US3774668A

US3774668A - Vacuum casting apparatus

Info

Publication number: US3774668A
Application number: US00126007A
Authority: US
Inventors: J Heimgartner
Original assignee: Sulzer AG
Current assignee: Sulzer AG
Priority date: 1969-02-28
Filing date: 1971-03-19
Publication date: 1973-11-27
Anticipated expiration: 1990-11-27
Also published as: NL6905546A

Abstract

A mold core and a mold casting are positioned to define a mold cavity and the melt of the material is drawn into the cavity under vacuum. The vacuum can be eliminated after the melt in the cavity has solidified about the melt entrance openings leading into the cavity or can be maintained to some degree to draw off gases. The resulting casting can be of any shape and, where annular, can be used to make piston rings.

Description

United States Patent 1 1 Iten et al. 1 1 Nov. 27, 1973 54] vAcUUM CASTING APPARATUS 2,082,588 6/1937 Menetrey 1641254 x Inventor: Julius Heimgarmer Post 2,210,544 8/1940 Galloway 164/119 X 5 Amkom swlilerland .n FOREIGN PATENTS OR APPLICATIONS [73] Assignee: Sulzer Brothers, Ltd., Winterthur, 644,194 7/1962 Canada 164/306 Switzerland 1,055,764 4/1959 Germany 164/306 22 Filed: Mar. 19, 1971 Primary Examiner-J. Spencer Overholser [211 P 126,007 Assistant Examiner-John E. Roethel Related U.S. Application Data Division of Ser. No. 820,385, April 30, 1969, 9 1199 225111,

ForeignAppllcation Priority Data Feb. 28, 1969 Switzerland 3034/69 U.S. Cl 164/255, 164/63, 164/337 Int. Cl B22! 27/16 Field of Search 164/113,114,118, 164/119, 61, 63,133,136, 253, 254, 255,

References Cited UNITED STATES PATENTS 10/1948 Higgins 164/114 Attorney-Kenyon & Kenyon Reilly 8L Chapin [57] ABSTRACT A mold core and a mold casting are positioned to define a mold cavity and the melt of the material is drawn into the cavity under vacuum. The vacuum can be eliminated after the melt in the cavity has solidified about the melt entrance openings leading into the cavity or can be maintained to some degree to draw off gases. The resulting casting can be of any shape and, where annular, can be used to make piston rings.

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SHEET 5 OF 5 In venfor uuuus HEIMGQRTNER ATTOR EYS VACUUM CASTING APPARATUS This application is a division of Ser. No. 820,385 filed Apr. 30, 1969, now abandoned.

This invention relates to a method and apparatus for casting of articles and to the article produced. Still more particularly, this invention relates to a method and apparatus for casting a hollow cylindrical blank for use in making piston rings.

The construction of modern internal combustion engines with elevated pressures in the cylinders and increased rotational speeds as well as the adoption of lighter construction methods have greatly increased the stresses imposed on piston rings. Moreover, there is a demand for the use of piston rings of progressively decreasing material cross-section and in particular for piston rings of small height. Accordingly, materials of high static and dynamic strength, high modulus of elasticity and high impact strength, for example certain mallcable cast and spheroidal graphite cast grades are increasingly employed for piston ring materials. In addition, at the present time, it appears to be necessary for the production of high-grade piston rings in most cases to produce such piston rings by the form turning method from cast blanks which substantially correspond to the finished ring shape.

The use of the aforementioned new materials as well as the very small height often adopted for piston rings leads to difficulties in casting and subsequent treatment of the blanks. Known casting methods for the production of piston rings, namely the individual casting methods, centrifugal casting methods and sleeve casting methods no longer meet the requirements. For example, the individual casting method is unsuitable because, in view of the small material cross-section of the piston rings to be cast, the metallurgical facilities militate against the metallurgical requirements with regard to the sliding and running characteristics of the wear resistance. Moreover, the efficiency of such methods is questionable in view of the solidification conditions which prevail with these methods. A principal disadvantage of the centrifugal casting method for the production of piston rings is its inability to cast noncircular blanks of the kind frequently required for the production of piston rings. Moreover, the machining allowances are large and not uniform over the entire length of the external circumference. The solidification conditions are also unfavorable in the sleeve casting methods, where the material is cast in wet or dry sand. Moreover, this method requires relatively large machining allowances on the external and internal sleeve circumference. However, these allowances have not been uniform over the entire length of the sleeve and thus render manufacture of the pistonrings more expensive. This added expense in also due in part to the high mechanical strength of modern piston ring materials.

