Page 254 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

236 Major Process Equipment Maintenance and Repair

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Flgure 6-1 1. Ball bearing (assembled).

contact ratio. For instance, if a gear has a contact ratio of 1.45, this
means that 45 percent of the time two teeth are in contact in the trans-
verse plane and 55 percent of the time one tooth is in contact. For helical
and spiral bevel gears, additional teeth are in contact in the axial plane at
all times due to the helix or spiral angle.
When trying to troubleshoot problems with gears, a good point to re-
member is that the action between gear and pinion profiles is both rolling
and sliding. The only point on the tooth profile that has pure rolling is on
the pitch line, and all other areas have a combination of rolling and slid-
ing. The sliding velocity is greatest at the tip, decreasing to zero at the
pitch point, and increasing again toward the root.

Bearings
Bearings of all types are used to support gear rotors. The types most
generally used are:

1. Ball Bearing-Generally used for lighter load and higher speed appli-
cations. Can also hundle moderate thrust loads. (See Figure 6-11.)