Tungsten disulfide (WS2) is a known dry-film lubricant that was developed for NASA by Stanford University in the 1960's. Following its initial debut, tungsten disulfide found its way into industrial applications. Tungsten disulfide is known to improve wear properties and to enhance lubricity. It also has an affinity for lubricants, resulting in oil-retention properties in “wet” applications.
Tungsten disulfide is commercially available as a powder that comprises finely divided tungsten disulfide particles with a mean particle size ranging between about 1 micron and about 3 micron, depending upon the commercial supplier. Tungsten disulfide adheres to a substrate surface through a molecular/mechanical interlock and takes on the characteristic of the substrate regardless of whether the substrate is ferrous, non-ferrous, a composite, carbide or plastic. When applied to a substrate material, tungsten disulfide also forms a very thin layer due to the fact that it does not bond to itself. As a result, the dimensions and tolerances of treated parts are not compromised or appreciably affected when a substrate is treated with tungsten disulfide. Further, these aspects of tungsten disulfide prevent chipping, flaking or contamination problems.
Known methods for applying tungsten disulfide include burnishing and various spray-on techniques. One known method of applying tungsten disulfide that has been used is high velocity impingement such as through air blasting tungsten disulfide over a substrate surface.
Prior to the present invention, the present inventor found it desirable to clean or prepare the substrate surface for better tungsten disulfide retention such as through blasting the substrate material with suitable blast media such as aluminum oxide or silicon carbide. Conventional sand blasting equipment and techniques allowed the present inventor to operate with blast media particle grit sizes of up to 400 grit size but not higher grit numbers (larger grit size numbers equal smaller sand blast particle sizes).
Based on various recent observations made after the making of the present invention, the typical prior process of preparing or cleaning the substrate surface with 400 grit size blast media (or larger blast media particle size having a smaller grit number) is believed to have resulted in a tungsten sulfide treated substrate surface that is represented in FIG. 1, which is an idealized schematic representation of a cross section of a treated surface. This treated surface 10 has formed pockets 12 in the substrate 13 that are created as a result of the sand blast process which are then filled with tungsten disulfide particles 14. As will be appreciated upon an understanding of the present invention, this type of treatment has deficiencies and does not maximize the full potential of tungsten disulfide.
When higher grit numbers of up to about 800 grit, were experimented with and attempted by the present inventor (i.e. smaller particle sizes) the blast media would cake up in the sand blast hopper due to its small size. Attempts at experimenting with higher grit numbers to allow use of smaller particle sizes included banging on the walls of the media collection hopper or vibrating the hopper wall. However, these attempts resulted in substantially uneven flow of blast media in which the density of blast media sent to the sand blast gun would increase dramatically when the caked blast media periodically collapsed to the bottom of the hopper. Likewise, there would be a notable absence of blast media through the media intake at the bottom of the hopper while the blast media was caked up in the sand blast hopper. When the blast media collapsed down, this increased the blast media density sent to the gun and thereby lowered the impingement velocity. This would also create a thick cloud of blast media in the blast cabinet that would severely impair or eliminate visibility of the workpiece, thereby making work on the workpiece difficult or impossible. When the blast media caked up, the blast media intake was often substantially free of blast media and sucking air which decreased the blast media density sent to the gun and likely increased the impingement velocity. The uneven media flow caused a substantially uneven prepared surface on the substrate surface. Some portions of the substrate would be blasted at very high velocities and low blast particle densities which are believed to create deep pockets in combination with missed areas or unprepared surface areas over the substrate surface, while other portions of the substrate would be blasted at lower velocities and high blast particle densities which are believed to create very shallow pockets over the substrate surface. As a result the prepared surface is now believed to have had a variable surface characteristic which in turn created an inconsistent tungsten disulfide surface treatment with different surface characteristics at different areas over the treated area.