Flour Milling and Gear Lubrication

Up to time grain enters the mills, conveyors are used for handling. These  may  take the  form  of screw,  bucket, ribbon or belt and  any  one of these  types can be  driven  by gear  reducers. A  turbine type of oil  having  a viscosity of 500 SUS  at 100 degree F,  that  is AGMA  No. 3 grade, can  be  used  throughout  these  gear  reducers. In  the  northern  states  this  oil  should  have  a pour point  of zero or lower. An  oil of this  viscosity  will not cause excessive  power   loss and  yet  it  will  protect the  moving  gear  teeth.

Gear motors may be used for some conveyors and blowers. The  same  type  and viscosity of oil  should  be  satisfactory  for the  bath  lubrication  of such  gears, especially  if bearings are  serviced from the same  source. Where the drives in gear motors run quite warm, an oil of about 750 viscosity SUS at 100 degree F or an AGMA No. 4, may be desired. If such motors have a plate showing the recommended viscosity of oil, this suggestion should be abided by.

A tight  housing  is  essential  in any  of the gear cases in flour mills, more  from  the  standpoint  of prevention of contamination  from dust  than  from  leakage. Since  the oil  level  in gear  cases  should  be  inspected  every  month  or  sixty days, care  should  be  exercised that  dust  does  not enter  when  the  filling  plug or cap is removed.

Open  gears  are not  used too  often  around  flour mills; but if  these  are  encountered, it  is wiser to use  a  light  oil  as the  lubricant  rather  than  a  residual type. This can be the same oil as suggested for use in conveyor gear reducers, that 500 viscosity SUS at 100 degree F. As  such an oil  becomes  mixed  with dust, the paste formed will  slump off rather  than pack  in  the  bottom  of gears; thus, misalignment should  not be a  problem.  

Flour mills  may  be  self contained, in that cleaning, tempering, grinding and  sifting may  all take  place  in one  enclosure, or the latter operation  may be  separated. Such machinery will vary, but often the rolls are driven by gears. Here again the turbine oil type 500 viscosity SUS at 100 degree F can be used. Machinery handling middlings or bran will be much the same as previously mentioned and if gearing is used, the same recommendation will hold.  

In the manufacture of corn meal or animal feeds the same type of processing and machinery will be found. Thus, conveyors  and screens  will have  similar  drives but the  crushing or milling  can be  by  rolls  or  discs. In any event the gear oil used can be the same type and grade as recommended for flour mills.

It will  be noted that  a simplified  lubrication  application for  reduction  gears  is suggested  in grain mills, that is, a  single  oil  throughout with one  exception. This  is in  gear motors and even here  the  sanction  of the motor manufacturer  might  be  obtained for use  of the  500 viscosity  oil.

Malfunctioning of Other Mechanical Elements

Misalignment may be due to wear of bearings and in extreme cases of failures it may be difficult to determine whether a bearing or a gear failed first. In case of bearing failures, when lubrication was at fault, either oil did not get to the bearing. Or the proper oil was not used. Where  a common  oil is used for bearings and gearing, the  viscosity of the oil is  generally  a compromise  since  the bearings operate best with  a lower  viscosity oil than  is dictated for the gear sets. Therefore, when bearing trouble is encountered, thought might be given to use of a somewhat lower viscosity lubricant.

Malfunctioning of flexible couplings may also contribute to trouble with gear sets. Such couplings are often used to connect reduction gears with a different piece of apparatus. These  couplings may not only  break but  also  become  jammed, so that  they  are no longer flexible; thus the  gear  shaft will  be thrown out of line. Another possible source of trouble might be a break in a gear case or supports which would permit a shaft carrying gears to be misaligned.

Methods of Application of Gear oils to Heavy Duty Gears

Older equipment employing heavy duty gears may make use of bath systems   for application. Many  plants  have  converted  such  systems  to  circulating  application such as  is used  on most  modern  machinery. By  this  means, oil sprays  can  be  directed  to  the line  of  meshing  of the  gear  teeth and  if  necessary the  oil can be supplied  to  other  machine  components, such  as  bearings. By  this  means, when  accompanied with  proper auxiliary equipment, such as coolers, filters, settling tanks etc., the life of the oil is prolonged and contaminants removed.

Problems of Feed of Gear oil to Bearings

At  first  thought  the  oil  in gear  cases  is there  primarily  to  serve  gear  sets. However, lubrication of bearings is often of equal importance. In circulating systems an oil supply can be provided for bearings no matter what the location. Bath or splash systems pose a different problem. Here troughs may have to be provided to direct oil to bearings, or flingers dipping into the oil, in addition to the gears, may be necessary.

If  the gear  runs on a  bearing and oil  holes  are drilled from  the roots  of the gear teeth  with  the  thought that  this will provide oil, Merritt^34  mentions  that this  will be  quite  deceptive. Thus, the oil will flow outward due to centrifugal force and will flow inward only if the gear is stationary. Such holes, if they  do not  seriously  weaken  the gear  teeth, can  be used  to lead  oil  outward  from  a supply  at the  center  of a  hollow shaft.

Deep Freezing of Foods Gear Lubrication

The  primary  mechanical  device  concerned  with  freezing  of  foodstuffs  is a  compressor. Many  compressors, used in  refrigeration, depend upon  forced  feed  lubrication and this  feed  is provided in many  cases by  either  gear  pumps or gear  driven  pumps. In both instances, the  oil  being  circulated  provides lubrication for the  gears and is  selected on the basis of that  needed for  the  compressor cylinders and  the bearings. While  deep  freezing is followed in most cases by  conveyor handling, either of packages  or of  containers, the lubrication of  conveyor drives  follows  conventional  practice and therefore, will not  be  detailed. If  reduction gears for conveyors  should  operate in cold rooms, an oil of about  100 viscosity SUS  at 100 degree F and with a pour  point  no  higher than  -40 degree F  should  be used  in  the gear case.