GB2524842A - Roll mill and method for reclaiming of a cured elastomer material - Google Patents

Abstract

A roll mill 100 features a pair of rollers 2,4 mounted closely adjacent one another, with a preset gap between them, a first pair of bearings 6,14 (614) and second pair of bearings 18,18 (20,20) mounted in two fixed frames 10,12, supporting shafts 8,16 (8,16) of the rolls 2,4. A pair of spacers 30,30 are between the second pair of bearings 18,18 (20,20). The spacers 30,30, which may be interchangeable for other shapes and/or sizes, may provide accurate and tight control of the gap between the rollers 2,4, as also may the frame members 10,12. The rollers 2,4 may be separately driven. The roll mill 100 may be used for the disintegration of rubber crumb from tyres.

Description

RoH miH and method for redaming of a cured elastomer materia

BACKGROUND

The present invention relates to processing machines, and more particularly to roll mills useful for grinding and reclaiming rubber or similar material.

There are a lot of plants in the world (ca 1200), which produce rubber crumb from the scrap tires. Most of them are dealing with the treatment of waste rubber by collecting, sorting and breaking it down to the required size as defined by the end user. Yet very few rubber industrialists deal with reclaiming and de-vulcanization.

However, at present the most acute challenge is what to do with this rubber crumb.

According to published data, 51 % of crumb is incinerated, 43 % is added to asphalt and only 6% are rejuvenated as new raw rubber material.

Various machines and technologies are used for production of cured rubber crumb.

One of the common known approaches is based on knife cutting as disclosed by patents US 5,695,131; US 5,299,744 and US 7,021,576. Multi-knife shredder or rotor knife mill are widely used in rubber recycling. Though this technique provides relatively high productivity, it yields only rough crumb and, in addition to that, cut crumb is contaminated by metal impurities.

Technique involving freezing of rubber (cryogenic methods) prior to or during processing in mills are known in the art. us patent us 4,813,614 and GB patent 1559152 disclose cryogenic grinding between two wheels provided by a set of crushing pins. US patent US 4,383,650 discloses grinding of frozen material between two toothed wheels. It is also known cryogenic milling in vibration mill or a rotary blade mill, where the material is maintained cooled below -60.degree C by supplying a coolant, particularly liquid nitrogen or carbonic acid. Cryogenic grinding provides rather fine particles with minimum impurities. However, extremely high cost of liquid nitrogen makes cryogenic methods uneconomical. Besides, cryogenic technology does not allow devulcanization by chemical agents, because these reactions do not occur at low temperatures.

In the last decades use of extruders for rubber grinding has been developed widely, as disclosed in US patent US 6,590,042; US 6,576,680 and US 6,335,377. Extruder could operate within a wide range of temperatures (up to 3000 C) and provides sufficient productivity. The great skill is required for adjusting the mill to achieve optimum results by this technology, because the material is intensely heated during processing in the mill and the extruder. Thus, a great amount of heat energy must be dissipated by water-cooling.

Disadvantages of this technique are: lack of possibility for ultra-fine grinding because clearance between screw and walls cannot be performed tightly enough; unfeasibility for effective cooling of solid bulk of processed material; extreme energy consumption.

Attrition or disc mills for rubber grinding also are known in the art. US patent us 4,535,941 for example, discloses grinding at horizontal mill, similar to those used in pigments industry. Later us patent of the same inventor, US 4,625,922 discloses improved technique, of grinding at elevated temperatures. This technique suffers from unfeasibility of continuous process. In order to overcome this drawback, it was proposed to perform rubber grinding in flow of liquid slurry (water, oil, etc.) as described in US patents Us 5,238,194, US 5,411,215 and US Patent Application US 20020086911. sufficient continuity could be achieved; however necessity in consequent drying of the produced crumb makes such a process impractical.

Construction of disc mill for grinding rubber between grinding wheel and shroud is also disclosed in US patent U5 6,976,646. setting of uniform clearance between wheel and shroud along entire perimeter of working zone at this design is problematic.

