Compounding.

Compounding

Lots of new continuous and batch compounding machines, PVC mixers, pelletizers, and control systems highlighted the compounding exhibits at K. Of special interest were sophisticated on-line control setups actually demonstrated in use, and novel methods of barrel heating, pelletizing, and compounding PVC and engineering resins.

ON-LINE MONITORING & CONTROL

As we reported last month (p. 13), the prize for most imaginative compounding exhibit goes to Werner & Pfleiderer for its demonstration of on-line color control. This was an especially complex feeding setup, as it involved feeding two different viscosities of nylon 6, an additive package, and four single-pigment concentrates. At a downstream port, chopped fiberglass was fed into the melt. Samples of compounded pellets were air-veyed to a nearby injection machine, which automatically molded a color chip. A robot removed the chip and placed it in an air-cooling station (sample temperature affects color readings). After a few minutes, the robot held the sample in front of a colorimeter sensor, and a computer calculated the necessary color correction, if any, and fed back instructions to one or more of the color feeder speed controls.

W&P also demonstrated an example of reactive compounding--silane grafting of polyethylene. Resin, silane, peroxide, and another additive package were compounded, and melt was sampled by both a Rheometrics on-line melt indexer (introduced at NPE'88 in Chicago) and an Automatik IROS-100 on-line infrared spectrometer. Thus, it was possible to check that both the right amount of silane was being added, and that it all had reacted completely.

NEW COMPOUNDING MACHINES

Compounding and reinforcing of engineering thermoplastics was introduced by Battenfeld Extrusionstechnik (rep. by Purnell International, Houston) as a completely new use for planetary-screw extruders, normally used for PVC calender feeding. Battenfeld showed a brand-new model with segmented barrel and rotor sections, allowing multi-stage configurations (see schematic) with alternating single- and planetary-screw sections. The planetary system's large surface area for mixing is thought to be an advantage. The company is currently testing its performance in comparison with standard twin screws.

Battenfeld also announced that its recent acquisition of unique, specially built machining equipment allows it to produce planetary screws from harder, more wear-resistant steels that will better withstand processing of highly filled materials. Also, the screws are now ground rather than milled, for more exact tolerances.

W&P introduced the concept of induction heating of the melting section on its twin-screw extruders, which is said to offer much greater heat input capability than conventional resistance heaters, raising output by as much as 15%.

The company also introduced a radial throttle valve (four independently movable barrel inserts on top, bottom and sides) as an alternative to its axial throttle valve. This mechanism varies the shear rate, increasing machine versatility for processing different materials--such as polyolefins of widely differing melt index--without needing to shut down for a change of screw elements. Customers want such flexibility today, says W&P, owing to Just-in-Time requirements for shorter runs and more frequent product changeovers.

A new range of twin-screw compounders was launched by APV Chemical Machinery. The HP 4000 series features changes in three critical areas: torque range, process optimization, and screw and barrel geometry. A twin motor drives the screws through a single gearbox, ensuring synchronous mixing action. The machine can reportedly be run at increased levels of fill of the screw flights, offering productivity improvements. Refinements to the agitator and bore perimeter of the screw are said to optimize shear and achieve a high level of mixing.

Buss introduced a 70-mm pilot-plant size (KKG 7-10) of its new kneader design for rigid PVC and other heat-sensitive resins, introduced this summer (see PT, July '89, p. 21).

A 30-mm counterrotating, nonintermeshing, twin-screw devolitizing extruder was introduced by Welding Engineers. The lab-size HT F32-323-2-E1 pelletizing system has a rear vent for extracting liquids and solvents, a flash chamber and two mechanical filters for vapor removal, and a new 50-mm size Turbulator pelletizer at the discharge end.

Leistritz introduced a multipurpose twin-screw system, ZSE 50. Its modular design allows the unit to be configured for compounding, reaction extrusion, or profile extrusion. Systems may be converted to other modes on-site with conversion kits. The unit is available in corotating and counterrotating modes, intermeshing and nonintermeshing (tangential) format, as well as single-screw mode.

Pomini displayed a new VIC (Variable Intermeshing Clearance) series of batch mixers with intermeshing twin rotors, in which the rotor clearance can now be varied by means of an eccentric sleeve that houses the rotor bearings. This permits not only varying the mix intensity, but also adjusting for rotor wear.

Reifenhauser displayed its relatively new Staromix mixing section on the end of a two-stage single screw. This is a rotor/stator device (superficially resembling the Rapra Cavity Transfer Mixer), of which the stator can be built into the barrel or flange-mounted on the end. With this unit, additives reportedly don't have to be introduced until the end of the barrel is reached, eliminating potential wear. It also greatly improves melt-temperature homogenity, which can permit downgauging of films, for example, according to the company.

