Automation In The Cast Polymer Industry
While sports car parts, yacht hulls and bridge decks often grab the composites industry spotlight, fabrication of cast polymer bath and kitchen fixtures is a vital and lucrative segment of the composites industry. For at least 50 years, kitchen and bath manufacturers have been combining polyester resin (and more recently, acrylic resin) with mineral fillers — originally ground marble, now a variety of fillers, additives, pigments and performance enhancers — to create smooth, glossy products available in myriad colors and patterns. Thousands of mostly small shops turn out vanity tops, bathtubs, shower stalls, kitchen countertops and other components for the new home and remodeling markets each year, to the tune of nearly $1 billion (USD) total.
Yet even today, many companies are still mixing small batches in buckets and using manual methods to make parts. With material and labor costs on the rise, says Gruber Systems Inc.'s (Valencia, Calif.) field service tech sales rep Doug Carney, at some point it makes sense to incorporate some automation into the process: "There are many small incremental steps that a manufacturer can take to increase shop efficiency." Gisco Inc.'s (Darien, Ill.) chief operating officer Tania Cogdill states that upfront equipment costs are lower today compared to a decade ago. "It may seem counterintuitive, but automating always saves money for customers," she maintains. "Machinery reduces resin use by at least 20 percent, based on our customers' experience. Automation steps can help small shops compete in the marketplace." Strategies for automating cast polymer manufacturing are more readily available than ever before, with benefits that accrue to offset the upfront investment.
CAST POLYMER CHRONOLOGY
The kitchen and bath industry can be divided into two general product types — cultured stone and solid surface. A smaller, relatively new third type (not described here) is "engineered stone," or ground quartz mixed with resin and molded to simulate natural granite, which is pricier, more esoteric, and produced by fewer companies.
The first, cultured stone, is made from a resin highly filled with calcium carbonate or alumina trihydrate (ATH) and pigments, with a gel-coated surface. The ultraviolet (UV) light-stabilized gel coat provides both aesthetic and protective functions, permitting the use of a resin, typically an orthophthalic unsaturated polyester, that doesn't require a lot of toughness or specialty additives. At the same time, it must possess a low viscosity that will easily accept up to 80 percent filler. Reichhold's (Research Triangle Park, N.C.) cast polymer application specialist Ken Lipovsky explains that the combination of various glycols (e.g., ethylene, propylene) and acids (e.g., maleic anhydride) together with a monomer (typically styrene) determines the final resin properties. Some shops use single-purpose polyesters tailored specifically for marble or onyx fillers, while others prefer "swing" or "universal" resins that are compatible with any type of filler. Resins also can be tweaked to take into account filler particle size, catalyst type and gel time, and even ambient humidity conditions in the shop, says Lipovsky.
"The resin, which makes up only about 20 percent of the part, bonds the filler particles," he notes. "Part producers want the filler loading as high as possible, to reduce costs — filler is less expensive than resin — and to increase part strength and reduce shrinkage during cure. Over time, techniques have evolved for blending fillers of different particle size to improve packing efficiency, which helps reduce resin demand." To make highly filled parts easier to manage, glass or polymer microspheres often are added to reduce the weight of large parts, such as bathtubs.
Resins and fillers are measured and mixed, then poured into one- or two-part molds, which can be made from fiberglass or metal. To simulate a natural product, some cultured stone shops add individual shots of highly colored resin/filler to the mold to create "veins," followed by a lighter-colored resin mixture. Molds are vibrated for a short time to help remove any air. Parts cure at room temperature, from one to eight hours. In some cases, finished work pieces are postcured in an oven. Postcuring has been shown to enhance physical properties of polyester-based products, Lipovsky explains. "Our study showed that if the part is cured to its glass transition temperature, physical parameters will be higher — barcol hardness, flexural modulus, tensile modulus and compressive strength, among others." Two hours in the oven is adequate, he notes.
Solid surface, which is not gel coated, usually requires a resin with greater strength, a higher heat distortion temperature (to handle the thermal shock from countertop stoves) and greater toughness to stand up to corrosive soapy water during extended use by homeowners. Typically, the resin used is an isophthalic unsaturated polyester (with a stronger backbone than orthophthalic polyester), with added UV stabilizers to minimize yellowing and specialty fillers (e.g., air release and wetting agents) to help eliminate voids. However, some producers make kitchen and bath products with polymethyl methacrylate (PMMA) thermoset acrylic. Despite a higher price, acrylic resin is more stain- and UV-resistant than polyester, and is preferred by some manufacturers for its thermal formability characteristics for complex applications.
