US3870444A

US3870444A - Plant for producing wax patterns for use in investment casting

Info

Publication number: US3870444A
Application number: US321676A
Authority: US
Inventors: Malachy Herron
Original assignee: Rover Co Ltd
Current assignee: Rover Co Ltd
Priority date: 1973-01-08
Filing date: 1973-01-08
Publication date: 1975-03-11
Anticipated expiration: 1992-03-11

Abstract

Wax patterns for use in an automatic flow-production investment casting plant are produced, in an extrusion-press die, by filling the die from a substantially cylindrical wax billet obtained by severance from a continuous extrusion of plastic wax issuing from a tube which is subjected to controlled heating, whereby the boundary layer of wax in the tube is melted to leave a solid core of wax affording a billet which has a smooth surface and is of the same diameter as the die opening.

Description

O United States Patent 1 1 1111 3,870,444

Herron Mar. 11, 1975 [54] PLANT FOR PRODUCING WAX PATTERNS 2,469,342 5/1949 Richardson 425/297 X FOR USE IN INVESTMENT CASTING 2,885,727 5/1959 Wright 425/297 X 3,368,244 2/1968 Mueller 164/45 X [75] Inventor: Malachy Herrera, a eso en, 3,612,147 10/1971 Kaplan 164/45 England [73] Assignee: British Leyland UK Limited, Primary p f" l London, England Attorney, Agent, or F1rmBr1sebo1s & Kruger [22] Filed: Jan. 8, 1973 [57] ABSTRACT [21] Appl' N07 3212676 Wax patterns for use in an automatic flow-production investment casting plant are produced, in an extru- 52 us. c1 425/143, 425/217, 425/297, Sim-Press die, by filling the die from Substantially 425/327, 264/145, 164/45 cylindrical wax billet obtained by severance from a 51 Int. (:1. B296 24/00, BZZC 7/02 Continuous extrusion of plastic Wax issuing from a 53 Field f Search 1 4/5 5; 425 297 3 5 tube which is subjected to controlled heating, whereby 425/327 143 217; 2 4 145 the boundary layer of wax in the tube is melted to leave a solid core of wax affording a billet which has a 5 References Cited smooth surface and is of the same diameter as the die UNITED STATES PATENTS Openmg 2,439,506 4/1948 Christian 164/45 UX 7 Claims, 7 Drawing Figures PATENTEB MARI 1 I975 SHEET 1 0F 5 PATENTED NARI 1 I975 SHEET 2 OF 5 PATENTEU MARI 1 I975 SHEET 3 OF 5 PATENTEU NARI 1 I975 sum 5 OF 5 PLANT FOR PRODUCING WAX PATTERNS FOR USE IN INVESTMENT CASTING This invention relates to the production of wax patterns, and is primarily intended to be used in an automatic flow-production investment casting plant.

In general, two alternative methods of producing wax patterns are extant in investment casting foundries, namely: (a) making a hollow die into which molten wax is poured and allowed to solidify: and (b) heating granulated wax and injecting it in a plastic condition into a die. Method ((1) is unduly costly because it not only necessitates using a lot ofdies to achieve quantity production, but it requires an expensive grade of wax; also, very considerable shrinkage occurs between the liquid and solid phases. Method (b) is prone to cause entrapment of air in the pattern, and also to engender uneven heating of the wax; both of these disabilities giving rise to patterns of non-uniform quality.

According to this invention a method of producing, in an extrusion-press die, a wax pattern for use in investment casting, comprises: making a substantially cylindrical wax billet which is in a plastic condition, is of the same diameter as the die opening and has a volume at least equal to the volumetric capacity of the die; locating the billet coaxially with respect to the die opening; and extruding the billet to fill the die.

The wax pattern die is in two halves which, before being brought together, are sprayed with a releasing agent to facilitate removal of the pattern. The remaining sequence of operations is as follows:

1. A holder for the wax pattern is placed in that die half which is carried by the movable platen of the extrusion press.

2. The halves ofthe die are brought together and held under pressure applied hydraulically to the movable platen of the press.

