Construction Equipment in General and Gear Lubrication

While one should  not go contrary  to the  recommendations of the  supplier of construction equipment, practically all enclosed gears  on such  machinery  can  no  doubt  be  serviced with SAE 80  or SAE 90  EP or  MP gear oil. An  exception  are  worm  drives which should be  lubricated with a  compounded  oil  of SAE  140  grade. The use of certain mild EP oils is permissible for the lubrication of worm drives provided the oil supplier so advises. Air and oil filters require the same attention as in the case of tractors. Also drain periods on any construction equipment should be established at a maximum of 1000 hours. It is best to drain immediately after operating and while the gear boxes are warm. If the discarded lubricant is very dirty, flushing of the gear compartments before adding fresh oil is desirable. Open gears will be found on many pieces of construction equipment. For example, large shovels, cranes, drag lines, concrete mixers, etc. The  recommended lubricant for  such  gears is a residual  type  having  a  viscosity of 1000 SUS  at  210 degree F for cold  weather  and 2000 for  warm  weather. If the machinery  is to be used  under wet  conditions, the lubricant should  contain additive which  will  insure that  the oil  adhere to gear  surfaces  when  water is present. Better  still  these  open  gear lubricants  should contain both  EP  and  rust  inhibiting additives. Exposed gears are lubricated as required, often on each eight hour shift. If  railroad  equipment  is used  in  construction, the  tractor  motor gears  can be lubricated  with  the heavier  grade of open  gear oil. 

Nonmetallic Gears and Their Lubrication

A variety of materials has been and will be used for the manufacture of special gears and thus a blanket recommendation cannot be made for the lubrication of all nonmetallic gears. While the concern  here is  lubrication, it is of  interest  that these materials  tend  to  have less  mass  per  unit  volume than  the  ferrous metals and thus the resulting  gearing  has  less inertia of  rotating parts. Further, injection molded gears are about as low in cost as any gears. AGMA 250.02, Dec. 1955, makes the following statement:

“The gears should be lightly loaded if lubrication is not permissible.”

Certain small gears, particularly if made from “Teflon” or “Nylon,” are run without lubrication. However, Carlyon^9, when considering plastics for bearings, found that: “Even small amounts of oil present during typical manufacturing processes often will improve” friction and PV ratings. It was also shown that the continuous presence of oil raises the PV values of “Nylon” and “Delrin”. Graphite is sometimes used as filler in plastics and may thus aid in lubrication.

Medium sized nonmetallic gears are generally used in mesh with metal gears. Thus, “Bakelite” spur gears, which are made by impregnating fabric with “Bakelite” resin and then applying pressure and heat, are used with metal gears. Laminates may also be made of paper impregnated with phenolic resins. Heavy oil or lubricating grease is used as the lubricant on such pairs and the amount and frequency of application depends upon the severity   of service.

Rawhide pinions  disintegrate  when  in contact  with  mineral oil and therefore, a mixture of tallow and  graphite can be used  for lubrication of  such  gears in mesh with metal  gearing. Such pinions furnish  noiseless,  resilient  service with  little  vibration  and  prolong  the life  of the metal  mate.

Pinions  can  be made  from most  materials which  can  be molded or cast, often  in  conjunction with  other material. Thus, “Fabroil” pinions  are  stated to  be  made of  pressed  cotton  held  under  compression by  steel  shrouds. The manufacturer of nonmetallic gears should be in position to recommend suitable lubricants for the same.

Plastic gears are sometimes used in small gear pumps, and here the material being handled, such as water, petroleum products or solvents, may serve as a lubricant.

Undoubtedly the use of gears made from plastics will increase both as to number and types. While it is not  the  function  here to  treat of  their  characteristics, some  of  the  qualities  should  be recognized in  applying  lubricants. The  fact  that these  synthetic  materials  have lower specific  gravities  and consequently  less  inertia  than  metals indicates  less  impact   when  gear  teeth mesh. Also plastic gears  tend  to  have greater  elasticity  than  metal; therefore, they  should  conform to a  mating  gear without  the necessity  of a thick lubricating  film. Since  some  of  the  non-metallic  gears are  thermoplastic they  will  not  be used  under  conditions  of  elevated  temperatures; consequently, high temperature  lubricants will  not  be required.

The solubility characteristics of plastics will vary with the type and a lot of gears made from such materials can advise as to any restrictions in fluids to be used with specific plastics. Bueche  and  Flom^7  who investigated “Surface Friction  and  Dynamic  Mechanical properties  of  Polymers” found  that  water solutions of  sodium  stearate  were satisfactory lubricants for either “Neoprene” or branched  or unbranched  polyethylene  when in contact with steel. While  “Delrin” can be  operated  in a bone-dry  state, pretreatment  with lubricating  oil  has  been  found  to  reduce its  erratic  operations and  improve  the  abrasion  resistance. The recommended  pretreatment  consists  of  complete  immersion in a low  viscosity  oil for one  hour at 250 degree (F) after  which the part is wiped  dry. Gears  of  this  materials  have been  operated  in  contact  with  both  oil and  lubricating  grease with no  deformation or  wear. Since the variety  of  types of plastics  used  in gears will  increase,  the  safest procedure in  lubricating  such  parts is  to  consult the  supplier.