DE102018101727B4 - Piston-cylinder unit for a molding machine and a molding machine - Google Patents

Abstract

Piston-cylinder unit for a molding machine (10) with - a first chamber (2), - a hydraulic pump (3) which is connected to the first chamber (2) for the application of a pressurized hydraulic fluid, and - a Resetting device (4) for resetting a piston (5) of the piston-cylinder unit (1) in a direction which is opposite to an effective direction of the first chamber (2), the resetting device (4) having a second chamber (6) of the Piston-cylinder unit (1) and a pressure accumulator (7), which pressure accumulator (7) is connected to the second chamber (6) and / or is formed integrally with the second chamber (6), characterized in that the reset device (4) is designed to reset the piston (5) into a reproducible basic position, in which basic position the pressure accumulator (7) is completely discharged.

Description

The present invention relates to a piston-cylinder unit for a molding machine according to the features of the preamble of claim 1 and a molding machine with such a piston-cylinder unit.

In this context, molding machines can be understood to mean injection molding machines, transfer presses, presses and the like.

Generic piston-cylinder units comprise a first chamber, a hydraulic pump, which is connected to the first chamber for loading a pressurized hydraulic fluid, and a return device for returning a piston of the piston-cylinder unit in one direction, which direction is substantially opposite to an effective direction of the first chamber. Resetting devices for piston-cylinder units can be used in molding machines if only the action of the piston-cylinder unit in the effective direction of the first chamber is important for the molding cycle itself. Then the piston-cylinder unit has to be returned to the starting position, for which the reset device is available. In the prior art, it is known to carry out the resetting through a second chamber of the piston-cylinder unit, which is connected to the pump of the hydraulic system (or another pump). By applying pressure to the second chamber, the piston-cylinder unit can be returned to the starting position.

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

Specifically in the case of pressure cushions, i.e. piston-cylinder units to build up a clamping force in a clamping unit of a molding machine, the pressure in the first chamber must first be reduced (clamping force reduction). Only then can the piston be reset by applying pressure to the second chamber.

To improve this situation, in the prior art electrical ( DE 10 2005 051 787 A1 ) or mechanically resilient ( US 2016/0067898 A1 ) Means for automatic reset proposed. However, this resulted in far more elaborate and complex constructions (see the figures of the prior art documents mentioned). In particular when using mechanical springs, the problem also arises that adaptation to the mold height of a mold which is to be mounted in a clamping unit is difficult, since the length and spring strength of the mechanical spring cannot be adjusted. This problem does not arise with an electrical reset, but an electrical drive must be provided in a shaping machine which is in principle hydraulic and which requires additional precision parts (for example threaded spindle) and is more complex. In addition, the hydraulics for the second chamber and the electric drive must be controlled in a coordinated manner.

Pamphlet DE102008007793A1 shows a hybrid drive with an entrained cylinder and hydraulic accumulator charge during the actuating movement to generate an actuating movement and to apply a large holding force, in particular to move molds and to apply a closing force to them, with a spindle drive for the actuating movement and with a differential cylinder unit required to apply the holding force a piston rod, a piston rod-side, annular pressure chamber and a piston rod-remote pressure chamber. It is provided that the piston rod is connected to an axially moving component of the spindle drive, that a hydraulic accumulator is present in which pressure medium can be displaced from the annular, first pressure chamber on the piston rod side when the piston rod is extended, that pressure medium from a tank into the piston rod side, second pressure chamber flows in, and that in order to apply the required holding force, the pressure chamber on the side of the piston rod is shut off from the tank and connected to the hydraulic accumulator.

Pressure accumulators of various types for resetting a piston of a piston-cylinder unit are also included in the DE19654917 A1 , the DE 1169117 B , the JP S59 33130 A , the JP 2009 228706 A as well as the DE 19842534 A1 disclosed. However, these always require the use of relatively complex hydraulic and valve arrangements in order to use the function of the pressure accumulator.

The object of the present invention is therefore to provide a piston-cylinder unit for a molding machine, which is simpler compared to the prior art, and a molding machine with such a piston-cylinder unit, which does not, or only to a small extent, delay the molding cycle due to the design caused.

This object is achieved by a piston-cylinder unit with the features of claim 1 and a molding machine with the features of claim 12.

This takes place in that the resetting device has a second chamber of the piston-cylinder unit and a pressure accumulator. The pressure accumulator is connected to the second chamber or is formed integrally with the second chamber. By applying hydraulic fluid to the first chamber and performing the actual task of the piston-cylinder unit, hydraulic fluid is displaced from the second chamber into the pressure accumulator and the pressure accumulator is thereby charged. In an embodiment in which the pressure accumulator is formed integrally with the second chamber, the pressure accumulator is charged directly.

