MXPA00006954A - Extruder head mandrel spider - Google Patents

Abstract

A spider in an extruder head has a plurality of internal plastic flow passages extending axially through the spider and a spider leg between each flow passage. Each spider leg has upstream and downstream spider leg parts. The upstream part is a flow splitter which splits flow of plastic along the extruder to the spider leg into a plurality of independent plastic streams. The downstream part of the spider leg has a plurality of flow guides staggered at different radial depths in the spider leg with all of the flow guides being directed at one another to guide the bonding of independent plastic streams.

Description

FIELD OF EXTRUSION HEAD MANDREL CENTERING FIELD OF THE INVENTION The present invention relates to a centering spider in an extruder.

BACKGROUND OF THE INVENTION A conventional mandrel of an extruder head used to extrude double-walled plastic tubing is made from a plurality of concentric mandrel tubes which center and stabilize in mutual relation through the use of a device known in the industry as a centering spider. The centering spider provides a spacer that allows the flow of plastic along the tubes beyond the centering spider. The existing centering spider has ends of the centering spider which have an extended diamond shape generally symmetrical to the sides upstream and downstream of the extended center of the end of the centering spider. The front edge of the diamond shape divides the plastic flow along the mandrel to the centering spider, such that the plastic flows as separate streams around the center of the end of the centering spider. The separated streams gradually merge back together after they pass the end downstream of the end of the centering spider. The slower the currents come back together and the less they intermingle with each other, the more the ability of the currents to bond to each other is adversely affected. British Patent 1, 553, 459 deals with the problems of bonding the plastic stream after passing a mandrel centering spider. According to the reference, additional flow separators are provided downstream of the centering spider to produce very thin, more easily bonded plastic streams. No adjustments are made to the centering spider per se.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a centering spider in the extruder head having centering spider ends designed to improve the bonding of the separate plastic streams flowing around the centering spider ends. More particularly, according to the present invention, a centering spider for an extruder head is provided, in which the centering spider has a plurality of internal plastic flow passages extending axially through the centering spider and a tip of the spider centered between each flow passage. Each end of the centering spider has spider parts centered upstream and downstream. The part upstream of the end of the centering spider has a flow separator which separates the flow of plastic at the end of the centering spider into a plurality of independent plastic streams which then flow separately around the end. of the centering spider. The downstream part of the end of the centering spider has a plurality of stepped flow guides at different radial depths at the end of the centering spider. All the flow guides are directed to each other to guide the independent plastic streams to join one another after they pass around the end of the centering spider. The stepped positioning of the flow guides provides a very efficient link of the independent currents to the downstream end of the end of the centering spider.

BRIEF DESCRIPTION OF THE DIAMETERS The foregoing as well as other advantages and features of the present invention will be described in greater detail according to the preferred embodiments of the present invention in which; Figure 1 is a sectional view through an extrusion die mandrel fitted with a centering spider according to a preferred embodiment of the present invention; Figure 2 is a sectional view along lines 2-2 of the centering spider of Figure 1; Fig. 3 is an exterior view that moves downward on one of the ends of the centering spider of the centering spider of Fig. 2.

Figure 4 is a final downstream or rear end view of the centering spider end in Figure 3; Fig. 5 is a perspective view of the end of the centering spider of Fig. 4; Figure 6 is a perspective view showing the general view of plastic streams coming together at the downstream end of the end of the centering spider of Figures 3 to 5; Figure 7 is a final view of a centering spider according to a further preferred embodiment of the invention; Figure 8 is a side edge view of the centering spider of Figure 7; Figures 9 and 1 0 are top and side views respectively of one of the ends of the centering spider of the centering spider of Figure 7.

