GB2344060A - Tyre granulator with hydraulic drive - Google Patents

Abstract

A tyre granulator 1 for granulating rubber in a recycling process includes a granulation chamber (24, Figure 2) housing a rotor 11, removably attached to stub shafts 12,13. The rotor has a plurality of flying blades (18a,18b) distributed circumferentially around, and longitudinally along, the rotor. Granulation chamber 24 has an infeed aperture for receiving input tyre material, a longitudinal fixed blade assembly (35, Figure 2) for cooperating with each of the flying blades, and a mesh screen (34, Figure 2). The mesh screen defines apertures for exit of granulated rubber material of the desired grade, or particle size. The granulation chamber defines a volume around the rotor in which infeed material circulates until it is reduced to particulate sizes suitable for exit from the chamber. The rotor 11 is driven by an hydraulic drive unit 14 fed by a variable displacement pump (8, Figure 4) with electronic control (52, Figure 4) in order to significantly reduce the risk of damage to the machine for example by initiating an automatic rotor reversing sequence.

Description

TYRE GRANULATOR The present invention relates to granulation machinery, and in particular to granulation machinery suited for the processing of used vehicle tyres for recycling.

During recent years, there has been much interest in reducing the quantity of rubber, in the form of used vehicle tyres, that is disposed of using conventional methods such as either land fill or incineration. In recent years, many uses for recycled rubber from vehicle tyres have been proposed or are already in use.

However, the recycling of vehicle tyres is a particularly difficult task owing to the nature of the material being processed. In particular, the material comprises a mixture of relatively soft, compressible rubber and high tensile steel in the beading and belts. Thus, complex and very robust shredding, separation and granulation equipment are required which are all subject to extremely harsh operating environments and excessive wear. Ensuring reliability of the recycling equipment is therefore a considerable problem in the industry.

Traditionally, the tyre recycling process requires at least three stages requiring different pieces of equipment. These processes are: (a) preshredding of the tyres, in which the whole tyres are fed into a shredder which, on a single pass through the machine, cuts or shreds the tyres into manageable chunks or strips; (b) separation of non-rubber components such as the steel belts conventionally used to strengthen tyre walls, which is normally carried out using a magnetic separation process; and (c) granulation of the shredded rubber, down to appropriate particle sizes as required for the end use of the recycled material.

For example, one use for granulated tyre rubber is in the creation of sports and play surfaces, where the particle size required is determined according to the construction of the artificial surface being laid.

The present invention relates to the granulation part of the recycling processes as discussed above. Tyre granulation machines typically comprise a granulation chamber having a rotor carrying a plurality of blades thereon, which rotates within the chamber. The granulation chamber has an open top, into which pre-shredded tyres are fed. The sides of the chamber include fixed blades, against which the moving blades chop tyre material within the chamber. The base of the chamber includes a screen having apertures of an appropriate dimension for the grade of rubber granules required.

In operation, chunks of tyre rubber are repeatedly driven around the chamber, by the rotor and moving blades, until cut small enough to fall through the apertures in the screen.

The rotor of a tyre granulator is conventionally driven by an electric motor with appropriate reduction gearing to provide the necessary torque. A problem that arises in conventional granulators relates to the drive system. By the nature of the processing carried out by the granulator, the loading on the drive system is subject to exceptionally high cyclic loads and significant variations in those loads causing high transient forces. This gives rise to excessive vibration and stress in the various components of the machine. In particular, the motor and gearbox would be rapidly damaged under normal variations in loading conditions.

To smooth out the effects of these varying loads and transients, it is customary to include a high inertia flywheel arrangement, intermediate the motor gearbox and the granulator rotor to reduce transient loading on the motor. However, to cater for the rare occurrences of an exceptional load on the granulator system, for example a foreign body entering the system or failure of a component within the machine, provision must be made for emergency disengagement of the flywheel to prevent destruction or severe damage to the machine.

This has traditionally been achieved using a mechanical clutch mechanism or other torque limiting device such as a shear pin arrangement. It has been found that such arrangements are susceptible to problems, particularly in tyre granulators because of the nature of material being processed and mode of use.

Typically, tyre granulators are used in an outdoor environment in dirty and oily conditions and the exceptionally high loads transmitted through the clutch plates require high contact forces between the plates.

