GB2045130A - Casting apparatus - Google Patents

Abstract

The cylinder 1 of an arrangement for closing a presser lid 3 on a mould which results in metal being forced from a cup above the mould cavity into the mould cavity (Figure 2 not shown) has a vent 14 to allow for rapid downward movement of the piston rod 2 and the lid 3. The cylinder is two-way. Small articles, eg dental inlays, can be cast. Compressed air forces the rod downwards and then acts down a bore of the rod 2 to move the metal. <IMAGE>

Description

SPECIFICATION Casting apparatus The present invention relates to a casting apparatus which is particularly suitable for producing small castings, such as dental inlays, of high quality free from cavities and other defects, using a small amount of metal, in a smooth and rapid operation.

Although the invention is described herein as applied to casting a dental inlay, it is not limited thereto and is applicable tO the production of other various castings using a small amount of metal.

Success our failure in casting small articles depends on how high a casting pressure is applied as soon as the casting operation is started (namely, the initial casting pressure). The same may be said of casting dental inlays. Casting apparatus for producing dental inlays is mostly of the centrifugal type. This type of apparatus, however, is naturally limited in initial casting pressure, and it ahs been pointed out that the apparatus often causes defects in castings particularlywhen metals of high melting point are used.

Moreover, the centrifugal casting process involves rotating the mould and molten metal at high speed, being liable to create dangers.

Under these circumstances, efforts have heretofore been made to provide a casting process which can supersede the centrifugal casting process. As a result, compression type casting apparatus using an air cylinder has been developed. The arrangement of this type of apparatus is, for example, as shown in front view, partly broken away, in Figures 1 and 2 of the accompanying drawings. In these figures, 1 designates an air cylider; 2 designates a cylinder rod; 3 designates a presser lid; 4 designates a mould; and 5 designates a mould pedestal.A compression spring 6 is disposed in a pressure chamber la on the rod retracting side of the cylinder 1, while a pressure chamber 1b on the rod advancing side has a compression air pipe 7 connected thereto which leads to a switching valve 8 operable to allow said chamber 1b to communicate with a compressed air source or with the atmosphere. Accordingly, when compressed air is fed into the pressure chamber 1b, the rod 2 will advance while compressing the spring 6 (Figure 2), but when the pressure chamber 1b is allowed to communicate with the atmosphere to release the compressed air therein, the pressure therein will return to atmospheric, resulting in the spring 6 moving the rod 2 to its retracted position (Figure 1).Further, the rod 2 is provided with a small throughgoing hole 9 on its longitudinal axis so that when the rod 2 is lowered until the presser lid 3 is urged against the upper surface of the mould 4, the air pressure acts on the top of the mould to force a molten metal 10 into a mould cavity 4a.

For the production of castings by the use of this type of apparatus, the rod 2 is held in its raised position (Figure 1) while a metal is placed in a well 4b in the mould 4 and is melted as by an oxygenacetylene burner 11, whereupon the rod 2 is lowered to carry out casting. The most important factor is the speed at which the rod 2 is lowered. Too low a lowering speed for the rod 2 would result in the molten metal 10 being cooled or oxidized, causing defects in the casting, since the molten metal for the small casting has a large specific area. This problem is liable to occur particularly when easily oxidizable high melting point alloys, such as Ni-Cr alloys recently developed for use as dental inlays, are used.

In such case, therefore, it is imperative that the lowering speed of the rod 2 be increased. With the illustrated casting apparatus, however, since the rod 2 has to be lowered against the force of the compression spring 6, its speed is limited and it is impossible to achieve a sufficient lowering speed.

Conventionally, therefore, in order to obtain a substantial initial casting pressure despite the low lowering speed, the vertical stroke of the rod 2 (indicated at S in Figure 2) has been shortened. Thus, the spacing between the mould 4 and the presser lid 3 is small to the extent that the operation of melting the metal is extremely difficult and the flame is liable to damage the presser lid.

With the above matters in mind, the present invention has been accomplished and has for its object the provision of a casting apparatus wherein the lowering speed and vertical stroke of the cylinder rod are increased and yet a sufficient initial casting pressure can be obtained. Another object of the invention is to provide an apparatus whereby even an easily oxidizable high-melting-point alloy can be satisfactorily cast without causing oxidation and other drawbacks. A further object of the invention is to provide an apparatus which allows a metal to be heated with ease for melting without the danger of damaging the apparatus by the flame. Still a further object of the invention is to provide an apparatus capable of securely casting small articles, such as dental inlays. These and other objects and features of the invention will become more apparent from the following description.

A casting apparatus according to the invention which achieves these objects comprises a vertical type cylinder containing a cylinder rod having a long stroke, and a mould pedestal positioned below said cylinder, wherein said cylinder rod, with a presser lid attached to its lower end, has a small hole axially extending therethrough substantially at its centre axis, and a small vent hole is formed in said cylinder in its lower wall portion or in a rod raising pressure line which connects the cylinder to a cylinder operating switching valve.

