Title of Invention

A COUNTER-ROTATING TWIN-SCREW EXTRUDER FOR WASTE RUBBER RECYCLING

Abstract

The invention relates to a counter-rotating twin-screw extruder for waste rubber recycling comprising a twin barrel (1) mounted in between two flange supports (11) with the help of two flanges (12), a pair of screws (3A, 3B), one left hand (3B) and the other right hand (3A), closely meshed together are fitted inside said twin barrel (1) having a very small clearance with said barrel, characterized in that each screw (3A, 3B) is divided into two zones with two different clearences, the first zone with 1 mm clearance occupying the first 40 % of the screw (3A, 3B) length and called feeding and conveying zone (17) and the second zone with varying clearance (1 to 0.5 mm) occupying 60 % length of the said screws (3A, 3B) is called compaction and pumping zone (18) for de-cross linking of rubber and expel out the air from waste rubber powder through the feeding zone during start of compaction, both screws (3A, 3B) are hanging at the delivery end with conical tips, and a detachable die assembly (4) having a small orifice (19) at the centre of said die assembly (4) is fitted to the twin barrels (1) at the end of twin screws (3A, 3B), the said screws (3A, 3B) at the other end are mounted in a housing (13) and the left handed screw (3A) is connected to the drive motor through a speed reduction gear (5) chain drive assembly (6) and the said left handed screw (3A) rotates the right handed screw (3B) in the opposite direction being closely meshed together, a feed hopper assembly (2) is provided on the barrel (1) at the beginning of the feeding and conveying zone (17) for regulated feeding of waste rubber and a barrel heating (7) and cooling (8) are provided along circumference of said barrel.

