EXTRUDER FEEDING ASSEMBLY AND EXTRUDER APPARATUS INCORPORATING IT

Abstract

Disclosed is an extruding apparatus and relative feeding assembly, including hopper unit in correspondence of an extruder-feeding area, wherein an extrusion screw having a first rotation axis and a drive roller having a second rotation axis are arranged at a distance each other so that a gap for raw material feeding is defined between the screw and the drive roller, wherein the drive roller has a substantially conical surface with respect to its own rotation axis, the conical surface having a taper vertex facing toward a progression direction of the extrusion screw.

Claims

1. Feeding assembly of an extruder, comprising hopper means in correspondence of an extruder-feeding area, wherein an extrusion screw (10) having a first rotation axis (X-X) and a drive roller (20) having a second rotation axis (Y-Y) are arranged at a distance each other so that a gap for raw material feeding is defined between a flight envelope of said screw (10) and said drive roller (20), characterised in that said drive roller (20) has a substantially smooth conical surface with respect to its own rotation axis (Y-Y), said conical surface having a taper vertex facing toward a progression direction of said extrusion screw (10).

2. Feeding assembly as in claim 1, wherein the taper of said substantially conical surface is comprised between about 0.1 and about 30, preferably between about 0.5 and about 5.

3. Feeding assembly as in claim 1, wherein the taper of said substantially conical surface is such that the difference between the minimum and maximum peripheral linear velocity on said surface, upon rotation about said second rotation axis (Y-Y), is comprised between 0.1% and 50%.

4. Feeding assembly as in claim 1, wherein said substantially conical surface is determined by a curved generating line.

5. Apparatus for the extrusion of rubber-based or silicon-based material, comprising at least an extrusion screw (10) and a drive roller (20), mounted side by side in a feeding area of semi-processed material, wherein said feeding area is provided with a feeding assembly as in claim 1.

6. Extrusion apparatus as in claim 5, wherein said second rotation axis (Y-Y) of the drive roller (20) is substantially parallel to said first rotation axis (X-X) of said screw (10).

7. Extrusion apparatus as in claim 5, wherein said second rotation axis (Y-Y) is converging with respect to the first rotation axis (X-X) of said screw (10) with an angle smaller than 30.

8. Extrusion apparatus as in claim 5, wherein said drive roller (20) is driven into rotation by a drive independent from the motor driving the extrusion screw (10).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Further features and advantages of the invention will anyhow be more evident from the following detailed description of a preferred embodiment, given by way of non-limiting example and illustrated in the accompanying drawings, wherein:

[0020] FIG. 1, as anticipated, is a schematic view of a prior art extruder system;

[0021] FIG. 2 is a schematic view similar to that in FIG. 1, yet concerning a feeding system according to the invention;

[0022] FIG. 3 is an enlarged view of the detail of the drive roller of the system of FIG. 2;

[0023] FIG. 4 is a schematic view comparing the operation of the system of the invention to a prior art system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] For a better understanding of the invention, reference is firstly made to FIG. 1, where a prior art extruder is outlined, having an extrusion screw 1 by whose side a feeding or drive roller 2 is placed. The figure does not show neither the extruder body/barrel, in which the screw 1 is housed, nor the hopper compartment, usually placed above the roller 2, as they are well known to those skilled in the art and do not require further description.

[0025] The drive roller 2 of the prior art is cylindrical, with a rotation axis parallel to the axis of the screw 1 and placed closely alongside to the helical outline of the screw 1. A single motor drives the screw 1 and the drive roller 2 by means of gears 3, whose transmission ratios allow a synchronized rotation of the drive roller 2 and of the screw 1.

[0026] Referring now to FIG. 2, according to the invention, it is suggested to provide an extruder screw 10 with a feeding or drive roller 20 having a smooth conical surface with respect to the rotation axis.

[0027] Therefore, according to a preferred embodiment, the drive roller 20 is in the form of a truncated conical body, mounted in rotation about its own longitudinal symmetry axis.

[0028] More precisely, the truncated conical drive roller 20 has its minor base facing forward, i.e., towards the downstream direction in which the extruded material moves within the screw 10, while the major base of the drive roller 20 is directed towards the rear end, i.e., towards the upstream direction. In other words, the taper vertex of the roller 20 faces towards the progression direction of the extruder screw 10.

[0029] With smooth surface of the conical roller it is meant that the surface of the drive roller 20 is substantially free of any projection or flight which could prevent the material from shifting from one end to the other along the length of the roller.

