US 2923041 A
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United States Patent MOLD RELEASE AGENTS FOR USE IN DIE CASTING John W. Ryznar, La Grange, Ill., assignor to Nalco Chemical Company, Chicago, Ill., a corporation of Delaware No Drawing. Application June 18, 1956 Serial N0. 591,805
12 Claims. (Cl. 22-192) The present invention relates to the chemical treatment of metal casting molds to prevent the adherence of nonferrous metals thereto. More particularly, it relates to new and improved mold release agents for use in the die casting of aluminum and aluminum alloys.
In the die casting of non-ferrous metals, such as aluminum, aluminum alloys, brass, zinc, magnesium, copper and the like, particularly Where high mold compaction pressures are applied, it has been the experience of the art that a large proportion of the castings stick to the surfaces of the metal mold making the parting operation diificult. This usually results in a spoiled casting. In attempting to alleviate the problem of mold sticking it is the practice in some foundries to apply mold release agents to the faces of the mold in an effort to minimize or reduce the number of spoiled castings.
For a mold release agent to be effective it must give satisfactory results at elevated temperatures and under conditions of extreme pressures. In the casting of aluminum and aluminum alloys for instance, the temperature of the molten metal usually ranges from l190 to 1450 F. It is also the practice of most casting plants to preheat and maintain the mold temperature at 200 F. or
Mold release agents now employed in die casting operations are composed of a wide range of ingredients and may contain several of the following chemical agents; various mineral oils, graphite, petroleum and natural waxes, molybdenum sulfides, heavy metal soaps and chlorinated aliphatic solvents. While in some instances satisfactory results have been obtained using presently known mold release agents they do not always operate to al-. leviate one or more of the following undesirable condi tions: 7
A. Staining of the casting (carbonizing), particularly where oil-based formulas containing graphite or molybdenum sulfides are used; 7 V r V B. Inadequate lubn'cation resulting in the sticking of the casting'to the die which interrupts the manufacturing procedure;
C. Metal porosity caused by entrapmentof the gases resulting from burning oil contained in the formulas;
D. Surface imperfections (flowers), injconsequence of excessive amounts of release agent on the mold, and
ful in the die casting of aluminum and aluminum alloys.
A further object is to provide a mold release agent for metal casting molds which will prevent carbonizing, flowering and provide lubrication to the die. w 7
Yet another object is to furnish a mold release agent for metal casting molds which is easily applied andwill last for more than one casting operation. Other objects will appear hereinafter. v V
In accordance with the invention it has been found that non-ferrous metal castings can be prevented from adhering to the surfaces of the metal molds in which they are cast by applying to the surfaces of such molds a uniform thin coating of a hydrocarbon polymer of an unsubstituted, monoolefinic, aliphatic monomer. Particularly good results are afforded-when the non-ferrous metal is aluminum or an alloy of aluminum.
The hydrocarbon polymer of an unsubstituted monoolefinic, aliphatic monomer may be prepared from any number of hydrocarbon monoolefins including crude mixtures containing substances other thanhydrocarbon providing such mixtures do not contain major amounts of monomers having functional substituents such as halogen groups, carboxylic acid groups, nitrile groups or other similar groups. The starting monomer or the resulting polymer may contain branched chain hydrocarbon groups such as methyl or ethyl groups. The polymer may contain minor amounts of keto, aldehyde or carboxylic acid groups which result from oxidation processes to which some of the hydrocarbon polymers are subjected.
Preferred hydrocarbon polymers are those derived from such low molecular weight olefins as ethylene, propylene, butylene, isobutylene and the like. Higher molecular weight monoolefins, such as are derived from petroleum may also be used but due to their unavailability and lack of chemical purity they are not entirely satisfactory.
While any hydrocarbon polymer within the prescribed class may be used it is necessary that it is capable of being applied to the mold face in a thin, uniform coating. The thickness of the coating is desirably around 0.000001 to 0.001 inch, preferably about 0.0001 inch. Excess polymer or partially adhering polymer particles on the mold face will tend to give a poor quality casting. If, however, the hydrocarbon polymer is uniformly coated onto the mold in a thin film, outstanding mold'release properties are achieved.
It has been found in the practice of the invention that certain low molecular weight hydrocarbon polymers can E. The application of the mold release agents after each casting operation in order to operate at peak efchemical treatment for metal casting molds to prevent the adherence of non-ferrous metals thereto.
