Improved hydraulic valves & pumps upgrade injection machinery.

Look under the hood of just about every new or redesigned model of injection molding press over the past year, and you will find proportional valves and hydraulic pump packages that can outperform the valves and pumps of just a few years ago. In some cases, the new hydraulic components can do a better job at lower cost than ever before.

MORE AND MORE CLOSED-LOOP

Proportional valves with onboard electronics to provide feedback control of spool position are already standard on high-end molding machines. Now, say hydraulic suppliers, press builders are adopting new, less costly valve technology and putting more proportional valves on the machine than in the past. "The majority of machines have had two proportional valves on them, but you're seeing a lot more machines with three or four," notes Dennis Meckler, industry manager for Rexroth Corp. in Bethlehem, Pa.

One reason is speed. "Right now there's a big push for higher injection and clamp speeds, so you're seeing machine makers use more high-performance valves than in the past," explains Ted O'Donnell, project application engineer at Bosch Corp. in Racine, Wis.

Cost reduction has also driven some recent valve choices. For example, improvements to solenoid technology and control electronics have let some Rexroth customers replace pilot valves with less costly direct valves in some molding applications, says Meckler. Not only do these newer direct valves (such as the company's WREE model) cost up to 10% less than some of the earlier generation valves, they perform about 10% better in terms dynamic response and flow capacity, Meckler explains.

Finally, there's the trend toward increased use of closed-loop control. "Just about every new machine has closed-loop control on injection," notes Sean Insalaco, marketing manager at Moog Inc. in Aurora, N.Y. "But there's still not nearly as much closed-loop on the clamp or mold itself." He sees control of slides and other mold actions as the next frontier for closed-loop technology. "It's a growing trend," agrees Bosch's O'Donnell. "When you're moving a large mass of metal in the mold, you don't want to slam it from one end of the stroke to the other."

Growing availability of valves with on-board electronics was evident at the June NPE show in Chicago. For example, Rexroth displayed at least four brand-new proportional valves in both direct and pilot configurations. "These were all higher-performance valves suitable for any closed-loop application," says Meckler.

And Bosch rolled out a new "full-flow-blocking" cartridge valve for clamp-safety applications. It features electronic position monitoring and an external pilot - the latter to ensure that the cartridge can be activated without any system flow. Available since the end of last year, this new safety valve replaces traditional cartridge valves that require system pressure.

QUIET CHANGES IN PUMP DESIGN

It's also clear that variable-volume pumps, which match pump output to demand for the sake of energy savings, have grown more common than ever. Rexroth's DFE pumping package with integrated electronics for closed-loop flow and pressure control takes cost savings a step further: In addition to energy conservation, the pump package may offer savings in hardware cost. "The pump can handle the injection control on small to medium-sized machines without an additional proportional valve. Its a very cost-effective solution," says Meckler. At NPE, machines from Engel, HPM, Krauss-Maffei, and Van Dorn Demag, among others, featured this pumping package.

Another trend in pumps is a quieter one - or, more precisely, it's a trend toward quieter pumps. Bosch, to take one example, brought out at NPE a new higher-pressure variable-volume vane pump called the Whisper Pump. "Vane pumps are quieter, but in the past, they weren't capable of the pressure levels needed for injection molding. They tended to self-destruct," explains O'Donnell. In the past, the company's vane pumps could achieve only about 140 bar, far short of the 210 bar the new Whisper Pump can attain. As for noise levels, the new pump runs about 6-7 decibels quieter than variable-volume piston pumps, says O'Donnell. Noise levels start at 67 dbA for the Whisper Pump. A 45-cc model running at 1800 rpm and maximum flow has been measured at 72 dbA.

Next up for Bosch is a Whisper Pump controlled by a servo solenoid valve, which puts the pressure control right at the pump and eliminates a pump-control manifold. O'Donnell says this PQ valve and Whisper Pump combination should be available at the end of the summer. Bosch already has a servo-controlled piston pump.