EP0403306A1

EP0403306A1 - Carrier-free forge lubricant and method of using same

Info

Publication number: EP0403306A1
Application number: EP90306572A
Authority: EP
Inventors: Andrew F. Lum; Juan M. Uribe; John M. Hogan
Original assignee: Castrol Industrial Inc
Current assignee: Castrol Industrial Inc
Priority date: 1989-06-16
Filing date: 1990-06-15
Publication date: 1990-12-19
Also published as: JPH0350298A

Abstract

The composition of the present invention is a carrier-free pulverulent forging lubricant having at least one component having adhesive properties at forging temperatures and the method of the invention is a method of forging a workpiece in a die which includes the step of spraying onto at least one of the die and the workpiece a coating of an effective amount of a carrier-free pulverulent lubricant composition at ambient pressure. The use of the composition and method of the invention significantly reduces smoke generation in hot forging operations by eliminating the use of oils or volatile organic compounds as carriers.

Description

This invention relates to the field of metal working lubricants in general and, in particular, to forging lubricants. More particularly, it relates to a new forging lubricant composition and a method of using that composition in the hot forging of metal workpieces.
Metal parts of a multitude of sizes and shapes are manufactured by various types of forging operations, and these parts are formed from stock composed of a great many metals and metal alloys. A great many parts are forged from such metals and metal alloys as, for example, steel, aluminum, and titanium, to name but a few.
The conditions under which metal parts are forged, of course, are widely variable, depending upon not only the nature of the metal, but upon the size and complexity of configuration of the desired part. Small, thin, simply shaped parts may obviously be forged from a relatively flowable metal such as aluminum under much less rigorous conditions than are required to forge large more complex shaped parts from a metal such as steel.
Each set of forging conditions requires a specialised lubricant, and there is therefore a multitude of aqueous-based, oil-based and organic solvent-based lubricants currently in use in various forging operations. Many such lubricant systems, particularly those used under the most demanding forging conditions, by their nature require the user to make compromises in order to achieve the desired functional characteristics while avoiding as much as possible any safety, occupational health or environmental hazards involved in their use. Moreover, in some instances, more restrictive health and environmental guidelines are now in force which may make use of certain lubricant systems either extremely expensive or simply unworkable. It is to these concerns which the present invention is directed.
In a typical high performance forging operation, such as one which might be devoted to the manufacture of large, complex parts from aluminum alloy stock, an effective lubricant is one which ordinarily contains a variety of lubricity agents in a carrier comprising mineral oil and/or volatile organic solvents. The dies used in such forging operations are maintained at high temperatures, in the range of 350°F to 700°F, in order to permit proper metal flow during the forging operation.
The forging lubricant is typically applied to the die and the workpiece by spraying, and, on account of the temperatures involved, the mineral oil and volatile organic compounds immediately flash off, leaving only a relatively small amount of residue which actually functions as the lubricant. As anyone who has observed such a forge operation well knows, the flashing off of the mineral oil and volatile organic compounds creates a significant amount of open flames, and the spray wand by which the lubricant is applied takes on the appearance of a flame thrower. Moreover, a large amount of smoke is typically generated when the mineral oil and volatile organic compounds flash off, since, at the same time, a rather significant portion of the lubricity agents may burn off as well. In this context, it is well known that any improvements in the performance of the forge lubricant which are achieved by reformulation frequently come at the cost of significantly higher smoke generation.
Similar difficulties are inherent when oil-based paste type lubricants are utilised. While the paste lubricants contain little or no volatile organic compounds, their oil carriers partially or completely burn at typical forging temperatures, resulting in significant heavy smoke generation.
The hazards, expense and environmental problems associated with such forging operations are of great proportion and are quickly becoming even more so.
In a state such as California, where environmental protection statutes and regulations impose rigid standards on industrial operations, and in other states which have similar environmental protection schemes, the smoke generated by a large forge operation creates tremendous difficulties.
Since environmental agencies frequently monitor smoke emissions by aerial surveillance, there is close attention paid to reducing the smoke generated in the forging operation. Unfortunately, this often limits the efforts made to vent the smoke from the buildings in which the forge operation is housed. The result of this is a sufficient degradation of the air quality within the buildings.
