"Your co-operation in making springs for us urgently has meant that the altar bread department did not have to close down for more than a day and, with Christmas orders being produced, this has meant a lot to us.
Please accept my grateful thanks for having obliged us in this matter. Your kindness is very much appreciated.
With kind regards,
Society of Vincent de Paul."
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Extension Springs
Extension springs work in the opposite manner to compression springs; they resist stretching, or tensile, forces. When the ends are pulled apart, the spring tries to bring them together again.
Like compression springs, extension springs absorb and store energy.
Unlike compression springs, most extension springs are always under some degree of tension, even when under no load. This initial tension is what determines how tightly together an extension spring is coiled when there is no load applied.
Springs can be manufactured with varying initial tension to suit different applications.
Key Design Parameters:
Wire diameter - The thickness of wire.
O.D. or Outside Diameter
I.D. or Inside Diameter
Free Length - The length of a spring when it is under no load.
Extended Length – The the length of the spring under maximum load, at its full extension.
Rate - Force per unit multiplied by deflection.
Maximum Load – the load at full extension.
Another common type of extension spring is the drawbar spring. In a drawbar, the load is applied at the ends of long steel loops which pass through the spring’s center and are hooked around the opposite end, thus compressing the spring upon loading.
Drawbar springs are excellent for use in potential overload situations and offer a built-in definite stop that will continue to carry a static load after reaching the maximum extended length.
A common application of the drawbar spring is used when supporting a porch swing.
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Size Range |
Steels Available |
Coatings and Finishes |
0.3mm to 16mm
Various flat strip sizes
on hand. |
Carbon, Stainless, Phospher Bronze. |
Paint
Electro plating, ie Zinc
Powder Coating |
Applications:
As with compression springs, the applications for extension springs are varied. Some of the most common uses for extension springs include trampolines, carburettors, garage door assemblies, medical devices, farm machinery, and toys.
At NZ spring works, extension springs can be manufactured from wire ranging from 0.3mm to 16mm, and diameters ranging from 3mm to 150mm.
They can be made with a variety of different ends, each suited to different applications. They include loop, hook, double twisted full loop ends, straight-cut, threaded inserts, extended twist loops, expanded eyes, reduced eyes, rectangular ends and teardrop-shaped ends.
The ends on an extension spring can vary in distance from the body of the spring. The length of the ends can be used to determine the overall tension of the spring when it is used in its application.
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