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.

Forced Feed Application of Gear Oils

Forced feed application of gear oils may take the form of circulating systems which deliver the lubricant as a stream running over the gearing or to jets or sprays of some type. Such methods not only provide lubrication but also utilize the gear oil as a cooling medium. Brewer^5 mentions three types of circulating systems, namely:

(1)    Wet sump, in which the oil is pumped under pressure directly from the sump to the lubricating points. Failure of the pump on such a system will cause almost immediate starved condition of lubrication.             

(2)    Dry sump, where a scavenging pump draws the excess oil from a sump and delivers it to a reservoir located above the gearing. A circulating pump then draws oil from this reservoir and delivers it to the point requiring lubrication. Since the scavenging pump has greater capacity than the circulating pump, the sump remains practically dry. A  pump failure  on  such a system  does not result  in as star rapid vation as in the  wet system  since some oil can feed by  gravity  from the reservoir  through  an idle pump.

(3)    Gravity  feed  which the sump  pump delivers  the oil, dripping  from the gearing, to a reservoir  set  high enough to give the desired  pressure. From this tank which may be thirty feet above the gear sets, gravity feed through regulating valves and perhaps sight glasses provides the lubrication.

Any of the above systems may also include oil filters, coolers, and even alarm devices to warm against malfunction of pumps. Gear oils used in paper mills, steel mills, and other locations are frequently contaminated with water, mill scale etc. Such lubricants may have to be reclaimed by settling, filtering and centrifuging before reuse. The oils used in forced feed applications are generally those which are quite fluid at ambient temperature and not of the residual type. However, if warmed, the latter type of lubricant can be handled in circulating systems.

                            Barring a pump or line failure, circulating oil systems provide a reliable flow of clean oil to gears. If necessary, this oil can serve additional functions, such as a hydraulic fluid in addition to lubricating practically any mechanism necessary. Such methods flush contaminants continually out of the lubricating areas and in most cases sufficient oil is in the system so that a portion can be withdrawn for a purification step during the cycle. Most of the heat  absorbed by  the oil  passing  through the  operating  area  is released  in the storage  or by coolers before  the return  cycle.

The lower the viscosity of a gear oil, the more satisfactory it will be for removal of heat from gear sets. In circulating systems, Dudley^16 considers that about a gallon of oil per minute will remove the heat developed when 400 hp are transmitted through a gear set. With larger installations considerably less than this ratio circulating oil to power is required.

Air-Oil Devices for Lubricating Gears

By injecting or pumping oil drop-by drop into an air stream the air will carry the lubricant to the points of application, such as gears. A similar mixture can be obtained by the aspiratory action of compressed air. With such systems, provision can be made to start the oil flow with the start of the machine and stop it when the gears stop. The delivery is positive and there is little chance for contamination because the gear box is under some pressure which prevents entry of dust. Also,rate of oil feed can be regulated.

On the negative side, it is necessary to provide compressed air and a considerable flow of air escapes through the vent of the gear case. While this air will have some cooling value, it may carry some oil mist. The oil is used on a once through basis and provision has to be made to drain the sump of the gear case at times.

Dripfeed Gear Lubrication

Dripfeed application of gear oils may be considered semi-automatic in that it is adjustable to a certain degree. The feed for the oil in this case may be by gravity or even by circulation if the stream in the latter instance can be throttled down sufficiently. In the first case a container can be filled by hand or even a small drum can be connected with piping ending in a valve or cock to permit adjustment of the feed. Here, as the amount of oil in the container becomes less, the feed will decrease. Where such a feed is partly mechanical, the oil will come either from a storage tank to which a pump has delivered it or directly from a circulating line. In either case the amount of used can be calibrated.

While dripfeed can be applied to enclosed gearing it is more often used on open gearing. Here it is applicable to softer types of gear oils including cut back types. This is more desirable method of lubricating open gears than the methods previously mentioned. Also, in case cut back gear oil is used, any vapor from the same will escape slowly and hence will be less of a hazard than if the mixture were sprayed on. Further, there are fewer tendencies to over lubricate by a drip method than with other methods of hand application. Therefore, there is a consequent reduction in waste and poor housekeeping.