Rubber Recycling Calendar

An estimated 17 million tonnes of tires are discarded annually. Re-use is achieved by retreading (9%), recycling (39%), energy recovery (37%) and landfill (5%). A preferred, but complex way of recycling is to make new tires from discarded tire rubber. Vulcanised car tire rubber has to be devulcanized before it can be re-used into car tire compounds. The department of Elastomer Technology and Engineering (ETE) of the University of Twente (UTwente) has developed a thermo- chemical process using downsized (ground) tire rubber particles (GTR) on a laboratory scale. An up scaled continuous process is currently under development. The up scaled process requires a calendering type machine to cool a flow devulcanized ground tire rubber (D-GTR) from an extruder. The development of this the cooling calender is described in this thesis. The calender prototype has to be able to decrease the temperature of a D-GTR flow of 100 kg/hr from 250°C to 90°C. The cooling process should take place in an oxygen free environment to optimize the rubber quality. The calender will be rated to a minimum of 200 running hours and will have to be safe to operate. An initial budget of €5000, - was available for parts and materials. The realisation of the prototype was included during the project period. The thermal and physical properties of D-GTR during a calendering process were determined from literature research. The properties were used as calculation input values in a parametric model. This model includes thermodynamical calculations and mechanical calculations of the various parts of the prototype. Laboratory testing is done as well, using a mixing mill. This was done to determine the necessary drive power of the calender and investigate milling behaviour of D-GTR. The parametric model was used during the design phase to define the basic machine parameters and dimensions. An overview of possible design choices and configurations was made, and the final choices were made based on the calculations output and prototype requirements. The design choices were implemented into a 3D model of the prototype. Drawings of all machine parts were made for production. Some parts were outsourced and other parts were made in-house. The finished design is a vertical, inclined three roller calender. The roller diameter is 250 mm and roller width is 200 mm. Heat is transferred from the D-GTR sheet to cooling water flowing through water channels near the roller surface. The required amount of heat which has to be cooled for the 100 kg/hr D-GTR flow is 8.2 kW. The prototype has two compression stages, where D-GTR passes through a roller pair. Both nip heights are designed to be adjustable to prevent the formation of a bank before the nip. One drive motor is used to drive the three rollers. The motor will be controlled using a frequency converter making the rotational speed adjustable. The speed ratios between the rollers can be varied by changing the drive sprockets. The initial speed ratio is 1:1.1. The machine, as displayed in this thesis has been built during the graduation period. The fabrication of safety covers and some final finishing still remains. Further testing will be done to verify the cooling properties, gas tightness and to check the performance of the prototype