US2518040A

US2518040A - Apparatus for producing investment molds

Info

Publication number: US2518040A
Application number: US682407A
Authority: US
Inventors: Carl P Mann
Original assignee: Selas Corp of America
Current assignee: Selas Corp of America
Priority date: 1946-07-09
Filing date: 1946-07-09
Publication date: 1950-08-08
Anticipated expiration: 1967-08-08

Description

Aug. 8, 1950 c. P. MANN 2,518,040

APPARATUS FOR PRODUCING INVESTMENT 'MOLDS Filed July 9, 1946 2 Sheets-Sheet 1 Eug.

Aug. 8, 1950 C. P. MANN APPARATUS FOR PRODUCING INVESTMENT MOLDS 2 Sheets-Sheet 2 Filed July 9. 1946 w -ac lcc;

QV. Ww mm1 Patented Aug. 8, T950 APPARATUS FOR PRODUCING INVESTMENT MOLDS Carl P. Mann, Riverton, N. J., assignor to Selas Corporation of America, Philadelphia, Pa., a corporation of Pennsylvania Application July 9, 1946, Serial No. 682,407

5 Claims. l

This invention relates to apparatus for producing investment molds. This application is a continuation in part of my application Serial No. 548,993, filed August ll, 1944, now Patent No. 2,496,170 issued January 31, 1950.

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 of which:

Fig. 1 is a vertical sectional view of apparatus embodying the invention;

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

Fig. 3 is a side elevation of the apparatus illustrated in Fig. 1;

Fig. 4 is an enlarged fragmentary vertical -sectional view of adjacent cars illustrated in Figs. 1

and 3;

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

Fig. 6 is a fragmentary sectional view similar to Fig. 2 illustrating a modification of the invention.

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 t which are attached one or more sprues. The form and shape that a model may assume is diagrammatically illustrated at l in Fig. 2 and may include a number of patterns 2 connected by runners 3 and a sprue 4 which extends to the extreme end of a flask which may be in the form of a metal ring. The runners and sprues of wax are formed separately from the patterns and attached thereto by heating irons in a well known manner.

The model I is then embedded in a material referred to as an investment E 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 l is completely enveloped by the investment 6, as illustrated in Fig. 2, and, before the refractory material of the investment has set, the ask 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 thesurfaces of the patterns.

The wax is then removed from the investments 6 and the latter cured or baked to prepare the iiasks 5 for casting. The metal is poured while the flask is at an elevated temperature to assure fluidity of the metal Vwhich 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 of 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 deposit of free carbon therein.

In order to make certain that the wax vapors cannot pass into the oven space in the event of 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 flow 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 ows 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 l of a direct gas fired type having vertical walls II and a roof I2 formed of suitable refractory material. The vertical walls II and roof I2 are disposed within a framework or outer shell I4 having a number of legs I5 for supporting the oven I8 on a. suitable supporting surface I6.

The flasks to be heated in space I1 Within the oven I0 are mounted on cars |18, as will be described presently, which are moved through the oven space I1 on a track I9. A suitable seal, such as, for example, a sand seal, is provided between the lower edges of side walls I I and opposite sides of the cars I8, as indicated at 2li in Fig. 1.

A number of burners 2| are mounted in and form a part of the roof I2. The burners 2| are disposed alongside of each other in a plurality of ro-ws, the number and disposition of the burners being such that the desired heating is effected of the asks 5 passing through the oven space I1.

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 24 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 24, and the supply of the gas mixture for each burner 2| may be individually controlled by valves 25 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 26 which is fixed to the inner end of the sleeve 22 and terminates at a cup-shaped space 21. The burners 2| are of such a type that combustion of the gas mixture is substantially completed in the cupshaped spaces 21, whereby flame impingement of the asks 5 is readily avoided.

The refractory wall surfaces of the cupshaped 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 I1, provides a heating effect which is readily controlled to effect the desired heating of the flasks 5 during their travel through the oven III.'

Thegburners 2| are of the kind described and illustrated in Hess Patent No. 2,215,079, granted /chjfJune 23, 1942 and assigned to the same asf signee 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 for withdrawing products of combustion from the oven space I1. 'I'he lower ends of the conduits 28 terminate at the inner surfaces of the side wal-ls II adjacent the bottom of the oven space I1, and the upper ends thereof extend upwardly and terminate a short distance from the top of the oven I 0. 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 vboth of the side walls II and at spaced intervals along the o ven I0, 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 I1. 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 al1 of the useful heat has been given up in the oven space |1. Thel 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 38 and exhaust fans 3| to handle gases at an unduly high temperature.