Accordingly, it is an object of the invention to provide an economical method of casting blanks for making piston rings.

It is another object of the invention to provide an apparatus for producing a casting in a relatively simple economical manner.

It is another object of the invention to produce a casting blank which can be readily formed into precision piston rings.

lt is another object of the invention to be able to cast modern casting materials into hollow shapes with a relative minimum of effort and with a high degree of efficiency.

It is another object of the invention to provide an apparatus for vacuum casting large castings economically, the filling opening having a large diameter so that the casting material can flow rapidly into the mold.

Briefly, the invention provides a method and apparatus for casting melts of materials into casting blanks with the use of a vacuum.

The method generally consists in bringing a mold cavity into contact with a melt through a relative movement between the mold cavity and melt, in subsequently evacuating the mold cavity so that the melt enters into and rises within the mold cavity until reaching a predetermined height, and in allowing the melt to solidify in the mold cavity. The evacuation of the mold cavity is maintained at least for as long as is necessary for the communicating filling passage between the mold cavity and melt to be interrupted by solidified melt material while a hydrostatically sealing means is used to close off the filling passage to a backflow of the melt material from the mold cavity.

The casting produced in accordance with the method may be a hollow cylindrical casting. The casting can be widely employed, either as an individual product or as a starting product for further processing, for example for processing into valve seat rings.

The apparatus of the invention includes a chamber which can be evacuated and which serves as a mold cavity. The chamber is provided with at least one filling passage for introduction of the melt into the interior of the chamber and is otherwise closed. In addition, the apparatus includes means for inducing relative motion between the mold and the melt.

In one embodiment of the apparatus, the chamber can be provided with an outlet for connecting to a suitable vacuum source for evacuation of the chamber interior. In another embodiment, the chamber can be made of porous material and can be evacuated by a suitable vacuum source through the walls of the chamber.

In another embodiment the chamber is formed with a core, a mandrel which engages the core and a split mold which envelops the core and mandrel so as to define a mold cavity therebetween.

In another embodiment, the chamber can be formed by a mold having a plurality of cores wherein the mold communicates through a sprue with the melt. In this instance, the mold is placed in a housing in spaced relation to the walls of the housing and the resulting space is connected to a vacuum source for evacuation. The mold is either porous to the passage of air and gas or is provided with outlets to communicate the mold cavity with the housing interior.

In addition, the sprue is provided with any one of a number of various sealing means to seal off the mold cavity against a back flow of the melt from the cavity prior to solidification. For example, a reverse bend or a valve arrangement can be used to block the back flow of melt.

The mold chamber of the apparatus can be filled from the bottom and can remain in a stationary position until solidification takes place or can be tilted about a horizontal axis after filling so as to prevent leakage while solidification takes place. Further, the chamber can be rotated about a vertical axis so that the melt can solidify under centrifugal force against the side walls of the chamber.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a cross sectional view of a casting apparatus according to the invention;

FIG. 2 illustrates a view of the riser tube of FIG. 1 after emerging from a melt;

FIGS. 3 and 4 each illustrate various embodiments of a sealing means according to the invention;

FIG. 5 illustrates a casting apparatus adapted for rotation according to the invention; and

FIG. 6 illustrates a further casting apparatus adapted for rotation according to the invention.