Construction of improved disc mill apparatus for grinding rubber between grinding wheel and flat stator is disclosed in PCI patent application No. PCI/I L2009/001206 -W02011077422. The apparatus (LIM) comprises a stator and a rotor in near face-to-face relationship with each other forming an operating zone for rubber grinding and reclaiming therebetween. The stator has a substantially flat smooth face surface and the rotor has a concave face surface with a depth gradually decreased from a center to a periphery thereof. The rotor further comprising at least one curved protrusion with a radius of curvature gradually increased from the center to the periphery of the rotor.

Breaking or grinding two-roll mills also are used for size reduction of rubber chips.

This technique is based on passing rubber chips through tight gap between rotating rollers and is widely used in the recycling industry. US Patent No. 6,831,109, for example discloses technology of rubber devulcanization based on multiple passing of raw rubber material mixed with special additives (modifier) through narrow gap of 2-roll mills.

For a variety of reasons, the rolling mill often runs empty, i. e. there is no product tracked. Then the rollers run against each other and could rub against each other because of the different peripheral speed, which can lead to damage to the roll surfaces.

Various improved designs of two-roll mills are known in the art. For example in order to prevent rolls rubbing against each other and make gap adjustable, means for displacement of at least one of the rolls toward and from another roll is used. It prevents the rollers running against each other and rubbing against each other because of the different peripheral speed.

In order to adjust gap width and to generate the necessary grinding the bearings of the rolls could be loaded by means of hydraulic system. While operating, rollers are adjusted for a very small gap and while runs empty, the hydraulic system "opens" the gap.

DE4323230C1 discloses roll mill for comminuting plastics, in particular polyurethane plastics, for reuse that combines displaceable rolls operable by hydraulic system with rolling-contact bearings defining the desired minimum gap width. Static roll of roll mill is provided with rolling-contact bearings having a peripheral ring with the radius being greater by the desired minimum gap width than the radius of the rolled section.

Such a construction with rolling-contact bearing requires expensive large diameter bearings, with enhanced sealing and high precision treatment of adjacent roll surface.

Therefore, a need still exists for an improved technique of producing commercially reusable rubber material by providing a simple, reliable, low-cost roll mills for performing continuous, cost-effective and generally ambient temperature process.

SUMMARY OF THE INVENTION

According to the invention a roll mill comprises two rolls mounted in a fixed frame and providing a desired stable dynamic nip through which material may be passed, The object is to improve the rolling mill of the type mentioned above, that between the rollers always remains a gap to avoid the collision rubbing the rollers, which on the other hand ensures a trouble-free restart of its length here.

According to one broad aspect of the present invention, proposed is a roll mill comprising a pair of rolls mounted closely adjacent one another to define a preset gap therebetween, first pairs of bearings mounted in two fixed frames and supporting shafts of the rolls. Each of pairs of bearings is pulled together. Second pairs of bearings mounted on the shafts, and a pair of spacers inserted between the bearings of the second pairs of bearings thereby providing the preset gap between the rolls through which material to be processed may be passed.

According to still another aspect of the present invention preset gap is ranging from about 0.1 mm to about 0.5 mm and preferably is about 0.2 mm.

According to another general aspect of the present invention, there is provided a method of reclaiming of a cured elastomer material performed by the roll mill which comprising a pair of rolls mounted closely adjacent one another to define a preset gap therebetween, first pairs of bearings mounted in two fixed frames and supporting shafts of the rolls. Each of pairs of bearings is pulled together. Second pairs of bearings mounted on the shafts, and a pair of spacers inserted between the bearings of the second pairs of bearings thereby providing the preset gap between the rolls through which material to be processed may be passed.

According to another aspect of the present invention method of reclaiming of a cured elastomer material is performed while a linear speed of the slowest roll is in the range of 7-40 meters per minute.

According to still another aspect of the present invention a method of reclaiming of a cured elastomer material is performed with a friction value between 1.8 and 3 and preferably with friction value of about 2.5.

According to still another aspect of the present invention a method of reclaiming of a cured elastomer material is performed under controlled temperature. Preferably controlled temperature is ranging from about 40 degree to about 60 degree of Celsius.

