Limitations on Heating of Lubricants for Application

Heavy bodied lubricants, particularly residual types used on exposed gears, are often heated in order to make application easier. If such lubricants are straight mineral oil products, the amount and intensity of heat should not harm them. However, if additives are included, only a very moderate heat should be used. Otherwise some change in the composition is possible. A supplier of the lubricant can advice the limitations on heating. A similar caution is necessary in case lubricating greases are used as gear lubricants. The thickeners for such products may be soaps which upon the application of considerable or prolonged heat will separate from the oil present. 

Potato chip Production and gear lubrication

The production of  potato  chips illustrates  food  handling  where  the gears  concerned are so  located that  little  contamination from the  lubricant  is possible. Numerous conveyors will be found for the potatoes, the slices, or the packages. Most of the gear reducers  for  conveyors will  be  subjected  to  only  moderate   temperatures  and not too  much  stress. Hence, either  straight  mineral  oil  or  MP  lubricant  of SAE  80  grade  can be used  for  the gears.

 If  a batch  peeler is used,  this may consist of  a  vertical  cylinder with  a rotating  abrasive  disc in the  bottom  which  will  be  driven  by  gears. Also, in washing potato slices, a gear driven drum will probably be used. The gear oil mentioned above will also serve these latter applications.  

Food processing Industries and Gear lubrication

A variety of industries are grouped together so that prevention of contamination by gear or transmission lubricants can be stressed. While such possibility is remote, Government Inspectors are becoming more particular in this regard. Also, both  manufacturers  of food processing  machinery  and operators of plants are  aware  of the  importance of cleanliness  and lack  of contamination. Proper seals, well maintained, should prevent leakage from gear cases. As an aid in this direction, over lubrication should be avoided and when and if lubricating grease is applied, this should be at very low pressure. As a general rule, straight petroleum oils can be used in gear lubrication of the subjected equipment. Some operators of machinery handling foodstuffs prefer light colored lubricants. White oils are available in viscosities up to 300 or perhaps 500 SUS at 100 degree F. The  same  oils can  be  thickened  to  a  semi fluid or non  flowing  nature  by the  use of fine silica  or non toxic  soaps, such  as  aluminum  or calcium. Light  colored  fillers, such  as  magnesium  oxide  or zinc oxide, can be added to  lubricating greases, although fillers have little  if any  place  in gear  lubrication.

Caution  should  be  used  in supplying  gear  lubricants containing additives  to  food  processing  plants. Oils  containing  EP agents should  only  be  used  if the gear  cases  containing such  oils are  sufficiently  removed  from  the food  products so that  leakage  will  cause no  contamination. Foam inhibitors are permissible because the concentration is quite low. Stable oils are recommended because they will require a minimum of oxidation inhibitors. Such additives, as well as  rust  inhibitors, which  will  be  desirable  under  wet  conditions, should only  be used  with assurance  that  the compounds are not  harmful to  animals  or humans.

Simplification  of gear  lubrication  should  be  kept  in mind and  if  possible, only  one type  and grade  of gear  oil be used in a  specific  plant. Thus, in spite of the  recommendations above for the  use of such oils  with  very  judicious  inclusion  of  additives, the suggestion  has been made^31  that  a  premium  grade  rust  and oxidation  inhibited turbine and  hydraulic  oil  be  used in all  gear reducers  in dairies. Therefore, similar oils will also be recommended for other foodstuff handling equipment. Open gearing will be found in some food handling machinery or plants.  It  is  presumed  that such  gears  will  be so located  that  drips from  the  same  will  not  contaminate food. Therefore, a  general  recommendation  is to  apply  a  residual  type  of  gear  lubricant  very  sparingly. The viscosity will be dictated by the service but will probably be one of 1000 to 2000 SUS at 210 degree F.

In the  group  to  follow, equipment  used  to process some medicinal  items, alcohol  products etc., will be  included since  they  are  restricted   to the  same  limitations as far as contamination is  concerned. By  mentioning  some  of the unit  operations  which may be  encountered   in food  processing, the  variety  of machinery  involved and therefore,  the  possibility of the  use  of  gear  drives will   be  evident. Thus, cleaning,  coating, conveying, decorating,  disintegrating, drying, evaporating, forming, heating, mixing, packaging, pumping and  separating are a few  such  operations. 

Compatibility of gear oils

Gear lubricants consisting of straight mineral oils will mix in all proportions at normal ambient temperatures. The resulting physical characteristics of the mixtures will not be an exact proportional average but will approximate this.   

On the other hand, gear lubricants containing additives may be changed either chemically or physically by mixing those of different compositions. For example, some EP additives have limited solubility in high V.I. oils. If then such additives are blended with naphthenic oils which will hold them in suspension and such blends in turn are mixed with high V.I. oils, a portion of the additive might settle out of the mixture. Also, if gear oil containing lead soap were mixed with such oil containing an active sulfur compound, a precipitate of lead sulfide might be formed. Compatibility of gear lubricants is of little concern in industrial service where either the life of the lubricant is long or, if additional oil is required in a gear case, it will likely be from the same source. However, in automotive equipment the necessity of compatibility of gear oils is important because vehicles may be serviced by distributers handling different brands of oil than that originally used in the gear cases. Recognizing the possibility of mixtures of gear oils from various sources U.S. Government agencies have the following requirement in most gear lubricant specifications: “the lubricant shall be compatible with each of the other lubricants qualified under this specification.”Commercial multi-purpose gear oils are almost universally compatible with each other.

Types of gears to be lubricated

Where   gears  are  on  parallel  axes, either  spur  or  helical  gears  are  generally  employed. Either type can be used as external or internal drives.   The  herringbone  gear  is  similar  to  two  helical   gears  having  reversed   directions   of   spiral, placed  side  by   side  so  that  the  teeth  come  together   to  form  a  chevron   pattern. The rack and pinion, used to convert rotary motion to reciprocating, generally   uses a spur gear.

For   intersecting   axes either straight   bevel    or   spiral   bevel   gears   are used   as a  rule. The   latter type may be used   on angle   drives where   the   shafts    do not    intersect at full   90 degrees. The contact   of the   teeth in such gears gives   a rolling motion. With  non intersecting  and   nonparallel  axes  the  types   of   gears  used  are  crossed   helical, single  enveloping  worm, double  enveloping    worm, or  hypoid. Here the  contact  of  the  teeth  gives  a  sliding  as  well  as  a  rolling   motion. In  most  cases  a  gear  set  will  be  used  to  change  speed, and  in  such  cases  the  smaller   gear  is  designated  as  the pinion. Both  the  number   of  teeth  on a  pinion  and  the  ratio    of  the  teeth  on  the  driving   and  driven   member   may  vary ,   but  with  bevel  gears  there  is  seldom  less  than  12 teeth  to  a  pinion.

While   some  spur  and  straight  bevel  gears  are  still   made  of  cast  iron, the  tendency  in  all   types   of  gearing  is  for  the  use of  steel. Exceptions   will  be found  to  such  practice, for  example,  in the   use  of  bronze  for   one  member   of  worm   gears. Some small gears and even   larger pinions are   made   of plastics, such as ‘Delrin,’’ ‘Nylon.’’ ‘Teflon,’’ etc. Pinions  have been and   may still be  made  of  rawhide, pressed  paper,  etc, but  our  concern  is  primarily   with   lubrication  of  metal  gears.