GB2082488A

GB2082488A - Injection assembly for pressure die-casting machines

Info

Publication number: GB2082488A
Application number: GB8113816A
Authority: GB
Original assignee: Italpresse SpA
Current assignee: Italpresse SpA
Priority date: 1980-08-25
Filing date: 1981-05-06
Publication date: 1982-03-10
Also published as: DE8114682U1; ES8203247A1; IT1132465B; FR2488822A1; DE3119697A1; ES502230A0; IT8024269A0; FR2488822B3

Abstract

The assembly includes an oil accumulator (23) to cause second- stage (rapid) advancement of an injection piston (3) and, in lieu of the usual piston multiplier there is provided a further oil accumulator (29), which is put into communication with the injection cylinder (1) through suitable valve means (34) at the end of the second stage of advancement of the injection piston (3). <IMAGE>

Description

SPECIFICATION Injection assembly for pressure die-casting molding machines The present invention is concerned with an injection assembly for pressure die-casting molding machines.

;The existing injection assemblies for machines of this kind substantially comprise an iection cylinder, an injection piston slidingly housed in said cylinder and valve means adapted to put sequentially into communication with said injection cylinder, firstly, an oil feed pump for a first stage of slow advancement of the injection piston and, then, an oil accumulator for a second stage of quick advancement of the injection piston. There is further provided a pressure multiplier, which has the function of raising subsequently the oil pressure on the injection piston for a third short stage of high-pressure advancement of the piston. The last mentioned stage allows the melted metal to reach surely even the most distant and difficult interstices of the molding cavity.

The pressure multiplier usually consists of a piston member, provided with suitable valve means, which is arranged upstream of the injection cylinder and, without acting during the first two stages, is driven in the third stage to insert a rod partially into the injection cylinder until the rod abuts against the injection piston, in order to raise quickly the oil pressure applied to the same injection piston.

Those working in the pressure die-casting art well know that just the multiplier is often a source of problems and drawbacks, which include its constructional complexity, the rather high starting times and the actual impossibility of varying as much as desired the starting instant of the multiplier and the pressure rising time.

An object of the present invention is therefore to realize an injection assembly for pressure die-casting molding machines, which is not involved in the typical problems and drawbacks of the existing multipliers.

According to the invention, such an object is attained by an injection assembly characterized in that as pressure multiplier there is used a further oil accumulator, which further valve means put into communication with the Injection cylinder at the end of the second stage of advancement of the injection piston.

It clearly appears that the replacement of the conventional complicated piston multiplier with a simple oil accumulator is not only to advantage of the constructional simplicity but also of the functional capacity, since it is obviously possible to obtain very reduced starting times, which can also be adjusted at will by acting merely on the adjustment of the pressure of the oil fed to the accumulator, that is by means of an usual pressure variator. By suitably choosing the instant and mode of opening of the valve means which control the communication between said oil accumulator and the injection cylinder, it is also possible to vary at will both the instant of application and the rising time of the piston final-advancement pressure.

The features and the advantages of the present invention will become more apparent after the examination of the following detailed description of a possible embodiment thereof, which is illustrated by way of non-limiting example in the enclosed drawing, which shows an injection assembly according to the invention as longitudinally sectioned along the axis of the injection cylinder.

With reference to the drawing, within an injection cylinder 1 provided with an inner cavity 2 there is slidingly housed an injection piston 3, the rod 4 of which provides, as usual, for the injection of the melted metal into the interstices of the die included in the machine.

There is fixed to the injection cylinder a head 5, which is passed through by a hole 6 arranged as a prosecution of the inner cavity 2 of the cylinder 1. Within said hole there is housed a fixed valve seat 7, which is provided with two diametrally opposed side ports 8 and 9 and a front axial port 1 0. The latter is controlled by the front head of a double-head poppet valve 12, which is urged to a closed position by a spring 35 acting on the rear head 13, which operates as a piston in a chamber 1 4 defined within a rear closing body 1 5 fixed to the head 5.

