JPH033382Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a mold clamping cylinder for a molding machine used for injection molding of synthetic resin.

In a hydraulically operated molding machine, after opening and closing the mold to take out the molded product or insert it, high pressure oil is supplied to the mold clamping cylinder to perform strong mold clamping and mold synthetic resin. There is.

In this case, once the mold clamping cylinder generates the required mold clamping force, if the switching valve is shut off and high pressure oil is filled in, the state of strong mold clamping is maintained, but due to leakage of pressure oil. It was not possible to prevent the mold clamping force from decreasing.

Leakage of this pressure oil occurs at the sliding seal surface of the switching valve and piston, and although switching valves can be prevented by a pilot check valve circuit, leakage at the sealing surface of the piston can be prevented by using a special packing. Even if it were possible to prevent such damage, such a gasket would have a shorter lifespan than a normal gasket, and would be difficult to maintain and assemble, making it difficult to adopt.

Conventionally, therefore, a pressure compensating device such as a pressure pump or an accumulator is used to prevent a reduction in mold clamping force due to leakage of pressure oil during strong mold clamping. However, the use of a pressure holding pump in combination complicates the hydraulic circuit and control circuit, and increases costs.
In the case of an accumulator, not only was the cost high, but it also took a long time to boost the voltage, and there were also problems with safe shutdown. Moreover, in both the pressure holding pump and the accumulator, high pressure oil equivalent to the discharge flow rate is lost.

This invention is an attempt to prevent the reduction in mold clamping force due to leakage of pressure oil during strong mold clamping without using a pressure holding pump or accumulator, etc., with an extremely simple structure. is a front chamber and a rear chamber separated by a piston in a hydraulic cylinder,
They communicate through small passages with the required cross-sectional area, ensuring pressure retention regardless of leakage of pressure oil from the sealing surface of the piston, and also making it possible to open the mold.

Communication between the front chamber and the rear chamber can be achieved by providing a small passage through the piston, or by providing a small passage between the hydraulic passage in the front chamber and the hydraulic passage in the rear chamber. The cross-sectional area of the cylinder differs depending on the inner diameter of the hydraulic cylinder, but it should be of a size that does not generate excessive pressure in the rear chamber during strong mold clamping.

The mold opening force is much smaller than the mold clamping force, and the piston pressure receiving area of the mold opening oil chamber B is formed to be much smaller than the piston pressure receiving area of the mold clamping oil chamber A.

This invention will be explained in detail below using illustrated examples.

In the figure, 1 is a hydraulic cylinder, 2 is a mold clamping ram integrated with a piston 3, and the inside is a high-speed mold closing cylinder 4, into which a booster ram 5 is inserted from the rear end of the hydraulic cylinder 1. . Further, valves 11, 12, and 13 are provided in each hydraulic path between the front chamber A, the rear chamber B, and the high-speed closed cylinder 4.

The hydraulic cylinder 1 is usually fixed to the machine base,
A movable plate 7 that moves using tie bars 6 as a guide is connected to the tip of the mold clamping ram 2.
A mold 9 for injection molding is separately attached to the fixed plate 8 and the fixed plate 8.

In this embodiment, a small passage 10 is provided in the piston 3 portion, which communicates the front chamber A, which has a large pressure receiving area, and the rear chamber B, which has a small pressure receiving area, in the hydraulic cylinder 1, which is partitioned by the piston 3. It is provided. The cross-sectional area of this small passage 10 is limited to a size that does not generate excessive pressure in the rear chamber B during strong mold clamping. Further, it is preferable that the small passage 10 is installed in the form of an orifice, because in this case, the amount of oil escaping changes less depending on the oil temperature, and the amount can be determined by calculation.

Further, the cross-sectional area of the small passage 10 varies depending on the inner diameter of the hydraulic cylinder 1. If the cross-sectional area of the small passage 10 is too large, the amount of oil that escapes when the mold is opened will increase, making it difficult to increase the speed. On the other hand, if it is too small, the amount of oil escaping during strong mold clamping is restricted, the pressure difference becomes large, and excessive pressure is generated in the rear chamber B.

