The Use of Processed Glass As Lubricating and Protective Coatings for Hot Processing of Titanium, High Alloyed Steel and Other Superalloys Used by the Aerospace Industry

There are several areas of metal forming that can benefit from the use of specialty glass coatings that are applied to a billet or substrate before forming. Such processes as forging, extrusion and roll forming sometimes employ glass to assist in the forming of titanium, nickel-based alloys and stainless steels. The coatings are typically comprised of lead-free glass frits dispersed in water and use a resin to help the glass adhere to the substrate during the handling and heating cycles. Specially formulated glass in a powder form can be used for extrusion and hot roll forming operations. The glass functions by liquefying and reaching a certain viscosity range during heating. The molten glass can provide lubricity, oxidation protection and thermal insulation as needed by the specific forming operation. These properties help to minimize oxides, reduce surface defects, prevent decarburization if needed, enhance metal flow for forging and extrusion and improve product yield. The proper application of the various forms of glass is essential to achieve optimum performance and process benefits. For example, water-based slurries should be applied on surfaces that have been thoroughly cleaned and heated to assure the glass coating is dry before placing in a heating source. This paper will discuss the optimal coating procedures and techniques needed to assure that cost saving benefits are realized. Application methods such as dipping, conventional spraying and other innovative methods such as electrostatic spray will be reviewed.