CN108361238B

CN108361238B - Piston-cylinder unit for a molding machine and molding machine

Info

Publication number: CN108361238B
Application number: CN201810077573.2A
Authority: CN
Inventors: A·洛纳克尔
Original assignee: Engel Austria GmbH
Current assignee: Engel Austria GmbH
Priority date: 2017-01-27
Filing date: 2018-01-26
Publication date: 2023-07-28
Anticipated expiration: 2038-01-26
Also published as: DE102018101727B4; AT519581A1; AT519581B1; CN108361238A; DE102018101727A1

Abstract

The invention relates to a piston-cylinder unit for a molding machine, comprising: -a first chamber (2), -a hydraulic pump (3) connected to the first chamber (2) for application of hydraulic fluid under pressure, and-a resetting device (4) for resetting the piston (5) of the piston-cylinder unit (1) in a direction substantially opposite to the direction of action of the first chamber (2), wherein the resetting device (4) has a second chamber (6) of the piston-cylinder unit (1) and has an accumulator (7), which accumulator (7) is connected to the second chamber (6) and/or is integrally formed with the second chamber (6), wherein the resetting device (4) is configured for resetting the piston (5) to a reproducible basic position in which the accumulator is completely depressurized.

Description

Piston-cylinder unit for a molding machine and molding machine

Technical Field

The invention relates to a piston-cylinder unit for a molding machine.

Background

Molding machines are understood to mean injection molding machines, die casting machines, molding presses and the like.

Such a piston-cylinder unit comprises a first chamber, a hydraulic pump connected to the first chamber for being acted upon by hydraulic fluid under pressure, and a resetting device for resetting the piston of the piston-cylinder unit in a direction substantially opposite to the direction of action of the first chamber. The resetting device for the piston-cylinder unit can be used in the molding machine when only the action of the piston-cylinder unit in the direction of action of the first chamber is important for the molding cycle itself. The piston-cylinder unit must then be returned to the starting position, for which purpose a resetting device is provided. It is known in the prior art to perform a resetting by means of a second chamber of the piston-cylinder unit, which is connected to a pump (or another pump) of the hydraulic system. The piston-cylinder unit can be returned to the starting position by the pressure loading of the second chamber.

However, this has the disadvantage that time is lost for resetting the piston-cylinder unit during the molding cycle. In addition, a higher volume of hydraulic fluid is required in the system of the second chamber and the pump must be actuated for resetting.

In particular, in the pressure pad, i.e. in the piston-cylinder unit, in order to establish the clamping force at the clamping unit of the molding machine, the pressure in the first chamber must be reduced for this purpose (clamping force reduction). The piston can then be reset by the pressure loading of the second chamber.

To improve this situation, electrical (DE 102005051787 A1) or mechanically resilient (US 2016/0067898 A1) mechanisms for automatic resetting are proposed in the prior art. But this results in a much more expensive and complex structural design (see the drawings of the mentioned documents of the prior art). In addition, a problem arises in that it is difficult to match the height of the mold of the molding tool to be mounted in the mold clamping unit, especially when using a mechanical spring, because the length and spring strength of the mechanical spring cannot be adjusted. Although this problem does not occur with an electrical reset, an electrical drive must be provided in a more costly, in principle hydraulic molding machine that requires additional precision components (e.g., a threaded spindle). The hydraulic means for the second chamber and the electric drive must additionally be controlled in coordination with each other.

Furthermore, different types of pressure accumulators for resetting the piston of a piston-cylinder unit are known from DE19654917A1, DE1169117B, JPS5933130A, JP2009228706a and DE19842534 A1. The accumulator always requires the use of relatively complex hydraulic and valve arrangements to take advantage of the accumulator function.

Disclosure of Invention

The object of the present invention is therefore to provide a simpler resetting device than the prior art, which does not cause or only causes to a small extent a retardation of the molding cycle caused by the design.

This object is achieved by a piston-cylinder unit.

This occurs in that the resetting device has a second chamber of the piston-cylinder unit and has an accumulator. The pressure accumulator is connected to the second chamber or is constructed integrally with the second chamber. By loading the first chamber with hydraulic fluid and fulfilling the original task of the piston-cylinder unit, hydraulic fluid is forced out of the second chamber into the pressure accumulator, which is thus pressurized. In embodiments where the accumulator is integrally constructed with the second chamber, the accumulator is directly pressurized.

If at this point the pressure prevailing in the first chamber decreases, the accumulator automatically releases pressure and the return of the piston takes place simultaneously with the pressure decrease.