A number of cars I8 are provided for movement through the oven I0 on the track I9. Each car I8 includes a box-like frame 32 enclosed by side walls 33 and 34, end walls 35 and a bottom 36 which may be fo-rmed of sheet metal. The tops 31 of the cars I8 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 48 may be moved into and withdrawn from the chamber 4I within the car. The frame 32 of each car is provided with side sills 42 for supporting the tray 4U 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|.

The cars I8 are maintained close together during their travel through the furnace or oven I0, so that the to-ps 31 of adjacent cars abut each other and collectively form the bottom or floor of the oven space l1. A horizontal duct 44 is disposed directly beneath one of the side walls Il and extends lengthwise of the oven I0 alongside the cars I8, 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 I8, as indicated at 46 in Fig. 1. The side wail 45 of the duct and side walls 33 of the cars II! 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 passes from the upper ends of the flues 48 into the conduits 38 at regions closely adjacent to the in-` lets of the exhaust fans 3l.

In the operation of -the apparatus just described the liasks 5, having Vthe wax models I enveloped therein by investment material 8, are placed in the cavities 39 formed in the refractory top 31 of a car I8.' As shown in Fig. 2, the flask 5 is in what is referred to as an inverted .position and the sprue 4 of the model I extends downwardly into and communicates with one of the openings 38 in the refractory top 31. The flasks 5 lit snugly and accurately in the cavities 39 to provide a gas tight seal between the flasks and the refractory top 31.

Afterthe flasks 5 have been positioned in all of the cavities 39 of a car I8, the car is then moved to the charging end 58 of the furnace or oven '|0, as shown in Fig. 3. The oven I8 may be provided with suitable gates 5I at opposite ends of the furnace which are vertically movable and arranged to be operated by any suitable mechanism. When the oven I is being operated a number of cars I8 are in end to end relation between the charging end 50 and discharge end 52, as shown in Fig. 3.

The cars I8 may be manually moved through the furnace I8 at a desired rate or moved intermittently by suitable hydraulically operated driving mechanism at the charging end 50 of the Atoven Il). Such mechanism may be arranged to move the car I8 at the charging end 50 which in turn pushes the cars I8 ahead of it toward the discharge end 52. The intermittent or 'step by step movement may be accomplished automatically in steps equivalent'to the distance between one or a number of flasks 5, and the mechanism operating the gates I may be synchronized with the driving mechanism, whereby the gates will be raised from a position between adjacent rows of flasks 5 to permit the cars to travel for a predetermined short distance and thereafter will be lowered between rows of flasks 5 and rest on the surfaces of the refractory tops 31 to close off the endsof the oven I0 when movement of the cars I8 has stopped. Y

In order to seal the oven space I1 completely from-the car chambers 4I, the end walls 35 of the cars I8 at regions adjacent to the tops 31 are provided with refractory wall sections each having a pair of horizontal grooves, as shown in Fig. 4. Compressible asbestos rope 58 is secured in any suitable manner, as by screws, for example, in one of the two-grooves 55 formed at each end of a car I8. The asbestos rope 58 at each end of a car I8 is at the same elevation as an open groove 55 of an adjacent car I8 so that, when the cars I8 are in abutting relation during movement through the furnace or oven I0, the asbestos ropes will snugly fit into the grooves 55 and form a gastight seal between adjacent cars. The seals formed between adjacent cars I8, together with the seals 28 formed between the lower ends of the walls II and the sides of cars I8, effectively seal the oven space I1 from the car chambers 4 I In order to seal the openings 4B formed between the horizontal slot in the duct 44 and the open- -'ings in the side walls 33 of the cars I8, compressible asbestos strips 51 are secured to the duct 5 side wall\45 at the top and bottom edges of the v slot, as shown in Fig. l. In addition, compressible asbestos strips 58 may be secured to the side walls 33 of the cars I8 at the ends of the cars, as shown in Fig. 5. The strips 58 project or extend beyond 10 the endwalls 35 of the cars, and adjacent strips of abutting cars snugly flt against each other when the cars I8 are moved through the furnace or oven I8.

The vertical strips 58 are co-extensive with the `l54 openings in the sidewalls 33 of the cars and terminate at their upper and lower ends at regions closely adjacent to the horizontal strips 51 secured to the duct 45. The strips 51 bear against the side walls 33 of the cars I8 while the strips 58 bear against the side wall 45 of the duct 44.

After being in use, the strips 51 and 58 adjust themselves to close. the gap between the duct 44 and cars I8 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 51 and 58 effectively close olf and seal the openings 46 formed between the duct 44 and the side walls 33 of the cars I8 and also the regions of the duct slot between abutting cars.

The oven space I1 is maintained at an elevated temperature, such as 1200 to l400 F.,for example, by controlling the operation of the burners 2I with the control valves just described. Suit- 35 able recording thermometers 53 may be provided at one of the side walls I I of the oven I0, as shown in Fig. 3, so that the temperature in different parts of the oven space I1 may readily be determined. If desired, the burners 2l may be controlled responsive to the temperature within the oven space I1, so that the oven space I1 will always be maintained at the desired elevated temperature.

