When Screen Classifying Cutters Outperform Hammer Mills and Knife Cutters
Screen Classifying Cutters combine the shear of a Knife Cutter with the impact of a Hammer Mill at high speeds, reducing friable, semi-friable, fibrous, semi-hard and hard materials into controlled particle sizes at high rates with minimal fines.
Like Knife Cutters they shear material against bed knives, but Screen Classifying Cutters can handle a greater diversity of materials and retain sharpness far longer. At medium to high speeds, they additionally impact material similar to a Hammer Mill, but add the flexibility of variable RPM for greater control of particles sizes. As a result, Screen Classifying Cutters are often more effective than either machine at reducing friable, hard and fibrous materials into uniform particle sizes from 2 in. (5 cm) down to 20 mesh or less, with fewer fines and/or less heat generation.
The infeed throat houses a horizontal rotor comprised of tightly-packed, staggered parallelograms or “stars,” each of which holds cutter tips that shear materials against twin stationary bed knives at lower rotor speeds, and additionally impart high impact at higher RPM. The rotor design generates many times greater force per inch with each cut than a conventional knife-type cutter of equivalent horsepower.
As material enters the infeed chute, it is subjected to successive mechanical shearing against the bed knives until small enough to pass through the screen apertures, the size of which determines residence time. The result is uniform, coarse grinding down to 20 mesh with minimal fines or heat generation, and reduced energy use.
Typical applications include reducing bulk foods, spices, sugar cane and hemp stalks, tobacco, plastics, batteries, brake pads and compounds, chemicals, clays, coal, minerals, detergent blocks, fiberglass insulation, filter cake, gypsum, ceramic honeycomb filter media, carbon/aramid fiber, leather, glass bottles, trim stock, wood products and a broad range of scrap.
The rotor can range in length from 10 to 72 in. (25 to 183 cm), and its geometry can be adapted to optimize the application.
Standard models have an 11 in. (28 cm) wide infeed throat that houses a 10.5 in. (26.7 cm) diameter horizontal rotor comprised of tightly-packed, staggered parallelograms, each of which holds two, half-inch wide (1.3 cm wide) cutter tips. An ultra-heavy duty Magnum™ version with 22.5 in. (57 cm) wide infeed throat has an 18 in. (46 cm) diameter rotor comprised of 4-sided “stars,” each of which holds four one-inch wide (1.3 cm wide) cutter tips, boosting capacity by approximately 75 percent and accommodating larger infeed sizes.
Available in food-grade, industrial and abrasion-resistant finishes, and in a range of sizes from mini laboratory units to ultra-large units six feet in length, Screen Classifying Cutters can mince, crush or crumble materials that are soft, moist, sticky, medium-hard, fibrous, or friable offering great flexibility in size reduction.
Following are seven case history examples that examine the performance of Screen Classifying Cutters in reducing a diverse range of materials.
Thermoformer recycles plastic scrap, reduces maintenance
A major plastics thermoformer, whose operations include sheet extrusion and calendering, installed 20 screen classifying cutters to assure efficient granulation and sizing of its process scrap.
The company runs the cutters at full capacity during production runs to deliver properly-sized granulate for processing. The Screen Classifying Cutters replace units that required frequent blade changes and could not keep pace with the high production rates.
The cutters have a 15 in. (38 cm) wide infeed throat and ½ in. (1.3 cm) cutting blades with carbide tips. The blades are designed to slide onto each machined holder and be screwed into place. Changeover requires minimal downtime.
Scrap from the extruders and a calendaring line ranges in thickness from 0.008 to 0.04 in (8 to 40 mils). The scrap is pneumatically fed to the cutters in a continuous operation that runs 24/7. Each cutter processes at a rate of 250 lb/h (113 kg/h).
The Screen Classifying Cutters enable the plant to reduce the size of process scrap in the required capacity, with the uniformity needed to reprocess the material efficiently, improving efficiency of the operation.
High volume size reduction of vanilla beans
Givaudan Flavors Corp., East Hanover, NJ, prepares and packages natural food flavors extracted from vanilla beans, cola nuts, ginger roots and cassia bark for food and beverage manufacturers.
The plant processes natural ingredients on a mass scale, placing high demands on its size reduction equipment. The plant grinds upwards of 6000 lb (2700 kg) per hour of ginger root, cassia bark, or cola nuts, and cuts about 3000 lb (1360 kg) per hour of vanilla beans into uniform size chips — within relatively tight tolerances required for efficient extraction of flavors.
A Screen Classifying Cutter reduces the vanilla beans to consistent particles sizes, presenting the best surface area for liquid extraction of flavors.
Cleaning of the equipment between batches proceeds rapidly. The operator flushes out the cutting chambers with nitrogen, and rinses with water.
Increased Yield and Uniform Grinding for Date Processor
Jewel Date Company of Thermal, CA, switched from using a Hammer Mill to using a Screen Classifying Cutter to reduce dates into granules and powders.
