US2201037A - Molding process - Google Patents

Description

May 14, 1940. H. F. HAGEMEYER MOLDING PROCESS Filed April 23, 1938 2 Sheets-Sheet 1 W M M:

INVENTOR HENRYFH/IGEMYER W ATTOR NEY May 1940.

H. F. HAGEMEYER MOLDING moor-ass Filed April 23, 1938 2 Sheets-Sheet 2 I NVENTO R HENRY E'Hfle'amm ATTORNEY Patented May 14, 1940 PATENT OFFICE MOLDING PROCESS Henry F. Hagemeyer, Chicago, Ill., assignor to Castiilisgs Patent Corporation, a corporation of Application April 23, 1938, Serial No. 203,872

9 Claim.

This invention pertains to a process for producing molds and in particular to the production of molds having gypsum as a basis of the mold material. This application is a continuation in part of my applications Serial No. 87,922, filed June 29, 1936, for Molding apparatus, continuation in part thereof filed May 5, 1938, as Serial No. 206,152, for Molding methods and apparatus) and Serial No. 91,897, filed July 22, 1936, for Drying apparatus, (see divisional application Serial No. 206,151, filed May 5, 1938, for Mold drying methods and apparatus) and is a companion to the application resulting in my Patent No. 2,101,677, issued December I, 1937, for Apparatus for producing molds and reissued as Re.

21,046 on April 11, 1989.

Molds having gypsum as a principal ingredient have long been proposed for use in a commercial general casting process, but prior to the development of my method such molds have been very expensive to make and have been difficult to pour satisfactorily. The expense has arisen largely because of the great length of time and the care required to dry the molds, despite which the percentage of molds broken or cracked too badly to use was high, and the difiiculty of pouring largely arose because of insufilcient porosity of the mold to convey away the air trapped in the mold cavity and the pouring gases. It has been desired topour such molds without the provision of a venting passage in addition to the sprue and gate.

The history of the art is replete with suggestions for increasing the porosity, of the mold material, but invariably pouring the metal under -pressure has been necessary to fill the mold cavity. With suflicient porosity of the mold the metal will flow into even the tiniest detail and branch of the mold cavity without pressure, the air and gases exuding through the walls of the cavity ahead of the inflowing metal.

In an attempt to obtain suflicient porosity of the mold material to allow this action, various skilled artisans have suggested mixing with the gypsum a fibrous or a granular material, among which appear asbestos, other rock of the homblende family, coal ashes, a combination of potters clay and asbestos, powdered carborundum, a combination of asbestos fiber and brick dust,

U and kieselguhr or cellite. None of these substances has proved to be capable of obtaining the porosity required.

A sand mold is rather porous, but it has other disadvantages, namely, the moisture therein causes a large amount of pouring gas especially when casting brass. The sand mold chills the hot metal comparatively quickly and prevents its flow into small crevices. The surface of a sand mold, and hence the resultant casting is granular instead of smooth.

In my process I am able to obtain great porosity in the mold, not by mixing the gypsum with a granular material, but by mixing in with the dry material a great excess of liquid, preferably water, which, after the mold is set, is evaporated out of it, to leave voids or cavities in the mold. Despite such great excess of liquid I am able to dry out themold ready for pouring in an hour or two by the application to all surfaces of each mold section of direct radiant heat. Such exposure is obtained by removing the mold sections from the flask and match plate as soon as the gypsum is somewhat set, the setting being expedited and controlled to obtain a minimum meniscus by employing hot water in the mix and keeping the mold material at about the temperature of the water until it is set. In order to obtain an intimate and homogeneous mixture of the mold material, violent agitation of the mix is necessary as pointed out in my application for molding apparatus mentioned above.

The principal object of my invention, therefore, is to obtain a mold of the gypsum base type which is sufficiently porous to enable the molten metal to flow into all the crevices of the mold cavity without being subjected to pressure above atmospheric, and which nevertheless will give a relatively non-porous molding cavity surface of great smoothness and extremely finerained.

A further important object is to make such a mold by a method employing a few simple steps and which requires a minimum of time, especiallyin the drying or baking operation.

A more specific object is to obtain the porosity of the mold by the use of a fluid substance in the mix which may be removed later and before the mold is poured to leave voids uniformly honeycombing the mold body.

Still another object is to prepare such molds 45 with a minimum of manual handling while utilizing the smallest amount of, and least expensive equipment consistentwith the production of accurate, strong and well finished molds.

Other objects, and more particularly those inherent in the steps of the particular process which I prefer, will appear as the detailed description of, my method progresses, it being understood that the apparatus pictured in the drawings and described is to illustrate one way in which the several steps may be performed, and-'my process is not to be considered as limited to performance by the mechanism. The inventive features of the process are pointed out in the appended claims.

