US3450190A

US3450190A - Low pressure casting apparatus

Info

Publication number: US3450190A
Application number: US644132A
Authority: US
Inventors: Armin F Mittermaier; Robert D Mees
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1967-06-07
Filing date: 1967-06-07
Publication date: 1969-06-17
Anticipated expiration: 1986-06-17

Description

A. F. MITTERMAIER ET AL 3,450,190

LOW PRESSURE CASTING APPARATUS June 17, 1969 Filed June 7, 1967 Sheet June 17, 1969 A, F M|TTERMA|ER ET Al. 3,450,190

LOW PRESSURE CASTING APPARATUS Filed June v, 1967 sheet A? of e June 17, 1969 A, F, M|TTERMA|ER ET AL 3,450,190

LOW PRESSURE CASTING APPARATUS Sheet Filed June 7, 1967 June 17, 1969 A, F, MlTTgRMAlER ET AL 3,450,190

Low PRESSURE CASTING APPARATUS Sheet Filed June v, 1967 Sheet IN VENTORSZ June 17,1969 A. F. MITTERMAIER ET AL llow PRESSURE CASTING APPARATUS Filed June 7,' 1967 June 17, 1969 A F, M|TTERMA|ER ET AL 3,450,190

LOW PRESSURE CASTING APPARATUS Filed June 7, 1967.

Sheet 6 of G Ffa. /0

tar/76g United States Patent O U.S. Cl. 164-309 10 Claims ABSTRACT F THE DISCLOSURE A low pressure casting machine having a fluid pressure operated press with a sealed hold furnace located under the movable platen of the press. The cover plate of the hold furnace serves as a mounting table for assembly of the mold. The mold includes a fixed base plate section supported on the mounting table, a plug section carried by the platen of the press and four movable side plate sections. The side plate sections of the mold are moved in and out of assembled relation with the fixed `base plate section by a unitary side plate actuator assembly which is carried on adjustable elements attached to the mold mounting table for selectively positioning the side plate actuator assembly in vertical relationship with respect to the mold. The actuators for driving the movable side plate sections of the mold are supported by a rigid stressabsorbing frame freely supported on the mounting table so that stresses resulting from the closure of the mold under pressure are not transmitted to the table or the press superstructure.

A stalk supported by the mold mounting table extends below the surface of the molten metal in the crucible of the hold furnace and has its upper end in communication with a removable sprue insert portion of the mold base section to feed molten metal into the mold cavity. The stalk is formed with a lianged portion which is sandwiched between an upper and a lower gasket and is supported in an annular groove formed in a split collar which takes up pressure applied by the press or actuator assembly to the middle portion of the base plate section. The hold furnace also includes a skewed fill tube with a mounting plate having stud-receiving slots extending in a direction to permit the lill tube to be replaced without need for removing the mold mounting table.

Background of the invention This invention relates to low pressure casting apparatus and more particularly to an improved low pressure casting apparatus for fabricating relatively thin-walled castings of varying sizes.

The low pressure casting is similar to permanent mold casting in that it utilizes a comparable mold design. Low pressure casting differs in that air pressures ranging from iive to ten pounds per square inch are employed to force molten metal into the cavity of the mold whereas in permanent mold casting hydrostatic pressure is used. The mold is supported over a hold furnace and receives molten metal through a stalk extending almost to the bottom of a crucible containing a supply of molten metal. At the low pressures employed, the molten metal flows slowly into the mold cavity thereby creating a natural temperature gradient in the mold cavity.

In low pressure casting the molten metal leaves the furnace below the surface thereby minimizing oxidation. Low pressure casting has the advantage as compared with normal permanent mold casting that one operator can handle several low pressure casting machines. Further, in low pressure casting no risers are necessary, and the gate of the casting is smaller than a comparable gate of a permanent mold casting. The weight of the runner and risers of a permanent mold casting very often may 3,450,190 Patented June 17, 1969 equal the weight of the finished casting itself. However, the weight of the gate of a low pressure casting may range from two to ve percent of the weight of the finished casting.

In the commercial production of low pressure castings, it is particularly desirable that the apparatus be capable of handling molds for castings of varying sizes. Where essentially rectangular shaped cases are to be cast, the height of the sides of the case may range from nine to eighteen inches, and the height of the side plate sections of the mold must correspondingly vary.

