US2126128A - Lubricant and method of lubricating metal during forming operations - Google Patents

Description

Patented Aug. 9, 1938 PATENT OFFICE LUBRICANT AND METHOD or LUBRICATING METAL DURING FORMING ornrm'rrons Harley A. Montgomery, Highland Park, Mich.

No Drawing. Application May 17, 1934, Serial N0. 726,177

7 Claims.

This-invention relates to a method of drawing or conflgurating metal at substantially atmospheric temperature by high pressures and more particularly to a method of lubricating the metal in relation to the forming dies during the configurating operations.

It has been conventional in the past to employ lubricating compounds for metal drawing or configurating operations; These compounds have had to be of anature such that they were easily applied to the metal, lubricated adequately during the configurating operation, and likewise could be readily removed from the metal after the conclusion of the configurating operation. These three properties are of outstanding importance but other properties are likewise requisite. Altogether there are ten required charactertistics for lubricants adapted for metal configurating and particularly for deep drawing.

1. Film strength-The lubricating film or coating must be strong enough to withstand the enormous pressure prevailing within the plastic range of the worked material under compression, so as to prevent metal-to-metal contact both 5 under static and "flow conditions of the worked metal. Scoring and abrasion of the dies and work-piece must be prevented, as well as pickups of the softer metal on the hardened die surface. It is generally agreed that where two 30 rubbing surfaces are of the same metal, without an interposing lubricating film, scoringand pickups" are the result of actual fusion of the microscopic surfaces in direct contact, due to the intense localized heat generated from friction, even though the duration of the phenomenon is only momentary. Aside from the heat due to rubbing friction of the metallic surfaces, there is also generation of heat due to the plastic deformation of the metal worked, and it is essential that the 40 lubricating film must not be unduly thinned down and weakened at the higher temperature.

2. oilinesal'he coeflicient of friction between the die surface and work-piece must be low, so that a minimum amount of energy be expended 5 in skin friction, both in the forward or working stroke and in the backward or pull-back movement of the dies. Lack of oiliness in the lubricant used results in localized drawing, or in uneven elongation and wall thickness. When 50 working on steel sheets of light gage, especially in fianging operations, fracture of the metal and development of seams and cracks should be reduced to a minimum when a good lubricant is used.

3. Adhesiveness and spreading.--'I'he lubricant 55 must adhere to the surface of the metal without being unduly tacky. It must also spread itself under the pressure of the dies in such a way that it will form a protecting film ahead of the working portion of the die. It should also be sufficiently light in body and possess marked affinity for the metallic surface so that it may be applied manually by means of a brush or mechanically by means of an automate spraying device or through plastic gelatine-like rolls.

4. Ease of cleaning.-As the finished product 10 from the draw press or stamping machine must generally undergo a further process of plating, tinning, galvanizing, lacquering, or painting, it is essential that all traces of the lubricant used must be easily removed by means of readily obtainable 15 and cheap cleanser, such as simple mixture of caustic soda. This requirement is generally met in a drawing compound that emulsifies in water.

5. Noncorrosiveness.--The lubricant must not contain mineral acids of any kind that may at- 20 tack the worked metal, should the cleansing process be delayed for any reason. Nor should there be any tendency to pit the surface of expensive dies and machinery used.

6. Stability and unijormity.--'I'he drawing compound must be stable in composition, and there must be no separation into its component parts during storage and handling, nor should it become rancid, decomposed or otherwise spoiled. One shipment must be exactly the same as the previous shipment, unless some modification was made in the formula by mutual agreement to meet a special working condition. This requirement is largely a problem of the lubricant manufacturer.

7. Physiological efiect.-The lubricant must be absolutely neutral in its physiological effect on the machine operators, and must not contain any ingredients which may lead to poisoning through skin absorption or inhalation of fumes, nor shall 40 it produce such skin diseases as pimples, eruptions, or boilsi As a further precaution, it might be permissible to introduce into the lubricant a harmless antiseptic-like creosol.

