US2791811A - Shell mold and apparatus for producing it - Google Patents

Description

May 14, 1957 .1. H. SCHMID 2,791,811

SHELL MOLD AND APPARATUS FOR PRODUCING IT Filed Aug. 17, 1953 4 Sheets-Sheet 1 \mu lllllll May 14, 1957 .1. H. SCHMID SHELL MOLD AND APPARATUS FOR PRODUCING IT Filed Aug. 17, 1953 4 Sheets-Sheet 2 Jakn E Ja'mm,

BY I @217 May 14, 1957 J. H. SCHMID 2,791,811

SHELL AND APPARATUS FOR PRODUCING IT Filed Aug. 11, 195:- 4 Sheets-Sheet 3 my wwx g 8 John- May 14, 1957 J. H. SCHMID SHELL MOLD AND APPARATUS FOR PRODUCING IT Filed Aug. 17, 1953 4 Sheets-Sheet 4 J06 BY; 2

United States Patent SHELL MOLD AND APPARATUS FOR PRODUCING IT John H. Schmid, Westfield, N. J.

Application August 17, 1953, Serial No. 374,491

3 Claims. (Cl. 22-9) This invention relates to the art of shell molding or the making of castings in molds that are merely shells of sand of a thickness usually of the order of from A" to and more particularly the invention is directed to a method and apparatus for making shell molds for use in shell molding processes.

According to known methods of shell molding, the shell molds are made in two or more sections that are usually referred to as cope and drag, and if the article to be cast is symmetrical in section, a single pattern for both of the cope and drag halves of the mold is made of suitable material, such as cast iron; while if an unsymmetrical article is to be cast, two patterns are required. The patterns are preheated and conveyed to a molding machine where a sand-resin mix is applied to the patterns, and after a few seconds, the portion of the mix in contact with the hot metal adheres to the pattern. The excess of mix, which has not adhered, then is removed as by inverting the patterns; and a shell of the sand-resin mix remains over the pattern, the thickness of the shell being controlled largely by the length of the period of contact between the mix and the hot pattern. The shells are then cured, generally in an oven, after which the shells are stripped from the patterns and are ready to be connected together to form the shell mold.

The outer surfaces of the shells are generally irregular, conforming roughly to the shape of the pattern, and because of this, difiiculty has been encountered in joining the halves of the sheel molds and holding them in position for the pouring operation. Various methods of joining and holding the shells have been utilized including (1) rigid backup in which the mold shells are pressed together by a clamping device whose contour matches the exteriors of the shells; (2) surrounding the molds with sand or metal shot; (3) cementing the mold halves together; and (4) grinding fiat surfaces on high points on the backs of the shells so one mold can be pressed between adjacent molds in a clamping device. All of these methods leave much to be desired, requiring much handling of materials which entails high labor costs as well as conveying and storage problems incident to the handling of the backup pieces, sand and shot.

A prime object of the present invention is to provide a method of making shell molds which shall overcome the disadvantages of the heretofore known methods, shall enable the production of castings of better quality and shall be relatively inexpensive both in labor and material handling equipment.

Another object is to provide a novel and improved shell mold which shall include a hollow section with a cope face and a drag face so constructed that'a large number thereof can be stacked to produce a plurality of molds for pouring either horizontally or vertically depending upon the arrangement of the sprues or pouring openings for the molds, which shall permit the mold sections to be firmly pressed together by a simple clamping device or by weights with each section in direct contact with the next adjacent sections and serving as a back- L 2,791,8 1] Patented May 14,1957

up therefor, and which shall provide adequate venting of the vapors and gases from the mold walls during the pouring of the hot metal into the mold.

A further object is to provide a novel and improved method of an apparatus for making shell molds wherein two patterns are hinged together and initially located in horizontal parallel planes for investment or application to the patterns of sand-resin mix, one pattern having a portion of the cavity of one mold and the other pattern having another portion of the cavity of another mold, and said patterns are rotated to remove the excess sand mix and are thereafter booked or swung into superposed relation to each other for curing of the mold sections, following which the mold sections are stripped, first from one pattern and then'from the other pattern, and the patterns are finally swung apart for the next cycle.