The invention may and be performed in various ways and specific embodiments, with possible modifications, will now be described with reference to the accompanying drawing which is a schematic view.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top partially sectional view of a roll mill showing an example of the present invention; FIG. 2 is a sectional view along axis A-A of FIG. 1 showing a schematic example of spacer, and FIG. 3 is a sectional view along axis B-B of FIG. 1 showing a schematic example of fixed frame mounting.

DESCRIPTION OF THE INVENTION

Generally the two-roll mill described herein may be utilized for grinding and recycling of different materials. Additionally, while the example disclosed herein is described in connection with the grinding and reclaiming of crumb rubber in the automotive tire recycling industry, the example described herein may be more generally applicable to different milling operations for different purposes.

Referring to the drawings a roll mill 100 comprises two rolls 2 and 4 rolls mounted closely adjacent one another to define a preset gap N therebetween. Rolls 2 and 4 rolls are mounted for rotation about their axes in a common preferably horizontal plane. Material to be processed is fed to gap N and passed there-through between rolls 2 and 4. Pair of bearings 6 and 6'support roll 2 shafts Sand 8' in a fixed frames and 12 accordingly and pair of bearings 14 and 14 supports another roll 4 shafts 16 and 16' in the same fixed frames. Fixed frames 10 and 12 could be mounted on roll mill base (not shown) and pull togetherorties up rolls 2 and 4 as will be described further below.

Two bearing blocks each including a pair of bearings 18 and 18'and 20 and 20' are mounted on roll's shafts 8 and 8' and shafts 16 and 16" accordingly. Spacers 22 and 24 are mounted (inserted) between bearings 18 and 18'and 20 and 20' accordingly for preventing contact between rolls 2 and 4 and providing desired preset gap (nip) N therebetween.

Referring to FIG. 2 spacer 22 has surfaces 30 and 30'at both sides adjacent to corresponding bearings 18 and 18'preferably with the same curvature as the curvature of the outer rings 32 and 32' of bearings 18 and 18 accordingly. Only spacer 22 is illustrated in Fig. 2 but spacer 24 has substantially the same configuration. Thus, spacers 22 and 24 are supported or cradled for almost half of their circumference. Such construction of spacers enables their self-aligning and tight fixation of outer rings of bearings for providing stable and reliable preset gap during operation (dynamic nip N) of roll mill. Between the rollers always remains a gap and collision and rubbing-together of the rolls rotating at different circumferential speeds during idling of the mill could be eliminated.

Referring to FIG. 3, construction of fixed frames 10 and 12 (only one frame lOis shown) is illustrated in more details.

In one preferred embodiment, (as illustrated in FIG. 3), each frame 10 and 12 could be formed by two U-shaped flanges 40 and 40' fastened, e.g. by rod/nut pairs, bolts, screws, etc. U-shaped flanges preferably have internal surfaces 42 and 42' with the same curvature as the curvature of the outer rings 44 and 44' of supported bearings 6 and 14 accordingly. Thus, rolls 2 and 4 are pulled together or tied up by fastening flanges 40 and 40' with mounted therein bearings 6 and 14. Flanges 40 and 40' could be fastened by using rods 46 and nuts 48 pairs.

Flanges are usually made of steel with appropriate characteristics resistance, allowing able to withstand the forces subjected rolls during operation of the mill rolls.

Preferably, rolling-element bearing e.g. ball bearings or roller bearings could be used. A lubrication system is optional.

Preferably, rolls 2 and 4 are made from hard casting and have substantially smooth surfaces.

According to still another embodiment, at least one of the rolls 2 and 4 could be made hollow or provided by channels for liquid or gas circulation. Such a construction enables roll(s) either be internally heated or cooled by passing e.g. steam or liquid/gaseous coolant accordingly. Alternatively, local external air conditioning of working area (gap) of roll mill could be used. Preferably, cold water could be used as liquid coolant. According to one embodiment of the present invention temperature in the working area (gap area) should not exceeding 40-60 degrees of Celsius.

The roll axes are parallel and preferably horizontal. The gap between the rolls allows the rubber to pass through to achieve grinding and devulcanization caused by the shearing action in the gap.

