Shutting Doors and Lifting Loads Using a Retractable, Constant-Force Spring

The counterbalancing of loads is a necessity for many designers. Facilities like self-closing fridges in shops, industrial hoods that shut themselves, and waste disposal units that automatically close all require a counterbalancing spring to work.

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NEG’ATOR constant force extension springs are often the best type of spring for this application and can be manipulated in a variety of ways to ensure that your design works.

Door Lift (Springs)

To counterbalance heavy doors, such as steel doors on furnace viewing ports, an extension spring can be used.

Springs for Closing Doors

To keep sliding doors on a commercial dispensing refrigerator closed when not in use, manufacturers can employ two NEG'ATOR extension springs to automatically pull them shut.

Constant Force Springs (NEG'ATOR)

The NEG'ATOR constant force spring is the most basic type of constant force extension spring, and it is also the most versatile. It is a prestressed flat strip of spring material that can beis formed into a virtually constant radius coils on a drum or around itself. When deflected, the spring material straightens as it leaves the drum. Through its tendency to assume its natural radius, the straightened length of spring actually stores the spring’s energy.

Constant force springs from Hunter Spring makes extremely long linear extensions possible and offerswith a low force gradient throughout the entire deflection range. Maximum force is generated at initial deflection and negative torque or negative force gradients can be achieved upon request.

Hunter Spring supplies constant force springs made from 301 High Yield Stainless Steel. Upon request, the company can also use other materials such as Inconel, Elgiloy, or high-carbon steel for custom applications.

Due to its inherent light weight and compact sizes, the constant force springs allow for small package sizes. Springs can be wound together in a laminated assembly to multiply output force in applications where there is limited space to multiply output force without any major impact on fatigue life and spring size.

Hunter Spring can supply both standard and custom constant force spring designs. Customers can specify their requirement using the design worksheet, which will enable the Hunter’s Application Engineers to provide the design that meets their requirements.

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Constant Torque Springs (NEG'ATOR)

When making a constant torque spring for use as a door closer or load lifter, a prestressed strip of spring material, the NEG'ATOR constant torque spring motor, is formed into a coil and is stored on a small storage drum. The free end, which is the "winding" portion of the constant torque spring's cycle, is then fastened and backwound onto a larger output drum.

The spring will return to the storage drum to assume its natural curvature when the torque on output drum is releasedreduced, rotating the output drum and providing virtually constant torque.

The Hunter Spring’s constant torque springs offer minimal intercoil friction and resultant hysteresis, while l, long deflections at nearly constant torque and limited negative or positive gradients can be achieved. Angular torque output from The NEG’ATOR constant torque springs can provide rotary motion directly from the output drum or can be translated into a provide linear force displacement through the use of a cable and spool. or rotary motion directly from output drum.

The springs are made from type 301 high-yield stainless steel and are supplied in coils for mounting on motor drums.

Hunter Spring offers a broad range of standard constant torque springs. Customers are invited to download the Standard Spring Design Guide for Constant Torque Springs for further details.
The company also offers constant torque springs as custom spring solutions to suit the customer’s specific requirements. Customers can specify their requirement by using the design worksheet, which will enable the Application Engineers to quickly provide the design that meets their requirements.

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Custom Springs

For customers who have a new product, an application for a flat spring, or are simply looking for advice about springs, Hunter Spring’s design engineers can provide skilled assistance.

Over the last 100 years, Hunter Spring has amassed an array of spring making dies and tools. Often, when customers request custom springs, the company simply modifiescan often modify a standard spring, saving customers both time and money.

If a new spring is required, Hunter Spring provides design worksheets that list the main specifications for all types of springs.

This information has been sourced, reviewed and adapted from materials provided by Hunter Spring.

For more information on this source, please visit Hunter Spring.