DETAILED DISCUSSION OF ACU E RDO TO THE PREFERRED MODALITIES OF THE PRESENT I NVENTION Figure 1 shows a mandrel generally indicated at 1 of an extruder head. This mandrel is formed of a plurality of concentric tubes, as shown. These tubes are centered and stabilized in relation m utua by means of a centering spider generally indicated at 3. The extruder head mandrel is used to mold double-walled plastic tubing. One of the walls is produced by a plastic stream flowing along a plastic flow path 4 ending in a hole in the mandrel 5. As seen in Figure 1, this hole is upstream of the centering spider 3. The mandrel further includes a second path 9 for flowing plastic to a second hole 7 which is downstream of the centering spider 3. The plastic emerging from the hole 7 is used to form an inner wall of the pipe . The plastic that flows along the path 9 must pass through the centering spider. Figure 2 shows that the centering spider is provided with a plurality of axially extending plastic flow paths 1 3 to allow passage of the plastic through the centering spider towards the hole 7. The flow passages are They provide between the annular portions of different diameter of the centering spider which are held together by the ends of the centering spider 1 5. In the embodiment shown, the centering spider further includes passages 1 7 which extend radially from the center. hollow center towards the outer edge of the spider centering through the extremities of, the centering spider. These passages can be used for different purposes such as air openings and / or service. All the ends of the centering spider are identical in construction and one of them is shown in Figures 3, 4 and 5 of the drawings. The end of the centering spider comprises a first end portion of the centering spider generally indicated at 1 9 on the upstream side of the extended central portion 16 of the end of the centering spider. Step 1 7 is provided in the portion 1 6. A second end part of the centering spider generally indicated at 27 is provided downstream of the centering spider portion 1 6. The end part of the centering spider 1 9 has a front apex 21 leading to the lateral edge surfaces 23 and 25. The front apex divides the plastic stream A which flows along the flow path 9 of the mandrel towards the centering spider. The plastic is separated by the apex 21 in a pair of independent plastic streams B and B 1, which are then deflected from each other along the lateral edges 23 and 25 of the first or front part of the end of the spider centered around the air passage portion 1 6 of the end of the centering spider. The downstream part 27 of the end of the centering spider is formed by a pair of end portions 31 and 39.