The invention thus enables the piston to be reset with a simple design and at the same time without loss of cycle time. No other driver than a hydraulic driver is required.

Furthermore, the adjustment of the basic position (resetting up to this basic position) can be achieved in a simple manner by changing the amount of hydraulic fluid in the second chamber together with the pressure accumulator.

According to the invention, the resetting of the piston is allowed until the accumulator is completely depressurized, which indicates a reproducible resetting. Since a corresponding pressure loss occurs once the pressure accumulator is depressurized, which prevents a return beyond the basic position.

This is a particularly simple embodiment of the piston-cylinder unit for a molding machine, since the resetting can be performed automatically and quickly without the need for controlling or adjusting the pump or valve for this purpose.

A further advantage when the piston-cylinder unit according to the invention is used as a pressure pad for generating a clamping force in a clamping unit of a molding machine is that a reproducible adjustment of the basic position can be achieved in a very simple manner by changing the amount of hydraulic fluid in the second chamber and by means of the hydraulic means which are usually already present and simple valve technology.

The force of the reset can also be adjusted in a number of situations. In a balloon reservoir, this may be achieved, for example, by varying the gas boost pressure.

Hydraulic oil may be used as the hydraulic fluid.

The piston-cylinder unit according to the invention can be used, for example, for applying a clamping force to a clamping unit of a molding machine. The ejector of the mold locking unit can also be driven with the piston-cylinder unit according to the invention. Ejectors are used to remove products molded in molding machines or tools from respective molds or from respective tools.

The pressure accumulator can be embodied in a particularly simple manner as a bladder accumulator and/or as a diaphragm accumulator.

The bladder accumulator has a pressure vessel in which the hydraulic fluid and the compressible medium are present separated from each other by a flexible bladder. The hydraulic fluid can here also be completely forced out of the pressure vessel by the pressure medium in the state of the pressure accumulator being relieved. In particular, a gas can be used as the pressure medium. An example of a pressure medium is nitrogen. The return ("spring constant") can be easily adjusted by adapting the inflation pressure.

In a diaphragm reservoir, a diaphragm replaces the bladder for separating the compressible medium and the hydraulic fluid.

The first chamber may be a rod-side chamber of the piston-cylinder unit. In particular in the case of a mold clamping unit of an injection molding machine, which is usually of the form of a double-plate construction with four beams, a particularly small mold clamping unit can be produced in this way, which also has a quick and automatic return beam.

The second chamber may have a smaller pressure-effective cross section than the first chamber. This is particularly advantageous when particularly high forces should be generated by the piston-cylinder unit, for which purpose a higher pressure-effective cross section of the first chamber is required. Furthermore, since the second chamber has a smaller pressure-effective cross section, the reaction force acting against the force of the first chamber by the pressurization of the pressure accumulator is smaller.

A small pressure-effective cross section of the second chamber can be produced, for example, more simply, in that the second chamber is delimited by a projection of the piston, wherein the projection has a smaller cross section than the piston. This embodiment can be used in particular advantageously in a piston-cylinder unit in which the first chamber is a rod-side chamber.

A particularly simple embodiment of the invention results when the second cavity is arranged at the end of the end side of the projection.

It can be provided that the second chamber is connected to the pump and/or to the further pump, wherein a check valve is provided in the connecting line between the pump and/or the further pump and the second chamber, whereby a particularly simple adjustment of the height or position of the mold can be achieved, and the resetting device actuates the piston back to this position (base position). Hydraulic fluid may be fed into the second chamber (or accumulator) by opening a check valve. When the accumulator is depressurized, the hydraulic pressure is automatically returned to a position corresponding to the volume of the hydraulic medium in the system formed by the two chambers and the accumulator.

The first chamber may have a discharge line for the hydraulic medium, wherein a check valve is preferably arranged in the discharge line. This makes it possible for the piston to be reset particularly simply and quickly, since in the state in which the first chamber is pressurized and thus the pressure accumulator is pressurized, only the non-return valve in the outlet line has to be opened in order to simultaneously bring about a pressure drop in the first chamber and a resetting of the piston.

Also claimed is a device consisting of at least two, preferably four, piston-cylinder units constructed according to the invention, wherein the second chambers of the at least two piston-cylinder units are connected to a single pressure accumulator.

Also claimed is a molding machine with the above-described device or at least one piston-cylinder unit according to the invention.

A number of travel sensors may be provided with which the position of the piston in the cylinder can be detected.

