Normal Wear. Loss of metal from surface of teeth. Wear must not prevent gears from meshing or
Initial Pitting. This may occur when gears are first put into service. It may continue until high spots have
been reduced. It will not affect contact surfaces. This pitting is not necessarily serious.
Destructive Pitting. This pitting occurs after initial pitting, often at an increasing rate This type will
destroy the contact area and reduce the load capacity of the gear. Rapid destruction will occur with use
Abrasive Wear. This damage is caused by fine particles carried in the lubricant or embedded in gear
tooth. This materiel may come from. Abrasives not removed during assembly. Sand or scale from
castings. Impurities from oil or the environment. Bearing or gear tooth material.
Scoring. Slight scoring, galling or other surface damage is seen as tears or scratches in the direction of
sliding It starts in areas of highest stress and speed. This is usually at tip of teeth.
Burning. Burning appears as discoloration, and causes loss of hardness of the metal. Burning is
caused by any of the following:
Lack of Backlash
Too Little Lubrication
If discoloration can be wiped off, such marks can usually be traced to oil-burn stains
which are not serious.
Rolling. This damage usually occurs only on plastic gears. Rolling is when material is pushed out of
shape but does not break off. It is usually caused by heavy, even loads and overheating.
Visually inspect all castings and weldments for cracks. Parts that carry a great load should be Inspected by
the magnetic particle method. Non-ferrous parts may be inspected by the fluorescent penetrant method
Magnetic Particle Inspection
This type of inspection can only be carried out on metals that can be magnetized. If in doubt check whether a
magnet sticks to the surface. It should only be carried out If parts are not easily replaceable (cost or special
order), or parts have been reworked or reground, or parts are subject to high stress. Magnetizing current
depends on parts being magnetized. For solid section parts, current shall be 1000 amps per diameter - in.
For variable diameter thickness, current shall be adjusted for diameter inspected. Parts shall be rejected if:
Indications of non-metallic inclusions are present (foreign body - solid, liquid, or gaseous) and these are
longer than one in, or indications are closer than 1/8 in. apart.
Any evidence of cracks are seen
Scattered short sharp bursts are seen. Bursts are caused by metals working at temperatures that
weaken and break the material. Bursts are not usually seen until the metal is cut through to the burst