Casting system and a method of casting using the same

Abstract

A casting system includes a casting surface; a rim area disposed on the casting surface or associated therewith; a heat resistant impermeable diaphragm having an edge area. The diaphragm covers a portion of the casting mold when it is positioned on the surface so as to form a space defined by at least a base constituted by the surface, and at least a casting face constituted, at least partially, by the diaphragm; a sealing arrangement for sealingly engaging the rim and edge areas, thereby sealing the space; an outlet for withdrawing gas from the space; a heat resistance coefficient of the diaphragm is such that it can melt when coming in contact with the molten material. The diaphragm covers an area larger than that through which molten material is case so that, when the space is sealed, vacuum application causes the diaphragm to adhere to a portion of the mold.

Claims

1. A casting system for the manufacture of a cast item by pouring molten casting material in a casting mold, the casting system comprising: a casting surface for positioning the casting mold thereon; a rim area disposed on the casting surface; a heat resistant impermeable diaphragm having a predetermined heat resistance coefficient and an edge area, the heat resistant impermeable diaphragm configured for covering a portion of the casting mold when the latter is positioned on the casting surface so as to form a casting space defined by at least a base constituted by the casting surface and at least a casting face constituted, at least in part, by the heat resistant impermeable diaphragm; a sealing arrangement configured for sealingly engaging the rim area of the casting surface and the edge area of the heat resistant impermeable diaphragm, thereby sealing the casting space; and at least one outlet configured for withdrawing gas from the sealed casting space; wherein the heat resistance coefficient is such that the heat resistant impermeable diaphragm can melt when coming in contact with the molten casting material; wherein the heat resistant impermeable diaphragm covers an area larger than that through which molten material is cast so that, when the casting space is sealed, application of vacuum to the sealed casting space through the at least one outlet causes the heat resistant impermeable diaphragm to adhere to a portion of the casting mold located juxtaposed with the casting face.

2. The casting system according to claim 1, wherein the rim area is constituted by a part of the casting surface itself; and wherein the heat resistant impermeable diaphragm is configured for covering a majority of the casting mold, thereby constituting not only the casting face but also a remainder of the casting space except for the base.

3. The casting system according to claim 2, wherein the heat resistant impermeable diaphragm wraps and encompasses the casting mold.

4. The casting system according to claim 1, wherein the casting surface is provided with a projecting side wall having, at an end thereof remote from the casting surface, the rim area, wherein the heat resistant impermeable diaphragm constitutes a majority or at least a part of only the casting face while the remainder of the casting space is constituted by the base and the projecting side wall.

5. The casting system according to claim 4, wherein the heat resistant impermeable diaphragm adheres only to a majority or at least a part of the casting face of the casting mold.

6. The casting system according to claim 1, wherein the heat resistant impermeable diaphragm is so dimensioned that the heat resistant impermeable diaphragm has a central portion configured for being juxtaposed with the opening of the casting mold through which molten material is poured therein, and a peripheral area, constituting a boundary area, which adheres to the casting mold under the application of vacuum.

7. The casting system according to claim 6, wherein, when the central portion of the heat resistant impermeable diaphragm is breached by being melted away by the cast molten material, the peripheral area is configured for remaining adhered to the casting mold, maintaining a required vacuum during casting.

8. The casting system according to claim 1, wherein the casting surface includes a stand configured for positioning the casting mold thereon, the stand configured to provide a space between the casting mold and the at least one outlet.

9. The casting system according to claim 1, further comprising at least one inlet configured for introduction of gas into the casting space.

10. The casting system according to claim 1, wherein when the casting space is sealed, application of gas through the at least one inlet, causes the heat resistant impermeable diaphragm to inflate.

11. The casting system according to claim 1, wherein the heat resistant impermeable diaphragm is provided with at least one protective element configured for preventing droplets of molten casting material from coming in contact with the heat resistant impermeable diaphragm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

(2) FIGS. 1A to 1F are schematic isometric views showing consecutive stages of manufacturing a casting mold according to the present application;

(3) FIGS. 2A to 2F are schematic isometric views showing consecutive stages of manufacturing a casting mold according to another example of the present application;

(4) FIG. 3 is a schematic top view of a casting system according to the present application;

(5) FIG. 4 is a schematic side view of the casting system shown in FIG. 3, shown during a casting process;

(6) FIGS. 5A to 5F are schematic side views of consecutive stages of casting an item using the system shown in FIGS. 3 and 4;

(7) FIG. 6 is a schematic side view of another example of a casting system according to the present application; and

(8) FIG. 7 is a schematic cross-section view of a casting system comprising a casting mold according to another example of the present application.

DETAILED DESCRIPTION OF EMBODIMENTS

(9) The casting mold preparation suggested herein uses the investment method. Casting mold herein combines a body (slurry after drying) together with one or two layers as will be discussed later on. The die suggested herein for the casting mold preparation is a frame made of plastic or metal (C). The frame can be designed in accordance with the unique shape of the part to be cast. The method described herein enables changing the sample orientation in a very simple manner, which simplifies the development process, and enables optimization between all casting considerations for best quality. It also enables cost reduction by lowering the slurry consumption.

