US3474854A

US3474854A - Die casting machine with means for hydraulically braking plunger retraction

Info

Publication number: US3474854A
Application number: US653417A
Authority: US
Inventors: Eric Arthur Roy Mace
Original assignee: Die Casting Machine Tools Ltd
Current assignee: Die Casting Machine Tools Ltd
Priority date: 1966-09-06
Filing date: 1967-07-14
Publication date: 1969-10-28
Anticipated expiration: 1986-10-28
Also published as: GB1173775A

Description

(kt 28 1969 E. A. R. MACE 3,

DIE CASTING MACHINE WITH MEANS FOR HYDRAULICALLY BRAKING PLUNGER RETRACTION Filed July 14, 1967 2 Sheets-Sheet 1 WES SURE URCE DIE MEA N5 3,474,854 ULICALLY 0d. 28, 1969 E. A. R. MACE on: CASTING momma WITH MEANS FOR HYDRA BRAKING PLUNGER RETRACTION Filed July 14, 1967 2 Sheets-Sheet 2 United States Patent.

US. Cl. 164-318 Claims ABSTRACT OF THE DISCLOSURE An injection die casting machine having dies forming a die cavity and a plunger movable to effect injection of material into the die cavity via a passage adapted to be filled from a reservoir through a port, and including means for hydraulically braking the plunger during its retraction such that said port is not opened until after said dies have been opened by a die opening means.

This invention relates to die casting machines having dies forming a die cavity and a plunger movable to eflfect injection of material into the die via an injection nozzle.

In conventional die casting machines, molten metal is supplied by a reservoir via a port which is uncovered when the plunger is withdrawn upwardly from the passage to permit molten metal or the like to flow into (usually) the goose neck which leads downwards from the plunger and upwards to a nozzle slightly above the level of liquid in the reservoir. Injection of the material into the die cavity is effected, when the dies are closed, by downward movement of the plunger which thereby forces the molten metal through the goose neck and through the nozzle into the die cavity. When the plunger starts on its downward journey the port leading to the reservoir is sealed off either by the plunger or by other suitable automatic means and the port remains closed until the end of the injection cycle when the injection plunger is fully withdrawn from the injection passage or sleeve.

A great problem often encountered in die casting is the dripping of the molten metal in the nozzle on to the face of the cover half of the die. Torches may be applied to the nozzle to keep this metal molten so that when the metal in the cavity is solidified, that which is in the nozzle will remain fluid to allow flow of metal during the next shot. If this molten metal is not withdrawn from the nozzle, it will drip, when the dies separate, on to the faces of the dies. This would prevent the dies from closing completely during a subsequent casting operation.

It is known that when the plunger is withdrawn from the injection sleeve a vacuum is created in the top of the (usually goose neck) passage in the region of the nozzle. If the inlet port is then opened, the metal in the goose neck rises and refills the nozzle with molten material. It is this refilling of the nozzle which gives rise to the problem mentioned above.

The present invention is directed to overcoming this problem; it provides a die casting machine having dies forming a die cavity, a plunger movable to effect injection of material into the die cavity via a passage adapted to be filled from a pot or reservoir via a port that is automatically covered and uncovered by the plunger or means actuated therewith as the plunger is respectively advanced and retracted, a fluid actuated piston and cylinder assembly for advancing and retracting said plunger, and means for opening the dies, wherein there is provided means for hydraulically braking the plunger during its retraction such that said port is not opened until after the dies have been opened by the die opening means.

With the present invention, the plunger starts to return from the fully advanced position at a high speed, in accordance with usual practice, to ensure that the injection plunger will not seize in the injection sleeve. At a point before the end of the return stroke, the member is slowed and thus the piston can only travel upwardly at a slow rate which may be adjusted by valve means to be sufficient to allow the dies to be opened before the port is opened to fill the injection passage.

