GB2076675A

GB2076675A - Mixing apparatus

Info

Publication number: GB2076675A
Application number: GB8109860A
Authority: GB
Original assignee: BHS Bayerische Berg Hutten und Salzwerke AG
Current assignee: BHS Bayerische Berg Hutten und Salzwerke AG
Priority date: 1980-04-01
Filing date: 1981-03-30
Publication date: 1981-12-09
Also published as: DE3012707A1; GB2076675B; JPS5815169B2; DE3012707C2; CH655861A5; JPS56150424A

Abstract

A mixer, for example for mixing building materials, having two contra- rotatable shafts (1,1') each carrying two helical paddles (4, 5 on shaft 1, 4', 5' on shaft 1'), of opposite hand and of different length. The shafts 1, 1' are advantageously horizontal and parallel, and the shorter paddle on one shaft lies opposite the longer on the other. <IMAGE>

Description

SPECIFICATION Mixing apparatus The invention relates to a mixing apparatus, especially to a mixing device for a trough mixer, having at least two horizontal, contra-rotatable mixing shafts for mixing pulverulent, granular or plastic material, especially mixtures of building materials, in which two helical worms the threads of which are of opposite hand are carried on each mixing shaft.

In order to achieve a good mixing effect together with rapid mixing action, that is, a short mixing time, the following requirements must be met by the mixing apparatus: intensive movements of the material in opposite directions at a maximum speed of conveyance in a rotating, repeating cycle of movement in the mixing trough.

These technical mixing requirements are best met, in the case of trough mixers that operate with a slowly rotating mixing device, by a helical mixing device. Conventional circumferential speeds measured at the outer diameter of the mixing device lie in this case within the range of from 1.4 to 2.0 m/s.

A concrete mixer has been proposed, in which two worms of opposite hand are carried on each of the two mixing shafts (DE-OS 2440461).

The worm bands of opposite hand on each shaft are of the same length and are furthermore constructed with the same pitch angles.

In practice this mixing apparatus does not give good mixing results. This disadvantage is essentially a result of too little cyclic movement of the material in the trough. No circular movement of the desired type takes places inside the trough.

There has also been proposed a mixing apparatus having a single shaft (DE-OS 2 311 579). In this case aiso, the ratio of the lengths of the two worm bands of opposite hand is 1:1. The mixing device is suitable only for singleshaft mixers and not for double-shaft mixers.

There still remains a need for a double-shaft trough mixer which permits rapid mixing and also a good mixing effect.

The present invention provides a mixing apparatus having two contra-rotatable shafts, each shaft carrying two helical worms of different lengths, the threads of which are of opposite hand.

Accordingly, in a mixer of the invention the helical worms of each mixing shaft have different system lengths and form an asymmetrical helical worm mixing apparatus, with each mixing shaft having one longer and one shorter helical worm.

The long helix conveys the material to be mixed in the longitudinal direction and the short helix conveys it in the transverse direction of the mixing trough, so that the material moves in a cycle. As a result, very good mixing effects together with rapid mixing of the material, especially of mixtures of building materials, may be achieved.

Advantageously, the helical worm having the greater total length on one mixing shaft is positioned opposite the helical worm having the smaller length on the other mixing shaft. As a result, a good circular movement is achieved in an advantageous manner inside the trough, which gives rise to a very good mixing effect.

The helical worms of different length on a given shaft can have either the same pitch angles or different pitch angles. In this case the pitch angle c of the shorter helix advantageously lies within the range of from 40 to 900 and the pitch angle a of the long helix within the range of from 25 to 400. Very good mixing results are achieved when, in a further advantageous feature of the invention, the system length ratio X :Y for the helical worms lies within the range of from 1:2 to 1 :7.

In another embodiment of the invention, the helical worms may be of interrupted construction and be in the form of individual helical paddles that are fastened to supports on the mixing shaft and are arranged one behind the other in helical line. The pitch angles of the individual helical paddles can in this case be the same as, smaller than or larger than the pitch angle of the helical connecting line between the individual paddles.

The helical worms may be constructed with multiple threads, that is, there may be two or more long helices and/or two or more short helices on each shaft, and, as indicated above, the apparatus may contain more than two shafts.

With reference to the distance A between the axes of the mixing shafts (which are normally parallel and horizontal) in relation to the outer diameter D of the worms on each shaft, the distance A between the axes may be smaller than the outer diameter D. The ratio of the distance A between the axes to the outer diameter D may lie within the range of from 1:1.1 to 1:1.4.

One form of apparatus constructed in accordance with the invention will now be described in detail by way of example with reference to the accompanying drawings, in which: Fig. 1 shows a cross-section through the trough of a double-shaft trough mixer with a view from above to the two asymmetrical helical worm mixing devices which are arranged horizontally in the trough; Fig. 2 shows a longitudinal section of the double-shaft trough mixer.

