Canadian Plastics

The Daily Grind

Uniformity is key to effective plastics-scrap recycling, says Hugh Smith, size-reduction product manager at Conair. "Pay attention to how the material is treated during size-reduction." Profitability ...

August 1, 1999   By Jocelyn Chu



Uniformity is key to effective plastics-scrap recycling, says Hugh Smith, size-reduction product manager at Conair. “Pay attention to how the material is treated during size-reduction.” Profitability depends on producing clean, uniform granulate at a high rate, economically and without a hitch.

To achieve this result, a two-stage, shredding-granulating process is often the preferred choice.

“While granulators, blurring at 500-to-1750 rpm, reduce parts to tiny fractions of an inch, shredders quietly reduce large scrap — like the 800-lb, ‘cow patties’ of extrusion — at 10 to 100 rpm” explains Uni-Shred’s president Tony Eccles.

Dual-stage units combine shredder-like, large-part-size reduction with the clean, uniform regrind from granulators. These systems are gaining prominence, with many manufacturers offering shredder-granulator combinations.

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Shredder, granulator or both?

Kazuo Otomo, executive director of Nissui, says their low-speed (30 rpm) shredder-granulator combination allows for larger sprue handling and easy use with sprue pickers. Dust is minimized, pellet size is uniform, and the closed-loop system prevents contamination. Hoppers, bases and electrical systems can be customized with pellet-remover systems and in-line filters.

AEC Nelmor’s new line of electric and hydraulic shredders and shredder-granulators — single-or dual-stage units — provide high volume size-reduction of hard-to-handle materials. They feature counter-rotating hex shafts that intermesh to grasp unwieldy materials and eliminate flyback. High torque and low-speed blade-rotation translate into tearing with little wear.

Sterling Ball and Jewell’s new SB Series shredders and shredder-granulators take on large, bulky parts and scrap. Single-stage shredder or combination, they are powered by electric or hydraulic, single or paired motors (10 to 226 hp). The combination

systems have lower peak loads than

grinder-only.

Amy Biddle, marketing manager at ReTech Industries, remarks that the recently introduced RG52 rotary grinder “functions like both shredder and granulator, while operating at lower cost.” Handling large rejects and purgings, and delivering usable particles without prior reduction, it has quick clean-out, “positive-feed” controls, and single-cutting rotor with inserts for durability.

“As the cross-over zone broadens between granulation and shredding, the design thrust in shredding moves towards granulator performance levels — the objective being single-stage reduction without jeopardizing throughput,” says Uni-Shred’s Eccles. Uni-Shred is readying a miniature-shredder line for dealing with purgings in-house.

Radical shuttle concept

B. Patrick Smith, vice-president of sales and marketing at Maguire Products Inc., touts the unique, economical Shuttle Granulator. Large scrap and reject parts are planed into small pieces and ground into uniform, reprocess-ready regrind. A shredder alternative, it transforms large blow- or roto-molded items, film rolls, and pipe sections.

In the low-cost, carpentry-inspired planing phase, staggered rotor knives reduce gravity-fed scrap to tiny bits. Maguire’s innovative Radial granulator, originally designed for press-side use, is used for the second stage in this central system. Granulate quality is improved, and flyback and dust problems overcome.

General-purpose units not so generic

Conair’s Smith stresses that even generic granulators don’t suit all tasks: “Even with general purpose grinding, the trend is to fit a relatively narrow scrap range.” Conair’s mid-size CG Series are general-use, press-side granulator lines whose range of applications can be fine-tuned by options.

Processing up to 600 lb./hr., the CG Series features tangential-feed cutting chambers and three-blade open rotors to handle batch-processing of tough injection molded parts and bulky, blow-molded containers. Material directed to knife downstroke is ingested instead of bouncing on the rotor top. The scissor-like action of slanted rotor knives augments regrind quality, garners energy savings, and produces less heat.

Joyce Candela, marketing manager for AEC/Nelmor, reports the development of a line of press-side granulators with new sizes to closely match applications. The Marathon Series processes from five to over 500 lb./hr. An exclusive, side-entry hopper door and wider access to the cutting chamber make for clean-out convenience. Bed-knife adjustments can be made at machine front; a double-walled hopper and base make for supremely quiet operation.