Figs. 1 and 1Av together, from right to left, constitute a side elevation view of the mold production line, and

Figs. 2 and 2A together, from right to left, constitute a plan view of such line.

Fig. 3 is a cross-section of a set mold section before its removal from the flask and match plate, and

Fig. 4 is a perspective view of the mold section after its removal from the match plate and flask, being as it would appear during the drying or baking operation.

As stated, the principal ingredient of the mold is gypsum. This is supplied commercially in the form of calcined gypsum or hemihydrate having therein one quarter of the water capable of chemical combination therewith, so that it has the formula (CaSOOaHrO. This calcined gypsum will unite chemically with water to produce gypsum represented by the formula CaSO4.2HzO

by the reaction represented by the equation given in the Toman Patent No. 1,893,309, issued January 3, 1933. There must therefore be at least enough water supplied to react with the calcined gypsum for setting purposes.

In addition to the gypsum I prefer to use some I tion with the calcined gypsum and to wet the asbestos, and then to such mixture is added enough liquid to give the desired porosity to the finished mold. Suchliquid may be any which can be homogeneously mixed with the water and calcined gypsum until the latter is set, and the liquid can then be evaporatedfrom the mold to leave voids uniformly distributed through the mold body. The amount of such liquid may, of.

course, also be varied within limits according to the degree of porosity of the mold desired. Sufllcient must be used to obtain the minimum desirable porosity, and the upper limit of such liquid content is set by the amount thereof possible to mix homogeneously with the other mold ingredients, or in which the solid ingredients will remain suspended until the gypsum is set. Suflicient liquid must not be used, however, to leave the mold material so porous as to be too weak to withstand the pouring stresses.

As the most satisfactory liquid I have used water greatly in excess of that required for chemical combination with the calcined gypsum. I have found that a satisfactory proportion by weight of water to calcined gypsum is two to one, whereas all that would be necessary for chemical combination with the calcined gypsum would be, by weight, three parts of water to sixteen parts of calcined gypsum, or less than one-fifth of a unit of water to one unit of calcined gypsum by weight, making the excess water more than one and fourfifths units. For general purposes, with one hundred parts of the dry mixture having, by weight, eighty percent calcined gypsum and twenty percent (20%) asbestos pulp or fiber, may be mixed one hundred sixty parts of water, by weight, which in simple figures is four parts of calcined gypsum to one part of asbestos to eight parts of water. Less than one and one-half parts of water to one ofcalcined gypsum, by weight, will result in a mold of insufficient porosity if strengthening material is used, although proportions up to as high as three parts or more of water to one of gypsum have been employed where extreme porosity was desired.

The first step in the process is to mix together the dry ingredients and then to mix these with the liquid, which, in the illustrative method to be specifically described, is an water. While these ingredients may all be mixed together before being placed in the flask, I prefer that the dry.

mixture and the water be placed in the flask separately and mixed therein to allow maximum time between the mixed material being in place in the flask and the setting of the gypsum. The order in which the liquid and the dry material are supplied is not mandatory, but I prefer to place the water in the flask first and thereafter to sift onto the water surface the dry material.

In the drawings, I have shown in Figs. 1 and 2 a water supply pipe I which leads from a supply.

tank (not shown) in which the water is maintained at a hot temperature, preferably about F. The valve I0 is opened until the measuring box I I, as indicated in the open-topped gauge tube I2, is full and then it is closed. Into the shaker 2 is placed a measured amount of mixed dry material.

The flask and match plate unit F is slid along the table under the water box II and the valve I3 is turned to allow the measured amount of water to flow from the box into the flask. Next, the flask is slid along under the sifter 2 which is suspended flexibly and is shaken by a motor mounted thereon and driving slightly eccentric weights.

When the material has all been deposited in the flask it is moved onto the hydrator or agitator 3. To obtain an intimate and homogeneous mixture despite the great excess of liquid employed, it is necessary to agitate the mixture violently, preferably by pounding the flask support against a stop so that the material will be subjected to concussion and by reason of its inertia will impinge forcibly against the flask walls. A hydrator for obtaining such action is described in detail in my application for molding apparatus cited above. The hydrator 3 supports the flask in the cradle 30 mounted on the swinging end of the arm 3| pivoted at 32. A hinged cover 33 is swung down over the flask and locked in sealing engagement with the upper flask edge to form a closed container. The motor driven shaft 34 carries an eccentric which engages a member connected to the arm 3|, and as it rotatesit forces the flask support 30 downward and tensions the spring 35 which is attached to the opposite end of the arm 3|. Upon further rotation ofthe eccentric the spring pulls the flask carrying end of the arm upward so that the bifurcations 3'I impact violently against the cushioned stop 36. The mold material continues upward into impact with the cover 33 and undergoes a circulating and churning action so that every part of the mixture is thoroughly and uniformly commingled.