In the mold clamping cylinder with the above structure, the mold clamping ram 2
When the piston 3 retreats together with the small passage 10
Pressure oil escapes from the rear chamber B to the front chamber A through the passageway, and the amount thereof is determined by the cross-sectional area of the small passage 10 and the pressure difference between the two chambers. Also, at the beginning of mold opening,
The pressure difference is large due to the resistance of the mold 9, but since the mold opening speed is not very necessary at this time, there is no particular problem even if some pressure oil escapes. Furthermore, the highest speed is required during the middle stage of mold opening, and although it is not desirable for pressure oil to escape, at this time only a pressure difference is generated that is sufficient to overcome the sliding resistance in the piston 3, movable plate 7, etc. , the amount of oil escaping is small.

The amount of oil passing through the small passage can be calculated using the following formula.

However, α: flow coefficient F: cross-sectional area of the small passage g: gravitational acceleration γ: specific weight of oil q: flow rate passing through the small passage △P: differential pressure before and after the small passage Next, to explain the operation, first, the valve 11 When the valve 12 is opened to supply pressure oil to the high-speed mold closing cylinder 4, and on the other hand, the oil in the rear chamber B is discharged from the valve 13, the valve 12 is opened to the front chamber A, and a large amount of oil is supplied from the tank to the mold clamping ram. 2 and piston 3 move in the mold closing direction. Then, when the mold closing is completed, the valve 13 is shut off, pressure oil is supplied to the front chamber A, and the pressure in both chambers is increased to perform strong mold clamping.

Next, valves 11 and 12 are shut off, pressure oil is stored in both chambers, and pressure is maintained. And finally valves 11, 12, 13
is opened, pressure oil is supplied from the valve 13 to the rear chamber B, and the mold is opened.

As is clear from the above operation, both chambers are connected to the small passage 1.
When communicating by 0, at the time of holding pressure,
Valves 12 and 13 can be shut off to store pressure. As a result, all of the pump discharge can be used for the operation of other devices, such as injection or screw rotation, and the hydraulic pump can be unloaded when the pump discharge is not needed in other devices.

As mentioned above, this device has a front chamber A and a rear chamber B separated by a piston 3 in a hydraulic cylinder 1, and a high-speed mold closing cylinder 4 in a mold clamping ram 2 integrated with the piston 3. , its high-speed type closing cylinder 4
A booster ram 5 is inserted into the rear end of the hydraulic cylinder 1, and valves 11, 12, and 13 are provided in the front chamber A, the rear chamber B, and the hydraulic passages of the high-speed mold closing cylinder 4, respectively. The front chamber A and the rear chamber B are connected by a small passage 1 having a cross-sectional area large enough to prevent excessive pressure from being generated in the rear chamber B during strong mold clamping.
0 to ensure pressure retention regardless of leakage of pressure oil from the sealing surface of the piston 3, and also enables the mold to be opened, allowing the pump discharge amount during pressure retention to be used effectively for other purposes. It also eliminates the need for the previously used pressure holding pumps and accumulators, which not only saves energy but also saves equipment.

[Brief explanation of the drawing]

The drawing is a schematic vertical cross-sectional view showing one embodiment of a mold clamping cylinder of a molding machine according to this invention. 1... Hydraulic cylinder, 2... Mold clamping ram, 3...
Piston, 10...Small passage, A...Antechamber, B...
back chamber.

Claims (1)

[Scope of Claim for Utility Model Registration] A hydraulic cylinder has a front chamber and a rear chamber separated by a piston, a high-speed mold closing cylinder is provided in a mold clamping ram integrated with the piston, and the high-speed mold closing cylinder has a front chamber and a rear chamber separated by a piston. A booster ram is inserted from the rear end of the hydraulic cylinder, and the front chamber and rear chamber are connected to each other in a mold clamping cylinder in which valves are installed in the hydraulic passages of the front and rear chambers and the high-speed mold closing cylinder. A mold clamping cylinder for a molding machine, characterized in that the mold clamping cylinder of a molding machine is communicated with by a small passage having a cross-sectional area large enough not to generate excessive pressure in a rear chamber.