Torsion springs are helical springs that exert a torque or rotary force and are subject to bending stresses.
Torsion springs should always wind up from the free position - never to unwind from the free position. As they wind up, torsion springs reduce in diameter and their length becomes longer.
Such springs should be supported over a rod whenever possible. Some spacing should remain between coils to minimize friction which can alter torque and deflection.
There are an infinite number of torsion end configurations. The most economic end type is the straight torsion end. Other types of popular torsion ends include
hook, hinged and straight offset. For more detailed information regarding types of torsion ends contact Katy Spring.
To define, torque is a force that produces rotation. Torsion springs exert force in a circular arc in which the arms rotate about a central axis. The stress is in bending.
In the spring industry it is customary to specify torque with deflection or with the arms at a definite position. Formulas for torque are in inch pounds.
When a force is specified at a distance from the centerline, the torque, is called the moment, is equal to the force multiplied by the distance.
Several methods for designing torsion springs can be used. The easiest would be to contact Katy Spring with parameters including; force needed, space limitations,
shaft size, maximum body length allowed, environment the spring is used in, and number of deflections. These can be calculated manually but are done much easier with
spring design software.
Ordering Torsion Springs
The space required by a torsion spring should be considered approximate until the wire size and the number of
coils is finalized. The wire size is dependent principally upon the torque. Katy Spring can assist customers in determining the torque required
by a torsion spring.
To follow is a list of notes to keep in mind when ordering torsion springs from Katy Spring:
A spring index (inside diameter divided by wire diameter) between 4 and 14 is best, because larger ratios require more tolerance and are more expensive and difficult to manufacture. Ratios under 3 do not give accurate results determined by design formulas and cannot often be coiled on automatic machines.
Torsion springs under 3 coils usually buckle and often do not produce accurate test results. 30 or more coils may cause only some coils not to deflect, especially under light loads with a supporting rod.
Specify number of coils to the nearest fraction; i.e. 5 ¼.
If torsion springs are not supported by a rod running through the center, they may buckle and are subjected to additional stresses.
The inside diameter of a torsion spring reduces during deflection. Allowance should be made for clearance in addition to the normal spring tolerances.
Torsion springs should have some space and no initial tension between the coils. If a torsion spring is wound tightly, they may not deflect uniformly or test accurately. A slight space of 20-25 percent of the wire size is desirable. Square and rectangular wire should be avoided as they are expensive and often hard to find.
The hand or direction should be specified when ordering torsion springs. As a torsion spring winds up it has more coils. The increase in coils and in overall length should be allowed for during design. Deflecting a torsion spring in the "unwind direction" causes high stresses and can cause early failure. A spring wound clockwise is a "left hand" wound spring.
Arms of a torsion spring can be calculated as active coils in some cases. Deflection of long extended arms cab be calculated by allowing one third of the arm length, from the point of force contact to the body of the spring, converted into coils. If the length of arm is equal or less than half the length of one coil, it can be safely neglected in most applications.
Bends in arms of torsion springs can be expensive and should be avoided whenever possible. Bend radii should be as large as possible to reduce stresses.
Double body torsion springs are used as a left hand torsion spring and a right hand torsion spring connected at the center. They can be expensive and it is better to use 2 torsion springs (1 right and 1 left) whenever possible.
Torsion Springs - Design
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