3. A substantially cylindrical wax billet (in a plastic condition, and of the correct dimensions) is placed in a breech in front of the die opening, this opening being located at the fixed platen of the press.

4. The ram of the press is operated to force the billet through the die opening until the wax fills the die.

5. Upon termination of injection ofthe wax, the fixed die (which contains the pattern) is cooled by an air blast for from about seconds to about 2 minutes, depending upon the size and shape of the wax pattern.

6. The die is opened by retracting the movable platen of the press, and the wax pattern is ejected in any of several known ways.

The holder mentioned at (1) above is preferably as set forth and claimed in British Specification No. 1,196,533.

As usual, when wax patterns of sufficiently small articles are to be produced for use in investment casting, several patterns can be made conjointly as a so-called tree (i.e., an assemblage of individual patterns conjoined with the requisite feed-ducts).

To achieve a sufficiently high rate of output of wax patterns to meet the demand imposed by a flowproduction investment casting plant. the requisite wax billets also have to be available. A convenient way of producing the billets is to employ a machine of the same kind as used in the manufacture of margarine, and known as a Votator.

A plant for use in carrying the invention into effect is characterized by having each of the following features:

a. an extrusion press incorporating a die for the wax pattern to be produced;

b. a container holding molten wax;

c. a machine by means of which molten wax supplied to it from the container is transformed into a continuous extrusion of plastic wax having a circular crosssection of the same diameter as the die opening;

d. the machine specified at (c) is arranged so that the extrusion of plastic wax issues from an outlet tube lying parallel to the line of action of the extrusion press;

2. a breech adjoining, and in alignment with, the die opening; and

f. a transfer mechanism which removes from the outlet tube a substantially cylindrical wax billet having a volume at least equal to the volumetric capacity of the die, and which conveys the billet to the breech, the latter locating the billet coaxially with respect to the die opening preparatory to the press extruding the billet to fill the die.

Referring to the accompanying drawings:

FIG. 1 is a schematic plan view of the general arrangement ofa plant for producing wax patterns by the method of the invention;

FIG. 2 is a broken end elevation of two hydraulic presses and an associated transfer mechanism, which are components of the assembly depicted in FIG. 1',

FIG. 3 is a part-sectional view on the line III-Ill in FIG. 2;

FIG. 4 is a fragmentary plan view of a portion of the plant illustrated in FIG. 1;

FIG. 5 is a perspective view, partly in section, of one half of a cylindrical, electrically heated, wax-transfer tube assembly which forms part of the transfer mechanism shown in FIG. 2;

FIG. 6 is a perspective view of a breech and ram pertaining to each of two hydraulic presses in the plant illustrated in FIG. 1; and

FIG. 7 is a schematic plan view illustrating a system of knife, edges which may advantageously be added to the plant depicted in FIG. 1.

The plant illustrated in FIG. 1 produces wax patterns for use in an automatic flow-production investment casting plant.

Molten wax, contained in a holding tank 1, is passed through a mesh filter (not shown) to effect removal of various possible solid contaminants. (These have been found to include: bits of cardboard from the cartons in which the wax is supplied; grit from a neighbouring shot-blaster; and dust from the ceramic shell coating unit ofthe investment casting plant). Under the control of an outlet valve 2, fitted to a delivery pipe 3, a pump 4 draws the filtered molten wax from the tank I and delivers it, via a pipe 5, to a machine 6 of the same kind as used in the manufacture of margarine, and known as a Votator.

In passing, it is to be mentioned that the wax pump 4 is continuously heated by a steam jacket 7 having a steam inlet 8 and an outlet 9 (which leads to a drain). As the pump 4 is kept continually hot, the wax is prevented from solidifying in it. A tray 10 is positioned to.

collect any wax which may drip from the pump 4. A valve-controlled steam supply pipe 11 is connected to the wax-delivery pipe 3 to preheat it before starting the plant, and also to cleanse the system after cessation of operation.

