GB2132549A

GB2132549A - Extrusion granulating head

Info

Publication number: GB2132549A
Application number: GB08329541A
Authority: GB
Inventors: David Prikladnicki; Paulo Cesar Soneghet
Original assignee: Pirelli SA Compania Industrial Brasileira
Current assignee: Pirelli SA Compania Industrial Brasileira
Priority date: 1982-11-08
Filing date: 1983-11-04
Publication date: 1984-07-11
Also published as: GB8329541D0; IT8323569A0; BR8206444A; AU2094683A; ES8500803A1; IT1169655B; GB2132549B; ES527435A0

Abstract

A granulator head, for granulating polymeric material for use in electric cable insulation, is provided with a separately mounted drive motor 1 arranged to transmit rotary drive to a pulley of a slidably-mounted bearing unit 6 which drives a shaft 10 floatingly coupled to a blade holder 8 to which cutting blades 7 are mounted for sweeping over a surface of a cutting plate 12, a conveying duct 14 being provided for the flow of material to said surface of the cutting plate (via holes 13). The blades 7 are mounted to the holder 8 at pivots 9, and the floating coupling between shaft 10 and holder 8 comprises a compression spring 11. The slidably mounted bearing unit 6 permits blade adjustment, and the drive motor mounting and spring 11 minimise vibrations, and spring 11 and pivotal blade mounting 9 also minimise wear of the blades 7. <IMAGE>

Description

SPECIFICATION Granulating head The present invention relates to a granulating head particularly applicable for granulating polymers, more particularly elastomers used in manufacturing electric cables.

As is generally known, granulators used at present, although relatively satisfactory for the purposes for which they are intended, nevertheless have certain disadvantages which are detrimental to the quality of the product obtained, and which in addition are difficult to control and give rise to frequent stoppages of production for the purpose of adjustment of components and general over-haul.

One of the most serious problems is in fact an excessive wear of the blades cutting the material to be granulated, this wear not being solely attributable to a natural loss of sharpness suffered by any tool cutting a material, in the present instance cutting the elastomer material, but being also caused by continual loss of adjustment.

This loss of adjustment is usually caused by excessive vibration of the head, which within a short time destroys the original adjustment of the granulator and changes the originally intended quality of the product, that is to say of the granules of elastomer material, these vibrations of the granulator head being almost always caused by the direct coupling of the motor shaft to the shaft of the granulator head.

Another factor which is very prejudicial to the good continuous operation of known granulator heads is an uncontrollable seizing of the cutting unit, which instantaneously stops the rotary movement of the latter, thus subjecting the entire equipment, and in particular the cutting blades, to very heavy instantaneous mechanical stresses.

Seizing of this kind is caused by an excessive accumulation of material undergoing granulation in the conveyor feeding the elastomer material to the cutting plate.

Ali the stoppages mentioned above have hitherto involved a complete dismantling of the granulator head and its readjustment before operation can be resumed.

Moreover, the quality of the granules obtained with known granulators, although unsatisfactory, has been accepted since to a certain extent it meets the quality requirements of electric cables which are to be sheathed with the elastomer.

Nevertheless, present cable manufacturing technology is proceeding in the direction of ever higher cable voltages, so that it is becoming increasingly necessary to obtain granules of the highest quality, that is to say granules having constant dimensions and free from filaments or fine threads.

In accordance with the present invention, there is provided a granulator head provided with a separately mounted drive motor arranged to transmit rotary drive to a slidably-mounted bearing unit which drives a shaft floatingly coupied to a blade holder to which cutting blades are mounted for sweeping over a surface of a cutting plate, and a conveying duct being provided for the flow of material to said surface of the cutting plate.

By mounting the drive motor separately from the granulator head, the latter is isolated from vibrations. Any remaining vibration is however absorbed, in the embodiment to be described, by mounting the blade holder to the drive shaft by a compression spring, thus further isolating the blades from any vibration.

