machinery | Thermoforming


walls; these attributes were reversed if the vacuum was turned on when the plug reaches the bottom position. The most expensive plug material saved an average


of 4mil compared to a cheaper material. Carlin said that, for a typical thermoformer in North


America, shifting to a slightly thinner starting gauge (0.037 rather than 0.038mil) would lead to an increased forming yield – and a revenue increase of nearly $17,000/year. He said this easily justified switching to the higher-cost plug assist. He said that plug selection can help to overcome key


production problems: in one case, one producer found that its flower pots were tearing in the corners. Using a tough thermoplastic plug was able to push more material into the corners, and prevent the tearing. Gary Sowden, North America sales director for


Above: Greiner’s barrier film incorporates regrind from the production process


can be extended up to Linknet, a comprehensive plant management system.


Plugging away Conor Carlin, sales and marketing manager at CMT Materials – which makes plug assists – told delegates at the recent Thin Wall Packaging conference in Chicago, USA that controlling wall thickness in thermoforming could have a big effect on part cost – and set out to determine the value of 1mil (0.001in – or 0.2mm) of material. CMT develops syntactic foam plug-assists for the


thermoforming process, in order to improve perfor- mance.


“Thermoforming is only slightly less precise than injection moulding when it comes to material distribu- tion,” said Carlin. He pointed out that around three-quarters of the


Right: CMT says that plug assists can


save material costs in


thermoforming


cost of a thermoformed cup is accounted for by the material. The company used a ‘design of experiment’ approach to determine the effect of different plug assist materials on material distribution. It tested seven different plug materials, and took 45 measurement points. Process variables – such as the speed at which the plug enters the cavity, and time at which the vacuum is turned on – were an important factor in determining the material distribution of the final part. For instance, if the vacuum was turned on before the plug reached the bottom position, the part would have a thin base, thin lower corners and thicker side


16 FILM & SHEET EXTRUSION | June 2017


Gabler – a German manufacturer of thermoforming machines – said that an updated version of its tilt-bed system had led to large improvements in the production of cups.


Tilt-bed thermoforming is aimed at precision


applications, and can work in a highly automated way with fast cycle times. However, the machines are typically smaller than in competitive processes, leading to a lower output despite the high cycle rates. He said that while Gabler’s new M98 has an 800 x 550mm mould, 65-tonne clamping force and 42 cycles per minute, its new M100 model has an identical cycle rate – but a clamping force of 100 tonnes and a forming area of 1350 x 550mm. This has allowed it to boost output in a number of


applications: for a 70.5mm diameter PP water cup, output was raised by 40%, by using an 84-cavity tool rather than one with 60 cavities; a 51mm K Cup saw a similar improvement, by moving from 84 cavities to 119; and a 75mm portion cup saw a 44% increase in output, by shifting from 54 to 78 cavities. The conference was organised by Applied Market Information.


Turning red WM Thermoforming Machines of Switzerland has recently delivered four in-line plants to make Ameri-


can-style ‘red cups’. Two of the plants are for the


American market – where this type of production is well-established – while the other two have been sold to Europe,


where it is an emerging application. The plants are Intec FT 900/3 models, which


www.filmandsheet.com


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