DE4029023C1 - Regulating gap in an extrusion moulding machine - by comparing actual value with threshold value of blank wt., varying width, measuring cycle time and determining material throughput - Google Patents

Abstract

Regulating the gap in an extension moulding machine, includes comp the actual value of the blank wt. with a threshold value and then varying the width. The cycle time is measured and the material through put is determined. The actual value is calculated using the cycle time and the through put. In order to produce multi-layered blanks, two separately controllable regulating circuits, comprising wt. and rotation as well as gap width and cycle time, are used. ADVANTAGE - The process enables a constant blank wt. to be achieved. (5pp Dwg.No.1/2)

Description

The invention relates to a method for weight-dependent Regulation of the basic gap on extrusion blow molding machines, at which is the actual weight with the target weight of the preform compared and the gap width is varied, the Cycle time is measured, the mass throughput is determined is, the actual weight of the preform from the measured Cycle time and the determined mass flow rate are calculated will, this actual weight with a predetermined target weight the actual weight is compared to the target weight Change in the wall thickness setpoint is adjusted, and the thereby changed cycle time by correcting the Extruder speed returned to the target cycle time is, according to the German patent 39 35 338.

The state of the art is DE-OS 29 40 418, which is a method for weight-dependent regulation of the Basic gap on extrusion blow molding machines concerns, in which the cycle time measured, a measured actual weight value compared with a predetermined target weight value by Change the wall thickness, the actual weight to the target weight is adjusted, and the thereby changed cycle time over a correction of the extruder speed back to the target Cycle time is reduced.

This method, as well as the method according to the Main patent P 39 35 338, used in the Production of extrusion blanks from one layer. It is therefore an extrusion blow molding process for Single-layer body or molded parts.

The prior art methods achieve one extensive specification or stabilization of the wall thickness of preforms and consequently cause increases in Quality and material savings.  

However, the methods according to the prior art permit not, by means of extrusion blow molding machines Manufacture blown bodies or multi-layer molded parts that in the entirety of their layers high precision of the Layer thickness stabilization, saving of material, precise coordination of the individual layers of the Require multi-layer body.

In contrast, the present invention has the object based on a method for weight-dependent control of the Basic column or the basic column To deliver extrusion blow molding machines, which with regulated Cycle time or preform length and preform wall thickness as well as constant mass throughput, or with several layers constant mass throughput per shift, a constant Preform weight guaranteed, the rule principle for one shift to several, if necessary separately controllable layers are used.

This object is achieved in a method of genus mentioned at the beginning the measures of the labeling part of claim 1 solved.

A special embodiment of the invention The method is claimed in dependent claim 2.  

It turned out in a surprising way that with the inventive method is possible, a plurality of Extrusion layers in the sense of a multi-layer extrusion with the precision that was previously only available for Single-layer body was achievable for multi-layer body apply, and if necessary variable targeted Layer thicknesses, different layer materials and Largest material savings as well as high quality of the to achieve the resulting multilayer body.

The original control principle according to the state of the art, in particular the German patent P 39 35 338 a relation or control of gap width s to weight Q and then the speed or extruder speed V.

In the present invention, this was original Coupling type canceled or modified to optionally independently controllable or also controllable at the same time or with a time delay Control circuits weight Q and speed V on the one hand, and Gap width s and time t on the other hand.

The present invention is thus two Pairs, two separate control loops.

The new summary of the control loops allows, compared to the prior art, a Multi-layer extrusion, with several layers in one Container wall introduced or to a container wall be brought together;  the method according to the invention is particularly suitable for PVC substitution.

The merged layers can be for example around polyethylene, an adhesion promoter and around Act polyacrylate, which then together the container wall form.

In the plastics industry, the so-called multi-layer Extrusion, also called co-extrusion, more and more for Commitment.

This multilayer extrusion process has the advantage the positive material properties of several materials in to combine a product.

So there is z. B. the possibility of a hollow body Transport of acids with an acid-resistant Manufacture interior material, increasing the Strength the middle layer from a recycling Material exists, or can exist, and the outer Layer, for example, a UV-stabilized material can.

Molded articles are produced in this way, the most varied industrial or environmental requirements better do justice as a single-layer body.

In the method according to the invention, it is now possible to further increase the efficiency of quality and Achieve environmental protection by virtue of the more precise Layer thickness and the saving of material less Tolerances for layers are possible and for example Multi-layer body from previously not usable Single layer combinations are possible.  

The invention described in more detail below now enables exact and reproducible production such multilayer hollow body in the blow molding process.

