slowed down, the ejector is prohibited from moving closer than 20mm towards the mould. Thermal imaging is another technique

that can be used to control the optimum point to eject parts from the mould. It can also help to ensure that the mould is clear of components prior to mould closing. Attached to the fixed platen on the machine, this infrared technology uses heat to determine if parts have been ejected from the cavities. The benefit for many is thermal

imaging provides users of hybrid and hydraulic machines with a safety solution. “Compared to vision systems, thermal imaging is approximately a third of the investment cost. Additionally, thermal imaging can also be used to monitor the temperature of parts, and document important production parameters,” notes Flowers.

HELP FOR HYDRAULICS For the large volume of moulders still using hydraulic-only machinery, safety systems are conventional and more limited. “Should an event happen within a mould in a hydraulic machine, the closing phase will continue, albeit at a slower speed, pushing gently in the hope it will come to a standstill before any permanent damage from the obstruction is done to the mould,” emphasises Flowers. “Setting these safety parameters is

reliant on machine operators having the skills and finesse to identify the region in the closing stroke where the mould is most at risk,” adds Flowers. Typically, this is just before the two mould faces

touch. Operators then set a slower speed and force based on the hydraulic pressure level. Getting it wrong can lead to increased cycle times and consequently lower output. The passive nature of this safety

system is its biggest drawback. It relies on an operative incrementally converting the toggle system characteristics and cylinder diameter to the hydraulic pressure to determine the most likely collision point. If, as the clamping proceeds, this pressure level is exceeded, the system pressure relief valve opens and the mould stops. Additionally, the safety system has to

account for and overcome the mechanical resistance of the mould (cheeks and slides etc.). This often requires increased closing force, which again can damage the mould. A slightly more sophisticated safety

option was introduced with second generation machines. Featuring toggle clamping technology and more powerful control systems, machines were able to calculate the mould position from the crosshead position by storing a model of the toggle system in the control. With this system, a consistent force is accomplished by adjusting the pressure according to how close together the platens are.

“Given that a well maintained precision

mould running 10-second cycles should have a lifespan exceeding 10 million cycles over five years, let alone the price tag these tools command, it’s worth giving your mould safety system the attention it warrants,” ends Flowers.

Right: Ejector technology ensures that components are clear of the mould before it closes again

Sumitomo Demag www.sumitomo- T: +44 (0) 1296 739 500

Below: The signal produced by activeProtect is so accurate it can detect even the slightest change in force patterns and respond in less than 10ms



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