If the pressure in the first chamber is now reduced, the pressure accumulator is automatically discharged and the piston is reset at the same time as the pressure reduction.

The present invention thus enables the piston to be reset with a simple construction and at the same time without loss of cycle time. Apart from a hydraulic drive, no other drives are necessary.

In addition, by changing the amount of hydraulic fluid in the second chamber together with the pressure accumulator, a basic position (up to which it is reset) can be set in a simple manner.

According to the invention, the resetting of the piston is permitted until the pressure accumulator is completely discharged, which results in a reproducible resetting. Because as soon as the pressure accumulator is discharged, a corresponding pressure loss occurs, which stops the reset beyond the basic position.

This represents a particularly simple embodiment of a piston-cylinder unit for a molding machine, because the resetting can take place automatically and quickly without the need to control or regulate a pump or valves.

Another advantage when the piston-cylinder unit according to the invention is used as a pressure pad to generate a closing force in a closing unit of a molding machine is that it is very easy to adjust the reproducible basic position - by changing the amount of hydraulic fluid in the second chamber - and can often be implemented using existing hydraulics and simple valve technology.

The force of the return can also be adjusted in many cases. In the case of a bladder accumulator, this can be achieved, for example, by changing the gas charging pressure.

Hydraulic oil can be used as the hydraulic fluid.

Further advantageous embodiments of the invention are defined in the dependent claims.

Piston-cylinder units according to the invention can be used, for example, for applying clamping force to clamping units of molding machines. Even ejectors of a clamping unit can be driven with a piston-cylinder unit according to the invention. Ejectors are used to remove a product formed in a molding machine or a molding tool from the corresponding mold or from the corresponding tool.

The pressure accumulator can be designed particularly simply as a bladder accumulator and / or membrane accumulator.

Bladder accumulators have a pressure vessel in which hydraulic fluid and a compressible medium are separated from one another by a flexible bladder. The hydraulic fluid can also be completely displaced from the pressure vessel by the pressure medium in the discharged state of the pressure accumulator. Gases in particular can be used as the pressure medium. An example of a pressure medium would be nitrogen. The reset ("spring constant") can be easily adjusted by adjusting the gas filling pressure.

In a diaphragm accumulator, a diaphragm is used instead of a bladder to separate the compressible medium from the hydraulic fluid.

The first chamber can be a rod-side chamber of the piston-cylinder unit. Particularly in the case of clamping units of injection molding machines in two-platen design with mostly four bars, a particularly small clamping unit can be created in this way, which also has a fast and automatic bar resetting.

The second chamber can have a smaller pressure-effective cross section than the first chamber. This is particularly advantageous when a particularly high force is to be generated by the piston-cylinder unit, for which a high pressure-effective cross section of the first chamber is beneficial. Due to the smaller pressure-effective cross section of the second chamber, the counterforce that acts against the force of the first chamber due to the loading of the pressure accumulator is also lower.

A small pressure-effective cross section of the second chamber can be generated relatively easily, for example, in that the second chamber is delimited by an extension of the piston, the extension having a smaller cross section than the piston. Such designs can advantageously be used in particular in the case of piston-cylinder units whose first chamber is a chamber on the rod side.

A particularly simple embodiment of the invention results when the second chamber is arranged at a front end of the extension.

It can be provided that the second chamber is connected to the pump and / or a further pump, a shut-off valve being provided in a connection line between the pump and / or the further pump on the one hand and the second chamber on the other hand. An adjustment of the height of the mold or an adjustment of the position up to which the resetting device effects a resetting of the piston (basic position) can thereby be implemented particularly easily. By opening the shut-off valve, hydraulic fluid can namely be conveyed into the second chamber (or the pressure accumulator). When the pressure accumulator is unloaded, it is automatically reset to the position that corresponds to the volume of the hydraulic medium in the system comprising the second chamber and pressure accumulator.

The first chamber can have a discharge line for hydraulic medium, a shut-off valve preferably being provided in the discharge line. This enables a particularly simple and quick resetting of the piston, since in a state in which the first chamber is pressurized and the pressure accumulator is therefore charged, only the shut-off valve in the discharge line has to be opened to simultaneously reduce the pressure in the first chamber and the To effect return of the piston.

In an arrangement which is not claimed and which is designed with at least two - in particular four - piston-cylinder units, the second chambers of the at least two piston-cylinder units are connected to a single pressure accumulator.

Protection is also desired for a molding machine with such an arrangement or at least one piston-cylinder unit according to the invention.