The investment molds are rapidly heated to a ldesired high temperature by heat derived from the heated products of combustion passing to the flasks 5 from the cup-shaped spaces 21, and by heat radiated from the incandescent wall surfaces formng the cup-shaped spaces, whereby the wax models I are melted and the Wax flows downwardly by gravity from the investment molds through the openings 38 in the refractory tops 31 into the trays 40 in car chambers 4I.

The products of combustion are withdrawn 56 from' the bottom part of the oven space I1 through the vertical conduits 28, and such spent gases mix with air drawn into the draft hoods 29 by the exhaust fans 3|. The mixture of air and the products of combustion may be dis- 00 charged by the fans 3| to the exterior of the enclosure in which the oven I0 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 35 melting the wax to cause flow thereof by gravity into the car chambers 4I. However, in many cases the wax models are of intricate design and formed with traps 1 from which melted wax cannot freely flow by gravity, as shown in Fig. 2.

Any melted wax which is trapped in the investment molds is heated above the liash point temperature during movement of the flasks 5 through the oven space I1, and the wax vapors formed pass from the investments 6 through the openings 38 into the car chambers 4 I The wax vapors passing into the car chambers 4I are diluted by relatively cool atmospheric air drawn into the car chambers through the openings 41 by the action of the exhaust' fans 3|. The wax vapors in the car chambers 4I are materially diluted by atmospheric air to produce a gas mixture containing 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 passing into the car chambers 4I, the likelihood of forming an explosive hydrocarbon gas mixture of the wax vaporsris avoided. The mixture of wax vapors and air passes from the car chambers 4I through the openings 46 into the duct 44 and thence through the vertical ues 48 to regions of conduits 30 immediately adjacent the inlets of exhaust fans 3|. The mixture of wax vapors and air mixes with the gas mixture entering conduits 30 from the draft hoods 2S which, as previously stated, is discharged from the exhaust fans to the exterior of the enclosure in which the oven I is installed.

While practically the full suction effect of the exhaust fans 3| is reflected back through the flues 48 and duct 44 to the car chambers 4I, this is not true wml respect to the oven space I1 by reason of the draft hoods 29 provided at the upper ends of vertical conduits 28. The pressure in oven space I1 may be maintained at atmospheric or slightly above that of atmosphere while the pressure in chambers 4I will be slightly below the pressure in the oven space I1. In the event of leakage between the oven space I1 and the car chambers 4I, therefore, outward ow of gas will always take place from the oven space I1 and wax vapors passing into the chambers 4I 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 I1, curing and baking of the investment material is effected simultaneously with the removal of the wax from the investment 6. When the asks 5 reach the discharge end 52 of the oven I0, the refractory investment material has been properly conditioned and cavities are formed therein which are identical in conflguration to the wax models I removed therefrom as the result of the heating just described.

In Fig. 6 is illustrated a modification of the invention in which the flasks 5 are supported on annular-shaped sleeves 59 instead of fitting directly in the enlarged cavities 39 at the tops 31 of the cars I8. The hollow sleeves 5S are preferably formed of a suitable high temperature alloy material and nt snugly and accurately in the cavities 39.

AIn Fig. 6 the ask 5 is supported in its inverted position about the top edge of the hollow sleeve 59. By supporting the flask 5 in a raised position with respect to the refractory top 31 so that the flask only contacts the top edge or rim of the sleeve 59, a poor thermal conductive path ls provided from the flask to the refractory top whereby the heat loss from the flask to the refractory top is minimized. In addition, by supporting the flask 5 in a raised position at the top edge of the hollow sleeve 59, more effective heating of the bottom of the flask is accomplished. This is so because the heated products of combustion in the oven space I1 can pass directly over the exposed investment material s at the bottom or the flask.

In the embodiment first described there is sometimes a tendency for the melted waxpass- 8 ing downwardly through the sprue 4 to flow laterally from the extreme lower end thereof over the bottom exposed surface of the investment material. When this occurs the melted wax is drawn into the investment material by capillary action. In order to free the investment-material of such melted wax, additional heating of the flask 5 is necessary to burn out or oxidize the melted wax drawn into the investment material.

In order to prevent melted wax from passing over the bottom exposed surface of the investment material, the model I in Fig. 6 is formed with a downwardly extending lip or rim 60 at the discharge end of the sprue 4 and the investment material about the sprue is formed to provide an upwardly inclined or arched roof 6I. In the embodiment shown in Fig. 6, melted wax flows downwardly by gravity through the sprue 4 to the rim or lip 60 -at which region drops of melted wax form. The drops of melted wax fall from the lip 60 in rapid succession through the opening 38 in the refractory car top I8 and into the tray 40 in the car chamber 4I. With this construction lateral flow of the melted wax over the bottom exposed surface of the investment material is prevented.

