GB2216456A - Process and apparatus for attemperating tools for processing thermoplastic masses - Google Patents

Abstract

In order to provide a process for attemperating, tools for injection moulding, by means of cooling water, in which process the tools possess several cooling channels which are each connected through inlet and outlet connections to a flow through device for controlling the cooling water, and all the inlet and outlet connections to the flow through regulating device open into common inflow and outflow channels in which, respectively, the cooling water is supplied through a pre- attemperating device and the returning cooling water is fed to the pre-attemperating device, and with which process a self-contained heating or cooling of the tools to the desired temperatures is possible, it is proposed that the pre- attemperating device controls the temperature of the flow in the pre-attemperating circulation by means of a temperature controller in such a way that during heating, the highest target temperature value of the flow through controller target temperatures, plus an excess, is chosen as the control variable and that heating is continued until the highest flow temperature so defined is reached, and after this highest temperature is reached the temperature controller is automatically switched off, and then the lowest target temperature value, minus an excess, of the flow through controller target values is then chosen as the control variable during cooling.

Description

PROCESS AND APPARATUS FOR ATTEMPERATING TOOLS FOR PROCESSING THERMOPLASTIC MASSES The invention relates to a process for attemperating tools for processing thermoplastic masses and the like, especially injection moulding tools, by means of cooling water, whereby the tool possesses several cooling channels which are each connected by means of inlets and outlets to a flow through device for regulating the cooling water, whereby in addition all the inlets and outlets of the flow through controlling device are connected respectively to common inlet and outlet channels into which, respectively, the cooling water is supplied through a pre-attemperating device or the returning cooling water is fed to the pre-attemperating device.

Conventional injection moulding tools comprise several cooling medium channels to which an appropriate cooling circuit can be connected on the inlet and outlet sides.

Normally there is a device for regulating the throughput of cooling medium, usually called a flow through controller, connected between the source of cooling water and the cooling channels of the tool.

Besides direct connection of the flow through controller to a source of cold water or another suitable stored supply of cooling medium, use has also already been made of connection to an intermediate pre-attemperating circuit.

There is a problem in that there are differences between the target values of the individual branches of flow through the tool so that, for example, with a tool provided with four cooling channels, target temperatures of 45 C, 40 C, 50 C and 480C may be desired. These temperatures are usually considerably higher than the basic temperature of the cooling water supplied from a cooling medium storage tank or from the supply network.

This means that heating of the tool, before production begins, for example, or after a break in production, is not possible with the cooling water available for use, and on the other hand the flow through controllers must operate with relatively small throughflows to ensure an appropriately balanced cooling of the tool during use.

Starting from this state of the art, the object of the invention is to provide a process of this kind with which self-contained heating and cooling of tools to desired target temperatures is possible.

To achieve this objective the invention proposes that the pre-attemperating device controls the flow temperature of the pre-attemperating circuit by means of a temperature regulator in such a way that, during heating, the highest target temperature value of the flow through controller target temperature values, plus an excess, is chosen as the control value and heating is continued until the highest circulation temperature so defined is reached, and after this highest value is reached the temperature regulator is automatically switched off, and then the lowest target temperature value of the flow through controller target values, minus an excess, is chosen as the control value during cooling.

This process is particularly useful when the tool attemperation requires flow through controllers operating at higher water temperatures than that of the available cooling water temperature, or when heating up of the tools before the start of production is necessary.

By means of the pre-attemperating circuit, water is made available to the flow through controllers with a temperature which on the one hand, for heating tools up, is above the highest target temperature of the appropriate flow through controller for a specific cooling channel of a tool. On the other hand, water is made available to the flow through controller, for cooling during production with the tool, with a temperature which is below the lowest target value set in the flow through controller for a cooling channel in the tool. The pre-attemperating circuit adjusts itself automatically to the temperature required for heating or cooling at the time. It thereby optimizes itself.