This means:

• 1. A target value specification of the cycle time for one Preform,
• 2. The target value specifications for the target weights of the individual layer materials per preform,
• 3. from 1. and 2. the target mass throughput per Layer material calculated,
• 4. Using scales, use the material hopper supplied mass flow rates recorded
• 5th and with the target mass flow rates calculated in 3rd compared.
• 6. If the actual mass throughput deviates the target mass flow rates per layer material, so is done by correcting the extruder speed of the an adjustment for each extruder.
• 7. The resulting change in Hose outlet speed and thus occurring Changing the cycle time is due to the correction the basic gap of the wall thickness programming compensated.

These measures take place in coordinated or where appropriate, coordinated form for the various Layers or the different columns instead and thereby enable the rapid improvement of the multilayer extrusion blow molding process.  

The invention is further explained with reference to FIGS. 1 and 2, FIG. 1 showing the weight-dependent preform control using the example of a three-layer blow molding system, and FIG. 2 representing a block diagram of the weight-dependent preform control in the case of multi-layer extrusion including extruders A to extruders n .

In this case 1, which, Fig. A central hydraulic cylinder supplied by a distributor head, the extruder A, B, C and the material which three extruders separate drive motors for the worm, separate evaluating the throughput of material, separate control of the extruder speed in dependence of desired - and actual throughput by means of a corresponding wall thickness programming with electrohydraulic servo system.

The Fig. 1 in detail, shows a distributor head 1, 3 extruders 14, 15 and 16, with feeders 24, 25, 26 to guide container 11, 12, 13, drive motors for worm 2, 3, 4, detection means 5, 6, 7 of the material for each extruder 14, 15 and 16 , control devices 8, 9, 10 of the extruder speeds of the extruders 14, 15, 16 in dependence on the target and actual throughput.

Furthermore, FIG. 1 is a hydraulic cylinder 17, a calculation unit 18 of the desired mass flow rate for material for the extruder 14, 15, 16, a weight setting unit 19 for coating material per preform, an input unit 20, the target cycle time for a preform , a wall thickness programming system 21 with an electro-hydraulic servo system, a setpoint specification unit 22 for the basic gap calculated from the set cycle and actual cycle time, and a detection unit 23 of the actual cycle time by means of a photocell.

Overall, FIG. 1 shows a schematic representation of a weight-dependent preform control using the example of a three-layer blow molding system.

Fig. 2 shows for each extruder A to optionally extruder n in a schematic way the various measures, such as input of the set value of the sheet material A, calculating the desired mass-flow rate for material A, control the extruder speed A and the detection of the mass - Actual throughput for extruder A by means of a balance, this control chain or this control circuit being connected to the input of the desired cycle time for a preform for the regulation of the basic gap g, the change in the hose speed and the detection of the actual cycle time by means of a photo cell, and this for all extruders from A to n.

Fig. 2 illustrates an overall block diagram of the ge weight dependent preform control for Mehrschichtenextru sion is to n in extruders A.

There is an input 24, 25 of the target value for the weight of the layer material of the extruder A (ws A) per preform or the target value, for the weight of the layer material of the extruder n (wsn) per preform and an input 26 of the target cycle time for a preform (wt).

Furthermore, there is a calculation unit 27 or a calculation unit 28 for calculating the target mass throughput for the material of the extruder A wm A = f (ws A, wt) or the target mass throughput for the material of the Extruder nw nm = f (wsn, wt) and a control 29 of the basic gap g = f (wt, xt).

Furthermore, FIG. 2, a control unit 30 and a control unit 31 of the extruder speed of the extruder A, e A = f (wm A, xm A) or of the extruder speed of the extruder n, s = f (Wmn, xmn) and a change control 32 the hose speed.

Further, Fig. 2 shows a sensing unit 33 and a detecting unit 34 of the mass-actual throughput of the extruder A by scale (xm A) or mass-actual throughput of the extruder n means balance (xmn) and a detection unit 35 the actual cycle time using a photocell (xt).

Claims (2)

1.Procedure for the weight-dependent regulation of the basic gap on extrusion blow molding machines, in which the actual weight is compared with the target weight of the preform and the gap width is varied, the cycle time being measured, the mass throughput being determined, the actual weight of the preform from the measured cycle time and the determined mass throughput is calculated, this actual weight is compared with a predetermined target weight, the actual weight is adjusted to the target weight by extending the wall thickness setpoint, and the cycle time thereby changed is returned to the target cycle time by correcting the extruder speed, according to patent P 39 35 338, characterized in that for Manufacture of multi-layer preforms for at least one of the layers each have two separately controllable control loops consisting of weight and speed on the one hand and of gap width and cycle time on the other. 2. The method according to claim 1, characterized, that the separate control by means of a programmable microprocessor.