Canadian Plastics

Controls : MATTERS OF CONTROL

W hile not absolutely the most inhospitable places on earth, the shop floor of a typical plastics processing facility is still a pretty rough environment. Heat, water leaks and sprays, grease, dirt an...

March 1, 2008   By Mark Stephen, Managing Editor



While not absolutely the most inhospitable places on earth, the shop floor of a typical plastics processing facility is still a pretty rough environment. Heat, water leaks and sprays, grease, dirt and dust — as well as more exotic hazards such as electrical noise and power fluctuations — are all competing to wreak havoc on every piece of equipment in every production line. And of all the equipment used during plastics manufacturing, perhaps none are as susceptible to these hazards as the relatively delicate controls guiding injection molding machines, extruders, blow molding machines, robots, and more.

For this reason, component suppliers for controls are under increasing pressure to develop products that are impervious to the slings and arrows of daily life on the shop floor.

TESTING, TESTING. . .

An important first step in ensuring that items such as microprocessor parts intended for controllers can stand up to difficult environments is subjecting them to worst case ambient conditions — from extreme temperature highs to extreme lows, according to Stan Ho, marketing manager at Rockwell Automation, which distributes Allen-Bradley controls. “Firstly, designers must select products that can operate in these conditions,” he said. “Once designed, engineers perform qualification testing to ensure long term reliability.”

Some manufacturers will go beyond this and perform HALT (Highly Accelerated Life Test) procedures, he continued. During these tests, conducted on products prior to market release, the component is forced to exceed the product specification, allowing the manufacturer to review design weakness and help ensure the product meets, or exceeds, product specifications as published. “Once a component fails, it’s typically replaced with a better part and the tests are repeated to see what the next component weakness is and so on,” said Stan Ho. “The same strategy is executed on electrical noise and power fluctuations.”

SLINGS AND ARROWS

Among its many unique characteristics, water will seep relentlessly into the smallest crack or fissure. For this reason, water resistance around the enclosures that surround a machine’s controls is of primary importance. Allen-Bradley products from Rockwell Automation offer a series of lightweight, impact-resistant push button enclosures designed to keep water, as well as other materials like grease and dust, at bay. The company’s 30.5 mm 800H push button enclosures, for example, are UL and CSA rated, available with 1-, 2-, 3-and 4-hold configurations, and cover-to-base orientation. Thermoplastic polyester blend material allows customers to customize the enclosures without the need for special tools.

As with overcoming challenges posed by extreme temperatures, performance testing is key. “For water resistance, our products that are rated for this environment are subjected to standardized tests of water sprayed at certain a PSI.” said Stan Ho. “If the design can withstand this water without water entry, we can rate these suitable for this environment.”

The dust and dirt that circulates around a typical shop floor can also threaten the functionality of a controller. The Allen-Bradley PowerFlex 40 AC motor control drive, available from Rockwell Automation, provides UL-listed protection against circulating dust, as well as high-water pressure, for equipment such as packaging machinery. The company also offers its PowerFlex 40 NEMA 4X AC drive components, available in 240, 480 and 600 volts, designed for particularly harsh production environments, including dust, splashing water, hose-directed water, caustic chemicals and corrosion, said Stan Ho.

An electrical surge can easily damage plastics processing equipment controls. Here, too, controls manufacturers are working to develop more resistant components.

Siemens, for example, has taken steps to combat both electrical and heat hazards. The company’s 3RV10 Motor Starter Protectors (MSPs), built for a wide range of applications, feature a manual ON/OFF switch, a Class 10 adjustable bimetallic overload relay (Class 20 available in the two largest frame sizes), and magnetic trip elements for short-circuit protection.

In addition, the company’s modular solid-state 3RB22/3RB23 overload relays provide full motor protection, and protect from current and temperature

Allen-Bradley’s 30.5 mm 800H push button enclosures, available from Rockwell Automation, are UL and CSA rated, available with 1-, 2-, 3-and 4-hold configurations, and cover-to-base orientation. Thermo-plastic polyester blend material allows customers to customize the enclosures without the need for special tools.

Photo Credit: Rockwell Automation

fluctuations through a connected PTC thermistor sensor. The PTC sensor measures and evaluates the electricity and temperature readings.

Rockwell Automation, meanwhile, operates a high-current test facility in Milwaukee, Wis. “We have the ability to generate high levels of current to review what our products might be subjected to with power utilities,” said Stan Ho. “We also have a high speed camera that provides a record of the type of collateral damage might take place if subjected to this phenomena.” The company also performs specific high voltage tests on its variable frequency drive instrumentation to understand how these products behave in the face of these hazards. “Engineers will analyze the result of these tests and design either more protection to accommodate this or select components that are better suited for this,” Ho continued.

BAD VIBRATIONS

There are other, less obvious dangers to controls. Vibrations caused by smaller equipment being moved or bumped can also wreak havoc with delicate circuitry.

Here, too, improvements are being made. Gems Sensors & Controls’ new PS98 series of pressure switches, which deliver more than 100 million switch actuation cycles, have been built without moving parts, to better resist the damage that shock and vibration can cause to mechanical switch units. In addition to pressure sensing electronics that range from 0 to 6000 psi (0 to 400 bar), the PS98 series offers a broad selection of pressure connections and several electrical termination options, including DIN plugs and IP68 cables.

TEAM EFFORT

Control designers agree that improvements are being driven both by customer demand and control

companies desire to anticipate changing needs. “We spend an enormous amount of time to determine what customers want,” Stan Ho noted. “We go out to cus- tomers to listen to their needs and wants, and ask pertinent questions about their next generation machine designs or issues that they need to overcome to become a market leader.”

An important part of this relationship is collaboration between control designers and systems integrators, to develop control solutions suitable for different, and extreme, manufacturing environments. For example, component supplier Omron Canada worked closely with controls retrofitter Plastics Process Technology Group (PPTG) to develop and install modern controls in PPTG’s retrofitted plastics processing machinery. Based on PPTG’s needs, for example, Omron recommended its 3G3MV high performance micro inverter as a crucial component in the controls for the company’s fully automated co-extruder. The 3G3MV offer device net communications to a PLC.

According to Omron, the current running in the co-extruder’s motor is monitored in real time to provide a snapshot of the overall health of the machine, as well as to prevent too much current at a set speed from causing a blown phase or improper plastic viscosity. The 3G3MV also offer an interlock function so that the extruder screw cannot be rotated until all of the temperature zones are at a minimum level. “In this situation, our technical service team worked shoulder to shoulder with PPTG to create a winning solution,” said Jeff Neal, national accounts manager at Omron Canada. With a customer service team located in Ca
nada, Omron has applications specialists available to visit customer locations in person, as well as offering free product support, Neal continued. Additionally, all of the company’s components are backwards compatible.

CPL


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