ArmaCoil Free Running Inserts
Manufactured from High Tensile Stainless Steel Wire
Free Running Inserts or Screw Lock Inserts
ArmaCoil inserts are manufactured from high tensile stainless steel wire that has been formed into a diamond section to exacting dimensional standards. When installed the ArmaCoil provides a precision female thread of high surface finish and strength.
Installation Process
Installation of the ArmaCoil is achieved using the appropriate inserting tool, listed in the Technical Data and Tooling PDF.
The driving tang is engaged in an abutment or slot in the Inserting Tool Mandrel. It is then pre-wound in the Nozzle. Placing the tool over the tapped hole the ArmaCoil is wound into place. No forward pressure should be applied once the insert has engaged with thread of the nozzle or whilst inserting into the work piece.
Withdraw the tool when the insert is to the correct depth below the surface, 1/4 to 1/2 turn below (plus any counter bore or chamfer).
The tang is removed using the Tang Break Off Tool. Place the tool inside the ArmaCoil and a sharp tap with a hammer will break the tang at the notch position. The configuration of this notch allows for bolt entry from either end of the assembled ArmaCoil.
Retention of the Insert
Correctly fitted the ArmaCoil will not move. It is secured in position through Radial Pressure exerted by the coils bearing on the thread flanks.
Radial Pressure exists due to the outside diameter of the ArmaCoil, in its free state, being larger by a calculated amount than the tapped hole into which it is to be installed.
Variability of Pitch
All male and female threads have Pitch and Angle errors. This means that of all the threads supposedly in engagement only one or two are actually in contact.
When loading the assembly the bolt stretches and causes further Strain Pitch Error - consequently about 70% of the load is imposed on the two threads in engagement at the mouth of the hole.
This extremely high stress concentration contributes to early loss of pre-load due to creep relaxation.
The result is a slack assembly and early fatigue failure.
Pitch and Angle Errors Cause
- Poor flank contact between male and female threads
- Unequal load distribution over thread engagement
- Early loss of pre-load
- Premature failure of assembly
For more information contact our Technical Department.
