Watch this space: Arburg's turnkey LSR production cell made a splash at K2016

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.

Another still recent 2-color LSR demonstration took place on the Arburg booth at Fakuma 2015. It involved soft key pads for passenger car interiors made by Trelleborg Sealing Solutions AG (TSS) in Stein am Rhein, Switzerland.

The LSR materials involved KET 1001/80 (Shore A 80) from ShinEtsu in Taipei, Taiwan, for the harder blue core and Elastosil LR 3004/50 (Shore A 50) from Wacker Chemie AG in Burghausen, Germany, for the softer orange flange around the core. Holland Colours Europe BV supplied the blue and red pigments which were mixed along with the A and B LSR components in mixing and dosing equipment from Reinhardt Technik.

The pads had part weight 0.09 grams and were produced with 30 seconds cycle time on an electric drive Allrounder 470A injection molding machine in a 32+32-cavity mold equipped with a cold runner system designed by TSS in Stein am Rhein. Electric drive was also used for dosing systems, injection units and mold rotation. A central Arburg Selogica control system provided analog vacuum monitoring and graphic display of the cylinder module's pressure pattern. Part removal was performed by an Arburg Multilift V15 vertical linear robot equipped with a visual inspection camera, prior to laying the parts down according to the cavity in which they were molded.

TSS said in mid 2015 that it had achieved a technical breakthrough in injection molding 2-color LSR components in a single shot from a single tool by means of a proprietary tool construction in which color pigment is added to the silicone material stream just prior to its injection into the tool cavity.

Ursula Nollenberger, TSS's LSR components product line director in Stein am Rhein, revealed in 2015 that the first application of this revolutionary technology had been for a leading automotive Tier 1 supplier. In this case, the customer needed to visually differentiate geometrically identical parts produced by TSS in a single tool, but for various vehicle platforms.

TSS operates more than 100 Arburg injection molding machines in 24 worldwide production facilities, with Arburg machines predominating at its LSR competence center in Stein am Rhein, where there are 135 employees and the machine park has 62 injection molding machines, 48 of them from Arburg, with clamping forces between 25 and 320 metric tons.

Aside from the LSR/LSR keypad application, TSS also uses what it calls a proprietary coinjection process to produce multi-component parts in tightly bonded LSR and engineering thermoplastics, with an option to have such parts produced in clean room conditions when this is required.

The company sees a number of automotive trends benefiting use of LSR injection moldings: the search for lighter weight components, increasingly sophisticated on-board electronic systems, as well as increasing driver safety and comfort features. It adds that two-component LSR part solutions can provide here for greater design latitude, feasibility of complex and micro components, high sealing functions, elimination of risks and costs associated with secondary assembly and significantly reduced total cost of ownership.

Arburg says it has been involved in processing silicone rubber since 1980, with several thousand silicone applications realized, both in LSR and in solid single-component high temperature vulcanization (HTV) silicone rubber. The company points out that precise process temperature control is required and that while LSR (and HTV) curing takes place at high temperature (160-220° C) in the mold, the cylinder module most be kept cool (20-25° C) by means of thermal separation from the mold, in order to prevent premature curing of the reactive material mixture. This is achieved by lifting the tip of the cool nozzle to retract it from the hot mold.

Trelleborg Sealing Systems (TSS) not only produces LSR seals on Arburg injection molding machines, but also supplies seals to Arburg for its injection molding machines, with up to 20 TSS seals and guide rings used in a single machine. TSS also recently also used for APF Arburg Plastic Freeformer additive manufacturing machines. None of these seals involve LSR however, but other materials such as ETFE, NBR and EPDM elastomers. TSS sales representative Theodor Mack has suggested “it is likely that it won't be long before the first of this newest generation of APF machines takes pride of place in a Trelleborg facility.”