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Page Title: General Inspection Instructions (cont)
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TM 5-4210-220-34 (1) Normal  Wear.    Loss  of  metal  from  surface  of  teeth.    Wear  must  not  prevent  gears  from  meshing  or performing properly. (2) 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. (3) 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 (4) 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. (5) 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. (6) Burning.    Burning  appears  as  discoloration,  and  causes  loss  of  hardness  of  the  metal.    Burning  is caused by any of the following: Gear Overload Overspeed Lack of Backlash Too Little Lubrication Wrong Lubrication If  discoloration  can  be  wiped  off,  such  marks  can  usually  be  traced  to  oil-burn  stains which are not serious. (7) 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. h. Metal Parts 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 j. 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: (1) 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. (2) Any evidence of cracks are seen (3) 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 area. 2-13

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