US 2629907 A
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March 3, 1953 R. H. HUGGER 2,629,907
METHOD OF MAKING MOLDS Filed April 19, 1949 mwza #5744 mm .A TTOFNEY Patented Mar. 3, 1953 METHOD- OF MAKING. MOLDS Richard H. Hugger, Ridgewood, N. J assignor to United States. Rubber Company, New York, N. Y., a, corporation? of New Jersey Application April19, 1949, S'erialN0..88;364:
This invention, relates to the manufacture Qf: molds wherein a metal negative of a mold model is prepared by spraying metal upon the mold model which may be of any suitable material such as rubber, metal, plaster, wood, etc. After building up the metal negative to a suitable thickness and strength, either by continuedspraying of the same metal or of a, diiierent metal or by electro-deposition or in any other suitable man-. ner, the sprayed metal negative is separated from the mold model.
In attempting to. makev molds by the process just described, a number of serious difficulties arise and as a. consequence no entirely satis-. factory method of making sprayed metal molds hasbeen known to theart. The principal diificulty is that of separating the sprayed metal negative from the model; usually the sprayed metal adheres so tightly to the model that separation is very difficult or often impossible. Another diincultyarises from the fact that at the start of spraying the metal does not adhere to the surface ofthe model because of the force.
of the blast and the lack of adhesion to the surface; expressed otherwise, the deposit. efficiency at. the start. of the spraying is objectionably low. Asa result, a great deal of metal is wasted and. an excessive amount of time is consumed.
Because of the foregoing phenomena, it is almost impossible by prior methods to successfully make a sprayed metal negativeon a smooth or highly finished metal model unless resort ishad to complicated and expensive procedures such as use of an intermediate metal covering on the mold model or of a metal mold model which is heated to an elevated temperature. at least until the model has been entirely covered with sprayed metal.
In the-case of rubber mold models, it has been impossible to obtain satisfactory results because the metal spray blows oil so that it is difficult to start the building-up of the sprayed metal layer and because the metal burns and-penetrates the rubber surface with the result that even though separation be effected in spite of great difficulty, the impression surface of the sprayed metal is rough so that it is not satisfactory as a molding surface.
I have made the surprising and remarkable discovery that the foregoing" difficulties in making sprayed, metal negatives of mold models can be completely; overcome in a simple and economical' manner and without any disadvantages by coating the surface of the mold model evenlywith nylon (which is a synthetic linearcondensation 2 polyamide) before beginning the metal spraying. The n onv coa n exh isf he s rp s ng result that the metaLsprayadheres at once and evenly over the area encountered by the metal spray. There isv no tendency for the metal spray to blow off or bounce off. It is well known in prior prac-a ties that hen... a par cleo molten metalv s a surface it splashes; However, when. it strikes a nylon sur a iit. do s. n t plash. o t i tained uniformly at the, instant of contact. As a result, there is no period of lessened deposit efficiency at the start of spraying; thusgreater production is adepo ible.
Furthermore, the; case of rubber mold. models made of ordinary soft vulcanized rubber and coated with nylon, there, is. no burning or the. rubber, so that the. sprayed metalsurfaee ob-.-. tained on separation is smooth and unbroken, and free from; rubber particles, and the rubber mold model is uninjured and can be used again, and again. This is. in marked contrast to the results obtained when, the nylon coating of my inventionis omitted; inisuch case itis so difiicult.
to get. the metal spray to take that the surface of. the rubber; is actually burned. and; decomposed.
before adhesion. begin Also the. use of nylon makes possible easy separation of. the spraYQd metalfrom the mold: model. Thus nylonv exhibits the surprising ad,- antae s ofcausin much bet er a he io o molten metal spray and at the, same time-per-- mitting subsequent; clean, separation,
In addition totheforegoing advantages bro ght about by the use. of anylon coating on, themoldmodel in accordance with my; inyention, 1, 3 .13? other advantages are obtained, The coating; of nylon may be made verythin, and in this way details of'the mold modelare accurately preserved and reproduced in. the sprayed metal negative surface. It would be difiicult to accurately state the exact. thickness 01" the nylon coating applied, for itmay varywithin. very wide limits. Usuallythe coating has a thicknesssuch asis-v obtainedby applying one coating of a: 11% t0,.:20 solution of nylon in a suitable. organic solvent; andevapcrating the solvent.
