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March 8, 1999

3 Min Read
Injection Moulding with Direct Compounding

A trio of Italian manufacturers have joined forces to create a system that combines three normally unrelated plastics processing technologies into a unified system for mixing, compounding, and injection moulding dissimilar materials. The first installation is being used by Tröster, a German moulder, to make automobile bumpers with a high percentage of recycled or reclaimed material.

DCIM technology—direct compounding injection moulding—combines gravimetric blending and dosing, a continuous, twin-rotor compounder, and an injection moulding machine into an integrated system. BM-Biraghi of Monza is responsible for marketing and support of the complete system, plus the injection moulding machinery; Pomini of Castellanza contributes the materials mixing technology and holds the DCIM-related patents; K-Tron of Montenegro supplies the gravimetric dosing expertise.

Automobile bumpers, which in Europe and especially in Germany heavily consume recycled material, provided a prime target for DCIM's integrated technologies. Biraghi says the technology has other applications, and also that it provides a new platform for creative moulders to offer unique services. DCIM permits the use of high molecular weight polymers like recycled soda and water bottles in the materials mix. Postconsumer recyclate, regrind, and virgin materials can be mixed and coloured using a variety of formulas, even if the PCR is a mix of several materials, and even if the materials are in a variety of forms: pellets, flake, or powder. Additives and masterbatch can be mixed in at the machine.

Viewed physically, DCIM is an injection machine with a compact compounding machine on top of it. Above the compounder is a platform holding the gravimetric dosing system. Floor space is a bit more for the platform supports than for a standard injection machine , and system height is 5.1 m (16.7 ft). The gravimetric system on Tröster's DCIM meters four components with varying specific weights and physical forms: granulated virgin polymer, 0.6 to 0.7 kg/l; granulated masterbatch, 0.5 kg/l; remilled material in chips, 0.4 to 0.8 kg/l; and powdered mineral-filled material, 0.8 kg/l. Each is in a hopper mounted on a weighing deck. A control unit meters the weight loss from each hopper. Output flow is kept at a setpoint by adjusting the ejector speed.

Gravimetrics has been the blending method of choice for film and sheet extrusion, where materials are metered by weight rather than volume. One of this system's biggest technological challenges was marrying continuous output devices, the blender/ doser and the compounding mixer, with an intermittent device, the moulding machine. Solution: The mixer remains constant while the dosing system functions in cycles synchronized with those of the injection machine.

Using the moulded part as a starting point, the injection machine is sized appropriately, though Biraghi says clamp force can be reduced because of the state of the moulding material. The mixer is matched to the plasticizing needs of the injection machine, and the mixer capacity is based on having the mixing time equal to the injection dosing time. BM-Biraghi's Sintesi HB machine line can overlap the dosing phase with the mould opening and ejection phases to extend dosing as long as possible without affecting total cycle time.

The mixer has a two-stage barrel. The first is for preheating and dispersion. In stage two, the premix is fused, mixed, homogenized, and ejected. Material grinding, longitudinal blending, and kneading are included in the unit's design, as well as continuous forcing of material from one side of the barrel to the other for good mixing.

The injection machine's modular design allows different clamp and injection unit combinations. DCIM clamp availability is 4,000 kN (400 tons) to 18,000 kN (1800 metric tons). The Tröster machine is 8,000 kN (800 tons). Clamps will be toggle-type or hydromechanical, depending on machine size. Material from the compounder is metered by the screw and injected using a 10-point speed control. Microprocessor controls use open architecture for easy customization. The operator screen uses superimposed windows, and icons continuously indicate the state of the machine processes. The machine and the dosing system controllers save product formulas for quick setup and changeover.

Contact Information
BM-Biraghi SpA
Ms. Nicoletta Pagani
Via Ercolano, 11
20052 Monza
Tel: (39) 2 83 3131
Fax: (39) 2 84 0915

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