It will be appreciated that after the metal has solidilied in the mold cavity, the mold is opened `by retracting the side plate sections out of engagement by means of hydraulic rams or other power driven means. After the casting has been removed and stripped, the plug section and the side plate sections are power driven into assembled relation. These operations are repeated for each casting produced. In the low pressure casting apparatus of the prior art, diiculty has been encountered in maintaining the alignment of the side plate sections of the mold as they are pulled apart from the solidified metal to open the mold. Misalignment when the mold is closed results in flash at the points while misalignment when the mold is pulled apart may cause the coating on the mold to come off and may result in damage to the mold actuator. Thus, there is a need for a side plate section actuator assembly that will permit the side plate sections to be repeatedly pulled apart and assembled without misalignment.

It is particularly desirable, if not necessary, in low pressure casting apparatus that the stalk which is continuously immersed in the molten metal be frequently inspected for possible defects. Also, it is desirable that the stalk be readily removed so that it can be cleaned in the event that it becomes clogged with solidified metal. Other parts, such as the ll tube, that have to be periodically replaced should be readily accessible and removable without need for dismantling the hold furnace. Further, it is desirable that an effective seal be maintained between the stalk and the sprue of the mold with which it communicates and also between the stalk and the opening in the hold furnace cover plate through which the stalk extends.

Accordingly, it is a general object of our invention to provide an improved low pressure casting apparatus.

It is a more specific object of our invention to provide an improved low pressure casting apparatus having an actuator assembly capable of driving the side plate sections having a wide range of dimensions in and out of engagement with Imisaligning the side plate sections.

Another object of our invention is to provide a low pressure casting apparatus having an improved stalk mounting and sealing arrangement.

Briefly stated, the improved low pressure casting apparatus, in accordance with one form of the invention, is comprised of a sealed hold furnace having an opening at the top thereof for a stalk which extends below the surface of the molten metal in the crucible of the hold furnace. The cover plate of the hold furnace serves as a mold mounting table. The low pressure casting apparatus also includes a mold, a fluid pressure operated press with a movable platen supported over the top of the furnace, and a side plate section actuator assembly. The 'mold includes a fixed base plate section supported on the top of the furnace, a plug section carried by the platen of the press, and movable side plate sections. The mold includes means for maintaining the mold within predetermined temperature limits and also includes means for cooling selected portions of the mold after iilling to facilitate solidification of the relatively heavier sections of the casting.

The side plate section actuator assembly includes a pair of vertically spaced frame members forming a stressabsorbing frame circumscribing the mold and also includes actuators supported by the frame members for engaging and disengaging the movable side plate sections of the mold. Means are provided for selectively positioning the side plate section actuator assembly in vertical relationship with respect to the mold. The low pressure casting apparatus also includes a means for applying a pressure above atmospheric ranging from two to ten pounds per square inch to the interior of the sealed hold furnace for controlling the ow rate for a preselected interval of time to force molten metal through the stalk to the cavity of the mold.

In a more specific aspect of our invention, we have provided a stalk mounting and sealing arrangement wherein the stalk is formed with a flange at the upper end and extends above the mold mounting table. To support the stalk the flange rests on an annular groove of a split collar and is sandwiched between gaskets to effect a seal where the upper end of the stalk joins the sprue of the mold. The split collar is disposed between the underside of the base plate section and the topside of the mold mounting table and provides a support for the middle portion of the base plate section, which is supported along its outer periphery by a support collar attached to the mold vmounting table.

In this improved stalk mounting arrangement the stalk does not bear the pressure transmitted by the press to the middle portion of base plate section of the mold, but this pressure is taken up by the split collar. Another important advantage of the improved arrangement is that the stalk can be readily removed without need for disassembling parts of the hold furance.

According to another aspect of our invention, we have provided a removable sprue portion insert for the base plate section. A cooling duct is also formed in the sprue portion insert to permit the sprue to be cooled when the mold cavity is filled. An advantage of this arrangement is that the sprue portion of the base plate section can be removed without having to replace the entire base plate section of the mold. Also, we have provided an improved fill tube that is skewed and has a slotted mounting plate that permits the lill tube to be readily replaced.

