China Plastic Molding

Low-Pressure Injection Molding Machines for Recycled Thermoplastics

Because of the important of processing recyclate, special technologies have been developed for the direct processing of untreated or untreated plastics waste. The simplest method is to process thermoplastic powder of granulated recycled thermoplastic into thick-walled products. The injection molding machines correspond in almost every detail to standard machines or machines fitted with preplastication and piston-injection. The only difference is that the volume of plastic processed per cycle is relatively high because the injection plunger, or the screw itself, only needs to generate relatively low injection and holding pressures.
One low-pressure machine that differs greatly from that described above is based on an entirely different5 concept.seo The machine is equipped with a shredder, if necessary with a cutter-densifier for film, an extruder for receiving the ground material, and a plunger injection unit (Fig.9.63). In the cutter-densifier, any form of waste can be dried, preheated, compressed, and compacted. The high-rotor speed causes a temperature increase. The cutter-densifier can be mounted either radically at the feed end of the screw or tangentially (Fig9.64). The screw deisgn allows collecting and plasticating the ground material. Degassification is provided.
 
      
 
 

 
The machine described in Fig9.63 offers the possibility of metering-in fibers and fillers. Downstream of the extruder, a cutter-densifier is connected and allows fibers and compounds to be metered-in in three zones. The first extruder stage is provided for adding power additives. The second feed designed for adding long glass fibers of 12 to 24 mm. In this zones, extrusion takes place under pressure less or low-pressure conditions to draw in the glass fibers as gently as possible and minimize the reduction in length. In the third stage, glass-fiber-based compounds can be added. Gravimetric metering is provided at all stages. The prepared melt is accumulated in a plunger injector. This plunger is responsible for injection into the mould. The nozzle is designed to minimize the reduction in glass-fiber length. It is recommended that injection be preformed into the open mould, and the clamping unit be closed under pressure to carry out the molding operation (low-pressure injection-compression).

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