Referring to FIG. 1, the casting apparatus has a housing 201 with a casting mold 202 incorporated therein. The mold 202 is constructed of cores 203 of a conventional mold sand or molding compound and is provided with a riser tube 204 of gas impermeable material which communicates with the mold cavity 222 of the mold 202. The riser tube 204 has a refractory lining 205 so that a sprue 206 is formed. The riser tube 204 also has a sealing means in the form of an integral U- shaped part 233 on the lower end of the riser tube 205 to form a communicating vessel and to extend into the lower end of the sprue 206. The housing 201 is hermetically closed with a cover 309 by means of screws 210. The cover 209 is provided with a suction line 211 which is connected via a flexible hose 212, a regulating valve 213 and a pipe section 214 containing a pressure gauge 215 to a vacuum line 216. The vacuum line 216 extends into a vacuum source (not shown). The pressure in the vacuum line 216 can be regulated by means of a regulating valve 217 which communicates via a pipe section 218 with atmosphere.

The casting mold 202 is located in the housing 201 by means of a plurality of screws 219 which bear upon a plate 220 so that the mold 202 is surrounded by a vacuum chamber 221. In order to enable the vacuum prevailing in the suction line 211 to extend into the mold cavity 222, the plate 220 is constructed of porous, gas permeable material. Alternatively, or in addition, the plate 220 can be provided with apertures 223 for communicating the mold cavity 222 with the vacuum chamber 221.

In use, the casting apparatus is disposed over a melting furnace or a ladle 224 containing a melt (casting material) 225. The riser tube 204 is immersed in the melt 225 so that the mold cavity 222 is sealed off from atmosphere. Next, with the sealing means 207 in the sprue 206 being open, the vacuum in the vacuum line 216 is adjusted to a value which, after opening of the valve 213, produces a vacuum in the mold cavity 222 which ensures that for a given specific gravity of the casting material, its vapour pressure and prevailing barometric pressure the casting material flows into the casting mold 202 at optimum velocity.

The gases formed from the mold material are drawn off via the suction line 211 through the plate 220 and through the porous mold material of the casting mold 202. After the entire mold cavity 222 is filled with casting material, the casting mold 202 may then be moved outside the ladle zone. When the riser tube 204 emerges after the casting operation from the melt (FIG. 2), the casting material is retained in the casting mold by virtue of the atmospheric pressure acting on the casting material level 234 in the section 233a of the U- shaped part 233, provided the vacuum in the casting mold is sufficiently high. The sealing means thus operates hydrostatically. After closing of the valve 213, it is possible for the housing 201 to be opened and the casting mold 202 to be dismantled and for the casting to be removed.

Instead of being constructed of porous materials such as molding sand, the casting mold 202 may also be constructed of solid material, for example ceramics, steel or a plastic. In order to vent such a mold cavity it is necessary for the cavity to be connected via one or more venting ducts to the vacuum chamber 221 which surrounds the casting mold. The venting ducts must also be sufficiently small to ensure that the casting material entering therein solidifies directly.

Referring to FIG. 3, the sealing means can also be constructed as an automatic ball valve 235 which is disposed in the sprue 206. The ball valve 235 has a valve ball 236 which cooperates with a seat cone 237 in the lining in order to control the flow in the sprue 206. The valve 235 is employed in the event that the weight of the ball is greater than its buoyancy in the casting material. For example, if the casting material comprises aluminium, it is possible for the ball 236 to be constructed of steel. When the casting material rises in the sprue 206 during the casting operation, the ball 235 is raised as far as a stop 238 so that the casting material can enter the mold cavity. On completion of the casting operation the ball 235 is once again lowered on to the seat cone 237 and in this position closes the sprue 206 to prevent the discharge of casting material.

Referring to FIG. 4, the sealing means can also be formed as a ball valve 240 having a ball 241 which cooperates with a seat cone 242. This valve 240 is used in the event that the weight of the ball 241 is less than its buoyancy in the casting material. This may occur, for example, in the case of a hollow sphere of plastic material and where wax or plastic, for example, Caprolactam, is used as the casting material. When the casting material rises in the sprue duct 206, the ball 241 is moved from the seat cone 242 by the casting material and thrust against a stop 243 so that the casting material can enter the mold cavity. After completion of the casting operation, the ball 241 is once again thrust on to the seat cone 242 by virtue of the casting material buoyancy thus closing the sprue duct 206.

