US2496170A - Method of producing investment molds - Google Patents

Description

m m m Ema W a. P. MANN BJZIETHOD OF monucms mvmswnam MOLDS 2 Sheets-Sheet 2 Filed Aug. 11, 1944 llllllilllllll fmm lllll ll lLlalll 44-3 -17 4 CECE WMNESS Patented Jan. 31, 1950 METHOD OF PRODUCING INVESTMENT MOLDS Carl P. Mann, Riverton, N. J., assignor to Sela: Corporation oi America, Philadelphia, Pa., a corporation of Pennsylvania Application August 11 1944, Serial No. 548,993

2 Claims. (Cl. 22-198) This invention relates to a method of producing investment molds, and it is an object of the invention to provide an improvement for removing from investment material the pattern or model embedded therein which is formed of wax, resin, plastic and like material, as will appear from the following description and accompanying drawings forming a part of this specification, and oi which:

t ig. l is a vertical sectional view of apparatus embodying the invention;

Fig. 2 is an enlarged vertical sectional view oi an. investment mold shown in Fig. 1 to illustrate the invention more clearly;

The. 3 is a side elevation of the apparatus illustrated in Fig. l;

Fig. i is an enlarged fragmentary vertical sec tional view of adjacent cars illustrated in Figs. 1 and 3: and

Fig. 5 is a fragmentary plan view of adjacent cars and a duct alongside of which the cars move.

In casting by the investment method, patterns of the parts to be made may be formed of a suitable material in a metal die or mold. While the material forming the pattern will be specifically referred to as wax in the following description and claims, it is to be understood that this term is intended to cover not only waxes but also resins, plastics and like material which are suitable for producing investment molds. The preparation of the wax and injection thereof under pressure into the metal die are controlled to produce accurate patterns that will not be deformed with subsequent handling.

The pattern of the part thus formed is sometimes referred to as a model, and a model may constitute a single pattern of a part to be cast or a plurality of patterns of a number of such parts which are connected by runners and to which are attached one or more sprues. The form and shape that a model may assume is diagrammatically illustrated at i in Fig. 2 and may include a number of patterns 2 connected by runners t and a sprue t which extends to the extreme end of a flask 5 which may be in the form of a metal ring. The runners and sprues oi wax are formed separately from the patterns and attached thereto by heating irons in a well own manner.

The model II is then embedded in a material referred to as an investment 8 which is inert with respect to the wax of the pattern or model. Ethyl silicate is one example of a chemical binder which is used to provide a suitable liquid mold material which upon standing is converted to solid silicate to form the investment. The model I is completely enveloped by the investment 6, as illustrated in Fig. 2,- and, before the refractory material of the investment has set, the flask 5 may be mechanically agitated or connected to a suitable suction line to remove air from the investment and eliminate voids about the patterns. Before embedding the model I in the investment 6, a suitable material may be applied thereto and allowed to dry to cause refractory material, such as an extremely fine sand, for example, to be deposited on the surfaces of the patterns.

The wax is then removed from the investments 6 and the latter cured or baked to prepare the flasks 5 for casting. The metal is poured while the flask is at an elevated temperature to assure fluidity of the metal which preferably is cast under pressure at a temperature considerably above the melting point of the metal, so that proper filling out of the mold is accomplished and sound castings are obtained. The investment 6 is then removed from the flask 5 after which the investment is separated from the casting. The parts cast are then separated. from the runners and sprues in any suitable manner and subjected to whatever machining or finishing operations are required.

In accordance with this invention, an improvement is provided for rapidly removing wax from investment molds and for curing or baking the investment material in a single operation and with a minimum amount of handling. This is accomplished by placing the flasks in a high temperature oven space in such a manner that the melted wax, together with the gases evolved from heating of the wax, are discharged to the exterior of and cannot pass into the ,oven space. In this way, the likelihood of producing in the high temperature oven space an explosive atmosphere oi gases resulting from heating of the wax, is avoided. Further, by discharging the melted wax and wax vapors from investment molds to the exterior of the oven space, the liberation of hydrocarbons in the oven space is prevented, and burning or cracking of such hydrocarbons cannot take place in the oven space and form a de- 7 posit of free carbon therein.

