GB1573940A

GB1573940A - Extrusion head incorporating a mixing means

Info

Publication number: GB1573940A
Application number: GB11573/77A
Authority: GB
Original assignee: Umformtechnik Herbert Warnke VEB
Current assignee: Umformtechnik Herbert Warnke VEB
Priority date: 1976-03-30
Filing date: 1977-03-18
Publication date: 1980-08-28
Also published as: SU870171A1; DD126550A1; DE2703922A1

Description

(54) EXTRUSION HEAD INCORPORATING A MIXING MEANS (71) We, VEB KOMBINAT UM FORMTECHNIK "HERBERT WARNKE" ERFURT, of 1, Schwerborner Strasse, 501 Erfurt, German Democratic Republic, a Corporation organised under the laws of the German Democratic Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to an extrusion head for producing tubular or hollow articles, such as pipes or blown plastics films.

Extrusion heads of this kind comprise an outer support ring and a mandrel, the mandrel being held by radial webs. The webs are located in the stream of melt material and divide the latter. This results in differing flow velocities, and so-called web markings appear on the article produced.

A number of solutions are already known wherein the support of the mandrel is effected without webs.

According to German Patent Specification No. 1,215,911, the support means for the mandrel is constituted by a single start or multiple-start worm, the external diameter of which corresponds to the internal diameter of the support ring. The worm is inserted firmly into the support ring and projects beyond it at both ends, the projecting end faces of the worm being constructed with a conical taper, so that passages orientated parallel to the axis of the worm are created in addition to the helical passages. This results in the superimposition of an axial and a radial partial stream during the flow of the melt. The radially and axially guided partial streams have different flow velocities.

The mixing action which occurs aunng the superimposition of the partial streams is not sufficiently intensive to achieve a total elimination of the flow marks and differences in wall thickness.

It is also known (German Patent Specification No. 1,182,420) to construct the mandrel support as an elongate hollow body closed at one end and to provide the circumferential wall of said body with a number of orifices orientated perpendicularly or inclined with reference to a mouthpiece wall. These orifices connect the interior space of the mandrel support to an annular cavity formed between the mouthpiece and the mandrel. The melt transported through the mandrel support is deflected twice, with the result that in passing through the orifices in the circumferential wall of the mandrel support it is subjected to an additional shear heating.

Due to this fact and to the double mass deflection, different flow velocities occur which produce a non-uniform wall thickness on the relevant product.

This arrangement also has the disadvantage that, for example in order to supply supporting air, a pipe leads into the interior space of the mandrel support, which constitutes a flow resistance for the melt.

It is also known (German Patent Specification No. 1,504,253) to construct the mandrel support ring as a stable loadbearing element and to provide it with spiral channels. The melt leaving the extruder passes through a radial bore arranged in the mandrel support ring into the spiral channels and flows into a ring channel. - During the transition of the melt from the radial bore into the spiral channels different flow velocities occur which influence detrimentally the quality of the product. On the other hand, due to the spiral guidance of the melt, flow marks appear which cannot be completely eliminated in the ring channel.

Another arrangement is known (German Published Specification No. 2,007,169) wherein the melt flows centrally into the mandrel and passes through a plurality of serially arranged groups of radial branch channels into the ring channel, while the branch channels of the serially arranged groups are staggered in the peripheral direction. The mandrel is constructed so that it is guided and supported in the extruder head. Due to the arrangement of the branch channels the melt is divided into individual streams which complement one another to the full wall thickness of the hollow profile on entering the rmg channel.

Intensive mixing of the melt, which would lead to better homogeneity, is not obtained.

Another disadvantage lies in the fact that the melt flows through the mandrel centrally, because due to this fact the supply of support air and the supply and discharge of cooling air for an interior cooling device is impossible.

It is an object of the invention to increase the output capacity of an extrusion head and to improve the mechanical and visual properties off the articles to be produced.

Thus the invention aims at providing an extrusion head wherein no interruption of the melt such as to influence the flow velocity occurs and which causes intensive mixing of the melt.

