Reducible glass lubricants for metalworking

A reducible glass lubricant on a metal workpiece provides a duplex film during hot working of the workpiece. A silicate glass powder which contains from about 3 to 50 mole percent of an oxide of bismuth, tin or copper is used for the reducible glass lubricant. During preheating in a preheat furnace the glass lubricant is reduced to the duplex glass film.

This invention relates to reducible glass lubricants for metalworking. More 
particularly, this invention is directed to a method of hot working a 
metal workpiece with a reducible glass lubricant thereon and to a metal 
workpiece with a reducible glass lubricant thereon. 
Industries such as aircraft engine and turbine manufacturing employ hot 
metalworking operations such as extrusion and forging to produce high 
quality, near-net-shape parts with good quality surface finishes. 
Achieving the necessary degree of consistent surface and dimensional 
quality requires metalworking lubrication capable of providing protection 
for the highly finished and accurate dies. The processing involves 
repeated contact between these dies and the hot workpiece metals under 
very high pressures. Under these conditions the workpiece tends to wear 
the dies by such mechanisms as erosion, galling and abrasion. The 
workpiece metals employed, such as titanium alloys, are often especially 
prone to aggressive attack on the dies. Worn dies then produce parts of 
unacceptable quality. 
Current practice in metalworking employs lubricant systems typically 
comprising a glass applied to the workpiece plus an accessory lubricant 
such as graphite applied to the dies. It has been found that glasses 
containing lead oxide are especially effective as lubricants for precision 
metalworking. However, the element lead is undesirable in an industrial 
process. 
It is apparent from the above that there exists a need in the art for a 
method of hot working a metal with an improved lubricant thereon. It is a 
purpose of this invention to fulfill this and other needs in the art in a 
manner more apparent to the skilled artisan and given the following 
disclosure. 
SUMMARY OF THE INVENTION 
The above-mentioned needs are met by the present invention which relates to 
a method of hot working a metal workpiece or core having an improved 
reducible glass lubricant coating thereon. A metal workpiece is also 
disclosed with a reducible glass lubricant coating thereon. More 
particularly, the present method of hot working of a metal workpiece 
comprises providing a metal workpiece, providing a silicate glass powder 
containing from about 3 to 50 mole percent of an oxide of a metal in which 
the metal is selected from the class consisting of bismuth, tin and 
copper, coating the workpiece with the silicate glass powder providing a 
reducible glass lubricant, preheating the workpiece with the silicate 
glass powder thereon producing a duplex lubricant film, and hot working 
the workpiece to produce a near-net-shape part with a good quality finish. 
In another embodiment, an article comprises a metal workpiece and a 
silicate glass powder thereon, the powder containing from about 3 to 50 
mole percent of an oxide of a metal in which the metal is selected from 
the class consisting of bismuth and copper.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows an article 10 of the present invention which comprises a metal 
workpiece 12, for example, of titanium or titanium alloy with a reducible 
glass lubricant coating or layer 14 thereon. This article is suitable for 
practicing the present invention by being hot worked in operations such as 
extrusion and forging. The coating or layer is a silicate glass powder 
containing from about 3 to 50 mole percent of an oxide of a metal in which 
the metal is selected from the class consisting of bismuth, tin and 
copper. The glass powder coating is applied to the metal workpiece by 
dipping or spray coating. In the dipping operation, the glass powder is 
dispersed preferably in water plus dispersants, binders, and rheology 
agents to provide a slurry. The workpiece is dipped into the slurry to 
coat the glass powder on all the surfaces thereof. If desired, the glass 
powder is spray coated onto the surfaces of the workpiece. In this 
operation, the glass powder is dispersed preferably in water plus 
dispersants, binders, and rheology agents to provide an adherent coating. 
As shown in FIG. 1, the powder adheres to all of the workpiece surfaces. 
Article 10 is suitable for practicing the method of the present invention. 
In FIG. 2, there is shown an article 20 which is an article such as article 
10 shown in FIG. 1 after the article has been preheated in a pre-heat 
furnace. Article 20 comprises a metal workpiece 12 with a duplex film 22 
thereon. Film 22 has two layers with inner layer or film of soft metal 24 
adjacent to workpiece 12. Metal layer 24 may be in a molten state. An 
outer layer or film 26 of molten glass is adjacent metal layer 24. Article 
20 is suitable for being hot worked in an extrusion or forging operation. 
In the present invention, a method of hot working a metal workpiece or core 
20 comprises providing a metal workpiece or core 12, for example, of 
titanium metal or alloy. An improved reducible glass lubricant coating is 
prepared from a silicate glass powder containing from 3 to 50 mole percent 
of an oxide of a metal in which the metal is selected from the class 
consisting of bismuth, tin and copper. The workpiece 12 is coated with the 
silicate glass powder to provide a reducible glass lubricant thereon. The 
glass powder is applied to the metal workpiece by dipping or spray 
coating. In the dipping operation, the glass powder is dispersed 
preferably in water plus dispersants, binders, and rheology agents to 
provide a slurry. The workpiece is dipped into the slurry to coat the 
glass powder on all the surfaces thereof. If desired, the glass powder is 
spray coated onto the surfaces of the workpiece. In this operation, the 
glass powder is dispersed preferably in water plus dispersants, binders, 
and rheology agents to provide an adherent coating. 
The silicate glass powder coating is a reducible glass lubricant coating. 
The workpiece with the silicate glass powder coating or reducible glass 
lubricant is preheated in a pre-heat furnace to a sufficient temperature 
to reduce the reducible glass lubricant to a duplex lubricant on the 
surface of the workpiece. This duplex lubricant is produced by including 
the metal oxide of bismuth, tin or copper in the formation of the glass 
which is chemically reduced to the respective metal as a soft metal 
portion of the film adjacent the workpiece. The soft metal may be in a 
molten state. The glass portion of the film is in a molten state adjacent 
the soft metal portion. The glass portion is the outer portion of the 
duplex film. 
The workpiece with the duplex film is generally prepared just prior to the 
hot working operation, such as extrusion or forging. As it is customary, 
there may also be employed customary die lubricants, such as graphite, 
applied to the dies. The preheated workpiece with duplex lubricant thereon 
is hot worked by extrusion or forging to produce high quality, 
near-net-shape parts with good quality surface finishes. 
The foregoing has described a method of hot working of a metal workpiece 
and a metal workpiece with a reducible glass coating thereon. It will be 
apparent to those skilled in the art that various modifications thereto 
can be made without departing from the spirit and scope of the invention 
as defined in the appended claims.