The subject matter which we regard as our invention is set forth in the appended claims, the invention itself, however, together with further objects and advantages thereof, may be best understood by referring to the following description taken in conjunction with the accompanying drawings in which:

Brief description of the drawing FIGURE 1 is a perspective view of the improved low pressure casting apparatus embodying one form of the invention with parts thereof broken away to show certain features of the apparatus;

FIGURE 2 is an enlarged perspective view of the mold actuator assembly with parts thereof broken away to show the specific structural details;

FIGURE 3 is an enlarged perspective view, partially exploded, of a side plate section with the back cover plate and gasket cut away to show the internal heating and cooling arrangement;

FIGURE 4 is a perspective view of the plug section of the mold with a part thereof broken away to show the internal heating and cooling arrangement;

FIGURE 5 is a front view, partially sectionalized, of the casting stripper;

FIGURE 6 is a view corresponding to the view shown in FIGURE 5 with the caster stripper shown in position with the plug section in assembled relation with the side platesections and base plate section of the mold;

FIGURE 7 is a partial sectional'view of a top portion of the hold furnace and base plate section of the mold illustrating the stalk mounting and sealing arrangement;

FIGURE 8 is a view corresponding to the view shown in FIGURE 7 illustrating a modified stalk mounting and sealing arrangement and a base section with a removable air-cooled sprue portion;

FIGURE 9 is a sectionalized partial view of the furnace illustrating an improved fill tube arrangement; and

FIGURE l0 is a view corresponding to the view of FIGURE 9 showing a prior art arrangement.

Description of the preferred embodiments Having more specific reference now to FIGURE 1, we we will now describe the illustrated exemplification of the improved low pressure casting apparatus, generally identiiied by reference numeral 10. The principal components of the low pressure casting apparatus 10 are a fluid pressure actuated press 11, a mold comprising a plug section 12, a fixed base plate section 13, and four

side plate sections

14, 15, 16, 17, a side plate section actuator assembly 18, a hold furnace 19, a casting unloader 20, and a furnace air pressure supply system 21.

lThe fluid pressure actuated press 11 includes a base frame 22, a pair of vertical columns 23, 24 attached to the base frame 22, a cross frame member 26 on which a two-stage telescoping cylinder 27 is mounted, a platen 28 and a platen hold ram 25. The press 11 used in the exemplilication of our invention was designed to accommodate the mold sections for casting cases havng heights ranging from nine to eighteen inches.

As the platen 28 of the press is driven by cylinder 27 supported on the cross frame member, it is guided by keys 29 supported on the vertical columns 23, 24. To insure that the platen 28 is positively held in a preselected vertical position, the second tiuid pressure operated hold ram 25 is arranged n opposing relation to the two-stage driving cylinder 27. The downward travel of the platen 28 is limited by a pair of adjustable stops 30, only one of which can be seen in FIGURE 1. When the

platen extensions

31, 32 butt against the stops 30, the plug section 12 is positioned with respect to the

side plate sections

14, 15, 16, 17 and the fixed base plate section 13.

Although the primary purpose of the fluid pressure operated press 11 is to raise and lower the plug section 12 of the mold, the press in the exemplilication of our invention was used to carry out other important and useful functions. As will hereinafter be more fully explained in connection with the description of the mold side plate section actuator assembly 18, two lifting pins 33, 34 on the platen `are provided for moving the mold side plate actuator assembly 18 to an elevated position. It will be understood that the electrical leads connecting with the mold side plate section actuator assembly 18 are flexible and have suficient slack to allow the actuator assembly 18 to be elevated to a suicient height to permit work to be carried out on the stalk 43 and other parts of the mold furnace 19.

When a mold for casting a part of a different height is to be used, it is necessary -to change the vertical position of the mold side plate section actuator assembly 18. It will be noted that the mold side plate section actuator assembly 18 is supported on four equally spaced positioning elements on the mold mounting table 46, only two of which, 47 and 48, are seen in the view illustrated in FIGURE l. The desired vertical position of the mold side plate actuator assembly 18 is obtained by lifting the actuator assembly 18 ot the positioning elements and placing shim collars of a predetermined thickness between the positioning element and the underside of the actuator assembly 18.

Another function carried out yby the fluid pressure operated press 11 is to effect the stripping of the completed casting from the plug section 12. It will be appreciated that when the casting has solidified the side

plate mold sections

14, 1S, 16, 17 are first withdrawn from the completed casting and then the platen is raised to remove the casting from the base plate section 13, the casting adhering to the plug section 12. The casting is stripped from the plug section 12, as will hereinafter be more fully explained, when the stripper 50 is `brought in contact with pins supported by the cross frame member 26 of the press 11.