Foremost Machine Builders, Inc.’s C-Series granulators, suiting HDPE applications, have tangential feed and high-shear rotor type to eliminate dragging of part against chamber for reduced dust and fines.

In the large granulator range, Rotogran International Inc. has expanded on the capabilities of its RO line with the WO Series. Cryogenically treated knives have prolonged life under adverse conditions, and quick cutting-chamber access is via a hydraulically assisted hopper and screen cradle. Torque-limiting safety coupling prevents rotor damage. (Available with 36 in. cutting circles, 500 hp motor, and a 72 in. wide by 36 in. deep hopper.)

Cumberland Engineering’s new Auto-700LS Series features a new cutting chamber design with multi-knife helical rotor, says Robert Bloom, vice-president of sales and marketing. Rotating side-end disks minimize heat build-up, dust and fines. An optional, three-blade, open rotor with scoop design “completes the criteria for use across the application spectrum.”

Quiet on the floor

Sterling’s Ball & Jewell Division recently announced the Maverick MVP Series of press-side granulators. “In direct response to customers saying they could not detect whether their super-quiet MVP units were actually running, we decided to offer two illuminated on/off switches,” reports Steve Petrakis, vice-president sales and marketing. The traditional choice of rotor has been expanded to include an open/solid rotor that combines inertia with the airflow of open design, and comes with counter-angled knives capable of true scissor-cutting. Maverick MVP granulators are available in five sizes of cutting chamber, with conveyor, robot and long-part chute options for adaptation to diverse applications.

Accessibility issues

The latest emphasis at New Herbold, Inc. is on “expedient, safe accessibility to grinder components for clean-out between material changes, maintenance, and blade changes,” says president Edward Ronca. A hydraulic cylinder or electrically operated screw jack are offered on all large-part, central-station granulators to expose the entire chamber. Knife-setting fixture allows resetting of knives outside the machine, reducing changeover time by more than half and avoiding rotor thread repairs, common under extreme conditions.

Kirk Winstead, vice-president of sales at Rapid Granulator, explains how rotating knives on its grinders self-adjust after resharpening, maintaining a constant cutting gap, with bed knives located against machine stops. The result is “no more clogged screens,” and longer knife life.

Rapid’s new Rapid Rage Series, for heavy-duty and central grinding, has a 13.8 in. rotor diameter, and cutter-house sizes up to 31.5 in. for throughput to 1,322 lb./hr. A three- or five-blade rotor configuration can be specified. Patented CleanGRIND cutting technology ensures consistent regrind and fewer fines. Finally, the new Rapid Force Series, in three sizes, offers low-speed, beside-the-press, small-scale grinding.

Granutec’s systems have an optional zero-speed switch on all systems to sense rotor-rpm loss, shutting down to prevent drive belt damage and the unit’s self-destruction. The heavy-duty package of Granutuf knives, hardened and replaceable wear plates, and carbide-coated screens extends granulator service.

For lightweigths only

Drew Schmid, director of sales at Foremost, reports the SCG-11 Series of granulators addresses LLDPE film, utilizing a unique spiral-cut rotor design for cutting tough stuff down to size without pounding vibration. (Ava
ilable in 11 x 16, 11 x 24, and 11 x 32-in. models.)

In reducing lightweight plastics, rotor action can kick pieces away from cutters to outside the hopper. Tom Ballus, marketing director at Nordfab Systems, says the VORTEX rotary granulator (from Vecoplan) with “bridge-breaker” option pushes lightweight material into the hopper and to an automatic ram, “like a trash compactor.”

Tim Hanrahan, vice-president at Erema North America Inc., says of their new Continuous Densifier System: “It reduces and densifies scrap without melting, accepting materials in many forms without presizing, and producing ready-to-use, high-bulk density agglomerate.”

Granutec boasts cutting-edge technology in thermoforming reclamation. Self-contained, multi-purpose granulators include the Crusher Roll System for in-line processing of skeletal web/sheet with whole thermoformed parts in place. The operatorless FRG Series is a multi-functional, under-the-press system for reclaiming guillotined skeletal material. CPL

Jocelyn Chu is a freelance writer-editor, illustrator and multimedia consultant who shuttles between Toronto and Fernie, B.C.


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