Constant Tension Spring
Constant Tension Spring
Monday Nov 23, 2020 By Nexim Alloys
We live in an era where we need prefect counterbalance for heavy moving parts. These moving parts requires a constant tension spring.
One example is the door on a moving van. When you pull down an open door, it takes additional force to get the door going the first few inches–that’s because the spring’s full load (1.25 times its diameter) must be overcome. After that, the door slides down easily, with nearly constant force.
You’ll find plenty of constant force springs in everyday products as well: retractable key holders, retractable dog leashes, vacuum cleaner cord reels, seatbelts, window balance systems, interior blinds and point-of-purchase displays, to name a few.
At their most basic level, however, constant force springs do exactly what other springs do. That is, they conform to Hooke’s Law. Hooke’s Law essentially states that when an elastic object is deformed, the force it exerts is directly proportional to the amount of the deformation. In other words, the farther you extend an extension spring, the more force it takes to pull it even farther; the more you compress a compression spring, the more force it takes to push it down even more.
In theory, a “constant force” spring would not obey Hooke’s Law, because the law mandates increasing force rather than constant force. In reality, the materials making up constant force springs do obey Hooke’s Law. However, constant force spring systems are still able to approximate constant force. In order to do so, the diameter of the coil must remain constant, or close to constant.
In standard constant force spring behavior, the user must first overcome the spring’s full load by extending the spring beyond 1.25 times its diameter. After that, the coil can be extended further by applying nearly constant force.
Constant force springs can be manufactured using the same spring coiling machines used for helical springs. The coiler will have to be modified to accommodate the flat strip of metal that makes up the constant force spring. Nexim Alloys offers constant force spring manufacturing as per requirements.
| Material | Stainless Steel 301, High Carbon Steel Sizes |
|---|---|
| Usage | Garage, Electrical Connection, Earthing, Fire Damper, Railway Window, Industrial |
| Dimension | thickness 0.005 to 0.70mm width 3.00 to 35.mm |
- The drum diameter should be 10% to 20% larger than its natural inside diameter.
- One and one-half wraps should remain on the drum at maximum extension.
- The strip becomes unstable at long extensions and should be guided to prevent twisting or kinking on recoil.
- Idler pulleys must be larger in diameter than the natural diameter and should never be used to cause back-bending against the natural radius of curvature.
A Constant Force Spring is usually mounted by first tightly wrapping it on a drum, then attaching the free end to the loading force such as in a counterbalance application. This relationship can also be reversed.
Belt webbing, tape measures and dog leads, seat recliner, window regulator mechanisms etc.
Click here to read about the Nexim Alloys, configured for constant force spring manufacturing.
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