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Bepex International Rubber Chopper

Machine Operation: The Bepex International Rubber Chopper is typically used in the tire, plastics and adhesives industries. In tire operations, Rubber Choppers are used to improve Banbury mixing efficiencies. Through granulation, mix times are shortened, a more uniform mix is achieved and electric power consumption is reduced. In systems where the rubber must be dissolved, Rubber Choppers are used to increase the particulate surface area thereby increasing the rate for stabilization. In extrusion plants, the Rubber Chopper size reduces scrap material for recycling. The Rubber Chopper granulates rubber through a combination of low speed and high torque. Low speed operation helps maintain feed temperatures while granulating at an acceptable noise level. Rugged construction practically eliminates unplanned maintenance and unnecessary downtime. Flexibility in design facilitated by various orifice plate sizes, cutoff knife speeds, main shaft speeds and hammer configurations provide the ability to granulate a wide range of rubbers and polymers. Rubber bales enter the feed hopper where the rotating hammers cut into the bale and shear it into chunks against the adjustable anvils. The chunks are repeatedly chopped by the hammers, which are shaped to convey the material towards the closed section of the body. While the material is conveyed, it is further reduced by the shearing action between the hammers and a row of fixed anvils located along the lower side of the body and around the circumference of the closed section. At the end of the closed section, the conveying action of the last double hammer forces the rubber through the orifice plate. Upon passing the orifice plate, the extruded rubber is sheared by the rotating Cutoff Knife Assembly. Granulated rubber exits via gravity through the discharge chute. Models: The Rubber Chopper comes in three basic sizes: the PB-15 standard duty, the PB-15 heavy duty and the PB-24. The number designates auger diameter in inches. Typical materials of construction are carbon steel (H designation) or 304 stainless steel (K designation). The standard duty PB-15 utilizes a shaft rated for 2 hp/rpm while the heavy-duty shaft is rated for 4 hp/rpm. The PB-24 shaft rating is 6 hp/rpm (shock load) and 8 hp/rpm uniform load. Shaft selection is based on the type of rubber (hardness, toughness) being processed.

Selection: Proper selection of the Rubber Chopper and drive requires knowledge of the following four criterion: 1) 2) 3) 4) 1) The rubber bale size, The desired product particle size, The torque demand of the particular rubber The desired capacity. Bale Size To insure smooth feeding of the rubber bales and to minimize bale bridging in the hopper, it is advisable to select a machine whose rotor diameter is a least twice the thickness of the bale. For example, a PB-15 (with a 15-inch diameter rotor) will accommodate a 7-1/2" thick bale, but only the PB-24 can process a 12" thick bale. 2) Discharge Size Granule size is determined by the diameter of the orifice plate openings, the number of knives on the quill assembly, the knife speed, the main drive speed, and the characteristics of the rubber. The orifice plate hole diameter determines one product dimension. The second dimension, thickness, is determined by a combination of the above. Generally, a 1-inch diameter orifice plate will produce a particle with a maximum size of 1 inch. Orifice plates are equipped with either ½ inch, ¾ inch or 1-inch diameter holes. Spoke plates are also available for coarse granulation. 3) Torque Demand The torque requirements to reduce a given rubber are functions of its physical properties. A tough rubber such as an SIR (styrene-isoprene) demands more torque than a soft rubber such as EPDM (ethylene propylene). Natural rubbers are generally tougher than synthetics. For a given rubber, the torque requirements are determined by the hopper fill level, the feed rate and the use of adjustable limiting anvils (see options section). 4) Capacity The discharge rate is primarily a function of the orifice plate hole size and the main shaft speed. Other contributing factors are the feeding characteristics in the hopper, the use of secondary hammers and the use of adjustable limiting anvils. For a given shaft speed, high capacities are obtained with a less restrictive, large diameter orifice plate. For a given orifice plate, the capacity varies linearly (approximately) with shaft speed. Maximum recommended shaft speeds for the PB-15 and the PB-24 is 70 rpm and 40 rpm respectively.

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Information required to provide quotation 1. 2. 3. 4. 5. 6. 7. 8. 9. Exact type of rubber being processed (i.e. Exxon Butyl 077, Uniroyal Royalene 502 EPDM) Bale dimensions (length by width by height) Feed temperature of rubber Desired product rate (lb./hr) Desired product size Process before and after the Rubber Chopper Are parting agents (calcium stearate, talc, water, etc) allowable to prevent reagglomeration? Existing process/machinery Motor voltage/frequency available

Test Rubber Choppers Rubber Chopper testing is available at the Bepex International Test Facility located in Minneapolis, Minnesota. A heavy duty PB-15 is available for testing. Information gleaned from testing is used for scaleup and quotation purposes. Rubber Types: 1. Butadiene's 2. Butyl's 3. Butyrate's Rubber Chopper Options Below is a list of options, which warrant use for granulation of specific rubbers in certain situations. 1. Hopper Guide. On occasion, rubber bales become wedged in the Rubber Chopper's feed hopper resulting in capacity reduction. The HG is a specially designed chute, which properly aligns the rubber bale as it enters the feed hopper. 2. Ram Feeder. The Ram Feeder is used to "force feed" rubber bales into hopper section. The Ram Feeder must be used in conjunction with the Hopper Guide. The Ram Feeder/Hopper Guide is used when the rubber bale "rides" the hammers. 3. Short bite hammers. In some instances, the main hammers remove portions of the rubber bale, but sections not in line with the main hammers remain intact. The intact rubber causes the bale to rest on the main shaft. 4. High Impact Polymers 5. Isoprene's 6. Natural rubbers 7. Nitriles 8. Reclaim 9. Styrene Butadiene

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On subsequent revolutions, the main hammers pass through the cut section of the bale, but are unable to remove the intact rubber located outside their travel path. Short bite hammers are mounted to the shaft between the main hammers and effectively remove the intact portions of the bale. 4. Cutoff Knife Seals. Sometimes the standard lip seal arrangement is not sufficient to prevent contamination of the cutoff knife bearings. A labyrinth seal, double lip seal or an air purge arrangement might be required to increase bearing life. Occasionally, granulated rubber passes through the annulus between the cutoff knife quill and structural members. This `extruded" rubber contaminates the cutoff knife belts. Bepex International manufactures a seal to prevent this condition. 5. Cutoff Knife Assemblies. Shaft driven or belt driven (two-blade or four blade) configurations are available. The shaft driven assemblies are used on crumbly rubber not requiring cutting beyond what the main hammers provide. Belt driven units provide the smallest product, which is adjustable, based on rpm. 6. Adjustable anvils. Adjustable anvils are located in the hopper section of the Rubber Chopper and control the machine's torque and throughput by effectively changing the hopper/hammer interface volume. Adjustable anvils allow fine-tuning of the Rubber Chopper and provide flexibility in processing various types of rubber using the same Rubber Chopper. 7. Reducers. Main drive reducers are chosen based on horsepower/torque requirements. A variety of manufactures will supply drives to meet specific conditions, i.e., CE, metric, temperature, etc.

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Microsoft Word - 27B.DOC