Drawings

Other advantages and details of the invention are apparent from the accompanying drawings and the description of the drawings concerned. In the accompanying drawings:

FIGS. 1a, 1b show two embodiments of the invention in a first position;

FIGS. 2a, 2b show two embodiments of the invention in a second position;

figures 3a, 3b show two embodiments of the invention in a third position;

figures 4a, 4b show two embodiments of the invention in a fourth position;

fig. 5 shows a cylinder-piston unit according to the invention for driving an ejector; and

fig. 6 shows a forming machine according to the invention.

Detailed Description

Fig. 1a shows a piston-cylinder unit 1 according to the invention with a first chamber 2, a piston 5 and a second chamber 6. The first rod-side chamber 2 is used, for example, to apply a clamping force in a clamping unit 15 of an injection molding machine. The first chamber 2 is connected to a pump 3 for this purpose. The second chamber 6 is then connected to an accumulator 7.

In the embodiment according to fig. 1a, the outlet line 12 is at the same time the inlet line 14 to the first chamber 2. A non-return valve 11 is also arranged in the outlet line 12, and the second chamber 6 is connected to the pump 3 in addition to the pressure accumulator 7, i.e. also to the pump 3 via the connecting line 9. Communication from the second chamber 6 to a tank (no reference numeral) of hydraulic fluid is also established through this connection line 9. Two non-return valves 11 are also present in the connection line 9, one of which is used for the connection of the second chamber 6 to the pump 3 and the other of which is used for the connection of the second chamber 6 to the tank.

Hydraulic oil is used as the hydraulic fluid.

The non-return valve 11 is preferably designed as a central valve. The check valve provides a high degree of tightness, which is advantageous in that the amount of hydraulic medium in the system of two chambers 6 and the pressure accumulator 7 and the corresponding lines is as constant as possible.

By means of the constancy of the amount of hydraulic fluid in the system formed by the two chambers 6 and the pressure accumulator 7, a reproducible and constant position is obtained up to which the resetting device 4 according to the invention resets the piston 5.

The pressure accumulator 7 is designed as a gas-bag accumulator, wherein, for example, a minimum supply pressure P is used ₀ About 10bar of nitrogen was used as pressure medium.

Fig. 1b shows a variant of the embodiment of fig. 1 a. It differs in that the second chamber 6 does not have the same cross section as the first chamber 2. This is achieved by the projection 8 of the piston 5, which projection 8 has a smaller cross section than the piston 5. The cylinders are shaped accordingly.

A further advantage of the design of the smaller cross section of the projection 8 is that the counter force exerted by the pressurization of the pressure accumulator 7 against the pressure loading of the first chamber 2 is smaller than in the case of the embodiment according to fig. 1a, since the pressure-effective cross section of the first chamber is in this case greater than the pressure-effective cross section of the second chamber.

Another difference between the embodiments according to fig. 1a and 1b is the hydraulic wiring. In the embodiment according to fig. 1b, the first chamber 2 has a separate outlet line 12 which opens into the tank. The feed line 14 to the second chamber has a corresponding check valve as the discharge line 12 and the connection line 9. It is noted that the hydraulic cabling according to fig. 1a and 1b, respectively, can also be used in other embodiments.

Fig. 1a and 1b show a corresponding embodiment in a standstill state in which no pressure loading of the pressure chambers 2, 6 is present.

The basic positioning of the piston 5 is shown in fig. 2a and 2 b. By opening the non-return valve 11 in the connecting line 9 (tank direction) and opening the non-return valve 11 in the inlet line 14 (or in the case of fig. 2a the outlet line 12), the amount of hydraulic fluid in the second chamber 6 can be reduced (piston 5 moving to the right). The amount can be increased by operating the pump 3 and changing the switching position of the non-return valve 11 accordingly.

Fig. 3a and 3b show a corresponding variant when the first chamber 2 is pressurized. The pressure reservoir 7 is thus pressurized, which is visible in the figure by means of the deformed diaphragm of the air-bag reservoir.

The pump 3 here carries the hydraulic medium into the first chamber 2. The check valve 11 required for this is open. The rest of the check valve 11 is closed.

Fig. 4a and 4b show a resetting according to the invention of the pressure accumulator for the respective variant. By opening the non-return valve 11 in the outlet 12, the hydraulic medium comes out of the first chamber 2 and (in the case of fig. 4a by the pump 3) flows back to the tank. The accumulator 7 now plays its role and simultaneously returns the piston 5 with the disappearance of the pressure in the first chamber 2 to the basic position, which has been described in connection with fig. 2a and 2b, wherein the accumulator 7 is completely depressurized in this basic position according to the embodiment.

