Thickness Measurement and Control in the Manufacture of Polyethylene Cable Sheath

摘要

Control of the concentricity and average thickness from the former method of end sampling resulted in eccentricity of the sheath in the order of 30 to 60%. At that time the safe practice was to make the average thickness greater than specified nominal in order to keep the thin side of eccentric sheath within the minimum spot limit. This excess amounted to approximately 10%. With the test set, concentricity within 10% is maintained under good operating practice and within 20% as a common condition. Average thickness can be controlled to within plus or minus .003 of an inch. This improvement in concentricity and thickness control permits operating at specified nominal thickness without varying below minimum limits and thereby eliminates the 10% excess usage of Polyethylene. In conclusion, this test equipment has proved to be practical means to the control of the concentricity and the average thickness of the Polyethylene sheath of Alpeth and Stalpeth cables. It measures the sheath wall thickness directly in thousandths of an inch both visually and as a recorded graph and does so non-destructively as the sheath is applied. It is accurate, reliable and of construction suitable for continuous shop use. The sheath is of consistently high dimensional quality not previously obtainable. Two major advantages have been gained. (1) Polyethylene is conserved and manufacturing cost reduced. Eleven percent thinner sheath wall thicknesses are practical with the improvement in concentricity. At capacity level, the polyethylene saving is 500,000 lbs. per year. (2) The quality of the sheath is improved through close dimensional control. (Author)