An important economic consideration is that in California, for example, a tax will soon be levied upon each gallon of volatile organic compounds emitted into the air. More importantly, as air quality standards are progressively raised, there will soon come a time when a forge operator will simply be prohibited from emitting large amounts of smoke. The choice then will be to find an alternative lubricant which produces significantly reduced amounts of smoke or to cease operations entirely.
Other related concerns create a strong demand for alternative forge lubricants.
As described above, open flame is generated when conventional mineral oil and volatile organic compound-based lubricants are applied to a heated die. One must therefore have available fire prevention and fire control equipment, such as fire extinguishers and sprinkler systems, in the immediate area of the forge operation. Indeed, fire extinguishers see regular use in many forge operations, and the cost of their maintenance is significant. In general, fire prevention, fire control and fire detection systems of all types are regular and significant capital and maintenance cost items for hot forge operations.
A related problem associated with the use of conventional volatile organic compound-based lubricants is the need for special storage facilities on account of their high flammability. This too imposes a significant cost associated with the use of conventional lubricants.
Transportation of these flammable lubricants in special containers and special vehicles is yet another source of additional cost, hazard, and inconvenience associated with their use.
A still further disadvantage of conventional lubricant systems which results from the flashing off of oil and solvent carriers is that the smoke generated forms tar-like deposits on machinery, finished parts, floors, windows, and nearly everything else housed in the same building with the forge operation. Quite apart from the aesthetic undesirability of such deposits, there are economic and health concerns as well. Many large forge operations maintain permanent steam-cleaning facilities at a significant cost. Moreover, a great variety of combustion products which are generated in the uncontrolled flashing of the volatile organic compounds used as carriers in conventional lubricants may themselves be hazardous to the health of personnel.
Many of the aforementioned disadvantages are overcome by use of a lubricant in powder form such as that described in US 4,228,670 in which lubricant powders of particle size 0.6 to 1.5µ are sprayed on to workpieces made from, for example, titanium alloys in high temperature isothermal forging operations. However, in order to ensure that the powder adheres to the workpiece, high pressure spraying apparatus is used to sand blast the powder onto the workpiece so that it is mechanically adhered. The use of such high pressure equipment has several disadvantages. Firstly, there are considerable safety risks since mis-directed spray can seriously injure personnel, secondly, large amounts of lubricant material are wasted and finally this type of equipment is expensive in comparison to conventional spraying apparatus.
It is the aim of the present invention to overcome the problems mentioned above of hitherto known forging lubricants and forging operations and in particular to provide a forge lubricant and a method of its use which significantly reduce the amount of smoke generated during the forging operation and to eliminate the organic carrier materials which are essential parts of conventional high performance forging lubricants.
A further general object of the present invention is to provide a lubricant which eliminates many health, environmental and safety drawbacks of conventional lubricants having mineral oil and volatile organic compounds as carriers.
Another more particular object is to eliminate the need for special transportation and storage facilities which are required for convention lubricants.
Other objects and advantages of the present invention will be apparent to those skilled in the art from the following description of the invention and the appended claims.
In accordance with one aspect of the invention there is provided a carrier-free pulverulent forging lubricant composition, i.e., one which is entirely free of the oils and volatile organic compounds commonly employed as carriers for forge lubricant compositions, wherein the composition has at least one component having adhesive properties at forging temperatures.
In accordance with a second aspect of the invention there is provided a method of forging a workpiece in a die which includes the step of applying to at least one of the die and the workpiece a coating of an effective amount of a carrier-free pulverulent lubricant composition having at least one component having adhesive properties at forging temperatures.
In accordance with the third aspect of the invention there is provided a method of forging a workpiece in a die comprising the step of spraying onto to at least one of said die and said workpiece a coating of an effective amount of a carrier-free pulverulent lubricant composition, said spraying being carried out at essentially ambient pressure.
The method of the invention may be carried out using conventional spraying apparatus which operates at ambient pressures and electrostatic spraying apparatus is particularly preferred.
