Canadian Plastics

Gateways to success

The history of technology is filled with "black arts" -- processes so complex only a select few can understand them.

June 1, 2007   By Mark Stephen, associate editor



The history of technology is filled with “black arts” — processes so complex only a select few can understand them.

A modern example often cited in the plastics industry is hot runners, the channels within an injection mold through which molten plastic is distributed.

But just because hot runners seem mysterious doesn’t mean plastics processors can’t take advantage of new developments to remain competitive; and the recent breakthroughs in hot runners relate mostly to valve gates, devices that regulate the melt flow via cylinder mechanisms connected to hot runner nozzle pins.

TAKING CONTROL

Hot runner manufacturers identify several advantages of valve gating over the more traditional thermal gating. “There’s no doubt valve gates offer better control, especially right at the gate,” said Martin Baumann, business development and marketing manager, hot runners, with Husky Injection Molding Systems Ltd. “With the mechanical shutoff offered by valve gate systems, molders are in control of what is happening with the gate vestige.”

Control is all the more necessary given continuing developments in both commodity and engineering resins. “Some of the new resins are so sophisticated that they’re not easy to flow into the mold, and require the quick, controlled mold close that valve gates provide,” Louis Hbert, president of Hasco Canada Inc., said.

According to Harald Schmidt, president of Mold Hotrunner Solutions, valve gates are also well suited for softer materials, like elastomers, which are characterized by material elongation of between 200 and 300 per cent. “Valve gates give a more effective packing or hold pressure to keep tight dimensions in the part,” he explained.

Soft, sophisticated resins allow for the possibility of superior looking plastic parts, and in this area too valve gates appear to trump their thermal counterparts. “The growing complexity and cosmetic requirements of today’s parts, including clear parts, is steering customers to valve gating,” said Bob Ameel, global business manager, hot runner systems, with D-M-E Company. “A thermal gate system often leaves a distinct witness mark, whereas on some of the valve gated parts the witness line is small and less distinctive than an ejector pin mark.”

For all these reasons, valve gates are growing in popularity, to the point that the relative high cost is ceasing to be a factor. “Customers are finding that the higher investment of valve gates pays off quickly because they add value to the automated molding process,” Harald Schmidt said.

Given these factors, it’s no surprise that developments in valve gates, and new product lines, are coming as thick and fast as resin through a melt channel.

COVERING THE SPECTRUM

Also not surprisingly, many valve gate systems are designed to cover a broad range of plastics applications that use a broad range of resins. D-M-E Company, for example, recently introduced the Polivalve system, designed to cover all markets where high-quality surface finish is important, from small medical and electronic applications to large auto parts. Polivalve is available in two formats: a full “Hot-Half” system, and a Simplicity “Drop-In” system. “The D-M-E Drop-In system differs from others in that it is supported by a manifold plate with all of the air, hydraulic, wiring and water channels contained inside,” D-M-E’s Ameel explained. “Secondary machining for service channels is not required, therefore improving the overall strength of the mold assembly.”

The new Accu-Valve CX and EX valve gate designs from Mold-Masters Limited are versatile with a wide range of resins, from polyolefins to filled crystal materials to such thermally sensitive materials as polyvinyl chloride (PVC), polyacetal (POM) and polyphenylene sulfide (PPS). The CX is intended for polyolefins and commodity resins where melt viscosity is relatively low, while the EX is built for engineering resins at higher temperatures. Both systems utilize a new V-Guide method of preventing material from migrating between the valve pin and valve disk by creating a thermal barrier within the valve disk itself.

The Rheo-Pro valve gates, from Mold Hotrunner Solutions, are also designed for versatility. “Successful exotic valve gate applications with, for example, 70 per cent copper-filled acrylonitrile-butadiene-styrene copolymer (ABS) or 60 per cent carbon-filled PA6.6 is not uncommon,” Harald Schmidt said. The company also offers top mounted valve control units with integrated PLC solenoid control.

