How to choose the appropriate length of wire thread insert for blind hole ?

Choosing the appropriate length of a wire thread insert in a blind hole requires comprehensive consideration of the hole depth, insert installation specifications, base material strength, and bolt fit requirements. The following is a detailed analysis:

1. Blind Hole Depth Structure and Insert Installation Specifications

Hole Depth Composition: The total blind hole depth includes the chamfer depth, the ST effective thread depth, and the taper hole depth. If the effective length of the wire thread insert is less than the ST effective thread depth, the insert will not be properly threaded, or the thread gauge or bolt will not be able to pass through.

Design Optimization Strategies:

Eliminating or minimizing the hole depth: This saves hole depth space and ensures more depth is available for effective thread generation.

Shortening the Tapered Hole Depth: This can be achieved by adjusting the length of the taper’s front guide cone or milling to the bottom of the hole to reduce the depth occupied by the taper hole.

Managing the Mounting Shank: For wire thread inserts with tails, the taper hole depth must be at least equal to the mounting shank length to ensure the mounting shank does not bend if broken. II. Base Material Strength and Insert Length Selection

2. Relationship between Material Strength and Insert Length: The lower the base material strength, the longer the wire thread insert is required to ensure that the strength of the machine screw hole is greater than the strength of the screw.

Recommended Length Standards:

Mild-carbon steel substrates: Wire thread inserts with a length of 1.5d to 2d are suitable. Aluminum alloy substrates: Wire thread inserts with a length of 2d to 3d are recommended.
Composite substrates: Extra-long wire thread inserts with a length of 3d or longer should be used in conjunction with locking inserts (SL designation).

Bolt Fit and Insert Length Requirements:

Bolt Insert Depth: The length of the bolt threaded into the insert should be no less than 1.5 times the bolt diameter to ensure an effective connection.Matching Insert Length to Bolt Length: Select an insert of appropriate length based on the bolt length, ensuring that the bolt can fully penetrate the insert and leaving sufficient excess length.

Precautions for Practical Applications:

Handling Extreme Situations: In extreme situations, the insert length can be increased as much as possible without sacrificing thread strength by optimizing the hook hole design and carefully controlling the taper hole depth. The relationship between the length after installation and the length in the free state: The length after installation will shrink and stretch due to the constraint of the internal thread on the screw sleeve, and is usually greater than the length in the free state.