AU684176B2

AU684176B2 - Plastic recycler

Info

Publication number: AU684176B2
Application number: AU26651/95A
Authority: AU
Inventors: David James Horne; Grant Andrew Wride
Original assignee: R H WRIDE Pty Ltd
Current assignee: BUSHMAN POLYPRODUCTS Pty Ltd; Collex Pty Ltd
Priority date: 1994-06-10
Filing date: 1995-06-09
Publication date: 1997-12-04
Anticipated expiration: 2015-06-09
Also published as: AU2665195A

Description

PO/AU 9 5 /0 A RECEIVED 2 5 M 1 PLASTIC REC YCL.ER This invention relates to a method and machine for the recycling of plastic waste materials.

BACKGROUND OF THE INVENTION Items manufactured from plastic materia',s are very widely used throughout the world and the tendency appears to be that many forms of plastics material will be more extensively used in the future. However it is well known that many plastic materials are not bio-degradable and that great problems exist in the disposal of such materials. Often hollow plastic articles are themselves 1 0 deposited in disposal areas, and this assists in producing the large volume of waste which is quickly filling the available disposal areas.

Various attempts have been made in an attempt to overcome the problem, ranging from simply crushing the articles to occupy less volume in the land fill or disposal area, to attempts to recycle the plastic for further use. However as 1 5 far as is known, in the recycling of plastic material, the plastic material has to be manually sorted into the various types of plastic, that is, into thermoplastic material and thermosetting material. However it is often necessary to sort these materials into more specific groups. The thermoplastic materials can be reheated and remoulded into suitable shapes or articles, while the 2 0 thermosetting materials are usually shredded or granulated for further processing which entails the addition of a suitable binder to bind the particles together in either an extruder or mould.

Thus the materials have to be manually sorted, and while most plastic articles have a code number printed or embossed thereon, this has first to be located 2 5 and the material sorted by this number. Error can occur and such errors can be disastrous resulting in the blockage or failure of the processing machine and the consequent complete dismantling of the processing machine so that the offending material can be removed, often by manually chipping away the material. Also in known recycling methods it is often necessary for any labels 3 0 and detritus to be first removed.

AMENDED SHEET

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PCT/AU 9 5 1 0 0 5 4 RECEIVED 2 5 MAR 1996 2 DESCRIPTION OF THE PRIOR ART One known apparatus for the recycling of thermoplastic material is shown in US 4,222,748 which comprises a vertical cylindrical container adapted to be charged with thermoplastic material from the top. At the bottom of the container is a rotatable member with a plurality of knives to rotate about the axis of the container. The material is discharged through an opening in the wall of the container into a screw extruder. The material is disintegrated and blended and softened before being fed into the plasticising screw extruder.

However as disclosed this apparatus is limited in use to thermoplastic 1 0 materials.

BRIEF DESCRIPTION OF THE INVENTION It is an object ot this invention to provide a method of recycling of plastics materials where both forms of plastic materials can be used at the same time without prior manual separation.

1 5 Thus there is provided according to the invention a method for recycling plastics materials including the steps of shredding and/or pulverising with such input energy and for such a time, plastics materials containing both thermosetting and thermoplastics materials such that some of the plastics material only is softened whereby on admixture the softened material binds the remaining shredded and/or pulvelsed material together.

Advantages are achieved by not causing the temperature to be raised past merely softening some only of the plastics materials. Over temperature results in noxious fumes being given off but this implicitly means that the plastics materials being over heated are being oxidised (in effect causing this to burn) 2 5 to form these fumes and this in itself has a result of significantly weakening any resultant cooled material which will as a result be somewhat brittle and lacking in substantial strength. Such a resultant material is of significantly less commercial value. This it is believed has been the reason previously that plastics materials for recycling needed to be separated especially separating 3 0 thermosetting from thermoplastics materials. By controlling the heating effect and accepting that the resultant material when cooled will be formed as a AMENDED SHEET

PEA/AU

RECEI 2PR il 3 matrix with one of the plastics materials only acting to bind the particles of the other plastics, then there is gained the substantial advantage discussed.

In a further form of the invention there is provided a method of recycling a mixture of plastics materials, said method including the steps of feeding a mixture of plastic material into a pulveriser mixing machine having a plurality of shredding mixing blades rotatable about an approximately vertical axis in a cylindrical casing, an opening in the wall of the casing at about a level of the rotatable blades, said opening leading to an auger in a tube positioned tangentially to the casing, the method including the steps of shredding and 1 0 pulverising the material by rotating the blades at a rotational speed sufficient to shred and pulverise the material with such energy and for such a time that only some and not all of the plastics material is softened, the plastics material being heated by friction whereby when heated to a plastic condition (that is to say some and not all of this) then this is expelled through the opening into the 1 5 auger.