The carrier-free pulverulent forging lubricant of the invention may include any material which will provide lubricating properties at the temperatures typically encountered in a forging process and which can be put into a physical form which permits it to be applied to the die and/or the workpiece by conventional powder-coating equipment.
In accordance with the present invention, the need to incorporate a mineral oil and/or a volatile organic compound-based carrier is completely eliminated, with the result that the smoke generated by conventional lubricants is significantly reduced.
The advantages inherent in the composition and method of the invention are numerous.
The elimination of much of the smoke previously generated by the flashing off of a mineral oil and volatile organic compound carrier permits a forging operation to continue in business in full compliance with environmental statutes and regulations. Moreover, the business may continue without the economic burden of tax payments based on the emission of volatile organic compounds. In many instances, the use of the composition and method of the present invention will permit a forge operation to continue in existence under a stringently regulated environmental scheme which would otherwise cause it to be shut down entirely.
Other economic advantages of the composition and method of the invention are of equally great importance.
The reduction in weight and volume which occurs when the carriers of conventional lubricants are eliminated lead to savings in the cost of shipment and storage. Even further savings are realised in transportation and storage costs because the carrier-free composition of the invention is neither flammable nor hazardous, and it can be shipped and stored in the same manner as any other non-hazardous material. Moreover, packaging costs are significantly reduced, since a five-gallon plastic pail of the carrier-free pulverulent forging lubricant of the present invention will be the functional replacement for a fifty-five gallon steel drum of a conventional lubricant.
In the forge operation itself, the composition and method of the invention results in significant reductions in the costs of installing and maintaining fire prevention and fire control systems, and in general permit the maintenance of a much safer environment for personnel at a much lower cost. A particular advantage of the method of the invention is the use of conventional spraying apparatus rather than expensive high pressure sand-blasting apparatus.
Still further savings resulting from the use of the composition and method of the invention may be realised in reduced premiums for fire, workmen's compensation, and liability insurance.
The elmination of the carrier material significantly reduces raw material costs, since on a weight and volume basis, the carrier in conventional lubricants accounts for well over 90% of the composition.
The need to maintain expensive and space-consuming cleaning facilities for plant and finished parts is also reduced by the use of the composition and method of the invention, since significantly less combustion residues will be produced in the absence of the flashing off of mineral oil and volatile organic compound carriers.
The composition of the present invention is a carrier-free pulverulent forging lubricant. It may include any material which will provide lubricating properties at the temperatures typically encountered in a forging process and which can be put into a physical form which permits it to be applied to the die and/or the workpiece by conventional powder-coating equipment.
Many materials which will perform the function of lubricating the die and maintaining a physical separation between the die and the workpiece are well known, and, of these materials, many are in the physical form necessary to the practice of the present invention; namely, a granular, short fiber or powder-like solid at room temperature. It is not necessary that the materials employed in the composition of the invention remain either solid or pulverulent at the temperatures typically encountered during the forging operation, e.g. about 600°F up to 1000°F for aluminum, and about 1500°F up to 2500°F for steel or titanium. It is enough that they may be made to exist in a particulate form. In that form, they can be applied by conventional powder-coating equipment, even though they may partially or completely melt or burn when in contact with the heated die or workpiece. Indeed, at least one component of the carrier-free pulverulent forging lubricant composition of the invention should become sticky upon being heated so as to assist in adhering the dry forge lubricant composition to the workpiece and die surfaces.
The lubricant composition of the invention may be applied to a heated or heating die in a manner analogous to the application of conventional lubricants. Alternatively, the composition may be sprayed onto a cold unforged workpiece, after which the workpiece is heated to achieve a partial melt of the composition and subsequently placed into a heated die for forging.
Typical materials which are capable of maintaining a physical barrier between the die and the workpiece and which function as solid lubricants are contemplated for use in the composition of the invention. They include, by way of example only, metal soaps, graphite, ceramics, polymer resins having high heat resistance, natural and synthetic waxes, gilsonite, glasses, and mixtures of these materials.