According to Fig. 1, two contra-rotating mixing shafts 1 and 1' mounted in a parallel and horizontal manner are positioned inside a mixing trough 6. Each mixing shaft 1 and 1' has two asymmetrical helical mixing worms 4 and 5 and 4' and 5', respectively, which have threads running in opposite directions. The individual helical worms have different system lengths X and Y, the ratio of the lengths X :Y lying advantageously within the range of from 1:2 to 1 :7.

The pitch angles (defined as the angle between the helical line of the helical worm and the direction of movement Z) are marked ( (for the shorter worm) and j. It is possible for the pitch angles r and /3 to be the same or different. In the case of different pitch angles, advantageous values are obtained when cz lies within the range of from 40 to 900 and il, within the range of from 25to400.

The two asymmetrical helical worms 4 and 5 and 4' and 5' are each fastened by means of supports 2 and 2', on the mixing shafts 1 and 1'.

From Fig. 1 it can be seen that the helical worm 5, of length Y, on the mixing shaft 1 lies opposite the helical worm 4', of length X, on the other mixing shaft 1'. Correspondingly, the shorter helical worm 4 on the mixing shaft 1 is arranged opposite the longer helical worm 5' on the mixing shaft 1'.

The helical worms 5 and 5' convey the material to be mixed in a longitudinal direction, whilst the shorter helical worms 4 and 4' convey it in a transverse direction. A very satisfactory cyclic movement of the material is thereby achieved in the trough so that, in effect, a type of circular movement takes place therein.

In Fig. 1 and 2 the diameter of the worm thread is marked D. As is clear from Fig. 1, the two helical worms 4 and 5 and 4' and 5', respectively, overlap; the distance A between the axes of the mixing shafts 1 and 1' being smaller than the diameter D. Advantageous ratios A to D lie within the range of from 1:1.1 to 1:1.4 and depend on the size and speed of the mixing apparatus.

In a further embodiment on the invention not illustrated the helical worms 4 and 5 and 4' and 5' are of interrupted construction. Individual helical paddles are thus obtained which are fastened to the supports 2 and 2' and arranged one behind the other in helical line; the pitch angles n and ,B of the paddles can, within the ranges of the system lengths X and Y, be the same as, smaller than or larger than the pitch angle of the helical connecting line between the individual paddles.

In summary, it should be noted that owing to the asymmetrical construction of the helical worms in a double-shaft trough mixer, rapid mixing and also a good mixing effect are obtained.

Claims

1. Mixing apparatus having two contrarotatable shafts, each shaft carrying two helical worms of different lengths, the threads of which are of opposite hand.

2. Mixing apparatus as claimed in claim 1, in which the helical worm having the greater length on one mixing shaft lies opposite the helical worm having the smaller length on the other.

3. Mixing apparatus as claimed in claim 1 or claim 2, wherein the helical worms of different lengths have the same pitch angles.

4. Mixing apparatus as claimed in claim 1 or - claim 2, wherein the helical worms of different length have different pitch angles.

5. Mixing apparatus as claimed in claim 4, wherein the pitch angle of the shorter worm lies within the range of from 50 to 900 and the pitch angle of the longer worm lies within the range of from 25 to 400.

6. Mixing apparatus as claimed in any of the preceding claims, wherein the length ratio of the helical worms lies within the range of from 1:2 to 1:7.

7. Mixing apparatus as claimed in claim 1 or claim 2, wherein the helical worms are of interrupted construction and comprise individual helical paddles which are fastened to supports on the mixing shaft and are arranged one behind the other in helical lines.

8. Mixing apparatus as claimed in claim 7, wherein the pitch angles of the individual helical paddles are the same as or smaller than the pitch angle of the helical line on which the individual paddles lie.

9. Mixing apparatus as claimed in claim 7, wherein the pitch angles of the individual helical paddles are larger than the pitch angle of the line on which the paddles lie.

1 0. Mixing apparatus as claimed in any of the preceding claims, wherein the helical worms are constructed with multiple threads.

11. Mixing apparatus as claimed in any of the preceding claims, wherein the distance between the axes of the mixing shafts is smaller than the outer diameter of the worm threads.

12. Mixing apparatus as claimed in claim 11, wherein the ratio of the distance between the axes to the outer diameter lies within the range of from 1:1.1 to 1:1.4.

13. Mixing apparatus, substantially as described with reference to, and as iliustrated by, either or both of the accompanying drawings.

14. Mixing apparatus for trough mixers, having at least two horizontal, contra-rotating mixing shafts for mixing pulverulent, granular or plastic material, especially mixtures of building materials, in which two helical worms that are wound in opposite directions are arranged on each mixing shaft, characterised in that the helical worms of each mixing shaft have different system lengths and form an asymmetrical helical worm mixing apparatus.

1 5. A process for mixing substances, using an apparatus as claimed in any one of claims 1 to 14.

1 6. Any novel feature hereinbefore described.