Casting flask with improved heat transfer characteristics

Abstract

A resurfacing for a worn interior wall of a cope or drag of a metal foundry flask includes a layer of thermal conducting substance between the outer surface of the liner plate and the inner wall surface of the flask.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to casting flasks and more particularly to a resurfacing for a worn interior wall of a cope or drag of a metal foundry casting flask.

[0003] 2. Description of Related Art

[0004] A typical foundry metal casting flask is formed of an upper cope and a lower drag which are aligned, one above the other, and filled with casting sand within which a casting cavity is formed. Typically, drag and cope inside vertical walls are smooth and flat. In some cases, the cope walls may be flat, and in other cases, they may be provided with horizontal grooves or lines for better retaining the casting sand when the cope is separated from the drag for the removal of the casting pattern.

[0005] In an automatic (flask-less) sand mold making machine, a single flask may be repeatedly used to rapidly form sand molds. When each sand mold is completed, the cope and drag are separated from the cake or the sand mold which is then removed on a conveyor to a place where molten metal is poured into the flask-less sand mold. Alternatively, in some operations, the flask remains with the sand mold until after the metal is cast and solidified. Then, the flask and sand mold are separated so that the flask may be reused. In that case, numerous flasks are used. Throughout this process, there is considerable wear and tear on the interior wall surfaces of the flask. Thus, the interior wall surface becomes rough, scratched, eroded or otherwise damaged by the abrading action of the sand. Once the interior wall of the flask is roughened or damaged, it becomes necessary to either replace the flask with a new one, or alternatively to rework the face to smooth and bring it back to its original finish. Either replacing the flask or refinishing the flask walls is relatively expensive and time consuming, requires stocking additional flasks, and may result in considerable downtime in the case of refinishing the flask walls in a automatic mold forming machine which uses a single flask for making flask-less molds.

[0006] In the present practice, when the interior walls of a flask cope or drag become damaged or worn, the interior wall surfaces are repaired by covering them with stainless steel liner plates. The liner plates are formed of flat, stainless steel metal having outer faces for face-to-face engagement with the inner surfaces of the flask walls and inner faces that provide resurfaces, forming the inner faces of the flask.

[0007] The liner plates are bolted to the flask walls so that they may be applied and removed for replacement when desired. Before applying the first liner plates, the worn inner wall surfaces of the flask may be ground relatively level and flat to form a support base for the liner plates. Subsequent liner plate replacement ordinarily does not require leveling the flask wall surfaces. In order to bolt the liners to the walls, a large number of boltholes are formed in each of the liners. These boltholes are provided with deep countersinks at their inner faces so that bolts may be positioned within the holes with their bolt heads deeply inset within the plates. That is, the bolt heads are spaced at a distance beneath the plane of the inner face of the liner plate.

[0008] Next, molten weld material is applied to the countersink openings by using a conventional welding process to weld the bolts in place. Excess weld metal, which forms a bump over the countersink openings, is ground flat. Thus, the inner face of each of the plates is smooth, and the exposed surfaces of the welds are co-planar with the surfaces of the inner face. The liner plates are applied against the respective flask wall surfaces with their welded-in-place bolts extending through the bolt receiving holes that are pre-drilled in the flask walls. Nuts are applied to the ends of the bolts for fastening the liner plates to the walls. Thus, the liner plates are rigid, but removably fastened within the flask walls to provide a replaceable surface.

[0009] A problem in replacing these work faces of cope and drag molds with the stainless steel liners is a reduction in heat transfer capacity from an outside heat source to the sand mold or cable inside the cope and drag of the mold. Another problem encountered in the prior art is that a small air gap that is inevitably formed between the liner and the interior surface of the exterior wall of the flask. This air gap presents a substantial barrier to the transfer of heat to the liner and thence to the casting sand inside the cope and drag molds, requiring the application of more heat to the exterior of the flask, either by increasing the level of applied heat or applying heat for a longer period of time.

SUMMARY OF INVENTION

[0010] An object of this invention is to provide a means for repeatedly resurfacing the interior wall surfaces of a conventional cope or drag of a flask used in a foundry for sand casting while maximizing heat transfer capability of the flask walls.

[0011] In accordance with one aspect of the invention, the problems of the prior art are alleviated by spreading a layer of a thermal conducting substance between the wall liners and the inside surface walls of the flask. Advantageously, the thermal conducting substance substantially eliminates any air gap between liner and the walls of the flask and aids in the transfer of heat through the flask walls to the sand mold.

[0012] In accordance with another aspect of the invention, the thermal conducting substance is a thermal conducting cement. In one particular embodiment of the invention, the thermal conducting cement is a commercially available, non-hardening product that allows for easy removal of the worn plates.

[0013] Advantageously, the layer of thermal conducting cement substantially eliminates the air gap between the liners and the interior wall surface of the flask and improves heat transfer from the exterior of the wall to the interior of the flask.

BRIEF DESCRIPTION OF DRAWINGS

[0014] The invention will now be described with reference to the drawings wherein:

[0015] FIG. 1 is a perspective view of a flask incorporating the principles of the invention;

[0016] FIG. 2 is a cross-sectional view along line 2-2 of the flask of FIG. 1;

[0017] FIG. 3 is an enlarged, cross-sectional view along the line 3-3 of FIG. 1;

[0018] FIG. 4 is a cross-sectional, exploded view of the wall of the flask in FIG. 1.