7 Another object is to provide a mold release agent use- 'be easily applied to casting molds in a molten state or from a liquid vehicle and form, a thin, uniform coating on the mold surfaces. These low molecular weight hydrocarbon polymers preferably have an average molecular weight of ,at least 300 and not in excess of about 5000. In a desirable embodiment polyethylenes and polyisobutylenes having an average molecular weight in the range of 300 to 2000 give outstanding results. The polyisobutylenes available commercially are derived by reacting certain olefinic cuts of petroleum fractions., ,They may be considered as mixtures of polyisobutylenes, polybutylcues and minor portions of aliphatic components such as parafiins. For the sake of convenience they will hereinafter be referred to simply as polyisobutylenes. 'Polyethylenes having an average molecular weight of 1500 to 2000 have given very good results. also been obtained with polyisobutylenes having an average molecular weight from about 300 to about 1000. For purposes of illustrating some of the preferred hydrocarbon polymers several polyethylenes and polyisobutylenes are listed below in Table I.
Good results have- TABLE 1 Average Molecular Weight Composition N0. Polymer Polyethylene ,rln
Polyisobutylene 1 Oxidized material containing minor amounts of carbonyl groups.
In the above table the various polyethylenes are soft, waxy solids melting between 88 C.106 C. The polyisobutylenes are usually viscous liquids.
'It is usually desirable to suspend or disperse the hydrocarbon polymers, such as those described above, in a suitable organic liquid. Such dispersions are admirably suited for application to metal casting molds since they can be applied by spraying, brushing or other similar expedients.
Dispersions employing the compositions listed in Table I can be prepared by using such organic liquids as kerosene, mineral seal oil, benzene, toluene, xylene, alkyl substituted benzenes, chlorinated aromatic compounds, carbon tetrachloride, trichloroethylene and suitable hydrophobic solvents derived from petroleum. The criteria for a suitable organic liquid are that under conditions for use it must be volatile, non-carbonizing and must uniformly wet the surface of the mold so that local concentrated zones of liquid or hydrocarbon polymer do not form. In choosing the proper organic liquid much will depend on the conditions under which it will be employed.
From the standpoint of practical formulation the dispersions generally contain from 2% to 30% by weight of the hydrocarbon polymer and preferably to by weight. A single hydrocarbon liquid vehicle or combinations of vehicles may be used in the formulation.
When hydrocarbon polymers such as polyethylene are employed the dispersions are readily prepared by melting the polyethylene and adding it in a liquid state to the organic liquid which is preferably heated. In the casting of aluminum and its alloys a good hydrocarbon liquid for the low molecular weight polyethylenes is kerosene.
In order to illustrate several typical dispersions of polyethylenes and polyisobutylenes in organic liquid the following compositions are listed below in Table II. Where polyethylenes were used they were first melted and then added to the organic liquids.
TABLE H Percent y Weight Composi- Cornposltlon No. tioInITaIble Organic L1quid(s) Puriged Kerosene.
o. 30% dodecyl benzene. 35% tetrahydronaphthalene. 26% trichloroethylene. Purified Kerosene. Odorless Kerosene.
1 Thick translucent jelly.
are generally preferred since they are capable of being readily emulsified in aqueous media.
Emulsions of Compositions I to XI in aqueous vehicles may be prepared using several well known emulsifying 5 agents such as aliphatic and/or heterocyclic amines and fatty acids. A typical emulsion is listed below:
Composition XVII Ingredients: Percent by weight Composition IV 20 Oleic acid 4 Morpholine 4 Water 72 In order to evaluate several compositions of the invention tests were run to determine the effectiveness of the materials on a commercial die casting machine under actual operating conditions. The conditions of the test were as follows:
EXAMPLE Aluminum metal was kept molten at 1200:25 F. in a gas furnace and was hand ladled into a Kux zinc die casting machine which was converted to aluminum casting. The die consisted of four major pieces, two side pieces containing bores being moved into position by sliding in a slot and actuated by slanted rods as the diehalves closed. The taper on cores (die pieces mostly surrounded by casting) and parts which required withdrawal from the die was from one to five degrees. Eight quarter-inch and 3 three-sixteenth inch diameter ejector pins were used to remove the castings under test from the die. As the molten metal entered the die a hydraulically actuated plunger under about 300 pounds per square inch of pressure was released a distance of eighteen inches and rammed the molten metal into the interstices of the mold cavity. The temperature of the mold was maintained at about 400 F.
There were numerous variables which could only be controlled by the operator but by and large mold release agents that were used in the machine prior to the compositions of the invention caused many poor castings to be produced. The compositions tested were applied to the mold by either brushing, spraying or trowelling depending on the formula tested and the equipment available for applications. The results of several of these tests are listed below in Table III:
TABLE 111 No. of Mold Castings Composition Tested Release Made Be- Remarks Obtained fore Reapplication XVII Good. 4 N0 staining present. XII o. 3 Sticking when die kept hot and not operating without reapplication.
