DE202010007275U1 - extrusion head - Google Patents

Abstract

Device for cleaning extrusion heads (10) during the extrusion of thermoplastic materials which are ejected from an extrusion nozzle (14), characterized in that mechanical engagement means (22) are provided directly below the extrusion nozzle (14) and are equipped with a corresponding drive ( 24) are equipped in such a way that the engagement means (22) can be brought into active contact with the extruded tubular preform (12).

Description

The present invention relates to an apparatus for cleaning extrusion heads in the extrusion of thermoplastics ejected (extruded) from an extrusion die.

problem:

In the processing of thermoplastics such as polyolefins - mainly in medium and high molecular weight polyethylene types such. As HDPE, for example, in extrusion blow molding, especially in continuous extrusion with continuous hose outlet, but also in discontinuous hose ejection (battery heads), the following adverse effect occurs:
When ejecting molten plastic, it is under high pressure inside the extrusion device (eg extrusion head). After exiting the extrusion die, the plastic relaxes to atmospheric pressure and swells up. During this discharge process, gel-like products (lubricants, additives) are separated from the hot plastic strand over time, especially during continuous extrusion, and deposit as disruptive material caking in the vicinity of the nozzle orifice, mainly on the inside of the core, but also on the outside of the nozzle , In the case of annular ejection nozzles, there is the problem that these deposits can not be seen either. The deposits (precipitates) originate from low-molecular-weight constituents of the polymer melt (eg short polymer chains, additives, wax-like constituents) which settle at the outlet edges of the nozzle channel on exit of the melt due to the sudden drop in pressure and the decrease in wall shear stresses.

The gel-like products are subject to constant high temperature action and harden and coke in a relatively short time. This embrittling ever-increasing excretions and break or crumble uncontrollably from. Such crumbs or chunks, which can be several centimeters long, fall into the extruded tubing and result in defective finished products (eg leaking bottom welds may occur during barrel manufacture when such porous coking particles enter the weld area.) For example, the particles may only be loose on the inner wall of the blown finished product (eg., A bung barrel) adhere / stick and break off when filling the hollow body with the actual contents and fall off and so get into this product and contaminate it.

The deposits (gel-like products, caking) initially have a low-viscosity consistency. Due to the high temperatures of the nozzle and the core, and under the influence of oxygen from the ambient air, the deposits oxidize over time and the viscosity increases until the first solid areas are formed by coking. These outer deposits on the outlet nozzle grow uncontrollably. In particular, in the blow molding technique, in which a tubular preform is ejected from an annular nozzle, the inner core region of the outlet nozzle can not be viewed in particular in continuous melt outlet. The deposits are from time to time, if they have grown too large and friable, entrained by the inside of the passing molten tube and stick to the inner surface of the product to be manufactured, eg. B. a plastic bung barrel. This leads disadvantageously after filling the barrel to contamination of the filling. In a later detachment from the inner wall of a barrel body, this can lead to blockages or damage of feed pumps and significant damage to Weiterverarbeitungsprozessen the contents. If such coking particles are in the region of the weld of a blow molded container, this leads to a very adverse and undue weakening of the container. Furthermore, such deposits can lead to the formation of longitudinal stripes and thus to optical and / or technical impairment of the extruded and then blow-molded product. This phenomenon is also referred to as "the built-up" in which the deposits of thermally damaged polymers at the nozzle outlet lead to undesirable surface irregularities. For commercially available plastics, it is usually individual additives (such as stabilizers or flow aids) for influencing wall sliding effects which lead to the adhering precipitates or cause them.

State of the art:

This problem is z. B. also known in the field of blown film extrusion. Here deposits are stripped by means of mechanical cleaning devices such as scraper or Abziehklingen and driven into the waste area, which blow in the film each time when changing the winder spindles. In this conventional cleaning of extrusion tools, however, the extrusion process must be stopped so that the usually manual mechanical cleaning of the nozzle core can be made directly below the outlet edge of the melt. The halting of the extrusion process on the one hand leads to a loss of production due to the standstill; on the other hand, the plant must afterwards in the Usually approached by an experienced process engineer and led into a stable operating condition.

