CLOSED MIXER HAVING PARALLEL ROTORS, WHOSE AXIAL SEPARATION IS ADJUSTABLE

Abstract: A closed mixer having rotors (4) whose axial separation is adjustable, comprising an external casing (1) containing a mixing chamber housing two rotors with projecting lobes (5) operating at a limited distance from one another, and caused to rotate by a motor unit via transmission means, wherein the rotors are equipped with end shafts (4a), having a relatively small diameter, rotatably supported within opposite heads of the external casing by means of supports (12) housed within elements (17) which can move and be locked in a number of positions, as a result of moving which elements the distance between the axes of the rotors can be varied, there being provided holding means between the rotors and the heads of the chambers across which they extend, in order to ensure that the axial separation of the rotors is held in the various positions.

Description: The object of the present invention is to provide a closed mixer having rotors in which the distance between the axes of the rotors is adjustable so that the gap between the rotors can be varied in order to achieve the best possible gap to suit different manufacturing processes, as well as to adjust for the wear and tear of the working surfaces, thereby offering steady operating features. In closed mixers, especially of the type having meshing rotors, the mixing and "cutting" action takes place mainly, or almost entirely, between the opposing surfaces of the two rotors. In order to ensure good mixing, the distance or 'gap' between the surfaces of the rotors by which the working process is carried out is highly important in these mixers and, therefore, there is a considerable advantage in being able to choose this distance depending upon the type of manufacturing process to be carried out. As time goes by, wear and tear of the working surfaces of the rotors also takes place, resulting in ever increasing play between the rotors to the extent that the working features of the machine are modified, the mixing becoming progressively worse until it becomes necessary to replace the rotors or to overhaul them, refacing the surfaces by means of welding, so as to obtain the original geometrical form. These actions are complicated and costly and the machine must be kept inoperative for a long time in order to allow the rotors to be taken to pieces, to be replaced or to be overhauled, as shown in US-A-2 015 618 and US-A-3 147 648. It is therefore important to provide a mixer, especially of the type having meshing rotors, in which it is possible both to vary the gap between the rotors to suit the various conditions of use and to allow for the wear and tear of the rotors to be made good, thereby allowing these rotors to be used for a long time before overhauling and rebuilding the worn surfaces, thus ensuring the best working condition throughout the whole period. These results are achieved by the present invention, which provides a closed mixer having rotors whose axial separation is adjustable, comprising an external casing closed at both ends by a head housing a mixing chamber containing two rotors with projecting lobes operating at a limited distance from one another, and caused to rotate by a motor unit via transmission means, wherein the rotors are equipped with end shafts, rotatably supported within opposite heads of the external casing by means of supports housed within elements which can move and be locked in a number of positions, as a result of moving which elements the distance between the axes of the rotors can be varied, there being provided sealing means between the rotor's ends and the heads of the chamber across which the rotors extend in order to ensure sealing in correspondence to the various positions assumed by the rotors. In a particular embodiment, the rotors have meshing lobes, whose complementary profiles define throughout their rotation one or more areas at short distance between the mutual working surfaces. According to one embodiment of the invention, the moving elements housing the supports for the rotors comprise, for each head, two rings rotatably carried within the respective head of the external casing of the mixer, and housing the supports for the rotors in an eccentric manner, there being provided controls for causing rotation of the rings, thus varying the position of the axes of rotation of the rotors and means for locking the rings in the wanted positions. The means for rotating the rings may suitably consist of a worm screw interposed between the rings and engaging with teeth extending around the perimeter of the rings themselves and caused to rotate by means of a suitable control via a motor reducing unit. The locking means may comprise indentations, cut-outs, holes or the like provided on the surfaces of each eccentric ring, in one or several of which there is inserted either a peg or a locking key secured to the external casing of the mixer, or locking screws adjustable in different positions, or the like. The holding means provided between the rotors and the heads of the chamber may comprise front sealing rings acting against flat surfaces which join the ends of the rotors to their respective support shafts, the sealing rings, which are carried by the head walls of the mixing chambers, having a bigger internal diameter than the diameter of the support shafts, so that the support shafts are allowed lateral displacement, as required, internally: alternatively, the holding means provided between the rotors and the heads of the chamber may comprise radial sealing rings acting on the cylindrical surfaces of the