By Mikell Knights, PMM Senior Correspondent

Article excerpted from Plastics Machinery Magazine September, 2015

Quick mold changes have been the primary selling point for magnetic mold mounting systems as an alternative to bolt-on mechanical clamping or hydraulic mold-clamping approaches. Suppliers of magnetic clamping systems expect to attract additional processors with design updates that further reduce downtime and labor costs related to mold changeovers while increasing operator safety.

Suppliers of permanent electromagnetic systems change the polarity of the magnet by applying a brief charge of electric current into a specially designed platen to clamp or unclamp the mold. Applying the electric current extends the magnetic field of the permanent magnet system several millimeters from the platen into an adapter plate attached to the mold. The magnetic field pulls back into the platen during mold unclamping.

The continuous, uniform force that the magnet generates tightly clamps the platen to the steel mold adapter plate, preventing mold deflection. At the same time, the short depth of the magnetic field into the mold does not interfere with other aspects of the tool, such as the cores, ejector pins or thermocouples. Magnetic clamping systems only clamp and unclamp when a charge from the system is sent; hence, a power outage or lightning strike has no effect on the mounting force of the clamping system.

The magnetic force generated is capable of holding molds weighing tens of tons.

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Magnetic platens are designed for mounting using locator-ring patterns approved by SPI, Euromap and Japanese Industrial Standards. The platens are compatible with non-standard tool configurations and not limited by bolt-hole patterns, requiring only a standard locator ring. To operate with peak magnetic holding force, suppliers say the adapter back-plate must be composed of a non-alloyed tool steel, be absolutely flat to mount flush against the platen, and be free of oil, dirt and rust.

Suppliers such as Carr Lane Roemheld Mfg. Co. have installed magnetic clamping systems in thousands of horizontal and vertical presses operating in North America over the last couple of decades.

HIGH CLAMPING IN HIGH-TEMPERATURE ENVIRONMENTS

The Hilma Division of Carr Lane Roemheld Mfg. Co., Fenton, Mo., says its M-TECS 130 magnetic clamping system, which is designed to withstand operating temperatures up to 266 degrees Fahrenheit, now delivers up to 20 percent more clamping force versus older designs. The company also offers its M-TECS 210 (410 degrees Fahrenheit operating temperature) for rubber compression molding operations, says manager Dave Fischer.

The company introduced the new M2C controller for the M-TECS 130 system at NPE. Hilma says it improves safety and has greater ability to be serviced, compared to the prior controller. Included is more sensitive and responsive mold-movement detection and monitoring of the current to the platen and system temperatures. The M2C provides more feedback to the operator regarding the status and performance of the clamping system.

Hilma utilizes long-pole technology, incorporating double magnets, to bump up the clamp force. With the magnetic systems, the time to change molds of different sizes can be as quick as a minute and doesn’t require retooling. Electrical power is required for 2 seconds to unclamp the tool from the platen. Because the custom-designed clamping systems evenly distribute the magnetic force across the clamping surface, tool wear is reduced considerably, says Fischer.

The design and magnetic forces required can be adjusted as needed for the application. The mold plates have a thickness of 55mm. The system provides magnetic penetration of 15mm to 20mm, and each specific magnet builds up a clamping force of 256 pounds per square inch. The M-TECS system features two electro-permanent magnet plates, a control system, remote control unit and a complete set of cables including plug-in type connections that connect the unit to the injection machine. The company also offers hydraulic, mechanical-electric and hydro-mechanical clamping systems, says Fischer.

This is an excerpt. You can read the full article on
Plastic Machinery Magazine’s web site

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