Object of the invention:

It is an object of the present invention to overcome the drawbacks of the prior art and a method and apparatus for cleaning the exit area of extrusion dies, particularly core ring dies, during continuous extrusion operation without interrupting the production process. Here, the material deposition should be specifically removed and discharged from the production process.

This object is procedurally achieved with the features of claim 1 according to the invention such that the tubular preform is briefly deflected and upsetting, wherein the outside adhering in the vicinity of the exit slit of the extrusion die deposits are wiped from the tubular preform and removed. The clou of the invention is that the tubular preform itself is used during its deflection as a cleaning element. In this simple manner can caking, which have formed in the course of the extrusion process and have set in the vicinity of the Austrittsdüe removed during operation of the continuous extrusion without interrupting the production process and removed. In an embodiment of the invention, it is provided that the deflection of the tubular preform for cleaning the extrusion die is carried out at predeterminable time intervals. Advantageously, namely, the deflection of the tubular preform for cleaning the extrusion die is performed just when the hose piece is ejected from the extrusion die, which is subsequently separated as a piece of sludge from the finished blown hollow body as waste. In order to be able to remove the material deposit in a targeted manner and to be able to discharge it from the production process, after the tubular preform has been deflected, those pieces of hose to which the cleaned deposits are stuck are sorted out of the further production process.

In a preferred embodiment of the invention, the deflection of the tubular preform takes place by means of part-circular pressure elements which enclose the preform directly below the outlet nozzle from the outside by almost 360 ° and deflect inwards.

The inventive device for cleaning extrusion heads in the extrusion of thermoplastics which are ejected from an extrusion die, is characterized to solve the underlying problem by the fact that directly below the extrusion nozzle mechanical engagement means are provided which are equipped with a corresponding drive such in that the engagement means can be brought into operative contact with the extruded tubular preform. The mechanical engagement means may comprise two or more circular segment elements which are radially actuated by actuators d. H. can be moved and then form a largely closed circular ring in the retracted position. The actuators can be actuated in various ways and this with a z. B. electro-pneumatic, electro-hydraulic or electric drive.

Functionality:

The closed circle segment elements forming a circular ring compress the exiting melt tube radially for an adjustable time. The compressed melt tube flows inward over the edge of the core for the set period of time, thus deliberately tearing the material deposited in this area. The time of retraction of the circle segments and the holding time in the retracted state are freely selectable and adjustable. The cleaning times are preferably adjusted so that the annular deposits, which are completely removed on the whole, located in the slug area of the subsequently produced container. The emerging melt tube itself is used as a cleaning medium. There is no mechanical contact between the engagement means, the actuators or the circle segments and the nozzle tool. This results in a gentle cleaning of the inner nozzle core without direct intervention of scratching, scraping or cutting mechanical aids. Due to the special type of nozzle cleaning, damage to the precisely manufactured flow channel geometries in the nozzle area is excluded.

The circular segment elements move without contact underneath the extrusion nozzle During nozzle cleaning, the short-term compression of the hose against the nozzle core results in swelling of the hose in the circumferential direction (outwards) between the nozzle outlet edge and retracted circular segments due to the continuous melt outlet. The swelling hose, which also swells outwards, thereby also tears the annular deposits adhering to the outside nozzle outlet edge.

In terms of process technology, the cleaning cycle (eg every 2 hours, every x cycles) can be freely adjusted with cleaning repetitions (1 × or several times in succession), depending on the tendency of the processing raw material to deposit and the growth of the caking. Contaminated hose sections or contaminated waste can be separated and discharged in a very targeted manner. This can prevent contamination of the raw material cycle (regranulate) with material containing coking deposits. If slug areas are too short for complete cleaning (eg if the hose outlet speed is too high), z. B. also the following entire article be discharged and disposed of (only one reject product).

The method according to the invention and the device designed for this purpose can in principle be retrofitted in principle for all extrusion blow molding machines with continuous melt outlet. In principle, the method and the corresponding device can of course also be retrofitted to battery-operated machines with discontinuous outflow of melt.