PVC COMPOUNDERS

Gelaplast, a W. German producer of PVC sheet for thermoforming, has entered the machinery business with continuous processing equipment of its own design. Its multi-stage system reportedly requires no dryblending beforehand. A weigh feeder starve-feeds material into a special horizontal heating mixer. Its rotor consists of an inner screw and outer wiping tool, which act in opposite directions. Temperature sensors in the barrel signal the appropriate time to inject liquid stabilizers. The resulting dryblend is discharged into a three-flighted single-screw extruder, which provides highly uniform feeding to a coaxial planetary-screw extruder. This reportedly differs from other planetary extruders in that material follows a very long path around all nine screws, rather than straight down the barrel. This provides lots of mixing area in a very short barrel (oil heated). (It reportedly can process PP, PE, and PS with no modifications.) Finally, material exits through a gear pump of the firm's own design, which is said to require less stabilizer in the compound than does a single-screw discharge extruder. This system can process 2 tons/hr and can be used for any sort of direct shape extrusion of the compounded product.

Papenmeier (rep. by Littleford Bros.) introduced its PXX Compounder, a quasi-continuous heating/cooling mixer that can handle 10 batches/hr. The heart of the system is a high-efficiency cooling unit, employing mixing tools that ensure maximum contact between the product and cooled surface at lowest speeds.

A smaller model of its truly continuous PVC dryblend mixer, model TK/D 125, was introduced by Thyssen Henschel (rep. by Purnell International). This model for throughputs of 660-1100 lb/hr is designed for direct feeding of a calender-feed extruder. It can also be used for coloring and stabilization of ABS, PE and PP.

Also new from Henschel was a laboratory mixer with easily interchangeable 4- and 10-liter mixing vessels. Shaft sealing is not affected during the change, avoiding accidental damage. The mounting of the vessel on the stand is done with a quick-release catch.

Henschel also introduced horizontal mixers for larger mixing volumes--3000, 4000 and 5000 liters. Stainless-steel construction, a large discharge valve for fast emptying, and optional heating/cooling jackets are some of the features.

NEW PELLETIZERS

Werner & Pfleiderer showed off a new pelletizer die design that permits processing more than 50,000 lb/hr of polyolefins through more than 2000 die holes at relatively low pressure (around 1150 psi). This low-pressure die design, in which each large-bore flow channel divides to feed as many as 10 die holes, is also used in novel applications for producing mini pellets of 1.0-1.2 mm diam. These small pellets are used for extrusion compounding of EPS beads. W&P sources say they also would be advantageous for masterbatches, offering easier melting for better letdown. The tiny holes (0.7 mm diam.) require an intensively heated (oil or steam) die plate to prevent freezing, and turbulent underwater pelletizing to prevent pellets from sticking to the die plate. A 200-mm-diam. die plate with 1120 tiny holes could produce over 1200 lb/hr.

Automatik introduced a new series of Type ASG strand pelletizers. The cover of the cutting chamber may be dismantled without tools, offering easy viewing of itnernal working parts in contract with product. The short distance between feed roller and cutter enables pelletizing flexible strands.

Automatik's semiautomatic alternative to the conventional strand pelletizer, called the Dry Cut Pelletizer type ATG 150-E, was also shown. Only one operator is needed for machine start-up, and strands that tear off during production are automatically rethreaded.

NEW CONTROLS

A new computer system, Macromatex 12.1, for pelletizing operations was shown by Leistritz. Operating data on the complete extrusion plant is displayed on a color graphic monitor. The graphic display supplies information for troubleshooting and pinpoints malfunctions, and hard copy can be supplied on a printer. The unit is capable of automatic start-up and operation during adjustable time periods, and has a timer for automatic preheating.

A process control that integrates weighing and dosing functions, thereby doing away with a separate dosing control, was shown by Thyssen Henschel. The Henschel Process Control consists of a standard Siemens S5 control for a maximum of six weighing units with 80 components. The standard storage capacity for 20 formulas can be extended with extra computer memory. Production planning and supervision is controlled from the PC, which can print out production data, formulations, charge records, and material consumption.

In the past six months, Buss has made available a Computer Graphic Control System (CGC) that costs less than half s much as a distributed control system (DCS) consisting of a large central computer and remote programmable logic controllers for controlling each subsystem of the process. Equivalent control sophistication now reportedly is available from a single control console that stands by the machine and displays schematics of all aspects of the process.

At K'83, W&P demonstrated how compounding can be controlled for constant energy input by means of altering screw speed or material feed rate (the level of filling of screw flights determines energy consumption). This year, the company says it has correlated the two variables in its control software.

With its planetary extruder for engineering resins, Battenfeld showed a new Siemens. S115U control system with color CRT for graphic display of the machine and all associated process parameters, processing diagrams, and a drive-control schematic. A remote PC workstation can also control and monitor the system, print out any screen display, perform trend analysis, and store recipes, including the screw configuration for that job.