Displacement transducers can be provided with which the position of the piston in the cylinder can be detected.

• 1a, 1b zwei Ausführungsformen der Erfindung in einer ersten Stellung,
• 2a, 2b zwei Ausführungsformen der Erfindung in einer zweiten Stellung,
• 3a, 3b zwei Ausführungsformen der Erfindung in einer dritten Stellung,
• 4a, 4b zwei Ausführungsformen der Erfindung in einer vierten Stellung,
• 5 eine erfindungsgemäße Kolben-Zylinder-Einheit zum Antrieb eines Auswerfers sowie
• 6 eine erfindungsgemäße Formgebungsmaschine.

Further advantages and details of the invention emerge from the figures and the associated description of the figures. Show it

• 1a , 1b two embodiments of the invention in a first position,
• 2a , 2 B two embodiments of the invention in a second position,
• 3a , 3b two embodiments of the invention in a third position,
• 4a , 4b two embodiments of the invention in a fourth position,
• 5 a piston-cylinder unit according to the invention for driving an ejector and
• 6th a molding machine according to the invention.

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

In the execution according to 1a is the derivative 12 at the same time the supply line 14th to the first chamber 2 . In derivation 12 is also a check valve 11 arranged next to the connection with the pressure accumulator 7th is the second chamber 6th also with the pump 3 connected, namely via the connecting line 9 . Via the connection line 9 will also connect from the second chamber 6th made into a tank for hydraulic fluid (no reference number). Also in the connection line 9 there are two shut-off valves 11 - one each for connecting the second chamber 6th to the pump 3 and one to the tank.

Hydraulic oil is used as the hydraulic fluid.
The shut-off valves 11 are preferably designed as seat valves. These offer a high degree of tightness, which is advantageous because the amount of hydraulic medium in the system then comes from the second chamber 6th and the pressure accumulator 7th and corresponding lines is as constant as possible.

Due to the constancy of the amount of hydraulic fluid in the system from the second chamber 6th and pressure accumulator 7th the result is a reproducible and constant position up to which the reset device according to the invention 4th the piston 5 resets.

The pressure accumulator 7th is designed as a bladder accumulator, for example as a pressure medium Nitrogen with a minimum supply pressure p ₀ of about 10 bar can be used.

1b shows a variant of the embodiment from 1a . It differs in that the second chamber 6th not the same cross-section as the first chamber 2 having. This is indicated by an appendix 8th of the piston 5 reached which appendix 8th a smaller cross-section than the piston 5 Has. The cylinder is shaped accordingly.

Another advantage of the design with a low-cross-section extension 8th lies in the fact that the opposing force created by the loading of the accumulator 7th against the effect of the pressurization of the first chamber 2 exercised is smaller than it is when executing after 1a the case is that the pressure-effective cross section of the first chamber is larger in this case than that of the second chamber.

Another difference between the designs after 1a and 1b is the hydraulic interconnection. In the execution according to 1b owns the first chamber 2 a separate derivation 12 that flows into a tank. The supply line 14th to the second chamber - like the derivation 12 and the connection line 9 - via appropriate shut-off valves. It should be noted that the hydraulic interconnections according to 1a and 1b each can also be used in other embodiments.

The 1a and 1b show the respective embodiments in an idle state in which the chambers are not pressurized 2 , 6th present.

In the 2a and 2 B is a basic positioning of the piston 5 shown. By opening the in the connection line 9 located shut-off valve 11 (Towards the tank) and opening the in the supply line 14th (or in the case of the 2a Derivation 12 ) located shut-off valve 11 can control the amount of hydraulic fluid in the second chamber 6th be decreased (piston 5 moves to the right). By operating the pump 3 and a corresponding change in the switching position of the shut-off valves 11 the amount can be increased.

In the 3a and 3b are the respective variants when the first chamber is pressurized 2 shown. This causes the accumulator 7th loaded, which can be seen in the figure based on the deformed membrane of the bladder accumulator.

The pump delivers 3 Hydraulic medium in the first chamber 2 . The shut-off valve required for this 11 is open. The remaining shut-off valves 11 are closed.

In the 4a and 4b the provision according to the invention by the pressure accumulator is shown for the respective variants. By opening the shut-off valves 11 in derivation 12 hydraulic medium escapes from the first chamber 2 and flows back into a tank (in the case of the 4a about the pump 3 ). The pressure accumulator 7th now unfolds its effect and sets the piston 5 at the same time as the pressure in the first chamber decreases 2 back to the basic position, which in connection with the 2a and 2 B has been described, the pressure accumulator 7th is completely discharged in the basic position according to these statements.

