Method and apparatus for producing highly active rubber powder from rubber scrap

摘要

Highly-active rubber powder is obtained from old tyres etc. by 2-stage pulverisation in a special extruder, involving an increase in volume stress to 15-250 MPa at 5-90 MPa/second, pulsating with an amplitude of +/- 5-20 MPa and a frequency of 5-600 Hz, and at 90-380degreesC (increasing at 50-150degreesC/sec), followed by a sharp reduction of volume stress at 50-150 MPa/sec. A method for the production of highly-active rubber powder (I) with a specific surface of 0.4-5 m2/g from old tyres and scrap vulcanised rubber articles based on various rubbers by 2-stage thermo-mechanical treatment in an extruder. This involves (a) fine pulverisation with a volume stress of 15-250 MPa (increasing at 5-90 MPa/sec and pulsating with an amplitude of +/- 5-20 MPa and a frequency of 5-600 Hz) at 90-380degreesC (increasing at 50-150degreesC/sec) with simultaneous saturation of the rubber with degradation products of plasticisers and other rubber components, to form a porous structure in the volume of the particles, and (b) sharp reduction of the volume stress at the rate of 50-150 MPa/sec resulting in destruction of the porous structure and an increase in the specific surface of the particles, after which the particles are cooled. An Independent claim is also included for apparatus for the production of (I) comprising a cylindrical housing with feed and discharge connections, a compression zone and pulverisation zone(s), each with a compression screw with grooves decreasing in depth in the machine direction and a rotating coaxial activator with grooves on its outer working surface (together forming an annular gap), the housing, screw and activator being provided with cooling elements. There are two pulverisation zones, one of which (A) is a zone formed by the housing and a multi-thread compression screw in which the inter-thread volume decreases towards the outlet and the inner surface is formed by a conical opening which slopes towards the outlet and by 3-6 meshing grooves of rectangular cross-section, and in which the internal surface of the housing is formed by a cylinder with a diameter which is 1.003-1.02 times larger than the diameter of the screw; the inner surface of the housing has screw-like recesses with 3-50 threads and a constant depth, facing forwards or backwards and with a chamfer slope which is 0.5-1.5 times that of the screw; the ratio of the extensions of the compression zone and the first pulverisation zone along the screw axis is (1:0.5)-(0.5:1); the compression and pulverisation zones are formed on replaceable shells mounted on the shaft or the housing, with the above working surfaces on one side of the shell and the screw-like grooves with enlarged wall surfaces for pumping coolant on the other side. The second pulverisation zone (B) is formed by (a) a rotating activator with a discharge screw rigidly fixed to it and aligned with the compression screw and (b) the surrounding housing; the outer surface of the activator has screw-like recesses as above (with the same slope and number of threads) with a chamfer slope which is 1.1-2.5 times greater than that of the compression screw, and the outer surface of the discharge screw has forward-facing, multi-thread, screw-like ridges with a slope which is 1.15-3.0 times greater than the chamfer slope of the compression screw, forming an inter-thread volume which increases towards the discharge outlet; the ridges on the screw are continuous or interrupted by screw-like recesses in the reverse direction, with a slope which is 0.5-1.5 times smaller than the chamfer slope of the recesses on the activator and the ridges on the discharge screw; in this case the ratio of the activator extensions to the screw extensions along the screw axis is (0.2:1)-(1:0.3). Screw-like coolant channels are also provided as in (A), with a semicircular profile with a radius which is 0.005-0.03 times the diameter of the screw and a depth which is 5-15% smaller than the radius, the numbers of channels in the forward and reverse directions being in the ratio (0.3:1.0)-(1.0:0.3