US2893082A

US2893082A - Device for increasing the capacity of die casting machines

Info

Publication number: US2893082A
Application number: US655650A
Authority: US
Inventors: Hodler Fritz
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-04-29
Filing date: 1957-04-29
Publication date: 1959-07-07
Anticipated expiration: 1976-07-07

Description

F. HODLER July 7, 1959 DEVICE FOR INCREASING THE CAPACITY OF DIE CASTING MACHINES Filed April 29, 195'! 2 Sheets-Sheet 1 INVENTOR /m, Au- 1 am ATTORNEYS July 7, 1959 F. HODLER 2,893,082

DEVICE FOR INCREASING THE CAPACITY OF DIE CASTING MACHINES Filed April 29, 1957 2 Sheets-Sheet 2 p :Zgfi.

ZZ'g fi? INVENT OR ATTORNEYS United States Patent DEVICE FOR INCREASING THE CAPACITY OF DIE CASTING MACHINES Fritz Hodler, Territet, Switzerland Application April 29, 1957, Serial No. 655,650

3 Claims. (Cl. 22-68) This invention relates generally to die casting machines, and more particularly to means for increasing the casting capacity of die casting machines.

In die casting machines, molten metal is fed to a sleeve, which communicates with the interior of the die. The molten metal is introduced into the sleeve and an injection plunger is actuated by means by a hydraulically operated ram to force the molten metal into the die. The hydraulically operated ram in hot and cold chamber machines is generally of a differential type so that return movement of the ram is effected by means of pressure applied to the smaller section of the ram. Other machines are equipped with one or more separate small hydraulic cylinders, the pistons of which are connected with the ram by means of a yoke. However, the principles of operation are the same since each system has directly or indirectly a differential ram, a pressure supply line to the larger section of the ram, and an alternating, outlet or pressure line to the smaller section of the ram. Following the filling of the die, the excess of metal in the sleeve is removed by further insertion of the plunger after the die has been opened and the casting removed.

The size of a casting or more particularly the projected surface area of a casting is limited by the locking pressure of the die casting machine and by the pressure exerted both on the metal in the sleeve and on the surface area of the casting. This pressure depends on the ram section and on the hydraulic pressure in the pressure cylinder, and because of frictional losses, the pressure is much lower during the'beginning and main period of the injection phase than at the end of the phase when, at the moment the die cavity is filled, all hydraulic losses in the supply line become zero. It is obvious that for a given locking pressure of a machine, the surface area of a casting must be limited in view of the final injection phase pressure and not of the reduced pressure prevailing during the injection phase. In the absence of this, the force in the direction of opening the die would be greater than the closing force or locking pressure and the fluid metal would spray outside the die.

Until now it has been a generally accepted theory that this inconvenience is inevitable in die casting practice and must therefore be accepted as being inherent in the process. Because of this, the maximum size of a casting produced on a machine of a given locking pressure had to be much smaller than that which would have been pertm-issible according to optimum theoretical considerations.

The object of the present invention is to provide a simple device which makes possible the utilization of the full capacity of die casting machines by eliminating the influence of the increased injection force at the end of the injection phase, this device limiting the injection force at the end of the injection phase to the value which prevails during the injection phase or even to a value which is lower than the latter.

By the instant invention, the surface area of a casting can be considerably increased without increasing the lock- 2,893,082 Patented July 7, 1959 ICC ing pressure of the machine. Therefore bigger castings than before can be produced on a die casting machine with a given locking pressure resulting in considerable economical advantages.

These and other objects, features and advantages of the invention will become apparent from the following description and drawings, which illustrate diagrammatically and by way of example an embodiment of the invention, in which:

Fig. 1 illustrates diagrammatically a conventional diecasting machine;

Fig. 2 shows a die casting machine equipped with a device according to the invention at the beginning of the injection phase;

Fig. 3 shows the same machine as Fig. 2 at the end of the injection phase;

Fig. 4 is a detailed drawing of the valve used in a device according to the invention.