Other objects, advantages and results of the invention will be brought out by the following description in conjunction with the accompanying drawings in which Figure 1 is a schematic partial side elevational view and partial vertical longitudinal sectional view through two hinged patterns in their initial positions before the application of the sand-resin mix;

Figure 2 is a plan view of the patterns as illustrated in Figure 1;

Figure 3 is a view similar to Figure 1 showing the sandresin mix on the patterns;

Figure 4 is a similar view showing the mold shells on the patterns after removal of the excess sand-resin mix;

Figure 5 is a top plan view of the, mold shells and patterns as shown in Figure 4;

Figure 6 is a partial side elevational view and partial central vertical longitudinal sectional view of the patterns and mold sections in booked relation to each other;

Figure 7 is a central vertical longitudinal sectional view through a plurality of the molds in vertically stacked relation to each other;

Figure 8 is a bottom plan view of one of the mold sections approximately from the plane of the line 8--8 of Figure 7;

Figure 9 is a view similar to Figure 7 showing the molds clamped together for the pouring operation;

Figure 10 is a vertical sectional view of a plurality of stacked molds similar to Figure 7 but taken on a plane at about 45 to the plane of Figure 7, showing the sandresin pillars in section;

Figure 11 is a top plan view of the castings formed in the molds arranged as shown in Figure 9;

Figure 12 is a side elevational view thereof;

Figure 13 is an enlarged fragmentary sectional per- I spective view approximately on the plane of the line 13-13 of Figure 2 showing the manner of forming one of the passages from the sprue opening to one of the mold cavities;

Figure 14 is a greatly enlarged vertical sectional view through the superposed patterns and mold sections as shown in Figure 6, illustrating the relationship between the sprue-forming stud of one pattern and the cooperating opening of the other pattern;

Figure 15 is a fragmentary longitudinal vertical sectional view through vertically stacked modified molds embodying the invention;

Figure 16 is a view similar to Figure 14 showing a modification of the sprue-forming stud or pillar;

Figure 17 is a similar view of a [further modification of the patterns and sprue-fonming studs or pillars;

Figure 18 is a, fragmentary vertical sectional view through a mold section formed by the patterns and sprueforming pillars shown in Figure 17;

Figure 19 is a view similar to Figure 18 showing another form of a sprue; Q1 1' t,

Figure 20 is a-centralvertical sectional view through ..another.modification of .arnoldsectionembodying the :plurality of mold sections arranged in side byside relation; for horizontal pouring.

While the inventionmakes it possible to produce comiplexror intricate castings, for the sake of simplicity the method and apparatus'have been described for the production of sirnple flat disks A that are best shown in Figures 11 and 12.

The apparatus has been shown as comprising a coae pattern-B and a drag pattern C, whichin this case are different-because the casting A does not require matching mold sections. As shown, each of the patterns is of dished formation, thepattern B having a recess in one ,side thereof surrounded by an upstanding rim 2 and the :patternjC "havingia similar recess '3 in one side thereof surrounded by an upstanding rim 4. The two patterns are connected by hinges 5 and are initially disposed with their-recessed sides facing upwardly and in substantially horizontaleparallelplanes. .Connected to each pattern is asuitable electrical heating unit 6 that may be connected in a-circuit in any suitable manner.

Thepattern B has a plurality of upstanding projections :orbosses 7 on its bottom wall, each of a size and shape corresponding to the disk A to be cast, and projecting upwardly from'the center of the pattern is a sprueifonming stud or pillar 8, between the base of which and each boss 7 is an upstanding rib 9 to provide gating in the shell mold for the pouring of molten metal into the mold. The bottom wall of the pattern C is flat and has a centralopening 10 of a diameter slightly greater than the free end of the sprue-forming pillar 8 and said pillar 8 is of a height and diameter to project slightly into said opening 10 in spaced relation to the wall thereof when the patterns are booked or arranged in superposed relation to each other as shown in Figure 6.

