SKL21 Rail Clip Railway Fasteners Manufacturer

The SKL21 rail clip is a crucial component of the W21 rail fastening system, designed to provide a permanent, highly elastic clamping force for rails on concrete sleepers, particularly in high-speed and conventional railway lines. 

Manufacturing Process of SKL21 Rail Clip 

The manufacturing process for the SKL21 rail clip (tension clamp) involves a series of highly controlled thermal and mechanical steps to ensure the high elasticity and fatigue resistance required for high-speed rail. 

1. Raw Material Preparation

• Material Selection: High-grade spring steel bars, typically 60Si2CrA or 38Si7, with a diameter of approximately 13mm are used.

• Inspection & Shearing: Bars are inspected for defects and then sheared into specific lengths, often around 430mm, using hydraulic cutting machines. 

2. Heating and Forming

• Induction Heating: The sheared rods are heated in an intermediate frequency furnace to forging temperatures between 950°C and 1050°C. This process must be rapid (about 10 seconds) to avoid surface decarburization.

• Stamping/Molding: The heated bars are transferred via robotic handling to a power press. They undergo three stages of punching/bending in custom molds to achieve the complex SKL shape. 

3. Heat Treatment (Hardening & Tempering)

• Quenching (Hardening): The formed clips are immediately immersed in a quenching oil tank (at roughly 70°C–80°C) for about 10–12 minutes. This creates a hard martensite structure.

• Tempering: After quenching, clips are heated in a tempering furnace at 350°C to 500°C for 55–90 minutes. This critical step reduces brittleness and improves toughness, achieving a final hardness of 42–47 HRC. 

4. Surface Treatment & Finishing

• Shot Peening: Often used to improve fatigue strength by inducing compressive stress on the surface.

• Anti-Corrosion Coating: Depending on customer requirements, clips receive various finishes:Plain (oiled),Oxide Black,Color painting,Hot-dip galvanizing (HDG) or Zinc plating .

5. Final Inspection and Testing

Before packaging, clips undergo rigorous quality control to meet international standards (like EN 13481-2):

• Fatigue Test: Must withstand up to 5 million cycles without breaking.

• Dimensional Accuracy: Checked using precision gauges to ensure a perfect fit in the W21 fastening system.

• Load & Hardness Tests: Verification of clamping force and HRC values. 

Kunshan Signum Machinery Technology Co.,Ltd is a manufacturer and supplier produce Vossloh SKL Clips(SKL Tension Clamps) and associated fastening systems. We are able to offer SKL clips with associated fastening parts according to your drawings, requirements and standards with competitive price and good quality.