Reverting to the above-mentioned Votator 6, of known construction, molten wax is pumped (via the pipe 5) into its working chamber, which is surrounded by a cooling jacket through which passes (in counter current) a controlled flow of cold water. A shaft driven by a 5 HP. motor is situated in the working chamber, and the molten wax flows downwardly between the shaft and the cooled chamber walls, on which it congeals in the form of a film. This wax film is removed from the walls by scraper blades which are rotated by the shaft, and the arrangement is such that the pressure exerted by the molten wax (pressurized by the pump 4) causes a continuous extrusion or sausage of plastic wax to issue from an outlet tube 12. The wax sausage (which has a circular cross-section of the same diameter as the die opening referred to earlier) is chopped into substantially cylindrical billets of predetermined length, such that the volume of each billet is at least equal to the volumetric capacity of the die of the above-mentioned extrusion press; and these billets are then inserted one at a time into the press to produce successive patterns in its die.

Experimental tests have shown that the wax delivered by the Votator 6 becomes superficially chilled during passage through the outlet tube 12; causing a skin of wax to be left adhering to the interior surface of the tube. In consequence, the extruded wax sausage has an undesirably rough surface and is also of smaller diameter than required. These defects are obviated by employing a subsidiary feature of the invention, namely, having means whereby controlled heating of the outlet tube 12 of the Votator 6 is effected to melt the boundary layer of the wax in this tube. Such heating is preferably effected by coiling around the outlet tube 12 an electrical heating tape 13 the current through which is controlled by a preset temperature sensor 14. The solid core of wax (which, in effect, floats on the liquid boundary layer) has a smooth surface, and also has the required diameter, upon emerging from the outlet tube 12.

So far, reference has been made to the use of only one extrusion press. But in the preferred mode of carrying the invention into effect two extrusion presses A and B are operated concurrently in order to increase the rate of production of wax patterns. These presses are located at opposite sides of, and equidistantly from, the outlet tube 12 of the Votator 6, and are disposed so that the line of action of each press is parallel to the length of the outlet tube 12. Each of the presses A and B has two fixed

platens

15 and 16, and a movable platen 17. The two halves of the wax pattern die (not shown), which are mounted respectively on the fixed platen l5 and on the movable platen 17, are brought together and held under pressure applied hydraulically to the movable platen 17. The presses A and B must be set up so that the left-hand faces of the platens 15 (as viewed in FIG. 1) are coplanar.

Each of the presses A and B has a breech 18 which adjoins, and is in alignment with, the die opening (located at the corresponding platen 15). In each case the press has its ram 19 (see FIGS. 3, 4 and 6) operated by an hydraulic cylinder 20, which is fixed to a support frame 21 and is served by an hydraulic power pack 22.

The breech l8 pertaining to each press is of semi- I cylindrical shape (see FIGS, 2 and 6), and has a pair of a bracket 26 (FIG/3) fixed to the support frame 21,

and is secured to the flanges 25 by screws 27 (FIG. 6).

A transfer mechanism 28 is employed to convey each wax billet, in turn, from the outlet tube 12 to the breech 18 of either the press A or the press B. This mechanism (see FIG. 2) has two tube-

carriers

29 and 30 each carrying its own transfer tube 31, which is just long enough to hold a wax billet of the required length. Each of the transfer tubes 31 is heated in the same manner as the outlet tube 12 of the Votator 6 (FIG. 1) and, in effect, may be regarded as constituting a laterally movable section of that tube. FIG. 5 depicts how each of the transfer tubes 31 (the one represented here being shown in central longitudinal section) is held in a cylindrical sleeve 32. The latter is made in two halves recessed to accommodate a thermostatically controlled electric heating tape 33 coiled around the transfer tube 31. The two halves of the sleeve 32 locate on recessed end zones of the transfer tube 31, and have holes 34 for screws 35 (see FIG. 2) by which they are clamped together.

The two tube-

carriers

29 and 30 are slidably mounted on two

horizontal guide rails

36 and 37, which are spaced apart vertically and disposed parallel to the vertical plane containing the end faces ofthe fixed platens 15 of the presses A and B. The ends of the guide rails 36 and 37 are supported in brackets 38, each of which is located vertically by an adjusting bracket 39 before being secured to the corresponding press platen 15.