XIII do 2 Excess of material did not produce flowers.
XIV .do When excessive amounts are applied staining occurs.
XV do Operator deemed results to be excellent.
XVI do.. 2 When excessive amounts are applied flowers produced.
Commercial Agent: Poor.... One in five castings Oil Base fouled.
Usually for optimum results to be obtained the compositions must be applied in a uniform coat. When the material is applied in blotches poor castings result even though mold release is achieved. When uniformly applied the compositions of the invention provide excellent mold release and high quality castings. When solid hydrocarbon polymers are used they may be applied in any form and by any means, such as flame spraying so long as a uniform coating is placed on the surface of the mold.
It is important to. choose organic liquid dispersants 75 which under conditions of use will uniformly volatilize Without leaving carbonaceous residues. It is believed the low molecular weight hydrocarbon polymers are particularly effective due to their ability to slowly difiuse in a gaseous state without leaving any residual carbonaceous deposits.
It will be understood that although good results are obtained by using individual hydrocarbon polymers alone and in various physical forms, satisfactory results may be obtained by blending two or more of the polymers in any practical proportions.
The metal casting molds are usually made of ferrous metals, e.g., cast iron and steel. In the past, many metal casting molds have been made of cast iron and have steel cores. Many molds are made of cold rolled steel.
In all the tests conducted with the compositions herein described casting stain was abolished or greatly mitigated. This is highly significant when it is understood this is the worst problem usually encountered in the use of conventional mold release agents.
The invention is hereby claimed as follows:
1. The method of casting a non-ferrous metal which comprises coating the metal face surfaces of a metal mold with a uniform thin coating of a hydrocarbon polymer of an unsubstituted, monoolefinic aliphatic monomer, said polymer having an average molecular weight not greater than 5000, and casting said metal in said coated mold.
2. The die casting method which comprises providing the metal face surfaces of a ferrous metal die with a uniform coating having a thickness in the range of about 0.000001 inch to 0.001 inch of a polymer from the group consisting of polyethylene and polyisobutylene, said polymer having an average molecular weight in the range of 300 to 5000, casting a molten metal from the group consisting of aluminum and aluminum alloys in said die, and separating the casting from the die.
3. The method of claim 1 wherein said polymer is selected from the group consisting of polyethylene and polyisobutylene having an average molecular weight in the range of from 300 to 5000.
4. The method of claim 1 wherein said non-ferrous metal is selected from the group consisting of aluminum and aluminum alloys.
5. The method of claim 4 wherein said polymer is selected from the group consisting of polyethylene and polyisobutylene having an average molecular weight in the range of from 300 to 5000.
6. The method of claim 1 wherein said polymer is applied to said mold dispersed in a volatile non-carbonizing organic liquid.
7. The method of claim 1 wherein said polymer is applied to said mold dispersed in an aqueous vehicle containing an emulsifying agent.
8. The method of claim 7 wherein said polymer is polyethylene having an average molecular weight in the range from 1500 to 2000.
9. The method of casting a non-ferrous metal selected from the group consisting of aluminum and aluminum alloys which comprises coating the metal face surfaces of a ferrous metal mold with a uniform thin coating of a dispersion of a hydrocarbon polymer selected from the group consisting of polyethylene and polyisobutylene in a volatile non-carbonizing organic liquid, said polymer having an average molecular Weight in the range of from,
300 to 2000, and casting said metal in said coated mold.
10. The method of claim 9 wherein said polymer is polyethylene having an average molecular weight in the range from 1500 to 2000.
11. The method of claim 9 wherein said polymer is polyisobutylene having an average molecular weight in the range from 300 to 1000.
12. The method of claim 9 wherein said organic liquid is kerosene.
References Cited in the file of this patent UNITED STATES PATENTS 2,092,296 Voorhees Sept. 7, 1937 2,153,553 Fawcett et al Apr. 11, 1939 2,326,955 Mack Aug. 17, 1943 2,335,930 Freeland et a1. Dec. 7, 1943 2,406,039 Roedel Aug. 20, 1946 2,488,446 Swiss Nov. 15, 1949 2,629,907 Hugger Mar. 3, 1953 2,695,246 Jurgensen et al Nov. 23, 1954 FOREIGN PATENTS 543,577 Great Britain Mar. 4, 1942 585,395 Great Britain Feb. 6, 1947'
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