The sealing means described hereinbefore are all disposed in or on the sprue of the casting mold. Further, by providing the floor of the casting mold with the appropriate shape and dimensions, the sealing means can alternatively be disposed in the floor itself. For the casting operation, the casting apparatus is thus lowered in the direction of the melt until the floor immerses to a reliable extent in the melt.

Referring to FIG. 5, a further construction for preventing the discharge of casting material after emergence of the riser tube from the melt consists in mounting the casting apparatus for rotation about its longitudinal axis. To this end, the housing 201 with the casting mold 202 disposed therein is supported by a hollow shaft 260 which is journalled in a bearing 261. A gearwheel 262 in which a pinion 263 of a motor 264 meshes is mounted on the hollow shafl 260. The motor 264 imparts rotation to the housing 201 and casting mold about the longitudinal axis 265 thereof. The stationary suction line 211 of the vacuum apparatus described hereinabove is connected to the hollow shaft 260 by means of a gland 266 with a seal 267 so as not to participate in the rotation. The casting mold in this instance comprises a vessel 268 of a porous or solid material. If the casting mold is made of molding sand, ceramic or the like, either a back filling 269 of sand or steel scrap is provided between the casting mold and the housing 201 or the casting mold is supported by other mechanical means relative to the housing 201. The floor 270 of the vessel 268 is provided with an aperture 271 while the top of the vessel 268 is closed with a cover 273 which has ducts 272 communicating the mold cavity with the housing interior.

In order to produce a casting the housing 201 is set into rotation while the riser tube 204 is immersed and the suction line 211 is connected to the vacuum apparatus. The casting material which flows into the mold cavity rises on the internal wall of the mold cavity due to the centrifugal force and thus forms a cylinder 274 of casting material thereat. After the casting operation, the vacuum is interrupted, while the rotation of the housing 201 is continued. This prevents discharge of casting material while the casting apparatus is moved outside the ladle zone in order to allow the next casting operation to commence immediately. After the casting material has sufficiently solidified, rotation may also cease.

Alternatively, it may be desirable to maintain the vacuum during rotation in order to enable any gases which may have developed to be directly discharged. During the casting operation, the casting mold need not be rotated while the casting material is drawn up into the mold since it is only necessary to set the casting mold into rotation after the casting material has reached that level in the mold cavity which is determined by the dimensions of the casting. Only then will the casting be molded.

Although rotation of the casting apparatus in this case serves to prevent the discharge of casting material, it is evident that the apparatus described herein may be employed generally as a centrifugal casting apparatus. In known centrifugal casting apparatus with a vertical centrifuging axis, the casting material is introduced through a casting trough, introduced from above into the casting mold and extending with its discharge end to the center of the casting mold. By contrast, the introduction of the casting material into the casting mold by means of suction in the illustrated apparatus (FIG. 12) is substantially simpler and more economical and is associated with less turbulence.

Referring to FIG. 6, a rotating casting apparatus can be constructed without a housing. For example, the casting mold 280 can be formed as a hollow cylinder 281 which is clamped by means of clamping bolts 282 between a supporting plate 283, fixedly joined to the hollow shaft 260 of a driving means (not shown), and a removable floor 284. The hollow cylinder 281, the supporting plate 283 and the floor 284 are made of a strong material, for example steel. The supporting plate 283 is provided with a centering disk 285, for example of ceramic, on which the hollow cylinder 281 is centered relative to the axis of rotation of the casting apparatus. The floor 284 is provided with a riser tube 286 having a lining 287 of a material resistant to the prevailing temperature. The lining 287 is supported by a disk 288 which covers the floor 284 and may be constructed of the same material as the lining 287. The disk 288 also serves to center the hollow cylinder 281.

During use, the casting material is drawn up by a vacuum to pass through the sprue 289 in the riser tube 286 and enters the mold cavity 290 and is centrifuged therein to form a cylinder 291. A centering disk 285 of the corresponding external diameter and a hollow cylinder 281 of corresponding internal diameter is employed depending on the diameter of the casting. Adaptation of the casting apparatus to the length of the casting is made possible without difficulty by the clamping bolts 282.

