constant force springs from emmott springs


	A tightly coiled wound band of pre-hardened spring steel or stainless steel strip. When extended a constant force is exerted and this is maintained as the spring is allowed to close. The full force is effective until the spring is in the fully closed position.

CONSTANT FORCE SPRINGS

This spring type derives its name from its ability to extend through its full working length while being maintained in any position by the same force. Constant force springs are available in a wide variety of sizes and the recent introduction of a purpose built plant ensures the price competitiveness of the smallest production run. Emmotts is one of the UK's most experienced manufacturers in this highly specialised field.

DESIGN CONSIDERATIONS


	= Load


	= Young's Modulus

	= Strip Thickness

	= Strip Width

	Load Calculation

W = Efbt³



		6.5D²

CONSIDERATIONS

Minimum diameters are a a proportion of material thickness; the greater the ratio, the greater the life cycle expectancy.

Any constitutes one cycle of a constant force spring, not just a cycle from fully closed to fully closed to fully extended.

Cycle life can be improved by correct strip edge finishing (edge dressing), thereby preventing edge cracks created during the strip shearing process from becoming stress raising points during operation.

CASE STUDY ONE

APPLICATION - A prestigious hotel room `honour bar', based on a large capacity refrigerated bar with choice of 14 different items. Items slide or roll into place down a shallow ramp to take the place of those removed by the user.

PROBLEM - The system worked perfectly where the item was contained in a bottle or can, but snack items did not fall into line in the same way as the heavier liquid products. In some cases they were simply too light , whilst in others the contents would settle produce flat spots that arrested movement. Heavier, rigid packaging was initially considered in order to provide the necessary weight. However, this proved to be too costly.

SOLUTION - Nudge the items into place using a constant force spring. Working to a design, produced by the manufacturer of the bar system, George Emmott engineered a constant force spring of the necessary thickness, width and coil that, when clipped to the ramp at the base of each magazine and positioned directly behind the snack product, produced the desired effect of propelling the item into position


	George Emmott (Pawsons) Ltd, Wadsworth Mill, Oxenhope, Keighley, West Yorkshire, BD22 9NE. Tel : 01535 643733; Fax: 01535 642108


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