By "excess" is meant the temperature difference which is necessary in order to transfer a defined amount of heat whilst the target value is maintained. The greater the quantity of heat to be transferred, the greater must the "excess" be. Consequently the excess is determined from the target temperature, the heat transfer surface area, the quantity of heat to be transferred and the flow volume. In all previously known control procedures this kind of excess is not used. However, in order for the device which is controlled to attain a genuinely constant temperature, such an excess must be included in the control circuit.

A preferred operational step in this connection consists of storing the target values of the flow through controller circuits in a target value selector. The highest target value is transmitted from the target value selector to the temperature regulator for the heating operation, but the lowest for the cooling operation.

The temperature target values are read at the appropriate flow through controllers which are each connected to a specific cooling channel in the tool. These target values are indirectly, through the target value selector, memorized in the temperature regulator which controls the circulation temperature accordingly. The temperature regulator controls the circulation temperature of the pre-attemperating circuit using the highest target value, plus an excess, when heating and using the lowest target value, minus an excess, when cooling. Switching over is controlled by an internal logic system.

Below the acceptable range for one or more control circuits, the highest target value, plus an excess, is taken over as the control value. Within or above the acceptable range for all the control circuits, the lowest target value, minus an excess, is taken over as the control value.

In order to be able to have good control even with small temperature differences, it is provided that cooling can be produced either indirectly by means of a cooling coil, through which cold water flows, arranged in the cooling medium, or directly by mixing cold water into the cooling water which is circulating. Cooling can be switched from direct to indirect, or conversely, by means of a reversing switch, when the temperature difference between the lowest target temperature value of the flow through controller circuit and the cooling water in circulation exceeds or does not reach, respectively, a value which can be pre-set.

By means of this switching-over which is controlled by the temperature difference, cooling can be switched from direct cooling to indirect cooling, or conversely, if the temperature difference between the control circuit with the smallest amount of flow and the cooling water temperature exceeds or does not reach, respectively, a value which has been pre-set.

The invention also provides apparatus for performing the process of Claims 1 to 3, for attemperating tools for processing thermoplastic masses and the like, especially injection moulding tools, by means of cooling water, whereby the tool possesses several water carrying cooling channels the inlets and outlets of which are connected to flow through controllers, and a pre-attemperating device is connected between a source of cooling water and the flow through controllers, which pre-attemperating device is connected by a cold water inlet and outlet to the source of cold water and by a further inlet and outlet to the flow through controllers, whereby the flow through controllers comprise a common collecting channel for the water flowing away from them and a further common collecting channel for the water flowing towards them, characterized according to the invention in that the pre-attemperating device comprises an attemperating apparatus, which is connected to the collecting channels of the flow through controllers, that a propelling device for the cooling water, especially a pump, is built into the attemperating circuit, and that a temperature probe which measures the temperature of the circulating water is provided in the pre-attemperating device, which probe is connected to a temperature regulator so that the latter switches on either the heating or the cooling of the attemperating apparatus, depending on the temperature of the circulating water.

By virtue of the apparatus provided according to the invention, the actual temperature of the circulating water can be used as the value for switching the state of the temperature regulator, so that the temperature regulator switches on the heating when the temperature of the circulating water is below the target value, and so heats up the circulating water and consequently the tool, whilst when the temperature of the circulating water exceeds the upper target value, plus an excess, this temperature is detected and is used to switch the temperature regulator over to cooling.

Preferably it is arranged that a target value selector is connected to the temperature regulator, which selector stores the target values of the flow through controller circuits and passes on to the temperature regulator the appropriate highest target value for the heating operation and the lowest target value for the cooling operation, whereby the temperature regulator controls the temperature of the attemperating water using the highest target value, plus a special pre-settable excess when heating, and using the lowest target value, minus an excess, when cooling.

Furthermore, it is preferred that the temperature regulator comprises a logic switching system which incorporates the highest target value, plus an excess, as the control value when the temperatures of the circulating water are below the acceptable range for at least one control circuit of the flow through controllers, and incorporates the lowest target value, minus an excess, as the control value when the temperatures of the circulating water are within or above the acceptable range for all the control circuits.

