As the requirements for the production of caps become increasingly exacting, machines manufacturers are scrambling to design machines that perform accordingly. The latest offering from Engel is the new generation e-cap and it is a case in point.
The Austria-based plastics processing machinery manufacturer presented the first - at the time, revolutionary - all-electric e-cap injection moulding machine at K 2010. To date, says Engel, the e-cap remains the most energy-efficient cap machine on the market. It is also one providing all-electric operation with a clamping force range that reaches 4,200 kN.
However, since 2010, the requirements for beverage caps have changed substantially, with continuous part weight reductions playing a central role, said Friedrich Mairhofer, product manager for all-electric injection moulding machines at Engel. Caps on still water bottles aweigh ‘significantly less than one gram’, he explained.
“As a result, the cooling and cycle times have continued to drop. Where the cycle times ten years ago were still 2.5 seconds, today's cap machines need to be able to produce at 2-second intervals and faster.”
This requires a highly stable machine bed to handle more frequent load cycles. Engel said it achieved cycle times under 2 seconds during tests on an e-cap 380, thanks to the fast dry cycle times of 1.3 seconds and parallel movement capability - included as standard, the company added.
New is the switchable hydraulic booster on the direct-drive servo-electric ejectors that can provide additional force to remove caps in situations – for example, after an interruption in production - when these caps have cooled. As Engel explained, such situations occur relatively infrequently, making it more efficient to use servo-hydraulic drive amplification than to equip the machine unnecessarily powerful ejector drives.
In addition, the new e-cap features a redesigned plasticising unit, as the properties of the materials to be processed have also changed in order to be able to produce lower-weight caps. The melt flow index of the HDPE grades used for carbonated soft drink caps today is between 0.8 and 1.4 g/10 min. With very short cycle times, these values require particularly high plasticising rates. This was achieved by increasing the torque of the plasticising drive and developing both a new plasticising screw that is able to gently process high-viscosity HDPE and a new highly wear-resistant sliding ring non-return valve specifically for cap manufacture.
With its all-electric drive technology, the machine is highly energy efficient: among others, braking energy is recuperated, reliably preventing the need for expensive peak power. According to Engel, the e-cap 380 operates at high speed with an energy consumption of 0,37 kWh per kilogram of pellets.
The new e-cap is available in the sizes 220, 280, 380 and 420 with clamping forces from 2,200 to 4,200 kN.