The side port 8 of the valve seat 7 constantly communicates with an inner passage 1 6 of the head 5, which passage may in turn be connected alternately either to an exhaust 1 7 (as represented in the drawing) or to a pressure oil feed pump 1 8 (the usual pump of the pressure die-casting machines) as a function of the state of an electric control valve 19. The same electric valve connects the chamber 14 to the feed pump 118 and to the exhaust 1 7 as alternated with the above said passage 16.

The other side port 9, in turn, communicates with another inner passage 20, which an electric valve 21 keeps closed (as represented in the drawing) or, alternately, connected to a charge and discharge port 22 of an oil accumulator 23, said port 22 being further connected permanently to the feed pump 1 8 through a pressure reducer 24 and a non-return valve 25.

The accumulator 23 includes an inner cavity 26 intended to receive oil and a thrusting piston 27 housed in said cavity and permanently urged to force oil delivery by a suitable gas, particularly nitrogen, contained in a bomb.

There is also provided a further accumulator 29, the inner cavity 30 of which is divided by a piston 31 into an upper part containing a prefixed quantity of nitrogen and a lower part containing oil at high pressure (higher than that of the oil in the accumulator 23), which is fed by the pump 1 8 through an adjustable pressure reducer 32 and a non-return valve 33. Said lower port of the inner cavity of the accumulator 29 further communicates with the internal hole 6 of the head 5, downstream of the valve 12, through a normally closed electric valve 34.

In operation, the two accumulators 23 and 29 are previously filled with oil at suitable pressure through the pressure reducers 24 and 32. In particular, by means of the latter reducer it is possible to adjust the oil pressure in the accumulator 29 at the desired value for the final stage of advancement of the injection piston 3.

The starting of the injection operation is due to a switching control imparted to the electric valve 19, which control causes the connection of the chamber 14 to exhaust, so that the spring 35 is allowed to cause the momentary closure of the valve 1 2 and, then, the supply of oil from the pump 1 8 to the internal space of the valve seat 7 through the passage 1 6 and the side port 8. Such a supply causes reopening of the valve 1 2 and, therefore, of the front axial port 10 of the valve seat 7, through which the oil can reach the injection piston 3 and cause a first stage of slow advancement of the piston at the speed fixed by the pump delivery.

The electric valve 1 9 is then returned to rest, while the valve 1 2 is kept open by the pressure thus restored behind its rear head 13, and there is switched, on the contrary, the electric valve 21, which allows the oil stored in the accumulator 23 to be thrusted by the nitrogen in the bomb 28 towards the injection piston 3 so as to cause a second stage of quick advancement of the same piston.

The third stage is finally caused by the switching of the electric valve 34, which allows the high-pressure oil contained in the accumulator 29, wherein it has preloaded the nitrogen also contained therein, to reach the injection piston 3 (further closing the valve 12) to cause the short final advancement at high pressure.

The value of said high pressure is determined, as already said, by the adjustment of the pressure reducer 32, while the pressure applying instant and the pressure rising time are determined by a suitable adjustment of the electric valve 34. It is important to note that, in any case, it is necessary to determine correctly, during the planning stage, the internal space of the accumulator, so as to allow accommodation of a quantity of oil well greater than that necessary for the advancement of the injection piston, so that pressure reductions during the injection stroke are avoided.

Claims

1. An injection assembly for pressure diecasting molding machines, comprising an injection cylinder, an injection piston slidingly housed in said cylinder, valve means adapted to put sequentially into communication with said injection cylinder, firstly, an oil feed pumps for a first stage of slow advancement of the injection piston and, then, an oil accu- mulator for a second stage of quick advancement of the injection piston, and pressure multiplying means for applying subsequently a higher oil pressure to the injection piston for a third short stage of advancement of the piston at high pressure, characterized in that said pressure multiplying means comprise a further oil accumulator and further valve means adapted to put said further accumulator into communication with said injection cylinder at the end of said second stage of advancement of the injection piston.

2. An injection assembly according to claim 1, characterized in that said further accumulator is fed through an adjustable pressure reducer and houses within its internal space a thrusting piston urged by preloaded nitrogen.