support shafts for the rotors carried by extensions of the eccentric rings and rotating together with them within the head walls of the mixing chambers. In a further embodiment of the present invention, the control means for the rotation of the eccentric rings comprises a shaft tangential to the circumference of both rings carrying two worm screw parts, each having a screw thread directed in an opposite direction from the other end engaging with corresponding teeth extending around the perimeter of the respective eccentric ring, and made to rotate by means of a control via a motor unit. According to yet a further embodiment, the movable elements may comprise slides within which the support shafts for the rotors are housed, it being possible to alter the position of the slides in relation to one another by means of controllable actuating means. The movable elements may also consist of polygonal bushes within which there are carried, in an eccentric manner, the support shafts for the rotors, the bushes being inserted within corresponding polygonal seats in the heads of the external casing of the mixer, wherein variation of the distance between the axes of the rotors is achieved by extracting the bushes from their seats and subsequently inserting them in a relatively rotated position. More detail will be found in the following description of some embodiments of the present invention, given by way of a non-limiting example only, with reference to the attached drawings, wherein: Fig. 1 shows a vertical cross-section of a closed mixer according to the invention, according to a line I-I of Fig. 2; Fig. 2 shows a horizontal cross-section of the mixer along the line II-II of Figure 1; Fig. 3 shows the cross-section according to line III-III of Figure 2; Fig. 4 shows a detail of the members for supporting and holding the rotors of the mixer of Figure 2; Fig. 5 shows the mixer of Figure 2 is an alternative embodiment; Fig. 6 shows a detail of the members for supporting and holding the rotors of the mixer of Figure 5; Fig. 7 shows a cross-section along a line VII-VII of Figure 4; Fig. 8 shows an alternative embodiment of the devices for varying the axial separation of the rotors; Fig. 9 shows an additional embodiment of the devices for varying the axial separation of the rotors; Fig. 10 shows an additional embodiment of the devices for varying the axial separation of the rotors; and Fig. 11 shows an additional embodiment of the devices for varying the axial separation of the rotors. As shown in Figure 1 and Figure 2, a closed mixer used for mixing elastomer, plastics and similar material comprises an external casing 1 provided with an upper opening 2 through which the material to be worked is introduced and a lower opening 3 through which the material is removed, the casing containing two meshing rotors 4 having projecting lobes 5. The casing 1, which comprises semi-cylindrical cheeks 6 provided with internal cooling channels 7, defines an internal chamber, having a cross-section in the form of an 8, accommodating the rotors. The upper opening 2 has a closing plug 8 which can be lifted to allow material to be introduced and lowered to press the material into the working area, whilst the lower opening can be closed by a door 9 which is rotatable about a shaft 10 and can be held in position by a catch 11. As shown in Figure 2, the end parts of the rotors are provided with respective shafts 4a, which are supported by rotatable supports 12 and which have end pieces 13 suitable for connection, via transmission members, for example of a universal type, not shown in the Figure, to the motor unit, whilst the opposing end parts 14 carry rotatable connections 15 for the supply of an internal cooling circuit. The rotors, which rotate in opposite directions, as indicated by the arrows in Figure 1, have sections along which there is, between a lobe 5 of one rotor and the central cylindrical core 16 of the other rotor, a small distance 'd' or 'air gap' in order to impart, to the material forced within the restricted space, blade stresses enabling mixing to take place as desired. In order to maintain the gap constant, thereby compensating for the wear and tear of the working surfaces of the rotors, or to vary the gap as required in order to obtain the best possible result during each manufacturing stage, the rotors are mounted on supports 12 which are able to be brought near to one another, as required, to allow variation in the initial gap and/or reset it periodically. In the embodiment shown in Figures 2, 3, and 4, the revolving supports 12 of the rotors are mounted, by way of example, within eccentric rings 17, rotating within respective circular seats of heads 18 of the casing 1. The eccentric rings 17 have peripheral teeth and the teeth are engaged by a worm screw 19 which is provided between them and which is operated by a motor 20. By operating a control, the screw can produce a rotation of the eccentric rings 17, bringing the rotors 4 nearer to each other, so as to enable any gap between the rotors to be restored to the initial value, after wear and tear. As shown in more detail in Figure 4, the seal between the rotor and the external casing may be achieved by means of a sealing ring 21 acting against the flat surface of end 22 of the rotor 4 and held tight against it by ring 23 secured to the head 18. The internal openings of the rings 21 and 23 have diameters which are greater than that of the end shaft 4a of a rotor 4 and are such as to enable the rotor to move transversely inside them, as a result of the rotation of the ring 17, and corresponding to the required modification in the