Referring now to Fig. 1 a die is used which consists of a stationary member 1 and a hydraulically operable longitudinally movable member 2. Rigidly secured to stationary member 1 is a sleeve 4 having an opening 5 in the wall thereof through which molten metal can be poured. Piston 6 is longitudinally slidable within sleeve 4- and can therefore force the molten metal 7 into the die cavity. The injection piston 6 is connected by rod 8 to the differential-type hydraulic ram 9. The ram 9 is longitudinally slidable in cylinder 10 and forms chambers 12 and 11 therein, the first being on the side of the larger surface of the ram and the second being on the side of the smaller surface of the ram. The displacement of the injection piston 6 and the hydraulic ram 9 is controlled by means of a four-way valve 13, which in the position shown in Fig. 1 allows the fluid under pressure arriving through the supply line 14 to flow into chamber 12 through line 15 having a regulating valve 16 therein. At the same time the chamber 11 is connected with the drain line 18 by means of line 17. When the valve 13 is in the position shown in Fig. l the hydraulic fluid displaces the injection piston 6 towards the left to effect injection of the molten metal into the die. When the injection phase is completed, the position of the four-way valve 13 is changed by rotating handle 19 counterclockwise to the position shown on the dotted line. This allows line 15 to communicate with the exhaust line 18 and the hydraulic pressure line 14 to communicate with the line 17 As a result of the pressure arising in chamber 11 the injection piston 6 will be returned to its initial position 6 shown in the figure. After the die halves 1 and 2 have been separated, the casting is taken out, and after the die has been closed again, molten metal is again poured into sleeve 4 and the cycle of operations is repeated. By means of the regulating valve 16 the speed of the injection piston during the injection phase can be regulated.

Fig. 2 shows a die casting machine of the same type as shown in Fig. 1, but including according to the invention a valve 21 placed in the line which connects the chamber 11 with the four-way valve 13. In this manner this line is divided into two parts 17a and 17b. The valve 21 contains a freely slidable piston 22 which is the closing element of the valve. The top end of the free piston is designed in such a manner as to fit upon the upper valve in order to close the line 17a when the piston 22 is displaced upwardly. The lower end of the piston is subjected to the valve control pressure supplied by line 23 which connects the valve control chamber 24 with the chamber 12 in the hydraulic circuit. The line 23 is provided with a pressure regulating valve 25.

Vertically adjustable threaded plug 26 provides stop means for limiting the lower extent of travel of the pis ton 22. The die casting machine is shown at the moment when the injection piston 6 has forced the fluid metal far enough to make it reach the contracted part 46 of the die, which in all dies forms the entrance to the die cavity. During this initial movement of the piston 6, the force which is exerted on the fluid metal is still weak and it is not suflicient to cause displacement of the free piston 22 inside the valve, because of the fact that the movement of the free piston 22 is prevented by the counter-pressure prevailing in the valve chamber 24a (Fig. 4) which communicates with the accumulator 38, as will be further described below. However, at the moment shown in Fig. 2 when the fluid metal reaches the contracted section of the die aperture, the pressure in the chamber 12 is caused to rise. By means of the line 23 this increased pressure is transmitted to valve 21 and as soon as this increased pressure has reached a value which is higher than the pressure prevailing in the valve chamber 24a, the free piston 22 will be moved in an upward direction. The speed with which the piston is displaced can be regulated by means of the valve 25 in the line 23 and the time which lapses between the beginning of the movement of the piston 22 and the moment it reaches its final position, when it closes the line 17a must be chosen in such a manner as to be no longer than the time required for the complete filling of the die cavity from the moment the metal reaches the contracted passage. The time required for the displacement of the piston 22 can be regulated not only by means of the valve 25 which controls the speed of the displacement, but also by means of the screw plug 26 which makes it possible to vary the length of the stroke of the free piston until it closes the line 17a.

