Transparent viscose film is extruded through cast 'hopper' or 'pourer' lips into a sulfuric acid bath, where the edges must resist aggressive acid attack and hold a flawless finish. Langley casts these lips in Langalloy 7R, a special nickel-chromium-molybdenum alloy, and supplies them to packaging film manufacturers worldwide, giving a service life of up to ten or fifteen years.
Transparent viscose film is one of the most in-demand packaging materials, and its use continues to grow. It lets the contents be seen clearly, enhances their appearance, and protects against contamination and deterioration.
Millions of miles of it are made every year, and much of it passes through hopper or pourer lips cast at Langley in Langalloy 7R, a special nickel-chromium-molybdenum alloy supplied to film manufacturers throughout the world.
The duty
At the critical stage of manufacture, the film is extruded into a sulfuric acid bath through a pair of these hopper lips. They must resist the corrosive effects of the acid, because the surface finish of the film depends entirely on a perfect finish to the edges of the lips. The slightest flaw produces second-class material.
Manufacture and service life
The lips are cast sections up to 12 feet long. After machining, the extrusion edges are micro-finished by grinding and hand lapping - anything less than a perfect edge is unacceptable. They are redressed periodically, and Langley's casting technique gives the lips a total service life of up to ten or fifteen years.