DUMP EXTRUSION

Many extruder manufacturers now produce dump extruders which are fitted beneath the discharge door of an internal mixer and receive into their feed hopper the full charge of the mixer. The speed of extrusion of the machine is governed by a series of sensors in the feed-hopper, to ensure that the process is continuous and that the screw will not be starved of compound, thus ensuring a continuous production of the mixed rubber compound. Product from such a machine can be slab or pellets. 

The mixing process for concentrate pellet product production via Leistritz-type extrusion equipment is essentially identical to that of dry color product mixing. Once weigh-out has been completed, the formula is usually transported to a mixer where the ingredients must be mixed to uniformity. The ingredients are usually manually dumped into the mixer, after which the lid is sealed and the mixer is operated until the formula reaches the desired uniformity. After mixing, the formula is manually removed from the mixer and placed into a hopper or container with a controlled outlet and is ready for the next operation. 

Starch is a renewable resource and is biodegradable. It can be an important raw material to make environmentally friendly products. The National Starch and Chemical Co. developed an extrusion process to make dry starch foam. The starch foam behaves like the styrene form and can be used as its replacement in the packing industry. After usage, the starch foam can be dumped into a sink... 

The question remains, as to whether or not the gel and long branch formation resulting from the reaction between TESPT and NR may be responsible at least as a part of the extrusion problem. This question may be answered by what is shown in Eigures 12.11 and 12.12 that when the dump temperature is higher, the waviness of the extrudate surface is more extensive. 

The studies in the previous section indicate that the higher temperature encountered during mixing generates more gel and long branching, leading to the extrusion problem. A basic problem is whether the dump temperature of 155 °C (or even 150 °C) is necessary or not to complete the reaction between silica and TESPT. 

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