gap. In the case in which a seal is provided on the cylindrical surface of the support shaft 4a of the rotor, as shown in Figs. 5 and 6, there is provided an eccentric ring 17a having an extending portion 24 stretching as far as the seal area, rotatingly housed within a seat 25 of the head 18, housing the seat for the annular sealing ring 26, making a seal on the cylindrical surface of the shaft 4a. The eccentric ring 17a, upon rotation, therefore brings about the rotation of the whole assembly of sealing rings 26 which follow the displacement of the rotor 4 and therefore guarantee a seal on the shaft 4a. As a rule, the distance between the rotors 4 can be periodically varied when the machine is inoperative by controlling the effective value of the gap between the various parts of the rotors. However, the structure of the mixer according to the invention also allows the distance between the rotors to be varied when the machine is operating, whenever, during mixing, it is advisable to have different gaps for the various stages of a process. A display system associated, for instance, with the rotation of the motor 20 is planned to allow control of the extent of variation in the distance between the rotor axes even when the machine is switched off and for equal distances to be obtained between the axes of the rotors and both the heads of the mixer. A reduction in the gap 'd' is necessarily associated with an increase in the distance between the lobes 5 and the walls of the mixing chamber : however such increase, as opposed to the increase in the distance between the rotors, has negligible effect on the quality of mixing, which mainly takes place in the area between the rotors. Moreover, displacement of each one of the rotors causes equal distancing of the rotors from the walls but the rotors are brought together by an amount twice such value, thus the advantage of bringing the rotors closer together is more effective than distancing them from the walls. In order to prevent the screw 19 from receiving stresses transmitted by the eccentric rings 17 or 17a, there has been provided a locking device against the rotation of the rings, suitable for preventing the rotation of the rings 17 or 17a after their position has been chosen. One embodiment of such device provides for the presence of slots 27 on the outermost surface of the eccentric rings 17 or 17a. A stopping member 28 is inserted in one or more of these slots, depending upon the existing stresses, in correspondence to the required position of rotation of the eccentric ring, such stopping element being secured to the head 18 by screws or the like and being suitable to carry the possible rotational stresses of the eccentric ring. As a replacement for the device using eccentric rings, as previously shown, it is possible to use different devices in order to obtain a required alteration in the distance between the axes of the rotors of a mixer. For instance, as shown in Figure 8, the support for a rotor 4 may be carried by slides 29 sliding within the head 18 of the machine and set near one another by means of screws 30 and controlled manually or by motor, or, as shown in diagram form in Figure 9, by means of an actuating cylinder 31. Also in the case of this embodiment, the holding members can be of a type enabling eccentricity to be obtained between the shaft and the holding seat which is fixed and joined to the heads, for example by using a front sealed surface, as previously described, or by using a seat with a movable seal joined to the slides 29 and therefore suitable to follow the displacement of the shaft 4a for the support of rotors 4. The rotors 4 may be also brought near each other by means of other parts, such as for instance eccentric bushes having a polygonal profile 32, as shown in Figure 10, within which the support 12 of the rotors may be housed, such bushes in their turn being inserted within corresponding seats 33. In this embodiment alteration of the distance between the rotors is achieved by extracting the bushes from their seats and inserting them again after rotation. If the supports 12 are inserted into eccentric rings having external teeth 34, as shown in Figure 11, rotation of the rings in order to vary the distance between the rotors, both when the machine is not working either to vary the working distance, or to make good the surface wear and tear of the rotors, and when the machine is in operation to vary the distance during mixing, may be carried out by means of a shaft 35, provided with two worm screw parts 36, 37 having opposite screw threads and operated by a motor 38. Particularly in cases in which alteration of the distance between the rotors can be carried out when the machine is in operation, provision is made for the presence of sensors to record the closeness obtained, in association, for instance, with the rotation or the sliding of the eccentric rings, or of the slides carrying the supports 12, such sensors being able to supply an indication on a control panel of the machine, or being associated with automatic control parts for altering the distance between the rotors throughout mixing. In order to avoid the rotors coming too close together, especially when new rotors are involved, with the danger that they interfere with one another during rotation, there can be provided mechanical means for stopping a displacement of the rotors whereby preventing the rotors from being too near one another with the risk of possible interference, it being possible for such means to be removed or displaced when a considerable displacement of the rotors is needed to take account of the wear and tear.