The invention will now be described with reference to Figures 3 to 8 of the accompanying drawings illustrating an embodiment thereof, and in which: Figure 3 is a front view, partly broken away, of a casting apparatus according to the invention; Figure 4 is a side view of the apparatus partly broken away; Figure 5 is a front view of the apparatus, partly broken away, showing a cylinder section, and Figures 6to 8 illustrate a sequence of operations of the casting apparatus of the invention.

Referring to Figures 3 to 5, the illustrated casting apparatus embodying the present invention comprises a vertical type cylinder 1 containing a cylinder rod 2 having a long stroke, a presser lid 3 attached to the lower end of said rod 2, and a mould pedestal 5 positioned below said cylinder 1. The cylinder 1 and the mould pedestal 5 are integrally connected by a pillar 16. The raising and lowering operation of the rod 2 is performed by a switching valve 12.Thus, the switching valve 12 has connected thereto a pipe 13a leading to the rod raising pressure chamber 1a of the cylinder 1, a pipe 1 3b leading to the rod lowering pressure chamber 1 b of the cylinder, a pipe 13c (to be later described) connected to a compressed air supply source, and a pipe 1 3d (to be later described) which opens to the atmosphere at its other end. The manipulation of the switching valve 12 enables the rod 2 to be raised and lowered, as desired. A 3-position valve is usually used as said switching valve 12, the operation thereof for raising and lowering the rod 2 being later described with reference to Figures 6 to 8.Further, the lower wall portion of the cylinder is provided with a smalldiameter vent hole 14, which plays a very important role in increasing the lowering speed of the rod 2.

The rod 2 is formed with a small-diameter throughgoing hole 9 substantiaily on its longitudinal axis, which, as in the case of Figures 1 and 2, serves as a compressed gas passage. The lower surface of the presser lid 3 and the upper surface of the mould pedestal 5 have installed thereon heat-resistant sheets, for example asbestos sheets 15, for the dual purpose of sealing in the compressed gas and absorbing a shock. For convenience of replacement, such sheets may be removably mounted as by an attaching member3' (Figure 3).

The casting operation of this apparatus is basically the same as that described with reference to Figures 1 and 2. Thus, with the rod 2 raised, the mould 4 is placed on the mould pedestal 4 and an alloy to be cast is put in a well 4b and heated until it becomes molten, whereupon the rod 2 is lowered so that the melt forcing effect of the compressed gas being fed via the throughgoing hole 9 forces the molten metal in the well 4b into a mould cavity 4a.

In the present apparatus, both the raising and the lowering of the rod 2 are effected by compressed gas, and the provision of the vent hole 14 in the lower wall portion of the cylinder 1 enables the lowering speed of the rod 2 to be surprisingly increased, with the resu It that the vertical stroke of the rod 2 can be increased. Therefore, when a metal to be cast is heated for melting, the spacing between the mould 4 and the presser lid 3 can be kept sufficiently large to provide for a smooth and secure melting operation.

The mechanism for raising and lowering the rod 2 will now be described in more detail with reference to Figures 6 to 8.

At the preparatory stage, as shown in Figure 6, the rod 2 is raised and the switching valve 12 is set at its neutral position. In this condition, the set-up of the mould 4, the placement of the metal in the mould and the heating and melting of the metal are performed. During these operations, since the rod raising pressure chamber 1a of the cylinder 1 is in communication with the atmosphere through the vent hole 14, the interior thereof is maintained at atmospheric pressure.

Upon completion of the melting of the metal, the valve 12 is switched to the rod lowering position, as shown in Figure 8. As a result, the compressed gas from the pressure source P is fed into the rod lowering pressure chamber 1b of the cylinder 1 successively through the pipe 13c, valve 12 and pipe 13b, and concurrently the air in the rod raising pressure chamber 1a is released to the atmosphere successively through the pipe 13a, valve 12 and pipe 13d. Accordingly, the rod 2 is lowered. The lowering speed will vary with the gas pressure being applied to the cylinder, but in order to increase the lowering speed to a maximum, it is necessary to discharge the air contained in the rod raising pressure chamber 1a as quickly as possible.With known cylinders of this type, however, there is a substantial flow resistance particularly in the switching valve section, tending to increase the pressure in the pressure chamber la as the rod 2 is lowered. The higher the lowering speed, the greater this tendency, thus further impeding the lowering of the rod 2. In contrast thereto, according to the invention, the vent hole 14 in the lower wall portion of the cylinder provides for quick discharge of air, there is no danger of the pressure in the pressure chamber 1 b rising owing to insufficient venting. Accordingly, the rod 2 will descend at a high speed determined by the gas pressure applied to the lowering pressure chamber 1b.

In this connection, it has been found that in the absence of the vent hole 14 in the cylinder shown in Figures 3 to 8, the application of 10-atm air gave a lowering speed of only about 500 mm sec at the most but that in the presence of a 1-mm diameter vent hole 14 in the cylinder, a lowering speed of 600 mm/sec was attained with a pressure of as low as 3 atmospheres.

Subsequently, feeding and casting is performed in the same manner as described previously (the pressurized condition being maintained usually for 20 to 60 seconds), whereupon the valve 12 is switched to the rod raising position, Figure 7. Since a portion of the compressed gas contained in the rod raising pressure chamber la flows out through the vent hole 14, the ascending speed of the rod 2 is somewhat decreased, but this does not matter in practice because the casting has already been completed.

