Düsseldorf, Germany — Although aimed at showing technical competence, live demonstrations on plastics machinery producers' booths at plastics industry fairs sometimes result in large queues for practical items such as large buckets and crates.
Probably the most popular demonstration at K 2016 in Düsseldorf was production of complete watches on the booth of Lossburg, Germany-based injection molding machinery producer Arburg GmbH + Co. KG. This involved a production cell molding 2-component watchstraps in two different colors of liquid silicone rubber, followed by application of watch cases (with a dial bearing the Arburg name) and buckles to form ready watches.
The watches went like hot cakes to trade fair visitors who were prepared to stand waiting up to two hours as they came off a conveyor belt, with 100 or more people lining up for them.
Arburg's turnkey production cell was based around an electric drive 200-metric-ton Allrounder 570A 2000 Alldrive injection press. The cell was designed together with Kiki Ingenieurgesellschaft mbH in Malsch, Germany. The two differently colored LSR materials both came from Momentive Performance Materials Inc. in Leverkusen. Germany: harder Silopren 2670 for the main strap component with Shore A hardness of 69 and the softer secondary strap component in Silopren 2620 with Share A hardness of 24. Silopren 2670 was the first 26XX series grade, launched in 1996.
Momentive says that compared with 2070 and 2020 grades with the same hardnesses, the 2670 and 2620 grades have lower viscosity, improved tear resistance and a higher reactivity, enabling lower vulcanization temperature at a standard crosslinking rate. That results in high curing speed and ease of demolding, so that fully automated production of large numbers of articles in short cycle times is possible, according to the company.
The cycle time for each pair of the Arburg watches was 75 seconds … maybe still not fast enough for those waiting in the line!
Following mixing and coloring of the LSR components in equipment from Kierspe, Germany-based Reinhardt Technik GmbH, the cold mixed materials were injected by size 700 and size 400 injection units arranged in an L-position to each other into a hot 2+2-cavity electrically rotating mold made by Rico Elastomere Projecting GmbH in Thalheim/Wels, Austria, that was equipped with a cold runner system. Shot weights for the individual LSR components were 31.8 grams (Silopren 2670) and 1.2 grams (Silopren 2620, resulting in 16.5 grams part weight for each watch strap.
An Arburg V15 vertical linear robot removed the LSR parts from the mold, placing them into a cooling station, then into a assembly station, all within the production cell. Circular feeding equipment from Hörmle GmbH in Denkingen, Germany, fed the buckles and laid them down in line for insertion into the straps. The robot widened the central aperture in each strap with 4-finger spreading device, allowing the robot to insert the watch cases into the straps, where they were subsequently held tightly by the Silopren 2670 material contraction. of an interchangeable tray system was used for case and buckle application.
All of this took place within the 75 seconds molding cycle, with the entire process controlled by the injection molding machine's Selogica control system. Other project partners were Regloplas AG in St. Gallen, Switzerland, for the temperature control system and Schuma Maschinenbau GmbH in Laichingen, Germany, for conveying equipment.