The flask is conveyed slowly through the setthe air and all surfaces capable of transferring radiant heat surrounding the flask at a uniform temperature, preferably at substantially the temperature of the water supplied, namely, 180 F. If one edge of the mold material is cooled more than the others the meniscus will be greatest, on

that edge. My 'aim is to preserve the heat content of the flask and material constant, neither withdrawing heat from nor supplying heat to them. This is accomplished by surrounding the conveyor 40 with a hood 4| and compensating for heat radiated therefrom by supplying regulated 'heat beneath the hood from a heat source 42 By the time the flask has such as a gas flame. passed through the setting table the material has set into the mold section M which still, of course,

contains all the excess liquid or water supplied in the mixture and is quite soft, being easily dented with the finger.

The next step is to separate the soft mold .section', as shown in Fig. 3, from the flask, so that it will appear as in Fig. 4. This may be done by an extractor such as described in my above mentioned patent, Re. 21,046, or by the use of a vacuum extractor plate as therein described mounted upon the spindle of a converted drill press 5 provided with suitable flask holding means.

The wholly uncontained mold section is then placed on the conveyor 60 of an oven 6 in which the excess liquid, preferably water, is dried out of the mold section. Moreover, substantially all the water riginally added, including that chemically combined with the gypsum, may be dried out, so that the resulting mold is not only extremely porous but is of very light weight. The

oven and drying method may be such as described in my application for drying apparatus above mentioned. The mold sections are preferably placed on the conveyor with the parting face upward. Both the upper and lower surfaces are then subjected to direct radiant heat from heat radiating surfaces disposed above and below the mold section and spaced therefrom about four inches. The heat of such surfaces will be within a couple of hundred degrees above or below 1400 F., which has been found to be the most suitable average temperature for most jobs and mold compositions.

As the vapor escapes from the mold sections it is removed from adjacent to their surfaces so that they will be blanketed as little as possible from the heat radiant surfaces. For this purpose a duct system 6| may be provided for removal of the vapor laterally from the drying chamber. If desired, such removal may be expedited by the use of an exhaust blower at the manifold exit.

The radiant surfaces may be heated principally over the entrance half by gas or oil vapor nozzles 62, the exit half being heated by withdrawing the hot combustion gases from the combustion chambers through a hood and vent 63 at the extreme discharge end of the oven. If desired, of course, the oven may be fired over its entire length. The passage of the mold through the oven requires only between one and two hours ordinarily.

Upon discharge from the oven, the mold sections pass through a cooling hood I where they cool gradually instead of being subjected to the possibility of severe stresses being set up by the sudden chilling of moving from the hot oven directly into the relatively cold open air. As the mold sections emerge from the cooling hood, the cape sections and complemental drag sections are ready for assembly for pouring.

The mold resulting from the described process has a substantially homogeneous body of ypsum, preferably intermixed with fibrous asbestos to give additional strength. The body is honeycombed with voids which are of minute character but very closely spaced, the solid material of the dried mold merely forming a skeleton. Through this structure the air and pouring gases may ooze from the mold cavity and be discharged from the outer mold surface. also forms an excellent insulating layer to prevent chilling of the casting metal. The mold may be made still lighter, and the pouring gases reduced to a minimum if, in addition to the excess water used to obtain porosity, there is dried out of the mold part of the water chemically combined with the gypsum. In fact, I have found that substantially all of the water added may be dried out of the mold without appreciable detrimental eifects,'so that the gypsum in the finished mold has its chemically combined water content reduced to that of the calcined gypsum originally entering into the mixture.

The porous mold body, after the drying or baking operation, has the water replaced by voids.

The specific gravity of calcined gypsum and asbestos is about 2.8 so that for the previously suggested proportions in the standard mix of four parts of calcined gypsum to one part of asbestos to eight parts of water, by weight, the volumetric proportion of solid material to water would be to 8 or 1 to 4.48. Hence in the dry mold, since the composition of the solid material is then the same as in the original mix, the volumetric ratio of solid material or skeleton to voids is also 1 to 4.48.

For the minimum water content for practical purposes mentioned, the mix is four parts of calcined gypsum to one part of asbestos to six parts of water, by weight, so that in the mold the volumetric proportion of solid material to voids is to 6 or 1 to 3.36. If more asbestos is employed with the same water to gypsum ratio, this ratio of solid material to void might occasionally be as low as 1 to 3, but greater porosity is desirable. For cases where extreme porosity is desired, on the other hand, such as where a mix of four parts of calcined gypsum to one part of asbestos to twelve parts of water, byweight, is used the volumetric ratio of solid material to voids is Such structure seven or more times the volume oi solid material, for ordinary purposes the ratio will be about four and one-half or five to one. No such proportion of void to solidmaterial can he obtained by the use of a granular substance mixed with the gypsum, and without the use of an excessive amount of liquid and the subsequent evaporation thereof from the mold.

