Gearboxes for shredders

Rubber and tire shredding requires truck and automotive tires to be broken down for use in by-products and as fuel for power companies.

Typical installations for shredders demand a planetary drive in several different configurations. These configurations can include one-, two- and three-stage gearboxes mounted horizontally. Brevini supplies various gearboxes, from standard series to high-torque models, suitable to the specific application. A typical shredder requires a cutting head to be driven independently by a single unit. Since most shredders require two elements that cut and shear material, two units are required for each shredder element. Both drive systems have an equal impact in today’s shredder design. The important considerations for successful application lie in unit capacities, motor mounting and flexibility, with ratios for either drive system.

Electrically driven units are normally used with a three-stage planetary unit. To obtain the proper speed and torque requirements, an electric motor is chosen, based on horsepower, with an input speed of 1750 or 1150 rpm. The unit is then selected to obtain an output speed range of 15 to 30 rpm and the proper torque, which is normally supplied by the motor. The gearbox must also be selected to handle the maximum torque supplied from the motor. An essential specification is the required duty cycle for the application, since many applications have an unknown duty cycle and can fluctuate based on customer usage. Proper selection can be obtained by sizing for the electric motor and by assuming the continuous torque requirement will be 70% of the applied torque. A unit is then selected for a minimum of 25,000 hours B10 life. Adding a torque limiter absorbs high shock and inertia from the motor.

Hydraulically driven units are used with either single or double reductions. A hydraulic system can absorb some of the shock load internally, unlike similar electrical systems. The typical speed range is 15 to 30 rpm, while torque varies by application. Units are sized to handle continuous and maximum torques. Typical duty cycles include a continuous torque for 85% of the time, and a maximum requirement for the remaining 15%. These applications are also sized with an application factor of 1.5 and minimum 25,0000 hours B10 life.

To complement selection of planetary gear units, the company has been involved with stub shaft designs and oil circulation. Use of the stub shaft is available to adapt the female spline output shafts to the driven shredder shaft. Oil circulation considerations are necessary for power requirements that exceed the company’s thermal ratings. 

 For more information:
Brevini USA, Vernon Hills, IL.

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