Compounding, mixing & blending.

Compounding, Mixing & Blending

Plenty of new continuous compounders and batch mixers were on hand, as were improvements in pelletizers, PVC compounders, and blending systems. Of special interest was a sophisticated on-line controls package capable of rapid, continuous learning and adjustment of multiple criteria, a low-cost rheometer, innovations in twin-screws, and a pelletizer that converts from underwater to water-ring mode in 30 minutes.

SOPHISTICATED CONTROLS

Werner & Pfleiderer Corp., Ramsey, N.J., had several new introductions at the show. One of the most interesting was its Economax control system, which was running a reactive compounding process involving dynamic vulcanization of a TPO-type material. Economax is described as a "multi-criteria, multi-output, internal-model controller." "Multi-criteria" means that the controller can be told to optimize several key control criteria simultaneously--such as viscosity, melt temperature, and cost. If these optimization goals are mutually incompatible, the controller prioritizes them according to user-selected weighting factors. "Multi-output" control refers to the ability of the Economax system to issue corrections for several different control variables simultaneously, rather than fine-tuning them one at a time. This means that the line can be optimized much faster. During a process-optimization demonstration at the show, the controller issued five setpoint corrections at a time, waited an operator-specified "lag time" for the corrections to take effect, and then issued a new group of setpoint corrections.

What makes all this possible is the "internal-model" control. By means of statistically designed experiments, the controller has "learned" a model of the process and how the many variables (feed rates of the various ingredients, temperatures, pressures, screw speeds, etc.) interact with each other. Economax is also capable of continuous learning--adjusting the model during the run if the system does not behave precisely according to its starting model, as opposed to learning from scratch like the "simplex" type of control in W&P's previous-generation Optomax control.

NEWS IN TWIN SCREWS

In the realm of larger-scale production machines, American Maris, East Brunswick, N.J., has a new higher-torque gearbox for its corotating twin-screw compounders. For example, a 150-mm model that formerly had a 280-hp drive now has 630 hp. Continuous chemical reactions is a main target for the beefed-up drives. Models with segmented screws and barrels range from 28 to 170 mm in diam.

W&P gave a first look at a number of twin-screw innovations. One was a side vent for its extruders. Although still in testing, this alternative to the usual top vent appears advantageous because either condensates or melt that has deposited in the vent and degraded over time cannot eventually fall back into the melt stream and result in black specs or other defects. With the side vent, any material that leaves the melt stream falls irreversibly into a cleanout trap.

W&P also showed off new low-shear distributive mixing elements. TME elements are said to be a traditional design but are offered in more varieties than usual: two right-handed elements with different pitch angles, two left-handed elements, and one neutral element. More innovative, says the company, are its ZME mixing elements, which are fully self-wiping on the screw root and barrel wall, unlike the TME type, eliminating possible dead spots and material degradation.

A number of new corotating twin-screw compounding extruders for lab and specialty applications were introduced.

* American Leistritz Extruder Corp., Somerville, N.J., introduced its Micro-18, an 18-mm convertible tangential machine featuring segmented screws and barrels. The machine is designed for 15 lb/hr output and is said to be suitable for medical plastics and research applications involving a limited amount of material and "precise" production applications.

* W&P introduced the ZR 80, its first lab-sized (80-mm) reactor extruder, with integrated gear pump and large devolatilization dome. And its ZSK-30 lab twin-screw has been redesigned for quicker product changeovers with more compact in-line drive.

*APV Chemical Machinery, Saginaw, Mich., showed a redesigned version of its MP 2015 15-mm corotating twin-screw for color matching and other lab work at up to 5 lb/hr. It costs $55,000 with feeder and controls.

LOW-COST RHEOMETER

An "affordable" rheometer suitable for both production and lab use was introduced by Randcastle Extrusion Systems Inc., Little Falls, N.J. The unit uses an extruder screw as the sampling tool; consequently it samples the melt stream at about the same shear rate as a production extruder. Also, no complex mathematics is required to estimate the viscosity. The rheometer is driven by a variable speed d-c drive, so shear rate can be changed by about a 20:1 ratio.