The means for braking conveniently comprises a conduit a member movable with said piston and in sealing relationship with said conduit, whose end towards which the member moves during retraction of the plunger is formed as a well adapted to be full of hydraulic fluid during said retraction and having an outlet arranged to permit the escape of hydraulic fluid from the well when said member enters therein at a relatively slow rate such that the speed of the member and the plunger is retarded when the member enters the well; the conduit may lead away from the end of the cylinder to which pressure is applied to advance the piston and plunger and the member extends from the outer face of the piston into the conduit.

The member may be a spool valve having a first thicker portion nearest the piston, a thinner connecting portion and a second thicker portion, furthest from the piston, that slides in sealing relation with the conduit, a port being provided in the conduit, at a point always adjacent part of said thinner connecting portion, for the application of inlet fluid pressure to advance the piston and plunger, said first thicker portion being arranged to ensure a throttled flow of inlet fluid pressure to the cylinder while the first portion is in the conduit. As is explained more particularly in our co-pending US. patent application No. 652,930, filed July 12, 1967, this provides a two stage injection stroke in which the piston moves relatively slowly at first to permit air to escape from the die cavity and then relatively more quickly to ensure a sharp casting.

The recess may be formed so that during the injection stroke said member permits hydraulic fluid to flow into said recess from a reservoir. For this purpose the recess may have an end portion in which said member is sealingly slidable and an outer larger section portion leading to said reservoir.

In the following, reference will be made to the accompanying drawings, in which:

FIGURE 1 is a simplified illustration of a die casting machine constructed in accordance with the present invention;

FIGURES 2 and 3 illustrate a detail of the machine of FIGURE 1 and show different phases in a die casting cycle; and

FIGURE 4 illustrates, to a larger scale, a detail of the die casting machine of FIGURES l to 3.

FIGURE 1 shows one embodiment of a die casting machine constructed in accordance with the present invention, the machine in FIGURE 1 being at the start of an injection cycle before the injection of casting material is effected. The main parts of the machine comprise a piston and cylinder assembly 10 for effecting movement of a plunger 11 into a well 12 which is or has been filled with molten die casting material. Downwards movement of the plunger 11 into the Well 12 forces the material in the well up a goose neck passage 13 through a nozzle 14 into a die cavity 15 formed when a fixed die plate 16 and a movable die plate 17 have been closed together. Said movable die plate is operatively connected to die displacement -means 27 shown schematically in FIG. I. Said die displacement means is of conventional construction and functions to open and close movable die 17. The construction of die cavities has been known for many years in the art and for convenience will not be repeated here. It is usual to provide air vents (not shown) leading away from the die cavity 15 in order that air entrapped when the dies are closed may leave the die cavity when injection of the material from the well 12 is eflected. After the die cavity is completely filled, it is conventional practice to withdraw the plunger 11 upwardly, subsequently break the casting seal by an initial separation of the die plates, finally separate the die plates completely and eject the casting from the die cavity.

In FIGURE 1, molten metal 18 for the casting is retained in a reservoir 19, the reservoir being replenished at intervals in accordance with the usual practice. The well 12 is retained in a central bush 20 near the centre of the reservoir 19 and a port 21 communicates between the reservoir 19 and the port 22 in the side of the well 12 so that when the plunger 11 is withdrawn to an upper position after injection, casting material may flow from the reservoir 19 to fill the well again. In accordance with usual practice, the machine is tilted so that the height of material in the goose neck passage after the well has been filled is as low as possible.

Secured to the reservoir 19 is a frame 23 holding a sleeve 24 in which is movable a collecting rod 25 which at its lower end is connected to the plunger 11. The connecting rod 25 is formed in two main parts, an outer part 25a and an inner part 251). The part 25b is attached to the plunger 11 and is retained within the hollow lower portion of the part 25, being retained within the portion 25a by a crosspiece 26, provided at its upper end.

The part 2511 is attached by means of the screw threading link 28 to the piston 29 which is movable within a cylinder 30. The piston itself is reduced at its upper end, a reduced part 35 engaging a circular central recess in a circular plate 36, the plate 36 and the piston 29 retaining between them a flanged annular sealing ring 37 whose outer flange is a close sliding fit within the cylinder 30.