In particular, because the granulator may run for extended periods without encountering a transient load sufficient to require the clutch disengagement, and also because of the severe environmental conditions in which the system operates, clutch plates often seize together such that when a critical transient load occurs, a drive shaft or other component may fail before the clutch has operated, if indeed it operates at all.

Similarly, the clutch mechanism itself may be damaged before the drive is properly disengaged.

The alternative use of sacrificial components such as shear pin devices has also been found to be unsuccessful in many cases, because the high and variable loads normally applied through the drive system often cause premature failure of the sacrificial components. Also, the need for disassembly and replacement of such components increases down time of the machine.

It is an object of the present invention to provide an improved tyre granulator which is better adapted to cope with the exceptional loading requirements of the tyre granulation process.

It is a further object of the present invention to generally improve the drive system and other components of the granulator to provide for smoother operation of the granulator and extended lifetime thereof.

It is a further object of the present invention to provide a tyre granulation machine capable of carrying out a granulation process on used tyre material both in its metal screened and unscreened condition, ie. with or without steel and other non-rubber material in the infeed.

Thus, another object is to provide a tyre granulation machine which can be used both for coarse pre-granulation processing of tyres prior to metal separation as well as fine granulation processing after metal separation.

According to one aspect, the present invention provides a tyre granulator for granulating rubber in a recycling process, the granulator including: a granulation chamber housing a rotor, the rotor having a plurality of flying blades mounted thereon, the granulation chamber having an infeed aperture for receiving input tyre material, a fixed blade assembly for co-operating with each of the flying blades, and a mesh screen having apertures defining an exit for granulated rubber material, the granulation chamber defining a volume around the rotor in which infeed material circulates until reduced to particulate sizes suitable for exit from the chamber, an (' drive means for rotating the rotor which drive means comprises an hydraulically powered drive unit.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a schematic plan view of the main moving components of a tyre granulator according to one embodiment of the present invention, including sections through the rotor shaft and outside view of the flying blade assembly; Figure 2 shows a schematic cross-sectional end view of the tyre granulator of figure 1, including detail of the housing and granulation chamber; Figures 3a and 3b show, respectively, front and side elevations of the tyre granulator of figures 1 and 2; and Figure 4 shows a schematic diagram of the motor, pump and control system for the granulator of figure 3.

With reference to figure 1, the tyre granulator 1 comprises a three piece rotor which includes a rotor shaft 11 extending longitudinally between two stub shafts 12 and 13. The rotor shaft 11 is coupled to each of the stub shafts 12,13 using circumferentially spaced, longitudinal bolts 22, 23.

The three piece design makes the removal of the rotor shaft 11 easier. It also enables the rotor to be formed from two different types of materials to optimise the performance and reliability of the granulator. In the preferred embodiment, the two stub shafts 12,13 are formed from a mechanically strong and hard wearing material particularly suited to the bearing loads, while the rotor shaft 11 is formed from a softer, more resilient material with high abrasion resistance and suitability for attaching further components to be described.

The rotor shaft 11 provides a supporting structure onto which are mounted a plurality of cutting blades 18, hereinafter referred to as flying blade assemblies 18a, 18b etc. Each of the flying blade assemblies comprises a mounting plate 20 onto which is bolted a blade 21, thus enabling easy replacement of the blade. Preferably, each blade is of rectangular, square cross-section design thus having four faces each of which may be used as the outer cutting face, in turn, before resharpening of all faces. This reduces operating costs, spare parts overheads and machine down time.

The flying blades 18a, 18b etc are preferably distributed regularly on the rotor shaft 11, both in a circumferentially spaced pattern around the rotor shaft and in a longitudinally spaced pattern along the shaft. The circumferential pattern ensures that the torque loading on the drive shaft is smoothed as much as possible. The longitudinal pattern may be adapted to cause granulated tyre material to migrate towards the centre to minimize wear on the ends of the chamber, or, if desired, towards one end where the chamber may be specially strengthened.

In a preferred embodiment, a total of approximately forty flying blades 18 are used on the rotor shaft 11.

Each of the stub shafts 12,13 is journalled for rotation within respective bearing assemblies 19a, 19b. Stub shaft 12 is at the idle end of the rotor, and stub shaft 13 is at the drive end of the rotor. Bearing assemblies 19a and 19b are mounted in main machine body plates 17a, 17b.

