Luck Started by Comparing Standard Non-Return Valves with ActiveLock Non-Return Vslves

At Sumitomo (SHI) Demag Plastics Machinery GmbH’s open house event in Wiehe facility in September, the company’s process development specialist André Luck described the ActiveLock and ActiveFlowBalance systems and how they can improve reproducibility and process consistency in precision molding. Luck started by comparing standard non-return valves with switchable ActiveLock non-return valves. Melt flow takes place via annular gaps in standard valves, and via drilled channels with ActiveLock valves. The system has been offered by Sumitomo in Japan for the past 10 years but it is new to Europe. While conventional valves close with axial movement, ActiveLock closes by a defined degree of rotation counter to the movement of the plasticizing screw. It remains closed during the entire injection phase, unlike ring or ball valve systems, which are open at the start of the injection phase. ActiveLock is recommended for high precision applications with materials that do not permit much or any screw withdrawal, or those that have glass fiber content below 30 percent. It is also useful when cycle times reach or exceed 5 seconds, with injection pressure below 2,200bar and holding time less than 15 seconds. The company showed an example of a 42g 25 percent glass fiber reinforced PBT electronic connector housing molded in an 8-cavity mold. Compared with a standard non-return valve, ActiveLock reduced weight deviation from 0.09 percent to 0.04 percent and melt cushion deviation from 0.19cm3 to 0.087cm3. There was also a 10 percent reduction in maximum injection pressure from 1,436 to 1,288bar. ActiveFlowBalance, a new system to compensate melt compression, also makes a positive contribution to reducing variations in part weight. It does this by ensuring consistent melt pressure in each cavity of multi-cavity molds during the holding pressure phase. The system also helps to avoid venting, over- or under-filling and overmolding problems. Sumitomo Demag says it is particularly beneficial for: parts with thin wall sections close to flow edges; small parts weighing much less than sprues; and parts with different flow paths or filling relationships. Luck addressed other issues in high precision molding: the need to adapt tool venting to clamping force; and internal pressure in the mold. At the open house event and at the Fakuma 2011 fair, ActiveFlowBalance was shown in a molding demonstration incorporating five other Sumitomo Demag “active systems”: ActiveLock, ActiveDynamics, ActiveQ, ActiveRemote and ActiveEcon (for managing energy consumption). In this demonstration, a 3.56g Tyco two-pole connector housing was produced in a 4-cavity Fischer mold. The molding was made with a 10 percent glass fiber reinforced PBT, using a 16.45g shot weight, in an 11 second cycle time, without producing flash in the contact area. Sumitomo Demag said that the use of active systems - in which mold internal pressure is measured by a Kistler sensor in each cavity, and mold temperature is monitored by the injection molding machine via the company’s new NC5plus control system - ensures zero defect molding of the part, expressed by a statistical Cpk value above 2.0. At the open house in Wiehe, Christian Renners, Sumitomo Demag sales manager, said sales by injection molding machine makers has grown 30 percent since the low point of the 2009 crisis. He presented data on the number of machines sold by European producers since 2006. This showed that, having fallen to lower than 50 percent of the 2006 number in 2009, producers have recovered to more than 80 percent of the 2006 total in 2011. Looking forward, Renners said that 2012 is likely to drop slightly below the 80 percent level again, representing stabilization of the market, but at a lower level than in 2006. Sumitomo Demag says its introduction of IntElect Smart all-electric machines in 2008 has enabled it to double its market share of electric machines, claiming that one-in-five electric drive machines sold in Europe are from the group. Working to full capacity, the Wiehe plant is expected to produce 750 injection molding machines in 2011 for Europe and the United States, of which 60 percent will be electric. Source: plasticsnews.com