In order to make certain that the wax vapors cannot pass into the oven space in the event oi. any leakage in the walls forming such space, the melted wax and wax vapors are discharged into a chamber adjacent the oven space which is maintained at a pressure lower than that in the oven space, so that the pressure in the oven space will be positive with respect to the pressure in the chamber and iiow of gas always will take place out of the oven space in the event of leakage about the space. The chamber into which the melted wax flows preferably is provided with a removable tray for holding the melted wax, so that it may be reclaimed and used again.

Referring to the drawings, apparatus which is shown embodying the invention includes an oven or furnace ll] of a direct gas fired type having vertical walls II and a roof l2 formed of suitable refractory material. The vertical walls H and roof l2 are disposed within a framework or outer shell |4 having a number of legs I5 for supporting the oven ID on a suitable supporting surface The flasks 5 to be heated in space within the oven H) are mounted on cars H3, as will be described presently, which are moved through the oven space on a track I9. A suitable seal, such as, for example, a sand seal, is provided between the lower edges of side walls H and opposite sides of the cars 8, as indicated at 29 in Fig. 1.

A number of burners 2d are mounted in and form a part of the roof I2. The burners 2i are disposed alongside of each other in a plurality of rows, the number and disposition of the burners being such that the desired heating is effected of the flasks 5 passing through the oven space ll.

Each burner comprises a molded block of ceramic material having a central passage within which is disposed a burner tube or sleeve 22. As shown in Fig. 3, the outer ends of sleeves 22 are connected by pipes 23 to manifolds 26 to which a gas mixture is delivered from a suitable source of supply. Suitable valves (not shown) may be provided to control the pressure and rate at which the gas mixture is supplied to the manifolds 2 3, and the supply of the gas mixture for each burner 2| may be individually controlled by valves connected in the pipes 23.

The gas mixture, which may be a mixture of a suitable fuel gas and a combustion supporting gas, such as air, for example, is supplied to each of the burners 2| and subdivided into a plurality of gas streams by a distributor or tip 25 which is fixed to the inner end of the sleeve 22 and terminates at a cup-shaped space 2'6. The burners 2| are of such a type that combustion of the gas mixture is substantially completed in the cup-shaped spaces 2l, whereby flame impingement of the flasks 5 is readily avoided.

The refractory wall surfaces of the cup-shaped spaces 21 are heated to incandescence and constitute high temperature zones or regions from which heat is radiated to the flasks 5. This radiated heat, together with convection heating derived from the heated products of combustion directed toward the flasks 5 and downwardly in oven space H, provides a heating effect which is readily controlled to effect the desired heating of the flasks 5 during their travel through the oven Ill.

The burners 2| are of the kind described and illustrated in Hess Patent No. 2,215,079, granted on June 23, 1942 and assigned to the same assignee as'this application. The burners 2| are fully disclosed in the aforementioned Hess patent which may be considered as being incorporated in this application, and, if desired, reference may be had thereto for a detailed description of the burner structure.

A number of vertically extending conduits 28 are incorporated in the side walls ll for withdrawing products of combustion from the oven space H. The lower ends of the conduits 2t terminate at the inner surfaces of the side walls adjacent the bottom of the oven space H, and the upper ends thereof extend upwardly and terminate a short distance from the top of the oven l0. At the upper ends of conduits 28 are provided draft hoods 29 connected to conduits 30 in which are provided blowers or exhaust fans 3|. The conduits 28 are provided in both of the side walls II and at spaced intervals along the oven III, as shown in Figs. 1 and 3.

By providing the draft hoods 29 the full effect of the exhaust fans 3| will not be reflected back to the conduits 28 and cause too rapid withdrawal of the products of combustion from the oven space H. The vertical conduits 28 are of minimum length, so that the draft effect produced by these conduits will be as small as possible and allow the products of combustion to be withdrawn therethrough after substantially all of the useful heat has been given up in the oven space H. The draft hoods 29 permit atmospheric air to mix with the products of combustion to dilute and cool the exhausted gases, whereby provision need not be made for the conduits 30 and exhaust fans 3| to handle gases at an unduly high temperature.