With regard to wear of the cutting blades, this is reduced to a minimum, in the embodiment to be described, by said spring and further by a pivotal mounting of them to the blade holder, thus permitting a certain flexibility of these blades and also their adjustment without interruption of the manufacturing process.

Apart from all this, in the embodiment to be described, with appropriate geometry of the conveying duct in conjunction with the provision in the cutting plate of a number of holes suitably shaped to permit the homogeneous flow of the elastomer material, while in addition drive to the bearing unit is provided by a belt trained around pulleys, it is possible to achieve better and more sensitive regulation of the cutting speed of the granulator head, it is possible to produce granules of elastomer material of higher quality and of constant dimensions, without the formation of fine threads or other irregularities.

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatical side view of a unit which comprises a drive motor and a bearing unit for the granulator head: Figure 2 is a view in longitudinal section of the granulator head; Figure 3 shows a granulation plate, likewise in longitudinal section; Figure 4 shows a detail of a material feed conveyor duct like-wise in longitudinal section; Figure 5 shows in longitudinal section the fully assembled granulator head; and Figure 6 is a view in cross-section of the assembly of Figure 5.

As illustrated in the drawings, the granulator head 2 is provided with a variable speed drive motor 1 (Figure 1) mounted separately from the granulator head 2, while rotary transmission is effected by means of belts 3 connecting a pulley 4 of the motor to a pulley 5 of a bearing unit 6 for the granulator head.2.

With regard to the actual granulator head 2 (Figure 2), this has its cutting blades 7 fixed to a radial blade holder 8 by means of circumferentially-directed pivot pins 9, this blade holder 8 being in turn attached to a tube which telescopically receives a shaft 10, a floating mounting between these two being provided by a compression spring 11 intended to absorb residual vibrations.

The blades 7 are thus urged against a surface of a cutting plate 12 (Figure 3), which plate is provided with a plurality of holes 13 through which the elastomer material to be granulated passes, these holes being arranged in a ring and having dimensions and geometry suitable for permitting a continuous homogeneous flow of material through them.

The elastomer material which passes through the plurality of holes 1 3 in the cutting plate 1 2 has flowed through a conveying duct 14 (Figure 4), the latter having dimensions and geometry suitable for supplying a continuous homogeneous flow, without contraflow, of the elastomer material supplied thereto by an extruder (not shown). In particular the duct 14 has a generally frusto-conical shape with its larger diameter end registering with the ring of holes 13.

Figures 5 and 6 show, in longitudinal and transverse sections respectively, the fully assembled granulator apparatus, and it can also be seen, particularly in Figure 6, that the bearing unit 6 is mounted on a support base 1 5 by means of a longitudinal key 16, thus permitting adjustment of the blades during the production process, without it being necessary to interrupt this process.

Claims

1. A granulator head provided with a separately mounted drive motor arranged to transmit rotary drive to a slidably-mounted bearing unit which drives a shaft floatingly coupled to a blade holder to which cutting blades are mounted for sweeping over a surface of a cutting plate, and a conveying duct being provided for the flow of material to said surface of the cutting plate.

2. A granulator head as claimed in claim 1, in which drive is transmitted from the drive motor to the bearing unit by means of at least one drive belt trained around pulleys mounted to the motor and bearing unit.

3. A granulator head as claimed in claim 1 or 2, comprising a compression spring acting axially between said shaft and said blade holder.

4. A granulator head as claimed in any preceding claims, in which said bearing unit is mounted to a support base by means of a key providing for said slidability.

5. A granulator head as claimed in any preceding claim, in which the blades are pivotally mounted to the blade holder.

6. A granulator head as claimed in any preceding claim, in which the cutting plate is provided with a plurality of through holes for the flow of material to said surface of the plate, from its opposite surface.

7. A granulator head as claimed in claim 6, in which said holes are arranged in a ring over which said blades sweep.

8. A granulator head as claimed in claim 7, in which said conveying duct is generally frusto-conical with its larger diameter end in register with said ring of holes.

9. A granulator head substantially as hereindescribed with reference to the accompanying drawings.