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One of the main causes for the
failure of heavily loaded gears can be put down to overheating generated
between abrading surfaces. This is known as "burning" and takes the form
of heat-induced damage to the ground edge zone of the workpiece. Modern
instances, for example, affect the gears of wind power stations: there
have been cases where gear manufacturers had to replace standard gears
at great expense because burning had verifiably caused damage to the tooth
profiles.
There are as many causes of burning as there are input quantities from
the wearing process - and they are multiplicative: infeed increment, feed
rate (metal-removal rate), state of the grinding wheel (loaded, worn, eccentricity),
inadequate coolant effects (specifications, additives, pressure, flow rate,
arrangement and shape of the nozzles), and the tooth geometry.
For a long time now there has been a test procedure for visualizing
this damage otherwise invisible to the unaided eye: as early as 1974 the
American Gear Manufacturers Association (AGMA) described temper etching
with nital as a sure means of visualizing damage caused by burning. This
procedure is also described in the US standard ANSI / AGMA
2007-B92 "Surface
Temper Etch Inspection After
Grinding". |
Test
procedure ensures greater safety for heavily loaded gears
