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Large Machine for Production of Wastewater Shaft Systems

Significant Benefits for High Shot Weights

Ettlinger Kunststoffmaschinen GmbH, Königsbrunn, Germany, has delivered an injection molding machine designed for large parts to a prominent European plastics processor. Its srm 2500/120, which has a clamping force of 25,000 kN and an injection capacity of up to 120 liters, produces parts for walk-in wastewater shafts in polypropylene. The shaft bottom alone, molded during the machine acceptance test, weighs 62 kg. The shafts are manufactured in different sizes and used for wastewater disposal in urban areas.

The 16.4 m long, 3.3 m wide and 4.9 m high machine, with a clamping force of 25,000 kN and a short volume of up to 120,000 cm³, is equipped for economical injection molding of wastewater shaft systems in PP (© Ettlinger)

A characteristic feature of the srm series of injection molding machines is the two-stage injection unit: An extruder functions as the plasticizing unit, while a plunger unit injects the melt into the mold. Both the plasticizing extruder and injection unit execute in cycles. The extruded melt is delivered to a cylindrical accumulator; from here, it is injected into the cavity by the injection plunger using a pressure- and speed-controlled forward motion. This permits processing of large shots volumes with high melt quality at low clamping forces.

Since smaller drives can be used for the smaller components of the two-stage plasticizing and injection system, the energy required is up to 60 % less than that needed for a conventional injection molding machine with comparable production parameters. Switching the hydraulic pump to standby during the molded part’s cooling phase and then restarting it with a soft start only at the end of cooling provides additional energy savings.

The clamping force advantage also helps in terms of the mold construction. "On our machine, we can often use cost-effective molds based on material combinations of steel and aluminum, even for very high shot weights. Furthermore, the high thermal conductivity of aluminum facilitates heat removal in the mold and in this way shortens the cycle times", reports Karsten Bräunig. The sales manager at Ettlinger points out an additional unique aspect: the frame that holds the core pulls on the stationary platen. "The core pulls needed for any particular part can be positioned almost anywhere, yet remain a fixed part of the machine. Separate core pulls in the mold are then no longer required, which reduces mold costs considerably, especially when there is a wide variety of parts", according to Bräunig.

At the same time, the large, tiebarless opening area can be accessed easily from the side for part removal and mold changes. For removal of the large shaft components, use of an industrial robot is a necessity in order to achieve short, economical cycle times.

Company profile

Ettlinger Kunststoffmaschinen GmbH

Messerschmittring 49
DE 86343 Königsbrunn
Tel.: 08231 34908-00

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