Molybdenum wire

  "Sprabond" 3.17 mm diameter molybden wire is used for spraying compression 
   piston rings, as well as rings of synchromesh gearboxes.

Molybdenum wire

Molybdenum has several properties that make molybden coating of special importance.  The high melting point (2620° C) and the volatility of the oxides are responsible for forming the molecular bonds with the substrate at different points of covering, which increases the adhesion strength of coatings and allows their application on smooth and even polished surfaces.

Molybdenum coatings have good adhesion to aluminum, iron, nickel and their alloys, but do not adhere well to copper, chromium and their alloys.  At a temperature of 500° centigrees in air molybdenum begins to evaporate, and at 700 centigrees the evaporation proceeds to energetically flowing sublimation.  Thereby the operating temperature of molybdenum coatings is limited to 400° C.

Molybdenum has a high chemical resistance to sulfuric, hydrochloric, phosphoric and other acids.  With sufficient thickness and impermeability these coatings are resistant to many molten salts of liquid sodium metal.  Molybdenum coatingsare characterized by high hardness (400 ... 900 HV), wear resistance and resistance to abrasion and erosion, so that their treatment is difficult and is performed only by grinding.

However, the most important property of molybdenum coatings is its very high anti-scoring property which is combined with good running-in.  According to the existing opinion high anti-scoring properties and wear resistance of molybdenum coatings are explained by chemical affinity of  molybdenum to sulfur and its ability to form sulfur of molybdenum disulfide contained in the lubricant that has properties of dry lubricant.

The above-mentioned properties of molybdenum coatings are not lost when operating at high temperatures (up to 400 centigrees in the air).

Thin molybdenum coatings are used not only as an intermediate layer - as an independent method of surface preparation - but also to improve the wear resistance of the necks of axles and shafts of machines, particularly of critical use.  They are also used for protection against abrasive wear, such as in fan blades subjected to erosive action of coal dust, as well as to repair and improve the stability of stamps.  For example, steel stamps for housing flange axle of vehicles became unusable after manufacturing of 200-300 parts due to adhesion and welding of metal.  Attempts to use stamps of their tool steel, as well as with chrome and carbide coatings turned out to be ineffective.  Applying the same coating of molybdenum increased the service life of stamps (40,000 to 30,000 parts).  After making such a number of parts stamps were subjected to re-deposition and were reused.

In addition, molybdenum coatings are used to remove scratches and reduce the wear of the guiding housings of precision machine tools.  Molybdenum coating increases service life of machines without compromising their accuracy ten times.

Anti-scoring properties of molybdenum coatings are used in the automotive industry, where the coating is applied to improve durability of piston rings and easily-worn synchromesh rings and plugs of gearbox switches.

Thus, despite the relative high cost of molybdenum, the application of molybdenum coatings usually is justified econimically sound.