DE3037441A1 - Automatic thermoplastics extruder regulation - where return to raw material of recovered heat losses is regulated by throughput meter - Google Patents

Abstract

An extruder for plastics is regulated by measuring the wt. of material fed in with a throughput meter, comparing the value with the target figure calculated from the wt. of finished prod. and adjusted the screw speed according to the deviation. The feedback to the raw material of heat lost in the extruder + nozzle + end product is regulated by the measurements on the throughput. Optimal prodn. in utilisation of heat losses to preheat raw material is obtd. without requiring regulation by the operator.

Description

Method and device for regulating

a plastic processing screw press The invention relates on a method for controlling a plastic-processing screw press, where the weight of the plasticizable raw material fed to the screw press measured by means of a throughput measuring device, with a weight setpoint, the results from the calculated weight of the finished product, compared and according to the deviation, the capacity of the screw press by changing the speed of the screw is regulated.

In such a known method and a device for Rules of a plastic-processing screw press (DE-AS 25 31 966) is the arising during operation on the extruder and its profile tools as well as on the end product Heat loss is not exploited, but heats up the operating room.

It is also a device for preheating powdery or granular thermoplastic plastics with a storage container that can be connected to an extruder known, which is provided with a line for supplying a heating medium. the The line is connected to a suction hood that releases the heat lost during operation Part of the extruder and its profile tools covered (DE-PS 2 235 023). The amount and the temperature level of the resulting heat loss depends on the type of plastic material to be plasticized and chemical / physical properties.

Due to the plasticization of plastics during processing the heat content of a plastic material to be processed comes from thermal energy - including the starting temperature of the material - is of considerable importance. Furthermore the degree of plasticization of a raw material is determined by density, melt index, shear modulus and shear stress determined.

The degree of plasticization and the output of a plastic product are in a causal relationship in the processing process.

Since the raw material temperature has an influence on the degree of plasticization, result from the use of waste heat for the purpose of preheating raw materials necessary limits when the power output as a result of the excessively preheated Material is restricted uneconomically.

Sufficient for a perfect regulation of the heat loss recovery not only a temperature monitoring of the process or the recording of the expended Energy.

The invention is based on the object of a method and a device to regulate the heat loss recovery for the purpose of preheating the raw material to be designed in such a way that device adjustments are made for different types of raw materials by the operating personnel and with economical energy saving optimal production is achieved through the use of waste heat.

This task is performed in a method of the type mentioned at the beginning solved in that the raw material fed by means of the throughput measurement, at the extruder and its profile tools as well as the heat losses generated on the end product will.

In an advantageous embodiment of the invention is means the throughput measurement of both the raw material fed to the extruder and its Profile tools as well as the heat loss arising on the end product as well as that of the screw and the basic heat energy supplied to the profile tools for plasticizing the raw material regulated.

With the method according to the invention and the device according to the invention, which is emphasized in the subclaims, a measurement and control system is available With which it can be recognized how much heat loss can be used to save energy can be returned to the raw material until the temperature point is reached, in which there is a loss of production output due to excessively heated material.

Embodiments of the invention are shown in the drawing and are described below.

The figures show: FIG. 1 a plastics processing machine which is equipped with a Measuring and control system is equipped, in a schematic representation, Fig. 2 a Throughput measuring device with associated evaluation device.

The plastics processing machine 1 has a Plasti-FizicrunrJt.3cl) necke which are fed via the functional line 2 with electromotive drive energy will.

Likewise, via function line 3, basic heat energy is used for plasticizing of the raw material 4, a thermoplastic synthetic material, fed to the screw.

After plasticization in the screw, the raw material is used in the profile tool 5 formed into the end product 6.

During processing, the raw material 4 is first placed in the container 7, which is designed as a heat exchanger, is transported and from there enters a throughput measuring device 8.

During processing, arises due to the application of Thermal energy, a change in the physical state of matter "hard-soft-hard". Included heat loss falls on the plastics processing machine 1, on the profile tool 5 and on the end product 6. This heat loss is collected in the device 9 and guided via the functional line 10 into the lower part of the container 7. At the Flow of the raw material 4 through the container 7 becomes part of the heat loss the raw material 4 is released before the residual heat loss via the functional line 12 is released into the environment.

The raw material heated in this way passes through the throughput measuring device 8 into the screw of the processing machine 1, which as a result of predetermined target values has a defined absorption capacity at a certain raw material temperature and also a definable drive power is required to get the raw material 4 to the desired one Convert end product 6.

This process results in a flow rate measuring device 8 measurable raw material throughput in kg / time.

