|
| |
Benefits and Applications |
| |
For Many years, helically coiled wire thread inserts have been vastly underestimated. The popular misconception that they were designed for the repair of damaged threads, has given this unique fastener a false image.
Manufactured to exacting limits, from high quality aircraft material, they have been used successfully in many applications, ranging from supersonic aircraft and space exploration to simple children's toys. Because of their unique mechanical performance they have, like all good designs, hardly changed since their introduction in the early 1950's.
They are much lighter and less expensive than any other equivalent type of thread insert and because of their compact size, can generally be introduced into existing designs where no previous provision has been made.
Unlike any other economic measure, their introduction reduces overall product cost, whilst increasing quality and performance.
In the following paragraphs we highlight some of the often overlooked realities of this simple but very special product.
Strength
 |
|
Due to their flexibility, wire thread inserts create internal threads which have a much improved distribution of residual stress loading when compared with conventional tapped holes, where up to 70% of the shearing forces are carried by the first three threads in the tapped hole. This extremely high loading, unfortunately, also applies to solid and thin walled inserts, due to their solid wall configuration.
The flexibility of wire thread inserts helps to compensate for pitch and flank angle errors, inherent in normal tapped holes, and significantly enhances the load bearing capacity by deflecting the residual forces into a
|
helical hoop stress which is dispersed into the wall of the tapped hole. This enables the design to be confidently based on the bolt strength utilising smaller and shorter threads even when used in low strength materials.
Corrosion Resistance
WTI inserts are manufactured in 18/8 austenitic chromium/nickel stainless steel and offer excellent corrosion resistance, preventing adverse seizing and galling even at elevated temperatures. For applications involving severe corrosive conditions or subject to the effects of galvanic corrosion, additional surface coatings are available, such as cadmium, zinc, aluminium, silver or molybdenum disulphide.
Temperature Range
Standard inserts, manufactured in 18/8 stainless steel are suitable for operation within temperatures ranging from -160ºC to +420ºC (-320ºF to + 800ºF).
For applications involving extreme and elevated temperatures wire thread inserts can be manufactured in creep resistant nickel based alloys.
Cost & Weight Benefits
Wire thread inserts are much lighter and less expensive than any other equivalent thread insert. As a result of their compact size they can generally be incorporated into existing designs where no previous provision has been made.
In many instances, because of their mechanical strength benefits their introduction may result in the use of thinner sections or lighter parent materials without sacrificing thread strength.
Wear Resistance
Due to a combination of material hardness and brilliant surface finish wire thread inserts create internal threads in which wear due to thread friction is virtually eliminated. This is of particular value in applications requiring repeated assembly & disassembly.
The low frictional coefficient ensures that virtually all of the applied assembly torque is converted into clamping load. Thus providing threads that stay tight.
|
|
|