Leading away from the outward end of the cylinder 30 is the conduit 100 in which the valve spool 101 is located. The spool valve is secured to the upper end of of piston 29 by means of a screw threading and comprises a first relatively thick portion 102 that is only slightly less in cross-section than is the conduit 100, a relatively thinner intermediate portion 103 connecting the portion 102 with a similar portion 104 whose function will be described in more detail hereinafter. The upper end of the conduit 100 is sealed by a conventional sealing ring 105 engaging the periphery of the upper portion 104.

Leading E the conduit 100 is the port 106 which is fed with pneumatic fluid pressure from the valve 107. The valve is operative by suitable conventional means (not shown) to supply pressure either to the port 106 or to the exhaust port 109 so as to lower and raise piston 29 respectively. The valve is supplied with pressure from a source indicated diagrammatically at 108. For convenience in the description of FIGURE 1 it will be assumed that the fluid pressure source is pneumatic but hydraulic operation may equally well be selected.

The downward (injection stroke) phase of operation of the die casting machine of FIGURE 1 is as follows. The valve 107 admits fluid into the port 106 and into the cavity formed in the conduit 100 between the

portions

102 and 104 of the spool valve 101. Air cannot pass upwards owing to the seal provided by the sealing ring 105 but can only slowly enter the main cylinder 30 through the small clearance between the portion 102 and the inner face of the conduit 100. Thus the piston initially travels downward at a slow rate, allowing air trapped between the metal level and the die cavity 15 to escape through the aforementioned vents in the die cavity. The slow downward movement of the piston continues until the 4 portion 102 and the spool valve start to leave the passage 100 (FIGURE 2).

At this point, fluid will enter the cylinder 30 at a greatly increased rate, since portion 103 is narrower than portion 102, and since the reverse side of the piston will have had time to exhaust through the exhaust port down to atmospheric pressure, the piston will travel downwardly at a high speed not only due to this equalisation of pressure but also due to the increase in fluid pressure provided by the increase of eflective area of the inlet port which now essentially comprises the lower end of the conduit 100 with the intermediate reduced portion 103 of the valve spool within it.

It will be apparent that when the plunger 11 is withdrawn from the well 12, a vacuum is created in the goose neck passage 13 so that when the port 22 from the reservoir 19 is uncovered molten metal from the reservoir rushes up the goose neck passage and out through the nozzle to drip on to the fixed die plate as well as the metal already in the nozzle.

It will also be apparent that the plunger has to be withdrawn to draw away the casting material in the nozzle before the dies are open. Withdrawal of the plunger is normally eflected by applying pressure from the valve to the exhaust port 107 and it will be appreciated that if the port from the reservoir is uncovered before the dies are separated (to destroy the partial vacuum in the goose neck) the goose neck will be substantially filled with casting material and the aforementioned dripping will occur. The machine shown in FIGURES 1 to 4 ensures that there will be sutficient time to open the die cavity before the port 22 from the reservoir is uncovered. This is essentially achieved by providing an initial fast rate of withdrawal of the plunger 11 (to ensure proper withdrawal from the nozzle of the molten metal) and then slowing down, but not stopping, the plunger until the die plates have been opened.

FIGURE 2 shows in detail the upper part of the piston and cylinder assembly of the machine of FIGURE 1. The upper end of the conduit 100 is flanged to provide a generally circular table on which is mounted a hollow cylinder 110 containing oil 111. Over the passage 100 is formed the well 112 into which the valve spool end portion 104 extends. The well 112 is formed with a lower part of somewhat greater cross-section than the portion 104 but has a shoulder 113 defining an upper part 114 of the well in which the portion 104 is a slidingly sealing fit. At the top of the well, and as more particularly shown in FIGURE 4, there is an exhaust passage 115 with a needle valve 116 adjustable in position by means of the screw threading 124 engaging a co-operating threading in the body of the well.

During the slow down of movement of the piston a partial vacuum will be left in the upper portion of the well. This partial vacuum is relieved when the valve spool portion 104 leaves the shoulder 113, the oil in the reservoir entering the well by means of the port 117 to fill the well completely.