(10) With reference to FIGS. 1A to 1F, the Various stages of forming a casting mold: are shown. In FIG. 1A, the model M (generally referred to as a wax pattern), mimicking the object to be cast, is shown positioned on a base B. The frame is installed on a silicon base (B). The wax pattern M can be mounted on the silicon base or hung from the top base.

(11) Thereafter, a case C is constructed around the model M, compactly fitting the dimensions of the model. M, as shown in FIG. 1B. The case is mounted on the silicon base B in an upright position.

(12) At the next stage, shown in FIG. 1C, a ceramic blanket 14 is inserted into the case C, fitted against the inner surface thereof. Fibers from heat resistant material are placed along the internal side of the frame walls. Its thickness and toughness allow the ceramic blanket to maintain its shape and stability after placement, and throughout the slurry pouring. This layer is called herein hot permeable layer or main layer. The main layer has at least two applications:

(13) a. preventing casting mold cracks during cooling. The slurry slightly penetrates the ceramic blanket. The penetrated thickness of the ceramic becomes a compound layerceramic body and ceramic fibers. The compound layer is strong and flexible which enables a good reaction to expansion/shrinkage during heating and cooling and therefore prevents cracks. The total order: body-body+fibers-fibers, is a strong and flexible order which enables good crack protection (in addition, it is preferable to use a steel net or fibers at the top or bottom of the casting mold base for extra strengthening).

(14) b. creating a permeable layer around the body for good protective gas penetration, and a good, uniform vacuum around the cast. There is only a partial permeation of the slurry to the ceramic blanket and the remainder of the blanket thickness retains its original qualities. This section of the ceramic blanket replaces the conventional vacuum chamber space.

(15) Other suggestions for use of ceramic blanketceramic blanket can also be used as cover of the inner side of a flasksealed or perforated. In a sealed flask, it creates a vacuum chamber on the inner surface of the flask and avoids cracks. In a perforated flask, it enable avoiding cracks without harming the vacuum

(16) Following the above, the internal space of the case C is filled with a slurry 16 as shown in FIG. 1D, and the bubble treatment begins (the common methods are vibration and vacuum treatment).

(17) Once the slurry is hardened, the case C can be removed as shown in FIG. 1E, during which the die (frame and silicon base) is disassembled leaving a solid mold (also referred herein as body), wrapped in a ceramic fibrous blanket 14.

(18) It is appreciated that drying and heating in the furnace can be performed. After cooling to a given point, the body with the ceramic blanket can be wrapped with an additional permeable layer as shown in FIG. 1F, referred herein as cold permeable layer or auxiliary layer (17).

(19) As will be explained in detail with respect to FIGS. 3 to 5F, during casting, the diaphragm, together with the two layers, create a vacuum chamber around the casting mold. The aim of the cold permeable layer 17 is to thicken the chamber in order to get better vacuum uniformity around the cast. The cold permeable layer material can be less heat resistant than the hot permeable layer, with less strength, much bigger pores and higher pore density. For the cold permeable layer a polymeric fabric can be used. This fabric can be reused many times.

(20) With reference to FIGS. 2A to 2F, the stages of forming a casting mold are shown, this time at a different positioning of the model M. In FIG. 1, the frame shape is rectangular, however for the orientation in FIG. 2A, a frame following the contour of the part saves slurry consumption, compared to a rectangular design of the box being placed around the model M as oriented in FIG. 2A.

(21) It is appreciated that while the stages of forming the mold are the same, the orientation of the model M and the shape of the box allow optimization of the space and amount of slurry required.

(22) The casting system S comprises a casting surface, casting mold, an impermeable diaphragm configured for covering said casting mold when positioned on said casting surface, so as to form with said casting surface a casting space, and at least one outlet configured for withdrawing gas from said sealed casting space. An addition of an inlet configured for inflating gas into the casting space makes great advantage as will discuss further.

(23) With particular reference being made to FIGS. 3 and 4, the casting system S comprises a casting surface in the form of a casting table (1), a sealing frame (2) with a rubber seal (3), clamps (4), and a stand for placement of the casting mold (5). A soft stand is recommended. Sealing frame (2) rubber seal (3) and clamps (4) are also called herein sealing arrangement.

(24) Two nozzlesinlet (6) and outlet (7), are located on table in an area which is configured for forming part of the casting space. The inlet nozzle (also inlet) is connected via a tube to a protective gas tank (8) with a valve (9), and the outlet nozzle (also outlet) is connected via a tube to a vacuum machine (10) with a valve (11).

(25) With reference now being made to FIGS. 5A to 5F, the casting mold is positioned on the stand (5) in a way that the inlet and outlet nozzles are located below the casting mold. The diaphragm 18 is placed over the casting mold so that the outer edge of the impermeable diaphragm (18) is anchored to the sealing arrangement via its edge area 18a (see FIG. 4), thereby forming a casting space which is constituted by the casting surface of the table 1, and the diaphragm (forming its top and side portions). The space which is created by anchoring the diaphragm to the casting table is called herein casting space.

