Sulfated Residue, Lead, Iron and Copper in Lubricating Oils

In this  methods, the sample  is completely  oxidized  by wet  ashing  with  concentrated  sulfuric acid, concentrated  nitric  acid and  hydrogen  peroxide, or  if  only iron and copper  are  to be  determined, by dry  ashing. To determine sulfated  residue, the  solution obtained by  wet  ashing  is  transferred  to a weighed  dish, evaporated  to  dryness, ignited at 775 degree C, cooled and  weighed. In determining lead, iron and  copper, the  solution resulting  from  the  wet  ashing is  mixed with  alcohol and  filtered  to give  a  precipitate  of  primarily  and  sulfate. This  precipitate  is  boiled  with  sodium carbonate and  then  precipitated  with  hydrogen  sulfide.

Iron  and  copper are  determined on  separate  aliquots  of the  filtrate  from  wet  ashing. The  iron is  separated  as the  hydroxide and  determined colorimetrically  as the  orange  ferrous  orthophenanthroline  complex,  while  copper  is  determined  colorimetrically  as the  yellow diethyldithiocarbamate  complex

Lubrication of Non-Reactive Surfaces at High Loads

By non-reactive is meant that the  surface will not react with  what  are  customarily  known  as EP elements such as  chlorine, phosphorus, or sulfur compounds. While there is little likelihood of extensive use of  some metal  combinations, it is well  to mention the possibilities. Thus,Antler suggests that 0.03 to 10  per  cent of trimeric  tin  sulfide compounds in  either  oils  or lubricating greases will  increase  the anti wear  qualities of the lubricant on surfaces such as  titanium-on-titanium, stainless steel-on-stainless steel, or gold-on-gold. The same  additives are also  said to be  effective on plastics, such as “nylon”, polyvinyl  chloride, polyethylene, etc.

Chromium is inert to most sulfur compounds but  will  react  with  most  chlorine compounds. Consequently, in  lubricating stainless steel  gears  under  heavy  loads, the  use  of chlorine compounds is  dictated.

Manufacturers  of gears  from  special  metals or  other  materials will no  doubt have  suggestions as to  the  proper  lubricants. Since EP agents are not  effective on  Babbitt, use of such  compounds in lubricants for  certain journal  bearings will  not  increase  the  lubricating  value.

Odor Control Agents

In general there has been no apparent  attempt  to cover up the odors  of gear  oils  which  arise  from EP  additives. Occasionally pine oil or pine tar will be detected in lubricants designed for exposed gears. Sulfur  compounds  perhaps  have  the most  disagreeable  odor  of any additives  and  consequently  Jonach^46  suggested  treating  such  agents  with  lead  peroxide  to  react  with  any  free hydrogen  sulfide  which might  be  present.

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.