Preferably the maximum temperature of the plastics material during the method of recycling is less than 2000C.

Preferably the method includes the steps of regulating the temperature of the extruding material into the auger by heaters positioned on and in relation to 2 0 the extruder.

Preferably the temperature of the material in the pulverising mixing machine is regulated by controlling the rate of addition of plastics material into the cylindrical casing.

Preferably the temperature is judged by a review of the magnitude of current 2 5 being drawn by an electric motor driving the rotating blades and steps taken to modify the temperature of the mixture in accord with such current magnitude.

BRIEF DESCRIPTION OF THE DRAWINGS In order to more fully describe the invention reference will now be made to the accompanying drawings in which: 3 0 FIG 1 is a side view of one form of the invention; AMENDED SHEET

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4 FIG 2 is a plan view showing the arrangement of the auger; and FIG 3 is a plan view partly in section of the shredder and auger.

DESCRIPTION OF THE PREFERRED EMBODIMENT In a preferred form of the invention the apparatus 1 comprises a vertical cylindrical casing 2 detachably attached to a horizontal base 3. Immediately above the base 3 there is positioned a plurality of blades 4 on a rotatable disc connected to a drive shaft 6 extending through the base 3, the drive shaft being driven by an electric motor 7. In alternate form the rotatable disc may be dispensed with, the blades being connected directly to the shaft 6. The blades 1 0 maybe of any desired shape but as shown are generally radial and being curved in the direction of rotation to thus provide a shredding, pulverising, mixing action of the material fed into the casing.

The casing 2 is open at the top to permit the mixture of plastic material to be charged into the casing. In order to ensure that the material during operation 1 5 is not ejected out of the top of the casing, and to ensure that the material is fed directly onto the blades without bridging in the casing, there is provided a central charging chute 8 extending from the top of the casing downwards to terminate above the rotating blades. The annular area at the top of the casing between the charging chute and the casing is closed by an annular cover 9 2 0 attached to the charging chute 8. The cover 9 and charging chute 8 can be lifted and removed from the casing for maintenance and cleaning purposes if and when required.

In this way the material is charged into the centre area of the blades, and when thrown out centrifugally, even it is thrown up by the blades, this will be 2 5 away from the centre of the blades into the annular space between the casing and the charging chute.

An opening 10 is provided in the wall of the casing for the discharge of the plastic material after processing. The opening is positioned in the side of the casing at about the level of the blades, the opening leading to an auger or 3 0 extruder screw 11 positioned tangentially to the casing. The extruder screw 11 operates in a tube 12, the screw being driven by an electric motor through 4 a reduction gearing. This may be via a reduction gear box, or by a belt drive.

-s AMENDED SHEET

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PCr/Au 9 5 0 0 3 4 2 RECEIVED 2 5 MAR 1996 Preferably there are means to vary the speed of the screw, and preferably this is via a variable speed electric motor, although a variable speed reduction gear box can be used the current being supplied to the electric motor being useful as a guide to control the amount of heating of the mixture.

The end of the extruder tube 12 has attached thereto a diverter valve 13 so that the processed material can be selectively directed to either of two outlets.

The outlets may be connected to a mould and in one example the outlets are connected in turn to a tubular mould so that the processed material produces cylindrical, square or rectangular posts, rods or rails. In other examples the 1 0 material is collected in moulds and by pressure various shaped objects can be formed, bricks, rings, discs and the like.

To control the temperature of the plastics material during the extrusion, in order to maintain the extruded temperature, heating elements 14 can be positioned along the extruder tube and the outlets from the diverter valve.

1 5 These heaters can be thermostatically controlled so that they only operate as desired. The material is fed into the loading chute via a belt conveyor 15, the material being shredded, chopped or divided into smaller pieces before loading onto the conveyor.

The temperature at which the material is extruded is in the range of 100oC to 2 0 2000C, the temperature in the embodiment being in the order of 140o0c. If the temperature is too high the processed material can be too fluid, and also the temperature must be below the temperature at which plastic materials ,an decompose and give off noxious gases. This results in a product where moulded and cooled that in the case of all currently known plastics has structural integrity. In order to assist in controlling the temperature, a fan 16 has its outlet connected to the bottom of the casing above the opening to the screw conveyor. Thus the fan preferably is temperature controlled so that it only becomes operative when the temperature of the processed material exceeds an upper limit in the order of 16000.

3 0 It is preferred that the extruder screw be between 500 to 1500 mm, the ideal length being 1000 mm. The screw is to be of a length such that the material is suitably compressed, but if the length exceeds 1500 mm the power and torque required can be excessive resulting in power losses and possible damage to the extruder screw and drive.