In a preferred embodiment the attemperating apparatus consists of a cylindrical housing with an inlet and outlet for the medium flowing through it, and with an electrical heating element arranged inside it, as well as a cooling coil through which cold water can flow, whereby the connecting pipe leading to the cold water supply can be closed or opened by means of a valve controlled by the temperature regulator, and the heating element likewise can be switched on or off by the temperature regulator.

Furthermore, it is preferred that a cold water supply is connected into the attemperating circuit and a water drain-off pipe, which can be closed or opened by means of a valve, is connected into the attemperating circuit in the direction of flow before this cold water connection, whereby the valve can be controlled by means of the temperature regulator.

Finally, it is advantageous if the the valves can be controlled by means of a temperature difference switch which compares the temperature of the circulating water with the temperature of the cold water in the cold water source by means of a temperature probe, and which closes the valve connected in the pipe leading into the cooling coil when the pre-selectable temperature difference is not reached, and on the other hand opens the valve leading to the water drain-off pipe, and when the temperature difference is exceeded it performs a similar but reversed switching operation.

An embodiment of the invention is shown in the drawings and is described in more detail in the following.

Figure 1 shows a block diagram of apparatus according to the invention; Figure 2 shows a simplified diagram of the pre-attemperating circuit.

The apparatus in Figure 1 consits of a schematically represented tool 1 with four cooling channels 11 - 14 each of which has an inlet and an outlet underneath as shown by arrows. The inlets and outlets of each of the cooling channels 11 - 14 are connected to an associated flow controlling device 21 - 24, by means of which the flow through them is controlled for the purpose of attemperating the tool. The target temperature values for the individual cooling channels can be set in the flow controlling device, and in the embodiment example are shown as 45 C, 40 C, 50 C, and 48 C.

Cold water can be fed directly into the flow controlling device from a cooling medium storage tank or from the supply network, as is indicated by 3. Above all then, when the attemperation of the tool using flow controllers requires a higher water temperature than the temperature of the cooling water available, or the tool needs to be heated up before production begins, a pre-attemperating circulation circuit 4 is necessary and is provided according to the invention.

This pre-attemperating circulation circuit 4 is connected between the cold water storage tank or the supply network, represented by 3, and the flow controller 21 - 24. The flow controller comprises a combined outlet channel from which the cold water at 5 is delivered to the pre-attemperating circuit. It also comprises a combined inlet channel 6, in which the pre-attemperated cooling water is fed in through the pipe 6 from the pre-attemperating circuit 4.

The pre-attemperating circuit essentially consists of a pump 41 which is connected in the cooling circulation circuit formed by the inlet pipe (designated 5) and the outlet pipe (designated 6).

Furthermore, the pre-attemperating circuit 4 consists of a heating/cooling assembly 42 with a cartridge-like heating element 42' and a cooling spiral 42", in which cooling water flows through the assembly 42 from left to right in the drawing. Furthemore, two valves of the solenoid valve type 43, 43t are provided, the function of which will be described later.

In addition, a temperature probe 44 is provided, for measuring the temperature of the circulating water, as well as another temperature probe 44', for measuring the temperature of the fresh water. A temperature difference switching system, which switches from direct to indirect cooling and conversely, is schematically represented by 45. This switch over occurs when the temperature difference between the control circuit with the smallest amount of flow and the cooling water temperature exceeds or does not reach a preset value.

Furthermore, a target value selector 46 is provided, in which the target values of the flow controllers 21 - 24 are stored, and which transmits the highest target value for the heating operation and the lowest target value for the cooling operation to a temperature controller 47. The temperature controller 47 is also electrically connected to the temperature probe 44, the signal from which is accepted by the temperature controller as the control variable. In addition, the temperature controller 47 controls, through an electrical connection 47', the cartridge heater 42'. Finally, the temperature controller 47 controls the solenoid valves 43, 43'.

