The constant force spring can be used to counterbalance items, such as windows (known in the window industry as coil balance springs), doors, display racks and trays. It can also be used as a return or retracting mechanism wherein the constant force spring will provide a smooth, even, uniform load through its entire length or travel (deflection). Travel (extension, deflection) is limited only by the length of material in the spring. Load is a function of material width, thickness and coil diameter. Increased loads can be obtained by using two or more constant force springs interwound or in tandem or in other configurations.

 

 

 

 

            Various end details are possible, and tooling for many are already available. The constant force spring can be installed in several ways. The spring is often mounted on a bushing or a spool for tension applications. Fastening the spring to the bushing, or guiding the spring with flanges, is only required when deflection is extreme. We can mount the spring(s) for you on bushings or spools that either you or we provide.

 

 

 

 

            Load values for stainless steel have been tabulated in the accompanying table for various cycles (fatigue life) and material thicknesses, using a basic design width of one inch. The load is directly proportional to the material width in a constant force spring, but is not directly proportional to material thickness. These springs can also be made of tempered carbon spring steel, but greater forces are obtained from stainless steel in this type of spring. And, springs made of stainless steel offer superior performance in harsh environments.

Coiled Diameters and Load

(lbs. per 1" width of stainless steel)

Material Thickness	2,500 cycles		10,000 cycles		20,000 cycles		75,000 cycles		150,000 cycles
	Coiled Dia.	Load	Coiled Dia.	Load	Coiled Dia.	Load	Coiled Dia.	Load	Coiled Dia.	Load
0.002	0.15	1.3	0.17	1.0	0.22	0.65	0.33	0.32	0.44	0.17
0.003	0.22	2.0	0.25	1.5	0.32	1.0	0.48	0.50	0.66	0.26
0.004	0.30	2.6	0.34	2.0	0.44	1.3	0.65	0.65	0.89	0.35
0.005	0.36	3.3	0.43	2.5	0.55	1.6	0.81	0.80	1.11	0.44
0.006	0.44	4.0	0.51	3.0	0.65	2.0	0.95	1.00	1.33	0.52
0.008	0.59	5.2	0.69	4.0	0.87	2.6	1.28	1.30	1.78	0.70
0.010	0.73	6.6	0.86	5.0	1.08	3.3	1.59	1.60	2.22	0.87
0.012	0.87	8.0	1.03	6.0	1.30	4.0	1.91	2.00	2.67	1.04
0.014	1.02	9.3	1.20	7.0	1.52	4.6	2.22	2.30	3.07	1.20
0.016	1.16	10.6	1.37	8.0	1.73	5.3	2.53	2.70	3.60	1.40
0.018	1.31	11.9	1.54	9.0	1.96	5.9	2.85	3.00	4.00	1.56
0.020	1.46	13.2	1.71	10.0	2.18	6.6	3.20	3.30	4.44	1.74
0.022	1.61	14.5	1.89	11.0	2.37	7.2	3.48	3.60	4.89	1.91
0.025	1.81	16.5	2.14	12.5	2.72	8.2	4.00	4.10	5.55	2.18
0.028	2.04	18.5	2.40	14.0	3.04	9.5	4.48	4.60	6.23	2.44
0.031	2.26	20.5	2.65	15.5	3.36	10.2	4.94	5.10	6.90	2.70

 

            The constant force spring can be installed in various ways. The spring is often mounted on a bushing or a spool for tension applications. Fastening the spring to the bushing, or guiding the spring with flanges, is only required when deflection is extreme. John Evans' can mount the spring(s) for you on bushings or spools that either you or we provide.

 

 

 

 

For samples, questions,
or design assistance, e-mail
or call our Sales Department.

 

 

 

 

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