US2127534A - Process and product for coating molds and cores - Google Patents

Description

' umrso stars Patented Aug. 23,

, amen I k raocsss arm rnonuc'r ron comma MOLDS AND corms Charles Marshall Saeger, In, Bowmanstown, Pa.

No Drawing. Application January 12,

(Cl- 2?r188) theact of March 3,1883, as

so, 1928; mo. 0. as?) 'while its vaporizing point (Granted under 6 Claims.

- amended April My invention relates to a new and useful method of making molds and cores for metal castings.

Previously in thisart the contact with the mold the sand in contact to hot metal coming in and core surfaces caused burn into the adjacent surfaces of the metal and produce castings of rough exterior and interior surfaces, which surfaces are formed of an integral film of mixed metal and sand. This, as well as the removal of 10 the cores and the cleaning of the un-integral sand from the casting, has heretofore been an expensive,laborious and dusty task frequently requiring the use of pneumatic chisels and other tools, while in the machining of such castings 5 the integral film of sand and metal is difiicult to machine unless the tool in its first cut-pene- In the prior art trates beyond the depth of such film.

many cracked castings have been produced due to hard cores and molds which do not crush readily as contracts and solidifies, and constant source of substan dries but more es ciaiiy n dre A further constant ource in the prior art of metal casting has resultedfrom mold and core blows due to the low perme-I the metal casting cools,

such castings area Aosyinall founaluminum and kinor substantial loss ability of the sand forming such molds and cores.

The oxidizing of the surfaces of castings, especially of the more oxidizing metals, due to contact with the prior ar t moidsand cores has many In" the past many -.endeavors very objectionable conditions "Ft 6T overcome these have been made andlosses. Some of these attempts have been to 35 form the molds and cores of green sand,

which is the ordinary molding sand of commerce, but the liability of such molds and cores'to be washed in part i'ntothe molten flowing metal being cast revents, or renders hazardous,

their use in many To provide molds and cores of more strength than possessed by green sand molds and cores,

,itheretofore has been comm body a binder in the sand of molasses and water, flour and on practice to emeither or all, clay, water, and oil, and

to indurate such molds-and coresby baking.

Such molds and cores 5 mg molten metal,

molds and cores increase the have all the aforesaid defects except the tendency to wash into the flowwhile the thus formed harder cracking liability of the castings as well as tend to increase the liability of the castings to blow due to the lesser porosity of such molds and cores. 55 a In the prior art water has been employed as binding rate a diluent ofthe active butits surface tension,

other conditions, are such that it requires submaterial employed, of evaporation and :stantial labor in order to properly mix the same 60 with the constituent material of the mold oncore.

much of the water in the adapted to be absorbed to a the application is so high as to leave mold or core or requires that such mold or core be baked sufllciently to remove such moisture, which baking to the degree required to remove such moisture produces a hard core or mold withits said liabilities.

To overcome the foregoing conditions and losses and to thereby and otherwise facilitate and cheapen the production of molds, cores and cast ings therefrom, l have devised a method of makaforesaid conditions and losses and contemplates the forming of the, molds and core or cores thereof of sand or any of the other desirable earthy materials and to apply upon the surface of such molds or cores, either or both, a rubber or rubber-like material. Said material is applied preferably upon all surfaces of the'mold and cores that come in contact with the casting. Where castings are made of material the class of mat e riais which are liquefied or en-i3 deredfluid-like in order 'surface of the-mold or core prevents or retards to cast, thesaiddoated wholly, or in part, the flow of moisture from such casting to the material forming such molds and cores.

a ing such molds and cores which precludes the which is xcasiwhile-heated;the heat" of the casting acts The manner of applying the rubber or rubberlike substance or material to the surfaces of the mold and core, or cores, that such mold may contain or require, may be by applyi the same to such surfaces in the form of a powder or in the form of a relatively thin plastic sheet or in the form of a more or less fluid paint. Where the same is so applied in the form of the more or less fluid paint, the liquid content of such paint is moreorless extent by the material of which the body of the mold or core is formed, and in so penetrating such body, such fluid carries withit more or less of the rubber or rubber-like material, which when dried acts as a binder or supplemental binder to such body of the mold or core throughout substantially the extent of such penetration.

More or less, of said paint applied upon such surfaces remain upon such outer surfaces where. they. are dried by atmospheric temperature or by thereto of amoderate heat.

By the term, moderate heat, is intended to be meant only such degree of heat as will dry said material without otherwise changing its characteristics. e

In this specification where the term rubber is employed it is intended to include rubber either as latex, coagulated rubber, or sap from trees such as Hevea brazz'lzensis, or from vines or schrubs, as well as from other kindred vegatation-such as guayule containing more or lessrubber hydrocarbon. The rubber may be unvulcanized or consist of vulcanized soft rubber, and may have been previously subjected to an elevated temperature.