Referring particularly to FIGURE 3, when pressure is applied to the exhaust port, the piston will start to return in an upward direction at high speed. This will ensure that the injection plunger, which is normally a nitraloy sleeve immersed in molten zinc (casting material) will not seize. The valve spool 101 will likewise travel rapidly upwards through the conduit 100 until it starts to enter the upper portion of the well 112. It has already been explained that during the injection phase of the casting cycle the well has been filled with oil from the reservoir (cylinder 110) through the port 117 provided. The initial upward rapid movement of the plunger withdraws all the casting material from the nozzle. When the portion 104 reaches the shoulder 113 in the well 112 the movement of the valve spool 101 and accordingly the piston 29 and plunger 11 will slow very substantially since oil from the upper part 114 of the well 112 can only escape very slowly through the passage 115 which is controlled by the needle valve 116. The needle valve 116 is adjusted so that the port 22 is not uncovered until the dies have started to open. The opening of the die cavity destroys the vacuum which is normally present and accordingly by the time the plunger 11 uncovers the port 22 from the reservoir 19 the vacuum in the goose neck passage 13 has been destroyed by the opening of the die cavity and the metal in the goose neck will not rise and refill the nozzle 14.

I claim:

1. In a die casting machine having dies forming a die cavity, a plunger movable to effect injection of material into the die cavity via a passage adapted to be filled from a pot or reservoir via a port that is automatically covered and uncovered by the plunger or means actuated therewith as the plunger is respectively advanced and retracted, a fluid actuated piston and cylinder assembly for advancing and retracting said plunger, and means for opening the dies, the improvement which comprises means for hydraulically braking the plunger during its retraction such that said port is not opened until after the dies have been opened by the die opening means, said means for hydraulically braking including a conduit, a member movable with said piston and in sealing relationship with said conduit, the conduit end towards which the member moves during retraction of the plunger being formed as a well adapted to be full of hydraulic fluid during said retraction and having outlet means arranged to permit the escape of hydraulic fluid from the well a relatively slow rate when said member enters therein, such that the speed of the member and the plunger is retarded when the member enters the well.

2. A die casting machine as claimed in claim 1 wherein the conduit leads away from the end of the cylinder to which fluid pressure is applied to advance the piston and plunger and the member extends from the outer face of the piston into the conduit.

3. A die casting machine as claimed in claim 2 wherein said member is a spool valve having a first thicker portion nearest the piston, a thinner connecting portion and a second thicker portion, furthest from the piston, that slides in sealing relation with the conduit, a port being provided in the conduit, at a point always adjacent part of said thinner connecting portion, for the application of inlet fluid pressure to advance the piston and plunger, said first thicker portion being arranged to ensure a throttled flow of inlet fluid pressure to the cylinder while the first portion is in the conduit.

4. A die casting machine as claimed in claim 3, wherein a hydraulic fluid reservoir and a port coupling said hydraulic fluid reservoir to said well is provided, said second thicker portion being operative to close said port when said second thicker portion enters said well.

5. A die casting machine as claimed in claim 4 wherein the well has an end portion in which said member is sealingly slidable and an outer larger section portion leading to said hydraulic fluid reservoir.

6. A die casting machine as claimed in claim 1, wherein the outlet means includes a needle valve.

7. A die casting machine as claimed in claim 2 wherein the outlet means includes a needle valve.

8. A die casting machine as claimed in claim 3 wherein the outlet means includes a needle valve.

9. A die casting machine as claimed in claim 5 wherein the outlet means includes a needle valve.

10. A die casting machine as claimed in claim 4 wherein the outlet means includes a needle valve.

References Cited UNITED STATES PATENTS 3,123,875 3/1964 Madwed 164-318 X 2,243,835 6/1941 Brunner et a1. 164-314 X 2,494,071 l/ 1950 Jeale 164-315 J. SPENCER OVERHOLSER, Primary Examiner ROBERT D. BALDWIN, Assistant Examiner US. Cl. X.R.