JB/T 9127-2000Cylindrical helical springs - Technical specification for shot peening (English PDF)

2.1 shot-blasting peening

a craft measure by jetting high-speed moving shot flow to spring to generate compression stress on its surface so as to enhance the fatigue strength, increase the service life and improve the stress corrosion resistance

2.2 arc height

the surface layer of test piece is plastically deformed under the impact of shot-blasting, so that the shot-blasting surface of the test piece is spherically curved, and the distance between the specific reference plane cut into the spherical surface and the highest point of the spherical surface is determined as the arc height

2.3 shot-blasting strength Q

the arc height at the saturation point of arc height curve is defined as shot-blasting strength

2.4 surface coverage rate

ratio of the area occupied by the crater on the shot-blasted surface to its total area is called the surface coverage rate.

3.1 Shot-blasting equipment

There are mainly 3 types of shot-blasting machine: pneumatic type, mechanical centrifugal type and wet type. The main function of the shot-blasting machine is to provide kinetic energy to the shot and to move the spring to ensure that the spring obtains the specified shot-blasting strength during shot blasting.

3.2 Shot

The shots used in shot-blasting peening include cut wire shot, cast steel shot, stainless steel shot, glass shot, etc. The shot must be spherical. The broken shots in the using process shall be screened and separated timely. For cut wire shot, the angularity shall be removed prior to use. The shot is selected according to the material, specifications and technical requirements of the shot-blasting spring.

3.3 Test piece

3.3.1 Materials

The test piece is fabricated from 70 steel or 65Mn cold-rolled spring steel strip.

3.3.2 Hardness

The test piece shall be subjected to heat treatment and the hardness is 44~50 HRC.

3.3.3

The dimensional accuracy is as specified in Table 1 and Figure 1.

Table 1 In mm

Test piece Thickness delta

N 0.787±0.025

A 1.295±0.025

Figure 1

3.4 Supporting fixture

3.4.1

The supporting fixture of test piece can be made of carbon structural steel, and the dimensional accuracy is as specified in Figure 2 or Figure 3.

Figure 2

Figure 3 3.4.2 The supporting fixture of test piece shall be inspected regularly and replaced in time if it is damaged.

3.5

The structure and dimensional accuracy of an arc height gage shall be as specified in Figure 4.

The four contacted ball heads shall be kept in the same plane, the tolerance is ±0.05mm.

Figure 4

3.6 Preparation prior to shot-blasting

3.6.1

The springs shall reach the specified process dimension before shot-blasting.

3.6.2

The springs shall be subjected to the specified heat treatment before shot-blasting.

3.6.3

The test piece and the supporting fixture for shot-blasting together with the spring shall comply with the requirements of 3.3 and 3.4. The test piece installed on the supporting fixture shall be fastened at four points.

3.6.4

Spring surface shall be dry, clean and free from oil and other corrosion.

3.7 Quality control for shot-blasting

3.7.1

The surface coverage rate of the spring after shot-blasting shall be above 90%.

3.7.2

When the shot-blasting strength is checked by type A test piece, the shot-blasting strength is selected within the range of 0.15A to 0.16A; when the shot-blasting strength is checked by the type N test piece, it is selected within the range of 0.15N to 0.46N.

3.8 Treatment after shot-blasting

3.8.1

The spring after shot-blasting is allowed to be tempered, but the tempering temperature shall not exceed 250°C.

3.8.2

If surface treatment is required for the spring after shot-blasting, the heating temperature in each step shall be controlled below 250°C.

3.8.3

The spring after shot-blasting is allowed to be mechanically repaired. The spring is usually only allowed to be repaired in its load-bearing direction.

3.8.4

After shot-blasting, the spring surface is prone to rust and must be subjected to rust-proofed treatment immediately.

4.1

A batch of springs shall be subjected to the shot-blasting strength test for the first inspection before the shot-blasting. Shot-blasting shall not be carried out for this batch of springs until the test result meets the technical requirements. Regular sampling inspection shall be carried out during shot-blasting.

4.2

The measurement method for arc height is as shown in Figure 5.