As long as the hydraulic fluid is in the accumulator, a certain minimum supply pressure (charging pressure) is provided. If the total oil quantity is taken out, the supply pressure is automatically no longer available and the connected consumer is stopped there.

Fig. 5 shows an embodiment of a piston-cylinder unit 1 according to the invention, which can be used, for example, in an ejector of a mold clamping unit 15 of an injection molding machine. The second chamber 6 is here a rod-side chamber of the piston-cylinder unit 1.

For ejecting the molded part, the first chamber 2 is pressurized. The piston 5 and an ejector (not shown) fixed thereto are thus moved rightward in the drawing. The accumulator 7 is thus also pressurized. In order to withdraw the ejector, hydraulic fluid only has to be discharged from the first chamber 2. The hydraulic circuit shown between the pump 3 and the first chamber 2 need not be described.

Fig. 6 shows a molding machine 10, in the present case an injection molding machine, according to the invention. The molding machine is composed of a mold locking unit 15 and an injection unit 16 with a plasticizing worm.

The mold clamping unit 15 has mold clamping plates for mounting the molding tools, which are moved relative to each other by a quick stroke cylinder. In injection molding, the mold clamping plate must be loaded with a large mold clamping force. For this purpose, a plurality of piston-cylinder units 1 (pressure pads) are provided.

The hydraulic cabling of the hydraulic worm drive and the fast-stroke cylinder in particular also does not need to be described.

The invention is not limited to the embodiments shown here. The piston-cylinder unit 1 can also be designed, for example, in the manner of a rotary piston structure. The pump 3 may be constituted by a system of a plurality of pumps 3. The cylinder of the piston-cylinder unit 1 and the piston 5 can each be geometrically round, polygonal or even more complex-base-surface cylinders.

Claims

1. Piston-cylinder unit for a forming machine, comprising:

-a first chamber (2),

-a hydraulic pump (3) connected to the first chamber (2) for loading with hydraulic fluid under pressure, and

a resetting device (4) for resetting the piston (5) of the piston-cylinder unit (1) in a direction substantially opposite to the direction of action of the first chamber (2),

wherein the return device (4) has a second chamber (6) of the piston-cylinder unit (1) and has an accumulator (7), wherein the accumulator (7) is connected to the second chamber (6) and/or is integrally formed with the second chamber (6), characterized in that the first chamber (2) is connected to a discharge line (12) for the hydraulic medium, wherein a non-return valve (11) is provided in the discharge line, wherein the discharge line (12) opens into a tank for the hydraulic medium, and wherein the return device (4) is configured to return the piston (5) to a reproducible basic position in which the accumulator is completely depressurized.

2. Piston-cylinder unit according to claim 1, characterized in that the piston-cylinder unit (1) is used for loading a clamping force in a clamping unit of a molding machine.

3. A piston-cylinder unit according to claim 1, characterized in that the piston-cylinder unit (1) serves as a drive for an ejector of a mold-locking unit of a molding machine.

4. A piston-cylinder unit according to any one of claims 1 to 3, characterized in that the pressure accumulator (7) is configured as an air-bag accumulator and/or as a diaphragm accumulator.

5. A piston-cylinder unit according to any one of claims 1 to 3, characterized in that the first chamber (2) is a rod-side chamber of the piston-cylinder unit (1).

6. A piston-cylinder unit according to any one of claims 1 to 3, characterized in that the second chamber (6) has a smaller pressure-effective cross section than the first chamber (2).

7. A piston-cylinder unit according to any one of claims 1 to 3, characterized in that the second chamber (6) is delimited by a projection (8) of the piston (5), wherein the projection (8) has a smaller cross section than the piston (5).

8. A piston-cylinder unit according to claim 7, characterized in that the second chamber (6) is arranged at the end of the end side of the projection.

9. A piston-cylinder unit according to any one of claims 1 to 3, characterized in that the second chamber (6) is connected to the hydraulic pump (3) and/or to another pump, wherein a further non-return valve is provided in the connecting line (9) between the hydraulic pump (3) and/or the other pump on the one hand and the second chamber (6) on the other hand.

10. A piston-cylinder unit according to any one of claims 1 to 3, characterized in that a stroke sensor (13) is provided, which is arranged to detect the position of the piston (5).

11. A forming machine comprising at least one piston-cylinder unit according to any one of claims 1 to 10.