Introduction
Gray cast iron is a common casting material used in the production of steam turbine headwear. It is an alloy of iron and carbon in which the proportion of carbon is usually between 2.5% and 4.0%. This type of iron is produced by adding steelmaking slag, foundry resin sand and other materials to a melting bath of pig iron, and is characterized by a relatively high iron content and low content of inclusions. As a kind of cast iron, cast iron is easy to process and at the same time, the surface of the casting product is relatively smooth, so it is a kind of widely used casting material.
In terms of the thickness of gray cast iron used in steam turbine headwear, it is generally 20 mm. As one of the important raw materials in steam turbine production, the thickness of casting will affect the quality of the turbine and the service life. Therefore, it is very important to ensure the continuous stability in the thickness of the casting. Otherwise, the production can not guarantee the normal assembly and installation of steam turbine headwear, and the service life of the product will be shortened.
The headwear of steam turbine is the overall casing of the turbine, the transmission shaft and some other components, which is usually cast from steel or gray casting iron. In order to ensure the regularity of steam turbine headwear, the average size and size of the headwear hole of the castings must be strictly controlled. The water inlet and outlet diameter of the turbine headwear should meet the relevant technical requirements, which is mainly restricted by the viscosity limit and the optimum operating efficiency at a certain flow rate. The size of the headwear hole should be considered through the operating temperature and pressure of the turbine.
The size of the steam turbine headwear hole is mainly determined by the size and angle of the turbine blades. For example, the inner diameter of the headwear should be equal to or slightly larger than the diameter of the blade tip circle at the largest. In this way, the steam can smoothly enter and exit from the headwear hole to drive the turbine rotation. In addition, the precision of the headwear hole should also meet the relevant requirements. The error should not exceed the size of the blade, otherwise the blade will collide with the inner wall of the headwear nozzle, resulting in a large degree of friction, and thus greatly reduce the working efficiency of the turbine.
In addition, the opening edge of the headwear hole also needs to be properly processed in order to reduce the edge concentration of stress. If the opening edge of the headwear is not properly processed, the metal near the edge will be subjected to a high degree of stress concentration and fatigue in the course of work, which will easily lead to the cracking or damage of the headwear. Generally, the opening chamfer of the headwear should not be less than 1mm and the opening angle should be greater than 30 degrees.
Finally, the surface treatment plays an important role in the headwear. In the production of steam turbine, the surface of the headwear is usually subjected to a series of processes such as shot peening, sandblasting, pickling and passivation. These processes can effectively eliminate and reduce the internal stress accumulated in the metal during casting, and improve the fatigue resistance and corrosion resistance of the steam turbine headwear.
Conclusion
In summary, the thickness and size of the headwear hole of steam turbine headwear must be strictly controlled, and the opening edge needs to be properly processed to reduce stress concentration and prevent cracking and fatigue of the headwear. In combination with surface treatment, the dimensional stability and service life of the turbine headwear can be effectively improved.