DETAILED DESCRIPTION

[0019] The cope 11 and drag 12 of a typical flask 10 as depicted in FIG. 1 are box-like in shape and have opposite end walls and opposite side walls 13, 14, 16 and 17 which are interconnected by corner wall strips 15, 18, 19 and 20. Some conventional flasks are rectangular in configuration, that is, with sharp corners, and other conventional flasks may have angled corners. Step one to refurbishing a worn flask is to refinish the interior wall surfaces of the flask to form a smooth surface. Next, a liner plate 30 is provided for each of the major interior walls of the flask. The liner plate is preferably formed of a flat, relatively thin, high quality low carbon steel liner plate provided with a chrome plating, preferably on both sides of the liner plate. An outer face of the plate is arranged for face-to-face contact against the flask wall interior face. The liner plate has an outer face 31 arranged for face-to-face contact against the flask wall interior face 29, and inner face 32 against which the sand is compacted. The liner is preferably sized to completely cover the interior surface of the flask wall. A layer of the thermal conducting cement 28 is spread on the interior surfaces of side walls 13, 14, 16 and 17, and preferably also on the interior side walls of the corner wall strips 15, 18, 19 and 20. One such thermal conducting cement is “TRACIT,” a well-known and commercially available substance made by Chemax Corporation located in New Castle, Del. The thermal conducting cement is preferably a non-hardening product cement to facilitate removal of the liner plates when the liner became worn.

[0020] The low carbon steel chrome liner plates 30 are secured to the flask wall, in a standard fashion, by means of suitable bolts 39 extending through boltholes 37. Each bolthole is formed with a conical countersink 36 at the liner interface as depicted in FIG. 3 and the head 40 of each bolt is closely fitted within the countersink of its respective bolthole. The countersink is relatively deep so that the bolt head is depressed or spaced beneath a plane defining the inner face 32 of the plate 30. After the bolts 39 have been fully inserted in the liner plate 30, the space left in the countersink between the bolt head and the outer surface of the plate 30 is filled with a deposit of weld metal. When the weld metal solidifies, it not only welds the bolt in place and fills the space, but it also leaves an inwardly arranged bump or roughness. That bump is ground down, as for example, by use of a rotary surface grinder, until its exposed surface 45 is co-planar with the inner face 32 of the plate.

[0021] Several tests were conducted to determine the effectiveness of the layer 28 of the thermal conducting cements the amount of energy going into the flask, as well as the amount of energy coming out. Energy going into the flask was determined by placing a first temperature gauge on an outside surface of the flask at a specified distance away from the electric heater. A second temperature gauge was placed on the inside of the flask directly opposite from the first temperature gauge to measure energy transmitted through the flask wall. For all of the tests conducted, the same heater was used. This insured that the identical amount of heat was going into the flask tested. All of the tests were performed in the same room, with all environmental variables being held constant from test to test. Each flask was allowed to reach a steady state condition (room temperature) before the test was performed on it. All flask surfaces were cleaned of any foreign materials before testing. The following is the procedure for one test:

[0022] 1. With the heater and temperature gauges in place and the heater turned off, the inside and outside temperatures are recorded. Since the flasks are all at steady state, both temperatures are the same.

[0023] 2. The electric heater is turned on and allowed to heat up. The time that the electric heater is turned on is recorded.

[0024] 3. Five minutes after the electric heater is turned on, both the inside of the flask and the outside of the flask temperatures are recorded. The elapsed time is also recorded.

[0025] 4. The inside and the outside flask temperatures are again recorded at various times after the heater has been turned on.

[0026] Table No. 1 shows the results of tests conducted on a rebuilt flask where no thermal conducting cement was used. Table No. 2 shows the results of tests conducted on a rebuilt flask where a layer thermal conducting cement 28 was applied between the flask wall 14 and the plate 30. 1 TABLE 1 REBUILT FLASK No Thermal Conducting Cement Used Outside Flask Inside Flask Elapsed Time Temperature Temperature Outside Temp (−) Time (minutes) (° F.) (° F.) Inside Temp. 1:40 0 70 70 0 1:45 5 72 71 1 1:50 10 80 80 0 2:00 20 102 92 10 2:15 35 110 108 2 2:35 55 110 111 −1

[0027] 2 TABLE 2 REBUILT FLASK Thermal Conducting Cement Used Between Liner and Flask Wall Outside Flask Inside Flask Elapsed Time Temperature Temperature Outside Temp (−) Time (minutes) (° F.) (° F.) Inside Temp. 10:40 0 76 76 0 10:45 5 81 88 −7 10:50 10 96 104 −8 11:00 20 106 110 −4 11:10 30 120 124 −4 11:35 55 134 132 2

Claims

1. A casting flask comprising a plurality of outer walls each having an interior wall surface and an exterior wall surface, said flask further comprising:

a liner plate mounted to said interior wall surface of at least one of said outer walls, said liner plate having an outer surface disposed adjacent said interior wall surface and an inner surface disposed opposite said outer surface; and

a layer of a thermal conducting substance disposed between said outer surface of said liner plate and said inner wall surface.

2. The casting flask in accordance with claim 1, wherein said thermal conducting substance is a substance known by the trade name of “TRACIT.”

3. A method of relining an outer wall of a casting flask having an interior wall surface, said method comprising the steps of:

applying a layer of a thermal conducting substance to said interior wall surface; and

attaching a liner plate to said interior wall surface adjacent said layer of thermal conducting substance, whereby said thermal conducting substance is disposed between said liner plate and said interior wall surface.

4. The method in accordance with claim 3, and further comprising the step of grinding said interior wall surface, to present a relative smooth interior wall surface, prior to said step of applying said layer of thermal conducting substance.