Preferably, each roll 2 and 4 could be rotated at constant speed by separate independent drive mechanisms e.g. using electric motors with or without gear (not shown). Electric motor(s) could be controlled electronically by appropriate controllers. The independent drive of each roll enables the friction ratio (the speed difference between the circumferences or surfaces of the rolls) to be controlled and varied during the operation.

Variable speed motors with frequency control or torque motors can be used. A variable speed motors for each roll in addition to providing desired friction ratio, also enables controlling speed of rolls in order to obtain desired quality of end product and roll mill capacity.

Speed of rolls could be characterized by two parameters: Angular speed n measured in revolutions per minute (rpm) and linearspeed V measured in meters per minute (rn/mm).

Linear speed V could be calculated by standard formulas: V = R*n*6.3 meter per minute, where R is radius of roll (m) and n is its angular speed (rpm). It was discovered by the inventors that appropriate quality of devulcanization and acceptable production capacity could be obtained within specific range of rolls' speed. Preferably, linear speed V of "slow" roll could be in the range of 7-40 meter per minute. The speed of another roll could be defined based on desired friction ratio.

It is clear that, the faster rolls speed provides higher capacity of the roll mill.

However, due to decreasing time of processing between the rolls and quality of end product could degrade. On the contrary, the lower the linear speed could provide better quality of the end product while capacity is decreased. From the above reasoning, one could define desired optimal combination for these parameters based e. g. on the type of raw material and desired quality of end product According to the present invention, most efficient grinding and devulcanization is reached at relatively high values of friction due to optimal shear-stress deformation values.

Based upon numerous experimental data, optimal range for friction could be from about 1.8 and up to about 3. Preferably, friction value of about 2.5 could be used.

Simple and rigid construction according to the present invention provides stable narrow working distance between rolls 2 and 4 during operation, so called "dynamic nip" that is required for rubber recycling.

Preset gap and dynamic nip accordingly can be varied, typically between 0.1-0.5 mm by providing appropriate spacers 22 and 24. Preferably according to the present invention dynamic nip of about 0.1 mm is used.

Conventional mixing/sheeting/warming roll mills operate at relatively large clearance between rolls (gap). Hence, difference between gap at operating and idle state for these mills is insignificant and may be neglected. Contrary, for small gap values working range 0.1-0.5 mm, change by 0.01 mm is equal to 10-20% from nominal. For initial crumb of <2 mm size, static gap at roll mills could be set as regular 0.1 mm. It could be further adjusted in accordance with measurement of dynamic nip and monitoring on process.

For initial processing (at first or initial roll mill) of crumb of> 2 mm size larger static gap could be set up, e.g. at level of about 0.3.0.5 mm.

Dynamic nip depends on outward thrust, on rigidity of parts of gap adjustment device and on compression set of rubber at high pressures.

Diameter and length of rolls do not influence quality of reclaim, but rather define productivity of process According to the present invention, rubber waste material in form of pieces of chips (crumb) or optionally mixture of said pieces with addition of chemical modifier could be continuously fed by appropriate feeder means (screw, belt conveyor, etc.) into gap N of roll mill. Upon passing through gap, rubber waste material is compressed and sheared (grinded) to smaller mesh size crumb particles. Ready material after processing can be evacuated by appropriate transporting means, e.g. belt conveyer, etc. Preferably, in orderto provide high level of devulcanization of grinded rubber, raw rubber waste material could be treated in accordance with co-pending PCI application PCT/1L2009/000808 the disclosure of which is incorporated by reference herein.

In that case rubber waste material in form of pieces of chips (crumb) could be previously mixed with modifier of PCT application PCT/1L2009/000808 in the dry state and further charged into the roll mill. Preferably according to the present invention the process is carried out under the following conditions: Preset gap during operation (Dynamic Nip) -0,1 -0,5 mm; Friction -1.8-3; Preferably, processing is performed under controlled temperature -temperature in the working area (gap area) could be in the range of about 40-60 degrees of Celsius (e.g. using internal or external cooling as described above).

