GB2033241A

GB2033241A - Continuous Multi-shaft Processor such as a Twin-screw Mixer

Info

Publication number: GB2033241A
Application number: GB7843112A
Authority: GB
Original assignee: Baker Perkins Inc
Current assignee: Baker Perkins Inc
Priority date: 1978-10-18
Filing date: 1978-11-03
Publication date: 1980-05-21
Also published as: CH632445A5; GB2033241B

Abstract

The invention relates generally to an improved system for treating material proceeding continuously through a processing barrel B having at least twin interconnected cylinders. Rotating parallel mixer shafts 10a, coaxially mounted in the cylinders, have radially interwiping screw or paddle elements between a material charging inlet O and a material discharging outlet which are configured to wipe the cylinders. Sets of paddle elements 42, 43 each of which includes a cylinder blocking paddle 42, are provided on the shafts at a flow control station U between the inlet and outlet, and a movable flow-controlling saddle or valve element V is mounted with relation to the cylinder blocking paddle sets in a position such that it can be moved from an opened position to a position to restrict or block flow past the sets of paddle elements. There is a degassing vent 100 downstream of the location where the saddle or valve element V begins to back up the flow of material and the saddle or valve element V directs the flow away from the vent 100. <IMAGE>

Description

SPECIFICATION Continuous Multi-Shaft Processor such as a Twin-Screw Mixer The present invention provides a processor as set forth in Claim 1. Claims 2 to 5 set forth preferred features of the invention.

The preferred form of the invention is a twinscrew continuous mixer of the type operated in a figure 8-shaped barrel which is heated to a material processing temperature and wherein distinct processing zones are provided between the material supply and downstream material discharge openings in the mixer. Such mixers are particularly used with various plastic resins and are of the type where the plastic resin enters a feed screw zone and is then forced into an intensive mixing zone where it is melted. The mixer in accordance with the invention has a vacuum vent port for degassing or like puposes in the barrel casing at a flow control station in a position in which its relationship with the elements is such as to avoid the flow of product out the port.

The invention will be further described, by way of example, with reference to the accompanying drawings, of which: Figure 1 is a fragmentary, sectional elevational view of a continuous processing machine with the selectively positioned saddle parts shown in a position to permit flow, the view being taken on the line 1-1 of Figure 2 and for the sake of clarity omitting the vent system illustrated in some other views; Figure 1 A is a perspective under plan view of one of the saddle parts:: Figure 2 is a transverse sectional view taken on the line 2-2 of Figure 1; Figure 3 is a view similar to Figure 2, but showing the saddle parts adjusted to block flow; Figure 4 is a fragmentary, sectional plan view taken on the line 4-4 of Figure 3; Figure 5 is a like view, but with the saddle part rotated to a position in which full flow is permitted; Figure 6 is a fragmentary sectional side elevational view of a continuous material processing machine in which the vent system is included; Figure 7 is a view of the modified machine similar to Figure 5 but with the saddle part in partly open position; Figure 8 is a transverse sectional view of a modified flow control part which can be used, the flow control element being shown in open position; and Figure 9 is a cross-sectional view taken on the line 9-9 in Figure 8.

Basically, the machine of Figures 1 to 5 is exactly as described in UK Patent Specification No (Application No 47948/76, a copy of which is attached hereto), and Figures 1 to 5 of the accompanying drawings are identical to Figures 1 to 5 of that UK Patent Specification; the description will not be repeated, but the accompanying drawings show the references used in that UK Patent Specification. It should be noted, however, that the material advancing or forwarding portions 1 Oa and 1 a may be integral with, ie formed in one piece with, the shafts 12 and 13. Furthermore O-rings (not shown) may be provided to seal the post parts 29 to the housing sections 21 and 22 to prevent the escape of lubricant supplied through the fittings 31.

The present invention is directed towards the degassing vent which is described below in relation to Figures 6 to 9.

In Figures 6 and 7, vacuum venting or degassing is disclosed as occurring at a degassing station designated U. For example, polybutane H300 with a viscosity of 335 to 500 poises at an operating temperature range in the 93 to 1020F area, and including entrained air, can be degassed satisfactorily utilizing vacuum on the leeside of the barrel valve V. The entrapped air can be removed at the vent 100, which preferably is in the slot shape shown, to obtain a more stable and bubble-free polymer. The barrel valve, if not fully open, must be opened "forwardly" in the sense of pitch of the forwarding screws 1 0an1 1 a and their common direction of rotation because, if opened backwardly, it will function as a plow and actually move the material into the vent port 100.

Typically speaking, the controlled feed of material into the barrel B is sufficient to fill it 3/4 full of material at the supply hopper H end, depending of course on the material and its viscosity, and good control of the flow of material is achieved by opening the barrel valve V to greater or lesser degrees.

In studies which were undertaken with corn syrup and when the vacuum at the vent 100 was kept below 15 inches of mercury, the vent stayed clear of syrup and significant deaeration of the product was accomplished. The partial rotation of the central element V to the position shown in Figure 7 permits the vane 37 to cooperate with the elements 42, 43a and 42a, 43 to direct material away from the vent 100.

