Views: 1 Author: Site Editor Publish Time: 2021-12-02 Origin: Site
Wear resistant elbow can be favored by the market and continue to replace some traditional wear-resistant materials. The fundamental reason lies in its excellent product quality and its various advantages compared with traditional wear-resistant materials, such as cast stone, cast steel and centrifugal casting ceramic materials, tortoise shell net and rubber lining coal hopper.
1. Before cast stone, most of the elbows in each plant used cast stone elbows. This material is characterized by fragile and cracking, and the wear surface is backpacked, with a wall thickness of 25-35mm, some of which are nearly 40mm. After the inner side is worn and cracked for a short time, the pulverized coal wears outward with the gap, and its service life is only one overhaul period. Moreover, there are often pores inside, which is easy to leave hidden dangers. Once worn out, it cannot be repaired on site.
2. Cast steel and cast steel (including alloy steel) bimetallic wear-resistant pipes are widely used in the field of wear prevention, and their manufacturing process is relatively simple. However, due to the limitations of material properties and process, the surface hardness (about 60) of cast steel is much lower than that of ceramics (more than 80), and the wear resistance is only one tens to less than that of ceramics (see the wear test report of Powder Metallurgy Institute of Central South University and the spray wear test results of Kyushu Institute of industrial ceramics in Japan for specific data), The elbow made of it is worn out after more than a year of operation. In addition, the cast steel pipe is thick, very bulky, high carbon content and poor weldability. It needs on-site weld heat treatment, which brings considerable difficulties to on-site installation and maintenance.
3. Centrifugal casting of self propagating composite ceramic pipe this process adopts the method of self propagating centrifugal casting, which mainly uses the technology of chemical reaction of substances themselves, exothermic combustion to produce high temperature, and synthesizing new substances in the process of combustion wave propagation. The ceramic layer is replaced on the inner surface of the ceramic composite pipe formed by this method. Compared with carbon steel and manganese steel pipe, the wear resistance is improved to a certain extent. However, due to the low reaction temperature (no more than 1200 ℃ on average) and short reaction time, the reduced alumina still stays in the low temperature phase β- Al2O3 was not able to convert to high temperature phase α- Al2O3 (transition temperature over 1300 ℃).
It is the same alumina, but there are great differences in strength, hardness and density between high-temperature phase alumina and low-temperature phase alumina. Due to the short reaction time and the non centrifugal separation of low-temperature alumina and molten iron, the ceramic layer is not dense, the particles are loose and the hardness is low. The wear-resistant elbow is lined with 95 ceramics, and the alumina content is not less than 95%, and all of them are high-temperature phase α- Al2O3, sintering temperature up to 1670 ℃, ensuring material quality. From the actual anti-wear effect, the durability time of wear-resistant elbow is more than 5 times that of composite ceramic elbow. Moreover, the technology of centrifugal casting composite ceramic pipe determines that it is not suitable for making elbows and large and small heads. Under ordinary technical conditions, composite ceramic pipe can only be made into straight pipe shape. To make elbows or large and small heads, the straight pipe must be divided into several sections for welding. The inner wall of formed elbows and large and small heads is not a streamlined structure, which hinders material transportation and reduces equipment output. At the same time, the ceramic pipe produced by this process has many micro cracks, brittle and fragile, easy to fall off and fail locally, and can not be repaired after falling off. In addition, in terms of the bearing capacity of the hanger of the whole boiler, cast steel elbow and composite ceramic elbow win with weight and thickness. The wall thickness of the worn surface of some elbows is more than 40mm. From the perspective of unit design, it undoubtedly increases the weight of the hanger and shortens the service life.