A number of cars |8 are provided for movement through the oven ID on the track l9. Each car l8 includes a box-like frame 32 enclosed by side walls 33 and 34, end walls 35 and a bottom 36 which may be formed of sheet metal. The tops 3i of the cars It! are formed of refractory material having a number of openings 38 therein which are enlarged at their upper ends to provide cavities 39 adapted to receive the flasks 5, as shown in Figs. 1 and 2.

One end wall 35 of each car I8 is formed with a horizontal slot through which a tray 40 may be moved into and withdrawn from the chamber 4| within the car. The frame 32 of each car is provided with side sills 42 for supporting the tray 40 which is provided with a front plate or cover 43 adapted to fit snugly against the end wall 35 when the tray is in position in the chamber 4 I.

The cars l8 are maintained close together during their travel through the furnace or oven Ill, so that the tops 31 of adjacent cars abut each other and collectively form the bottom or floor of the oven space H. A horizontal duct 44 is disposed directly beneath one of the side walls H and extends lengthwise of the oven l0 alongside the cars l8, as best shown in Fig. 1. The duct 44 is formed with a slot in a vertical side wall 45 which is at the same elevation and in alignment with horizontal openings formed in the side walls 33 of the cars l8, as indicated at 46 in Fig. 1. The side wall 45 of the duct and side walls 33 of the cars |8 are relatively close to each other and the gap therebetween is closed by a suitable seal, as will be described presently.

In order to dilute the hot wax vapors with atmospheric air and also bring down the temperature of the hot vapors immediately upon being discharged into the chambers 4|, the side walls 34 of the cars are provided with a number of openings 41 to permit air from the surroundings to pass into the interiors of the cars. A plurality of exhaust flues 48 are connected at their lower ends to duct 44 at spaced intervals corresponding to the spacing of the vertical conduits 28. The upper ends of dues 48 are connected to the conduits 30, whereby the blowers or exhaust fans 3| are also eifective to withdraw the mixture of wax vapors and air from the chambers 4| of the cars it. The mixture of wax vapors and air passes from the upper ends of the lines 48 into the con- 5 duits at at regions closely adjacent to the inlets of the exhaust fans ti.

In the operation of the apparatus just described the flasks 5, having the wax models 6 enveloped therein by investment material t, are placed in the cavities it formed in the refractory top ii of a car it. As shown in Fig. 2, the flask b is in what is referred to as an inverted position and the sprue t of the model I extends downwardly into and communicates with one of the openings it in the refractory top ill. The flasks t fit snuc'ly and accurately in the cavities ill to provide a gas tight seal between the flasks and the refractory top tl.

after the flasks it have been positioned in all of the cavities of a can ill, the car is then moved to the charging end bit of the furnace or oven it, as shown in Fig. 3. The oven it may be provided with suitable gates til at opposite ends of the furnace which are vertically movable and arranged to be operated by any suitable mechanism. When the oven it is below operated a number oi cars it are in end to end relation belit tween the charging end lit and discharge end it,

as shown in The cars it may be manually moved through the furnace ill at a desired rate or moved intern'littently by suitable hydraulically operated driving mechanism at the charging end it of the oven ill. Such mechanism may be arranged to move the car it at the charging end it which in tum pushes the cars it ahead of it toward the discharge end The intermittent or step by step movement may be accomplished automatically in steps equivalent to the distance between one or a number of iiaslrs and the mechanism op eratlng the gates til may be synchronised with the driving mechanism, whereb the gates will be raised freon a position between adjacent rows oi flasks t to permit the cars to traveller a predetennined short distance and thereafter will be lowered between rows of t and rest on the surfaces of the reiractory tops iii to close oft the ends oi the oven ill when movement or the cars has stopped.

in order to seal the oven space l'l completely train the car chambers d i, the end walls oi the cars it at regions adjacent to the tops are provi ed with refractory wall sections each havilu a pair of iiorlaontal grooves as shown in his. 4.