Preferably the component having adhesive properties at forging temperatures is selected from natural and synthetic waxes, polymer resins having high heat resistance, gilsonite and glasses.
Of the metal soaps, fatty acid soaps such as zinc stearate and sodium stearate are preferred on account of their known properties, their ready availability and low cost. Other metal soaps, including, by way of example only, those of tin and lithium, may, however, function equally well.
Materials such as graphite and certain ceramic materials such as boron nitride are useful for maintaining a physical separation between the die and the workpiece. While the precise mechanism of the physical separation is not known, this characteristic is believed to be attributable to the relatively planar crystalline structure of these materials.
Useful polymer materials having high heat resistance include poly(tetrafluoroethylene) (PTFE), high density polyethylene (HDPE), and poly(vinylchloride) (PVC).
Of the natural and synthetic waxes which may be advantageously employed, polyethylene waxes of relatively high molecular weights are in general preferred on account of the lubricity which they impart.
Glass materials useful in the present invention are preferably the low melting glasses, including alumina, alumina/silica, silica, boric acid, and borax. Optionally, these glass materials may be used in chopped fiber form.
A particularly preferred lubricant composition comprises by weight about 15 to 50% metal soap component about 15 to 50% of a component selected from graphite or ceramics and about 25 to 45% of a component having adhesive properties at forging temperatures.
The average particle size of the materials present in the carrier-free pulverulent forging lubricant of the invention may vary anywhere from about 10 microns up to about 70 microns, with a preferred size being between about 30 and about 40 microns. These particle size limitations have little significance as far as the performance of the composition as a forge lubricant is concerned; they relate principally to the limitations of currently available spray equipment.
As mentioned above within the scope of the invention is a method of forging a workpiece in a die comprising the step of spraying onto at least one of said die and said workpiece a coating of an effective amount of a carrier-free pulverulent lubricant composition said spraying being carried out at essentially ambient pressure.
The application of the lubricant in accordance with this method of the invention may be accomplished by conventional electrostatic powder-coating equipment. It is well known that, in a conventional electrostatic powder coating apparatus a fluidized bed of powder feeds a spray wand having an electrode at the tip. While the apparatus injects air into the powder at low pressure to form the fluidized bed, by the time the powder reaches the tip of the application wand (typically a distance of about 20 feet) the air carrying the powder is at essentially ambient pressure. The charge imported to the powder provides the necessary acceleration to carry the powder to the die or workpiece which is maintained at ground. Electrostatic spraying of the type is essentially a low pressure operation when compared with the kind of high pressure sand-blasting apparatus described in US 4,228,670 and is therefore advantageous from the point of view of safety and cost. Furthermore, the electrostatic attraction of the particles to the die means there is little loss of the lubricant material during the spraying operation.
In this method of the invention the lubricant may be applied to a heated or heating die in a manner analogous to the application of conventional lubricants. Alternatively, the lubricant composition may be sprayed onto a cold unforged workpiece, after which the workpiece is heated to achieve a partial melt of the composition and subsequently placed into a heated die for forging.
A particularly preferred method comprises spraying the workpiece with a coating of an effective amount of the carrier-free pulverulent lubricant composition, heating the workpiece to a pre-selected temperature, inserting the workpiece into the die and forging the workpiece into the desired configuration.
It has been found that on account of their very powdery, even dust-like, nature, such materials as graphite and amorphous boron nitride are less easily retained on the surfaces of the die and workpiece than are some of the other materials enumerated above. Drafts or currents of air may therefore undesirably remove the pulverulent forging lubricant from the die and/or the workpiece prior to the forging operation. Thus, when including one or more of these materials in the method of the invention, it is preferred, either to include at least one component having adhesive properties at typical forging temperatures, such as a glass, gilsonite, or polymer resin, or alternatively apply the powder using electrostatic apparatus for the purpose of retaining the lubricant on the die and the workpiece.
Preferred polymer resins are poly(tetrafluoroethylene), high density polyethylene, poly(vinylchloride) or mixtures thereof.
The following lubricant compositions are preferred for use in the method of the invention:-