The temperature controller regulates the temperature of the water circulating in the pre-attemperation circuit, using the highest target value, plus an excess, for heating, and using the lowest target value, minus an excess, for cooling. Switching over is performed by an internal logic system. Consequently, below the acceptable range of one or more of the control circuits, the highest target value, plus an excess, is adopted for control purposes. Within or above the acceptable range of all the control circuits, the lowest target value, minus an excess, is adopted for control purposes. The value of the excess can be pre-set.

A three position controller, having an input for the target value (controlled by the target value selector) and a variable setting for the excesses used with the highest and lowest target value (adjustable), is used as the temperature controller 47. The controller also comprises a logic input for switching from cooling to heating.

Normal operation of the pre-attemperating circuit is as follows.

At the start of production the target temperature values are established in the flow controller 21 - 24. These target values are automatically or manually stored in the target value selector 46.

Since these target temperatures are considerably above room temperature and also above the normal temperature of the cooling medium, especially of cold water, the temperature probe 44 must have a temperature considerably below every target temperature value. This measured value is read into the temperature controller 47. As a result of this signal the temperature controller closes the valves 43 and 43' and switches on the heating cartridge 42'. The cooling medium becomes warmer as a result of flowing through the assembly 42 and it flows with a raised temperature through the flow controllers 21 - 24 into the appropriate cooling channels of the tool, and so heats the tool up to the desired temperature.As soon as the temperature measured in the circulating flow by the temperature probe 44 exceeds the highest individual target value plus the preset excess, the controller switches from heating to cooling by means of an internal logic. This means that the heating cartridge 42' is switched off and the valve 43 is opened. The temperature controller has thereby accepted the lowest individual target temperature value from the target value selector, and uses this to control within the acceptable range of all the control circuits by taking into account the lowest target value minus an excess.

As a result of the opening of valve 43, fresh water streams from a cooling medium storage tank or from the supply network through the inlet pipe 3 and to the left, in the drawing, of the valve 43 into the cooling spiral 42", and emerges to the right from the cooling spiral and can flow away through the drain pipe 3. This cooling is referred to above as indirect cooling.

When the temperature difference between the circulating medium, measured by the temperature probe 44 and the cold water, measured by the temperature probe 44', is less than 10 C for example, switching over by the temperature difference switch will take place so that the valve 43 is closed by it and the valve 43' is opened. This results in a direct mixing in of fresh water through the inlet pipe 3, and in addition it results in a draining off (to the right) of cooling medium from the assembly 42 through the valve 43' and the outlet pipe 3. In this way fresh water is continuously mixed with the circulating cooling medium, as a result of which the desired cooling is obtained.

The latter method of operating is referred to as direct cooling.

The invention is not limited to the embodiment example, but can be modified in many ways within the scope of the claims.

Claims (11)

1. A process for attemperating tools for processing thermoplastic masses and the like, especially injection moulding tools, by means of cooling water, whereby the tool possesses several cooling channels which are each connected by means of inlets and outlets to a flow through controller for the cooling water, whereby in addition all the inlets and outlets of the flow through controller are connected respectively to common inlet and outlet channels into which, respectively, the cooling water is supplied through a pre-attemperating device or the returning cooling water is fed to the pre-attemperating device, characterized in that the pre-attemperating device controls the temperature of the flow in the pre-attemperating circuit by means of a temperature controller in such a way that, during heating, the highest target temperature value of the flow through controller target temperatures, plus an excess, is chosen as the control value and heating is continued until the highest flow temperature so defined is reached, and after this highest value is reached the temperature controller is automatically switched off, and then the lowest target temperature value of the flow through controller target temperatures, minus an excess, is chosen as the control value during cooling.

2. A process according to Claim 1, characterized in that the target values of the flow through controller circuits are fed into a target value selector and the highest target value for the heating operation and the lowest target value for the cooling operation are transmitted from the target value selector to the temperature regulator.