The rheometer is small and versatile and can be easily adapted to either large production or lab equipment, according to the company. It comes complete with d-c drive, speed control with indicator, two-zone temperature controls, hardened barrel and screw, barrel heaters, two thermocouples, torque sensor, digital indicator, filament die, and heaters. Cost is about $10,000.

NEWS IN PELLETIZERS

There was lots of news in pelletizers from Conair Jetro, Bay City, Mich. One entry was the CVR 225 that converts in 30 min from underwater to water-ring pelletizing operation. High-alloy knives are mounted on a spring-loaded hub that holds them against a carbide die plate. Center axis of the knife hub is offset so that wear is distributed all across the blades. Also, the die-plate/cutter assembly is mounted on a pivoting shaft for easy access. Purging is made easy by a drop-down section of the water trough. This 5000-lb/hr system sells for around $70,000.

Also new from Conair was the cartmounted UWP 150 underwater pelletizer. It also has a spring-loaded knife hub, though manual adjustment is available as an alternative. The carbide-surfaced die plate has a ceramic coating for insulation. When the unit is opened, the die plate is fully exposed for easy access. And a spring-loaded chassis permits easy alignment of cutter to die plate; machined mating surfaces on both are said to guarantee that the knives will be perpendicular to the die plate when the two sections are clamped together. Two belt-driven models are rated at 2000 and 5000 lb/hr, costing around $30,000 and $63,000, respectively.

S-Series strand pelletizers have been redesigned with standardized parts, resulting in faster delivery, 20-in. shorter "footprint," and 10-15% lower prices. Conair also has a new vacuum-type strand dryer.

PVC COMPOUNDING

Buss America, Inc., Bloomingdale, Ill., has modified its Buss-Kneader model PRK/E to perform continuous, direct feed of fully gassed rigid PVC to calendered film rolls. The upgrade addresses the need to degas the compound before feeding it to the first nip of the calender. The new model PRK/E simplifies this process and eliminates the roll mill function by intensively degassing the flux in the last stage of the compounder. An additional processing section with an L/D of 4:1 has been added to the standard 7:1 L/D kneading section to accommodate the degassing stage.

After degassing, the product is discharged through a newly designed rotary cutting device to produce small, wedge-shaped chips, which then are fed directly to the first nip of the calender by a conveyor. The direct feed is said to provide lower capital cost, reduced maintenance, and energy efficiency.

Another improvement to the Buss Kneader line is equal-shear elements, designed to lower high-shear peaks that occur in certain materials--particularly rigid PVC compounds. These equal-shear elements are said to decrease operating temperatures and thus increase outputs by as much as 30% over standard kneading elements.

Entex Plast Consulting, Pottsville, Pa., is a new firm representing the German firm Entex Rust & Mitschke GmbH. Included in Entex's product line are planetary roller extruders, as well as a new two-stage extruder for PVC featuring vacuum and compression degassing. Variations can be used for calender line feeding, straining, and pelletization. (Entex also represents the German firm of Bastian Wickeltechnik GmbH, a producer of slitters and winders, and displayed calendering systems of Klockner Wilhemsburger GmbH. It claims it will be able to supply complete lines for PVC processing.)

BATCH MIXERS

Purnell International, Houston, showed a new drum mixer from Henschel of Germany. It consists of a pedestal with an arm attached to a drum cover with a rotary mixing blade inside. The cover is fastened to an open drum, and then the arm lifts the entire drum and turns it upside down; then the mixing propeller goes to work.

Also new from Purnell is a horizontal lab mixer of its own design. This medium-intensity unit has two rotors, bottom discharge, and heating jacket.

In other news, American Barmag Corp., Charlotte, N.C., is now marketing the Mixaco line of universal, highspeed batch mixers with working capacities of 32 to 8000 liters. These German machines (made by a sister company of Barmag) were formerly marketed by Berstorff Corp.

BLENDING SYSTEMS

A large number of gravimetric and volumetric blending systems were on hand at this year's show.

