Metal deforming – With cleaning – descaling – or lubrication of work or product – Lubricating
Reexamination Certificate
1999-03-01
2001-11-20
Larson, Lowell A. (Department: 3725)
Metal deforming
With cleaning, descaling, or lubrication of work or product
Lubricating
Reexamination Certificate
active
06318139
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a waterborne lubricant for the cold plastic working of metals (referred to below simply as the waterborne lubricant) that can be used in the cold plastic working (e.g., forging, tube drawing, wire drawing, and the like) of metals such as carbon steel, stainless steel, high-alloy steel, and the like.
DESCRIPTION OF THE RELATED ART
A lubricant is typically used in the cold plastic working of metals, and a variety of lubricants are used for this purpose. As a general rule, the lubricant becomes sandwiched between the tool and workpiece and functions to reduce the friction coefficient and to extend tool life by preventing metal-to-metal contact.
Conversion coatings are used in one approach to the application of the lubricating film to the workpiece. It is known that very good working results can be obtained when the lubricant is applied to the workpiece subsequent to the execution of a conversion coating treatment on the workpiece. This methodology makes possible working at high working ratios and also improves tool durability (see Kinzoku Hyomen Gijutsu Benran [Title in English:
Handbook of Metal Finishing Technology
], page 719 (1987), edited by Kinzoku Hyomen Gijutsu Kyokai [Title in English: Metal Finishing Society of Japan], published by Nikkan Kogyo Shinbunsha). In a broad sense the lubricant can be said to include the conversion coating, but in fact the conversion coating as initially applied does not have a lubrication-improving activity. As a result it is used in combination with a fluid lubricant, of which typical examples are lubricating oils and waterborne lubricants, or with a solid lubricant such as molybdenum disulfide or a metal soap. As a consequence, the conversion coating is in some cases regarded in a narrow sense as a pretreatment (Tekko Shinsen yo no Junkatsuzai Manyuaru, Kaiteiban [Title in English:
Revised Lubricant Manual for Drawing Iron and Steel Wire
], page 18 (1994), edited by the Lubricant Working Group of the Wire Drawing Technology Section of Nippon Sosei Kako Gakkai [Japan Society for Technology of Plasticity]).
The conversion coating itself will vary as a function of the material of the workpiece. For example, in the case of carbon steels a phosphate coating (components=zinc phosphate, iron zinc phosphate, calcium zinc phosphate) is usually executed on the workpiece by dipping in an acidic aqueous solution containing phosphoric acid, nitric acid, zinc, and sometimes calcium. With stainless steels and high-alloy steels, an oxalate coating (main component=iron oxalate) is usually executed on the workpiece, using an acidic aqueous solution whose main component is oxalic acid. In the overall process of forming the lubricating film for cold plastic working, these conversion treatments are normally carried out after pickling with a prescribed concentration of hydrochloric acid or sulfuric acid to remove annealing scale and after a post-pickling water rinse.
Production of the lubricating film by dipping the conversion-coated workpiece in an aqueous solution whose main component is the alkali metal salt of a higher fatty acid (for example, sodium stearate) is generally known as “reactive soap treatment” (cf. Tekko Shinsen yo no Junkatsuzai Manyuaru, Kaiteiban, page 26).
Reactive soap treatment was first disclosed in German Patent Number 673,405 and subsequent thereto has gone on to become very widely used in wire drawing, tube drawing, and forging for the production of lubricating films for cold plastic working.
In reactive soap treatment, the conversion-coated workpiece is dipped in a treatment bath consisting mainly of the aqueous solution of an alkali metal salt of a monomeric higher fatty acid, a so-called “soap”. The phosphate coating dissolves into the aqueous soap solution, and the metal component of the phosphate and the fatty acid participate in a metathesis reaction that produces a divalent metal (e.g., zinc or calcium) soap. This divalent metal soap, being insoluble in the aqueous alkali metal soap solution, precipitates onto the surface of the phosphate coating to generate a lubricating film. The reaction equation for the reaction of zinc phosphate with sodium stearate to produce a divalent metal soap are provided below by way of example:
Zn
3
(PO4)
2
·4H
2
O+6NaC
17
H
35
COO→3Zn(C
17
H
35
COO)
2
+2Na
3
PO
4
+4H
2
O
Treatment bath is also taken up by the workpiece as it is withdrawn from the treatment bath, and as a result reactive soap coatings are believed to be composed of the following three layers considered in sequence from the metal surface: the phosphate coating, a divalent metal, water-insoluble soap layer, and a water-soluble soap layer.
While the main component in a reactive soap treatment bath is a so-called soap, that is, the alkali metal salt of a monomeric fatty acid such as sodium stearate, a buffer and rust preventive are ordinarily also added to the bath (James, Sheet Material Industries (3) (1961)). This reference also notes that the acidity or alkalinity of the reactive soap bath governs the reactivity.
The English-language abstract for German Patent Application Number 256,804 describes a lubricant for the cold plastic working of metals that comprises an insoluble but water-dispersible soap, inorganic additive, polyvinyl alcohol, and surfactant. In this lubricant the polyvinyl alcohol is derivatized by 0.2 to 3% modification with oxidant, and the lubricant composition contains a keto, carboxyl, and/or carboxylate modified salt.
The English-language abstract for Russian Patent Application SU 279,841 describes a lubricant for the cold plastic working of metals that comprises alkali metal soap which is 25 to 50% oleic acid, 15 to 20% linoleic acid, and 5 to 10% dihydroxystearic acid, and the lubricant also contains some triglycerides and other esters of these acids.
As a countermeasure to the lubricating layer exfoliation that can occur during cold working, Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 57-40200 [40,200/1982] teaches the addition of an aqueous borax solution or a lime soap solution to a 2 to 5% emulsion of ethylene/vinyl acetate copolymer. The lime soap solution used here comprises quicklime, metal soap, aluminum stearate, and water.
Japanese Patent Application Laid Open [Kokai or Unexamined] Number Hei 5-156279 [156,279/1993] teaches a waterborne lubricant (reactive soap) for the plastic working of metals that characteristically contains (a) alkali metal salt of C
8
to C
22
saturated fatty acid and (b) alkali metal salt of C
8
to C
22
unsaturated fatty acid, wherein the quantity of the alkali metal salt of unsaturated fatty acid (b) is from 5 to 25 weight % of (a)+(b). The use of this lubricant reportedly results in low dust generation during the working operation as well as little lubricant adhesion to the tool.
While the above-described reactive soaps do have good lubricating characteristics, bath life is a characteristic problem with lubricants of this type (Tekko Shinsen yo no Junkatsuzai Manyuanu, Kaiteiban, page 27). Since reactive soap treatment produces a lubricating film through dissolution of the phosphate film, the components in the conversion coating, such as zinc, iron, and phosphoric acid, are thought to accumulate in the treatment bath with a concomitant decline in lubrication performance.
In actual line operations, the aged treatment bath is discarded and replaced with fresh bath when defective lubrication attributable to reactive soap bath life is detected. Since reactive soap treatment baths are ordinarily treated as industrial wastes, extending the bath life is not simply a cost issue, but is also an important issue for environmental protection.
Moreover, the dimensional accuracy of the worked products has undergone continual improvement in recent years, which has made reducing dust generation during working operations a much more important issue than in the past. For example, the dust produced
Ishikura Kazuhiro
Karube Kenji
Miyafuji Kazutomo
Davis Garrett V.
Harper Stephen D.
Henkel Corporation
Jaeschke Wayne C.
Larson Lowell A.
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