Faster, Faster

Traditional compounding equipment like continuous mixers and kneaders still has its place, but the current challenges of custom compounding are driving more investment in twin-screw extruders as compounders upgrade.

Wedtech Inc. of Toronto targeted high-volume compounding of polyolefins with the opening of its Houston facility last year. The new plant is equipped with twin-screw extruders from Berstorff and Krupp Werner & Pfleiderer, including one KW&P ZSK MEGAcompounder. Another MEGAcompounder is forthcoming.

“The increased productivity we get with the high speed MEGAcompounder means we get more production per capital investment,” notes John Lefas, president of Wedtech. “Another advantage of this machine is that it can handle smaller volumes as well. We can use it to develop a small amount at first, then use it to produce a truckload when we’re happy with the formulation.”

Wedtech’s MEGAcompounder is equipped with variable speed drives, and delivers far more than its stated capacity of 1100 kg/hr, adds Lefas.

The Houston plant is highly automated, with computerized controls and automated feeders.

Another MEGAcompounder is installed at Wedtech’s Brantford, Ont. facility, which also is the R&D centre for the company. It also has a 30 mm KW&P ZSK lab-sized extruder, a blown film line and rotomolding equipment for testing compounds.

DSM Engineering Plastics (Stoney Creek, Ont.) is also finding a productivity edge with a Krupp Werner & Pfleiderer 58 mm twin screw extruder. “We have installed a unique screw configuration, and are exceeding the stated maximum throughput by up to 200 lb./hr.” says John Wilkie, general manager of the Stoney Creek operation. “We’re getting output that you would traditionally expect from a 70 mm or 90 mm machine. We are also able to run a multitude of different products with this configuration.”

The benefit for DSM clients is that some companies previously served by the Evansville, IN facility can now deal with a local supplier that can provide shorter lead times and more flexiblity to handle urgent situations.

DSM has also made some changes to quality procedures at Stoney Creek, empowering operators to do their own quality checks. “There’s been a direct improvement in the quality of the product because the quality checks are being done real-time, on the floor,” says Wilkie. A mini-lab has been set up on the production floor where operators can test melt flow, dispersion, pellet integrity and ash content. These tests were previously the responsibility of the quality assurance department.

At A. Schulman Canada Ltd. (Mississauga, Ont.), the emphasis is on creating higher performance polyolefins that can challenge engineering resins, particularly in the automotive field. “For the most part, this requires twin-screw extruders,” says Jeff McCoy, business manager, polyolefins. “The performance-enhancing additives we use tend to be dispersed on an angstrom level, such as the new nanocomposite fillers. So the challenge is how to get favorable economics for producing such materials out of a twin-screw machine. There are high torque, high speed machines that can do this.”

Schulman recently installed a 92 mm KW&P ZSK high speed line at the St. Thomas, Ont. plant.

NEW FILLERS HAVE SPECIAL NEEDS

Organic clay platelets called nanocomposites are the current darlings of the additive world. At very low loadings, these materials can enhance both impact strength and barrier properties of resin.

Schulman’s McCoy elaborates some of the challenges of nanocomposites. “It is important to look at screw design. The fillers are extremely fine, so you have to determine how best to assemble the screw segments to achieve the best dispersion and the most favorable output level.”

Farrel Corp.’s Mike Hotchkiss says a number of compounding equipment manufacturers are working on the challenges of incorporating nanocomposites. “They are difficult to compound because they are analogous to little plates. They need to align with the polymer matrix, in some cases to form almost a physical barrier.”

Hotchkiss says Farrel is currently developing a new machine based on continuous mixer technology that will address the new challenges in compounding: micro dispersion of nanocomposites, moisture removal, increasingly higher additive loadings and incorporation of rubber. Look for the introduction of this new machine in the second quarter of 2000. The first unit will be a developmental machine for Farrel’s lab.

EQUIPMENT INNOVATIONS PROMISE FLEXIBLITY, EASE OF USE

One piece of specialty compounding equipment that continues to maintain a toe-hold in Canada and elsewhere in North America is the Buss Kneader — a compounding extruder that has maintained its presence in the market for over fifty years.

“The markets that we serve find the operating principle of the Kneader offers flexibility in compounding that is unmatched by competitive twin screw extruders,” says Michael R. Reynolds, president of Buss America Inc.

Buss recently revamped its line of compounding extruders and introduced the Buss Kneader MKS Modular Series. Buss America says that the new series offers flexible solutions to compounding problems and provides customers with high process reliability for cost-effective compounding. The process section can be built up from four basic modules, each having a length of 3 L/D. These modules can be combined into various processing chambers with processing lengths of between 8 and 20 L/D.

Farrel’s FTX twin-screw extruders use a co-rotating, intermeshing double screw system with a patented Polygon element that maintains controlled shear pressure and temperature along its entire length. The Continuous Mixing Element is similar to conventional kneading blocks, but the asymmetrical design induces cross-channel flow for aggressive mixing.

The result, says Hotchkiss, is enhanced dispersion with lower energy requirements.

Processing Technologies Inc. offers a high-torque, single screw extruder configured for compounding applications. The Trident HT Series is equipped with a heavier drive train with 30 percent more horsepower than the standard Trident extruders, oversized thrust bearings, and a longer L/D to accommodate mixing and blending. Multiple additive ports permit side feeding at various locations, and intensive barrel cooling systems are applied to areas that experience heat build-up due to high shear rates.

COMPOUNDING MOVES IN-HOUSE

“We are experiencing growth in the on-line compounding end of the business,” says Bernie Kiernan, business area manager for compounding, reclaim and fibre extrusion, Davis-Standard Corp. Manufacturers of medical, construction, electrical/electronic, and conductive packaging products are the showing most interest in purchasing compounding lines for in-house operations. “There’s a high level of expense in the initial development ($1 million to $1.5 million). And on-line users generally invest in sophisticated controls because process stability is a major consideration.” CPL

The Buss Kneader compounding extruder model MKS 140 features the new Modular Kneader System that sets current Kneader models apart from older versions. This 140 mm (screw diameter) machine has applications for a wide range of compounding applications, including engineering plastics and wire and cable.