Full Text

The invention relates to a counter rotating twin-screw extruder for waste rubber recycling and more particularly to a counter rotating twin-screw extruder for thermo-chemical shear extrusion for recycling waste rubber in powder or granular form. The disposal of worn out tyres and rubber products is a global problem as they are not biodegradable. The waste rubber cannot be processed like thermoplastics, as it is cross-linked,. In 1999, India consumed 6,20,000 metric tonnes of Natural Rubber (NR) but produced only 64,125 metric tonnes of NR reclaim. Thus , only .12% of the consumed NR is recycled usefully, while the rest remains in the environment causing pollution. The waste tyres at present are disposed by (1) Pyrolysis, (2) Reclaiming by chemical processes; and (3) Incineration, Landfill, etc.. PRIOR ART Presently, the following rubber reclaiming processes are used. PAN PROCESS The ground rubber powder is mixed with various reclaiming oils and inserted into an autoclave. It is then subjected to steam pressure for a period of time to get reclaim rubber. DIGESTER PROCESS This process uses a steam vessel equipped with a paddle agitator for continuously stirring the crumb rubber while steam is being applied,, The wet process uses caustic and water mixed with the rubber crumb while the dry process uses steam only. Varius reclaiming oil are added to get the reclaim rubber. RECLAIMATOR PROCESS Fine rubber crumb of 30 mesh size is mixed with various reclai- ming oils and subjected to high temperatures with intense mecha- nical working in a modified single screw extruder for the devul canisation of the rubber scrap. U I. T R A S O N1C P R 0 C E S S A sing1e screw extruder i s used to give a uniform feed of rubber crumb into a horn where the crumb is subjected to ultrasonic waves, which causes the devulcanisation. DELINK PROCESS This process involves the direct devulcanisation of rubber crumb by the addition of 7 phr of a patented devulcanisation agent o called DeLink, and masticating the mass at 7ØC for 1Ø minutes in the presence of 2 phr plasticizer and 6 phr of virgin Natural Rubber. There are disadvantages associated with the present system of waste rubber reclaiming processes. One of the main disadvantage is that the yield is poor and these processes are costly. Another disadvantage associated with the present system of waste rubber reclaiming is that these processes presents serious health hazards - Yet another disadvatage associated w i t h the present system o f waste rubber reclaiming is that rubber obtained by severing the crosslinks by chemicals is normally of poor quality and only about 15% of it is being recycled. At present, there are no known commercial processes for effective and large scale waste rubber recycling. SUMMARY OF THE INVENTION Therefore, the main object of the present invention is to provide a counter-rotating twin-screw extruder for waste rubber recycling which is a continuous devulcanisation technology for volcanised rubbers recycling having high yield with lower cost. Another object of the present invention of waste rubber reclamation is to provide an apparatus and a method to produce devulcanization of the waste rubber which gives better mechanical properties of vulcanizates. Upto 70 % of the waste rubber reclaimed from the proposed process can be recycled giving vulcanizates having upto 16 MPa tensile strength and 350 % elongation at break. Yet another object of the present invention of waste rubber reclamation is to provide a counter-rotating twin-screw extruder which uses a continuous devulcanisation technology. In this process, the breakage of carbon-sulphur crosslinks occur selectively under combined action of shear stress, high temperature and chemicals. According to the present invention, there is provided a counter rotating twin-screw extruder for waste rubber recycling comprising a twin barrel mounted in between two flange supports, a pair of screws, one left hand and the other right hand, closely meshed together are fitted inside said twin barrel having a very small clearance with said barrel, characterized in that each screw is divided into two zones with two different clearances, the first zone with 1 mm clearance occupying the first 40 % of the screw length and called feeding and conveying zone and the second zone with varying clearance in the range of 1 mm to 0.5 mm occupying 60 % length of the said screws is called compaction and pumping zone for de-cross linking of rubber and expel out the air from waste rubber powder through the feeding zone during start of compaction. Both screws end with the conical tips at the delivery end. A detachable die assembly having a small orifice at the center of said die assembly is fitted to the twin barrels at the end of twin screws, the said screws at the other end is mounted in a housing and the left handed screw is connected to the drive motor through a speed reduction gear assembly and said left handed screw rotates the right handed screw in the opposite direction being closely meshed together. A feed hopper assembly is provided on the barrel at the beginning of the feeding and conveying zone for regulated feeding of waste rubber and electrical heating and air cooling arrangement are provided along circumference of said barrel. BRIEF DESCRIPTION OF THE INVENTION The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non-limiting exemplary embodiments of the invention represented in the accompanying drawings. The invention is described in detail with reference to the accompanying drawings:- Figure 1 shows schematically the counter rotating twin-screw extruder; Figure 2 shows the sectional view of the twin barrel; Figure 3 shows the arrangement of twin-screw with two zones; Figure 4 shows the twin-screw extruder layout; Figure 5 shows the sectional view of the housing; Figure 6 shows the GM bush DESCRIPTION OF THE INVENTION This invention , Counter-Rotating Twin-Screw Extruder for waste rubber recycling, consists of two modular screws (3A,3B) lying side—by—side in a common bar-real (1) in a figure of eight pattern. The two screws (3A,3B) rotate in opposite directions to each other. The two screws (3A,3B) are completely intermeshing with each other, thereby one screw wipes its mate completely and the feed material is pumped forward by positive