It will now be understood that an improvement has been provided for removing wax from investment material in which a minimum amount of handling of the flasks is required, and in which a large number of investment molds may be prepared for casting at a relatively fast rate to expedite production. After the flasks 5 are placed on a car I8 and such ear is moved through the oven space I1, the flasks i after passing thrOugh the oven space are ready for casting.

If desired.` the oven I0 may include a cooling zone at the discharge end 52. The cooling zone may be contiguous to the oven space I1 and maintained at a temperature lower than that in theoven space, such as 250 to 350 F., for example. In such case the cars I8 pass from the oven space directly into the cooling zone and are then disharged from the heating unit.

Although several embodiments of the invention have beenshown 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 I0 shown is of a direct gas fired type having radiant burners ZI of the kind described, the oven or furnace may be provided with burners other than those described, or the oven may be of an lndirect'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 claimed is:

1. Apparatus for preparing investments for casting including an elongated oven having opposed side walls and a roof of refractory material forming an oven space, a, movable floor of refractory material having a, number of openings therein over each of which is adapted to be positioned an investment. means forming a seal btween the edges of the movable floor and the bottom portions of the side walls, means for heating the oven space, means to withdraw the products of combustion therefrom, means forming a plurality of chambers below the oven space, means in the chambers foxholding melted wax flowing thereto from the investments through the openings, and means for withdrawing wax vapors from the chambers.

2. Apparatus for preparing a number of investments for casting including an elongated oven having opposed side walls and a roof of refractory material forming an Oven space, a number of cars movable lengthwise of the oven and each having a top of refractory material provided with a number of openings therein over each of which is adapted to be positioned an investment, the refractory tops of the cars collectively forming a, movable floor for the oven space, means forming a seal between the edges of the refractory tops and the bottom portions of the side walls, means embodied in each car to provide a chamber below the refractory top, and means in each chamber for holding melted wax flowing thereto from the investments through the openings.

3. Apparatus for preparing a number of investments for casting including an oven having side walls, roof and `floor of refractory material forming an oven space, said floor having a number of openings therein over each of which is adapted to be positioned an investment, means to supply a combustible fuel and combustion supporting gas to the oven space to effect heating of the latter, means forming a chamber below the oven space, means in the chamber for holding melted wax flowing thereto from the investments through the openings, and means includlng a common exhaust fan and passages from the oven space and the chamber to said fan for withdrawing products of. combustion from the oven space and for withdrawing wax vapors from the chamber.

4. Apparatus for preparing a number of investments for casting including an oven having side walls, roof and floor of refractory material forming an oven space, said floor having a number of openings therein over each of which is adapted to be positioned an investment, means to supply a combustible fuel and a combustion supporting gas to the oven space t effect heating of the latter, 9, vertically extending conduit having the lower end thereof communicating with the oven space, a. draft hood at the upper end of said conduit, means forming a chamber below the oven space, a vertical flue having the lower end communicating with said chamber,

means in the chamber for holding melted wax flowing thereto from the investments through the openings, said chamber having an aperture to admit air from the surroundings into the chamber to mix with wax vapors passing into the chamber from the investments through the openings, and a common exhaust fan connected to the draft hood and to the upper end of the ilue.

5. Apparatus for preparing an investment for casting including an elongated oven having a roof and opposed side walls of refractory material forming an oven space, a number of cars movable lengthwise of the oven and each having a. top of refractory material provided with openings over each of which is adapted to be positioned an investment, the refractory tops of the cars collectively forming a movablefloor for the oven space, means forming a seal between the sides of said oven and the tops of said cars, means between the ends of said cars to form a seal whereby said oven space is substantially closed around its entire periphery, and means carried by each car below said top for holding melted wax flowing from investments mounted thereon.

CARL P. MANN.

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

UNITED STATES PATENTS Number Name Date 1,199,429 Roth Sept. 26, 1916 1,291,588 Maves Jan. 14, 1919 1,294,756 Benjamin Feb. 18, 1919 1,484,800 Stark Feb. 26, 1924 1,497,514 Knapp June 10, 1924 1,499,207 Folsom June v24, 1924 1,534,592 Houck Apr. '21, 1925 1,596,214 OBrien Aug. 17, 1926 1,602,808 Burnham Oct. 12, 1926 1,639,253 Ayers Aug. 16, 1927 1,796,264 Grondal Mar. 10, 1931 1,914,718 Hagman June 20, 1933 2,112,310 Schultz Mar. 29, 1938 2,157,975 Wilson May 9, 1939 2,160,645 Cooper May 30, 1939 Weyhing Apr'. 23, 1946