A nylon coating provides the necessary high film strength and thermal stability: to withstand the impingement of the molten metal, from the metal spray. gun. Nylons. are readily available which exhibit the desired high, soften ng point required to. withstandv the. molten metal spray. I prefer to. employ those nylon polymers which have softening temperatures of. 300 R. or higher in order that. the coating" obtained shall; not-be 3 melted and deformed to an objectionable extent upon the impingement of the molten metal particles.
As a result of the foregoing advantages, a nylon coating gives very remarkable results as a parting agent in the manufacture of sprayed metal molds.
In making sprayed metal molds in accordance with my invention, inexpensive mold models are almost invariably used and in fact are required for commercial production. Such models may be made of plaster, rubber, wood or metal, including metals of low melting point such as lead and low melting point alloys. The mold models used may be rough or may have any surface configuration whatsoever. For example, the method of my invention enables the most minute patterns or structures in the surface of the model to be accurately reproduced, even though the model be made of rubber or a low melting point metal. The invention is equally applicable to highly finished, i. e., smooth, mold models.
In practicing the present invention, I apply a uniform nylon coating over the entire surface of the mold model in any suitable way. I may apply the nylon in any manner which gives an unbroken film of nylon over the face of the mold model. I find it most convenient to apply the nylon in the form of a solution in any suitable organic solvent which can be volatilized by drying at room temperature or at an elevated temperature. The solids content of the solution used may vary as desired according to the mode of application and the thickness of the coating desired. The solution may be applied to the mold model in any suitable manner, as by dipping, brushing or spraying. For brushing, the nylon content of the solution may typically range from 5-15% by weight. For spraying application, a somewhat lower nylon content, say 1-4% by weight is generally desirable.
Any solvent for nylon may be used in making up the solution. I often use an alcohol-soluble nylon polymer and use a solvent comprising a lower aliphatic saturated monohydric alcohol to dissolve it. Very often I use a mixture of solvents.
A single coatin with the nylon solution is sufficient. However, if desired a plurality of coatings may be applied with drying after each application. The thickness of the nylon coating applied should be suflicient to give good parting of .the sprayed metal mold, but not so great as to obliterate the surface detail of the mold model. The coating should be applied in such manner that the surface of the nylon coating accurately conforms to the surface of the mold model.
After application of the nylon solution, it is dried. As soon as the coating is dry, spraying with the molten metal spray can be begun. After a sprayed metal layer of the desired depth has been built up, with Or without further deposition of metal upon the spray deposit in any suitable manner, for example by continued spraying with the same or a different metal or by electro-deposition, the sprayed metal layer is separated from the mold model by simple mechanical separation.
The manner of spraying the molten metal to build up the sprayed metal layer need not be set forth in detail because it is the well-known and conventional method of spraying molten metal. In the case of porous mold models, especially those made of plaster, separation of the metal negative from the model can be facilitated by application of a solvent to the interface through the porous mold model. Any inert solvent for the nylon may be used for this purpose, the lower aliphatic saturated monohydric alcohols, for example isopropyl alcohol, being usually employed.
The accompanying drawing is a vertical sectional view f a mold model upon which a sprayed metal negative has been deposited in accordance with my invention. The mold model is designated by reference numeral I. To model I there is applied a coating 2 of nylon in the manner described above, the thickness of this coating 2 being greatly exaggerated. Thereafter molten metal is sprayed onto the surface of the coated mold model until a layer 3 has been built up. If desired, the application of the sprayed metal layer 3 may be followed by electro-deposition of more metal in order to make a mold of still greater thickness. Alternatively, there may be superimposed upon layer 3 a sprayed metal layer of another metal. For example, it is often highly desirable t have an initial layer of zinc backed by a sprayed layer of aluminum for strength.