Fig. 3 shows a die casting machine at the moment when the die cavity is almost entirely filled. The valve between the lines 17a and 17b is almost entirely closed, which causes a rise of the pressure in chamber 11, which in turn will cause a reduction of the effective injection force exerted by the ram 9 during the latter part of its active stroke. The ratio between this pressure prevailing in chamber 11 as compared with the pressure in chamber 12 is to the greatest extent determined by the ratio existing between the surface area of the lower surface 22a of the free piston 22 and the surface area 22b of the part which closes the line 17a. It is obvious that the valve 22 will not be entirely closed until the die cavity 4a is completely filled. In this manner the pressure prevailing in chamber 11 during the latter part of the active stroke of the ram 9 is higher than the one prevailing in chamber 12, and therefore the force then ex erted by the ram 0 will be less than the force it would develop without the valve in the return line 17a. It will be understood, that this reduction of the force exerted on the metal in the die cavity should occur during the last stage of the injection phase only, since any reduction previous to this would increase the filling time of the die, which must under all circumstances be avoided. Therefore the injection piston is subjected to a braking action only immediately before the complete filling of the die cavity, resulting in a reduction of the pressure then exerted on the molten metal.

Fig. 4 shows in greater detail a valve of the type shown in Figs. 2 and 3. It will be seen that the body 21 has two threaded apertures 27 and 28 to which are connected respectively the lines 23 and 17b. The lower end of the valve is formed by a seat provided by the screw plug 29 which is screwed in the body 21, and which has a threaded aperture 30 intended for connection with line 17a. The bottom end of the valve body is closed by closure member 31 which is screwed in the body 21. Through member 31 is screwed a screw plug 26 which provides stop means for limiting the final position of the free piston 22. A pressure-tight connection between the piston 22 slidably movable within the body 21 is obtained by means of the

piston rings

33 and 34, whereas the piston ring 35 makes the connection between the part 31 and the lower end of the free piston 22 a pressure-tight one. The screw plug 26 is provided with a lock-nut 36 which secures the position of the screw plug 26.

It will be noted that the free piston 22 is a differential piston. When the injection ram is returned to its initial position, the pressure in the chamber 12 and consequently on the side of the larger surface area of the piston 22 is zero, and therefore the piston 22 will be moved back under the influence of the pressure prevailing in the valve chamber 240: until the lower surface 22d of the piston 22 will contact the end of the screw plug 26.

The pressure in the valve chamber 24a is supplied by liquid 42 under pressure in the accumulator 38. The accumulator 38 consists of a reservoir containing a cushion of compressed air 43 which keeps the liquid 42 under pressure. The reservoir 38 is provided with lateral line 39 containing a valve 40, which permits the accumulator to be filled with liquid 42 and with compressed air 43. Pressure gage 41 makes it possible to check the pressure. This pressure must be such as to be able to bring the free piston 22 back to its initial position and to keep it in this position during the first phase of the movement of the ram 9 until the moment when the fluid metal reaches the contracted passage at the entrance of the die cavity and the pressure in the injection cylinder 12 begins to rise.

As described above the adjustable screw plug 26 together with the valve 25 makes it possible to determine the lapse of time between the beginning of the displacement of the piston 22 and the closing of the aperture 30 within very small limits. If for example the time required for filling the die cavity completely is 30 milliseconds, the valve can be set in such a manner that it is practically closed 25 milliseconds after the fluid metal has reached the contracted passage at the entrance of the die. If properly timed the ram 9 will continue to move with progressively decreasing injection force, until the die cavity is completely filled and also for the subsequent period in which the injection piston 6 continues to force fluid metal into the die as the metal contracts during its solidification. This supplementary amount of metal is forced into the die with reduced injection force thus reducing the force resulting from the specific pressure of the fluid metal in the sleeve 4 and the surface of the casting in the die, and consequently avoids the opening of the die halves. When the piston 22 is di mensioned in such a manner as to cause the injection force which is applied to the injection piston to be reduced to 50% near the end of the period for complete filling of the die cavity, the speed of the injection piston will be reduced by only approximately 30% of its original value, since the speed is a '\/p function. Thus according to the invention, the casting can be effected with high pressure and at high injection speed during the first 80%90% of the required filling time, whereas during the last 20%10% of the required filling time, the injection force will gradually be reduced to half its value, while at the same time the injection speed will be reduced by only 30% of its initial value.

