Rotomolding nylon 6 parts directly from caprolactam monomer and pulsed-air pressurization of molds to make tougher parts were new developments presented at the 29th annual Fall meeting of the Association of Rotational Molders (ARM) in Cleveland. A new source for automated material batching, an anti-microbial mold spray, and several new machines—both maxi and mini—were also introduced at the meeting.
Making nylon in the mold
A process that polymerizes liquid caprolactam in the mold has been brought to the U.S. by rotomolder Centro Inc., North Liberty, Iowa. Called Rotomolded Anionic Polymerization, or RAP, the process is claimed to offer cost savings relative to using standard nylon 6 resin. Centro developed the process with several other European companies. RAP has been used in Europe for several years to make fuel tanks, but Centro worked with several U.S. and European companies (which it declined to name) to improve the safety and productivity of the process. Centro is not currently offering to license it, but only to use RAP to make parts itself.
In the RAP process, a robot dispenses liquid caprolactam plus a catalyst and activator into a heated aluminum mold, which is then rotated while the mixture reacts to produce a virgin nylon 6 part. The process is said to be faster than molding with nylon 6 and reportedly makes superior parts free of surface porosity. In addition, RAP makes it easy to customize formulations with pigments, impact modifiers, and uv stabilizers, plasticizers, etc.
This mold has a pulse
A new pulsed pressurization and venting method is being developed to cut molding cycle times while also reducing shrinkage and warpage and increasing part quality by eliminating trapped air bubbles. This “DynamiKventing” method comes from 493K Ltd. in Northern Ireland, a relatively new spinoff from Queen’s University Belfast. The firm supplies mold-temperature and pressure measuring equipment based on R&D conducted at the school’s Rotational Molding Research Centre.
DynamiKventing delivers pulses of 1- to 3-psi air into the mold in timed cycles. The pulses can be as long as 10 sec and spaced as much as 10 sec apart. The system measures the air pressure and flow into and out of the mold to detect problems such as a blockage in the vent pipe and ensure that the mold is depressurized prior to being opened. Research has shown that part impact strength can improve up to 10%. The company expects to launch the process sometime in 2005.
Automate charge batching
Material-handling and dispensing systems for individual machines or plant-wide use are now available from reSource Inc., which has supplied custom material handling systems for plastics since 1994 but not previously for rotomolding. The company’s line of material preheaters, mixers, and automated dispensing equipment reportedly can help trim overall cycle times by up to 25% while reducing scrap and allowing for just-in-time material delivery.
The firm offers powder preheating, weighing, blending, and dispensing systems. For example, reSource can supply systems with a central resin preheat station that delivers material to as many as eight gravimetric blending hoppers where different colors and/or additives are blended in. Systems use PC-based controls with easy-to-use touchscreens, recipe storage and retrieval, and real-time reports.
The firm also offers systems that use high-intensity blenders to heat the material so no preheating is necessary. And instead of central blending, individual dispensing systems can automatically blend and dispense mold charges on demand at the press. Charges can be dispensed at up to 10 lb/sec for shot sizes up to 30 lb with accuracy within 0.02 lb (10 g).
No more roto-moldy parts
Part discoloration due to the growth of bacteria, yeast, molds, and fungus can be suppressed with Microface 1, a new antimicrobial aerosol coating for polyolefin parts from Mold In Graphic (MIG) Systems. The permanent, silver-based spray was developed by MIG and AgIon Technologies, Inc., Wakefield, Mass. The colorless, odorless spray impregnates the part surface to combat microorganisms, which are killed by silver ions. The spray combines silver with a polyolefin and a ceramic that permits controlled release of the silver over time. This biocide reportedly does not affect the part’s color or physical properties and is tolerant of rotomolding process temperatures. The coating can be applied in the mold or to the part after molding.
Ferry Industries is developing a huge new shuttle machine with a 26-ft (312-in.) swing diameter, capable of supporting 15,000-lb molds. Model RS7300 is designed to mold large parts such as chemical or agricultural tanks. It can be ordered with a straight or offset arm.
Ferry also plans to roll out a rock-and-roll unit for large parts that delivers better wall-thickness uniformity, allowing for possible part-weight reductions. The new RO-6100/3300 machine lifts the oven from both ends and controls the tilting angle of the oven precisely and repeatably. This allows for much more uniform wall thicknesses than conventional rock-and-roll machines, which have a center pivot. The new model can produce tanks up to 20 ft long and 11 ft in diam. It also holds up to 15,000 lb.
Meanwhile, Ferry’s Quintax line of routers has been expanded with a new range of three-axis CNC units that have PC-based controls. The models are said to deliver finer part finishing.
Machine builder STP Equipment has re-engineered its High Volume Shuttle (HVS) machines for large parts. These “rocking shuttle” units have a rocking oven. What’s new is the operator stands at floor level instead of up on a platform, which has been eliminated. In addition, the touchscreen control interface has been revised with more user-friendly graphic icons. The HVS series takes up half as much space as a conventional rock-and-roll oven.
STP is also building its two largest machines ever. These Hurricane in-line shuttle units will have a 220-in. swing radius and will produce septic tanks and a marine product for molders in the U.S. and France.
Prototype or lab-size rotomolding machines are becoming more widely available. One example is Rotoline’s new Lab 0.5 model, its smallest yet. The unit has a single offset arm and a cylindrical horizontal oven 18 in. long x 18 in. diam. It is designed for short runs of parts that measure no more than 18 in. in diameter. The whole machine (electrical panel, cart, and oven) is mounted on a single base. Major and minor axes have infinitely adjustable speeds from 0 to 24 rpm. Cooling is done with fans and water-spray nozzles. The PLC controls permit manual or fully automatic operation. Price is around $50,000.
Powder King, a two-year-old supplier of pulverizing equipment, rolled out its first milling machine for lab-scale work. The new PK18 pulverizer is a scaled-down model of the firm’s bigger units. It uses the company’s disposable dual-disc and air-flow management technologies and can process samples from 1 to 50 lb at up to 50 lb/hr. The equipment is designed for cleaning in less than 10 min. Other features include a variable-speed drive, vibratory feeder, and gap adjustment for the milling discs from outside the mill with single-stud, push/pull adjusters.
Powder King also rolled out the smallest production pulverizing system in the PK line. The PK120 can grind from 600 to 900 lb/hr of rigid PVC to 20-mesh fineness or 500 to 800 lb/hr of LLDPE to the standard 35 mesh.
More equipment news
Wheeler Boyce, a maker of cast and machined aluminum tools for rotomolding, last June joined in a joint-ownership alliance with Rotoline and Reduction Engineering, a manufacturer of material pulverizing systems. The three companies will remain separate entities.
Wheeler Boyce also announced it is now distributing mold clamps from De-Sta-Co. Industries,Madison Heights, Mich. One new model is the MPLA-1000 pin-clamp system, an alternative to the standard 311 clamp. In addition, De-Sta-Co simplified the design of its 311 bolt receivers and offers a new dual-bolt-receiver design that more easily installs on the mounting frame.