AMENDED SHEET IPEA/AL Pcr/A'u 9 5 0 P 3 1 3 RECEIVED 2 5 AR 6 6 In operation the belt conveyor is operated to charge a quantity of material into the casing. The belt conveyor is then stopped, the heaters on the tube and diverter valve be turned on and the motor driving the blades in the casing be activated. The screw extruder is not driven at this stage. The degree of processing of the materials in the casing is monitored. This is achieved by noting the load on the blades on the disc as indicated by the current drawn by the driving motor. As the material is processed, the softened material begins mixing with the finely comminuted material and the material becomes more viscous thus creating a load on the blades a, id motor. This increase on the 1 0 load is indicated by the current flow to the motor and when this reaches a desired level, the extruding screw is driven. The feeding conveyor can also be controlled by the load on the blades, so that it is actuated to add more material when the load is high. Thus the rate of feeding of the material is determined by the condition of the material being processed in the casing.

1 5 It is preferred that the casing diameter be in the range of 300 mm to 2000 mm and the rotor and blades are driven in a speed range of 900 to 2400 RPM, preferably 1480 RPM whereby the material is shredded and pulverised, and during this operation the frictional forces of the shredding and pulverising of the material inside the casing develops heat sufficient only to soften and not 2 0 oxidise the thermoplastic material to the extent that it binds the finely comminuted other plastic materials into a soft mouldable and workable mass.

It appears that the thermoplastic material shrinks or contracts and becomes soft and so is in a condition to bind the other finely commuted material into a coherent mass as a means of keeping the temperature of the mixture within 2 5 the required range.

The speed of the rotor and blades can be varied, and also preferably the speed of the screw conveyor extruder screw is variable to be adjusted to the rate of processing of the material in the casing.

The product which emerges from the extruder screw and while still hot has a 3 0 consistency of putty or workable clay, and so can be moulded, pressed or otherwise formed into any desired shape. On cooling the product is solid, hard, has strength against breakage. As an example it is suitable for the manufacture of fence posts, building bricks, and so is suitable for the manufacture of a large range of products.

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PCt/AU 9 5 0 0 3 4 2 RECEIVED 2 5 MAR 1996 7 Although one form of the invention has been described in some detail it is to be realised that the invention is not to be limited thereto, but can include variations falling within the spirit and scope of the invention.

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Claims

1. A method for recycling plastics materials including the steps of shredding and/or pulverising with such input energy and for such a time, plastics materials containing both thermosetting and thermoplastics materials such that some of the plastics material only is softened whereby on cooling the softened material with adequate strength binds the remaining shredded and/or pulverised material together.

2. A method of recycling a mixture of plastics materials, where the mixture includes both thermosetting and thermoplastics materials, said method including the steps of feeding the mixture of plastics material into a pulveriser 1 0 mixing machine having a plurality of shredding mixing blades rotatable about an approximately vertical axis in a cylindrical casing, an opening in a wall of the casing at about the level of the rotatable blades, said opening leading to an auger in a tube positioned tangentially to the casing, the method including the steps of shredding and pulverising material by rotating the blades at a 1 5 rotational speed and for such a time sufficient to shred and pulverise the material but only to such an extent that some of the plastics material only is softened whereby on admixture the softened material combines the remaining shredded and pulverised material together, and such that when heated to a plastic condition the mixture will be transferred through the opening into the auger.

3. A method of recycling as in any one of the preceding claims further characterised in that the plastics materials are heated only to within a temperature range of from 1000 to 200oC.

4. A method of recycling as in any one of the preceding claims wherein 2 5 the plastics materials are heated by reason of the shredding and pulverising action so as to be raised to and maintained at and not substantially exceed a temperature of approximately 140C. A method of recycling plastics as in anyone of claim 2 or claims 3 or 4 read through to 2, wherein there is the further step of regulating the 3 0 temperature of the extruding material by heaters in conjunction with the extruding auger so as to maintain the temperature at approximately 140o0c while being within the auger.

AMENDED SHEET iOnMA 1A

6. A method of recycling as in any one of the preceding claims wherein the temperature of the plastics material is adjusted by adjusting the rate at which new material is added to the mixture being shredded and pulverised.

7. A method of recycling wherein the rate of addition of further plastics materials to be pulverised and shredded is varied in accord with the magnitude of current being drawn by an electric motor being used to rotate the blades effecting the pulveriser and shredder.

8. A method of recycling as hereinbefore described and with reference to the accompanying drawings. 1 0 Dated this 5th day of September 1997 R H WRIDE PTY LTD By their Patent Attorneys COLLISON CO. 0 f o *o I_