In the event of excessive heat loss, the situation could arise that as a result of the changed shear modulus conditions of the raw material, the desired Energy savings occur, but production output also falls back.

This behavior, which cannot be striven for, can be caused by the throughput measuring device can be detected by measurement. Via the function line 13, a control signal is sent to the Device 9 given so that a cooling medium, e.g. air, for temperature control of the heat loss 11 can be supplied.

In this way it is ensured that an optimal production process with high efficiency in terms of energy consumption and production output arises.

From the screw, the profile tool 5 and from the end product 6 the heat loss is fed to the device 9 via function lines 15, 16, 17.

In Fig. 2, the throughput measuring device 8 is shown schematically, by regulating the use of waste heat at the various Types of raw materials is made possible.

The throughput measuring device 8 consists of a measuring container 18, the is generally designed as a funnel and is attached to a load cell 19. The load cell 19 detects the weight of the measuring container 18 and that located therein Raw material 4. The total weight or

its change over the tent will begin with a start signal from measuring point M1 to measuring point M2 recorded as actual value in selectable time segments and via function line 20 as an electrical signal to an electronic scale 21 passed. This actual value is sent to an evaluation device via function line 22 23, which has a process computer, forwarded for comparison with a target value. The target value is the result of an arithmetic operation outside the process entered into the evaluation device 23 in kg / time.

The value entered via function line 22 is now entered in the evaluation device The actual value is compared with the nominal value entered via a function line 24 and if so If there is a difference, an electrical signal is generated for control purposes Delivered to the device 9 via the function line 25, for example.

In order to design the regulation optimally, i.e. it approximately continuously carry out, it is necessary that the weight change as often as possible partial unit between the measuring points M1 and M2 is detected. this happens in that in individually selectable time segments with corresponding frequency beginning with the start signal of the measuring point M1 within the electronic balance 21 or the load cell 19, the partial change weights are detected. Of the Process computer within the evaluation device 23 is designed in such a way that that the selected time segments for the actual value are simultaneously a signal, to form the same time for the partial weights of the target value.

The output signal 25 for regulating can depending on the change difference be positive or negative between the target and the actual value. In addition, is this signal depends on the quantity of the change difference from the target / actual value comparison also quantitatively large or small in its capacity.

Switching points S1 and S2 are provided on the measuring container 18.

These switching points can be accessed via the function lines 26, 27 on the signal conditioning instrument 23 act, with the task that the measuring container 18 is not overfilled or can be completely emptied.

The measuring container 18 is generally the means of the heat loss Preheated raw material is supplied. However, it is also conceivable to use the measuring container 18 as To train heat exchangers and the heat loss to preheat the raw material in insert the measuring container.

Reference number 1 plastics processing machine 2 function line 3 Functional line 4 Raw material 5 Profile tool 6 End product 7 Container 8 Throughput measuring device 9 Device 10 Function line 11 Heat loss 12 Function line 13 Function line 14 Function line 15 Function line 16 Function line 17 Function line 18 Measuring container 19 Load cell 20 Function line 21 Scales 22 Function line 23 Evaluation device 24 Function line 25 Function line 26 Function line 27 Function line M1 measuring point M2 measuring point 51 switching point 52 switching point

Claims (5)

Method for regulating a plastics processing plant Screw press in which the weight of the screw press can be plasticized Raw material measured by means of a throughput measuring device, with a weight setpoint, which results from the calculated weight of the finished product, compared and according to the deviation, the capacity of the screw press by changing the speed of the screw is regulated, that is to say e t that by means of the throughput measurement the raw material (4) fed to the extruder and its profile tools (5) as well as the heat loss resulting from the end product (6) is regulated. 2. The method according to claim 1, characterized in that means the throughput measurement of both the raw material fed to the extruder and its Profile tools as well as the heat loss arising on the end product as well as that of the screw and the basic heat energy supplied to the profile tools for plasticizing the raw material be managed. 3. Apparatus for performing the method according to claim 1 or 2, characterized in that the throughput measuring device (8) and the heat exchanger trained raw material container (7) directly in a structural unit at the screw inlet or are installed on the cylinder of the processing machine. 4. Apparatus for performing the method according to claim 1 or 2, characterized in that the measuring container (18) the throughput measuring device (8) is designed as a heat exchanger to which the heat loss can be fed. 5. Device for performing the method according to the claims 1 or 2, characterized by an evaluation device (23) with a process computer, in the weights from an electronic balance (21) beginning with a start signal are queried as actual values after specified, selectable time periods and with synchronous equal time segments of the target value, which result from the weight-bearing capacity Snail can be compared over a period of time, the difference being a according to the sign and quantity of the corresponding control signal (25) is determined.