The right hand vertical column 23 of the press 11 serves as a support for the casting unloader 20. The casting unloader 20 includes a rotatable arm 51 having a tray 54 for receiving the casting. A Huid pressure actuated ram 52 is connected to the arm 51 to adjust and hold it in a preselected vertical position. When the casting is ready for stripping from the plug section 12 of the mold, the arm 51 is rotated into a position under the platen 28 for receiving the casting by drive motor 53. After the casting is placed on tray 54, the arm 51 is swung out away from the press 11 where the casting is placed on a conveyor (not shown).

Having reference now to both FIGURES 1 and 2, we will now more fully describe the mold side plate section actuator asesmbly 18. In FIGURE 2 the mold

side plate sections

14, 15, 16, 17 are shown in the open or fully extended position. The four mold

side plate sections

14, 15, 16, 17 are actuated by uid pressure rams 55, 56, 57 and 58 respectively. The cylinders of the

rams

55, 56, 57 and 58 are rigidly held between upper and lower essentially O-shaped frame members S9, 60. To provide a unitary stress-absorbing frame, the frame members 59, 60 are rigidly braced by eight braces or struts, of which struts 61, I62, 63, 64, 65 and 66 can be seen in the view shown in FIGURE 2. The struts are Ibolted to the frame members 59, 60 to form a rigid stress absorbing frame for supporting the

rams

55, 56, 57 and 58. It will be noted that the entire mold side plate actuator assembly 18 is freely supported on the positioning elements two of which 47 and 48 are shown so that any stress resulting from the extension of the

rams

55, 56, 57 and 58 is taken up by the stressabsorbing frame and not by the mounting table 46 or the vertical columns 23, 24 ofthe press 11.

It will `be appreciated that the mating parts of the mold sections are machined for an accurate lit in order to prevent flash from forming at the joints. In order to obtain a desired alignment of the

side plate sections

14, 15, 16 and 17 with respect to each other and with respect to the fixed base plate section 13, the side plate sections are adjustably mounted on support pieces which are supported for reciprocating movement on slide blocks which slide between upper and lower guide slots formed in the guide members located at the sides of each

ram

55, 56, 57 and 58. Only two of the support pieces 67, 68 can be seen in the view shown in FIGURE 2. Since the support pieces and their associated mounting arrangements are the same for all of the

side plate sections

14, 15, 16| and 17, we shall only describe in detail the support piece 68 and its mounting arrangement.

As is seen in FIGURE 2, the side plate section 17 has four studs 69 attached to the back side and is aligned with respect to the support piece 68 by the adjusting nuts 70. Attached to the support piece 68 is a pair of horizontally spaced slide blocks 71 and 72. The slide blocks 71, 72 each have a pair of wear inserts, only wear inserts 73, 74 and 75 being seen in the view shown in FIGURE 2. As the ram 58 drives the support piece 68 and its side plate section 17, the movement of slide blocks 71, 72 is controlled by the upper and lower guide slots formed in the guide members 76 and 77 thereby to maintain the alignment of the side plate section 17. It will be seen that the ram 58 is rigidly secured to the frame members 59, 60 by bolts 80. In the interest of simpllication, the bolts securing the

rams

55, 56 and 57 are not illustrated. The hose connections 81, 82 connect ram 58 to a suiable fluid pressure supply (not shown).

Each of the

side plate sections

14, 15, 16 and 17 rides on a pair of guides for-med on the fixed base plate section 13 to insure that the vertical alignment of the side plate sections is maintained as the mold is opened and closed. Only the slides 78 and 79 can be seen in FIGURE 2. An important advantage of the improved guide and slide arrangement is that buckling of the side plate sections 14,

15, 16 and 17 is effectively prevented when the side plate sections are pulled apart from the casting. Also, precise alignment of the side plate sections can be maintained for extensive periods of operation thereby enabling the low pressure casting apparatus to be operated on a production basis.

In the exemplilication of our invention, the side plate sections are operated at a selected temperature between 325 and 475 degrees centigrade. Preferably, the temperature over any area of the mold section should not vary more than 25 degrees. To limit the temperature, thermocouples are located in each of the mold sections, and temperature controllers are provided to regulate the temperature of the mold sections within plus or minus five degrees. Electric resistance heaters are installed in the back side of each of the

side plate sections

14, 15, 16 and 17, and the

leads

35, 36, 37, 38, 39, 40, 41 and 42 are brought out for connection to temperature controllers to regulate the amount of current supplied to the heaters in order to maintain temperature within predetermined limits.