Accordingly, the present invention consists in an extrusion head comprising a cylindrical body having at one end face inlet means for the melt to be extruded and at the other end face outlet means for the melt, said body including first and second ring elements arranged sequentially in the direction of melt flow, a mandrel defining internally said outlet means, a first intermediate ring disposed coaxially between said first and second ring elements and a further intermediate ring disposed coaxially between said mandrel and the adjacent second ring element, each said ring element having a plurality of flow channels for dividing the melt into separate streams, at least two of which channels respectively constitute a mixing zone and which extend from one end face of the ring element to the other end face, the inlets of the channel in each mixing zone being aligned on a circular path and the outlets of said channels being aligned on a radial path, the ring elements being so disposed relative to one another that the mixing zones in one ring element are angularly staggered relative to the mixing zones in the other ring element, each said intermediate ring having passages each of which constitutes a melt deflection zone and which causes the streams combined from the outlets of said channels to be deflected back to the alignment of that of the inlets.

Preferably, four of said channels respectively constitute a mixing zone, the two flow channels whose inlets are located externally within a mixing zone extending so that their outlets are located internally within a mixing zone, and the two flow channels whose inlets are located internally extending so that their outlets are located externally within a mixing zone.

The outlets of the melt deflection zones advantageously form a ring slot. The intermediate rings may comprise two partial rings. Channels for the supply and discharge of air preferably extend axially through the mandrel, the intermediate rings and through the ring elements. The channels may be connected to supply and discharge pipes which are arranged between the mixing zones in the ring elements. The extrusion head may be provided with drive means for rotating the extrusion head.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example one embodiment thereof, and in which: Fig. 1 is a longitudinal section on the line C-C of Fig. 2 through a film blowing extrusion head; Fig. 2 is a cross-section on the line A-A of Fig. 1; Fig. 3 is a cross-section on the line B-B of Fig. 1; and Fig. 4 is an enlarged view of three melt deflection zones.

Figure 1 shows a simplified film blowing extrusion head. The head comprises a bottom section 1, ring elements 2; 4, intermediate rings 3; 5, an outer ring 6 and a mandrel 7. The ring elements 2; 4 and the intermediate rings 3; 5 are attached firmly by screws 8; 9 to the extrusion head bottom section 1 and to the outer ring 6. The mandrel 7 is screwed to the top intermediate ring 5 and to the ring element 4. It is also possible to screw the mandrel 7 directly into the intermediate ring 5.

In Fig. 1 of the drawing, only two ring elements 2; 4 and two intermediate rings 3; 5 are shown. The number of the ring elements 2; 4 and intermediate rings 3; 5 may be increased infinitely depending upon the mixing action desired. It is, however, advisable to restrict the number of the ring elements 2; 4 and intermediate rings 3: 5 to a maximum of four, to avoid having excessive extrusion head heights. The ring elements 2: 4 constitute a predetermined number of mixing zones. In the present embodiment, eight mixing zones 14 are arranged in each ring element 2; 4, while four flow channels 15, 15', 15", 15"', form a mixing zone 14.

The number of the flow channels forming a mixing zone, and the number of the mixing zones, is a function of the desired mixing action. The mixing zones 14 are located on a circular path (Fig. 3) at the inlet side of the ring elements 2; 4. The flow channels 15, 15', 15", 15"' constituting the mixing zones 14 are machined into the ring elements so that the mixing zones 14 occupy a position rotated from a circular alignment, Fig. 3, through an angle of 90" into a radial alignment at the top of the ring elements 2; 4 (Fig. 2). The arrangement of the flow channels 15, 15', 15", 15"' within a mixing zone is as follows: the two flow channels 15, 15"' whose inlets are located externally (Fig. 3) extend so that their outlets are located internally (Fig. 2), and the two flow channels 15', 15" whose inlets are located internally (Fig. 3) extend so that their outlets are located externally (Fig. 2) within a mixing zone.

The intermediate rings 3; 5 immediately adjoining the ring elements 2; 4 have melt deflection zones 16 which return the melt back into a circular path. A melt deflection zone 16 is associated with each mizing zone.

Three melt deflection zones 16 are illustrated on a larger scale in Fig. 4. Each melt deflection zone 16 comprises a slot-shaped base surface 17, the slot width of which is at least as great as the diameter of the flow channels 15. The lateral surfaces 18, 19, 20, 21 are arranged so that the top surfaces 22 of all the melt deflection zones 16 of an intermediate ring 3; 5 produce a ring slot.

The melt deflection zones 16 are machined into the intermediate rings 3; 5.

For technological reasons it is advantageous to fabricate the intermediate rings 3; 5 from two partial rings. In order to increase the mixing action, the ring elements 2; 4 are so arranged relative to one another that the mixing zones in one ring element are angularly staggered relative to the mixing zones in the other ring element.

According to the present embodiment, the mixing zones in the top ring element 4 are staggered by two inlets of the flow channels with reference to the lower ring element 2.

