Extruder for rubber materials

The present invention relates to an extruder for mixing, homogenizing and extruding rubber materials, such as natural rubber and synthetic rubber.

A conventional extruder of this type, as shown in Japanese patent publication 56-53500 published on December 19, 1981 and claiming priority from West German application P 22 35 784.2 filed on July 21, 1972, includes a casing enclosing a cylindrical bore that contains a rotatable screw which forms a helical passage for rubber materials along the casing. A number of mixing pins extend radially into the casing, so that adjustable lengths of the pins project into the helical passage. Some of the pins extend through a passage in the casing provided for a heating or cooling medium. The thread of the screw is formed with notches for the pins to pass through when the screw rotates.

In a conventional extruder of the foregoing type, it is troublesome to adjust the projecting lengths of the pins, and the arrangement limits the volume of the passage for the cooling medium. In addition, the cooling medium may leak through seals around the pins.

It is a general object of the present invention to provide an extruder for rubber materials, which enables mixing means such as pins to be easily changed to obtain the desired projecting lengths and intervals (pitch) of the pins according to the type of material being processed, and for easy inspection and repair.

It is another object of the invention to provide such an extruder which has a sufficient flow volume for a heating/cooling medium, without risk of leakage of the medium into the material being processed.

It is a further object of the invention to provide such an extruder containing a helical passage, wherein undesirable resistance to the flow of the material is reduced, thereby improving the mixing effect.

In EP-A-144192 there is disclosed a machine in which the casing or barrel is divided up into a plurality of short flanged axial segments. Then, instead of the mixing pins or fins being carried by the barrel segments, they are formed integrally on plates that are clamped between the end flanges of consecutive barrel segments, which each pin plate itself split diametrically so that, if the flange bolts are slackened and those connecting consecutive barrel segments are withdrawn, the two halves of a plate can be slid out radially and replaced with the two halves of a different plate. This construction alleviates the problem of replacing groups of pins but only by, in effect, chopping the barrel up into short lengths. Thus, the method of assembling the barrel becomes quite an exacting task, each segment of the barrel needing to be threaded along the screw in turn from one end, in order to do which the screw has to be demounted from its bearings, after which the barrel segments have to be maintained as far as possible in true alignment while the flange bolts for joining the segments together are all inserted and tightened.

According to the present invention, there is provided an extruder comprising a casing having a cylindrical bore formed therein and passages outside of said bore for a heating or cooling medium, a screw extending axially in said bore and adapted to be rotated, said screw having a thread or threads which form a helical passage or passages along the bore for material to be processed, an axially extending cylindrical sleeve mounted in said bore around said screw, and a plurality of projections extending radially inward into said helical passage or passages, said thread or threads having notches for the projections to pass through when the screw rotates, characterised in that said sleeve bears said inward projections, said casing and said sleeve are each split at respective axial planes into at least two part-circular parts, and clamp means are provided applied to said casing for releasably clamping said parts together in the assembled condition.

In this way, an extruder is provided that affords easy changing of the mixing pins or fins, without resorting to dividing up the casing axially into segments.

Preferred embodiments of the invention are now described, by way of example, with reference to the accompanying drawings, wherein: <ul id="ul0001" list-style="none"><li>Figure 1 is a plan view in axial cross section of an extruder according to a first embodiment of the invention;</li><li>Figure 2 is a cross-sectional view taken along line 2-2 of Figure 1;</li><li>Figure 3 is a cross-sectional view taken along line 3-3 of Figure 1;</li><li>Figures 4a and 4b are end and side views, respectively, of one form of mixing pin for the machine of Figures 1 and 2;</li><li>Figures 5a and 5b are end and side views, respectively, of another form of mixing pin;</li><li>Figures 6a to 6d are diagrams corresponding to Figure 2, but showing how the parts of the extruder are disassembled;</li><li>Figure 7 is a cross-sectional view illustrating a modification in which the sleeve surrounding the screw bears integral mixing fins; and</li><li>Figure 8 is a view taken along line 8-8 of Figure 7.</li></ul>

With reference to Figure 1, an extruder includes an inlet section 11 into which rubber materials are fed, a main or centre section 13 in which the materials are mixed together, and a head section 15 from which the mixture is extruded in a predetermined cross-sectional shape.