In carrying out the method, the patterns B and C are arranged with their recessed sides facing upwardly as shown in'Figure 1, and a parting agent is applied if there is none in the mix. The patterns are preheated to a temperature of from 350 to 500 P. Then a sandresin mix D of known composition is heaped upon the upper surfaces of the patterns to overflow the rims as shown in Figure 3 and .allowed to stand for a few seconds, say ten to thirty seconds, whereupon the portion of the mix in contact with the hot surfaces of the patterns adheres to the pattern due to the fluxing of the thermosetting resin. The excess of the mix which has not adhered is removed from the patterns in any suitable manner, for example, by rotating the patterns to dump the mix or by brushing or blowing the mix D from the patterns. A shell E of about A to 4; in thickness remains on the pattern B with its lower surface formed with recesses produced by the bosses 7 and ribs 9. The shell E also has a perimetral rim 11 and a. hollow projection 12 formed by the sprue-forming pillar 8 projecting from its upper side. A shell F is for-med on the pattern C and has a flat smooth surface corresponding to the bottom wall of the recess in the pattern, a perimetral flange 13 and central hole 14.

Suitable pillars such as conical piles 15 of sand-resin mix may be deposited on the upper surface of the shell E of height greater than the aggregate of the depth of the recesses on the upper sides of the shells E and F fora purpose to be hereafter described, after which the patterns and shells are hooked or arranged in superposed relation toeach other .asshown in Figure 6. The flanges 11 and 13 are thus brought into contact with each other, the shell F is pressed into contact with the pillars 15 and the sand-resin on the sprue'pillar 8 contacts that around the hole 10, the entrance of the-pillar 8 into the hole 18 tending to shear the-mix on top of the sprue pillar. During 'this:step thesand resin is plastic, and so where contact is made, an homogeneous weld is effected. Heatfor-example of the order of 400 F., to cure the sandresin rnix. Cure will be completed in about one to two minutes and then the shells are stripped first from one pattern and then from the other, the hinging being designed to permit vertical movement between the patterns, and any suitable stripping mechanism (not shown) is utilized. The patterns are then swung apart into position for the next investment, that is, for the formation of another pair of shells'E and F.

The sealing together of the two shells E and F is completed during the curing operation so that when they are removed from the patterns they constitute a unit section G of a mold, the flat upper surface of the shell F constituting the drag of a-rnold and the recessed lower surface of the shell E constituting the cope of another mold when the mold sections G are arranged in vertically stacked relation as shown in Figure 7. More particularly "describing this construction, it will be observed that the outersunface of the shell E has a plurality of recesses'17 corresponding in shape and size to the bosses 7,-said surface also having grooves 18 corresponding to the-ribs 9 and forming gates from a sprue opening 19 fonmed by the sprue forming pillar to each of the recesses17. -When this shell is set upon the outer surface-of a shell Fof another section G, the recesses 17 are closed-and form-mold cavities for the production of the disks A, and the grooves 1t form passages or gates for conducting molten metal from the sprue 19 to the cavities. Before-the mold sections G are stacked, the thin wall 20 of sand-resin mix formed between the end of the sprue for-ming pillar and the wall of the hole 10 (Figures 6 and 14) falls out due to the shearing action incident to the close relation of the sprue to the wall of the opening, or-is knocked out, so that the sprue 19 is open fromend to-en'd. Generally this thin wall 20 will be broken away when the shells are stripped from the patterns.

'It will be observed that the mating surfaces of the shell Eof one mold section and the shell F of another mold section provide a liquid tight abutment between the mold sections and make itpossible to stack a large number of the mold sections either vertically or in side by side relationfor either vertical or horizontal pouring and with the use of a simple clamping device or weights as contrasted withthe complicated clamping devices, shot or sand, heretofore used when the opposite surfaces of a'shell mold are irregular. Figure 9 shows three of the mold sections vertically stacked with a'bottom clamping plate 21, a top clamping plate'22. and at least two C-clarnps 23 that hold the mold sections and plates 21 and 22 in stacked relation. The sprues ,19 of the mold sections are in vertical alignment and in register, and a pouring cup 24 is shown for directing the molten metal into the uppermost sprue. At this point it might be explained that the taper of the sprue openings is exaggerated in the drawings for clearness in illustration and that said taper is the result of providing a draft on the sprue-forming pillars.

