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Affordable price, fast delivery claimed for twin-screw compounders.

Affordable Price, Fast Delivery Claimed for Twin-Screw Compounders

A line of twin-screw, corotating compounding extruders now being introduced in the U.S. is claimed to be about 30% lower in cost than comparable machines, and deliverable in six months or less. The machines are co-manufactured by ICMA San Giorgio S.p.A. of Italy and Wayne Machine & Die Co. at Wayne's plant in Totowa, N.J., under a joint trademark. According to an agreement finalized last July, Wayne is the sole supplier of the ICMA machines in North America, and is responsible for installing electrical components and accessories, as well as providing all troubleshooting and repair for the machines. ICMA is supplying most of the mechanical parts in the venture.

LOW-SPEED MACHINES OFFERED

Wayne/ICMA is offering models in both low-speed (90-120 rpm) and high-speed (350 rpm, optional to 500 rpm) configurations. The extruders reportedly incorporate heavy-duty thrust bearings, gearboxes, screws, barrels, and drives, and are said to be designed for 24-hr production. Wayne Machine's operations manager, Joseph V. Scuralli, says low-speed, corotating machines are unique in the compounding market, and adds they are suitable for most applications. The low-speed, two-lobe units, available in 50 to 170 mm diam., are said to have several advantages, including reduced wear and longer machine service life. Because of their lower operating pressure, the low-speed units are claimed to be able to incorporate more filler per pound of material. For the same reason, they are also said to handle abrasive materials such as glass without the use of bimetallic liners. In addition, the low-speed units reportedly are capable of handling degradable polymers, such as PVC. Predicted output rates on a 170-mm low-speed machine are 3000 lb/hr for rigid PVC and 6000 lb/hr for flexible PVC (see table). Finally, the low-speed units are said to consume 10-15% less power than their high-speed counterparts.

The high-speed machines, available in two- or three-lobe versions from 33 to 120 mm, are said to be suitable for compounding polymers with high melting points because they reportedly allow quick plastification, short residence time, and optimum temperature control. The machines are vented to achieve degassing of humidity and solvents.

Both high-speed and low-speed units in the line are equipped with variable-profile screws, which can be configured for optimum installation of mixing, kneading, and conveying sections at various locations along the screws. Barrels and screws on these units are made of nitrided steel and are guaranteed against excessive wear; on the low-speed machines, for example, barrel and screws are guaranteed against elevated wear for 10,000 hr at 250-bar backpressure and gearbox and thrust bearings are said to be guaranteed for 20,000 hr at the same backpressure. Wayne/ICMA screw-and-barrel wear guarantee is said to represent three to five times the service life of a typical single screw or fixed-profile twin screw, in which compounding occurs in the first compression zone where viscosity of the polymer is still elevated, according to the company. Bimetallic liners are also available for special applications, such as glass filling.

The variable-profile screw design is also said to result in energy savings. For example, a mixture of 50% talc and 50% PP reportedly would require only 0.15 kwh/kg on a Wayne/ICMA model, compared with 0.35 kwh/kg on a single-screw or fixed twin-screw counterrotating model.

DEMONSTRATION LINE SET UP

Wayne recently set up in its Totowa plant a demonstration line based on a 70-mm, 32:1 low-speed extruder with a Barber-Colman MACO 8000 controller. The line is driven by digital d-c drives and includes three Hasler gravimetric feeders--one each for the addition of polymer, mineral, and glass.

Such a unit would have an output rate of about 700 lb/hr when mixing PP with 50% talc or calcium carbonate and 20-40% glass fiber, according to the company. Polymer is initially fed into the system using a belt-type gravimetric feeder. The resin is melted upstream and volatiles are vented out of the machine through a free vent.

After the material is melted, a twin-screw side feeder with loss-in-weight metering control is used to feed mineral filler. Scuralli claims that the machine's special mixing section in this stage is an asset, allowing the right arrangement of lobes to be employed to knead the material without causing excessive abrasion.

Glass is fed in as far downstream as possible through a weight-loss vibrating trough. The line is equipped with a vacuum pump that removes the gas resulting from the kneading of glass fibers, to ensure a smooth product.

A complete line is sold with a Wayne strand pelletizer or Beringer water-ring pelletizer; a hot-face pelletizer is also available.

COMPLETE 'TURNKEY' SYSTEM

Scuralli claims that quality and features have not been sacrificed for the lower cost. The 70-mm demonstration line, for example, including three gravimetric units and strand pelletizer, runs about $290,000, says Scuralli. Price of the three-lobe, 65-mm twin-screw extruder with two gravimetric feeders, discreet temperature control, and strand pelletizer is about $330,000.

The company will guarantee output for specific materials on turnkey lines--including extruder, gravimetric feeders, hoppers, temperature-control panel, and pelletizing unit. Wayne/ICMA also says that it can reliably scale up from lab-machine production to performance on larger extruder sizes.
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Author:De Gaspari, John
Publication:Plastics Technology
Date:Mar 1, 1990
Words:870
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