(26) The impermeable diaphragm is flexible, strong, and heat resistant to the casting mold temperature before casting, but will melt at the temperature of the liquid metal.

(27) To insure protection of the diaphragm from liquid metal droplets, a ceramic blanket (19) and a metal sheet (20), which is called herein also protective element, are placed above the sprue, leaving the sprue exposed. A funnel (21) and filter (22) are placed on the metal sheet, above the sprue.

(28) After positioning the casting mold, attaching the diaphragm, positioning the protective blanket, ceramic blanket and protective element and assuring that valve (11) is closed, valve (9) is opened. Protective gas inflates the diaphragm and penetrates to the casting mold's pores. When the diaphragm is fully inflated, valve (9) is closed. At this point it is suggested allowing a suspension or rest time. In any case, inflation of the diaphragm with protective gas enables good gas penetration to the casting mold's pores which promises a protective atmosphere all around the cavity during casting. Inflating the diaphragm also enables leakage testing before the vacuum operation.

(29) Before casting, valve (11) is opened and the vacuum machine (10) is turned on. The diaphragm wraps the casting mold. The vacuum suction works all around the cavity thanks to the permeable layers that surround the casting mold. Initially, the diaphragm attaches to the casting mold and only after that, the diaphragm adheres to the sprue.

(30) At this point, the casting mold may still contain remnants of gas that flow to the cavity before and during casting. The timing for pouring can be controlled by a vacuum gage, to the point where the casting mold still contains some remnants of gas but the vacuum is strong enough for casting. After pouring, a protective gas supply above the sprue may be beneficial.

(31) After the metal solidifies, the vacuum machine is shut off, and the valve (11) is closed.

(32) FIGS. 5A to 5F show the process steps. In FIG. 5A the casting mold is positioned on the casting surface. In FIG. 5B the outer edge of the impermeable diaphragm is anchored around and above the casting mold. In FIG. 5C a ceramic blanket, metal sheet (protective element), funnel and filter are added to the system. In FIG. 5D, protective gas inflates the diaphragm and in FIG. 5E, the vacuum machine is turned on and the diaphragm wraps the casting mold. FIG. 5F present the system after pouring the liquid into the cavity.

(33) Turning now to FIG. 6, another example of a casting system S is shown, in which the casting table comprises a casting surface 2 and a side wall 5 having, at a top end thereof, a rim area. This side wall 5 forms a portion of the casting space, so that when the diaphragm 18 is positioned over the side wall and is secured to the fastening arrangement, the casting space is defined by:

(34) a base constituted by the casting surface 2;

(35) a side portion constituted by the side wall 5; and

(36) a casting face constituted by the diaphragm 18.

(37) The diaphragm 18 is so dimensioned that it has a central portion configured for being juxtaposed with the opening of the mold through which molten material is poured therein, and a peripheral area, constituting the boundary area, which adheres to the casting mold under the application of vacuum (these are demonstrated in FIG. 7 with respect to another configuration of the casting system). Thus, when the central area of the diaphragm is breached by being melted away by the cast molten material, the peripheral area is still adhered to the casting mold, maintaining the required vacuum during casting. It is noted that since the diaphragm is breached, the level of vacuum may not be identical to that before the breaching, but it is still sufficient for maintaining a 20 required level for the purpose of casting.

(38) One of the advantages of this unique design, both in the casting system S and the casting system S described above, lies in the fact that the diaphragm, when vacuum is applied, adheres to the casting mold. This allows the casting system with a greater degree of flexibility in terms of the molds which can be used in the system.

(39) Turning now to FIG. 7, another example of a casting system is shown in which the casting system further comprises a side wall F and a top closure T, both being rigid. The top closure T constitutes a part of the casting face and is formed with an opening through which molten material is cast into the cavity 15 of the mold 16.

(40) The diaphragm 18 comprises an edge area 18a, a peripheral area 18b and a central area 18c, constituting the remainder of the casting face. The arrangement is such that upon application of vacuum to the casting space, as shown in FIG. 7, the central portion 18c of the diaphragm 18 is sucked into the sprue and the peripheral area 18b is adhered to an area surrounding the sprue.

(41) Thereafter, when molten material is introduced into the mold through the casting face, it melts away the central portion 18c of the diaphragm 18. However, as long as air is removed from the casting space via the outlet (designated by the arrow below the casting surface), the peripheral portion 18c of the diaphragm 18 remains adhered to the surrounding area of the sprue, whereby a certain level of vacuum in the casting space is maintained.

(42) This arrangement of the diaphragm allows maintaining the required level of vacuum during the entire casting process, even after the central portion 18c has been melted away, thereby optimizing the casting process.

(43) Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations, and modifications can be made without departing from the scope of the invention, mutatis mutandis.