What is a Helicoil?

Helicoil, also known as a pin bushing, is a type of threaded insert designed with both internal and external threads. The internal thread is typically either metric or imperial coarse thread, while the external thread is metric or imperial fine thread. Depending on the size, Helicoils may feature either two or four pin keys (specifications ≤ M4 typically have two pin keys).

Functional Characteristics

The primary function of a Helicoil is to repair damaged internal threads and strengthen the holding power of internal threads. It has been widely adopted across various industries, including aviation, aerospace, rail transportation, instrumentation, hydraulics, electrical power, and textiles. Helicoils are particularly useful in environments where lightweight metals, such as aluminum alloys, are used but high torque is required, demonstrating excellent tensile and torsional strength.

Common Materials

Helicoils are typically made from two materials:

• Austenitic stainless steel: Often used for applications involving aluminum alloy substrates. The surface is passivated for enhanced corrosion resistance.
• Plain carbon steel: Generally used for cast iron substrates. These Helicoils are commonly treated with blackening or phosphating for surface protection.

Types of Helicoils

Helicoils can be categorized in different ways:

1.By external thread size:

• • Light
  • Standard
  • Heavy
  • Extra Heavy
    As the name suggests, the nominal diameter of the external thread increases with each category.

2.By structure:

• • Standard Type: The most common form, featuring through-hole internal and external threads.
  • Locking Type: The middle or end of the internal thread is deformed through stamping, creating a locking effect.
  • Solid Type: Unlike other types, the solid Helicoil has no internal threads, only external threads and pin keys.

Use Case for Solid Type

Some may wonder why a solid-type Helicoil is used if it cannot accommodate a screw. Its primary purpose is filling holes. For example, if an unnecessary hole is drilled into a part and welding is not an option due to the poor weldability of cast iron or aluminum alloy, a solid-type Helicoil can effectively remedy the mistake.

Processing

Helicoils are manufactured using a complete turning process, ensuring concentricity between the internal and external threads. This method allows for easy customization and small-batch production. Helicoils with special outer diameters can be customized for specific equipment maintenance needs.

Installation Steps

Installing a Helicoil is straightforward:

1. Drill a bottom hole in the substrate.
2. Use a tap to cut the external threads.
3. Screw in the Helicoil.
4. Tap the pin key to secure it in place.

This simple process makes Helicoils an efficient solution for repairing or reinforcing threaded connections.

When a problem is found in the installation of Helicoil, how should the Helicoil sleeve be removed?

When the screw hole of the base product is wrong, the Helicoil needs to be removed without damaging the base screw hole.

1. Use a specified standard drill bit to drill into the screw hole where the plug thread sleeve has been installed, and drill the wall of the plug thread sleeve thin.
2. Use a pointed cone to insert it along the small holes of the several pin keys of the plug screw sleeve and bend it inward.
3. When the Helicoil is loose, the screw sleeve can be removed using the screw sleeve removal tool.