The company grows, processes and packages approximately 8 million pounds (3.6 million kg) of dates and date products a year. In addition to whole dates, a portion of the crop is processed into date granules and date powder.
A Hammer Mill previously processed 2000 lb (907 kg) of dates in an 8-hour shift. The Screen Classifying Cutter processes the same amount of product in only one hour with more uniform results, increasing productivity eight-fold.
Dates have a high moisture content and range in size from 1-1/4 in. (3 cm) to nearly three inches (2.8 cm) long. To process them, the dates are air-dried for two days to reduce the moisture content from 50% to 7%. According to the company, anything greater than 7% moisture would cause the dates to clump during processing.
Unlike a Hammer Mill which uses a series of hammers strike and break the material apart, the Screen Classifying Cutter repeatedly shears it into uniform-sized particles.
With the variable speed motor, the plant can run the cutter at 1,500 RPM to produce particles down to 1/16 in. (1.6 mm), or at 1,200 RPM for particles down to 3/16 in. (4.8 mm) to achieve the output of powders or granules required by its customers.
According to Sales Manager John Ortiz, "The Screen Classifying Cutter has not required parts or maintenance in its first four years of operation, and it has fewer moving parts than our Hammer Mill." He adds, "Stainless construction with a food-grade finish allows us to clean it quickly."
Producer of calcium chloride satisfies high demand
Cal-Chlor of Opelousas, LA, operates five, 30 in. (76 cm) Screen Classifying Cutters to meet demand for calcium chloride powder used by the petroleum industry.
The plant reduces CaCl2 pellets into a powder comprised of uniformly sized particles that is used in drilling shale formations, flushing mud from oilfield holes, and filling casings when drilling ends.
Each Screen Classifying Cutter processes up to 26,000 lb (11,793 kg) of product per hour, says Brett Davis, operations director. The cutters are so important to meeting oilfield on-time demand that Cal-Chlor runs four of them and keeps the fifth for emergency use if one goes offline. The plant's daily CaCl2 powder production ranges from 200 to 400 tons (181 to 363 tonnes).
According to Davis, the cutters are "near bulletproof" when it comes to processing CaCl2, which is abrasive, generates heat when collected in large volumes, attracts moisture, and is extremely difficult to handle. He notes that as little as 3-4 oz (84-112 gm) of CaCl2 in a cup with water will become too hot to hold in minutes.
Each cutter at the Opelousas plant has a 30 in. (76 cm) long by 11 in. (28 cm) wide infeed chute. The cutters are made of stainless steel, which resists abrasion, corrosion and other problems that CaCl2 presents. Cal-Chlor operates the machines at between 1,200 to 1,800 RPM to achieve the desired particle size.
Mini Paper Mill Increases Efficiency, Lowers Energy Requirement
The University of Maine (Orono) Process Development Center (PDC) provides the paper industry with leading-edge, collaborative pulp and paper research. The process lab — originally part of the university's forest and paper industry program — houses a virtual "mini" paper mill with a broad range of processing equipment.
The PDC is equipped to work with a range of raw materials including wood, bark, herbaceous crops, and agricultural residuals. Available processes include extraction, pulping, bleaching, papermaking, coating, and finishing. To facilitate its process work, the lab requires efficient size reduction capabilities to downsize materials into uniform particles.
At the outset, the lab used a Hammer Mill which proved to be inefficient and failed to produce consistently sized particles due to its crushing and pulverizing action. The PDC replaced it with a Screen Classifying Cutter. "We specified that unit because it efficiently reduces materials into uniform particle size with a lower energy requirement than the Hammer Mill," said Mark Paradis, the PDC's group leader of engineering. He added that it requires minimal maintenance.
The Screen Classifying Cutter played a key role in one initiative to reduce perennial grasses and hay into 1/8 in. (3.2 mm) particles which were then compressed into biofuel pellets.
In another project, a University of Maine chemical engineering professor developed a biodegradable golf ball partially composed of lobster shells. Here, the Screen Classifying Cutter reduced the shells to powder form for downstream processing.
High Throughput with Difficult-to-cut Cinnamon
ForesTrade, based in Brattleboro, VT, produces and distributes tropical, organically grown spices, coffee and essential oils. In 2004, the company built a state-of-the-art cinnamon processing plant in Indonesia. According to Mary Porter, manager of Indonesian operations, the company equipped the plant with a 15 in. (38 cm) Screen Classifying Cutter, based on the recommendation of another local spice producer.
The harvested cinnamon arrives at the plant in bags as rolled sticks, known as quills that range in length from 3 in. (7.5 cm) to 39 in. (1 m). The bags are then manually emptied onto a belt conveyor, where workers remove stones and other extraneous material, and arrange the quills inline for the cutting operation.
The quills are fed pneumatically into a high-speed model 15 in. (38 cm) Screen Classifying Cutter. Driven by a 20-hp (15-kW) motor, the blades rotate at 2,200 RPM and continuously shear the quills against the bed knives, cutting them into 2 in. (5 cm) lengths. Despite the high rotation speed, there is little to no heat generation and minimum fines.
