Of all the packaging materials transparent viscose film is one of the most in demand and its use continues to expand. Certainly, it is a sales aid. It allows the contents to be clearly seen and enhances the appearance of the contents or enclosed pack. It also gives protection against contamination and deterioration of the contents, perishable or otherwise.
Millions of miles of it are made every year and a very great deal of this passes through ‘hopper’ or ‘pourer’ lips cast at Langley in Langalloy 7R, a special nickel-chromium-molybdenum alloy, and supplied to packaging film manufacturers throughout the world.
In the critical stage of manufacture, the plastic film is extruded into a sulfuric acid bath through a pair of these hopper lips, which must obviously have very high resistance to the corrosive effects of the sulfuric acid, since the quality of the surface finish of the film produced depends entirely on the maintenance of a perfect ‘finish’ to the edges of the lips. The slightest flaw cannot be tolerated as this results in the production of second-class material.
The lips are cast sections of up to 12 feet in length, and after various machining operations, the extrusion edges are micro-finished by griding and hand lapping. Anything less than a perfect edge is unacceptable. They are, of course, redressed from time to time, and it says much for the casting technique at Langley that the ‘lips’ have a total service life of up to ten or fifteen years. That’s one reason why Langley’s hopper lips are used throughout the world.
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