Having more specific reference now to FIGURE 3, we have illustrated therein a partially exploded view of side plate section 15 which forms the side of a casting 83 having mounting

brackets

84 and 85. Air cooling ducts 86, 87 adjacent to the mounting

brackets

84, 85 are provided in the side plate-section 15 to eiect a solidilication of the molten metal in proper sequence thereby to eliminate stress cracking where thick and thin sections of the casting are involved.

Connections

88 and 89 from the cooling ducts 86, 87 are brought out externally at the back side of side plate section 15 and are connected to an air pressure source by exible hose connections 44 and 45. Electric resistance heating element 90 is supported on the back side of the side plate section 15 by

brackets

91, 92, 93. A lead 94 connected to a thermocouple is brought out for connection to a temperature controller circuit (not shown). Threaded stud bolts 69 are provided for securing and aligning the side plate section with respect to the ram actuated support piece. A sheet 95 of insulating material, such as asbestos, is interposed between the electrical resistance heating element 90` and a steel back plate 96.

Having reference now to FIGURES 4, 5 and 6, we will now more specifically describe the plug section 12 of the mold and the casting stripper 50. As is shown in FIGURE 4, the cooling of the plug section 12 is effected by a cooling line 97 having a plurality of jets 98 and perforations 99 which direct the flow of air against the inner walls of the plug section 12. A lead 100 connected to a thermocouple is brought out to the top of plug section 12 for connection to a temperature controller circuit. An electrical resistance element 101 generally conforming with the inner configuration of the mold is disposed along the inner walls to provide relatively uniform heating of the plug section 12. The heater terminals 163, 102 are adapted for connection to a temperature controller circuit.

In FIGURE 5 the stripper 50 is shown in the position where the casting 83 is being stripped from the plug section 12 and ready for placement on the unloader. The stripper 50 is comprised of a plurality of stripper pins 103 disposed in an essentially rectangular array around the top edge of the casting 83. When the platen 28 of the press is elevated to the position shown in FIGURE 5, it will be seen that the

rods

104, 105 attached to the cross frame member 26 butt against the stripper plate 106 forcing the stripper pins 103 against the upper edge of the casting 83 thereby stripping the casting 83 from the plug section 12. When the platen 28 is in the mold closed position as shown in FIGURE 6, dowels 107, 108 engage the top of the

side plate sections

14, 16 and prevent the stripper pins 103 from dropping into the mold cavity.

Having reference to FIGURES l, 7, 8, 9 and l0, We will now more fully describe the hold furnace and its associated equipment. The hold furance 19 includes a 7 ceramic crucible 109, a stalk 43 that projects almost to the bottom of the crucible 109, heating elements 110, 111, a cylindrical insulating brick wall 112, a bottom insulating wall 113, a cover plate insulating wall 114, a pot-like outer cylindrical casing 115, and the mold base table 46 which serves as a cover for the case 115.

The crucible 109 rests on the bottom insulation wall 113 of the hold furnace 19 and in the exemplication of our invention had a capacity of approximately 2,000 pounds of aluminum. The outer casing 115 includes a flange 117 welded thereto to provide a support and joint for the -mold mounting table 46. As will be seen in FIG-

URES

7, 8, 9 and 10, the mold mounting -table 46 rests on

gaskets

118, 119 which provide an airtight seal with the flange 117 of the cylindrical casing 115.

Having reference now to FIGURES 7 and 8, we will now more fully describe two stalk mounting and seal arrangements that can be used in the improved low pressure casting apparatus 10. Referring more particularly to FIGURE 7, it will be seen that stalk 43 is formed at one end with a flanged collar 120 sandwiched between

annular gaskets

121 and 122. The lower annular gasket 121 has an inside diameter essentially equal to the outside diameter of the stalk 43 and is positioned between the underside of the flanged collar 120 and the topside of the mold mounting table 46. The upper annular gasket 122 is formed with a central opening essentially equal to the inside diameter of the stalk 43. The flanged collar 120 at the upper end of the stalk 43 serves as a spacer for an electric heater 123 which is located between the upper and lower gaskets.

The purpose of the heater 123 is to maintain the stalk 43 at a sufficiently high temperature so that the molten aluminum in the stalk 43 will not freeze during the cool down period of the mold. The upper annular gasket 122 serves to thermally insulate the heater 123 from the mold base plate section 13, and the lower annular gasket 121 serves also to thermally insulate the stalk heater 123 from the mounting table I46. Although single gaskets have been shown, it will be appreciated that more than one gasket can be used to provide a suitable seal for the furnace 19 and the desired thermal insulation for the stalk heater 123.

