Nuclear Power plants Gear Lubrication

Present indications are that the principal gearing in nuclear power plants will be in connection with turbines. Such  reduction units should be  far  enough removed  from the area of high  radiation that no degradation  of the oil  from such  a source  will occur.

Cox et al.^14 who have considered this matter state: “Irradiation tests of turbine oils show that maximum expected radiation doses in  current and projected power plants over a twenty year period  does not change the  physical  properties of the oil. Oxidation stability and other properties are, therefore, still of most importance in turbine oil selection”.

Also  Okrent^43  in treating  design considerations of nuclear powered  surface vessels concludes that the  reduction gearing  in connection with  the  turbine presents no problems  from a radiation standpoint. In spite of the  above thoughts, Watson^51  mentions  that in  nuclear  power  generating  stations, a  number of applications  will be found where  gears  should  be run  without  lubrication. Experiments were, therefore, made with various materials, run in a dry state, with latter wear. As a  result, it is suggested that if loads are not heavy, spur gears, made of  case hardened  En steel, phosphate prior to coating  the flanks with  molybdenum  disulfide, can  be run  continuously, in a dry state, without  measurable  wear. Also  a worm wheel , made  from  woven  asbestos base  with  a case  hardened  steel worm, is promising for  operation in a dry  state.

No doubt, when and if gear oils with radiation resistance are necessary, suitable fluids will have been developed. Thus, polybenzenoid   compounds containing short alkyd groups show promise in such applications.

One  interested  in this subject might  avail himself  of a series of  eight  papers devoted to “Non-conventional  Lubricants  and Bearing  Materials such  as Are Used  in Nuclear  Engineering”. These were presented at the Manchester college of Science and Technology on April 12, 1962 by the lubrication and Wear Group of The Institute of Mechanical Engineers (British).   

Method of application

The best lubricant in the world will fail to accomplish its purpose if it fails to be present on the moving surfaces when required and in the proper amount. Therefore, it should be kept in mind that method of application is as important as the product used. Lubricants may be applied to gearsets and auxiliary mechanisms either manually or mechanically. Hand application is seldom practiced except in the case of exposed gears. Minor exceptions to this rule  will  be  found  in the case of small mechanisms, couplings, etc; where  most often  lubricating greases are  added  by hand, either upon installation of the equipment or  at  very  infrequent intervals. Mechanical application may take the form of bath, drip, splash, or forced feed. The  latter method  may  simply involve a  stream  of  oil  but  most  often  will  be  in the  form  of  jets  or spray,  fog or mist.

Normally one thinks of gear lubrication in terms  of fluids but an occasional  situation will permit  or  require  either  a  lubricating  grease or  a solid.

The  manufacturer  of equipment will  generally  provide a method for application of gear lubricants, but  sometimes  the  user of a  machine  will  consider  a  change  in lubrication methods.  Therefore, enough detail  of  each  method  of application will  follow  to  permit  selection of the  most  desirable.

The  most  important  factor in a lubricating  system is  reliability  because  failure  to  supply  lubricant will  cause damage  to  machinery . This  then points  to  automatic  gear  lubrication which  is more certain  than  hand  lubrication. Another factor to consider is cost. Circulating oil systems entail a high first cost as they are usually complex. Hand application devices cost little  but  there  is a  possibility  that  use of this method  of  application  may  lead  to higher  maintenance charges than if  the  lubrication were  automatic. Where an  oil is  used  on  a once-through basis, as in hand  application, a less expensive oil  may be used  than  in  bath, splash, or circulating  lubrication. Cleanliness, which  carries with it  less fire  hazard, greater safety, and reduced possibility of damage  to material  being  processed, is  best  obtained  by  enclosed systems  of gear lubrication. While  automatic  methods of gear  lubrication are  the most  efficient and  reliable  of  the systems  mentioned, such  devices  require  some  attention  to  see  that  a  proper  supply  of  uncontaminated oil  is  available  and that  the  feed  is  properly adjusted.

Further, installation of  a particular type of a  lubricating  system does not  necessarily  mean  that  this  will  function as  desired. While some  problems which may  be  encountered will  be mentioned, either  when  different methods  of application  are  described or  in  a  future  chapter devoted  to problems, there  is  often  greater  possibility  that  the  trouble  is  mechanical  rather  than  due  to  the  means  of  application. Therefore, a correction  of a gear  lubrication  problem  may be  a step- by step  process, such  as  that  described by  Gesdorf^21  when  an  automatic spray  system was  developed  for  open  gears. When and  if  unsatisfactory lubrication of gears  occurs  and  an  automatic  system is  involved, the  best  procedure  is to  bring  in  both  the  oil  supplier  and  the   manufacturer of the  lubricating equipment.