Lubrication of Gear Sets on Agricultural Equipment

While some open gears are still encountered on farm machinery, modern equipment, for the most part, has precision cut gear sets operating in enclosed gear cases. Therefore, most gearing on farm machinery can be satisfactorily lubricated with two types of gear oils.

First , for  open gears  a  residual  type  of  adhesive  gear lubricant, which can  also  be used on  wire ropes  and  some  chains, is  recommended. Such  a  lubricant is available as a material  which will  hardly  pour at ordinary temperatures  and  must  sometimes be  heated in  order to apply. Much more convenient is a cut back from of such lubricants which can be applied by pouring or dipping. Likewise, aerosol containers of the same type of material permit spray application.

The enclosed gearing on farm equipment is bath lubricated so that the partially submerged gears, when in operation, pick up the gear oil and where necessary, transfer a portion to bearings. While  it is  not  possible  to  list every  variation  in the  mechanisms of  gearing  on  agricultural  machinery, the  rules for  lubrication of such expensive  and  often  intricate  equipment follow  general  pattern. That is, the use of the proper gear lubricant in the proper amount and the regular replacement of such oils as required.

While the  recommendations  of  the  manufacturer  are a  guide  as to the proper  gear  oil to use  in each  piece of  equipment, there  is a  tendency  to  simplify the  number of  lubricants  required  on a farm. With this in mind, multipurpose gear oil will serve most enclosed gear sets. This  can be  a  mild  or  regular EP  type with  the  use of an SAE  140  grade for   hot weather  and  an SAE 90 grade  for  winter. In very cold weather an SAE 75 grade of gear oil can be used.  The  matter  of  reduction in the number  of  lubricants  necessary  for  farm  equipment  will have  further mention in  the next section. It  will  then be  evident that  manufacturers   of  such  machinery also  have  this  in  mind.     

Dynamic Loading of Automotive Hypoid Gears

While the  tests just described  permit  rating and screening  of  gear  oils  for  various purposes, an illustration of  further tests, their result  and  the  conclusions reached,  indicate  both  the  possibility of  extension of   full  scale and road  tests  and  also  the  extreme conditions to  which  gear  oils  can be subjected. Powell  and  Barton  reported  the  results  of an  investigation  relative  to the   magnitude of  tooth   loading  in  hypoid rear axle  gears  under  normal and  severe operating  conditions. For  the  purpose  they  used  a   6-cylinder  passenger  car  with  a  pre- war  torque drive; a drive   system   duplicating  that  of  this car  on a  “T”   dynamo meter  stand; and  Army  M-37  truck  with  a 4 ton  load  plus  a   1.75  ton  trailed  load; and  an  Army  M-211  truck with  a 12 ton  load  plus  a 4 ton  trailed  load. The conclusions reached were:

      (a)    With  heavily  loaded trucks  the  climbing  of  steep  grades  can  increase  the  ring  gear  torque         as  much  as  13 to  24  times  that  of  level  road  under  steady  speed.

      (b)   The addition of trailed loads causes large increases in gear torque.

      (c)    The  highest  gear  loads  produced   under  normal  operating   conditions  occur as  a  result  of     gear  shifting.

      (d)   Engine  misfiring  resulting  from  spark  plug  fouling  causes   repetitive  gear  loadings  equal  to  the  60 m.p.h. drive  side  shock  in  the  CRC  L-19  test.

      (e)   Changes  in  rate of  throttle  opening  result  in large   differences in  the  drive  side  shock  loading  of  the  gears. The  substitution    of  electric  solenoid  throttle  controls  for  hydraulic  controls in the  CRC L-19  test  nearly  doubled  the  drive  side  shock  torque.

      (f)     Rate  of  throttle  closing  appeared  to  have  little   effect  on  the  coast side  gear  shock  loads.

      (g)    Shocks  imposed  in gear  shifting  of  heavily  loaded  trucks   on  steep  grades  produce  severe  lubrication  requirements  by  imposing  large  stepwise  changes  of loading  on a   contact  point  in one   revolution  of the  pinion.

Pour Point Depressants

Certain  polymers when  added to wax containing lubricating oils in  proportions of 0.1 to 5 per  cent, will  alter  the  crystal  structure  of the  wax  and  thus  permit  movement  of the  oil  at a much  lower  temperature  than  before  the addition. Some  agents  used  for  other  purposes, for  example V.I. improvers, may  have a similar  influence on  pour  points.

Most  industrial  gear  oils do not  require  this  type  of  additive but  pour  depressants are  often  included in  automotive  gear  lubricants. The agents  normally  used  include  “Acryloids”  which  are  methacrylate  polymers,  and  “Paraflow”  or “ Santopour”  which  are  wax condensation  products with either  naphthalene or  phenol. 

Venting Gear Housings

While Forbes et al.^20  mention that gear housings should be vented so that oil vapors may escape, such openings  may  tend to permit  entrance of humid air. In fact water has been drawn off from gear cases which could only have arisen from condensation. If such conditions generally prevail, the gear oil should contain a rust preventive additive. Cartridges or filters containing dehydrating agents and attached to the vent of gear cases are not too practical because of the necessity of frequent renewal. Removal of condensed water from circulating systems is simpler than where the gears are bath lubricated. Entrance of contaminants other than water through gear housing vents is possible and often problem. The location and atmosphere surrounding the gear set will determine such possibilities and also what corrective measures need be taken. Thus, gear cases of large tractors, such as are used on road and construction work, have a breather with an air filter which should be renewed at 250 hours operation intervals. One manufacturer reports some trouble with dirt in gear cases probably due to the filter not being changed at the required interval. Farm tractors also have the same problem and a proper air filter and frequent renewal is desirable on vents from gear cases. 

Automobile and truck gear cases are subjected to similar contamination. Thus, a large car manufacturer  mentioned in a service bulletin that two major  contributing factors  to  a considerable number of ring and pinion  failures in axles  was moisture  and  foreign  materials  entering  the axle  and contaminating the lubricant. The corrective action was to install a new vent system. The vent was fitted with a hose and hose clamp. The hose, 19 inches  long , goes  up under  the  frame  and  body of the car  and  is  clamped  so  that  the  open  end  faces  toward  the  side of the  vehicle.

Industrial gear set installations may require similar filters or extensions of gear case vent opening to points where the concentration of contaminants is at a minimum.

Dripfeed Gear Lubrication

Dripfeed application of gear oils may be considered semi-automatic in that it is adjustable to a certain degree. The feed for the oil in this case may be by gravity or even by circulation if the stream in the latter instance can be throttled down sufficiently. In the first case a container can be filled by hand or even a small drum can be connected with piping ending in a valve or cock to permit adjustment of the feed. Here, as the amount of oil in the container becomes less, the feed will decrease. Where such a feed is partly mechanical, the oil will come either from a storage tank to which a pump has delivered it or directly from a circulating line. In either case the amount of used can be calibrated.

While dripfeed can be applied to enclosed gearing it is more often used on open gearing. Here it is applicable to softer types of gear oils including cut back types. This is more desirable method of lubricating open gears than the methods previously mentioned. Also, in case cut back gear oil is used, any vapor from the same will escape slowly and hence will be less of a hazard than if the mixture were sprayed on. Further, there are fewer tendencies to over lubricate by a drip method than with other methods of hand application. Therefore, there is a consequent reduction in waste and poor housekeeping.