It will be noted that the stalk 43 is disposed under a sprue 124 of the mold base plate section 13. The base plate section 13 is supported at the ends by a support block 125 which is attached to the mold mounting table 46 by screws 126. Clamping lugs 127 securely lock the base plate section 13 to support block 125, and any lateral movement of the mold base section is further restrained by means of a key 128.

A thermocouple (not shown) is also attached to the stalk 43 and is connected to lead 129 which also is connected to a temperature control circuit for maintaining the temperature of the stalk 43 within certain predetermined limits. In the exemplication of the invention, the current to the stalk heater 123 is controlled by a variable transformer, and the stalk temperature was maintained between a minimum of 580 degrees centigrade and a maximum of 600 degrees centigrade.

Referring now more specifically to FIGURE 8, we have illustrated a preferred stalk mounting and seal arrangement wherein a sprue portion insert 130 is utilized in a base plate section 131. The sprue portion insert 130 is formed of an upper and a lower part defining annular cooling duct 132 and a sprue 135. The annular cooling duct 132 communicates with an outlet (not shown) for discharging air to the atmosphere and an inlet opening 133 connected to flexible tubing 134 supplied with air from a suitable source. It will be noted that the upper and lower parts of the sprue portion insert 130 are readily disassembled from the base plate section 131 in the event that metal freezes in the sprue 135 and can be renewed without replacing the entire base plate section 131. The base plate section 131 is rigidly held in position on the support block 125 by a plurality of clamp lugs 127 and a key 128. It will be appreciated that the support block essentially takes the weight of the mold and pressure developed by the press 11, and any pressure at the middle portion of the -base plate section 131 is borne by a collar 161.

In the preferred arrangement shown in FIGURE 8, a relatively thin flange 136 is formed at the upper end of the stalk and the flange 136 is held in position within an annular groove machined in the collar 161. The collar 161 is comprised of a pair of split sections. In the sectional view of FIGURE 8, only one of these split sections 138 is shown. The split sections 138 are fabricated of stainless steel and are bolted together. The

gaskets

162, 139 and 140 provide an effective airtight seal for the upper end of the stalk 137.

A stalk heater 123 is provided to maintain the upper end of the stalk 137 at a sufficiently high temperature so that molten aluminum in the stalk 137 will not solidify during the cool down period of the mold. A thermocouple (not shown) is installed in the collar adjacent to the upper end of the stalk 137 and is connected to lead 129.

With the improved stalk mounting and seal arrangement, it is possible to readily remove a stalk from the hold furnace without need for removing the mold mounting table. This may be accomplished by lowering the platen 28 and attaching the actuator assembly 18 to the lifting pins 33, 34 by means of a pipe and lifting the actuator assembly 18 off the .

positioning elements

47, 48. The mold base plate section is then removed by unclamping it from the support block 125, and the stalk lifted out of the opening in the hold furnace.

The primary purpose of the hold furnace 19 is to maintain the temperature of the molten aluminum 141 in the crucible 109 at a casting temperature. In the exemplication of the invention the hold furnace 19 was capable of maintaining the temperature of the molten aluminum 1-41 at a temperature between 400 and 800 degrees centigrade. The outer casing 115 of the furnace is preferably designed to retain an air pressure ranging from 2 to 30 pounds per square inch.

Molten aluminum is transferred to the hold furnace 19 as needed from a premelt furnace (not shown) in which aluminum ingots are heated to a liquid state. During operation of the low pressure casting apparatus 10, a sucient volume of hot molten aluminum is maintained in the premelt furnace so that molten aluminum can be periodically added to the crucible 109 through a ill tube of the hold furnace 19.

In FIGURE 9 we have illustrated a preferred arrangement of a ll tube 142. Preferably, the till tube 142 is skewed and has a mounting plate 143. The mounting plate 143 has four

slots

144, 145, 146 and 147 which, extend in a radially inward direction relative to the table 46 so that the fill tube 142 can be readily inserted into the hold furnace 19, and the engagement of the mounting plate 143 with studs 148 determining the proper position of the fill tube 142 with respect to the crucible 109. The mounting plate 143 is secured to studs 148 on the table 46 by means of wing nuts 149. The fill tube 1'42 has an airtight cap 160 at one end which is removed when molten metal is poured into the crucible 109. A gasket between the mounting plate 143 and the table 46 is used to provide an airtight seal.