After the casting metal has hardened, the molds are broken apartand leave a casting like that shown in Figures 11 and 12, where the portions 0 and P represent respectively the metal left in the sprues and the grooves 18, respectively. These portions 0 and P are removed in any suitable manner to leave the completed cast disks A.

.Atthis point it will now appear clear to those skilled in thetart why the sand-resin pillars 15 were provided. These pillars are so disposed between the shells E and F as to reinforce the shells against the clamping pressure exerted on the mold sections by the clamping devices as well'as against the pressure of the molten metal, and in the present instance each pillar 15 is disposed at approximately the .center of 'one of the mold cavities 17.

Insteadof sandpillars, suitablewedges 25 could be inserted before booking as shown in Figure 15, and instead of rims 11 and 13 on the shells, pillars 26 could be formed by suitable studs on the patterns; and the pillars on the two shells H and I, corresponding to the shells E and F, could be pressed together during the curing operation as indicated at 27 in Figure 15.

Instead of the pillars, the space between the shells E and F of the mold sections could be filled with loose sand or other filler that could be blown or otherwise forced into said space.

In some instances it may be desirable to vent the space between the shells of the mold sections, especially during the pouring operation, and for thispur'pose, mating notches 28 in the rims of the two patterns could be provided to form vent apertures 29 between the rims of the shells as best shown in Figure 6. Obviously loose sand could be blownthrough such vent openings into the space between the shells.

The same advantages that flow from the flat mating surfaces of the mold sections and from the sand pillars are present when the mold sections are arranged in side by side relation for horizontal pouring as shown in Figure 21. Here the plurality of mold sections G are arranged between the clamping plates 30 and 31, and the clamping plate 31 has a sprue passage or groove 32 into which the sprue cup 33 is inserted for pouring the molten metal.

Instead of heaping the sand-resin mix on the patterns and then dumping the excess of the mix, a layer of the mix may be applied to each of the patterns level or flush with the top of the rim of the pattern; and then the layers are heated throughout to form mold shells, after which the shells can be booked so as to bring the backs or the initial upper surfaces of the shells into contact with each other. Then the shells can be cured and stripped from the patterns in the same manner hereinbefore de scribed.

Preferably grooves will be scribed or otherwise formed in the upper surfaces of the layers or shells before they are cured, so as to form vent passages in the mold section after the shells have been booked and cured. Instead of scribing the grooves, draw-out pieces can be pressed into the uncured mix and withdrawn after booking or ouring of the mold section.

In accordance with the usual practice, the sprues and gates will be formed in such a manner as to cause proper flow of the molten metal into the mold cavities without turbulence, and also suitable means will be provided for choking the stream of metal.

It will also be understood that a shoulder 34 may be provided at the base of the sprue-forming pillar to provide clearance for any irregularities at this point when the mold sections are stacked.

It will also be understood that the sprue openings can be formed in different ways. For example as shown in Figure 17, each pattern K and L may have a sprue-forming pillar 35 complemental to the pillar on the other pattern when the patterns are booked, and the thin wall 36 of sand-resin mix between the pillars can be easily broken away by suitable hand punch or cutter. Figure 18 shows shells M having the sprues 37 and pillars 39 formed by studs on the patterns, the wall 36 and the abutting surfaces of the pillars 39 being ground away into a common plane and the contacting surfaces of the shells being cemented together.

In some instances it may be desirable to form holes in the two shells and then insert a sprue bushing 40 as shown in Figure 19, which may be formed of any suitable material such as the sand-resin mix.

Also in some cases, especially with intricate mold cavities, it may be desirable to reinforce the mating surfaces of the mold sections as shown in Figure 20 where sheets of wire mesh 41 are embedded in the shells and suitably shaped to roughly conform to the contour of the pattern. These sheets can be supported on the rims of the patterns or on buttons during the heaping of the sandresin mix on to the patterns.