The invention thus provides a method of producing hollow cylindrical cast blanks which can be used in the manufacture of piston rings with the piston rings being parted from the blanks. Since the material is not cast into sand, the casting material solidifies rapidly. Accordingly, the material structure of the cast blanks is finer, a feature which in turn increases the mechanical strength of the piston rings. Rapid solidification also renders the method more economical. This also applies to the fact that the necessary machining allowances are small so that the subsequent machining work required is small. Piston rings produced in accordance with the invention fully meet the demands of modern engine construction and of efficient production of high-grade piston rings. The method is equally suitable for the production of circular as well as non-circular, for example oval piston rings. The mold and core can also be constructed of appropriate radial cross-sections for the production of non-circular piston rings.

The casting may be made asymmetrical by employing an asymmetrical casting mold and/or core mold. Also, by adopting a suitable shape for the interior wall of the casting mold and/or of the circumferential surface of the core, it is possible to construct the circumference or cavity of the cast object as desired.

The method described above is suitable for the casting of articles of cast iron having spheordial graphite, of malable cast, of mild steel, bronze and other materials. The articles may be heat treated either before, during or after further processing in known manner in order that the material properties adapted to the appropriate requirements may be obtained. The method permits a very rapid casting operation. Further, owing to its simplicity, the method can be adapted without any extensive effort for the purposes of automation by means of suitably designed machines.

The invention further allows the use of a mold with a large filling opening to permit rapid filling while effectively sealing the mold for casting purposes. This permits the vacuum casting of large castings economically.

What is claimed is:

1. A vacuum casting apparatus comprising a mold chamber having a mold cavity therein,

at least one opening in said chamber communicating said mold cavity with the exterior of said chamber for introducing a melt of casting material into said mold cavity,

a sprue extending from said opening,

means for evacuating said mold cavity to draw the casting material through said opening into said mold cavity,

means for moving said chamber and the melt relative to each other to immerse said opening in said melt, and

a U-shaped tube disposed in and extending from said sprue to provide a substantially unhindered rising of the casting material in the mold chamber, said tube further being adapted to hydrostatically prevent a back flow of casting material from said mold cavity after filling thereof.

2. A vacuum casting apparatus comprising a mold chamber having a mold cavity therein,

a sprue extending from said opening,

a ball valve disposed in said sprue to provide a substantially unhindered rising of the casting material in the mold chamber, said ball valve further being adapted to hydrostatically prevent a back flow of casting material from said mold cavity after filling bouyancy in the casting material.

Claims

1. A vacuum casting apparatus comprising a mold chamber having a mold cavity therein, at least one opening in said chamber communicating said mold cavity with the exterior of said chamber for introducing a melt of casting material into said mold cavity, a sprue extending from said opening, means for evacuating said mold cavity to draw the casting material through said opening into said mold cavity, means for moving said chamber and the melt relative to each other to immerse said opening in said melt, and a U-shaped tube disposed in and extending from said sprue to provide a substantially unhindered rising of the casting material in the mold chamber, said tube further being adapted to hydrostatically prevent a back flow of casting material from said mold cavity after filling thereof.

2. A vacuum casting apparatus comprising a mold chamber having a mold cavity therein, at least one opening in said chamber communicating said mold cavity with the exterior of said chamber for introducing a melt of casting material into said mold cavity, a sprue extending from said opening, means for evacuating said mold cavity to draw the casting material through said opening into said mold cavity, means for moving said chamber and the melt relative to each other to immerse said opening in said melt, and a ball valve disposed in said sprue to provide a substantially unhindered rising of the casting material in the mold chamber, said ball valve further being adapted to hydrostatically prevent a back flow of casting material from said mold cavity after filling thereof.

3. A casting apparatus as set forth in claim 2 wherein said ball valve includes a seat and a ball located above said seat and being of a weight greater than its bouyancy in the casting material.

4. A casting apparatus as set forth in claim 2 wherein said ball valve includes a seat and a ball located below said seat and being of a weight less than its bouyancy in the casting material.