It is to be understood that wherever in this specification the expression "rubber-like is used, it is to include materials which are like rubber in that they afford substantially the same reaction as the rubber in or on the core or mold to the heat ofthe cast metal, and which reaction is new and unexpected in this art. It may also include any subtsance, either or both plastic and elastic, that has any of the substantial characteristics of rubber, balata, or gutta percha, and may include. any rubber or old scrap rubber, either or both, that has been subjected to an elevated temperature alone or in the presence of sulphuric acid or a sulphonic acid or a sulphonyl' halide or it may also include a substance such as'is an article of commerce under the name Thermoprene. Wherever the state of the art permits, the terms "rubber and rubber-like are constructively construable as within the spirit and scope of my invention.

I 35 sulphuric acid, or a sulphonicacid or-a sulphonyl halide, and also the stated prene fall within the less chemical unsaturation than rubber grouping. The included material would also come within the heat plastic as well as the rubber isomer groupings. Said included materials also embrace a reaction product of rubber with a sulphonic compound having the'grouping R-SO2X, in which R represents hydrogen or an organic radical and X represents chlorine or a hydroxicor hydroxyl group. J

Inthis artybinders for the constituents of cores and molds are recognized compositions of commerce used in the production of molds and cores for the making of castings of hot metal.

When an additional thickness of outer coating is desired more than one application of said rubber orrubber-like material may be made to such surfaces of the mold or core. Successive dryings are required where several coats of such liquid are applied.

Any of the class of well-known facing materials may be added in desirable amounts to the rubber or rubber-like material coating, which accomplishes a saving in the amount of the rubber or rubber-like material otherwise required to be used.

, Such facing addition tothe coating will also give a smoother surfaceto the casting cast there againstdue to the fact that such coating will tend to level out the hollows between the grains of sand and lessens the rubber or rubber-like content which would otherwise be required therefor.

The material of which-the mold and its required cores, either or both, is made, which is usually sand or other earthy material, is formed either of what is known as a green sand core, or sand bonded with any of the heretofore described binders or others which have been in prior use;

but where the mold or core is relatively thin, no

*binder may be necessary. In such cases, the

A number of the foregoing materials come with material Thermm;

depth of penetration or absorption of the liquid content of such coating would in such cases afford an ample binder.

In the binders of the prior art with which water has been present in the molds or cores or has been employed as a diluent, it is the theory that, when the hot metal is cast into or against molds or cores bonded with such binder, the heat-of the liquid metal vaporizes the water content-of the mold or core relatively slowly and fills the cavity of the mold with water vapor which oxidizes the surface of the metal and which water vapor or gas tends to prevent the charring of the organic substances on the mold and core surfaces and thus causes contact of said oxidized surfaces of the cast metal with the uncoated or uninsulated sand grains, and which results in the fusing,

ter, and which contains substantially less Bx'ygemthetheoryis -that when the hot metal is cast into or against molds or cores bonded with such binder, the heat of the liquid metal vaporizes said diluent relatively more rapidly and quickly forms a gas or vapor which expels or replaces the air content of the cavity of such mold, and whichgas or vapor thus formed is in itself more free from oxygen than water vapor. These conditions, namely, the

substantial absence of air and the, occupation of i said cavity by a reducing or non-oxidizing gas. or vapor, promote the charring of the binder.

upon the mold or core surfaces, tend to prevent the removal of such charred coating by oxidation or combustion, and thus preclude the fusion or adherence of the mold or core particles with or to the surfaces of the casting.

Upon said conditions in the prior art, and in my invention, the prior art castings are-formed in the presence of an oxidizing gas or vapor, while i in: my invention the castings are formed in the presence of a non-oxidizing gas or vapor formed by the combustion of the rubber or rubber-like coating of the surfaces of the mold or core;

My said coating of the surfaces of the molds and cores, either or both, and their amalgamation therewith, in a sense, produces what is-somewhat analogous to case-hardened in somewhat the employed to designate certain treated metals. I

Said coating is substantially more or less inipervious to water, and the molds or cores so coated preferably have substantially no water content, as it is desirable for the best results with some castings that such moisture as the same may'contain should be that of a fluid which has substantially more volatility than water and whose volatilization does not result in the formation of an oxidizing gas or vapor, and which liquid may be gasoline, benzol, or other such liquid.