Claims: A closed mixer having rotors (4) whose axial separation is adjustable, characterised in that it comprises an external casing (1) closed at both ends by a head (18) and housing a mixing chamber containing two rotors (4) with projecting lobes (5) operating at a limited distance "d" from one another, and caused to rotate by a motor unit via transmission means, wherein the rotors (4) are equipped with end shafts (4a) having reduced diameter and being rotatably supported within opposing heads (18) of the external casing (1) by means of supports (12) housed within elements (17, 34) which can move under the action of driving means (19, 20; 29, 30, 31; 32; 35, 38) and be locked in a number of positions by the action of locking means (27, 28), as a result of moving which elements the distance between the axes of the rotors (4) can be varied, there being provided sealing means (21) between the end shafts (4a) and the heads (18) of the chamber across which the rotors extend in order to ensure sealing in correspondence to the various positions assumed by the rotors (4). A closed mixer according to Claim 1, characterised in that the rotors (4) have meshing lobes, (5) whose complementary profiles define throughout their rotation one or more areas at short distance "d" between the mutual working surfaces. A closed mixer according to Claim 1 or Claim 2, characterised in that the moving elements housing the supports for the rotors (4) comprise, for each head (18), two rings (17) rotatably carried within the respective head (18) of the external casing (1) of the mixer, and housing the supports (12) for the rotors (4) in an eccentric manner, there being provided controls for causing rotation of the rings (17), thus varying the position of the axes of rotation of the rotors (4) and means for locking the rings in the wanted positions. A closed mixer according to Claim 3, characterised in that the means for rotating the rings (17) comprise a worm screw (19) interposed between the rings (17) and engaging with teeth extending around the perimeter of the rings (17) themselves and caused to rotate by means of a suitable control via a motor reducing unit (20). A closed mixer according to Claim 3, characterised in that the locking means comprise indentations (27), cut-outs, holes or the like provided on the surfaces of each eccentric ring (17), in one or several of which there is inserted either a peg or a locking key (28) secured to the external casing (1) of the mixer. A closed mixer according to Claim 3, characterised in that the locking means comprise holes obtained on the surface of each eccentric ring, in one or several of which there is inserted a locking key secured to the external casing of the mixer. A closed mixer according to Claim 3, characterised in that the holding means provided between the rotor's ends (4a) and the heads (18) of the chamber may comprise front sealing rings acting against flat surfaces which join the ends of the rotors to their respective support shafts, these sealing rings, which are carried by the head walls of the mixing chambers, having a bigger internal diameter than the diameter of the support shafts, so that the support shafts are allowed lateral displacement as required, internally. A closed mixer according to Claim 3, characterised in that the holding means provided between the rotors and the heads of the chamber may comprise radial sealing rings acting on the cylindrical surfaces of the support shafts for the rotors, carried by extensions of the eccentric rings and rotating together with them within the head walls of the mixing chambers. A closed mixer according to Claim 3, characterised in that the control means for the rotation of the eccentric rings (17) comprises a shaft (35), tangential to the circumference of both rings (17), carrying two worm screw parts (36, 37) each having thread screws directed in an opposite direction from the other and engaging with corresponding teeth extending around the perimeter of the respective eccentric ring (17), and made to rotate by a control via a motor unit (38). A closed mixer according to Claim 1, characterised in that the movable elements comprise slides (29) within which the support shafts (4a) for the rotors (4) are housed, it being possible to alter the position of the slides (29) in relation to one another by means of controllable actuating means (31). A closed mixer according to Claim 1, characterised in that the movable elements comprise polygonal bushes (32) within which there are carried, in an eccentric manner, the support shafts (4a) for the rotors (4), the bushes (32) being inserted within corresponding polygonal seats (33) in the heads (18) of the external casing (1) of the mixer, wherein variation of the distance between the axes of the rotors (4) is achieved by extracting the bushes (32) from their seats (33) and subsequently inserting them in a rotated position.

Inventors: PASSONI, GIAN CAMILLO
Applicants: POMINI FARREL S.P.A.
Application year: 1987
Main classification: B01F7
IPC codes: B29B7, B23Q16, B01F7