The sections 11, 13 and 15 include tubular casings 17, 19 and 21, respectively, which are secured together in end-to-end relationship. The three casings have aligned cylindrical bores 18, 20 and 22 formed through them, and a rotatable screw 23 extends through the bores. The screw 23 is journalled at both ends in bearings on the casings 17 and 21, and it is coupled at one end thereof to a drive (not shown).

The inlet casing 17 has its bore 18 closed at its rear end by a closure 24, and an inlet port 25 is formed in one side. The port 25 is provided with a feeder 27 and a hopper (not shown) may be provided on the feeder. The head casing 21 has an open front end 28.

As shown in Figures 2-3, the centre casing 19 includes an outer axially extending wall 29 which is oval in radial cross section, and an inner cylindrical wall 31. The casing 19 is circumferentially divided into upper and lower halves.

Each casing half is formed with a longitudinal passage 33 between the outer and inner walls 29 and 31 for the flow of a heating/cooling medium for maintaining the materials being processed at a desired temperature.

Each casing half also has a pair of longitudinal flanges 35 projecting outwardly from the outer wall 29 on both side edges thereof. Provided adjacent the flanges 35 are a pair of longitudinally extending clamps 37, each formed with a longitudinal groove 39 therein for engagement with the flanges 35 on one side of the casing 19 when closed. The clamps 37 engage tapered outer surfaces 36 of the flanges 35 and tightly secure the flanges (and the casing halves) together. The flanges, as shown in Figure 2, are welded to the outer and inner walls.

The inner casing walls 31 surround a tubular sleeve 41 which is circumferentially divided into two half circle parts, and the two parts are axially divided to form a plurality of axially aligned pairs of arcuate segments 43.

The screw 23 has a pair of helical ribs or double male threads 45, which form helical passages 47 for the rubber materials inside the sleeve 41. The outer surfaces of the threads are closely adjacent the inner surfaces of the sleeve 41. The threads 45 have a pitch which reduces gradually from the rear end 24 of the inlet section 11 to the front end of the main section 13. The pitch reduction produces a gradual increase in pressure on the materials to heat and mix them. The threads 45 of a section of the screw within the centre casing 19 are formed with axially spaced pairs of circumferentially aligned notches 49 therein.

As shown in Figures 1-2, a plurality of bolts 51 extend loosely through the clamps 37 and are threaded into the lower casing flanges 35. Threaded on the bolts 51 are nuts 52 for engagement with the clamps 37 to clamp the halves of the casing 19 and the segments 43.

Threaded holes are formed through the clamps 37 and a plurality of releasing bolts 53 are threaded into the holes and engage the lower flanges 35. By screwing the bolts 53 in, the clamps are pushed away and released. The bolts 51 and 53 are provided alternately along the length of the clamps 37, but only some of the bolts are shown in Figure 1.

The arcuate segments 43 of the sleeve 41 and the inner wall 31 of the upper casing half are formed with corresponding axial grooves 55 for engagement with an axially extending key 57 (Figures 2 and 6a) to normally fix them together and prevent relative rotation. The grooves 55 are positioned so as to angularly displace the diametrical border edges 59 of the segments 43 away from the side flanges 35 of the casing, as shown in Figure 2.

As shown in Figure 3, a plurality of tightening bolts 61 are threaded through one of the lower flanges 35, and extend through the casing 19 in parallel with the bolts 51 and 53.

Each bolt 61 is provided for engagement with one arcuate segment 43 of each pair at an angular location away from the border edges 59. The bolts 61 can be passed through holes 63 formed in the appropriate clamp 37, in order to more positively clamp the segments 43 in addition to the clamping by the clamps 37.