A prior art lill tube arrangement is illustrated in FIGURE 10. The fill tube y159 is welded to the table 46. With such an arrangement it will be apparent that the mold mounting table 46 must be removed in order to replace the rlill tube 159 whereas in the arrangement shownA in FIGURE 9 the fill tube 142 can be replaced and properly positioned in a matter` of minutes by removing the wing nuts 149, pulling out the fill tube 142, and inserting a new ll tube 142.

In order to Iforce the molten metal 141 into the mold cavity, a pressure between two to ten pounds is supplied to the interior of the sealed hold furnace 19 from an air supply system 21 (see FIGURE 1). The air supply system 21 includes a tank 15-1, tank gage '152, a pressure regulating valve 153, a cutoff valve 154, a furnace gage 155, piping 156, 157, and a solenoid-operated exhaust valve 158. EIn the exemplification :of our invention, a pressure regulating valve was used to maintain the pressure on the surface of the molten metal 141 at a preselected value. The air pressure is applied to the surface of the molten metal 141 to feed the cavity mold during the fill operation. When the metal in the cavity mold solidifies, the air pressure is released.

Referring again to FIGURE 1, we will now more fully describe the sequence of loperations for making a casting. Before initiating the operation of the apparatus 10, the hold furnace 19 is charged :with molten aluminum. The mold sections are coated and preheated. The operator then initiates the operation of the mold control system. The

side plate sections

14, 16 are moved into engagement with the fixed base plate section 13, and then side plate sections V15, 17 are moved in. The platen 28 moves down contacting the stops 30 to bring the plug section 12 into engagement with the side plate sections 14. 15, |16 Iand 17 thereby closing the mold. The hold furnace 19 is pressurized 'for a preselected interval. This time interval is determined experimentally by the amount of molten metal required to fill the mold cavity. The pressure in the hold furnace 19 is released by actuating the solenoid-operated exhaust valve 158, and with hold furnace depressurized excess metal falls from the stalk 43 back into the Crucible 109. After a short interval to assure complete solidification of the casting, the unloader 20 is moved in and catches the casting as it is stripped from the plug section 12. The unloader 20 is then returned to its initial position.

It is believed that molten metal when drawn into a mold cavity at relatively low pressures solidiiies from the top of the mold down back to the sprue. Due to the elimination of gates and risers, the low pressure casting provides the advantage of high yield, and this is particularly advantageous where relatively large castings are to be manufactured. The finished casting is characterized by high density and is relatively free from flash, oxidation, porosity and shrinkage. It will be appreciated that the operations carried out by the improved low pressure casting apparatus can be effected by conventional control systems. The molds may be automatically filled and actuated to permit one operator to operate more than =one machine thereby increasing the productivity of the operator.

From the foregoing description of the operation and structural features :of the low pressure casting apparatus incorporating the invention, it will be apparent that an advantageous arrangement has been provided for actuating the side plate sections of a mold, for mounting and sealing the stalk of the hold furnace, for cooling the sprue of the mold and for mounting the fill tube of the hold furnace. The improved low pressure casting apparatus is capable of handling castings of a wide range of sizes and of maintaining the alignment of the mold sections as they are brought in and out of engagement to the mold closed and mold open positions.

It will be understood that the particular embodiments of the invention described herein are intended as illustrative examples and that the invention is not necessarily limited to such embodiments. Although in the particular embodiments of the invention fixed positioning elements were employed Lfor the side plate actuator assembly, it :will be apparent that power units can be utilized to adjustably position the side plate section actuator assembly in vertical relation with respect to the mold. Also, it will be apparent that the actuators of the side plate actuator assembly, the ram controlling the platen, the cooling fair pressure, the temperature controllers for the mold sections, the air supply toV the cooling ducts of the mold sections, and the valves in the hold furnace air pressure system can be automatically controlled. It will be understood, therefore, that other modifications of the invention described herein may be made, and that it is intended by the appended claims to cover all such modifications that fall within the true spirit and scope of the invention.

What we claim as new and desire to secure .by Letters Patent of the United States is:

1. A low pressure casting apparatus comprising: a fluid .pressure actuated press including a pair of vertical columns and a vertically movable platen; a hold furnace including a sealed enclosure and crucible for containing molten metal and a cover plate serving as a mold mounting table; 'a mold including a fixed base plate section formed with a sprue and supported on said mold mounting table, a plug section carried on said platen, and movable side plate sections; a side plate section actuator assembly including a stress-absorbing frame With a central opening for said mold and actuators for engaging and disengaging said movable Side plate sections of said mold, said actuators being carried by said stress-absorbing frame; means for selectively positioning said actuator assembly in vertical relationship with respect to said mold; a stalk communicating with the sprue of said fixed base plate section and extending downwardly to a point near the bottom of said Crucible; means for heating selected portions of said mold; means for applying a pressure to the sealed enclosure for a preselected time interval to force molten metal through the stalk to fill said mold; and means for cooling selected portions of said mold.