Upon completion of the raising of the rod 2, the valve 12 is switched to the neutral position, as shown in Figure 6, to cut off the supply of compressed gas, resulting in the compressed gas in the rod raising pressure chamber 1a flowing out through the vent hole 14. Accordingly, the pressure in the pressure chamber 1a is restored to atmospheric. If such vent hole 14 is not provided, the shifting of the valve to the neutral position results in the pressure chamber 1b being completely sealed, so that the pressure used in raising the rod is maintained as such in the chamber, thus forming a major cause of impeding the lowering of the rod 2 in the next casting operation. The provision of the vent hole 14 also solves this problem.

As has been described so far, the vent hole 14 serves to (1) restore the pressure in the rod raising pressure chamber 1a present before rod lowering operation (namely, before casting operation) to atmospheric and (2) accelerate the discharge of gas from the rod raising pressure chamber 1a during the rod lowering operation, thereby surprisingly increasing the speed at which the rod 2 is lowered. As considered from these functions, the greater the diameter of the vent hole, the more desirable.

However, if the vent hole 14 is too large, the raising of the rod 2 would become impossible or extremely slow. Therefore, a compromise must be made between these two factors in deciding the diameter of the vent hole. Generally, it is effective to select values of about 1/100 to 1/10 of the effective cross-sectional area of the pipe 13a connected to the rod raising pressure chamber la. The vent hole 14 is not limited to a circular shape. In fact, it may be an "irregular" shape, such as an ellipse, rectangle or slit-form.Further, in the exmple shown in Figures 3 to 8, the vent hole 14 has been shown as provided in the lateral wall of the cylinder 1, but substantially the same effectiveness may be retained even if it is provided in a suitable portion of the pipe 13a (which is connected to the rod raising pressure chamber la), said pipe 13a connecting the cylinder 1 to the switching valve 12.

The configuration and construction of the entire casting apparatus and of the components thereof may be modified, or other mechanisms may be affixed, as needed. For example, a vibrator (shown at 16 in Figure 4) may be attached to the bottom of the mould pedestal to vibrate the moulding during the solification of the molten metal, thus retarding the growth of the metal structure of the casting to make the crystals finer, while homogenizing the metal structure throughout from the surface to the innermost part. Accordingly, castings of superior quality can be obtained. Further, a pressure gauge may be affixed to the pressure line or a rod lowering speed indicator may be installed.

The present invention arranged as described above has the following merits.

(1) The greatly increased lowering speed of the rod provides for sufficiently increasing the initial casting pressure essential for castings using a small amount of metal. Thus, castings of high quality can be obtained.

(2) The greatly decreased time interval from the melting of the metal to the forcing of the melt minimizes the possibility of developing defects in the casting owing to the cooled solidification and oxidation of the molten metal.

(3) The increased rod stroke permitted by the increased lowering speed of the rod provides for a sufficient spacing between the mould and the presser lid in the heating and melting operation on the metal to facilitate and ensure such operation.

(4) The features (1) to (3) enumerated above qualify the present invention for application to the production of a variety of small castings, including dental inlays and dental metal bases, with the greatest advantage.

The invention is not limited to the embodiment described above and may be modified without departing from the scope of the appended claims.

For example, the shape and construction of the components, and the position where the vent hole is formed, may be changed, or pressure gauges, raising and lowering speed adjusting means or other devices may be affixed to the apparatus.

Claims (10)

1. A vertical type casting apparatus for casting small amounts of metal, comprising a vertical cylinder containing a cylinder rod having a long stroke and a presser lid attached to the lower end thereof, a mould pedestal positioned below said cylinder, said cylinder rod having a small hole extending longitudinally therethrough substantially on its axis, and a vent hole formed in the lower wall portion of the cylinder in a rod raising pressure line which connects said cylinder to a cylinder operating switching valve.

2. An apparatus as set forth in Claim 1,wherein the area of said vent hole is from 1/100 to 1/10 of the effective cross-sectional area of the gas feeding and discharging piping.

3. An apparatus as set forth in Claim 1 or 2, wherein said mould pedestal is arranged so that it can be vibrated.

4. An apparatus as set forth in Claim 1, 2 or 3, wherein a heat-resistant sealing material is applied to the lower surface of said presser lid.

5. An apparatus as set forth in Claim 4, wherein said heat-resistant sealing material is asbestos.

6. An apparatus as set forth in Claim 4 to 5, wherein said sealing material is removably attached to the lower surface of said presser lid by an attaching member.

7. An apparatus as set forth in any one of the preceding claims, wherein the switching valve is a 2-position valve.

8. An apparatus as set forth in any one of the preceding claims, wherein the vertical cylinder and mould pedestal are integrally connected by a pillar.

9. An apparatus as set forth in any one of the preceding claims, when used for casting dental inlays.

10. A vertical type casting apparatus for casting small amounts of metal, substantially as hereinbefore described with reference to Figures 3 to 8 of the accompanying drawings.