The applicability of the method and the particular device is versatile and can be combined with a variety of extrusion head designs, such. B. with fixed nozzle / core design (without axial Wanddickeneinstellung), with conventional nozzle / core design (axial wall thickness control only) or with fully adjustable wall thickness of the extruded tubular preform with nozzle and / or core with static and / or dynamically adjustable Diameter geometries (axial and radial wall thickness adjustment).

The invention will be explained and described in more detail with reference to embodiments schematically illustrated in the drawings. Show it

1 in cross-section an extrusion head according to the invention with detail drawing in the operative position "open",

2 in cross-section an extrusion head according to the invention with detailed drawing in the operative position "closed",

3 in plan view from below an extrusion head according to the invention with two circular segment engagement means in the operative position "open",

4 in top view from below an extrusion head according to the invention with two circular segment engagement means in the operative position "closed",

5 in plan view from below an extrusion head according to the invention with two circular segment engagement means in the operative position "open",

6 in top view from below an extrusion head according to the invention with two circular segment engagement means in the operative position "closed",

7 in side view a blow-molded bung barrel with two pieces of slugs

In 1 is with the reference number 10 an inventive extrusion head referred to, in which a tubular preform 12 made of heated thermoplastic material from an outlet nozzle 14 is ejected. The outlet nozzle 14 is on the outside of a housing ring 16 and inside by core 18 Are defined. The core 18 is axially adjustable to the wall thickness of the ejected preform 12 of molten plastic (eg HD-PE), to be able to change or adjust during the extrusion process, depending on the requirement of the hollow body to be blown. In the vicinity of the outlet nozzle 14 Form in the course of the extrusion process on the outer edge of the inside core 18 and also on the inner edge of the outer housing-side outer ring 16 annular caking 20 from which, if they have grown too large, from time to time fall off in an uncontrolled manner and then disadvantageously render the respective finished product useless. To get this adverse effect under control and the process of eliminating these caking 20 to run controlled, are in the extrusion head according to the invention 10 two or more engaging means 22 provided, each by an actuator 23 are operable. The engagement means are formed as a pliers-like, strip-shaped pressure tool, which is arranged directly below the outlet nozzle of an extrusion head and equipped with a displacement drive, so that it can be pivoted into the normal course of the ejected plastic tube. The pressure tool for an annular extrusion die consists of at least two or more pincer-like, part-circular pressure elements which enclose the ejected plastic tube from the outside and can move substantially transversely to the ejection direction of the plastic tube. The pressure elements or engagement means 22 are with actuator 23 just below the outlet nozzle 14 on the housing side on the outer ring 16 the outlet nozzle or directly on the housing of the extrusion head 10 attached. In the enlarged circle is the at the outer edge of the inside core 18 adherent annular caking 20 clearly. The intervention means 22 stand here in position "on" and the tubular preform 12 flows close to the annular caking 20 past. In comparison, in 2 the intervention means 22 each via their actuator 24 in the "on" position and in operative engagement with the ejected tubular preform 12 brought. It can be seen that the tubular preform 12 is briefly deflected inwards and at the outer edge of the inside core 18 adherent annular caking 20 wipes off so that these now inside the tubular preform 12 adheres (sticks) and is transported away. At the same time, the tubular preform 12 above the engaging means 22 but also briefly upset and dammed to the outside, so that there - at the inner edge of the outer housing-side outer ring 16 - Also adhering annular caking pressed, wiped and the outside of the tubular preform 12 glued and transported away. Here, therefore, the tubular preform 12 itself used as a cleaning element during its deflection.

In 3 is the extrusion head according to the invention 10 shown in plan view from below, wherein the two engagement means 22 with their respective actuator 24 can be seen in the "on" position. The two intervention means 22 consist in this embodiment of two movably suspended 90 ° circle segment elements 26 that still from the tubular preform 12 are clearly spaced. In contrast, in 4 the intervention means 22 again by means of an actuator 24 in the "closed" position and the four circle segment elements 26 in operative engagement with the ejected tubular preform 12 brought. The tubular preform 12 is thereby deflected inwards and on the annular caking 20 pressed so that these now inside the tubular preform 12 adhere or are glued and subsequently transported away.