By this means the melt stream of the melt deflection zones 16 is again divided and a boundary layer rearrangement takes place.

As Figures 1 and 2 show, the film blowing extrusion head is provided with an interior air cooling system. The supply and discharge of the cooling air is respectively effected through radial channels 12 and 13 (Fig. 2) machined in the ring elements 2; 4 and through axial channels 10, 11. The rotation of the mixing zones through an angle of 90" within the ring elements 2: 4 permits the arrangement of the respective air supply 12 and discharge pipes 13 between the individual mixing zones 14 (Fig.

2). By virtue of this arrangement, any desired volumes of air can be supplied and discharged without disadvantageous effects upon the flow of the melt.

The path of the melt in the extrusion head of the invention is as follows: The melt, fed centrally to the extrusion head, is divided radially in the bottom section 1 and flows into the flow channels 15 of the ring element 2, the inlets of which are arranged on a circular path. The rotation of the mixing zones 14 through 90" and the relative arrangement of the flow channels within a mixing zone as described above, causes a boundary surface rearrangement.

The separate streams in the channels 15, 15', 15", 15"' forming a mixing zone 14 are subjected to an intensive mixing in the melt deflection zones 16 and are restored back on to a circular path. The melt deflection zones 16 are constructed so that no "dead corners" can be produced. The melt present in the ring slot formed by the outlets of the melt deflection zones 16 flows through the ring element 4 and the intermediate ring 5 in an analogous manner. A mixing effect between the mixing zones 14 among themselves is created by the angularly staggered arrangement of the mixing zones in ring element 4 relative to those in ring 2.

The melt leaving the extrusion head is characterized by very good homogeneity, and no flow or web marks appear on the article produced. Because the flow path lengths for the individual streams are approximately equal, no flow velocity differences occur. This results in a reduction of the thickness fluctuations. The intensive mixing of the melt by boundary layer rearrangement leads to an extremely good homogeneity and thus to an increase in the output capacity. Furthermore, the mechanical and visual properties of the articles produced are improved.

Another advantage of this arrangement lies in the fact that when using an internal air cooling device, adequate volumes of air can be fed centrally through the mandrel without creating any disadvantageous influence upon the melt. It is also immediately possible to make the extrusion head rotate. The rotary drive of known construction which is required for this purpose is not shown in the drawings.

The field of application of the invention is not restricted solely to the embodiment illustrated. Thus, for example, the extrusion head may also be used in extrusion apparatus for the production of substantially rigid tubes or other substantially rigid hollow bodies.

WHAT WE CLAIM IS:- 1. An extrusion head comprising a cylindrical body having at one end face inlet means for the melt to be extruded and at the other end face outlet means for the melt, said body including first and second ring elements arranged sequentially in the direciton of melt flow, a mandrel defining internally said outlet means, a first inter

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

15', 15", 15"' constituting the mixing zones 14 are machined into the ring elements so that the mixing zones 14 occupy a position rotated from a circular alignment, Fig. 3, through an angle of 90" into a radial alignment at the top of the ring elements 2; 4 (Fig. 2). The arrangement of the flow channels 15, 15', 15", 15"' within a mixing zone is as follows: the two flow channels 15, 15"' whose inlets are located externally (Fig. 3) extend so that their outlets are located internally (Fig. 2), and the two flow channels 15', 15" whose inlets are located internally (Fig. 3) extend so that their outlets are located externally (Fig. 2) within a mixing zone.

The intermediate rings 3; 5 immediately adjoining the ring elements 2; 4 have melt deflection zones 16 which return the melt back into a circular path. A melt deflection zone 16 is associated with each mizing zone.

Three melt deflection zones 16 are illustrated on a larger scale in Fig. 4. Each melt deflection zone 16 comprises a slot-shaped base surface 17, the slot width of which is at least as great as the diameter of the flow channels 15. The lateral surfaces 18, 19, 20, 21 are arranged so that the top surfaces 22 of all the melt deflection zones 16 of an intermediate ring 3; 5 produce a ring slot.

The melt deflection zones 16 are machined into the intermediate rings 3; 5.

For technological reasons it is advantageous to fabricate the intermediate rings 3; 5 from two partial rings. In order to increase the mixing action, the ring elements 2; 4 are so arranged relative to one another that the mixing zones in one ring element are angularly staggered relative to the mixing zones in the other ring element.

According to the present embodiment, the mixing zones in the top ring element 4 are staggered by two inlets of the flow channels with reference to the lower ring element 2.

