US2214308A - Means for controlling hydraulically operated working cylinders - Google Patents

Description

Sept. 10, 1940. J Q A 2,214,308

MEANS FOR CONTROLLING HYDRAULICALLY OPERATED wonxme CYLINDERS Filed Nov. 15, 1938 a Sheets-Shed z a A9 I 1414 a m l3 L I J. POLAK 2,214,308

MEANS FOR'CONTROLLI NG HYDRAULICALLY OPERATED WORKING CYLINDERS Sept. 10, 1940.

Filed Nov. 15, 1938 3 Sheets-Sheet 3 Ihv n-lzw Patented Sept. 10, 1940 UNITED STATES MEANS FOR CONTROLLING HYDRAULI- CALLY OPERATED WORKING CYLIN- DERS Josef Polak, Prague, Czechoslovakia Application November 15, 1938, Serial No. 240,582 In Czechoslovakia November 16, 1937 3 Claims.

For obtaining a high mould closing power in hydraulically operated die-casting and like machines it has already been proposed to employ a pressure intensifier which many times increases the pressure in the closing cylinder shortly before the casting operation. Up to this increase this pressure has corresponded to that of the hydraulic accumulator operating the machine. The operative sequence of the pressure intensifier and of the press cylinder are controlled jointly by a controlled slide valve, the piston of which during its axial motion first uncovers successively control passages which convey the water under pressure to the pressure intensifier, in order to place the closing cylinder under the increased pressure referred to, and thereupon uncovers passages which conduct the water under pressure to the press cylinder for bringing about the casting operation. The motion of the slide valve must proceed very rapidly, in order that the control passages may be also rapidly uncovered, as otherwise (should the passages be opened sluggishly) high losses due to throttling will occur, resulting in the motions in the con- 25 trolled working cylinder proceeding not with the required suddenness, but with a slowly increasing speed, which is undesirable.

The period which elapses between the opening of the passages for the pressure intensifier and of those for the press cylinder shall hereinafter be referred to as the advance interval. In view of the required very rapid motion of the slide valve and of the short distance available it is very short. During the advance interval the pressure in the pressure intensifier must have reached its full height, in order that at the start of the casting operation the mould shall be held closed with the necessary force. For this a definite period of time is necessary, which in very many cases is longer than the advance interval referred to above, so that the requisite increase in pressure in the closing cylinder will not yet have been reached, when the force produced by the casting operation (the metal injected into the mould) seeks to open the mould. It has hitherto been sought to meet this difficulty by either retarding the motion of the slide valve or increasing the distance of the controlled passages leading to the intensifier or the press cylinder. The former expedient is combined with greater losses through throttling and a retardation in the operative motions, whilst such limits are set to the latter expedient through the dimensions possible in carrying it into practice that the purpose aimed at cannot be realised.

To overcome these disadvantages is the object of the present invention which is best described with reference to the accompanying drawings, in which is illustrated a constructional example of a die-casting machine installation for carrying the method under discussion into effect.

Figure 1 shows diagrammatically the entire arrangement,

Figures 2, 3 and 4 show the controlled slide valve with the passages controlled by it to an 10 enlarged scale and in difierent positions,

Figure 5 shows a modified form of the slide valve and Figure 6 a section on line (1-1) of Figure 5.

A is the closing cylinder, B1 the cylinder in u communication with it of the pressure intensifier, B2 the intensifier piston, 01 the press cylinder, C2 the press piston, D the control apparatus of known construction, used for controlling the closing cylinder and containing a non-return 20 valve l, E the control apparatus used for actuating the slide valve and comprising two valves of known construction and F the casing for the slide valve. I

Into the space H of the closing cylinder A 25 pressure liquid is introduced by actuating the control apparatus D. The space J of the closing cylinder A is under the constant pressure of the accumulator. The piston G is thus capable of bringing the half K of the mould, which is fixed to it, against the immovable part L of the mould. l

The piston Q of the slide valve is of greater cross-sectional area than each of the two seatin'g surfaces of the piston 0. When the space N is filled with pressure liquid, the piston 0 is forced against its lower seating A11, whereby the admission of water under pressure through P from the accumulator is shut 01! (Figures 1 and 2).

The auxiliary control apparatus E is connected by its passages with the passages of the casing F for the slide valve and with the hydraulic system of the machine. By depressing the foot lever M the valve 2 is raised and the valve 3 is pressed down on its seating by the water under pressure. The space N in the casing F is thereby connected by way of the passage S and the pipe A9 with the outflow and the pistons O and Q of the slide valve will move in the direction of the arrow shown in Figures 1 to 5 under the pressure of the water entering at P under pressure.