Solid surface parts typically have filler loadings of 50 to 65 percent — with the greater amount of resin needed for finer filler particle sizes, says Lipovsky. The colored granules or "specks" that give the product its distinctive granite-like character are usually particles of cast pigmented polyester or acrylic that have been crushed to the desired particle size. These filler chips are lighter in weight than natural granite or stone chips and, therefore, are less abrasive and easier to suspend in the resin, says Rick Marshall, quality control manager for The R.J. Marshall Co. (Southfield, Mich.), a supplier of filler materials to the industry. During solid surface production, resin and filler are mixed under vacuum to remove all air, and some producers also heat the resin mixture to help guarantee consistency and good flow. After filling, the molds are vibrated to remove any remaining air bubbles and the material is cured in a time frame similar to that used for cultured stone.
After deflashing, gel coated cultured stone parts are buffed and polished to final finish. Solid surface parts are generally sanded lightly and buffed.
With the exception of a relatively small number of large high-production facilities, however, batch processes with hand mixing and hand fabricating methods are still the norm. Batch processing requires workers to manually lift heavy bags of filler into an electric blender or a bucket and estimate an amount of resin to add. Even conscientious employees are likely to spill raw materials, and if the batch isn't quite enough to fill the molds, a partial batch has to be mixed, leaving product behind as waste. Cleaning the buckets and the mixer after each part takes time and requires a cleaning solution to remove catalyzed resin.
SMALL STEPS IN THE RIGHT DIRECTION
"Anything, from adding an automatic mixer, to a conveyor system, to putting casters on a mold to enable workers to move it more easily, are steps that make a shop more efficient," says Gruber's Carney. His company, which started as Gruber Man Made Marble, was one of the first manufacturers of cultured stone products, beginning in 1958. When demand for cast polymer products boomed, the company changed its name to Gruber Systems and began to focus on improving the cast polymer process with off-the-shelf equipment, better molds, granite-effect fillers and other products for the burgeoning industry.
One basic piece of equipment that the company recommends to shops considering an upgrade is an automated metering system that measures both bulk fillers and heated resin directly into a separate mixing vessel. When the operator enters a preset batch size into the computerized control system, Gruber's Batchmaster III machine measures and dispenses the correct amount of material, on either a volumetric or a weight basis, via gear pumps. Hoppers are equipped with anti-bridging vibrators, and a three-way air valve (driven by shop air) controls resin and catalyst. Batch size is limited only by the size of the mixer and the filler supply. And, since the resin and catalyst are combined only in the mixer, the machine does not require cleaning of cured material. Add-on options are available that allow the addition of pigments as well, says company president John Hoskinson.
"In addition to better color consistency and reduced labor, significant cost savings come from the built-in resin heater, which reduces resin consumption by 2 to 3 percent because of lower viscosity and better flow," Hoskinson notes. "That translates to about 10 percent of part cost."
The company's general rule is that if a cultured stone or solid surface manufacturer is producing more than 6,000 lb/2727 kg of material per day, an automatic continuous casting machine, such as its trademarked Autocaster Economizer, is the right answer. Both Carney and Hoskinson are quick to point out that even smaller shops can benefit. Adjustable from 10 lb/min to 40 lb/min (4.5 kg/min to 18.1 kg/min) of output with the standard auger and capable of 30 lb/min to 80 lb/min (13.6 kg/min to 36.4 kg/min) with a high-capacity auger, the small-footprint machine can handle up to eight preset recipes and three base colors. It's equipped with resin heating, a closed-loop solvent purging system for cleaning, and a hardened steel mixing auger and barrel available with an optional vacuum mixing system. The dry material hoppers can handle fillers up to 2mm/0.080 inch in size.
Other shop improvements available from Gruber include conveyors, gel coating tunnels, grinding booths, sanding machines, vibration tables, postcure ovens, cranes, gantries and bulk handling systems, any of which can improve work flow with a nominal investment.
MODULAR AND CUSTOMIZED MACHINES
Another automated equipment supplier to the cast polymer industry is Gisco, started in 1991 by Jerry Gisko, company president. Customized, reliable automation tailored for any operation, large or small, is the company's hallmark, says Gisco's Cogdill.
The company's equipment is manufactured at its facility near Chicago. Codgill notes that Gisco strives to customize new equipment for each customer's throughput, and offers used machines and financing options as well. Multiple gravity-feed hoppers can accommodate a variety of fillers that are metered and mixed with screw feeders. Polyester resin systems are metered with volumetric gear pumps and the extruder nozzle enables easy mold filling. Gisco also sells a specialty system called the Acrylinker, a unit that enables smaller operations to process acrylic resin-based solid surface products. For all its machines, options are available that enable mold recognition by radio frequency identification (RFID) methods, and that lift, rotate and transport molds rapidly in and out of the machine area, for faster filling and mold turn, says Jerry Gisko. "With automatic mixing and the rapid mold filling that results, not only do you achieve faster mold turn but styrene emissions can be cut by 40 to 50 percent," he notes.
