GB2191713A

GB2191713A - Mixer for polymeric materials

Info

Publication number: GB2191713A
Application number: GB08615228A
Authority: GB
Inventors: Ronald Harry Pointon
Original assignee: W&A Bates Ltd
Current assignee: W&A Bates Ltd
Priority date: 1986-06-21
Filing date: 1986-06-21
Publication date: 1987-12-23
Anticipated expiration: 2006-06-21
Also published as: GB8615228D0; GB2191713B

Abstract

A feed mixer (11) for use with rubber or plastics materials has two axially parallel cylindrical bores (15) and (16) which open into each other to form a mixing chamber (14) having two rotors (17,18) therein which rotate in opposite directions. Each rotor has a cross-section such that it has at least five radial arms with non-helical axially extending channels arranged between adjacent arms. Each channel may have a dam (33, 34, Fig. 3) therein and at least one of the dams makes a bias angle relative to a cross-sectional plane of the respective rotor. <IMAGE>

Description

SPECIFICATION Mixerssuitableforusewith polymeric materials The present invention relates to mixers for polymeric materials and in particularto mixers for rubber compositions.

In British Patent 1 550364there there is described a mixer having two parallel rotors each having a mixing section of non-helial form. Each of the rotors has a cross-section, normal to the axis of rotation, that is derived from a polygon and in particularthere is disclosed a first rotor derived from a triangle and which is described in detail, and a second rotor derived from a square. The rotors are arranged in two parallel cylindrical chambers which open one into the other. The two rotors rotate in opposite directions and the mixing action is achieved by the sheartips ofthe rotors smearing the rubber composition over the internal surface ofthe respective chamber in which each rotorturns.The material is passed along the rotor by pressure caused by material being forced into the feed inlet art one end ofthe rotor.

The present invention seeks to increase the material throughput of the above type of mixer; which issubstantiallyindependantofthe rotational speed of the rotors.

In GB 1550364, it is stated that in large mixers it would be an advantage to have rotors of square cross-sections. It is also stated that rotors based on pentagons and hexagons are feasible but because of the approximation of such rotors to a circle, the capacity of such a mixer would be undesirably small.

On the contrary, the applicant has developed a mixer having at least five shear tips and which has a very large throughput, something in the order of 51/2 ton/hourfrom a dual rotor mixer.

Accordingly there is provided a mixer suitable for use with plastic and rubber material and comprising a mixing chamber having two axially parallel cylindrical bores and which open one into the other to form a chamber having two rotors mounted one in each bore and which rotate in opposite directions, each motor having a cross-section normal to its axis of rotation which has at leastfive outwardly extending radial arms the tips of which are arranged on a circle and axially extending non helical channels along each rotor between adjacent arms.

Also according to the invention there is provided a mixer as described above, wherein the surface between adjacenttips has a concave arcuate cross-section forming the axially extending channels along lengths of the rotors.

Also according to the present invention there is provided a mixer suitable for use with plastic and rubbery material and comprising a mixing chamber having two axially parallel cylindrical bores and which open into each other, and two rotors mounted one in each bore and which each have a plurality of shearing tips thereon which each extend axially the length ofthe respective rotor, there being axially extending channels between pairs of adjacenttips wherein each channel has at least one dam therein and wherein at least one of said dams is arranged to make a bias angle relative to a plane normal to the axis of rotation of the respective rotor.

Also according to the present invention there is provided a mixer suitable for use with plastic and rubbery material and comprising a mixing chamber having two axially parallel cylindrical bores and which open into each other,andtwo rotors mounted one in each bore and which each have a plurality of shearing tips thereon which each extend axiallythe length of the respective rotor, there being axially extending channels between pairs of adjacenttips, wherein each channel has at least one dam therein and at least some of said dams have a relief passageway axially crossing the respective dam and which is located at an intersection of a tip and the respective dam.

The invention will be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic cross-section of a mixer according to the invention and which is mounted directly onto a screw extruder, Figure2 is an enlarged cross-section through the rotors and chamber of the mixer shown in Figure 1, Figure 3 is a perspective view of the pair of rotors used in the mixer of Figure 1, and Figure 4 is a section on the lines A-A of Figure 3.

With reference to Figure 1 there is illustrated a through feed mixer 11 mounted on an extruder 12 and which can process rubbery or plastic materials received in powder or granularform. The mixer according to the invention comprises two rotors 17 and 18 which are mounted substantially parallel with each other in a mixing chamber 14. The mixing chamber 14 comprises two parallel cylindrical bores 15 and 16 located in a body portion 12 of the mixer.

The two cylindrical bores 15 and 16 are parallel to each other and open one into the other to form the chamber 14with a substantially figure of eight cross-section. The rotors 17 and 18 are mounted in bearings in the body of portion 12 and are arranged to rotate in opposite direction towards each other, and are turned by a drive mechanism (not shown). A feeding device 13 is arranged to feed material to be mixed to an inlet passageway 19 leading into the chamber 14 at one axial end thereof and the extruder 12 is located beneath the mixer 11 to receive masticated material via a passageway 26 located at the other axial end ofthe chamber 14from the inlet passageway 19. The terms axial and axially refer to displacement along the rotational axes of the parallel rotors.The granular material to be mixed is fed into the chamber 14 where the contra rotating rotors 17 and 18 masticate and mix the material which is forced along the rotors and then passes into the extruder 12.

With reference to Figure 2, Figure 3 and Figure 4, each rotor is without helical twist and has a substantially uniform cross-section throughout its lengths. The cross-section of the rotors is shown in detail in Figure3and isbased on a regularpentagon.