2. The low pressure casting apparatus set forth in claim 1 wherein said stress-absorbing frame includes a pair of generally O-shaped frame members rigidly braced in vertically spaced relation with respect to each other and wherein said actuators are fluid pressure powered motor means attached to said stress-absorbing frame for selectively moving said side -plate sections in a generally horizontal direction in and out of assembled relation with said base plate section.

3. The low pressure casting apparatus set forth in claim 1 wherein said side plate sections are adjustably mounted on support pieces driven lby said Iactuators and each of said support pieces are attached to a pair of slide blocks supported for generally horizontal movement in vertically spaced guide slots formed in a pair of guide members.

4. The low pressure casting apparatus set forth in claim 1 wherein said fixed base plate section includes a removable sprue portion with a cooling duct formed adjacent to said sprue and a heater is disposed near said stalk to maintain the temperature of the upper end of said stalk within predetermined limits.

5. The low pressure casting apparatus set forth in claim 1 wherein said hold furnace includes a skewed fill tube extending through said mounting table into said crucible, a mounting plate having stud-receiving slots extending in a direction to permit said fill tube to lbe removed and inserted and gasket means interposed between said mounting plate and mounting table to effect `an airtight seal therebetween.

o. The low pressure casting apparatus set forth in clalm 1 wherein said stalk is supported by a split collar, said split collar being positioned on said mounting Itable and under said base plate section for .bearing the pressure exerted on the middle portion of said ybase plate section when the vertically movable plug section is moved by said platen into assembled relation with said side plate sections of the mold, and means for effecting an airtight seal are disposed between the topside of said split collar and the underside of said base plate section Iand between the urderside of said split collar and topside of said mounting ta e.

7. A low pressure casting apparatus comprising: a hold furnace including a sealed enclosure and crucible within said sealed enclosure for containing molten metal; a mold including a fixed base Aplate section formed with a sprue and supported on top of said sealed enclosure,

a plug section and side plate sections; means for effecting a vertical movement of said plug section; a side plate :actuator assembly including frame members circumscribing said mold, and actuators supported by said frame members for engaging and disengaging the side plate sections to an open mold and a closed mold position, said side plate sections cooperating with said fixed base plate section and said plug section when in the closed mold position to define a mold cavity; means for selec-l tively positioning said side plate actuator assembly in vertical relationship with respect to said mold; means for maintaining selected portions of said mold within predetermined temperature limits; a stalk having one end communicating with the sprue of said iixed base plate section of said mold and having its other end disposed for extension below the level of the molten metal in said Crucible; -means for applying air pressure above latmospheric to said sealed enclosure of the hold furnace for a preselected interval of time to force lmolten metal through said stalk thereby to till the mold cavity; and means for cooling selected portions of said mold to facilitate solidilication of the molten metal after filling.

8. The low pressure casting apparatus set forth in claim 7 wherein said side plate sections are adjustably mounted on support pieces driven by said `actuators and each of said support pieces are attached t0 a pair of slide blocks, each of said slide blocks supported for generally horizontal movement in spaced guide slots formed in a guide member.

9. The low pressure casting apparatus set forth in claim 7 wherein said iixed base plate section includes a removable sprue portion with a cooling duct disposed adjacent said sprue.

10. The low pressure casting apparatus set forth in claim 7 wherein said hold furnace includes a skewed ll turbe extending through the top of said sealed enclosure into said Crucible, a mounting plate having studreceiving slots extending in a direction to permit said ll tube to be removed and inserted, and a gasket means interposed between said mounting plate and top of said sealed enclosure to eiTect an airtight seal therebetween.

References Cited UNITED STATES PATENTS 1,980,333 11/1934 Haessler 164-343 X 2,581,418 1/1952 Kohl 164-340 X 3,279,004 10/1966 Hartman et al. 164-343 J. SPENCER OVERHOLSER, Primaly Examiner.

JOHN S. BROWN, Assistant Examiner.

U.S. Cl. X.R. 164-348; 249-161