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.

Cement Mills Gear Lubrication

The lubrication problems of gearing  in connection with  quarrying  and  handling  rock, shale etc., for  use  in  cement manufacture  will  be  treated under  the  section devoted to  surface  mining and  quarrying. In cement mills proper, grinding or pulverizing. Mixing,  conveying  and  heating  of  ingredients are  required  and  most  of these  operations  employ  gear  drives  which  in  turn  need  lubricants.

Dust  of an  abrasive  nature  is an  ever  present  possibility  in the case  of  any  gear  lubricants  in  cement  plants, even  in  enclosed  gear  cases. In  some  applications  this  threat  to  lubricated   surfaces  is  countered   by  the  use  of  circulating  oil  systems. If this manner of application is used, filtration is possible. This  is true with  some  types  of rock  crushers, such  as  gyratory  crushers or  hydraulic  cone  crushers. The  gear  oil  employed  in either  of  the  above  can  be  a  mild EP  type  having  viscosities  of 300  to  500 SUS  at 100 degree F.

Whether  the  process  used  for  cement  manufacture  is the  dry  or wet  one, agitators, conveyors, elevators, mixers, grinders and  various  other  mechanisms  are  driven  by gear  reducers  from  electric  motors. In  the wet  process  the  listing  may  include  pumps for  handling  slurries, thickeners  which  may  have  worm  drives, as well as  the first  types of  machines. A  general  recommendation, which  simplifies  the  storage  and handling of  gear  lubricants, is  to  use  a mild  EP  oil  having a  viscosity  of 300  to 500  SUS  at 100  degree F. If  the  EP  agent  includes  a  lead   soap, such  an oil  might  be used for worm  drives.

                                                                                 

Open gears are also found in cement plants. One illustration is a ring gear and pinion driving a ball or rod mill. Here  a  residual  type  of  petroleum  product  having  a  viscosity  of  2000 to  3000 SUS  at 210 degree F  can  be  used.  This  lubricant will  pick  up  and carry  with  it rock or  cement dust, and  since  this  will  be  true no  matter  what  the  viscosity of  the  product ,  the  best procedure  is  frequent application. By this means the excess lubricant will be rejected and carry with it some of the abrasive material.

Cement  kilns  are  rotated  by  a  speed  reducer, followed  by a  pinion  and girth  gear. Different methods for lubrication of the exposed pinion and gear have been used. While  dust and  grit  are  present, the main  problem  is heat,  radiated  from  the    hot  shell  of the  kiln  to the  gearing. High  melting  point  lubricating  greases  have been  used to  some  extent,  but  require frequent application  unless they  are  in the  form  of a brick  which  is  pressed  against  the  pinion. This method has led to excess consumption.

A  better  procedure  for lubrication  of  cement  kiln  girth  gears  and  pinions is to  provide  a bath  for the latter. Cylinder stocks or SAE 250 EP gear oils have been used in this bath. In  this case,  the cylinder  stock  used  should  have  a  minimum  flash  point  of 600 degree F. However, perhaps  the  most  common  method of  lubrication of such  a drive  is to use  residuum  having a viscosity of about 5000 SUS at  210 degree F. This can be heated to aid in application. Also this  open  gear  lubricant may contain  three  to  five  per  cent  of  graphite  or  molybdenum  disulfide, which  of course are  no melting  and will  adhere  to the  gear  teeth and act  as a  lubricant.