The cross-section of each rotor resembles a five pointed star, the five tips 31 of each rotor are arranged on a circle and there are axially extending channels 32 along each rotor between adjacenttips 31. Each channel 32 informed in cross-sections as a concave arcuate surface extending between the tips 31.The rotors 17 and 18 each have a plurality of dams located along their length, preferablythe dams 33, and 34 are located in the channels 32 at approximately one third and two thirds of the length of the rotors dividing the rotors into three sections.

The dams are formed in circularsetswhich have a diametersubstantially equal to that ofthe circle on which the rotortips 31 are located. The dams 33 and 34 are formed as two different sorts of dam, a straight dam 33 which is located in a plane normal to the axis of rotation ofthe rotor, and an angled dam 34which makes a bias angle with a plane normal to said axis. Preferably the bias angle is between 1/2" and 5", and is more preferably 1". The two rotors 17 and 18 are arranged so thatthe straight dam 33 on each rotor 17 and 18 is axially aligned with the angled dam 34 ofthe other rotor 18 or 17 respectively.The angled dams 34 allow material to flow more easily across the dam and thereby assist the flow of rubber along the rotor, as compared with a straight dam, which acts primarily to pass material from one rotorto the other.

Amixerofthe above type is considered capable of a throughput of 51/2 tons per hour. In orderto maintain this throughputthe interaction between the rotor and chamberwall must be capable of low temperature rubber shear, rubber mixing flow, and rubbertransferfrom inletto outlet.

A large capacity mixer will have cylindrical bores 14 and 15 with a diameter of about 600mm and a length of about 2400mm, so thatthe length/diameter ratio is4. There is a clearance of 1 0mm between the outer diameter of each rotor 17 and 18 and the internal surface of the bores 14 and 15, and the two rotors are, preferably, arranged so that the distanced between two rotors is 20mm.

It is considered that rotors 14 and 15, rotating art a speed of 18 rpm and having a tip land width 'L' of 30mmwould achievethe output of about 51/2 tons per hour, with material having a dwell time in the chamber 14 of approximately 4 minutes. The pressure angle B on the leading face of each rotortip i.e. the angle the face makes relative to a tangent at thetipshould be between 5" and 45" and preferably ofthe order of 400.

The angled dams 34 have relief passageway 35 which are cut into the tips 31 of the respective rotors 17 or 18 to assist the flow of material past pairs of circumferentially adjacent angled dams. The passageway 35 can be angled to assist the flow of material in a desired direction, e.g.forwards along the rotor, or backwards, depending on the mixing effect to be achieved.

While the invention has been described by way of example with reference to the single embodiment shown in the drawing itwill beappreciatedthat minor modifications can be made without departing from the scope and spirit ofthe invention. For example, the rotors could be made to rotate at different speeds, orthe dimensions of rotors and bore could be altered.

Claims

1. A mixer suitable for use with plastic and rubbery material and comprising a mixing chamber having two axially parallel cylindrical bores and which open one into the otherto form a chamber having two rotors mounted one in each bore and which rotate in opposite directions, each rotor having a cross-section normal to its axis of rotation which has at least five outwardly extending radial armsthetips of which are arranged on a circle, and axially extending non helical channels along each rotor between adjacent arms.

2. A mixer as claimed in Claim 1 wherein the surface between adjacent tips has a concave arcuate cross-section forming the axially extending channels along lengths ofthe rotors.

3. Amixeras claimed in Claim 1 or Claim 2 in which there are a plurality of dams in each channel.

4. A mixer as claimed in Claim 3wherein at least one dam in each channel is making an acute angle in relation with a plane normal to the axis of rotation of the respective rotor.

5. A mixer as claimed in Claim 4wherein the angled dams in each channel are substantially axially aligned.

6. A mixer as claimed in Claim Swhereinthe angled dams on one rotor are in axial alignmentwith the straight dams on the other rotor.

7. Amixerasclaimed in anyoneof ClaimsLtoG wherein the angled dams make a bias angle relative to a plane normal to the axes of the rotors, and said bias is between 1/2" and 5".

8. A mixer as claimed in any one of Claims 4to 7 wherein there are relief passageways atthe intersection of the tips of the rotors and some ofthe dams and which are located between pairs of circumferentially adjacent angled dams to assistthe flow of material axially acrossthe angled dams.

9. A mixer suitable for use with plastic and rubbery material and comprising a mixing chamber having two axially parallel cylindrical bores and which open into each other, and two rotors mounted one in each bore and which each have a plurality of shearing tips thereon which each extend axiallythe length of the respective rotor, there being axially extending channels between pairs of adjacenttips, wherein each channel has at least one dam therein and wherein at least one of said dams is arranged to make a bias angle relative to a plane normal to the axis of rotation of the respective rotor.

10. A mixer according to Claim 9 wherein the angled dams make a bias angle of between 1/2" and 0

11. A mixer suitable for use with plastic and rubbery material and comprising a mixing chamber having two axially parallel cylindrical bores and which open into each other, and two rotors mounted one in each bore and which each have a plurality of shearing tips thereon which each extend axially the length of the respective rotor, there being axially extending channels between pairs of adjacenttips, wherein each channel has at least one dam therein and at least some of said dams have a relief passageway axially crossing the respective dam and which is located at an intersection of a tip and the respective dam.

12. A mixerfor plastic and rubber materials having rotors substantially as described herein and as illustrated in Figures 3 and 4 of the accompanying drawings.