beneath the guide would have given more uniform load distribution and lesser chances of failure? Do you say these rollers shall also be of the hardness of top balls? Yes the bottom line is "experience" that is why I am drawn to this forum to have members' expertise to decide where I have gone wrong. Thank you for your time. The guides and the body of the bearings are Gothic Arch profiles as shown in the accompanied sketch.

As soon as I use a zoom + the figure are not any more clear and I cannot read values nor see details on your picture. Could you send a DWG or DXF File via the private channel if I give you, there, my e-mail ?

With respect to rollers the problem is that you have a hyperstatic condition since there are more than 2 rollers. This can lead to a non uniform load distribution on the balls over their travel. Non uniformity = risk of peak values!

What I wanted to say is that you make a test with one linear bearing if you put 2 bearings and move the in between element you test at same time 2 and have much more confident results in same test time. The load distribution is more uniform and thus you can eliminate one of the failure reasons.

Which class are the balls as tolerances ? If you agree use the private channel to give the information since I shall not put my e-mail in the open access.

i can share the info through your personal e-mail. Balls are of grade 20.

Good morning Guru, and Happy new Year. These balls are made conforming to DIN 5401 and the variation in ball dia is 0.5 microns and the variation in ball lot dia is 1 microns. They are through hardened to 60-62HRC. Is there any recommended value of hardness difference between the elements of contact. like 70 and 62 HRC is alright or the balls should have been harder for better wear resistance?