Since, according to the example given, the forces operating in the direction of the opening of the die halves against the locking force of the machine after the complete filling of the die cavity, are reduced by 50%, it is clear, that castings of double the size (as far as surface area is concerned) can be made on a machine of a given locking pressure without running the risk of the uncontrolled and undesired opening of the die.

In order to be able to check the proper movement of the piston 22 from the outside of the machine at all times, the piston 22 has the extension 220.

It is also clear that the figures given are given by way of example only and that the injection force at the end of the complete filling of the die cavity may be reduced in any manner required, according to conditions prevailing without department from the spirit and the scope of this invention.

Owing to the fact, that it is essential for the closing time of the valve according to the invention, to be controlled within extremely small limits, no pressure reducing valve of conventional design can be used. Therefore even the use of the valve 25 alone will not result in the required effect. Close adjustment is made possible by the comparatively large active stroke of the piston 22 and by the fact that the adjusting screw plug 26 permits very fine adjustment of the length of this stroke.

It is to be understood that the above described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and the scope thereof.

I claim:

1. In a hydraulically-operated die casting machine having an injection plunger, differential-type hydraulic ram and cylinder means for longitudinally displacing said plunger, a first conduit for applying fluid under pressure to the cylinder pressure chamber associated with the large area side of the hydraulic ram during the injection-cycle, and a second conduit connected to the cylinder counterpressure chamber associated with the small area side of the hydraulic ram for the return of fluid from the cylinder; means causing the pressure of fluid in the counterpressure chamber of said cylinder to be increased near the end of the injection cycle to oppose the influence of the increased injection force which occurs in the cylinder pressure chamber near the end of the injection cycle comprising a valve having an inlet and an outlet connected in series in the return conduit of the cylinder, said valve having a piston element slidably movable therein for controlling the passage of fluid through said valve, pistoncontrolling conduit means connected at one end to said valve and at the other end to said cylinder pressure chamber to cause said piston element to reduce the flow of fluid through said valve when the injection pressure in the cylinder pressure chamber exceeds a predetermined value near the end of the injection cycle, and means for adjusting the closing time of the piston element within the valve comprising screw means mounted in the wall of said valve to control the length of the stroke of the piston element therein.

2. A die-casting machine as defined in claim 1 wherein said closing time adjusting means further includes a control valve connected in series with said conduit means.

3. In a hydraulically-operated die casting machine having an injection plunger, difierential-type hydraulic ram and cylinder means for longitudinally displacing said plunger, a first conduit for applying fluid under pressure to the cylinder pressure chamber associated with the large area side of the hydraulic ram during the injection cycle, and a second conduit connected to the cylinder counter-pressure chamber associated with the small area side of the hydraulic ram for the return of fluid from the cylinder; means causing the pressure of fluid in the counter-pressure chamber of said cylinder to be increased near the end of the injection cycle to oppose the influence of the increased injection force which occurs in the cylinder pressure chamber near the end of the injection cycle comprising a solely hydraulically-operated valve having an inlet and an outlet connected in series in the return conduit of the cylinder, said valve having a piston element slidably movable therein for continuously adjustably controlling the passage of fluid through said valve, and piston-controlling conduit means connected at one end to said valve and at the other end to said cylinder pressure chamber to longitudinally displace said piston element to cause reduction of the flow of fluid through said valve when the injection pressure in the cylinder pressure chamber exceeds a predetermined value near the end of the injection cycle.

References Cited in the file of this patent UNITED STATES PATENTS 1,023,267 Mock et al. Apr. 16, 1912 1,194,549 Schnitzler Aug. 15, 1916 1,940,063 Sherman Dec. 19, 1933 1,972,462 Schafer Sept. 4, 1934 2,214,308 Polak Sept. 10, 1940 2,415,462 Cherry Feb. 11, 1947 2,669,760 Venus Feb. 23, 1954 2,671,247 Lester Mar. 9, 1954 2,753,849 Becker July 10, 1956