Mixing of waste rubber crumb with modifier could be performed in batch mixer (for small-scale plant), continuous mixer, etc. In some cases multiple passing of rubber material trough roll mill could be required in order to obtain desired degree of devulcanisation and size reduction of rubber crumb. To this end, multi-pass processing could be performed on single roll mill by re-entering rubber under processing. Also, multiple roll mills in succession forming rubber reclaiming line could be used. Such reclaiming line could include automatic batch-weightiers for crumb and modifier, feeding conveyer, continuous mixer (by type of standard concrete mixer) and single or multiple roll mills in succession and processed material evacuating conveyer.

According to international and local safety standards the roll mill could be provided by various safety features. For example, manually and/or automatically operated electric switch that instantly stop and alternatively reverse the rolls could be provided. Such switch (s) could be operated by safety bar(s), knee activated panels, presence detectors installed in the vicinity of the gap, etc. Protection cage(s) with interlock switches which stop the rolls when opened also could be provided. In order to satisfy for example, European Safety standards CE the rolls can be equipped with instant reversing of around 1/3 turn when any of the emergency stops are activated.

In that case additional safety bars/detector should be provided below the rolls.

Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore described without departing from its scope defined in and by the appended claims.

Claims (22)

1. WHAT WE CLAIM IS: 1. A roll mill comprising a pair of rolls mounted closely adjacent one another to define a preset gap therebetween, first pairs of bearings mounted in two fixed frames and supporting shafts of the rolls, each of said pairs of bearings is pulled together, second pairs of bearings mounted on said shafts, a pair of spacers inserted between the bearings of said second pairs of bearings thereby providing said preset gap between the rolls through which material to be processed may be passed.
2. 2. A roll mill according to Claim 1 wherein said two rolls has substantially smooth surface.
3. 3. A roll mill according to any Claim 1 or 2, wherein said bearings are rolling bearings.
4. 4. A roll mill according to any one of proceeding claims, wherein said preset gap is ranging from about 0.1 mm to about 0.
5. 5 mm.

   S. A roll mill according to claim 4, wherein said preset gap is about 0.2 mm.
6. 6. A roll mill according to any one of proceeding claims, wherein said spacers have a curvature surfaces.
7. 7. A roll mill according to claim 6, wherein said curvature surfaces has a curvature as a curvature of outer rings of adjacent bearings.
8. 8. A roll mill according to any one of proceeding claims, wherein each of said rolls has independent drive mechanisms.
9. 9. A roll mill according to claim 8, wherein said independent drive mechanisms provide different linear speed of said rolls.
10. 10. A roll mill according to claim 9, wherein said independent drive mechanisms provide linear speed of the slowest roll in the range of 7-40 meter per minute.
11. 11. A roll mill according to claim 10, wherein said different linear speed of the rolls provides a friction value between 1.8 and 3.
12. 12. A roll mill according to claim 11, wherein said friction value is about 2.5.
13. 13. A roll mill according to any one of proceeding claims, further comprising external cooling of said preset gap area.
14. 14. A method of reclaiming of a cured elastomer material performed by the roll mill of claim 1 the method comprising the steps of: mixing said cured elastomer in form of crumb or chips with a devulcanization-aiding chemical composition and passing said mixture through said preset gap of the roll mill.
15. 15. A method of reclaiming of a cured elastomer material according to claim 14, wherein said preset gap is ranging from about 0.1 mm to about 0.5 mm during roll mill operation.
16. 16. A method of reclaiming of a cured elastomer material according to claim 15, wherein said preset gap is about 0.2 mm.
17. 17. A method of reclaiming of a cured elastomer material, wherein the rolls of said roll mill has different linear speed.
18. 18. A method of reclaiming of a cured elastomer material according to claim 17, wherein a linear speed of the slowest roll is in the range of 7-40 meters per minute.
19. 19. A method of reclaiming of a cured elastomer material according to claim 17, wherein said different linear speed of the rolls provides a friction value between 1.8 and 3.
20. 20. A method of reclaiming of a cured elastomer material according to claim 11, wherein said friction value is about 2.5.
21. 21. A method of reclaiming of a cured elastomer material according to any of claims 14-20 wherein said reclaiming is performed under controlled temperature.
22. 22. A method of reclaiming of a cured elastomer material, wherein said controlled temperature is ranging from about 40 degree to about 60 degree of Celsius.