Canadian Plastics

Spin-off benefits

By Cindy Macdonald, associate editor   



In the quest for high productivity on pipe and profile extrusion lines, groove feed and conical designs are gaining favor as the market gains an understanding of their multiple, inter-related benefits...

In the quest for high productivity on pipe and profile extrusion lines, groove feed and conical designs are gaining favor as the market gains an understanding of their multiple, inter-related benefits. Downstream, ongoing research by equipment manufacturers is leading to a greater body of knowledge on how to cool, calibrate and cut in the most efficient manner.

“The trend is to go faster, generate less scrap, achieve the greatest repeatability and use the least labor possible,” says Bob Bessemer, Conair senior product applications engineer, downstream equipment. “People are not buying equipment unless it’s going to save them money.”

Get in the groove

Davis-Standard’s groove feed extruder line supports a range of pipe and profile applications, as well as film and sheet processes. Advances in both groove feed bushing and screw design have increased throughput and improved polymer homogenization at reduced melt temperatures. The company reports that many of its groove feed customers have increased output by 40% or more, compared with the output of a similar-sized conventional extruder.

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Jim Murphy, vice-president of sales for Davis-Standard’s profile and sheet lines, explains that the groove feed design has good linearity, that is, it maintains a consistent output per screw revolution through a wide range of speeds. As well, the groove feed extruders can maintain their output in spite of varying head pressure. “If the head pressure varied from 2000 psi to 4000 psi, you’d see no loss of output with the groove feed units,” says Murphy.

Another benefit is that groove feed designs can generally produce a lower melt temperature exiting the extruder, which means the material is easier to shape, has more strength, and needs less cooling to achieve handling temperature.

As a technology partner of Kuhne GmbH in Germany, American Kuhne promises European groove feed technology in a North American-designed extruder. American Kuhne’s groove feed design is optimized for polyolefin pipe and profiles, and boosts productivity by achieving higher output rates, lowering melt temperatures and improving the stability of both pressure and melt temperature to maintain tighter tolerances.

As well, American Kuhne states that certain blends may require less color masterbatch when processed on the groove feed extruder. After testing several masterbatch percentages, the company concluded that acceptable color mixing could be achieved with a reduction of 50% compared with the normal masterbatch level. In addition, static mixing may not be required, since American Kuhne’s test samples yielded good color dispersion without the use of any additional static mixing devices.

American Kuhne has also joined the trend to provide lower-cost, well-equipped “off-the-shelf” extruders with its Ultra line. This marketing technique has proven successful over the last few years for Davis-Standard with the Super Blue line, American Maplan’s Compact products, and Cincinnati Extrusion’s Alpha line.

Cincinnati Extrusion was an early adopter of this “low-cost, well-equipped standardized line from stock” concept, demonstrated by the introduction of the Alpha series of extruders at K 2001. The Alpha concept has caught on; more than 200 Alpha Series extruders have been sold since its introduction.

As the next step in its program of producing standardized complete extrusion lines, American Maplan has introduced a modular line concept. The winBEX system consists of five components: an almost-completely assembled downstream package, and a choice of four twin-screw extruder models. Customers can choose from the large, negative-flight conical twin-screw AMC-BEX 72, or three parallel extruder models. Due to the high degree of standardization, the winBEX lines are available at competitive prices within extremely short delivery times.

Conical designs evolve

Conical twin-screw extruders from American Maplan are distinct from conventional models because of their negative flight depth. The screw flight depth is reduced in the feed zone and increased in the output zone. The AMC-BEX 72, the largest model of the conical twin-screws, is extremely versatile, and suitable for the production of window profiles at an average line speed of 3 m/min.

According to American Maplan, the most critical area of conical screws is the metering zone where the available screw volume decreases significantly. Therefore, a deeper screw flight depth in this area has major advantages in terms of reducing wear and improving material homogeneity.

Simple, precise single screw

Boston Matthews has launched a new range of single-screw extruders. The Logic range has been designed to provide processors with an extruder that is energy-efficient, therefore offering low operating costs, and is quick and easy to maintain.