For the small-to-medium shop considering automation, Cogdill recommends Gisco's ECONO-VAC model, a small-scale and affordable system for solid surface parts. For an investment of about $80,000, the equipment offers a range of features, including a marble veining system in which various colored resin/filler mixtures can be incorporated into the part; a fiber chopper attachment for fiber-reinforced applications; a resin heating system; a vacuum system for degassing and air removal; and a Windows-based control system that can be preprogrammed with part recipes. One advantage of the latter is that the machine operator can change the resin/filler recipe on the fly, without having to stop the production line and mix a new batch.
Gisco's customers report that automated machinery reduces casting time by 75 percent, while resin use, on average, is reduced by approximately 20 percent. Says Cogdill, "A shop operating eight hours a day, using 2,400 lb of resin at $1.40/lb can save over $120,000 per year just in resin savings alone."
INCREASED PRODUCTION AND HIGHER MORALE
"Good reasons for automation in the cast polymer industry are to decrease material waste and scrap, increase consistency and quality and improve overall plant productivity — but nonproduction reasons, like worker health and safety, are just as important," says Gary Perry, North American sales manager for Respecta-KWM GmbH (Wulfrath, Germany), maker of automated cast polymer equipment. He argues that employee morale is important, too — increased productivity doesn't cause layoffs but actually increases labor demand. Employees are freed for other plant tasks or for shepherding the greater number of parts produced. Further, workman's compensation claims go down, since fewer injuries occur. And, Perry points out, "It's more prestigious to be a 'machine operator' than a laborer."
Respecta makes a variety of machines for the industry, featuring multicomponent automatic metering and mixing capability for large and small applications in both cultured stone and solid surface. (The machines are manufactured in Germany and shipped to customers worldwide.) Resin and catalyst are metered and mixed with volumetric gear pumps (see "A Roundup of Meter/Mix/Dispense Equipment," CT February 2002, p. 12) and hookups are available for buckets, drums, totes or bulk tanks. Solid fillers are conveyed into hoppers on the top of the machine and then metered and mixed via screw feeders. A proprietary "hardened" alloy makes up the mixing barrel where the catalyzed resin and fillers come together, says Perry. Different screws are available for a range of materials, with selection based on filler hardness and grain size. The barrels can be moved from side to side, to allow easy filling of molds.
Resin mixture discharge can be varied from as little as 2 kg/min to over 800 kg/min (4.4 lb/min to 1,760 lb/min) and filler size up to 16 mm/0.625 inch in diameter can be accommodated. Machines are customizable for up to 20 dry fillers mixed with polyester, epoxy or acrylic resin systems, says Perry. For example, the company's trademarked VacuCast machine, model DB-VaC11/10-20 can deliver up to 20 kg/min (44 lb/min) of mixture, with four filler components up to 4 mm/0.16 inch in size. The machine is equipped with a vacuum pump, a resin heating system and a computerized control system to store and implement product recipes.
Machines can be operated continuously, 24/7, or in batch mode. Cleanup is easy since the machines are self-purging, meaning the machine expels any mixed and catalyzed resin with a cleaning solution, with no manual cleanup required.
Rynone Manufacturing Corp. (Sayre, Pa.), one of the largest cultured stone bath fixture suppliers in the U.S. with more than 250 employees, is a Respecta customer. Director of sales and marketing Scott Sulzbach says his company manufactures 800 or more bath vanity tops per day, in standard and custom sizes up to 160 inches/4.1m long, in 150 color offerings. Four Respecta machines, fed by a single, large gravity-feed hopper, run two shifts per day producing parts; the third shift purges and flushes the machines, explains Sulzbach.
Although they required a significant investment, the machines have reduced resin consumption and resulted in more consistent part color, Sulzbach reports. Production is much faster, with more turns per day per mold, and less maintenance is required than with a manual operation. "Our automation efforts, which also include a robot for gel coat spraying, have resulted in improved overall part quality and less raw material waste," he says. Notes Perry, "The human error factor in the mixing process can be virtually eliminated."
Gruber's Carney sums up: "The combination of the material savings, reduced air emissions and more efficient use of labor makes the move to automation a necessity for the cast polymer industry."
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