"ible asbestos rope ti t is secured in any nner, as by screws. for chain-plain one crooves formed at each end ed a car estos rope it at each end of a car "in same elevation as an open groove 55 of an adjacent car it so that. when the cars it are in abutting relation during movement through the l-urnace or oven ill, the asbestos ropes will snugly ilt into the grooves it and 'l'ori'n a gas-tight seal between adjacent cars. The seals formed between adjacent cars ill, together with the seals it formed between the lower ends of the walls ii and the sides of cars it, effectively seal the oven space ll iroin the car chambers In order to seal the openings to ionned between the horizontal slot in the duct it and the openings in the side walls it of the cars l t, compressible asbestos strips b'lare secured to the duct side wall it at the top and bottom edges oi the slot, as shovm in Fig. 1. In addition, compressible asbestos strips it maybe secured to the side walls it of the cars it at the ends of the cars, as shown in Fla. 5. The strips in project or extend beyond the end wallstt of the cars, and adjacent strips of abutting cars snug y v t against till lift

till

lid

bit

6 each other when the cars I8 are moved through the furnace or oven It.

The vertical strips 58 are'co-extensive with the openings in the side walls 33 of the cars and terminate at their upper and lower ends at regions closely adjacent to the horizontal strip bl so cured to the duct to. The strips 51 bear against the side walls it of the cars [18 while the strips lit bear against the sidewall d5 of the duct M. After being in use, the strips 51! and to adjust themselves to close the gap between the duct M and cars ill and at the same time allow the cars to move alongside of the duct with no objectionable rubbing taking place between the duct and the cars. The seals formed by the strips ill and it effectively close oh and seal the openings it formed between the duct it and the side walls of the cars it and also the regions of the duct slot between abutting cars.

The oven space ll is maintained at an elevated temperature, such as 1200" to ii00 PR, for examp e. by controlling the operation or the burners it with the control valves just described. Suitable recording thermometers til maybe provided at one of the side walls l l of the oven ill, as shown in Fig. 3, so that the temperature in ditlerent parts of the oven space ll may readily be determined. If desired, the burners it may be controlled responsive to the temperature within the oven space ll, so that the oven space ill will. a ways he maintained at the desired elevated tomperature.

The investment molds are rapidly heated to a desired h gh temperature by heat derived from the heated products of combustion passing to the fiaslrs ll from the cup-shaped spaces ill, and by heat radiated from the incandescent Wall surfaces forming the cup-shaped spaces, whereby the wax models i are melted and the wax flows down-- wardly by gravity from the investment molds through the openings ill in the refractory tops ill into the trays ill in car chambers ll.

The products of combustion are withdrawn from the bottom part of the oven space it through the vertical conduits ill, and such spent gases mix with air drawn into the draft hoods it by the exhaust fans The mrrture of air and the products of combustion may be discharged by the i'ans ill to the exterior of the enclosure in which the oven it is installed.

in many instances the Wax models i may be of such design that all of the wax can be removed from the investment molds simply by melting the wax to cause iiow thereof by gravity into the car chambers ii. However, in many cases the wax models are of intricate design and formed with traps i from which melted wax cannot freely flow by grav ty. as shown in Fla. 2. Any melted was which is trapped in the investment inc'ds is heated above the flash point temperature during movement of the flasks it through the oven space ii, and the was vapors thus formed pass from the investments t through the openings it into the car chambers ii. The wax vapors passing into the car chambers ii are diluted by relatively cool atmospheric air drawn into the car chambers through the openings ll! by the action of the exhaust fans ill. The wax vapors in the car chambers it are materially diluted by atmospheric air to produce a gas mixture containn'z air in an amount considerably above that which would produce an explosive mixture. Further, since the wax vapors are immediately cooled by mixing with relatively cool atmospheric air pass- 111g into the car chambers M, the likelihood of 6 forming-an explosive hydrocarbon gas mixture of the wax vapors is avoided. The mixture of wax vapors and air passes from the car chambers il through the openings 46 into the duct 44 and thence through the vertical lines 48 to regions of conduits 30 immediatel adjacent the inlets of exhaust fans 31. The mixture of wax vapors and air mixes with the gas mixture entering conduits 30 from the draft hoods 26 which, as previously stated. is discharged from the exhaust fans to the exterior of the enclosure in which the oven 10 is installed.

