Marginal Column

Better in pairs

The new generation of the Uniloy Milacron blow molding machines is even safer and more efficient with technology made by Rexroth.

 
Photo | Bosch Rexroth AG

Uniloy Milacron’s extrusion blow molding machine satisfies current safety standards and uses Sytronix to save energy.

How can we make our machinery safer and more energy efficient, as well? This is the question posed by Uniloy Milacron, a manufacturer of plastic blow molding machines. The company, located in Magenta near Milan in Italy, had developed a new range of extrusion-type blow molding machines with two mold clamps and a movable accumulator head.

Two models of this new range of machines are already at work in production, one for large automotive parts and the other one for school seats. Uniloy Milacron has long appreciated Rexroth’s capabilities as an expert supplier of hydraulic components and system solutions. When building these new machines, the company once again turned to this time-tested partner for expert support.

Safety meeting the latest standards

In force since 2009 is a European safety standard that imposes more stringent minimum requirements for semi-automatic machinery. To provide relief here, Rexroth’s engineers used SISTEMA software while designing the hydraulic system. This program evaluates the safety-critical components in machine controls, adhering exactly to the European standard, and takes account of the techniques derived from theories of probability. In order to enhance operating safety, the machine is now equipped with an additional, redundant logic element with an inductive position monitoring.

The operator’s risk is reduced since the clamping plates no longer present a hazard. A hydraulic unit automatically stops the cylinders as soon as the operator opens the guard flap. In this way Uniloy Milacron’s new machinery design satisfies the European standard, fulfilling the requirements for Performance step E, Category 4.

Frugal and quiet

Complying with the standard was one objective but, in addition, the machine was also to be thriftier. The engineers offered a solution here, too: the Sytronix DFEn 5000, a variable-speed system in closed-loop control that regulates both pressure and flow rate. The intelligent servo regulator in the Sytronix DFEn 5000 acts while the process is running. It regulates the speed of the electric motor and the angle of the variable-displacement pump to match the machine’s needs. The amount of power drawn is thus optimized and the hydraulic system saves energy.

This is true above all when the operating cycle involves fluctuations in the flow rate. This effect will increase as the machine cycle dictates a greater share of operation at partial load. The reduced amount of energy drawn means that the hydraulic fluid will not be heated up quite so much. This in turn means a reduction in the amount of cooling needed. All in all, Uniloy’s new extrusion blow molding machine requires – when compared with the previous model – 20 percent less energy and 25 percent less cooling power. The machine is far quieter, as well, so that the company spends fewer resources on secondary noise abatement. And in this way the drive itself makes its contribution to occupational safety.

 

Blow molding

Almost everyone will run into one blow-molded item or another – every day. That’s because plastic bottles, canisters, car trunk spoilers, and even toys like bobby cars or dolls – or to put it more abstractly: hollow objects made of plastic – are formed inside a mold. To accomplish this, a hollow tube made of hot, moldable plastic is extruded and, rather like an empty sausage casing, hangs from a die flanged to the extruder. This tube is then enclosed by a mold and is inflated with compressed air. The plastic is pushed toward the walls of the mold, cools, and then adopts its ultimate shape, either as a bottle or a toy.