These two end portions as shown, they are staggered, that is, they are decentralized from one another and they are located as shown in Fig. 4 at different radial depths within the centering spider. The end portions 31 and 39 have been configured to cooperate with each other in acting as guides specifically to direct the flow of the first and second streams of plastic B and B 1 into each other after these currents have passed. around the centering spider portion 16. The end portion 31 of the centering spider has a flat, inner, lateral edge surface 33 that is inclined through the longitudinal axis of the centering spider end. The end portion 31 is further provided with an outer edge surface 34, a front surface which is formed by a flat surface region 34 at right angles to the edge surfaces 33 and 36 and furthermore by a channel 37 which borders the flat surface 35. End portion 39 has an inner edge surface 41. This lateral edge surface of the second end portion of the centering spider is inclined through the longitudinal axis of the end of the centering spider in the opposite direction to the inclination of the side edge surface 33 in the first limb portion of the centering spider 31. The end portion of the centering spider 39 further includes an outer edge surface 42 and its own front surface at generally right angles to its side edge surfaces 41 and 42. This front surface is defined by a flat surface region 43. and a channel 45, both of which radially are located internally of the end portion 39, the front surface of which radially is located externally of the side edge surface 33 of the end portion 31. As described above, the plastic impacting the front end of the end of the centering spider is divided into two plastic streams B and B 1 which flow along the edge surfaces 23 and 25 at the front of the center. the tip of the centering spider. The first plastic stream B is fed externally around the centering spider portion 16 which contains the passage 1 7. Part of this stream is then redirected as the current C through the surface 35 of the extremity 31. . The rest of the stream B flows as the stream D along the outer edge surface 34 of the end 31, where it is collected in the channel 37, which runs parallel to the edge surface 41. Therefore, the channel 37 again directs the current D to flow with the current C. The second plastic stream B 1 also flows around the spider portion of centering 1 6, where it is divided into the currents C 1 and D1. The stream C 1 flows along the lateral edge 33 of the end portion 31 below the stream C and is directed in the stream D flowing through the channel 37. The stream D 1 flows along the stream. lateral edge 42 of the end portion 39 where it is collected and redirected through channel 45 in stream C. As a result of all of the above, there is a substantial alteration or turbulence or of the original current A in a host of smaller streams, all of which are redirected to one another at the downstream end of the tip of the centering spider. This greatly improves the bonding of all currents to form a common current required to form the inner wall of the pipe. Figure 6 shows how the plastic generally flows at the downstream end of the end of the centering spider. The two streams B and B 1 are combined as streams E and E 1, respectively. As will be seen in Figure 6, these two currents are joined in a coating junction of the two currents, which provides a much better bond for example, a standard butt joint as found with conventional centering spider tips. Figures 7 to 10 of the drawings show a further preferred embodiment of the centering spider generally indicated at 51. This centering spider is used again in an extruder and is particularly suitable for use in an extrusion head mandrel of a pipe, forming the apparatus used to make double-walled pipes. The outer wall of the pipe leaves the mandrel upstream of the centering spider and the inner wall of the pipe is formed by plastic flowing through axially extending flow passages 52 of a centering spider 51. In this embodiment, the entire centering spider including its ends of the centering spider 57 has a novel construction. The centering spider itself is made of two different anuses and specifically separated the front anchor 53 and outer ring 55, with the plastic flow passages being provided between the two rings. The ends of the centering spider 57 act as both spacers and connectors for the two rings 53 and 55. As opposed to a solid one piece construction, working with a multi-part spider as shown in Figure 7, it allows the inner and outer rings to be terminated separately from each other. It also allows the finish to be separated from the ends of the centering spider. Therefore, all the outer surfaces of the three parts are easily accessible for finishing purposes, substantially improving the plastic flow through the centering spider. FIGS. 9 and 10 show one of the ends of the centering spider 57 of the centering spider 51. It should be noted that all the ends of the remaining centering spider have the same construction as that shown in Figures 9 and 1 0. The end of the centering spider 57 again has a downstream end with guides of radially staggered flow, as described above with respect to the end of the centering spider 1 5. In this particular case, the end of the centering spider 57: has an upstream end 59 and a downstream end generally indicated in FIG. 62. The downstream end is formed by separate end portions 63 and 69. The end of the centering spider 57 has an extended body portion 75 with a direct passage 79 which again provides access through the centering spider. for different functions such as air and services. In this particular case, the opening 79 is skirted on opposite sides by an additional pair of smaller openings 81. These openings are used to receive positioning pins 83 shown in Figure 8 of the drawings to hold the two rings 53 and 55 together. Figure 8 also shows a sleeve 85 fitted through passage 75 at the end of the centering spider. This sleeve is substantially higher than and projected both below and above the tip of the centering spider. In fact, the sleeve 85 is sufficiently long that it projects through the rings of the centering spider both inside and outside not only to provide a passage 87 from the inside to the outside of the end of the centering spider but that to further stabilize the safety of the two rings in relation to each other. The mechanical fasteners described above, that is to say, the positioning pins 83 and the sleeve 55 are accessible to free the ends of the centering spider from the centering spider rings. This allows the dismantling of the centering spider which is very beneficial if one of the parts of the centering spider is damaged or otherwise requires service. Only the affected part needs to be replaced instead of requiring a new full centering spider, as is the case with a conventional one-piece centering spider. The tip of the centering spider 57 has a number of additional features to improve the flow of plastic around the end of the centering spider. As will be clearly seen in Figures 9 and 10, the front projection of the front separator, the rear tips of the two end portions of the centering spider 63 and 69, as well as the channels 65 and 71 at the running end below the tip of the centering spider have round, smooth configurations. This substantially eliminates any plastic immobilization region along the end of the centering spider. In addition, the projection ridges on the end of the centering spider are provided at the edges, upper and lower, on the front projection 59 on the end of the centering spider and these flanges respectively extend as the projecting flange 67 in the center. the tip portion of the centering spider 63 and the projecting flange 79 in the centering spider portion 69. Again, there is a curved transition of the projecting ridges to the main body portions of the end of the centering spider. According to the above, these projecting ridges provide smooth guides for directing the flow of plastic over the spacer and guides of the end of the centering spider.