By this means the melt stream of the melt deflection zones 16 is again divided and a boundary layer rearrangement takes place.

As Figures 1 and 2 show, the film blowing extrusion head is provided with an interior air cooling system. The supply and discharge of the cooling air is respectively effected through radial channels 12 and 13 (Fig. 2) machined in the ring elements 2; 4 and through axial channels 10, 11. The rotation of the mixing zones through an angle of 90" within the ring elements 2: 4 permits the arrangement of the respective air supply 12 and discharge pipes 13 between the individual mixing zones 14 (Fig.

2). By virtue of this arrangement, any desired volumes of air can be supplied and discharged without disadvantageous effects upon the flow of the melt.

The path of the melt in the extrusion head of the invention is as follows: The melt, fed centrally to the extrusion head, is divided radially in the bottom section 1 and flows into the flow channels 15 of the ring element 2, the inlets of which are arranged on a circular path. The rotation of the mixing zones 14 through 90" and the relative arrangement of the flow channels within a mixing zone as described above, causes a boundary surface rearrangement.

The separate streams in the channels 15, 15', 15", 15"' forming a mixing zone 14 are subjected to an intensive mixing in the melt deflection zones 16 and are restored back on to a circular path. The melt deflection zones 16 are constructed so that no "dead corners" can be produced. The melt present in the ring slot formed by the outlets of the melt deflection zones 16 flows through the ring element 4 and the intermediate ring 5 in an analogous manner. A mixing effect between the mixing zones 14 among themselves is created by the angularly staggered arrangement of the mixing zones in ring element 4 relative to those in ring 2.

The melt leaving the extrusion head is characterized by very good homogeneity, and no flow or web marks appear on the article produced. Because the flow path lengths for the individual streams are approximately equal, no flow velocity differences occur. This results in a reduction of the thickness fluctuations. The intensive mixing of the melt by boundary layer rearrangement leads to an extremely good homogeneity and thus to an increase in the output capacity. Furthermore, the mechanical and visual properties of the articles produced are improved.

Another advantage of this arrangement lies in the fact that when using an internal air cooling device, adequate volumes of air can be fed centrally through the mandrel without creating any disadvantageous influence upon the melt. It is also immediately possible to make the extrusion head rotate. The rotary drive of known construction which is required for this purpose is not shown in the drawings.

The field of application of the invention is not restricted solely to the embodiment illustrated. Thus, for example, the extrusion head may also be used in extrusion apparatus for the production of substantially rigid tubes or other substantially rigid hollow bodies.

WHAT WE CLAIM IS:- 1. An extrusion head comprising a cylindrical body having at one end face inlet means for the melt to be extruded and at the other end face outlet means for the melt, said body including first and second ring elements arranged sequentially in the direciton of melt flow, a mandrel defining internally said outlet means, a first inter

mediate ring disposed coaxially between said first and second ring elements, and a further intermediate ring disposed coaxially between said mandrel and the adjacent second ring element, each said ring element having a plurality of flow channels for dividing the melt into separate streams, at least two of which channels respectively constitute a mixing zone and which extend from one end face of the ring element to the other end face, the inlets of the channels in each mixing zone being aligned on a circular path and the outlets of said channels being aligned on a radial path, the ring elements being so disposed relative to one another that the mixing zones in one ring element are angularly staggered relative to the mixing zones in the other ring element, each said intermediate ring having passages each of which constitutes a melt deflection zone and which causes the streams combined from the outlets of said channels to be deflected back to the alignment of that of the inlets.
2. An extrusion head as claimed in claim 1, wherein four of said channels respectively constitute a mixing zone, the two flow channels whose inlets are located externally within a mixing zone extending so that their outlets are located internally within a mixing zone, and the two flow channels whose inlets are located internally extending so that their outlets are located externally within a mixing zone.
3. An extrusion head as claimed in claim 1 or 2, wherein the outlets of the melt deflection zones form a ring slot.
4. An extrusion head as claimed in any of the preceding claims, wherein each intermediate ring comprises two partial rings.
5. An extrusion head as claimed in any of the preceding claims, wherein channels for the supply and discharge of air extend aixally through the mandrel, the intermediate rings and through the ring elements and wherein the channels are connected to supply and discharge pipes which are arranged radially between the mixing zones in the ring elements.
6. An extrusion head as claimed in any of the preceding claims, including drive means for rotating said head.
7. An extrusion head, substantially as herein described with reference to and as shown in the accompanying drawings.