* The versatile Mini Mega-Blender from Universal Dynamics, Woodbridge, Va., can handle up to three components and is designed for "on-the-machine" blending. Auger assemblies allow for rapid disassembly and change. The blender can be assembled with two or three auger feeders in various combinations of augers and gear motors that permit throughput rates of up to 125 lb/hr. Various control options are available for extrusion and injection molding, including new Omni IV-B microprocessor controls, which handle from two to four components in three modes of operation: virgin/slave, as well as the traditional blender settings of percentage and rate. In the virgin/slave mode, the proportion of additives is kept constant to the virgin ingredient while the regrind is dosed independently. This reportedly simplifies recipes by entering only regrind percentage and the percentage of additives to virgin; the control calculates the virgin. Approximate price of the blender with controller is $5000.

* A new gravimetric gain-in-weight batch blender for processing two to four ingredients was introduced by the Conair Group, Wexford, Pa. The Autocolor II has a throughput capacity of 300 lb/hr, and is accurate to 1 gm (using a two-point weigh suspension system) for maintaining accuracies of up to 100:1 ratios. The unit has an auto-calibration feature. Price starts at $9100.

* K-Tron Vertech, Pitman, N.J., introduced its low-speed blending unit, the S-Loader, that can process from 1 to 250 lb/hr per ingredient module. The units are available in one-, four-, six-, and eight-component modules. The blenders have only one moving part--the feed screw--which can be quickly disconnected for cleaning and material changes.

* A new gravimetric blender that handles up to five components was introduced by Thoreson-McCosh, Troy, Mich. Ninety-nine recipes can be stored, and accumulated throughput in total per ingredient and as a percentage can be displayed. The blending system works on a mixing auger principle to avoid material separation due to gravity, and has an automatic feature that shuts off after blending to a preset value. It is said to be accurate to 0.5% and blends at a rate of 1200 lb/hr. Price is about $40,000. Also introduced was a volumetric blender with the ability to handle up to 99 recipes.

* A number of new blenders were introduced by Novatec Inc., Baltimore. A new continuous loss-in-weight blender has the ability to blend two to eight or more materials at rates ranging from 200 to 2000 lb/hr. The unit is said to provide accuracy of [+ or -]0.5% of fullscale capacity. Integral loading is provided by vacuum chambers, and the system employs a starve-feed process using variable-speed augers mounted over the extruder throat. A quick-change feature allows feed rates at individual points to be adjusted from 0 to 2000 lb/hr in minutes.

An integrated, self-loading, automatic Loss-Weight Batching Blender from Novatec meters each ingredient by weight into an integrally mounted hopper that also serves as a mixer to ensure that weighed materials are homogeneously blended. Programmed setpoints are achieved with accuracies of 0.1% per batch by using dual-speed, dual-setpoint feeder controls.

Novatec's new gain-in-weight Batch/Blending system is said to have a repeatable accuracy of 0.1% of fullscale capacity. The unit's load cell suspension system is said to eliminate the need for mechanical devices. The blending section is removable so that the batching section can be used with existing processes or it can serve several remote-mounted mixers. Price is under $9000.

* A microprocessor-controlled volumetric dosing and mixing unit for granular materials was introduced by Labotek Inc., Briarcliff Manor, N.Y. The Mini-Contimaster, or MCM, can dose from two to five different materials, and can be mounted either on the lid of the material hopper or straight to the machine throat. The MCM is said to have an operation accuracy of [+ or -]0.02%; dosing accuracies of [+ or -]0.5% for additives and [+ or -]0.1% for virgin and regrinds are said to be possible.

* A new gravimetric blending system with controller was introduced by L-R Systems, New Lenox, Ill. The WSB-600 can store up to 99 recipes and blend up to eight materials.

* Motan Inc., Kalamazoo, Mich., introduced a new volumetric blender that can mix up to three components and reportedly requires no tools for calibration or cleanout. The unit fills only to a small level in the cylinder, keeping a tight mix so it can't separate as it would in a large chamber.

* A.C. Hamilton & Co., Ltd., Mississauga, Ont., introduced two new blenders. The 400 DXS, a 400-lb/hr weigh blender, uses microprocessor controls and can blend up to four ingredients while supplying the operator with histograms, printouts, and on-line monitoring. The Accublend, a 600-lb/hr volumetric unit, is designed for mixing virgin and regrind.

PHOTO : An on-line rheometer from Randcastle Extrusion Systems, shown here sampling polymer in a 3/4-in. vertical extruder, can be adapted for either production or lab. Cost is $10,000.