As shown in Figure 2, each segment 43, except for those at both ends, is formed with a number of circumferentially aligned radial holes 65. Each hole 65 has an inner bore portion and a radially outer counterbore which is increased in diameter relative to the inner bore. The holes 65 are aligned with the notches 49 of the threads of the screw. Through each hole 65 extends a pin 67. As shown in Figures 4a, 4b, 5a and 5b, each pin 67 has a double diameter head 69 for rotatable engagement within a hole 65, and a smaller diameter leg 71 which projects radially inwardly from the associated segment 43 into one helical passage 47. The leg 71 is axially located to pass through the thread notches 49 when the screw 23 rotates. This construction enables a larger number of pins 67 to be provided for more uniform mixing of the materials. As shown in Figures 4a and 5a, the legs 71 preferably have a tapered or streamlined shape in cross-section.

In operation, with reference to Figure 1, the screw 23 is rotated by a drive. Rubber materials are fed through the intake port 25 into the inlet section 11, and thrust axially forwardly (toward the left) by the screw 23 to the main section 13. In addition, because the pitch of the threads 45 decreases in the forward direction, the materials are thrust helically forwardly along the passage 47 with increasing pressure, and consequently kneaded and mixed. The materials then move in contact with the stationary (but rotatable) pins 67, which promote the mixing.

The materials move at various angles depending on the pitches of the threads 45 and the firmness of the materials. As previously mentioned and as shown in Figures 4a and 5a, the pins 71 are preferably streamlined or tapered, and the pins are rotatable in their holes. The flow of the processed material causes the rotatable pins 67 to rotate to the positions where they have the minimum resistance to flow. This also reduces the loads on the pins.

The mixed material is extruded from the open end 28 of the head section 15 in a predetermined cross-sectional shape which is determined by the shape of the opening 28 or a die (not shown).

The pins 67 may have a shape and/or length depending upon and suited to a specific type of material. The pins may be replaced depending on the nature of the material, or the sleeve 41 can be disassembled for inspection and repair, in the following manner:    The tightening bolts 61 (Figure 3) and the nuts 52 (Figures 1-2) are released.

As shown in Figure 6a, the releasing bolts 53 are threaded into the clamps 37 to push the clamps from the casing flanges 35.

As shown in Figure 6b, the upper half of the casing 19 and the key 57 are separated from the lower half and removed.

As shown in Figure 6c, one or more pairs of arcuate segments 43 are rotated by the necessary angle to the position where the upper segment is accessible, and the upper segment is removed.

As shown in Figure 6d, the lower segment 43 is then rotated upwardly and removed.

New pins and segments can then be assembled in the reverse order.

The second embodiment shown in Figures 7-8 differs from the first embodiment in that it includes arcuate segments 143 with a number of fins 167, instead of the pins. The fins 167 are formed integrally with and extend from the inner surfaces of the segments 143, inwardly toward the screw (not shown), and the fins are at an angle with respect to the axis of the segments 143 and the screw. The shape and direction of the fins 167 are predetermined depending on the pitch of the screw threads and the kind of materials being processed.

In either of the embodiments, the sleeve 41 may otherwise include a number of undivided rings (not shown) without pins 67 or fins 167, which are interposed between other axially shortened arcuate segments (also not shown) which are provided with pins or fins. Also, the sleeve 41 may be circumferentially divided into three or more arcuate segments instead of two as illustrated.

The major advantages of the extruder according to this invention are as follows: <ul id="ul0002" list-style="none"><li>A. The main body of the apparatus can be readily disassembled and reassembled, and particularly the segmented sleeve having the pins or fins can be easily replaced. This facilitates repair and inspection, and permits replacement with a sleeve having pins or fins suitable for the types of rubber materials to be processed.</li><li>B. The heating/cooling medium passages 33 are formed in the casing body, which is separate from the sleeve having the pins or fins. This enables the passages to have a sufficiently large volume. Also, the pins do not extend through the passages, thus preventing the medium from leaking around pins.</li></ul>