The cutter contributes to quality by producing uniform pieces and a cleaner cut. Ms. Porter points out that having a clean, uniform cut is not only important for meeting size specifications, but makes for consistency in drying.
Ordnance fabricator saves money, recycles tungsten heavy alloys
Aerojet Ordnance of Jonesborough, TN, fabricates parts from tungsten heavy alloys and other refractory metals for defense-related products like ammunition, warheads and electronic shielding.
Tungsten heavy alloys are one of the densest metals produced. Reclaiming fabrication scrap was difficult and costly, prompting Aerojet to sell the scrap at significantly lower prices than it was worth as a recycled and reusable material.
Looking for a better solution, Aerojet experimented with techniques to reclaim tungsten heavy alloys scrap, including using a Hammer Mill and manually downsizing pieces. None of the methods was efficient or produced consistently sized particles. According to Tim Brent, project engineer, a Hammer Mill's crushing, pulverizing action was not effective with material of this density and generated dust. With manual reclaim, "labor costs were prohibitive and the results uneven."
"If we can reuse the material, it is worth two- to three-times more to us than selling it as scrap," says Brent. "But we couldn't reuse the material without an effective means of size reduction."
After testing several size-reduction machines, comparing particle sizes, consistency and economy, Aerojet decided on a Screen Classifying Cutter with a 15 in. (38 cm) long rotor. Aerojet's engineers were aware that the machine had a successful record in similar applications. "The design is simple and stands up to the tungsten heavy alloys," says Brent.
Aerojet specified an abrasion-resistant interior and a special stand to accommodate containers used in moving scrap to the process machines.
"Downsizing different grades of tungsten heavy alloys raises the risk of batch contamination if the interior isn't properly cleaned," he notes. "The cutter is easy to clean, compared to other machines," he says.
Conclusion
Hammer Mills and Knife Cutters are often default choices for size reduction due to their long term existence, familiar names and broad capabilities. However, the range of applications they can satisfy efficiently is narrow. Indeed, many Hammer Mill users sacrifice particle size control and excessive fines, while many Knife Cutter users are resigned to frequent shutdowns for re-sharpening of blades that quickly lose their edge. In these and other situations, plant engineers would do well to test their material on a Screen Classifying Cutter side-by-side with a Hammer Mill and/or Knife Cutter in manufacturers’ test labs. Only in this way can he or she quantify the difference in efficiency, output and product quality afforded by each machine, and reap performance benefits over the long service life of the ultimate purchase.
Screen Classifying Cutter reduces the size of hard, soft and/or fibrous materials in controlled sizes ranges with minimum fines at high rates.
Bedscreens range from 2 in. (5 cm) down to 20 mesh or less. Aperture size determines dwell time and allows tight size control with minimal fines or heat generation.
Close up of Screen Classifying Cutter with 15 in. (38 cm) long, 11 in. (28 cm) diameter rotor illustrates helical array of staggered, carbide tipped holders that continuously shear material against twin, stationary bed knives.
Magnum™ version of Screen Classifying Cutter employs 4-sided stars, each of which holds four one-inch wide (1.3 cm wide) cutter tips, increasing capacity and infeed sizes.
Edge trim from a calendering line is fed pneumatically into a tube atop the rotor enclosure of the Screen Classifying Cutter for downsizing.
Screen Classifying Cutters produce plastic granulate of consistent size and properties.
Screen Classifying Cutter grinds vanilla beans at the rate of 3000 lb/h (1360 kg /h).
Vanilla beans are chopped into uniform particle sizes with minimal fines.
This specialized Screen Classifying Cutter employs re-sharpenable solid stainless steel cutter blocks that are seamlessly welded in a staggered array, and cut against two bed knives — one on the upswing, one on the downswing. The crevice-free rotor assembly and housing facilitate rapid, thorough cleaning.
Jewel Date Company grows, processes, packages and ships dates and date products including whole and diced dates, date flours, granules and powders.
Each Screen Classifying Cutter reduces calcium chloride pellets into powder comprised of uniformly sized particles at rates to 26,000 lb (11,793 kg) per minute.
Cal-Chlor is the world's largest distributor of calcium chloride powder, which is shipped in 50 lb (23 kg) plastic valve bags.
Photo Courtesy of the University of Maine
Screen classifying cutter downsizes raw materials into uniform particles at University of Maine's Process Development Center. In one alternative energy project, perennial grasses and hay are pelletized to make compressed biofuel pellets.
Cutter tips attached to a helical array of staggered holders continuously shear oversize materials against twin, stationary bed knives
As bags of raw cinnamon quills arrive at the plant, they are emptied onto a belt conveyor for processing.
Screen Classifying Cutter reduces cinnamon quills into 2 in. (5 cm) lengths.
Screen Classifying Cutter downsizes tungsten heavy alloy scrap (2.5 times the density of steel) into powder for reuse in the compaction process.
Screen Classifying Cutter downsizes tungsten heavy alloy scrap into controlled particle sizes with few fines and no heat buildup.