(a) A composition comprising graphite or ceramic component in an amount from about 25% to 60% by weight and a component having adhesive properties in an amount of from about 40 to 75% by weight.
(b) A composition comprising about 40% by weight alumina/silica glass and about 60% by weight graphite.
(c) A composition comprising about 75% by weight borax and about 25% by weight of boran nitride.
(d) A composition comprising about 35% by weight graphite and about 65% by weight borax.

The lubricant composition for use with the method of the invention may contain a metal soap such as zinc stearate, sodium stearate or mixtures thereof.
Some examples of the composition and method of the invention are set forth below.

Examples 1 and 2

The following compositions were used to forge a box channel with high walls, approximtely 0.125 inches thick, in a wrap die from aluminum alloy stock. The press was of the hydraulic type, with the workpiece temperature being 700°F and the die temperature 375°F:

Example 1

Component Weight%

gilsonite 5

zinc stearate 34

sodium stearate 10

graphite 17

polyethylene wax 34

100

Example 2

Component Weight%

gilsonite 5

zinc stearate 34

sodium stearate 10

graphite 17

amide wax 34

100
Only seven parts were forged; thus, optimisation of spray techniques could not be achieved. However, examination of the forged parts showed excellent metal movement, with a complete die fill of the walls of the channel. There was excellent downsize of the critical part dimension, and the parts released easily from the die, with no sticking. The dies had some tendency to stick together; however, this is normally experienced with this configuration of parts. Smoke levels were noticeably lower than those produced when a conventional solvent, oil and graphite lubricant was used. Based on this rather limited trial, the composition of Example 1 outperformed the composition of Example 2 in each of the observed respects, though both were effective as forging lubricants.

Example 3

In a comparative trial, the composition of Example 1 was evaluated using a conventional solvent-based zinc stearate forging lubricant as a standard. The press was of the mechanical type, with the workpiece temperature being 700°F and the die temperature 400°F.
Forty parts were forged from each composition. Examination of the forged parts showed excellent metal movement with no drag. There was excellent downsize of the critical part dimension. The parts released easily from the die, with no sticking, and there was no build up of lubricant residue on the parts. Smoke levels when using the composition of Example 1 were significantly lower than those produced during the trials reported in Examples 1 and 2.
Each of the following compositions were evaluated under the same conditions as those of Example 3, and each was found to perform satisfactorily with significantly lower smoke generation than conventional solvent-based lubricants.

Example 4

Component Weight%

graphite 33.0

zinc stearate 34.5

gilsonite 10.9

polyethylene wax 21.1

99.5

Example 5

Component Weight%

graphite 23.8

sodium stearate 33.4

gilsonite 23.8

polyethylene wax 9.5

zinc stearate 9.5

100

Examples 6 and 7

The following carrier-free pulverulent forging lubricant compositions are also useful for the forging of aluminum and aluminum alloy workpieces:

Example 6

Component Weight%

graphite 75

gilsonite 25

100

Example 7

Component Weight%

graphite 50

gilsonite 25

zinc stearate 15

poly(tetrafluoroethylene) 10

100

Examples 8 to 11

Other carrier-free pulverulent forging lubricant compositions are useful for high temperature forging of titanium and steel, and they include the following:

Example 8

Component Weight%

alumina/silica glass 40

graphite 60

100

Example 9

Component Weight%

boron nitride 25

borax 75

100

Example 10

Component Weight%

graphite 35

borax 65

100

Example 11

Component Weight%

graphite 40

gilsonite 30

borax 30

100
In particular, the following composition produced excellent results in a steel forging operation:

Example 12

Example 12
Component	Weight%
graphite	40
gilsonite	30
boric acid	30
	100

From the foregoing description and examples, it is apparent that the objects of the present invention have been achieved. While only certain embodiments have been set forth, alternative embodiments and various modifications will be apparent to those skilled in the art. These and other alternatives and modifications are considered equivalents and within the spirit and scope of the present invention.

