Application of shot peening in connecting rods

1. Why the connecting rods require shot peening?

The connecting rod plays the role of power transmission between the piston and the crankshaft in the engine. It converts the linear motion of the piston into the rotational motion of the crankshaft. In this motion process, the connecting rod has been subjected to periodic bending stress, and its body is easy to cause fatigue fracture. At the same time, the big and small ends of the connecting rod are connected to the crankshaft and the piston, respectively. In the high-speed operating, the assemble load is carried by them, resulting in fretting friction and fatigue.

The diesel engine is used for the large marine engine. The engine body is large and the connecting rod is heavy. Once it fails, it is difficult to maintain and repair. Therefore, to ensure its long-term fatigue performance, the shot peening technology is introduced in China and abroad. At the same time, in the advanced automotive industry, the shot peening of connecting rods is also used more often, and the fatigue life after shot peening can be significantly increased by 40-50%.

2. Where are the failure positions of the connecting rod?

Failure positions of connecting rod:

a) Transition area from connecting rod body to big and small ends-- Bending stress

b) Big and small ends-- Assemble loads

c)Assembled gear of the big end-- Assemble loads



3. Commonly used shot peening process for connecting rod

3.1 Overall strengthening of connecting rod

a) Shot peening intensity:0.4-0.6mmA

b) Coverage (Fluorescent agent method): 95%

c) Recommended shot: S330(0.8mm)/HV640

d)Shot blasting position: the whole body

e) Requirements for residual pressure stress: The surface stress≥500 Mpa

3.2 Shot peening for big end and small end holes of connecting rod (Multistep shot peening)

a) The first peening intensity: 0.35-0.40mmA

The second peening intensity: 0.35-0.40mmA

b) The first coverage  (Fluorescent agent method):200%

The second coverage (Fluorescent agent method):100%

c) Recommended shot: S330(0.8mm)/HV640

d) Shot peening position: Inner wall of big end and small end holes of connecting rod

e) Requirements for residual compressive stress: The compressive depth≥500μm

3.3 Connecting tooth surface of connecting rod big end

a) Shot peening intensity: 0.2-0.25mmA

b) Coverage (Fluorescent agent method): 150%

c) Recommended steel shot: S110(0.8mm)/HV640 

d) Shot peening position: Tooth root

e) Requirements for residual pressure stress: The compressive depth≥500μm

4. Type of shot blasting/peening strengthening of marine connecting rod

4.1 The overall shot peening

Recommend equipments: 2RT500-P380/3/7.5

                                          2 Station turning table shot blasting machine


4.2 Shot peening for inner wall of big end and small end holes and tooth surface(Local shot peening of connecting rod)

Recommended equipment: MT12-3G15/1/R

                                             Trolley type robot shot peening machine