Another embodiment of an extrusion head according to the invention 10 is - also in plan view from below - in 5 illustrated, wherein the two engagement means 22 with their respective actuators 24 in position "on" are disabled. Here, each of the four 90 ° circle segment elements 26 with its own actuator 24 fitted. In 6 are the means of intervention 22 moved back to the "closed" position and the four circle segment elements 26 are in operative engagement with the preform 12 , while the tubular Vorfomling is completely enveloped from the outside, with the four 90 ° circular segment elements 26 in the retracted position form a largely closed circular ring. According to the invention, the ejected plastic tube is used as a "cleaning agent". During the ejection process, the hose is briefly pressed and displaced laterally by means of a corresponding engagement (by means of) device, so that the caking is "wiped off" and "glued" to the plastic hose. The actuators 24 can be provided with an electropneumatic, electro-hydraulic or electric drive.

In 7 is an example of a blow-molded product a plastic bung barrel 28 shown, which has just been removed from the blow mold, and at the top and bottom still squeezed the waste pieces, the so-called Butzenstücke 30 hang. According to the procedure of the invention, the caking 20 from the outlet nozzle has been driven exactly in these pieces of waste, so that usually no product failure caused by these coking coking residues

With this invention, the technical teaching is taught how process and device can be automatically cleaned in a relatively simple and cost-effective manner with low design cost of the exit area of extrusion dies during ongoing operation of the continuous extrusion without interrupting the production process. In the process, the product-contaminating material deposits are deliberately removed and removed from the production process.

LIST OF REFERENCE NUMBERS

10

extrusion head

12

tubular preform

14

exhaust nozzle

16

housing ring 16

18

core

20

caking

22

engagement means

24

actuator

26

Circular segment elements

28

Plastic tight-head drum

30

Butzenstücke

Claims (9)

Device for cleaning extrusion heads ( 10 ) in the extrusion of thermoplastics produced from an extrusion die ( 14 ) are ejected, characterized in that directly below the extrusion die ( 14 ) mechanical means of intervention ( 22 ) provided with a corresponding drive ( 24 ) are equipped such that the intervention means ( 22 ) in operative contact with the extruded tubular preform ( 12 ) are brought. Device according to claim 1, characterized in that the mechanical engagement means ( 22 ) two or more circle segment elements ( 26 ) by actuators ( 24 ) are formed movable in the radial direction. Apparatus according to claim 1 or 2, characterized in that the circular segment elements ( 26 ) the extruded preform ( 12 ) enclose from the outside by almost 360 ° and form a largely closed circular ring in the retracted position. Device according to claim 2 or 3, characterized in that the actuators ( 24 ) with a. electro-pneumatic, electro-hydraulic or electric drive are provided. Use of the tubular preform ( 12 ) as a cleaning element for cleaning the extrusion head ( 10 ), wherein the tubular preform ( 12 ) by means of the mechanical intervention means ( 22 ) is briefly deflected and puffed, wherein the outside in the vicinity of the exit slit of the extrusion die ( 14 ) adhering deposits from the tubular preform ( 12 ) are wiped off and transported away. Use of the tubular preform ( 12 ) as a cleaning element for cleaning the extrusion head ( 10 ) according to claim 5, wherein the deflection of the tubular preform ( 12 ) is performed at predetermined intervals. Use of the tubular preform ( 12 ) as a cleaning element for cleaning the extrusion head ( 10 ) according to claim 5 or 6, wherein the deflection of the tubular preform ( 12 ) is performed just when the hose piece from the extrusion die ( 14 ), which is subsequently separated as a piece of sludge from the finished blown hollow body as a waste piece. Use of the tubular preform ( 12 ) as a cleaning element for cleaning the extrusion head ( 10 ) according to claim 5, 6 or 7, wherein after deflecting the tubular preform ( 12 ) that piece of tubing to which the cleaned deposits are stuck is sorted out of the further production process. Use of the tubular preform ( 12 ) as a cleaning element for cleaning the extrusion head ( 10 ) according to claim 5, 6, 7 or 8, wherein the deflection of the tubular preform ( 12 ) is carried out by means of part-circular pressure elements, the preform ( 12 ) directly below the outlet nozzle ( 14 ) enclose from the outside by almost 360 ° and deflect inwards.

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