Thermoforming - ILLIG Maschinenbau GmbH & Co. KG

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Product Jogurt cup, PS 73 mm dia., 1.25 mm wall thickness Drink cup, PS 73 mm dia., 0.8 mm wall thickness Jogurt cup, PS 75 mm dia., 1.15 mm wall thickness Drink cup, PP 75 mm dia., 1.2 mm wall thickness 2nd Generation level control system, the downholder force is matched perfectly to the time curve of the thermoforming process, so that the undesirable material deposit is drawn completely into the side wall as the cup is formed. The result is a highly uniform wall thickness distribution (Case 1 in Fig. 1). Moreover, the “additional” material thus drawn into the side wall gives added strength to the cup, i.e., the top load rating is increased. Conversely, a thinner web material (10% less basis weight) would suffice to produce a molding of the same strength. This corresponds to a direct reduction in material costs. Cycles /min 3rd Generation Increase [%] 22 36 63 25 37 48 28 36 28 28 36 28 Numerous innovations on the 3rd generation RDM-K automatic pressure forming machines (exemplified by an RDM 70K with a 24-cavity mold in this case) have yielded marked productivity gains (increased cycle rate). Tangible increase in product quality and productivity Compared to the previous series, these 3rd generation automatic pressure forming machines consistently achieve around 30% shorter operating cycles in drink cup thermoforming service, depending on the material type and shape of the cup. In some cases, much higher gains are achieved (cf. Table). The same applies to product quality parameters. For economic reasons, cup walls are kept as thin as possible (reduced material cost) while on the other hand, the thermoformed product is expected to withstand a certain minimum top load. In the case of Fig. 2: One notable feature of the new stacker is the turning head system which now supports rotation through 180 degrees. Its “two-sided” operability allows aftercooling of products after removal from the mold (left) for an entire cycle before they are put down in the stacker cage (right). a yogurt cup, for instance, which must be securely sealed after filling, the flatness of the sealing rim becomes crucial over and beyond the given thickness of the material. A maximum rim angle variation of 5 deg. is not to be exceeded since the cup will otherwise not be positively sealable in a volume production line. The RDM-K automatic pressure forming machines and 3rd generation mold technology remain far below the tolerance limits specified for the above criteria. Notwithstanding the major increase in cycle speeds achieved, the cups are consistently less susceptible to rim angle deviations – even when measured across all cavities of a multi-cavity mold. Process reliability in stacking In order to cope reliably with the enhanced output of the new thermoformers, stacker technology has been advanced as well (Fig. 3). Even short, bulging cups which are difficult to keep properly aligned are reliably transferred to downstream equipment in unattended operation, whether for packing counted cup stacks into a transport container or for direct filling, sealing and packing on integrated lines. All stacker components are made of wear-resistant materials throughout. Contamination of the cups with foreign particles – as can never be fully avoided, e.g., with stacking cages comprising brushes, rubber or similar stack holder materials – is thus prevented. Freedom from contamination is an important criterion not only if the cups are to be subsequently filled with food products. The high precision and repeatability of 3rd generation RDM-K automatic pressure forming machines also becomes evident when they are started up in production. As soon as the mold has reached operating temperature the first true-to-specification cups emerge, ready to be stacked. The new RDM-K generation is suitable both for offline roll-fed operation and for in-line use downstream of a flat-film extruder. The standard range comprises four machine sizes addressing various requirements in industrial practice, with the RDM 54K (mold surface area: 520 x 300 mm²), RDM 70K (680 x 280 mm²) and RDM 78K (760 x 420 mm²) having now been joined by the most recent RDM 75K (735 x 465 mm²) model. 8 thermoformer 1/2010
NEWS FROM MOLDMAKING The 3rd generation of RDM-K molds High dynamics and product uniformity at one stroke Synchronous pressure build-up – in all cavities Second-generation RDM-K molds reflect the state of the art of their time, with central valves handling the supply of forming air to all cavities. In the development of 3rd generation thermoformers, lateral valves – integrated into the mold – were used as a first step. Each of these valves controlled the supply of forming pressure to one single row of cavities. Although this method already constituted an improvement over the prior-generation, an absolutely synchronous airflow to the cavities could not yet be ensured in this manner. The task of forcing the material into conformance with the cavity contours and pressing it against the cooled mold wall (thereby initiating cooling) was completed within a given inter-cavity “time window”, resulting in non-uniform product characteristics. In the current 3rd generation molds, forming air is separately supplied to each cavity directly via the pre-stretcher (Fig. 1). Compressed air is thus gated directly into each cavity. To this end, a solenoid valve assigned to each cavity is fitted in the upper mold part for a defined, synchronous build-up of forming air pressure. The synchronous admission of forming air is all the more important in view of the severely reduced forming air input per cavity which is achieved through improved design (see p. 7). Even with this diminished air demand, a dynamic (steep) build-up and release of forming air pressure (Fig. 2) occurring simultaneously in all cup-forming cavities can thus be ensured. Advanced mold technology contributes in a major way to the high productivity and product quality attained by the 3rd generation RDM-K automatic pressure forming machines. Forming air Fig. 1: Each cavity now has its own solenoid valve for a controlled, precise and repeatable supply of forming air. Forming pressure [bar] 3 2 1 B 0 1 3 5 7 9 11 13 15 17 19 21 Time [ms] A Solenoid valve Time gained Fig. 2: Compared to the prior standard (Case A), the reduction in forming air volume (Case B) results in a significantly more dynamic build-up and release of forming air pressure. The associated time gains can be used to run higher cycle rates. Controlled pressure profile On 2nd generation molds, the full downholder force was commonly applied upon closing of the mold. This practice invariably resulted in the formation of a bead along the upper cup rim, as described in detail on page 7. However, in terms of process technology, the maximum downholder force is needed only during application of the full forming air pressure. During pre-stretching of the material and punching of the molded product the downholder force may be lower. With the new pressure level control system, the downholder contract pressure is adapted to the specific phase of the thermoforming process. The full downholder force is not exercised until the main forming air pressure sets in; it is then reduced toward the end of the molding cycle (Fig. 3). Another innovation is that that the downholders are cooled directly to support short cycle times. Optimized mold cooling The mold now comprises up to four cooling circuits. Individually controllable, these supply coolant separately to the upper mold part, the downholders, the lower mold part and the ejectors. In order to accelerate the dissipation of heat from the cavities, the molds have contour-following cooling passages of adequately sized crosssection. It is not necessary to reduce the coolant temperature – quite the opposite is true. While previously the coolant had to be at 12 °C, the new molds can be cooled with water in the 16 …18 °C range. This saves energy but also reduces the risk of moisture condensation in the mold, which is always extant at elevated air humidity levels. Pressure 1 3 Time 1: Pre-cooling 2: Cooling 3: Punching Fig. 3: The clamping pressure of the cooled downholders is applied in stages matching the process to avoid bead formation along the upper cup rim. At the same time, the shorter application of the full pressure benefits mold and machine life. 2 thermoformer 1/2010 9
Page 1 and 2: 1/2010 Thermoforming, packaging & m
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Thermoforming - ILLIG Maschinenbau GmbH & Co. KG

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