While practically the full suction effect of the exhaust fans 3| is reflected back through the fines 4B and duct 44 to the car chambers 41, this is not true with respect to the oven space I] by reason of the draft hoods 29 provided at the upper ends of vertical conduits 26. The pressure in oven space H may be maintained at atmospheric or slightly above that of atmosphere while the pressure in chambers 41 will be slightly below the- I pressure in the oven space 'i'i. Inthe event of leakage between the oven space H and the car chambers 48, therefore, outward flow of gas will always take place from the oven space H and wax vapors passing into the chambers 91 from the flasks 5'cannot pass from the car chambers into the oven space.

During the travel of the flasks 5 through the oven space I], curing and baking of the invest ment material is effected simultaneously with the removal of the wax from the investment 5. When the flasks 5 reach the discharge end 52 of the oven 19, the refractory investment material has pedite production. After the flasks 5 are placed on a car I8 and such car is moved through the oven space ll, the flasks 5 after passing through the oven space are ready for casting.

If desired, the oven 10 may include a coolim zone at the discharge end 52. The cooling zone may be contiguous to the oven space it and tion has been shown and described, it will be apparent to those skilled in the art that changes can be readily made and that certain features may be used independently of others without departing from the spirit and scope of the invention. .While the oven 10 shown is of a direct gas fired type having radiant burners 2| of the kind described, the oven or furnace may be provided' with burners other than those described, or the oven may be of an indirect gas fired type or an electrically heated oven. I therefore aim in the following claims to cover all such changes and modifications as fall within the true scope of the invention. I

What is claimedis:

1. The art of removing wax from an investment having a cavity therein with a passage extending from the cavity to a surface of the investment comprising converting the wax from a solid to a fluid state by subjecting the investment to a source of heat above the melting point of the we! in a first space, flowing the melted wax downwardly through the passage from the investment in a path of flow which is out of physical contact with the first space and includes a second space below and separated from the first space by a, wall, and producing a. suction effect in said second space to maintain the pressure inseid second space at a value below that of said am space and of the atmosphere whereby atmospheric air can be drawn into said second space to cool the melted wax.-

2. In the art of removing wax from investments having cavities opening to exterior surfaces thereof, such wax being held in the cavities and convertible from a solid to a fluid state by heating, the improvement which comprises moving a group of investments through a heating space, heating the investments as they are moving through said heating space by subjecting them to a high temperature source of heat above the melting point of the wax, flowing the melted wax through the openings in the investments downwardly in a path of flow which is out of physical contact with the heating space and includes a second space below and separated from the heating space by a wall, producing a suction effect in saidsecond space to maintain a pressure therein lower than the pressure in said heating space, and controlling the heating of the investments by regulating the. heat source at different zones in said heating space.

CARL, P. MANN.

' REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,070,500 Mackenzie Aug. 19, 1913 1,199,429 Roth Sept. 26, 1916 1,291,588 Maves Jan. 14, 1919 1,362,809 McManus Dec. 21, 1920 1.484300 Stark Feb. 26, 1924 1,497,514 Knapp June 10, 1924 1,499,207 Folsom June 24, 1924 1,534,592 Houck Apr. 21, 1925 1,596,214 OBrien Aug. 17, 1926 1,639,253 Ayers Aug. 16, 1927 1,658,084 Hudson Feb. 7, 1928 1,659,638 Shapiro Feb. 21, 1928 1,660,869 Feike et a1 Feb. 28, 1928 1,796,470 Meyer Mar. 17, 1931 1,822.285 Hagman Sept, 8, 1931 1,835,411 I Lewis Dec. 8, 1931 1,863,445 Kerr .4 June 14, 1932 1,914,718 Hagman June 20, 1933 1,942,981 Schmitz Jan. 9, 1934 2,017,337 Berryman Oct. 15, 1935 2,080,059 Peebles May 11,1937 2,112,310 Schultz Mar. 29, 1938 2,281,184 Dykstra et a1 Apr. 28, 1942 2,398,874 Weyhing Apr. 23, 1946

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