8. Orion-No perceptible disagreeable odor should be noticed. The addition of a perfuming substance to disguise the real odor of the lubricant should be avoided.

9. Efiect of climatic conditions.-There should be no pronounced change of the consistency or other properties of the lubricant with the usual variations of temperature and humidity between summer and winter weather.

10. Economy.--'I'he drawing compound must be low in cost. a

In the past it has been conventional to use water soluble oils or emulsions of water soluble oils as drawing lubricants. For many metal drawing operations these water soluble drawing oils are entirely suitable and adequate. In many cases pigments or finely divided solid material have been added to these drawing oils to give the lubricating film greater strength. These solid pigments, however, irender removal of the lubricant from the work difllcult after the drawing operation. In recent years, however, it has become desirable particularly in relation to the fabrication of automobiles to press or draw very large parts by means of extremely heavy pressures. It has also become more and more desirable to impart to the metal by such operations a greater amount of relief or configuration than was previously attempted.

Under the very heavy pressures required for this new type of drawing, the ordinary lubricating film breaks and causes the metal either to be drawn unevenly or to become scored or marked or broken so that the part cannot be used.

In the past graphite has been used to withstand heavy pressures and while graphite is suitable as a lubricant, it is very difiicult to remove from the metal after the forming operation, for the reason that the heavy pressure grindsit into the surface of the metal.

It is the'object of this invention to provide a method of lubricating metal parts to be configurated under heavy pressures which normally tend to destroy or impair the efiicacy of the lubricating films provided by the normally employed water soluble lubricants.

The preferred method 'of this invention comprises the application of solid, fatty material of relatively high melting point to the work while the fatty material is in a molten state, then chilling the material on the work so that it adheres closely to the surface of the work prior to the forming operation, configurating the metal with the fatty solid lubricant adhering to it, and removing the fatty solid lubricant by means of a hot alkaline solution.

In practicing this method it is requisite that the fatty material chosen be of such nature that it is solid at the highest room temperatures encountered during normal operation, that is, temperatures approximating to F. It is likewise requisite that the fatty material chosen be susceptible to removal from the work by a reasonably economic treatment. For instance, if a high melting point neutral fat be employed rather than a high melting point fatty acid, the cost of the drawing lubricant itself is lessened, but the cost of removal is increased, due to the fact that a fatty acid is more readily converted into a water soluble alkaline soap than is a neutral fat.

In. view of the present price level, high titre commercial stearic acid is believed to be the best solid fatty material adapted for use in this process. Moreover, stearic acid has'the property of providing a film which when in solidfied form on the metal being configurated, stands up under the most severe pressures. In order to augment the lubricating power of the stearic acid a mineral oil may be mixed with it. For instance, the drawing compound employed may comprise substantially 65% commercial stearic acid of a titre above 45, and 35% mineral oil of 100 Saybolt at 100 1". viscosity.

In producing the drawing lubricant the stearic acid is melted, the oil mixed therewith, after which compound may be poured in the shipping containers and allowed to solidify. Prior to its use, compound is melted and applied to the metal to be configurated by brush, by dipping, or by spraying. Next, the film is either chilled or permitted to cool so that it assumes the condition of a solid upon the metal to be conflgurated. Next the metal is subjected to the heavy pressure and is drawn, formed or configurated. Next, the work is immersed in ahot, aqueous, alkaline bath for saponifying the stearic acid, thereby removing it together with the oil from the work which may then be subjected to finishing treatments of any nature desired.

The invention in its broadest aspects may be said to reside in forming, drawing, or configurating metal by means of dies and heavy pressure when the metal is protected by a lubricating film of solid fatty material. From this point of view the stearic acid or equivalent material may be applied to the work not only in the manner described, but, for instance, by dissolving the fat in a volatile solvent and permitting solidification by evaporation or applying the stearic acid or equivalent lubricant to the work in finely divided condition in a vehicle and permitting the initial pressure of the dies to convert the stearic acid from finely divided condition to a solid film. The latter method is the subject-matter of my copending application, Serial Number 726,178, filed April 23, 1934.

