UNI 3545 / GB/T 1222 Standard 38Si7 60Si2CrA SB Rail Clip
Oct 16, 2025
The SB rail clip is the spring element of the SB W3-type rail fastening system, a design used on prestressed monoblock concrete sleepers. In this system the rail is laid on a rail pad between cast-in anchors, and the SB-type spring clip is mounted with one side connected to the anchor and the other side pressing down on the top of the rail foot like a spring. The clip is produced in spring steel grades such as 38Si7 and 60Si2CrA, and the material and product requirements follow standards including UNI 3545 and GB/T 1222.
How the SB W3-Type System Works
In the SB W3-type fastening system, the rail sits on the rail pad between the anchors, which are cast into the sleeper at installation. The SB clip is installed so that one end engages the anchor and the other end bears on the top of the rail foot, pressing the rail down. Under the rail foot, the rail pad cushions the rail and distributes the load. The rail foot is insulated from the clip and the anchors by electro-insulating hold-down parts, so the fastening system maintains the electrical insulation required for track circuits.
The system is used only on prestressed monoblock sleepers, where the cast-in anchors provide a stable, corrosion-resistant fixing point for the clip. The elastic action of the clip absorbs the vertical and lateral forces of traffic and keeps the rail firmly seated between the anchors.
Technical Parameters
| Parameter | Value |
|---|---|
| Material | 38Si7, 60Si2CrA |
| Standard reference | UNI 3545, GB/T 1222 |
| Hardness | 42-46 HRC |
| Fatigue testing | 5 million cycles minimum |
| Clamping force | 10.7-10.9 kN |
| Coating | Plain, painting |
UNI 3545 is the Italian standard for rail fastening elements in this system family, and GB/T 1222 is the Chinese standard for spring steel, which defines the material requirements for grades such as 38Si7 and 60Si2CrA. The hardness range and the clamping force are verified on the finished clip, and the fatigue performance is demonstrated by laboratory cycling tests.
Materials: 38Si7 and 60Si2CrA
Both 38Si7 and 60Si2CrA are spring steels with high strength and good toughness. 38Si7 is a silicon-manganese spring steel with an economical processing route, while 60Si2CrA adds chromium for improved hardenability and fatigue resistance. The choice between the grades is made by the specification; both are heat treated to the required hardness range so that the clip works elastically over its service life.
System Components
The SB W3-type fastening set includes, per rail seat:
The SB spring clip (two per seat in the standard arrangement).
The rail pad under the rail foot.
The electro-insulating hold-down parts separating the rail from the clip and anchors.
The cast-in anchors in the sleeper, which locate and hold the clip.
The components are matched as a system: the clamping force of the clips, the stiffness of the pad and the insulation properties are designed together to hold the rail in gauge and transfer the traffic loads into the sleeper.
What to Check When Specifying
Material grade and hardness certificate (38Si7 or 60Si2CrA per GB/T 1222).
Clamping force within the specified range (10.7-10.9 kN).
Fatigue test report (5 million cycles minimum).
Coating type: plain or painting, per the environment.
Compatibility with the sleeper anchor spacing and the rail section.
FAQ
What is an SB rail clip?
It is the spring element of the SB W3-type rail fastening system, installed between a cast-in anchor and the top of the rail foot to press the rail down elastically on prestressed monoblock sleepers.
What standards apply to the SB clip?
UNI 3545 covers the fastening system elements, and GB/T 1222 defines the spring steel material requirements for grades such as 38Si7 and 60Si2CrA.
What is the clamping force of the SB clip?
The specified clamping force is in the range 10.7-10.9 kN, verified on the finished clip at the defined installation position.
Which sleeper types is the SB W3-type system used on?
The system is designed for prestressed monoblock concrete sleepers with cast-in anchors. It is not used on timber or other sleeper types.
How is the rail insulated in this system?
Electro-insulating hold-down parts separate the rail foot from the clip and the anchors, so the fastening maintains the electrical insulation required for track circuits.
What surface finishes are available?
Plain and painted finishes are standard. The finish is selected according to the corrosion environment of the line.