Claims

1. A carrier-free pulverulent forging lubricant composition having at least one component having adhesive properties at forging temperatures.

2. A composition according to claim 1 comprising a component selected from graphite or ceramics.

3. A composition according to claim 1 comprising graphite and gilsonite.

4. A composition according to claim 3 comprising, by weight, about 75% graphite and about 25% gilsonite.

5. A composition according to claim 2 further comprising a metal soap component.

6. A composition according to claim 5, wherein said metal soap is selected from zinc stearate, sodium stearate, or mixtures thereof.

7. A composition according to any preceding claims wherein said component having adhesive properties at forging temperatures is selected from natural and synthetic waxes, polymer resins having high heat resistance, gilsonite, and glasses.

8. A composition according to claim 7, wherein said polymer resin is poly(tetrafluoroethylene), high density polyethylene, poly(vinylchloride), or mixtures thereof.

9. A composition according to claims 5, 6 or 7 comprising zinc stearate, sodium stearate, gilsonite, graphite, and either polyethylene wax or amide wax.

10. A composition according to claim 9 comprising, by weight, 34% zinc stearate, 10% sodium stearate, 5% gilsonite, 17% graphite, and 34% polyethylene wax or 34% amide wax

11. A composition according to claim 5 comprising, by weight,
about 15 to 50% metal soap component,
about 15 to 50% of a component selected from graphite or ceramics, and
about 25 to 45% of a component having adhesive properties at forging temperatures.

12. A method of forging a workpiece in a die comprising the step of spraying onto at least one of said die and said workpiece a coating of an effective amount of a carrier-free pulverulent lubricant composition, said spraying being carried out at essentially ambient pressure.

13. A method according to claim 12 wherein said carrier-free pulverulent lubricant composition is applied by electrostatic spraying.

14. A method according to claim 12 or 13, comprising the steps of

(a) applying to said workpiece a coating of an effective amount of said carrier-free pulverulent lubricant composition;

(b) heating said workpiece to a pre-selected temperature;

(c) inserting said workpiece into said die; and,

(d) forging said workpiece into a desired configuration.

15. A method according to any one of claims 12 to 14 which uses the carrier-free pulverulent lubricant composition described in claim 2.

16. A method according to claim 15, wherein said graphite or ceramic is present in an amount of from about 25 to 60% by weight and said component having adhesive properties is present in an amount of from about 40 to 75% by weight.

17. A method according to claim 16, wherein said composition comprises about 40% by weight alumina/silica glass and about 60% by weight graphite.

18. A method according to claim 16, wherein said composition comprises about 75% by weight borax and about 25% by weight boron nitride.

19. A method according to claim 16, wherein said composition comprises about 35% by weight graphite and about 65% by weight borax.

20. A method according to claim 15 wherein said pulverulent forging lubricant composition further comprises a metal soap.

21. A method according to any one of claims 15 to 20, wherein said component having adhesive properties at forging temperatures is selected from the group consisting of polymer resins having high heat resistance, natural and synthetic waxes, gilsonite, and glasses.

22. A method according to claim 21, wherein said polymer resin is poly(tetrafluoroethylene), high density polyethylene, poly(vinylchloride), or mixtures thereof.

23. A method according to claim 20, wherein said metal soap component is selected from the group consisting of zinc stearate, sodium stearate, and mixtures thereof.

24. A method of forging a workpiece in a die comprising the step of applying onto at least one of said die and said workpiece a coating of an effective amount of the carrier-free pulverulent lubricant composition as described in claim 1.