Wherelit'is desirable to use-armour piecesiin the molds, the rims of the pattern can be omitted entirely or provided only at one or two sides.

It will occur to those skilled in the art that various types of sand-resin mixes can be utilized, with or without fillers such as iron oxide, and that a thin layer of highly graded sand and resin mix could be used for the faces of the mold sections and backed up by a mixtureof coarser sand and a'lower grade or quantity of resin by investing the patterns in two stages.

From the foregoing, it will be clear that the invention provides a shell mold and method and apparatus for making it whereby delicate and sharp castings can be pro duced rapidly and at low cost. Each mold section G serves as a direct backup for the next adjacent sections, thereby eliminating the complicated and expensive backup or clamping devices, handling of shot, cementing, or grinding of flats on the reverse side, etc. according to the heretofore known practices. It permits direct vertical investment of the patterns which improves mold quality in deep sections as compared with dump box and blowing methods and eliminates the pattern wear associated with blowing. The mold sections are hollow, comprising side walls and two opposite end walls so that the gases that may be formed by evaporation of the resin during the pouring operation can be easily and quickly vented to the atmosphere. This construction in conjunction with the reenforcing pillars provides strong mold sections of minimum weight that are highly resistant to warping under the influence of the molten metal and are capable of withstanding high pressure incident to clamping the mold sections in stacked or side by side relation for the casting operation. The method provides an easy and simple way of obtaining the hollow mold sections as well as the sand-resin pillars integral with the end walls of the mold sections.

Other means of forming a hollow mold section, such as introducing a measured quantity of sand-resin into booked patterns and rotating the assembly, or directional controlled blowing of the sand-resin into booked patterns, or use of a draw-out piece between the patterns couldbe used.

Many modifications and changes in the steps of the method, in the apparatus and in the structure of the mold will occur to those skilled in the art as within the spirit and scope of the invention.

What I claim is:

1. A shell mold section comprising two shells of sand and thermosetting resin one of which has at least one wall with a face constituting the drag portion of a mold while the other has at least one wall with a face constituting the cope portion of another similar mold, said shells being secured together with air-circulating spaces between said walls and with said faces facing in opposite directions, outwardly and away from each other.

2. Apparatus for making shell mold sections comprising a pattern having the drag portion of a mold in the face thereof, a pattern having the cope portion of a similar mold in the face thereof, means hingedly connecting said patterns together so that selectively they can be disposed in horizontal parallel planes and facing upwardly and can be swung into superposed relation to each other with the cope portion of one pattern in spaced relation to and facing the drag portion of the other pattern, and means for heating said patterns, each pattern having a dished portion in the bottom of which is one of said cope and said drag portion, and said dished portions having rims of the same perimetral dimensions, one pattern also having a sprue-forming stud projecting from its said face and the other pattern also having a hole into which the free end of said stud enters in spaced relation to the walls of said hole when said patterns are in superposed relation to each other.

3. Apparatus for making shell mold sections comprising a pattern having the drag portion of a mold in the face thereof, a pattern having the cope portion of a similar mold in the face thereoflmeans hingedly connectingsaidipatterns together so that selectively they can be disposed in horizontal ;.paralle1 planes and facing upwardly and can be swungzintosuperposed relation to each other with the cope portion of onepattern in spaced relation to and facing the drag portion of the other pattern, and means for heating said .patterns, at least onepattern also having projectionson its said face so References Cited in'the file of thispatent UNITED STATES PATENTS 738,277 Beckwith Sept. 8, 1903 5 1,252,945 Rabun etal. Jan. 8, 1918 1,389,722 Webb Sept. 6, 1921 1,698,836 Bartley Ian. 15, 1929 1,773,732 Hines Aug. 26, 1930 2,587,061 Nelson Feb. 26, 1952 10 FOREIGN PATENTS 643,778 Great Britain -Sept. 27, 1950 OTHER REFERENCES .Fiat Final Report No. 1168. PB 81284. May 30, 15 1947.

The Foundry, Aug. .1950,lpp. 92, 96, 206,217 relied Foundry, June 1952, page'289 relied on.

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