The following formulations are typical of those which may be used to form the nylon coating of my invention.
Example 1 Parts by weight Nylon powder (softening point at least 300 F.) Isopropyl alcohol 176 Denatured ethyl alcohol 44 Furfuryl alcohol 10 Water 5 Example 2 Parts by weight Nylon powder (as in Example 1) 2 Isopropyl alcohol 98 Furfural The foregoing ingredients are mixed in the same manner as in Example 1. The resulting formulation is especially suitable for application by spraying.
Example 3 Parts by weight Nylon powder (as before) 5 Isopropyl alcohol 76 Water 19 These ingredients are mixed as before and give a brushing solution which evaporates somewhat more rapidly than the formulation given in Example 1.
From the foregoing description it will be seen that the present invention provides a very successful solution of the problem of making sprayed metal models. The process of my invention is particularly advantageous because of the ease and rapidity of parting of the sprayed metal mold from the mold model and the uniform and unbroken surface of the sprayed metal mold obtained. The process is simple and economical and is such that the operator can consistently obtain excellent molds without special training. Many other advantages of my invention will be obvious to those skilled in the art.
Having thus described my invention, what I claim and desire to protect by Letters Patent is:
1. A method of making a sprayed metal mold which comprises coating a mold model with a thin. continuous, uniform, smooth coating of a synthetic linear condensation polyamide, spraying molten metal upon the polyamide-coated surface obtained until a sprayed metal layer of the desired thickness has been built up, and sub sequently separating said sprayed metal layer from said mold model.
2. A method as set forth in claim 1 wherein said polyamide is applied to said mold model as a solution in an organic solvent which is thereafter volatilized, thereby forming a thin, continuous, uniform, smooth coating of said polyamide accurately reproducing the surface of the mold model.
3. A method as set forth in claim 1 wherein said polyamide has a softening point of at least 300 F.
4. A method as set forth in claim 1 wherein said polyamide has a softening point of at least 300 F. and is applied as a solution in a solvent comprising a lower aliphatic saturated monohydric alcohol which solvent is thereafter volatilized.
5. A method as set forth in claim 1 wherein said mold model is of rubber and wherein said polyamide protects said rubber against thermal decomposition and causes substantially more rapid adhesion of the molten metal spray and formation of a smooth, unbroken surface of sprayed metal over the rubber mold model.
6. The method which comprises spraying molten metal upon a mold model having over a substantial area thereof which is to be reproduced a thin, continuous, uniform, smooth surface coating of a synthetic linear condensation polyamide until a sprayed metal layer has been built up upon said surface coating, and subsequently separating said sprayed metal layer from said mold model.
7. The method of claim 6 wherein said polyamide has a softening point of at least 300 F.
8. A method of making a sprayed metal mold which comprises coating a porous mold model with a thin, continuous, uniform, smooth coating of a synthetic linear condensation polyamide, spraying molten metal upon the polyamidecoated surface obtained until a sprayed metal layer of the desired thickness has been built up, subsequently applying a solvent for said polyamide to the polyamide coating through the porous mold model and thereby softening said polyamide coating, and separating said sprayed metal layer from said mold model.
9. A method as set forth in claim 8 wherein said solvent is a lower aliphatic saturated monohydric alcohol.
10. As an article of manufacture, a mold model, over a surface of said mold model a thin, uniform, unbroken, smooth coating of a synthetic linear condensation polyamide accurately reproducing said surface, and superimposed upon said coating a sprayed metal layer deposited directly upon said coating by a molten metal spraying operation, said metal layer being readily separable from said mold model as a result of the presence of said coating and also having a smooth unbroken surface adjacent said mold model as a result of the presence of said coating.
11. An article as set forth in claim 10 wherein said polyamide has a softening point of at least 300 F. and wherein said coating is deposited from a solution of said polyamide in a solvent comprising a lower aliphatic saturated monohydric alcohol which is volatilized after application of said solution and prior to the metal spraying operation.
RICHARD H. HUGGER.
REFERENCES CITED The following references are of record in the file of this patent:
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