When the casting cast against suchimold or against such core surfaces is of molten metal it is-the theory that the heat of the metal consame sense that said term has heretofore been verts the rubber or rubber-like coating into a.

casting and of the mold and its core or cores,

and thereby or otherwise precludes the material of which such mold'and core is formed from adhering to or being imbedded in the surfaces of .such castings so that. the casting comes from the mold substantially clean in the sense of having no sand-or the like adhering thereto or being imbedded therein. This method lowers the cleaning cost of castings, facilitates their machining and may require less metal to be added to the casting for the purpose of machining the sand film.

As'to this last named phenomenon, applicant -has not yet been able to learn the agencies which produce this end. He has with his associates accounted for said phenomenon on two. theories either or both of which may explain the existence of said phenomenon.

One of said theories is that the hot surface of the casting in contact with the rubber impregnated sand mold and core forms a gaseous layer adjacent to the hot metal surfaces which prevents the sand adhering to or being imbedded into the hot metal surfaces.

The other theory being that such hot metal in contact with such rubber-like impregnated sand results in the formation of free carbon which coats the grains of sand and thereby prevents 'such coated sands from either directly coming in contact with or being imbedded in the surface of the casting. 1

It has. further been found that the grains of sand forming the mold and the cores that have had applied-thereto said rubber. or rubber-like material are, due to the heat of the casting, coated with decomposition products of rubber occasioned by'the conversion of said rubber or rubber like material, and this condition is believed to'be the main or contributing factor in rendering especially the cores to be most readily removed from all castings; whereas in the prior art it .has been the usual custom of requiring as much as a day for the removal of some cores from-a single casting with the best labor-saving appliances.

. In making castings of oxidizablemateria'l my said coating for the surfaces of the mold and its required cores enables un-oxidized castings to be produced, the substantially bright, clean and u oxidized surfaces of the metal appearing from the time the castingis taken from the mold; where-'- as'in the prior art the water or other content of the mold and cores, if any, causes oxidization of the surfaces of the metal cast there. against and which oxidizing castings are not as good in appearance and otherwise as castings of oxidizable metal made with my said mold and core. The bright and unoxidized surface, produced by my said mold, tends to preserve the casting and to retard oxidization thereof. This is of great importance as such castings or portions thereof which are required to be thin and unfinished as'well as with the metalsjthat are more readily oxidizable.

A further accomplishment of my said coating is that the same avoids substantially all actions or re-actions detrimental to the casting, or the surface thereof, that would otherwise exist if the casting were in direct contact with the sand or other material of the mold.

Where my coating for the surfaces of molds and cores is applied as a liquid I employ, with the other ingredient or ingredients thereof, a fluid intimately mixed therewith which has a substantially lower surface tension than water so that said liquid will readily penetrate a substantial distance into the surface of the material comprising the mold or core and thus can}? therewith gredient or ingredients of said fluid. Such penetration causes my said coating to not only adhere to the surfaceto which the same is applied, but as well to form a substantial bond with the material comprising said surface to the extent of said penetration.

Said added liquid is also a solvent of the soluble ingredient or ingredients of my said coating so that when an additional coat or coats thereof is or are applied to a mold or core, such additional coat or coats render fluid the outer film of the previously dried coating so that the subsequent coat thereby forms a good bond with the previous coat.

' Said'added liquid is also'substantially more volatile than water in order that it may readily evaporate from the material of the mold or core which it penetrates, as well as from the surface coating, at the temperature of the place where said coating is applied, or without the application of any more than moderate heat.

As to certain features set forth in the foregoing specification see also my copending applications Serial No. 332,225, filed January 12, 1929, for Method. and means for foundry practice and Serial No. 429,227, filed February 17, 1930, for Method and means for foundry practice.

' Having now so fully described my invention that others skilled in the art may therefrom make and use the same, what-I claim'and desire to secure by Letters Patent is:

1. In the method of producing molds and cores for the casting of metal, the steps of forming the mold or core of the desired shape, and applying a coating of a rubber substance to the surface or surfaces of such molds and cores adapted to come in contact with the casting. V

2. In the method of producing molds and cores for the casting of metal, the steps of applying a coating of a fluid rubber substance'to the surface or surfaces of such molds or cores adapted to come in contact with the casting.

3. 'In the method of producing molds and cores for the casting of metal,.the steps of applying a coating of a liquid rubber substance to the surfaces of such molds and cores adapted to come in contact with the casting, and drying such coating.

4. A. mold or core for the casting of metal haying a coating, applied after the mold or core is formed, containing rubber.

5. A mold or core for the casting of metal having a coating, applied after the mold or core is formed, containing rubber and a facing ma-- terial.

6. A composition to be applied to the surface or surfaces of molds or cores adapted to come in contact with the casting, said composition containing rubber, a liquid solvent of said rubber having a surface tension substantially less than water and being substantially more volatile than water.