displacement. The counter-rotating twin-screw extruder is an assembly of following parts and is described with reference to Figs.1-6. The two screws (3A,3B) are mounted side—by—side and fits inside a hollow cylinder called barrel (1) as shown in Figs, .1 & 2. The internal diameter of the barrel (1) is 39mm having two circular cylinders connected in the shape of 8. The barrel (1) is made of gun metal to withst and tbe high stresses deve1oped during shearing of the rubber . The feed hopper assembly (2) of Figs.1 & 2 consists of a hand operated rotating feeder screw (16) mounted vertically inside a conical feed chute (14). With each turn of the screw (16) inside the hopper, a uniform amount of rubber powder is fed into the barrel (1). The feeder screw (16) is supported on a steel frame on the conical feed chute (14) and is operated manually with the help of a wheel (15) and handle (2Ø). The two screws (3A,3B) are made of mild steel and their surfaces are machined to have thin flights through which the material is conveyed. these are forward pumping right handed (3B) and left handed (3A) combinations of the two screw (3A,3B) elements. The two screws (3A,3B) fit inside the cylindrical barrel (1) closely and have s very small clearance with the barrel (1). Each screw (3A,3B) is divided into two zones (17,1S) with two different clearances,, The first zone (.1.7) with 1mm clearance occupying the first 40% of the screw length is called feeding and conveying zone. The next zone (18) with a varying clearance in the range of 1 to Ø.5mm occupying the remaining 6Ø% of length of the screw (3A,3B) is called compaction and pumping zone where maximum shearing action takes place. The axial distance of one full turn of the screw (3A,3B) called the pitch, is 17.5mm. This optimum design is chosen for higher degre e o f f i11 and maximum conveyance rate. The distanc e b e t ween the root surface of the screw0 (3A,3B) and the internal surface of the barrel (1) is 5mm. The axial distance between flights is 17.5mm. The width of the thin flights is 2.Ømm. The flights move forward with a helix angle of 17.66 degrees. The length to diameter (L/D) ratio of the screws is 10:1 . Both screws are hanging at the discharge end with conical tips. The rotational speed of the screws (3A,3B) is measured by an inductive proximity switch, which can measure in Ø-150 rpm range. A detachable circular die assembly (4) as shown in Figs..I & 4 which is a circular metal plate with a small orifice (19) at the center is fitted at the discharge end of the two screws (3A,3B). This enables the exit of the processed rubber powder as a soft and loosely bound rod. The extruder drive assembly comprises of a DC motor (not shown) drive system. The motor turns; the extruder screws (3A,3B) at the desired speed vis a reduction gear- (5) and a chain transmission assembly (6). The motor supplies the required amount of torque to the shaft of the extruder. A 3-phase AC power supply with rectifier circuit is the input for the DC motor. The motor used is a 3 HP continuous rating BE DC motor with maximum speed of .1.5ØØ rpm. The speed is variable by a rheostat arrangement. Speed reduction gear assembly of Fig.l consists of a reduction gear (5) with a 1Ø:1 reduction ratio which is used to drive the extruder system at the required speed. The gear box and the motor are mounted and aligned together with the barrel screw assembly on a common frame. Barrel heating is shown in Fig.l and consists of heating of the extruder for bringing the machine up to the proper temperature for start up and for maintaining the desired temperature under normal operations. This is done by an electrical heating. A cylindrical heating cartridge (7) is placed along the circumference of the barrel (1). The temperature range is from o o room temperature to 25Ø C. A thermocouple (9) of 0-250 C with good response is fitted at the exit end of the barrel (1) for accurate temperatur e measurernent. Barrel cooling is shown in Fig.l and is switched on when the temperature of the barrel crosses the set temperature, heating is switched off and cooling is necessary to maintain it. This is done by air circulation at an inlet of the air chamber (8) over the cartridge (7). An AC motor is used for air blowing. Temperature control system shown in Fig.l is an on-off type control system which is used to maintain the temperature control of the barrel (1). The thermocouple (9) is connected electroni-cally to the airblower. From the control unit, a signal is sent to the air blower to blow air through the air chamber (8) which in turn adjusts the temperature such that the temperature control o is within + 2 C. The twin screws (3A,3B) are mounted in a GM bush assembly (10) of the housing (13) as shown in Figs. 1,4 & 5. The housing (13) is bolted to the flange support (11) with the help of a flange (12). Figs.4 & 5 show details of the housing (13) and GM bushes (10). The barrel (1) and screw assembly is mounted at two ends on two flange supports (11) with the help of a flange (12). The counter rotating twin-screw extruder for waste rubber recy-cling is a continuous devulcanisation technology for vulcanised rubbers recycling. In this process, the breakage of carbon-sulphur crosslinks occur selectively under the combined action of shear stress, high temperature and chemicals. The extruder is designed with a screw feeder hopper for uniform input, two counter rotating screws with two different zones, s circular die at the e>:it and temperature and screw speed control systems. The zonc?s are (i) feeding ang conveying zone, and (ii) compaction and pumping zone. The first zone has the constant cross section area whereas the second zone has progressively decreasing cross section area. The process is investigated with variation in parameters like, concentration of chemicals, temperature and speed of rotation of screw. Optimum temperature for extruder o operation is 17Ø C while using disulphides as devulcani sing agent. The extrudate has been re vulcanised with and without virgin natural rubber (NR) using sulphur vulcanisation systems. After mixing the extrudate with the virgin natural rubber in the ratio of 70:30, we get a tensile strength (TS) of .1.6 MPa, and elongation at break (EB) 465% and the sample without NR gives TS = .1.6 MPa and EB = 370. These properties are