3. A process according to Claim 1 or Claim 2, characterized in that the cooling occurs indirectly by means of a cooling coil, through which cold water flows, which is arranged in the cooling medium, or directly by mixing cold water into the cooling water in the circulating flow, whereby the cooling can be switched from direct to indirect cooling, or conversely, by means of a reversing switch, when the temperature difference between the lowest target temperature value of the flow through controller circuit and the cooling water in the circulating flow exceeds or does not reach, respectively, a value which can be pre-set.

4. Apparatus for performing the process of Claims 1 to 3, for attemperating tools for processing thermoplastic masses and the like, especially injection moulding tools, by means of cooling water, whereby the tool possesses several water carrying cooling channels the inlets and outlets of which are connected to flow through controllers, and a pre-attemperating device is connected between a source of cold water and the flow through controllers, which pre-attemperating device is connected by a cold water inlet and outlet to the source of cold water and by a further inlet and outlet to the flow through controllers, whereby the flow through controllers comprise a common collecting channel for the water flowing away from them and a further common collecting channel for the water flowing towards them, characterized in that the pre-attemperating device (4) comprises an attemperating apparatus (e.g. 42), which is connected to the collecting channels of the flow through controllers, that a propelling device for the cooling water, especially a pump (41), is built into the attemperating circuit, and that a temperature probe (44) which measures the temperature of the circulating water is provided in the pre-attemperating device, which probe is connected to a temperature regulator (47) so that the latter switches on either the heating (42') or the cooling (42") of the attemperating apparatus depending on the temperature of the circulating water.

5. Apparatus according to Claim 4, characterized in that a target value selector (46) is connected to the temperature regulator (47), which selector stores the target values of the flow through controller circuits (21 - 24) and passes on the at that time highest target value for the heating operation and the at that time lowest target value for the cooling operation to the temperature regulator (47), whereby the latter controls the temperature of the water flowing in the pre-attemperating circuit to the highest target value, plus a special adjustable excess when heating, and to the lowest target value, minus an excess, when cooling.

6. Apparatus according to Claim 4 or 5, characterized in that the temperature regulator (47) comprises a logic circuit, which, at flow temperatures below the acceptable range, incorporates as control value the highest target value, plus an excess, of at least one control circuit of the flow through controllers, and which at flow temperatures within or above the acceptable range of all the control circuits, incorporates as target value the lowest target value minus an excess.

7. Apparatus according to one of Claims 4 to 6, characterized in that the attemperating apparatus (42) consists of a cylindrical housing with an inlet and outlet for the medium flowing through it, and with an electrical heating element (42') arranged inside it as well as a cooling coil (42") through which cold water can flow, whereby the connecting pipe leading to the cold water supply (3) can be closed or opened by means of a valve (43) controlled by the temperature regulator (47), and the heating element (42') likewise can be switched on or off by the temperature regulator (47).

8. Apparatus according to one of Claims 4 to 7, characterized in that a cold water pipe (3) is connected into the attemperating circuit, and a water draw-off pipe (3), which can be closed or opened by means of a valve (43'), is connected into the circuit in the direction of flow of the circulating water upstream from this cold water connection, whereby the valve (43') can be controlled by means of the temperature regulator (47).

9. Apparatus according to one of Claims 4 to 8, characterized in that the valves (43, 43') can be controlled by means of a temperature difference switch (45) which compares the temperature of the circulating water with the temperature of the cold water in the cold water source by means of a temperature probe (44'), and which closes the valve (43) connected in the pipe leading into the cooling coil (42") and on the other hand opens the valve (43') leading to the water draw-off pipe when the preselectable temperature difference is not reached, and when the temperature difference is exceeded it performs a similar but reversed switching operation.

10. A process for attemperating tools for processing thermoplastic masses and the like substantially as described herein with reference to the accompanying drawings.

11. Apparatus for attemperating tools for processing thermoplastic masses and the like substantially as described herein with reference to the accompanying drawings.