As previously indicated, several materials other than the commercial stearic acid may be used in place of it with good effect. For instance, parafiin wax, Montan wax, ceresin wax, beeswax, as well as neutral fat of high titre may be used. Generally speaking, the removal of such materials is much more difficult than the removal of stearic acid. Other solid fatty acids of high titre may be used in place of commercial stearic acid, though the latter is recommended for the reasons indicated.

It is generally advisable to mix mineral oil with the stearic acid. Straight stearic acid may be used but it is recommended that mineral oil be added. While the previously specified example comprises 65% stearic acid, 35% mineral oil 100 Saybolt at 100 F. viscosity, the proportions may be varied so that the formula contains as small a percent of stearic acid as 50%. The mineral oil may range in viscosity from 80 Saybolt at 100 F. to 200 Saybolt at 100 F. Vegetable or animal oils may be used in place of the mineral oil but for economic reasons mineral oil is recommended at the present time.

It is requisite, however, that the titre of the stearic acid or substitute therefor, the quantity and nature of oil employed and the solvent power of the oil, be so reconciled and adjusted that the resulting film which hardens on the metal to be configurated is a solid, adhering, durable film.

In practicing the present invention the solid lubricant is melted and applied to the work by dipping, brushing or spraying. The lubricant is then permitted to solidify upon the work after which the conflgurating operations are performed. The work is then subjected to a hot, aqueous, alkaline bath, such as, for instance, 10 pounds NaOH dissolved in 100 gallons of water, the temperature preferably being held at about 212 F. By this process the metal is thoroughly protected during the conflgurating operations by a lubricant which is readily removed from the work after it has served its purpose.

Having described my invention, I desire to be limited only by the ensuing claims:

1. A process of lubricating metal during a 75 forming operation, said process, comprising, coating the surface of the metal with a molten lubricant comprising stearic acid and mineral oil, solidifying the film of said lubricant on said suriace, forming the metal and then removing said lubricant by treatment with a hot aqueous alkaline solution.

2. A lubricant adapted for metal drawing operations under heavy pressure, said lubricant consisting of. substantially stearic acid oi sciently high titre to provide a solid at to F. and substantially 35% mineral oil.

3. A process of lubricating metal during the forming operation, said process, comprising, coating the surface oi the metal with a molten lubricant consisting of mineral oil and an ingredient normally solid selected from the group which comprises stearic acid, paramn wax, Montan wax, ceresin wax, beeswax, and high titre neutral lat, solidifying the film of said lubricant on said suri ace, forming the metal, then removing said lubricant by treatment with a hot, aqueous, alltaline solution.

it. in a process oi lubricating metal during the forming operation, the step which comprises,

coating the surface or 'the metal with a molten 5. In the art of forming metal at substantially atmospheric temperature under heavy pressure,

the step which comprises, coating the surface of the metal to be formed withva molten lubricant comprising mineral oil and an ingredient selected from the group which consists of stearic acid, paraflin wax, Montan wax, ceresin wax, beeswax, and high titre neutral fat, then solidifying the film of said lubricant on said surface.

6. A piece of metal adapted to be formed at substantially atmospheric temperature under heavy pressure, the metal having on its surface a solidified coating of stearic acid and mineral oil.

7. In the art of forming metal at substantially atmospheric temperature under heavy pressure. the method which comprises, chilling a molten lubricant comprised of an oleaginous vehicle of the type of mineral oil in which an ingredient selected from the group consisting of stearic acid, ramn wax, Montan wax, ceresin wax, beeswax. and high titre neutral fat, is dissolved, to provide a solid, continuous film on the metal surface, then forming the metal in the presence of the solid, then removing said him from said metal alter the metal has been formed.