Wire Manufacture

Thanks to these improvements, the melt temperature rise as a function of screw speed is significantly less than before. This enables screw speeds up to 750rpm. Production trials prove that compounding quality with the MX Kneader is higher; moreover throughput is about 2.5 times more than the MKS Kneader without any size increase. Apart from reduced floor-space, this brings users considerable savings not only in investment costs, but also in operating costs thanks to the lower power consumption.

Lower production costs thanks to higher efficiency

With the new MX Kneader, Buss once again asserts its technological leadership in temperature and shear sensitive plastics compounding. The most important field of application for MX Kneaders is in the production of halogen-free flame-retardant (HFFR) cable compounds based on polyethylene/EVA (EVA = ethylene vinyl acetate copolymers). In case of fire the aluminium hydroxide flame retardant used in these compounds releases water in an endothermic reaction at temperatures as low as approximately 200°C. For this reason the melt temperature during compounding must be maintained below 190°C. For effective flame retardance, filler levels of up to 68° wt.% are common – while the cable insulation must still exhibit good values for strength and elasticity.
Development tests and customer production trials have confirmed the expected improvements in throughput and production quality with these challenging HFFR compounds. For this application the processing section of the MX Kneader has an L/D ratio of 15 (L = screw length/D = screw diameter) and two infeeds. After compounding, a rugged flanged-on extruder screw builds up the necessary pressure for melt filtration and pelletizing by air/water-cooled die-face cutting. An automatic screen changer is optionally available for melt filtration.

Primary application: HFFR compounds

Thanks to the modular design layout of MX Kneaders, they are easily adapted and optimized for compounding many kinds of temperature and shear sensitive plastics. Typical examples are:

Modular design layout enables wide applications

– Semicon compounds (semi-conducting cable compounds). These normally contain more than 30  wt.% of conductive carbon black, whose fine-grained structure must not be destroyed during compounding. MX Kneaders for this application have an L/D ratio of 15 or 22, with two or three infeeds. They are fitted with a gear pump for building up discharge pressure, optionally with an automatic screen changer and with an underwater pelletizing system.
– Silane cross-linkable cable compounds, produced on an MX Kneader with 15D screw length and one infeed; also with gear pump and underwater pelletizing system.
– Masterbatch containing carbon black in very fine particles that must be uniformly dispersed in the polymer melt. MX Kneaders for masterbatch compounding are similar to those for semicon cable compounds, but with higher throughput due to the higher density of the carbon black.

Quiet-running and easily accessible

MX Kneaders are available in six sizes with screw diameters from 34 to 140mm. Table 1 shows the throughputs attainable for various applications.
Buss has also innovated the MX Kneader drive, comprising a compact water-cooled combination of four asynchronous motors actuating the screw shaft through a planetary gearing. It is largely thanks to this quiet-running drive that the high-performance Buss MX Kneader already complies today with the stricter noise limits to be expected in future.
All modules downstream of the MX Kneader, such as the discharge screw or gear pump, melt filter, screen changer and pelletizer, can be shifted at will on two linear axes. This not only facilitates access to each module for cleaning and maintenance purposes, but also enables rapid product changes.

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