Despite the high porosity or proportion of voids in the mold, the moldcavity has a surface layer which, while somewhat porous, is much less so than the body of the mold. This layer or skin. however, is paper thin so that the air trapped in the mold cavity and the pouring gases have no difficulty exuding through it into the voids of the mold body. The surface, in fact, is little more porous than, and is as smooth and finegrained as that which would be formed by the same grade of calcined gypsum used in an article having a relatively non-porous body, namely one formed without the use of an excessive amount of water, but with just enough for chemical combination with the gypsum and the minimum required for a good mix. Since the patterns are made of metal or other non-porous material dressed to a very smooth surface, the greatest smoothness and fineness of surface of which the ypsum in contact therewith is capable is obtained. I

The casting produced in the mold will in turn have a very smooth and accurate surface, so that no finishing machine operations will be required.

' Because of the superior insulating qualities of the porous gypsum mold and the ready escape of the air and the pouring gases, the metal will not be chilled before entering every detail of the mold, nor will it encounter any gaseous resistance to such entry. Fine and sharp detail may thus be obtained, and precision machine parts may be cast to tolerances not exceeding plus or minus three thousandths of an inch. I have obtained such results both with aluminum alloys, poured at 1300 F. to 1400 F'., and with various bronze and brass alloys poured at temperatures above 2000 F. and approaching 2500 F.

As my invention I claim:

1. The method of making molds of plastic material for use as a casting matrix, which comprises preparing an intimate, homogeneous mixture of solid material including calcined gypsum and asbestos, an amount; of mixing water at least equal to that capable of combining chemically with the calcined gypsum, and a quantity of mixing liquid, the ratio by weight of mixing water and liquid to solid material being of the order of 1.6 to 1, and after setting of the gypsum drying out of the mold the mixing liquid and substantially all the mixing water, including that chemically combined with the gypsum,

2. The method of making molds of plastic ma-v terial for use as a casting matrix, which comprises preparing an intimate, homogeneous mixture including calcined gypsum, asbestos, and an amount of mixing water by-weight of at least one and one fifth times the combined weight of the calcined gypsum and asbestos, allowing such mixture to set into mold form, and thereafter drying out of the mold substantially all the mixing water supplied, including that part of such water chemically combined with the gypsum.

3. The method of making molds of plastic material, which comprises homogeneously mixing together predetermined amounts of water and calcined gypsum base material, allowing the resulting mixture to set and until set maintaining the mixture in an atmosphere having a temperature of the order of 180 F. 4

4. The method'of making molds of plastic material, which comprises mixing together into a homogeneous mixture water at approximately 180 F. and calcined gypsum base, solid material in the ratio, by weight, of the order of 1.6 parts of mixing water to one part of solid material, and allowing the resulting mixture to set into mold form.

5. The method of making molds of plastic material, which comprises homogeneously mixing together predetermined amounts of water at a temperature of approximately 180 F. and calcined gypsum base material, allowing the resulting mixture to set and until set maintaining the mixture in an atmosphere having a temperature of the order of 180 F.

6. The method of making molds of plastic material, which comprises mixing together into a homogeneous mixture water .at approximately 180 F. and solid material, containing by weight a minor portion of heat resistant substance and a major portion of calcined gypsum, in the ratio, by weight, of the order of 1.6 parts of mixing water to one part of solid material, allowing such mixture to set into mold section form in a flask and match plate assembly, and until set maintaining such mixture in an atmosphere having a temperature of the order of 180 F.

7. The method of making molds of plastic material, which comprises placing together mixing water at a temperature of the order of 180 F. and solid material including calcined gypsum in the ratio, by weight,-of the order of 1.6 parts of water to one part of solid material, agitating such mixture within a flask and match plate assembly and about the patterns therein, thereby intimately depositing the mold material about such patterns, allowing such mixture to set into mold section form in the flask and match plate assembly and until set maintaining such mixture in an atmosphere having a temperature of the order of 180 F., and exposing the mold to a proximate radiant heating surface at a temperature of the order of 1400 F. for approximately one hour, thereby drying out of the mold substantially all the water added to the solid material in the preparation of the mixture, including that part of such water chemically combined with the 8. A foundry mold comprising a body substantially homogeneous throughout, having therein a casting cavity for reception of molten metal, and composed of gypsum base material incorporating asbestos, honeycombed with voids of at least three times the volume of solid material, and having a smooth, relatively non-porous skin.

having a smooth skin.

HENRY F. HAGEMEYER.

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