[0030] In the embodiment shown in FIG. 2, the rotation axis Y-Y of the conical drive roller 20 is parallel to the rotation axis X-X of the respective extruder screw 10 and the two axes X-X and Y-Y are arranged at a mutual distance such that the drive roller 20 lateral surface is adjacent to the flight envelope of the screw 10 only at its major base, for example at a relative distance in the range of 2 mm to 15 mm. Thus, between the helical profile (flight envelope) of the screw 10 and the conical lateral surface of the drive roller 20, a gap is formed which increases starting from the major base towards the minor base of the drive roller 20.

[0031] The taper of the drive roller is 0.1 to about 30, preferably in the range of 0.5 to 5.

[0032] According to another aspect, the arrangement of the drive roller 20 is such that the difference between the minimum and maximum peripheral linear velocity on the surface thereof, in the rotation about its own rotation axis Y-Y, is comprised between 0.1% and 50%.

[0033] This innovative arrangement has proved extremely effective in providing a solution to the problems existing in the prior art. The relative different speeds between the drive roller 20 lateral surface and the extruder screw 10 flights along the longitudinal extension of the roller, together with the fact that the gap between the screw 10 and the drive roller 20 enlarges downstream, result in a perfect filling of the channels between flights of the screw 10 with the material to be extruded and strongly reduce any problem of inclusion of the material being fed into the overflowing material.

[0034] Such advantageous results are believed to result mainly from the speed profile along the variable-section roller, as outlined in the detailed view of FIG. 3. It can be easily understood that, with a given rotation speed of the drive roller 20, a linear peripheral speed V.sub.R at the major base and a linear peripheral speed V.sub.P at the minor base are obtained, such that V.sub.R>V.sub.P. Such difference between the peripheral speeds on the drive roller cause the incoming material into the hopper, which adheres to the surface of the roller 20, to naturally move from the lower speed area to the higher speed area.

[0035] This axial driving action, in an upstream direction, tends to lead the material towards the spiral flights of the screw 10 which are further upstream (which is a dead area for the material, in the prior art), facilitating the perfect filling of all the channels between flights of the screw 10. In addition, the dragging effect upstream prevents the incoming material from interacting with the overflowing material which, by contrast, is in the area which is further downstream of the hopper.

[0036] This advantageous effect is also shown in FIG. 4 in comparison to the behaviour of the prior art arrangements.

[0037] The drive roller 20 can be made of metallic materials, whether ferrous or non-ferrous, be solid or hollow, and possibly provided with thermal adjustment means.

[0038] The control of rotation of the drive roller 20 can be made either in a traditional way by direct coupling, by means of gears, with the extruder screw 10 (as shown in FIG. 3), or it may occur by coupling with the same motor-reducer actuating the screw 10 or, still, through independent drive unbound from the rotation speed of the extruder screw.

[0039] Preferably, a cleaning blade or doctor blade (not shown in figures), intended to maintain the surface of the drive roller 20 clean during its rotation, is associated with the roller 20. The positioning of the blade can be fixed or movable in order to stay in contact (or nearly in contact) with the lateral surface of the roller.

[0040] According to one alternative embodiment, not shown in the drawings, the drive roller 20 has a rotation axis Y-Y not perfectly parallel, but inclined, e.g. in the range of 0.1 to 30, with respect to the rotation axis X-X of the screw 10.

[0041] According to another variant, also not shown in the drawings, the geometry of the drive roller 20 is not strictly truncated conical, but the generating line of the rotation solid of the roller 20 is a curved one, e.g., elliptical or parabolic, arranged with a general overall taper ratio with respect to the rotation axis (i.e., the line connecting the two furthest points of the generating curve is tilted with respect to the rotation axis Y-Y).

[0042] As can be understood from the above disclosure, the solution provided by the invention perfectly achieves the purposes stated in the introduction. Indeed, the drive roller of the invention draws the semi-finished material at the entrance of the hopper towards the area upstream of the loading area, which ensures a perfect filling of the channels between flights of the extruder screw 10, as well as minimizes the possibility that the raw material being fed into the hopper comes into contact with the overflowing material formed in the area downstream of the feeding area.

[0043] It has also been experienced that this mode of material feeding, directly in the area upstream of the extruder screw 10, makes it easier to find an optimum rotation speed of the drive roller 20 which produces a self-regulated feeding, so that the operator is no longer forced to continuously correct the dragging action on the incoming material.

[0044] It is understood, however, that the invention is not to be considered as limited to the particular arrangement illustrated above, which represent only exemplary embodiments of the same, but different variants are possible, all within the reach of a person skilled in the art, without departing from the scope of the invention itself, as defined by the following claims.

[0045] In particular, it should be noted that in the description reference has always been made to material fed in the form of strips, but the system of the invention is certainly also suitable for being fed with material in other forms, e.g., in grains.