Valve spring usage
The valve spring determines the opening pressure, the stroke of the flap and the stability of the seal in the closed state in the valve. If these springs have problems, the entire valve will be difficult to operate normally.
Then we come to summarize the reasons for the failure of the valve spring, so that everyone can pay attention and avoid in the future operation.
The reason for the frequent failure of our valve springs is summarized as follows:
1, high pressure - spring load can be divided into static load, impact load, vibration load according to the form of external force, most spring failure is due to large deformation and high load caused by high stress caused.
High stress only applies to static load springs, and low stress fatigue life is longer.
2. Hydrogen embrittlement - If the spring is not properly hydrogen treated after electroplating or pickling, the spring steel will fail due to brittleness, but the non-ferrous metal valve spring is not affected by this.
In electroplating solutions, for the electrolysis of water molecules, a certain number of hydrogen ions are always present in a more or lesser extent. A part of the hydrogen ions forms hydrogen gas to overflow, and some of them are infiltrated into the plating layer and the metal body in the state of hydrogen atoms to make the metal body and The toughness of the coating decreases and becomes brittle, which is hydrogen embrittlement. So should be in the electroplating or acid washing after the oven or resistance furnace hydrogen treatment, according to the size of the spring and the thickness of the coating to determine the warm and time, the general normal temperature is selected between 150-250 degrees Celsius, holding time 0.5-5 hours between.
3. Severe bending and notches ---- Tension, twisting, and sharp bends produced by flat springs. Notches or scratches in flat springs can cause high stress concentrations and cause failures. Therefore, the bending radius should be as large as possible and avoided. Print notes.
4. Fatigue ---- Repeated deformation of the spring, especially if it is greater than 106 cycles, even moderate stress may cause fatigue damage.
When the operating conditions are severe, low stress should be used, and the fatigue resistance of the spring should be improved. In a reasonable material selection, shot peening can not only make the spring obtain a smooth surface, but also can improve the fatigue resistance of the spring and extend the spring. The service life can relieve or even prevent the decarburization, pitting, indentation, and cracks on the surface.
Shot peening can make the surface undergo a slight plastic deformation, and the residual stress generated can partly offset the tensile stress generated by the spring when it is repeatedly loaded, and the tensile stress is the origin of the crack.