far better than obtained by any other commercially available devulcanised waste rubber powders. Thus, the extruder design is quits? effective to modify the waste rubber, which can replace about 70% of the virgin NR in various applications, like tyre tread, conveyor belts, rubberised sports-ground, mats, roofing, etc. . The invention described hereinabove is in relation to non-limiting embodiment and as defined by the accompanying claims. WE CLAIM 1. A counter-rotating twin-screw extruder for waste rubber recycling comprising a twin barrel (1) mounted in between two flange supports (11) with the help of two flanges (12), a pair of screws (3A, 3B), one left hand (3B) and the other right hand (3A), closely meshed together are fitted inside said twin barrel (1) having a very small clearance with said barrel, characterized in that each screw (3A, 3B) is divided into two zones with two different clearances, the first zone with 1 mm clearance occupying the first 40 % of the screw (3A, 3B) length and called feeding and conveying zone (17) and the second zone with varying clearance (1 to 0.5 mm) occupying 60 % length of the said screws (3A, 3B) is called compaction and pumping zone (18) for de-cross linking of rubber and expel out the air from waste rubber powder through the feeding zone during start of compaction, both screws (3A, 3B) are hanging at the delivery end with conical tips, and a detachable die assembly (4) having a small orifice (19) at the centre of said die assembly (4) is fitted to the twin barrels (1) at the end of twin screws (3A, 3B), the said screws (3A, 3B) at the other end are mounted in a housing (13) and the left handed screw (3A) is connected to the drive motor through a speed reduction gear (5) chain drive assembly (6) and the said left handed screw (3A) rotates the right handed screw (3B) in the opposite direction being closely meshed together, a feed hopper assembly (2) is provided on the barrel (1) at the beginning of the feeding and conveying zone (17) for regulated feeding of waste rubber and a barrel heating (7) and cooling (8) are provided along circumference of said barrel. 2. The counter rotating twin-screw extruder as claimed in claim 1 wherein the barrel (1 ) :is made of gun metal. 3. The counter rotating twin—screw extruder as claimed in claim 1 wherein the feed hopper assembly (2) comprises a conical feed chute (14) with straight end fitted to the barrel (1) and is provided with a feeder serew ( 16) with a wheel (15 ) and hand1 e (20) at the top. 4. The counter rotating twin-screw extruder a is claimed in claim 1 wherein the screws (3A,3B) are made of mild steel having a pitch of 17 .5mm and a helix angle of 17 .66 degrees. 5. The counter rotating twin-screw extruder as claimed in claim 1 wherein the length to diameter ratio of the screws (3A,3B) are 10:1. 6. The counter rotating twin—screw extruder as claimed in claim 1 wherein the barre1 heatin g is provided by a cy1indrica1 elecrica1 heater cartridge (7) placed along the circumference of said o barrel ( 1 ) up to a temperature of 250 C. 7. The counter rotating twin-screw extruder as claimed in claim 1 wherein cooling of the barrel to maintain a particular temperature of is provided by air circulation through the said a i r chamtaer (8) . 8. The counter rotating twin-screw extruder as claimed in claim 1 wherein the temperature control system comprises a o thermocouple (9) of Ø-25Ø C range fitted at the exit end of the barre1 ( 1 ) . 9. The counter rotating twin-screw extruder as claimed in claim 1 wherein the twin screws (3a,3B) &re mounted in GM bushes (1Ø) of the housing (13) at the feed end of the barrel (1). 10. The counter rotating twin-screw extruder as claimed in claim 1 wherein said circular die assembly (4) fitted at the barrel (1) at the delivery end is detachable having an orifice (9) at the c e n t r e o f s a i d circu1ar die ( 4 ) . 11. The counter rotating twin-screw extruder as claimed in claim 1 wherein a reduction gear (5) with a 1Ø:1 reduction ratio and a chain transmission (6) are provided to drive the extruder at the required speed. 12. A counter rotating twin-screw extruder for waste rubber recy-cling as herein described and illustrated with the accompanying drawings. The invention relates to a counter-rotating twin-screw extruder for waste rubber recycling comprising a twin barrel (1) mounted in between two flange supports (11) with the help of two flanges (12), a pair of screws (3A, 3B), one left hand (3B) and the other right hand (3A), closely meshed together are fitted inside said twin barrel (1) having a very small clearance with said barrel, characterized in that each screw (3A, 3B) is divided into two zones with two different clearances, the first zone with 1 mm clearance occupying the first 40 % of the screw (3A, 3B) length and called feeding and conveying zone (17) and the second zone with varying clearance (1 to 0.5 mm) occupying 60 % length of the said screws (3A, 3B) is called compaction and pumping zone (18) for de-cross linking of rubber and expel out the air from waste rubber powder through the feeding zone during start of compaction, both screws (3A, 3B) are hanging at the delivery end with conical tips, and a detachable die assembly (4) having a small orifice (19) at the centre of said die assembly (4) is fitted to the twin barrels (1) at the end of twin screws (3A, 3B), the said screws (3A, 3B) at the other end are mounted in a housing (13) and the left handed screw (3A) is connected to the drive motor through a speed reduction gear (5) chain drive assembly (6) and the said left handed screw (3A) rotates the right handed screw (3B) in the opposite direction being closely meshed together, a feed hopper assembly (2) is provided on the barrel (1) at the beginning of the feeding and conveying zone (17) for regulated feeding of waste rubber and a barrel heating (7) and cooling (8) are provided along circumference of said barrel.

Documents:

00208-cal-2001-abstract.pdf

00208-cal-2001-claims.pdf

00208-cal-2001-correspondence.pdf

00208-cal-2001-description (complete).pdf

00208-cal-2001-drawings.pdf

00208-cal-2001-form 1.pdf

00208-cal-2001-form 13.pdf

00208-cal-2001-form 18.pdf

00208-cal-2001-form 2.pdf

00208-cal-2001-form 3.pdf

00208-cal-2001-form 5.pdf

00208-cal-2001-gpa.pdf

00208-cal-2001-letter patent.pdf