The rotor shaft 11 includes a stepped face at each end to which is attached a wear ring 10 extending around, and projecting from, each stepped face. The circumferential edges of the wear rings 10 are each in close proximity to a respective baffle plate 9 in the granulation chamber to prevent or minimise metal swarf from the granulated tyres from reaching the bearing assemblies 19a, 19b.

The drive end stub shaft is connected to an hydraulic drive unit 14 via a shrink disc coupling 16.

The hydraulic drive unit 14 replaces the conventional electric motor, reduction gear and high inertia flywheel arrangement customarily found on tyre granulators.

The hydraulic drive unit is preferably coupled to main framework of the granulator, or other suitable ground reference point, to provide the necessary reaction force required for the hydraulic motor. This thereby reduces the load on the bearing assemblies 19a, 19b.

Referring now to figure 2, the cross-sectional end view illustrates features of the granulation chamber 24 in which the rotor shaft 11 rotates. The main machine body 32 includes the end body plates 17 (17b shown). A screen cradle assembly 33 defines an exit chamber 25 through which the granulated tyre material falls. The upper portion of the exit chamber 25 includes a mesh screen 34 attached thereto having apertures 39 suitably sized for the desired grade of rubber granules.

Preferably, the screen 34 is readily interchangeable for varying the size of apertures. In preferred embodiments, screen aperture sizes ranging from 14mm to 80mm are used. In a preferred embodiment, the screen is formed from 15mm thick red diamond or similar through-hardened abrasion resisting steel.

Preferably, the entire screen cradle assembly 33 including exit chamber 25 and screen 34 is pivotable about an axis 26 so as to facilitate opening of the granulation chamber 24 for clearing blockages, changing the screen 34 and general maintenance and repair activity. The screen cradle 33 is preferably supported, particularly during the opening and closing operations by a screen pivot ram 27 (partially revealed by cut away section of the end plate 17b). The screen pivot ram 27 supports the screen cradle while locking bolts are removed.

On one side of the granulation chamber 24, a fixed blade assembly 35 includes a mounting plate 40 and fixed blade 41 which extend along the length of the chamber and are positioned so as to be in register with each of the flying blades 18a, 18b in turn, as the rotor shaft 11 rotates.

A series of guide plates 42,43 at the upper end of the granulation chamber form a guiding hopper feed for the pre-shredded tyre material.

A cover or hood over the granulation chamber, as shown in figure 3, may be lifted for blockage clearance and maintenance using a hood lift ram 28 (figure 2).

Within the granulation chamber 24, the chamber walls, including plates 41,42 and end plates 17a, 17b are preferably formed as easily replaceable wear plates.

An overall view of the type granulator apparatus 1 is shown in figures 3a and 3b. The main machine body 32 including the granulation chamber body plates 17, hood 5, and screen cradle assembly 33 is mounted onto a skid frame 2 which can be bolted to a suitable platform, or even be free standing. A fixed chute assembly 6 coupled to the skid frame is provided for directing granulated tyre material to an appropriate collection device, such as a conveyor.

A significant advantage of the present design is provided by eliminating a flywheel and clutch mechanism and by deploying the hydraulic drive unit 14, so that the stability of the unit is improved. Conventional granulators are typically sited on specially prepared concrete aprons to which they can be bolted. The present arrangement requires no concrete foundation and can be winched into free-standing position in a suitable yard space.

In the preferred embodiment, the hydraulic drive unit 14 derives a maximum torque of 56000Nm and rotates the rotor shaft at approximately 73rpm. The hydraulic drive unit 14 is of the radial piston cam curve design and is mounted via the shaft shrink disc coupling 16 to the drive end stub shaft 13, eliminating gears and clutch mechanisms and also heavy flywheel configurations.

With reference to figure 4, the hydraulic power to the drive unit 14 is provided by a 160kW electric motor 7 driving a 501cc/rev piston pump 8 of the variable displacement variety which feeds the drive unit 14 by way of high pressure flexible hoses 50,51. The pump displacement effectively determines the speed of rotation of the granulator rotor.

The preferred hydraulic drive unit 14 as described above provides a peak cutting force of 49000Nm and a maximum cutting frequency of 60Hz with the installed power of 160kW.

An electrical signal is used to control the pump displacement and also to control the forward/reverse operation of the rotor. The operating pressure of the hydraulic pump is controlled by a control unit 52 which is used to effectively limit the forces transmitted within the granulator.