Claims (9)

CLAIMING IS

1 . A centering spider (3) for an extruder head, said centering spider having a plurality of internal plastic flow passages (1 3) extending axially through said centering spider and one end of the centering spider (1 5) between each flow passage, each end of the centering spider having a part of the spider centered downstream (27) and a part upstream (1 9), at opposite ends of said spider end of centering, said upstream part presenting a flow separator which separates the plastic flow around said end of the centering spider in a plurality of independent plastic streams around said end of the centering spider, said centering spider in that said part downstream of the end of the centering spider has a plurality of flow channels (31, 39) staggered at different depths of radius at said extremity of the centering spider, all said flow lines being directed to guide the independent plastic streams so as to merge with one another after flowing around the end of the centering spider.

2. A centering spider according to claim 1, characterized in that said plurality of flow guides comprises flow guides, first and second, (31, 39), which produce independent plastic currents, first and second, having said gu flow paths edge surfaces (33, 34, 41, 42) and front surfaces (35, 43), the edge surfaces of both guides inclining through the axis of the tip of the centering spider by which the surface The edge (33) of the first guide (31) directs the first plastic stream through the front surface (43) of the second guide (39) and the edge surface (41) of the second guide (39). 39) directs the second plastic stream through the front surface (35) of the first guide (31) to produce a coating junction of the independent currents, first and secondly, with each other after passing around the tip of the centering spider.

3. A centering spider according to claim 2, characterized in that the front surfaces (35, 43) of the guides (31, 39) comprise flat surface regions (35, 43) bordered by channels (37, 45) that They are embedded in the front surfaces.

4. A centering spider according to claim 3, characterized in that the channel (37) on the flat surface (35) of the first guide (31) is parallel to the edge surface (41) of the second guide. (39) and the channel (45) on the front surface (43) of the second guide (39) is parallel to the edge surface (33) of the first guide (31):

5. A centering spider according to claim 1, characterized by a multi-piece construction comprising an inner centering spider ring (53) and an outer centering spider ring (55) formed separately and held apart from each other by said ends of the spider of centered (57).

6. A centering spider according to claim 5, characterized in that the mechanical fastening means (83) releasably securing said ends of the centering spider to said inner and outer centering spider rings.

7. A centering spider according to claim 1, characterized in that each end of the centering spider (3) is bordered on opposite sides of the same by a projecting flange (67, 73). A centering spider according to claim 7, characterized in that each protruding flange (67, 73) has a curved inner surface. 9. A centering spider for an extrusion die, said centering spider being characterized by hollow rings, inner and outer, (53, 55) made separately and secured to each other by centering spider ends (57) attached to each other. releasable way to said rings, interior and exterior. 1 0. A centering spider according to claim 9, characterized in that the mechanical fasteners (83) secure the rings, inner and outer, with the ends of the centering spider. eleven . A centering spider according to claim 10, characterized in that said mechanical fasteners (83) comprise positioning pins secured within sleeves (85) having open ends for sliding the positioning pins in and out of the sleeves. 2. A centering spider according to claim 9, characterized by passages (17) that provide service openings through said ends of the centering spider (3). RESU M IN A centering spider in an extruder head has a plurality of internal plastic flow passages extending axially through the centering spider and one end of the centering spider between each flow passage. Each end of the centering spider has parts of the end of the spider that are centered upstream and downstream. The upstream part is a flow separator that separates the flow of plastic along the extruder to the end of the centering spider in a plurality of independent plastic streams. The downstream part of the end of the centering spider has a plurality of stepped flow guides at different radial depths at the end of the centering spider with all the flow guides directing one another to guide the link of the centers. independent plastic streams.