GETTING INTO IN-MOLD LABELING

In-mold labeling is all the rage among today’s packaging manufacturers, and hot runner suppliers are responding. Incoe Corp. has teamed up with Traverse City, Mich.-based control systems provider RJG Inc., for example, to introduce the GSC2 valve gate system, suitable for in-mold decorating, as well as for painted or chromed parts. According to Incoe, the GSC2 technology provides weld line positioning or elimination; consistent part weights in family molds; clamp force reduction; and reduction of warping or flash from over-packing.

SMALL DIAMETERS AND CYLINDERS

It’s a paradox that as a technology grows more popular it can also grow smaller.

Husky recently unveiled the Ultra 350, its smallest ever valve gate, which has a seal diameter of 8mm, a bore diameter of 16mm and a minimum nozzle spacing of 25.4mm. According to Husky’s Baumann, the system provides throughput of up to 30 g/sec for low viscosity resins, and uses a pneumatically actuated plunger style gate designed to be efficient in small, high cavity applications. The company has also recently introduced the B2B VG, a back-to-back valve gating system for stack mold operations, designed for applications ranging from thin-wall packaging to automotive.

Other developments relate to cylinders. Synventive Molding Solutions recently introduced two types of valve gate cylinders suited for either hydraulic or pneumatic valve gate systems. The HYC 4018 and PNC 7518 are available with tapered or cylindrical shut-off; adjustment of the needle position (+/- 1.5mm) without prior removal, to facilitate assembly and service; anti-twist needle lock for safe positioning of bevelled nozzle tips to the needle; and compact design for limited-space applications.

GOING ELECTRIC

Until recently, valve gate cylinders operated either hydraulically or pneumatically, but as injection molding machines go electric, valve gate technology is following suit. Ewikon Hot Runner Systems, for example, recently unveiled an electrical needle drive designed for valve gates running on fully electric injection molding machines. According to the company, the valve pin positioning has an accuracy of 0.0007 inches, and is suitable for use with nozzles with flow channel diameters of three to nine millimetres. And if a deviation is detected during molding, the needle automatically re-adjusts its position within one molding cycle.

Hasco’s new Z1081 needle-drive valve gating system, which can be used with hydraulic, all-electric or hybrid machines, operates by use of an electromagnetic coil built into the cylinder housing that creates a magnetic field to actuate the pin. “The unit requires 24 volts to operate, which is essentially provided by the molding machine itself,” Hasco’s Hbert said. “There is no oil leakage or air issues, making it ideal for the food packaging and medical technology industries, where cleanliness is always an issue.” And if a molder doesn’t have access to the 24 volts required to run the system, Hbert continued, the company can supply a PowerPC to boost the amperage.

HOW TO DO IT

Reaping the full benefits of new valve gate technology requires more than simply purchasing a system, however. Hot runner suppliers stress that proper installation and servicing — with input into these processes from the suppliers themselves — are necessary for the plastics processor to get the most out of the
investment. “Many molders can valve gate,” D-M-E’s Ameel explained. “What we’re finding is that the interface with the customer up front, and planning out the design and assembly of the system based on what the customer is trying to achieve, is an extremely important step. This way, starting up the system becomes more conventional.”

Resource List

D-M-E of Canada Ltd. (Mississauga, Ont.);www.dme.net; 800-387-6600

Ewikon Hot Runner Systems of America Inc. (East Dundee, Ill.); www.ewikonusa.com; 800-980-4815

Hasco Canada — Div. of Hasco America (Toronto); www.hasco.com; 800-387-9609

Husky Injection Molding Systems Ltd. (Bolton, Ont.); www.husky.ca; 905-951-5000

Incoe Corp. (Troy, Mich.); www.incoe.com; 248-616-0220

Mold Hotrunner Solutions Inc. (Georgetown, Ont.); ww.mhsinc.ca; 905-873-1954

Mold-Masters Limited (Georgetown, Ont.);www.moldmasters.com; 905-877-0185

Synventive Molding Solutions (Peabody, Mass.);www.synventive.com; 800-367-5662

Lutek Plastics Equipment Inc. (Dorval, Que.); 888-505-8835

Precision Mold Supplies Ltd. (Delta, B.C.); 604-943-7702


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