The tops of the tube-

carriers

29 and 30 are rigidly interconnected, by a plate 40, at a horizontal spacing such that when onetransfer tube 31 is in the breech 18 of either the press A or the press B, the other transfer tube 31 is aligned with the outlet tube 12 ofthe Votator 6 and is receiving its charge of plastic wax.

The transfer mechanism is operated by an hydraulic cylinder 41 mounted on the plate 40 and having its piston rod 42 fixed to one of the brackets 38. The cylinder 41 is fitted near its ends with hydraulic hoses (not shown) which alternately effect admission and exhaust of hydraulic fluid at opposite sides of the fixed piston; so that the tube-

carriers

29 and 30 are caused, by the operation of the cylinder 41, to slide along the guide rails 36 and 37 first in one direction and then (upon reversal of the flow of hydraulic fluid) in the opposite direction.

The tube-

carriers

29 and 30 have their lower end portions recessed, below a demarcation line 43, to accommodate the thickness of each of two pivot blocks 44 which are fixed to opposite ends of a pivot shaft 45 that lies parallel to the length of the transfer tube 31. The pivot blocks 44 are shaped to conform to the curvature of the sleeve 32, and the latter is secured to them by screws; the arrangement being such that each of the pivot blocks 44 is flush with the corresponding end of the sleeve 32. The pivotal mounting of the transfer tube 31 allows accurate alignment of the wax billet in the breech 18, in the manner already described. The tube-

carriers

29 and 30 are each fitted with a springloaded plunger 46., although only the one pertaining to the tube-carrier 29 is illustrated. In each case the plunger 46 acts radially upon the corresponding sleeve 32 to urge it downwardly against an adjustable stop (not shown), which determines the downward limit of pivotal movement of the sleeve 32 about the axis of the shaft 45.

When the plant is in operation, plastic wax issues continuously from the outlet tube 12 of the Votator 6, and emerges from the transfer tube 31 whenever either of the tube-

carriers

29 and 30 is in alignment with the outlet tube 12. Referring to FIG. 7, one of the transfer tubes 31 (having been moved from its position of registration with the outlet tube 12) is depicted on its way to the breech 18 of the press A. The wax sausage has consequently been sheared, but excess wax 47 protrudes from the exit end of the transfer tube 31. There may also be an excess of wax at the entry end of that tube.

To ensure that every wax billet received by the breech 18 is of the correct length, i.e., such that each end of the billet is flush with the corresponding end of the transfer tube 31, two knife-edge systems are employed (one for each of the presses A and B). The system illustrated in FIG. 7, comprising two

vertical knifeedges

48 and 49, is associated with the press A; and a duplicaate of it, located at the opposite side of the centre line of the outlet tube 12, serves the press B. The knife-

edges

48 and 49 are individually adjustable horizontally to a position such that each scrapes any surplus wax off the corresponding end of the transfer tube 31 as this passes through the gap between the knife-

edges

48 and 49, on its way to the breech 18. The knife-edge 48 is mounted on a stand 50 secured to the floor, and the knife-edge 49 is mounted on the platen of the corresponding press.

The movement of the transfer mechanism 28 (FIG. 2) is stopped automatically when one of the transfer tubes 31, charged with its wax billet, has been placed in the breech 18 of either the press A or the press B. The transfer tube 31 remains in the breech until the ram 19 of the press, having performed its working stroke, returns to its fully retracted position. The transfer mechanism 28 then operates to return the empty transfer tube 31 for this to be charged with another wax billet. The other transfer tube 31, having already been charged with its wax billet, is now in the breech 18 of the other press.

The surplus wax issuing from the outlet tube 12 of the Votator zjor from one of the transfe r tubes 31 when it is in registration with the outlet tube 12, falls into a melting unit 51 (FIG. 1). This comprises a doublewalled tank 52, the cavity between the walls being filled with oil which is electrically heated under thermostatic control. To aid its melting, the surplus plastic wax is also heated by falling through a steam-heated coil 53 of copper tubing situated at the top ofthe tank 52; the coil 53 being a helically wound structure of frustoconical shape.