An AC motor with encoder feedback combined with a flux vector drive with forced ventilation are standard, providing the basis for energy-efficient and “energy aware” operation. Intelligent electronics ensure that when certain systems of the extruder are not required, the are automatically shut down. One example is the temperature sensor system that shuts down the ventilation fans when not required.

The Logic range also has the Accutrol barrel temperature control system, which offers improved response time and increased precision for process control.

To bring older extruders up to current standards, Merritt Extruder offers a gearbox retrofit upgrade package, which includes a new high-capacity, double-reduction gearbox, an adapter to allow the existing screw to be used without modification, and new motor mounts to either remount an existing motor or upgrade to a higher level of horsepower.

Not only will a new gearbox renew the drive train, but it will allow for the upgrade of the motor. According to Merritt, typical demand for horsepower has increased 30% to 50% in the last 20 years because screw design has allowed the machines a significantly higher throughput capacity.

Replacement of the motor and/or gearbox is possible on 4-1/2 in., 6 in. or 8 in. extruders from almost any manufacturer.

Ramp up the downstream functions

Improvements to downstream operations can also have a significant effect on productivity, both by increasing throughput rate and by improving product quality.

Cooling plastic pipe and profiles has always been a challenge, and it is particularly challenging at today’s extrusion rates, which can be in excess of 1500 lb./hr. “You might think the secret would be found in getting the water as cold as possible,” says Bob Bessemer, senior product applications engineer, downstream extrusion, for equipment manufacturer Conair. “And you might be wrong.”

Bessemer explains: “Cold (turbulent) water can do a lot toward optimizing heat-transfer rates, but only within a specific wall-thickness range. In pipe, anything above Schedule-40 wall thickness is a good point at which to think about going from cold water to tempered water to optimize cooling rates. As the extrudate goes from its hot, plastic state to a rigid state, the heat transfer rate decreases. So, as the pipe or profile outer surface skins, it actually insulates the inner material from the cooling water. As the wall thickness increases, this becomes a more severe issue. You may in fact be wasting chilled water, which can be very expensive. It may actually be better to temper the water temperature in the initial cooling tank (80 to 100F) to pull BTU’s out without freezing off the skin.”

Complex hollow profiles, such as window and door lineals, and PVC fencing, can take advantage of Conair’s high intensity spray cooling technology to both enhance cooling rate and reduce scrap. The secret to the high-intensity tank’s effectiveness is turbulent cooling created by a uniform, 360 high-volume spray pattern of water that covers all profile or pipe surfaces with extremely small water droplets that efficiently pull off BTUs. Custom Downstream
Systems (CDS) also offers a high-volume spray sizing tank.

Bessemer recommends high-intensity spray tanks for thin-wall pipe. Heavy-wall pipe, solid profiles and foamed profiles should investigate the use of tempered water to optimize cooling rates.

A water temperature control system could be integrated to allow the processor to use precise temperature as a means to minimize warp, bow and twist, Bessemer suggests.

“Injection molders have been doing it for years. There’s no reason extruders can’t apply thermocouples to monitor water temperature to decrease scrap and improve repeatability.”

Quick-change artists

Several new features on CDS’ servo travelling saw allow processors to make faster adjustments for product changeover, and optimize blade speed for various materials. A multi-angle blade positioning clamp permits the operator to set the angle of the cut (90, 30 and 45 degrees) without making any adjustments to the machine or the line. Also, variable blade speed gives processors greater flexibility to cut materials of different hardnesses. A user-friendly touch-screen operator panel allows quick troubleshooting and programming.

AEC’s AC Series puller/cutter combinations are designed for tubing and profile applications, and use an AC flux vector variable speed belt drive. The ACC models offer a touch screen control system, quick-change bushing, quick-change blade, and height adjustable swivel casters. A high-torque option is also available on most units for increased force and clean cuts on heavy wall tubing.

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