VACUUM IMPREGNATION OF SINTERED MATERIALS WITH DRY LUBRICANT

Abstract: A method for vacuum impregnation of sintered bearings parts with dry lubricants. The impregnation is performed in the following way. The cleaned parts (1) to be impregnated are placed in a glass basin (2) containing a mixture of, for example, molybdenum disulphide and graphite, a termosetting resin, a solvent and a termosetting resin extender. The glass basin is placed in a vaccum chamber (3) and the vacuum chamber is then vacuum pumped for a sufficiently long time in order to evacuate the air from the pores of the sintered parts. After that air is again let in into the vacuum chamber until normal air pressure is reached. The sintered parts are taken out and are allowed to air dry. The coating is then cured.

Description: The invention described and claimed herein relates to vacuum impregnation of sintered bearings parts. More particularly, this invention is concerned with vacuum impregnation of bearings parts, so that a supply of a dry lubricant will be integrally contained therein. It is prior known that finely divide metals may be sintered under appropriate conditions of heat and pressure to yield a porous structure that can be impregnated with a lubricant. This type of bearing has proved of utility in certain limited applications, but is generally found lacking in that the fugitive lubricant is not tightly held in the interstices of the sintered metal. As a result, the lubricant may bleed out of the bearing under no load conditions or may be extracted therefrom by centrifugal forces if the bearing is subjected to rotation. For this reason, it is generally necessary to provide means to replace the supply of lubricant in such self-lubricated bearings, either continuosly or at predetermined intervals. Metal bearings have also been lined with certain solid non-metallic substances that have low coefficient of friction and will serve as lubricants. Bearings of this type are, for example, those that are lined with low friction resinous materials such as polyethylene and polyamides. Under comparatively light loads these bearings have sometimes proved satisfactory, but they do not have the necessary wear resistance to permit their use under moderate to severe pressure-velocity conditions. Thus, their utility is limited. A third type of self-lubricated bearing may be prepared by applying a layer of adhesive material to a metal substrate, contacting the adhesive layer with a finely divided absorptive resinous material, and causing the adhesive material to harden, whereby a layer of finely divided synthetic resinous material is bounded to at least the surface of said substrate. The metal substrate may be shaped into the form of a bearing either before or after the finely divided resinous material is applied to the surface. Such a bearing is described in US Patent 3.380.843. Another similar process is described in US Patent 4.104.176. According to this patent there is applied to the surface of the bearing a matrix of closely spaced, solid discrete particles held together, not through the compaction and sintering of powder metallurgy, but with a bonding material disposed in the interstices between the particles. The bonding material only partially fills the interstices and leaves an interconnected uniform porosity sufficient to provide at the bearing surface the lubricant needed for a lubricant-impregnated bearing. The main disadvantage of the bearings according to these patents is that the fabrication of them is relatively complicated. The invention as claimed is intended to remedy the above mentioned drawbacks. Briefly stated, this invention relates to vacuum impregnation of sintered bearing's parts with dry film lubricant in order to reduce wear. This is accomplished by applying a dry film lubricant to the surface of the sintered parts in such a way that the dry lubricant is integrally contained within a surface layer of the sintered parts. The advantages offered by the invention are mainly that all the above mentioned disadvantages are eliminated and that the preparation of the sintered parts can be done in a very simple and economical way. The increase in life time of the parts prepared according to the invention has proved to be several times more as compared with prior known techinque. The method is applicable to already existing manufacturing process without change of dimension/tolerance of bearing details. Besides, the impregnation protects the pores of the parts from smut and humidity which may cause corrosion of the sintered parts. The invention, which is defined in the attached claims, is described in detail below with reference to the drawings, in which: Figure 1 shows a schematical view of a vacuum chamber for vacuum impregnation of sintered bearings parts with a mixture containing dry lubricant's ingredients. Figure 2 shows cross sectional views of a bearing's part. This invention is applicable for all sorts of sintered bearings or the like where parts are subjected to wear. The invention is described in detail below with reference to the drawings. Figure 1 shows in schematical form a vacuum chamber for use in connection with the invention. The application of the dry film lubricant is accomplished in the following way. The cleaned parts (1) to be impregnated are placed in a glass basin (2) containing a mixture of, for example, molybdenum disulphide and graphite, a termosetting resin, a solvent and a termosetting resin extender. The glass basin is placed in a vacuum chamber (3) and the vacuum chamber is then vacuum pumped for a sufficiently long time in order to evacuate the air from the pores of the sintered parts. After that air is again let in into the vacuum chamber until normal air pressure is reached. When the pressure rises in the vacuum chamber the mixture is forced into those pores of the sintered parts which are in connection with the surface and therefore has been air evacuated. When the normal air pressure has been reached the parts are taken out and are allowed to air dry for 10 to 15 minutes. The coating is then cured by bringing the substrate temperature to 180°C for one hour or to 210°C for thirty minutes. Figure 2A shows a sintered axle in a bearing. Figure 2B is a cross sectional view of an enlarged part of said axle showing how the axle is built up of finely divided solid particles which has been sintered together under pressure and heat leaving pores therebetween. Some of these pores are completely closed while other are connected to the surface of the axle. Figure 2C shows a further enlarged surface part of the axle which has been impregnated in accordance with the subject invention. The dry lubricant has been forced into and fills those pores which are in direct connection with the surface. Further, the dry lubricant extends from the pores sligthly above said surface and thus constitutes the only contact between the axle and the other bearing part (not shown).

Claims: 1. Method for vacuum impregnation of sintered bearing parts with dry lubricants, characterized by the steps of placing the cleaned sintered parts (1) in a basin (2) containing a mixture of the dry lubricant and a termosetting resin dissolved in a solvent, placing the basin (2) in a vacuum chamber 3, vacuum pumping the vacuum chambre for a sufficiently long time in order to evacuate the air from the pores of the sintered parts, letting in air into the vacuum chamber until normal air pressure is reached, taking out the sintered parts and letting them air dry, curing the dry lubricant coating of the parts. 2. Method according to claim 1, characterized in that the dry lubricant consists of molybdenum disulphide and graphite. 3. Method according to claim 1 or 2, characterized in that the mixture further contains a termosetting resin extender. 4. Method according to any of the previous claims, characterized in that the curing is performed by bringing the substrate temperature to 180°C for one hour or to 210°C for 30 minutes. 5. Methods according to any of the previous claims, characterized in that the parts are allowed to air dry for 10 to 15 minutes.

Inventors: AL-JAROUDI, MOHAMMED YOUSSEF
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1985
Main classification: B22F3
IPC codes: F16C33, C08J5, B22F3