As long as there is hydraulic fluid in the pressure accumulator, a certain minimum supply pressure is made available (gas filling pressure). If the entire amount of oil is withdrawn, there is automatically no longer any supply pressure available and the connected consumer will stop precisely at this point.

In 5 is an embodiment of the invention of a piston-cylinder unit 1 shown, for example, in an ejector of a clamping unit 15th an injection molding machine can be used. Here is the second chamber 6th a rod-side chamber of the piston-cylinder unit 1 .

The first chamber is used to eject a molded part 2 pressurized. This causes the piston to move 5 and thus the ejector (not shown) attached to it to the right in the illustration. This also reduces the pressure accumulator 7th loaded. To withdraw the ejector, only the hydraulic fluid has to be removed from the first chamber 2 be drained. The illustrated hydraulic circuit between the pump 3 and first chamber 2 is self-explanatory.

6th shows a molding machine according to the invention 10 - in this case an injection molding machine. This consists of a locking unit 15th and an injection unit 16 with plasticizing screw.

The clamping unit 15th has mold mounting plates that are moved relative to each other by rapid stroke cylinders for the assembly of a mold. When injecting, the mold mounting plate must be subjected to a large clamping force. This is what the piston-cylinder units are for 1 (Pressure pad) provided.

The hydraulic interconnection - in particular the hydraulic screw drive and the rapid stroke cylinder - is also self-explanatory.

For example, the piston-cylinder unit 1 also be designed in rotary piston design. The pump 3 can consist of several pumps from one system 3 consist. The cylinders and pistons 5 the piston-cylinder unit 1 can each be cylinders in the geometric sense with a circular, polygonal or even more complex base area.

List of reference symbols

(1)

Piston-cylinder unit

(2)

first chamber

(3)

hydraulic pump

(4)

Reset device

(5)

Piston

(6)

second chamber

(7)

Pressure accumulator

(8th)

Appendix

(9)

Connecting line

(10)

Forming machine

(11)

Check valve

(12)

Derivation

(14)

Supply line

(15)

Clamping unit

(16)

Injection unit

Claims (12)

Piston-cylinder unit for a molding machine (10) with - a first chamber (2), - a hydraulic pump (3), which is connected to the first chamber (2) for loading with a pressurized hydraulic fluid, and - a Resetting device (4) for resetting a piston (5) of the piston-cylinder unit (1) in a direction which is opposite to an effective direction of the first chamber (2), the resetting device (4) having a second chamber (6) of the Piston-cylinder unit (1) and a pressure accumulator (7), which pressure accumulator (7) is connected to the second chamber (6) and / or is formed integrally with the second chamber (6), characterized in that the reset device (4) is designed to reset the piston (5) into a reproducible basic position, in which basic position the pressure accumulator (7) is completely discharged. Piston-cylinder unit according to Claim 1 , characterized in that the piston-cylinder unit (1) is used to apply the closing force to a closing unit (15) of the molding machine (10). Piston-cylinder unit according to Claim 1 or 2 , characterized in that the piston-cylinder unit (1) serves as a drive for an ejector of the closing unit (15) of the molding machine (10). Piston-cylinder unit according to one of the preceding claims, characterized in that the pressure accumulator (7) is designed as a bladder accumulator and / or a diaphragm accumulator. Piston-cylinder unit according to one of the preceding claims, characterized in that the first chamber (2) is a rod-side chamber of the piston-cylinder unit (1). Piston-cylinder unit according to one of the preceding claims, characterized in that the second chamber (6) has a smaller pressure-effective cross section than the first chamber (2). Piston-cylinder unit according to one of the preceding claims, characterized in that the second chamber (6) is delimited by an extension (8) of the piston (5), the extension (8) having a smaller cross-section than the piston (5) having. Piston-cylinder unit according to Claim 7 , characterized in that the second chamber (6) is arranged at a front end of the extension (8). Piston-cylinder unit according to one of the preceding claims, characterized in that the second chamber (6) is connected to the pump (3) and / or a further pump, wherein in a connecting line (9) between the pump (3) and / or the further pump on the one hand and the second chamber (6) on the other hand a shut-off valve (11) is provided. Piston-cylinder unit according to one of the preceding claims, characterized in that the first chamber (2) is connected to a discharge line (12) for hydraulic medium, the shut-off valve (11) preferably being provided in the discharge line (12). Piston-cylinder unit according to one of the preceding claims, characterized in that a displacement transducer is provided which is set up to detect a position of the piston (5). Molding machine (10) which has at least one piston-cylinder unit according to one of the Claims 1 to 11 includes.

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