DE2240880A1 - Extruded plastic tubular products - with rate of extrusion calculated from extrusion volume and tube wall thickness - Google Patents

Abstract

The actual extrusion rate is regulated to coincide with the calculated speed. Pref. the extrusion volume is maintained constant.

Description

"Process for extruding tubular plastic semi-finished products" The invention relates to a method for continuously extruding tubular Semi-finished plastic product from an extrusion head with an adjustable ring cross-section.

It is already known for a variety of uses and in particular For the production of plastic containers in tubular form and semi-finished products to extrude and then further process. The wall thickness of the semi-finished product and thus the container made from it is changed by changing the cross-section of the annular gap in the extrusion head as required.

However, it has been found to be disadvantageous in this known method that the wall thickness of the exiting plastic tube by swelling and / or Unintentional cutting to length and without the possibility of the previous calculation being changed.

Especially when changing to a new batch of raw material, it treads easily other and new swell and cut-to-length ratios, which increases the wall thickness of the emerging semi-finished plastic product changes in an undesirable manner.

It is known to minimize the influence of time on swelling and cutting to length to keep it low by initially storing the continuously processed melt and then extruded in a short time. However, this method has opposite the conventional extrusion significant disadvantages: It has to be expensive mechanical and hydraulic means are used, the melt is heavily stressed, and there still remains a noticeable residue of those caused by cutting to length Wall thickness reduction, which in turn is due to fluctuations in production and raw material conditions subject.

The object of the invention is now to provide a method for the extrusion of To find semi-finished plastic products in tube form, which have the aforementioned disadvantages and that of the prior art no longer has and which allows plastic in the form of a tube, in particular as a semi-finished product, with a precisely adjustable wall thickness. There should be changes in the material used and the extrusion and melting conditions be compensable.

This object is achieved according to the invention in that the extrusion speed calculated from the extrusion volume and the desired wall thickness of the hose and the actual speed of the exiting hose to match is regulated at the calculated speed.

still advantageous; is thereby. to e a fixed setpoint have kept the extrusion volume constant, in another version of the However, according to the invention, the speed as a function of any one can also be used adjustable extrusion volume, i.e. with a changeable setpoint.

In detail, it can be used to measure the speed of the exiting hose the length of an extruded tube can be measured as a function of time and the measured speed vt of the plastic hose can be compared with that from the quotient Velocity vr calculated from the extruded volume and extrusion cross section can be compared, in which case vt is the extrusion cross-section if the speed is too high and if the speed v @ is too low, the extrusion cross-section is reduced will.

When extruding tubular plastic semi-finished products occurs during "swell" and "cut to length" during extrusion and during the final forming process Depending on the different depths of draw, a further reduction in wall thickness on.

During the wall thickness reduction during the final molding process can be controlled depending on the drawing depth, so far it has been known as swelling and length of the emerging plastic tube have been shown to be uninfluenceable.

It is surprising to the skilled person with the measures of the invention but possible to absorb the effects of swelling and cutting to length and create one To extrude plastic tubing with precisely adjustable wall thickness, which in turn an end product with a previously unattainable exact wall thickness setting can be produced is.

In individual cases, thresholds are defined as the increase in wall thickness Uber beyond the amount resulting from the geometrical dimensions of the calibrating Annular gap of the extruder head and cut to length as an increase in Length beyond the amount resulting from the cross-section of the entrance gap and the extruded volume results.

Neither thresholds nor cutting to length are legally ascertainable or reproducible, although there may be a dependency between the two.

Surprisingly, the solution according to the invention makes it possible the uncontrollable processes of swelling and cutting to length through simple technical control Measures to balance out, while it would be more obvious for the expert, by perfect Uniformity in the processed material and in the processing conditions, especially when melting unl when extruding, reproducible swelling and To create cut-to-length ratios.

But it has been shown that the solution according to the invention is more economical, - simpler and, in particular, much better in terms of function than that for the specialist the obvious solution is.

In the following, an exemplary embodiment of the invention is based on a Describes the illustration of the process scheme in more detail.

According to FIG. 1, in which the basic sequence of the arithmetic and Control method is set out, the extrusion volume X is initially at 1 as constant material cross-section that is required from an application point of view A is used at 2, from which the speed Vr at 3 is calculated as the quotient SA will. The actual speed vt of the exiting plastic hose is measured, converted into a control signal at 4 and calculated with the signal from the Speed vr at 5 of the same.

The measurement of the speed of the exiting semi-finished product lies At the discretion of the person skilled in the art, mechanical, optical, acoustic or measurements with radioactivity sources can be used.

The comparison of the speeds at 5 is followed by a decision at 6 such that the extrusion cross section is equal to the gap cross section 12 through an actuator 10, if necessary after amplification at 9, is changed by the actuator the conical stopper in the extrusion head lifts or lowers and thus makes the exit cross-section smaller or larger.

if the difference in speeds is greater than zero, i.e. is positive, then the gap cross-section is reduced via the rule branch 7, so that the extrusion speed increases and the actual speed increases approaches the calculated speed. If the speed difference is less than zero, i.e. negative, the gap cross-section becomes via the control circuit 8 increases so that the actual speed decreases.

The new extrusion speed set by the respective gap change will again compare with the calculated extrusion speed and if necessary a further regulation takes place until the calculated extrusion speed is reached and has thus set the wall thickness calculated in advance.

Furthermore, ea is surprising to the person skilled in the art because of the process According to the invention possible in a simple manner, semi-finished products with adjustable different Wall thicknesses, regardless of cutting and threshold influences, according to the requirements to manufacture.

This is achieved by entering A at 2, as time or distance dependent Size, in a known manner, from any program input.

It is particularly advantageous according to this solution according to the invention not necessary, the input values with appropriate corrections to achieve the desired To provide end wall thickness.

The method according to the invention is particularly advantageous in that Unpredictable malfunctions during extrusion can also be detected and that furthermore, both positive and negative changes in the swell and cut-to-length ratio can be easily compensated for.

This advantage remains regardless of whether the setpoint vr and / or the control value A for the production of Kunstsiffkodies different (Change between two bodies produced one after the other) or more irregular (Change in the manufactured body) Wall thickness is changed depending on the side or ffeg.

These changes can be made by means of any program entries that are known per se take place. Changing the setpoint Vr has the advantage of also making changes in the swell and cut-to-length ratio due to the changes in the outlet cross-section A to be able to take into account.

Claims (5)

P a t e n t a n s p r ü c h e 1. Process for the continuous extrusion of tubular Semi-finished plastic product from an extrusion head with a variable ring cross-section, d a d u r c h e k e n n n n z e i n e t that the extrusion speed vr from the extrusion volume Q and the desired wall thickness of the hose are calculated uni the actual speed vt to match the calculated speed vr regulated we. 2. The method according to claim 1, characterized in that the extrusion volume Q is kept constant. 3. The method according to claim 1 or 2, characterized in that to measure the speed as a function of time, the length of an extruded hose end is measured. 4. The method according to claim 1 to 3, d a d u r c h g e k e n nz e i c h n e t that the measured speed vt of the plastic tube with the from the quotients from the extruded volume Q and Extrusion cross-section compared to the calculated speed vr and if the speed is too high vt the Cross-section is enlarged and if the speed is too low, the cross-section is reduced will. 5. The method according to claim 1 to 4, characterized in that the Semi-finished product cross-section A as a time-dependent or path-dependent variable by means of a known per se Program input is changed. Ö. Method according to Claims 1 to 4, characterized in that, for the production of hollow plastic bodies with different or uneven wall thicknesses, the calculated speed vr changes as a setpoint as a function of time or distance is entered.