Troubles Connected with venting of gear cases

Vents are necessary on practically all gear cases. However, such openings may lead to trouble. Thus, with  a  humid  atmosphere and  considerable  change  in  temperatures  of  gear  boxes, moisture will  enter and  condense, thereby  increasing  the possibility of rusting. Also dirt may enter through such openings. On  automobile  manufacturer actually  experienced  the  entrance of  both  dirt  and moisture  through the vents  in  differential  housings. The  correction was  to  extend  a house  from  the  vent  forward  with  the open  end  placed  on the frame, under  the  body and  facing  toward  the side  of  the car. A location for  the  opening  was chosen where  the  least  throw off from  the  tires  would  the present. If  the  intake  of  dust  or  dirt  is  material, the  use of air  filters is  suggested. Such precautions are taken in the case of machines operating in very dusty atmospheres. Thus, most tractors use filters on vents of gear cases. However, this adds another problem in that such filters must be kept clean. Suggestions have been  made  that  gear  cases  be kept  under  slight  pressure, thus  preventing  entrance of  contaminants. However, this is impractical in most cases. Installation of  filters  containing  silica  gel  on  vents  from  gear boxes has  been  suggested. While this would remove moisture, the value would depend upon the frequency of renewal of the absorbent. 

   

Automobile Assembly Lines and Gear Lubrication

The conveying  machinery  of  automobile  assembly  plants is  driven by gear  reduction  units  which  are  powered  by  electric  motors. Floor level conveyors may have variable speed transmission units and spur gear trains in order to obtain the very slow rate of travel desired. The  speed  reducers first  mentioned  are enclosed and  lubricated  with  grades of oil  conforming  to AGMA  recommendations for the average  speed   of  the gear  train. Spur gears driving the floor conveyors may be too large to house economically and will be lubricated by intermittent spray of SAE 90 gear oil. Gear lubrication in additional facilities of automobile factories or of auxiliary plants supplying parts to assembly lines will be treated elsewhere.

Prevention of Contamination of Gear Lubricants

Gear sets operate under such varied conditions that it is difficult to give general suggestions for prevention of contamination of the gear lubricant. The two contaminants most often encountered are water and dust. In the latter are included large particles such as scale in steel mills. Less trouble is encountered where a circulating  system  provides  the  lubricant  rather  than  a  splash system, since the former  can  be  supplied  with settling  tanks  or filters. Even here regular inspection is necessary and accumulated water should be drawn off whenever noted. Such accumulations may  be quite  large  in the case of  gear  oils  for  ship  propellers or in oils servicing  paper  mill  machinery  or steel  mill  gears.

Where  gear cases  are  vented, the location  of the vent or a pipe  connection to the  same  should  be so  located  that  the least  dirt  possible  can enter. One automobile  manufacturer reduced  contamination in  differential cases by  extending  a  line  from  the  vent  and  securing  it  forward  under  the  car  frame  with  the  opening  toward  the  side  of  the  vehicle.

Prevention of contamination of lubricants by chemicals must have individual consideration. In  extreme  cases it  may  be  necessary  to  provide  pressure  on  gear  cases to  prevent  entry  of contaminants.