By means ofa steam-jacketed pipe 54 and a pump 55 (having an inlet at 56 and an outlet at 57) molten wax from the tank 52 is returned to the holding tank 1 for re-use.

I claim:

1. A plant for use in producing a wax pattern for use in investment casting which comprises:

a. an extrusion press incorporating a die for the wax pattern to be produced;

b. a container for holding molten wax;

c. a machine supplied with molten wax from said container for forming said wax into a continuous extrusion of plastic wax having a circular cross-section of the same diameter as the die opening;

d. said machine having an outlet tube lying parallel to the line of action ofthe extrusion press and from which said extrusion of plastic wax issues;

. a breech adjoining, and in alignment with, the die opening; and

. a transfer mechanism comprising a heated transfer tube movable between a position in alignment with said outlet tube in which it receives from the outlet tube a substantially cylindrical wax billet having a volume at least equal to the volumetric capacity of the die, and a position within said breech, and means for moving said transfer tube laterally between said two positions, said breech being positioned to locate the billet coaxially with respect to the die opening preparatory to extrusion of the bil let by the press from the breech to fill the die.

2. A plant according to claim 1, in which the breech is of semi-cylindrical shape and has a pair of longitudinal slots located symmetrically with respect to the longitudinal axis of said breech and accommodating stopplates which jointly define a V-block to ensure accurate alignment of the wax billet in the breech.

3. A plant according to claim 1, comprising two vertical knife edges defining a gap through which the transfer mechanism, in the course of its movement towards the breech, passes and by means of which any surplus wax is scraped off the ends of the wax billet.

4. A plant according to claim 1, comprising a thermostatically-controlled melting unit from into which surplus wax issuing from the outlet tube falls and from which molten wax is pumped, through a steamjacketed pipe, to the holding tank for reuse.

5. A plant according to claim 1, having means whereby controlled heating of the outlet tube is effected to melt the boundary layer of the wax in it.

6. A plant according to claim 1, in which the transfer tube is held in a cylindrical sleeve made in two halves which are recessed to accommodate a thermostatically controlled electrical heating tape coiled around the transfer tube.

7. A plant according to claim 3, in which said transfer mechanism comprises a sleeve holding the transfer tube and mounted on a pivot shaft that lies parallel to the length of this tube, and a radial spring-loaded plunger urging the sleeve against an adjustable stop determining the downward limit of pivotal movement of the sleeve.

Claims

1. A plant for use in producing a wax pattern for use in investment casting which comprises: a. an extrusion press incorporating a die for the wax pattern to be produced; b. a container for holding molten wax; c. a machine supplied with molten wax from said container for forming said wax into a continuous extrusion of plastic wax having a circular cross-section of the same diameter as the die opening; d. said machine having an outlet tube lying parallel to the line of action of the extrusion press and from which said extrusion of plastic wax issues; e. a breech adjoining, and in alignment with, the die opening; and f. a transfer mechanism comprising a heated transfer tube movable between a position in alignment with said outlet tube in which it receives from the outlet tube a substantially cylindrical wax billet having a volume at least equal to the volumetric capacity of the die, and a position within said breech, and means for moving said transfer tube laterally between said two positions, said breech being positioned to locate the billet coaxially with respect to the die opening preparatory to extrusion of the billet by the press from the breech to fill the die.

2. A plant according to claim 1, in which the breech is of semi-cylindrical shape and has a pair of longitudinal slots located symmetrically with respect to the longitudinal axis of said breech and accommodating stop-plates which jointly define a V-block to ensure accurate alignment of the wax billet in the breech.

4. A plant according to claim 1, comprising a thermostatically-controlled melting unit from into which surplus wax issuing from the outlet tube falls and from which molten wax is pumped, through a steam-jacketed pipe, to the holding tank for re-use.