Combined with the much lower inertia of the drive mechanism than conventional granulators, this means that any shock loading of the granulator can be absorbed by the hydraulic drive mechanism and not by the granulator components.

The variable displacement pump is thus pressure compensated so that pressure applied via the hydraulic supply lines is maintained within a control band, thereby providing the required protection of the granulator components. Preferably, a second overload protection is provided by a high pressure switch 53 in the fluid supply hose 50 which, in the event of a predetermined over-pressure condition, shuts off the fluid flow to the pump. Preferably, a third overload protection is provided by a high pressure relief valve (not shown) on the drive unit 14 which, in the event of a predetermined over-pressure condition, diverts fluid flow from the drive unit 14.

In the event of a high transient load on the granulator, eg. by a foreign body entering the granulation chamber, the hydraulic pressure in the fluid supply lines to the drive unit 14 will rise and is detected by a suitable pressure switch coupled to an electronic control system. The electronic control system can initiate immediate shut down or, in the preferred embodiment, initiate an automatic reversing sequence to attempt to free the jammed granulator rotor. In a further arrangement, the control system is also operative to stop any infeed conveyor system during a granulator shut down or reversal.

A suitable hydraulic drive unit for the granulator described above can be readily obtained from a number of sources.

Because the hydraulic pump, motor and control system can be remotely sited from the drive unit 14 and granulator, connected by high pressure hoses, this offers greater flexibility in the construction and positioning of the granulator unit 1 and can significantly reduce the weight of the granulator unit. It also enables the motor and control system to be better protected from the harsh environment of the granulator, its infeed and outfeed systems.

The tyre granulator 1 is preferably provided with a heavy duty conveyor belt infeed which provides pre-shredded tyre material to the top of the granulation chamber 24. The tyre granulator is also preferably provided with a heavy duty discharge conveyor connected to receive granules from the exit chamber 25 and fixed chute 6.

The electronic control system may be fully integrated with such infeed and discharge conveyor systems.

Claims (11)

1. CLAIMS 1. A tyre granulator for granulating rubber in a recycling process, the granulator including: a granulation chamber housing a rotor, the rotor having a plurality of flying blades mounted thereon, the granulation chamber having an infeed aperture for receiving input tyre material, a fixed blade assembly for co-operating with each of the flying blades, and a mesh screen having apertures defining an exit for granulated rubber material, the granulation chamber defining a volume around the rotor in which infeed material circulates until reduced to particulate sizes suitable for exit from the chamber, and drive means for rotating the rotor which drive means comprises an hydraulically powered drive unit.
2. 2. A tyre granulator according to claim 1 in which the rotor comprises a rotor shaft longitudinally intermediate a pair of stub shafts mounted on a supporting structure of the tyre granulator, the rotor shaft being removably attached to the respective stub shafts.
3. 3. A tyre granulator according to claim 2 in which the stub shafts are formed from a relatively more hard wearing material compared with the rotor shaft which is formed from a relatively more resilient material.
4. 4. A tyre granulator according to claim 1, claim 2 or claim 3 in which the granulation chamber further includes a screen cradle assembly forming a lower part of the granulation chamber, pivotable to open the granulation chamber by an hydraulic ram.
5. 5. A tyre granulator according to claim 2, claim 3 or claim 4 in which the plurality of flying blades each include a mounting plate on said rotor shaft and a respective detachable blade having a plurality of cutting surfaces, the blade being adapted for fixing onto the mounting plate in a plurality of orientations, each orientation bringing one of said cutting surfaces into cutting position with said fixed blade during each rotation of the rotor shaft.
6. 6. A tyre granulator according to any preceding claim further including a base having skids for free standing support.
7. 7. A tyre granulator according to any preceding claim in which the hydraulic drive unit is directly coupled to the rotor shaft.
8. 8. A tyre granulator according to any preceding claim in which the hydraulic drive unit is powered by a variable displacement pump.
9. 9. A tyre granulator according to claim 8 in which the hydraulic drive unit further includes a control unit incorporating a pressure sensing device coupled to the hydraulic output of the pump, for limiting the torque which can be applied to the rotor by the drive unit.
10. 10. A tyre granulator according to claim 9 in which the control unit further includes means for automatically reversing the drive unit when a predetermined hydraulic pressure level of the pump has been reached.
11. 11. A tyre granulator substantially as described herein and with reference to the accompanying drawings.