As Figure 6 indicates, the screws at the flow control station U, which includes the elements 42-43a, 42a-43, and V, may take the form of mating greater conveying capacity sections D-1 and, downstream thereof, mating end discharge sections D-2. The sections D-1 are configured to have a capacity to operate in a partly starved (non-full) condition while the end discharge sections D-2 are configured so as to operate fully loaded with material. Typically the flow control V is adjusted angularly to provide a barrel section m immediately rearward of the station U in which the material backs up and which is operated full of material while an upstream section n is only partly loaded during operation.

The section m achieves the melt seal which prevents a vacuum source attached to the vacuum pipe 1 00a at vent 100 from sucking air and material in from the feed hopper H. The barrel portion at element 43a, and housing screws D 1, operates partly full so that suction venting is possible. With adjustment of element V, a positive discharge pressure can be achieved at D-2 where this is necessary while venting upstream, which means that the immediately subsequent processing equipment downstream can be pressure fed and need not incorporate a vacuum venting station. The helix angle of screws D-2 is tight enough, dependent on the material being processed, to have the capability of pumping the material up from vacuum or moving it under positive pressure to a die or suitable forwarding device.

In Figures 8 and 9, another embodiment of the flow control element is illustrated in which the valve V, which is utilized is similar but does not in effect form a barrel by-pass. In this embodiment of the invention, parts used in previous embodiments have been given like numbers and only the different parts have been differentiated, for purposes of more clearly pointing out the invention. For instance the forwarding screws are shown at 10 and 1 1 as screws which are rotated in a direction to advance the material in the direction a. The upstream full bore paddle is shown at 42 and the downstream full bore paddle is shown at 42a, but this time in a sidewisely reversed relationship and located a spaced distance t from one another.The reduced diameter paddles of circular shape, 43 and 43a, are shown as elongated and having diametrically opposite grooves 101 and 102 of curvate configuration. Provided in the space tthat is created, to rotate about an axis b, is a plate 103 having curvate edges 103a complementary to the configuration of grooves of 101 and 102. Plate 103 is supported upon a rotatable shaft 104 rotating about the axis b in a bearing opening 105 provided in the barrel B. Seal rings 106 are preferably provided, as is handle 107 which may be manually grasped to adjust the position of plate valve 103. As Figure 8 indicates, the plate 103 spans the distances between the upper and lower saddle portions 38 of the barrel B, and when in the position indicated by the broken lines in Figure 9, effectively prevents flow through the barrel B. By virtue of the fact that it substantially spans the distance t between the upstream and downstream full bore circular paddles 42 and 42a, except for an operating clearance, the melt seal obtained is such at this point as to prevent flow for practical purposes when the plate 103 is turned to the position as indicated in broken lines in Figure 9. Of course, intermediate positions of the plate 103 are possible to control the restriction in the manner desired. When the device is turned to the particular 450 position indicated by the lines p, or some position in the 900 between the solid line position and the other broken line (closed) position, the vacuum vent 100, which has a removable cover 108, can be opened and degassing can occur.

Claims

1. A continuous processor having: a longitudinally extending barrel housing, with a material supply device and a downstream discharge opening, configured to form an axially extending processing barrel with at least twin interconnected cylinders therein and wherein the distance between the axes of the twin cylinders is substantially equal to or less than twice the radius of the cylinders and the housing has saddle portions of generally V cross section at the points of interconnection of the cylinders; and at least a pair of parallel longitudinally extending rotatable shafts with radially intercooperating material forwarding portions thereon; radially adjacent cowiping flow control elements provided on said shafts downstream from the material supply opening at a flow control station; and a movable flow restricting part, provided at said station disposed to interact with said flow control elements to back up the flow and permit less than full barrel flow downstream, mounted to move toward and away from a position in which it permits less restricted flow; the barrel having a degassing vent opening therein downstream from the location where the flow restricting part commences to back up the flow of material, and the flow restricting part being configured to direct the flow material away from said vent.

2. The processor of claim 1 wherein co-wiping, mating, material handling elements are on said shafts at the flow restricting station downstream from said co-wiping elements and have a greater volumetric capacity than said material forwarding portions.

3. The processor of claim 2 wherein the cowiping elements comprise pairs of radially adjacent paddles, one element of each pair being of full bore shape to substantially block flow through one of the cylinders by leaving only wiping clearance between the said element and cylinder, and the other element of each pair being of reduced size and permitting flow past it peripheraily, the vent being substantially radially adjacent one of the reduced size elements downstream from the location where the flow restricting part tends to back up the flow of material so that this portion of the barrel is not filled with material and material is not wiped across the vent opening.

4. The processor of claim 3 wherein said flow restricting part has a vane portion disposed at an angle to the axes of the shafts and at an angle relative to the vent to tend to direct material away from the vent.

5. The processor of any one of the preceding claims and also being as claimed in any one of Claims 1 to 13 of UK Patent Specification No 1559019 (Application No 47948/76).

6. A continuous processor, substantially as herein described with reference to, and as shown in, Figures 1 to 7 or Figures 6 to 9 of the accompanying drawings.