TECHNOLOGY | MOULDS
system for a family mould to show how three very different parts can be moulded at the same time, with weights of 547, 330, and 56 g. The system, with eight tips, uses conical valve gates, with separate control over each needle. “With servo drives, it is possible to control
pressure and flow at each gate independently, based on pressure sensors in the mould,” says Harvey. “With servos, we can have these family moulds with vastly different part weights, without compromise. We can make high quality parts in every cavity.” “A cylinder is a dumb device, you cannot extract
any process information out of it, you cannot communicate with it,” says Harvey. “ You energise it, it goes forward; you energise, it comes back. You don’t control the speed, you don’t have visibility of its position. With piston control, every gate in the mould is subject to one process, the speed and pressure profile of the injection machine injection screw.”
He said: “The servo is smart, you can communi-
Below: Servo controls over hot runners, as offered here by HRSflow, make it possible to design family moulds where individual cavity shot sizes vary greatly
cate with it, it knows where it is all the time, it knows how fast it is going all the time, you control its position, its speed and acceleration all the time. In addition, the servo gives you the ability to stop the pin in an intermediate position and articulate the pin throughout the cycle. It is not simply open or closed.”
Servo controls also mean that pressure can be
controlled across a single cavity that has multiple gates. Packing pressure can similarly be modulated across a cavity. This can reduce overall force on the cavity wall, possibly reduce required machine clamp force, reduce variations in part stress and
Right: Husky’s ISVG actuator
hence warpage, and reduce mould bending. Another advantage of servo systems is that they have no fluids. “Hydraulic systems are sensitive to the pressure of the plastic that the pin is pushing against and the number of gates in the mould, the length of the lines, and other variables,” Harvey says. “Fittings, seals, hoses, downtime to fix oil leaks, all this is completely eliminated by the servos. “The No 1 consumable in hydraulic and pneu-
matic systems is normally the seal kit. That adds to cost of ownership. With servos, there is no piston, so no seal.” Not all applications demand servos though, and HRSflow also has systems with hydraulic and pneumatic control. It also has thermal gates.
HRSflow now has an “Sa” extra-small nozzle, for technical parts up to around 15 g in weight, and for tight-access gating. “This completes our product line,” says Harvey. At K 2019, Husky Injection Molding Systems
introduced an Individual Servo Valve Gate (ISVG), based on its existing Ultra Helix plate actuation system for valve gate nozzles. ISVG offers technol- ogy that ensures complete control of the valve stem motion throughout the entire moulding cycle, Husky says. Precise control over force, speed, and profiling stem movements in up to 100 steps is possible. The company points to the compact size of the purpose-designed electric servo actuator and the fully integrated controls in the Altanium mould controller. This is not the first time that Husky has intro- duced a servo system for individual hot runners, but this time it reckons it has a more cost-effective package than before. ISVG hot runners are available with Husky’s Ultra
350, 500, 750 VG, VX and Ultra Helix nozzles, with the ability to process with part fill pressures up to 26,000 psi and mould temperatures up to 90°C. Control over up to seven drops is possible at the moment, but this may be increased in future. In low-cavitation moulds, individual servo
38 INJECTION WORLD | November/December 2019
control fully synchronizes valve stem movements. �
www.injectionworld.com
PHOTO: PETER MAPLESTON
PHOTO: HUSKY
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