MXPA99001313A - Lubricant powder for powder metallurgy - Google Patents

Abstract

The invention concerns a lubricant for powder metallurgical compositions containing 10-60%by weight of a lithium salt of a fatty acid, 0-40%by weight of a zinc salt of a fatty acid and 40-90%by weight of a fatty acid bis-amide. 10-60%by weight of the lubricant is made up by the lithium and the zinc salt.

Description

LUBRICANT POWDER FOR POWDER METALLURGY DESCRIPTIVE MEMORY The present invention relates to a lubricant for powder metallurgical compositions, as well as to a metal powder composition containing the lubricant. The invention also relates to a method for manufacturing products specified by the use of the lubricant. The powder metallurgical industry has developed iron-based powder compositions that can be processed into integral metal parts that have various shapes and sizes for use in the automotive and electronics industries. A processing technique to produce the parts from base powders, is to load the powder in the cavity of a die and compact it under high pressures. The resulting crude part is then removed from the die cavity, and concreted. To avoid excessive wear on the die cavity, lubricants are commonly used during the compaction process. Lubrication is generally carried out by mixing a solid lubricating powder with the iron-based powder (internal lubrication), or by spraying a liquid dispersion or lubricant solution onto the surface of the die cavity (external lubrication). In some cases, both techniques are used. Almost all the lubricants that are currently used are derived from naturally occurring long-chain fatty acids. The most common fatty acid is stearic acid (C17H35COOH), which consists of an aliphatic chain of CH3 (CH2)? 6 combined with the carboxylic acid group -COOH.

When mixed with metal powders, it provides fast flow, high bulk density and good lubricity. Its low melting point (64 ° C) can lead to softening during mixing with the powder, causing problems. Therefore, salts of stearic acid, i.e., metallic soaps, are more popular. The main drawback of soaps is their metal content. During combustion, the fatty acid chain volatilizes rapidly, but the metal remains as oxide or carbonate, although this can undergo reduction to the metal in a reducing atmosphere. The most widely used metal soap is zinc stearate, because of its good flow properties. In reducing atmospheres, zinc oxide remaining after initial decomposition is reduced to zinc, which volatilizes rapidly, due to its low boiling point (907 ° C). Unfortunately, when coming into contact with the cooler parts of the furnace or the outside atmosphere, zinc tends to condense, also forming a certain amount of zinc oxide. A consequence of this condensation is that the production has to be interrupted, since the oven has to be cleaned regularly.

The problems associated with metallic soaps can be avoided by the use of completely organic materials such as waxes. The wax that is most widely used in powder metallurgy is ethylene bis-stearamide (for example, Acrawax C). This material has a high melting point (140 ° C), but is calcined at relatively low temperatures, and leaves no metal residue. Its most important disadvantage is its reduced flow behavior in metal powders. In addition, mixtures of zinc salts of fatty acids and fatty acid bis-amides have not yet been accepted by the P / M industry, due to the poor performance of said mixtures. It has now been unexpectedly found that a lubricant can be obtained which allows the manufacture of compacted products having high green strength and high green density in combination with reduced ejection force, by a lubricant comprising a lithium salt and optionally a zinc salt of one or more fatty acids and a fatty acid bis-amide product. More specifically, the amount of the metal salts of the fatty acids should constitute approximately 10 to 60% by weight of the lubricant according to the invention. The amount of the lithium salt is from 10 to 60% by weight, and the amount of zinc salt is from 0 to 40% by weight. Preferably, the amount of the zinc salt is at least 10%, and more preferably at least 15% by weight of the lubricant. The amount of the bis-amide product is from 40 to 60% by weight. Typical examples of lithium salts of fatty acids are lithium laurate, lithium myristate, lithium palmitate, lithium stearate, lithium behenate, lithium montanate and lithium oleate, which are lithium salts of fatty acids having 12 to 28 carbon atoms. Typical examples of zinc salts of fatty acids are zinc laurate, zinc myristate, zinc palmitate, zinc stearate, zinc behenate, zinc montanate and zinc oleate, which are zinc salts of fatty acids having 12 to 28 carbon atoms. Typical examples of fatty acid bis-amides are methylene bis-lauramide, methylene bis-myristamide, methylene bis-palmitamide, methylene bis-stearamide, ethylene bis-behenamide, methylene bis-oleamide, bis-lauramide ethylene, ethylene bis-myristamide, ethylene bis-palmitamide, ethylene bis-stearamide, ethylene bis-behenamide, ethylene bis-montanamide and ethylene bis-oleamide. The lubricant is preferably prepared by mixing and melting the components, and the mixture obtained is subsequently cooled and micronized to a suitable particle size. The invention is further illustrated by the following non-limiting examples.

EXAMPLES 1 TO 5 different lubrication samples having the composition shown in Table 1 below were prepared.

TABLE 1 Powdered steel powders were mixed (10 kg) with sample lubricants 1 to 5 (80 g), and each powder mixture was investigated with respect to bulk density, raw density (at 5 and 7 ton / cm) , force of expulsion, resistance in crude and concrete density. The concretion was carried out at 1120 ° C for 30 min. with a base atmosphere (?). The results are shown in table 2.

TABLE 2 Subsequently, 5 different lubrication samples (comparative examples 1 to 5) having the compositions shown in Table 3 below were prepared for comparative purposes.

TABLE 3 These samples were tested in the same manner as was done previously, and the results are shown in table 4.

TABLE 4 EXAMPLE 6 The lubricant used in the production of compact raw materials by concretion in a large size concreting furnace (production amount of approximately 200 ton / month) and a medium size concreting furnace (production amount of approximately 100 ton / month ), was changed to zinc stearate, which had been used for many years (comparative example 6) in a powder lubricant prepared according to the weight ratios shown in table 5 (example 6). As a result, when the interior of the kiln had been cleaned periodically at the frequency of three times per year when zinc stearate was used, the accumulated matter of the kilns had not been cleared even after 1.5 years which had elapsed after the lubricant change, and no remarkable accumulated matter was observed even after that.

TABLE 5 EFFECT OF THE INVENTION As is evident from Examples 1 to 6, this invention can provide a powder lubricant for powder metallurgy that can achieve a high overall density when a metal powder is packaged in a metal mold, as well as low ejection pressure from the metal mold, improved density and strength in the formed compact, improved density of the particular compact material, and without any contamination of the concreting furnace.

Claims (6)

NOVELTY OF THE INVENTION CLAIMS

1. - A lubricant for powder metallurgical compositions, containing from 10 to 60% by weight of a lithium salt of a fatty acid; from 0 to 40% by weight of a zinc salt of a fatty acid; and from 40 to 90% by weight of a fatty acid bis-amide, characterized in that from 10 to 60% by weight of the lubricant is formed by the lithium and zinc salt.

2. The lubricant according to claim 1, further characterized in that the fatty acid is selected from the group consisting of saturated or unsaturated fatty acids having from 12 to 28 carbon atoms.

3. The lubricant according to claim 2, further characterized in that the fatty acid bis-amide is ethylene bis-stearamide.

4. The lubricant according to any of the preceding claims, further characterized in that the amount of the zinc salt is at least 10, more preferably at least 15% by weight of the lubricant.

5. The lubricant according to any of the preceding claims, further characterized in that it is in the form of a molten micronized powder.

6. A composition of metal powder containing an iron-based powder and a lubricant according to any of the preceding claims.