The motion of the slide valve can continue with undiminished velocity until the edge R of the u piston Q closes the e 8. when the piston Q has reached this position (Figure 3), the edge T of the niston has completely uncovered the passage U, through which and the pipe V connected to it liquid under pressure is conveyed unhindered 'to the pressure intensifier 131. Before the edge T commences to uncover the passage U, the edge A4 of the piston 0 will have moved beyond the passage As and closed it, so that the connection of the latter by way of the space Am with the passage Ac which communicates with the outflow is interrupted.

In the space H of the closing cylinder A a high pressure is thus produced through the action of the intensifier, which pressure produces, the mould closing force required for the casting operation. During the continued motion of the slide valve pressure liquid can escape out of the space N only by way of the passages W1 and W2 and the adjustable throttle valve X, as through the pipe A: no water can flow out by way of the closed valve 3 of the auxiliary control apparatus E. The piston O of the slide valve can therefore move only at a velocity determined by the adjusted opening at X. This velocity remains constant until the edge Y of the piston Q again uncovers the passage S, the edge T of the piston 0 not having yet reached the edge Z of the passage A2. As soon as the edge Y of the piston Q uncovers the passage S, the liquid can again flow unhindered out of the space N above the'slide valve through the bores min the piston Q and the annular space As, the passage S and the pipe A9. The piston 0 therefore again moves under the pressure of the pressure water with an undiminished velocity, until its rests on its upper seating A12 (Figure 4), the edge T having uncovered the passage A2 and the pressure water entering the press cylinder C for carrying out the casting operation.

Thus, to sum up, the essence of the controlling method consists in this, that the slide valve moves at first rapidly, then slowly in an adjustable manner and finally rapidly again. The duration of the adjustable slow motion of the slide valve is that period of time, by which the pressure water has to enter into the press cylinder appropriately later than into the pressure intensifier.

On the foot lever M at the auxiliary control apparatus E rising, the space N above the slide valve receives pressure water through the pipe A3, which acts on the piston Q of the slide valve and forces the piston with full velocity on to its lower seating A11 (Figures 1 and 2). By this means however the supply of pressure water into the press cylinder and the pressure intensifier is shut off, and their communication with the outflow passage As by way of the pipe A14, the passages A1, A5 and the annular space A or by way of the pipe V, the annular space A13, the passages A2, A1, A5 and-the annular space A10 is established.

It will be obvious, that instead of the pressure intensifier cylinder and the press cylinder used in the constructional example described above for die-casting machines other working cylinders can be controlled in accordance with the present controlling method, the hydraulically operated pistons of which are to be moved in such a manner that their movements are interdependent with respect to time.

In die-casting and like machines the press piston together with the masses taking part in its motion has imparted to it on the way from its position of rest, until itimpinges onthe material to be pressed, from which moment only it can impart its pressure-exerting action on the latter, a high velocity and a consequent kinetic energy which manifests itself at the moment, at which the pressing pressure commences to act, as a highly undesirable increase in the speciflc'pressure in the material being pressed. In many cases this results in the mould opening. In order to overcome this disadvantage the press piston is at first brought up to the material to be pressed as slowly as possible (starting motion'of the press piston) and is from this moment onwards caused to perform its actual operative motion which proceeds under high working pressure and at a-velocity adapted to the requirements.

Figure 5 shows a constructional form of the slide valve, which enables the press piston to be given the slow starting motion just referred to. For this purpose the piston O has in its lower controlling part a groove A forming a passage of relatively small cross-section. In that position of the slide valve, in which the admission of pressure water into the pressure intensifier can already take place (Figure 3), the pressure water will therefore flow into the press cylinder C1 through the passage groove A15 as well, although greatly throttled in this passage, by way of the passage A2, the passage A1 and the pipe A14 and will move the press piston C2 with less force and a slower starting velocity. This continues, until the slide valve has reached the position shown in Figure 4 or the piston O of the slide valve has uncovered the passage A2 for allowing the pressure water to flow through unhindered.

What is claimed is:

1. In die casting and like machines, intensifier and press cylinders including fluid operated pistons adapted to move in predetermined timed sequence, a valve device having first and second outlets connected respectively with the intensifier and press cylinders and having an inlet, said valve device including a sliding piston actuated by the fluid entering said inlet to successively uncover the outlets connected with the intensifier and press cylinders, means for retarding the movement of the sliding piston following the opening of the first outlet and prior to the opening of the second outlet, the movement of the sliding piston before and after retardation being substantially unimpeded and relatively rapid, and a device for controlling said sliding piston.

2. A die casting machine as claimed in claim 1 characterized in that said retarding means includes adjustable throttling means cooperating with a part of the sliding piston, said part of the piston having a passage therein whereby fluid may by-pass said throttling means.

3. A die casting machine as claimed in claim 1 characterized by the provision of a passage in the sliding piston for passing a quantity of fluid to effect a slow starting motion of the press cylinder piston.

JosriF PoLAK.

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