For the classification of rock features under complex geological conditions, the factors considered are not only the physical and mechanical properties such as the strength of the rock. Moreover, various factors such as rock structure type, fracture, joint, development degree of the fracture, characteristics of the filling, water content of the rock formation, etc., should be comprehensively considered. In order to make the project practical and simple, and easy to select the construction plan, the rock layers under complex geological conditions can be divided into four types:
A weakly expanding rheological rock mass is weak or soft and hard. Its solidity coefficient is generally f≤3 , and the structural surface is poorly bonded. It is mostly argillaceous shale , schist, phyllite, argillaceous slate, etc. When the rock mass is rich in clay minerals such as montmorillonite, illite, kaolin , chlorite, etc., the water will expand, and the roadway will exhibit obvious side bulging under the rock.
In this kind of rock, the roadway is dug, and it is generally necessary to carry out secondary support or multiple support.
B. The loosely fractured rock strata are developed by fractures and other geological failures or joint fissures. They are criss-crossed and criss-crossed. The rock mass is cut into pieces, and they are not cemented or poorly cemented. It is easy to form loose bodies after excavation. The self-stability of such rock formation is poor. No support, exposure is generally no more than 1~2.5m , exposure time is not more than 8~24h .
C water layer and flowing sand
When the fractured rock and glutenite contain water, their stability decreases sharply with the increase of water content. When the rock layer is rich in water, the glutenite layer can form flowing sand. In the construction of roadways in such rocks, it is generally necessary to carry out drainage or take special measures.
D. The roadway in the subsidence area has been in disrepair for a long time, or the ground pressure is very large, the roadway bracket is damaged, the roof is collapsed, and when the roadway passes through the loose broken belt, improper measures are taken, causing a large amount of collapse of the working surface, which will seriously affect the construction section. Special measures must be taken before they can pass safely.
Tungsten carbide roller has characteristics of good wear resistance, high temperature red hardness, thermal fatigue resistance and thermal conductivity and high strength , have been widely used in high-speed wire rod, bar, rebar, seamless steel tubes, etc. Domestic production of tungsten carbide roller materials mostly WC- Co, WC- Co- Ni- Cr two series, and the content of Co, Co- Ni - Cr is in the range of 6wt% ~ 30wt%. From the use of perspective, tungsten carbide rollers has good mechanical properties, its flexural strength up to 2200 MPa or more, shock toughness up (4 ~ 6) × 10^6 J/ m^2, Rockwell hardness (HRA) is up to 78 to 90, widely in the high-speed wire rod rolling process, which is much higher than single-slot chilled cast steel or high speed steel rolls.Tungsten carbide is made of Tungsten Carbide Powder and binder phase (such as drilling, nickel, etc.), and then pressing and sintering, regardless of the conditions under cold rolled or hot rolled has excellent wear resistance, tungsten carbide rollers has been widely used in pre-finishing mill and finishing of high-speed wire rod currently. On the performance of tungsten carbide roller in hot-rolling wire rod , the material must meet the following requirements:
1. Sufficient anti-fracture strength;
2. Good abrasion resistance;
3. The smooth surface finish;
4. Excellent corrosion resistance, thermal fatigue, thermal cracking performance.
Tungsten carbide roller rings can working in bad conditions , small profile rolling (especially rebar rolling) process conditions is harsher than the high-speed wire rod, and therefore corresponds to the profile rolling ,tungsten carbide rollers recommend using high binder phase carbide.
Tungsten carbide roller material design
Pre-finishing all vehicles roller should ensure its high toughness, strength, rigidity and thermal conductivity, followed before considering its wear resistance. When designing each vehicles roller, pre-finishing materials should choose carbide grades of Co, Co- Ni- Cr binder content is high (greater than or equal to 25wt%) , requiring an average WC grain size of coarse (5μm ~ 6μm), to obtain a higher shock toughness, proper strength and hardness. For the finishing of the roller movements, particularly the last two rollers of the finish rolling, which suffered load is small, and high relative velocity of the material to be pressed (80 m / min ~ 120 m / min). In this case, the wear resistance of the roller to be the most important requirements, and must ensure the strength , timpact toughness and hardness of a reasonable match, so the binder of Co / Ni content ratio and the average grain WC control of particle size and other factors must have greater control in front of different pre-finishing rolling roll.
Tungsten carbide roller category
According to the structure of tungsten carbide rollers, it can be divided into solid tungsten carbide roller and composite tungsten carbide roller. Solid tungsten carbide rollers have been widely used in pre-finishing and finishing stands high speed wire rod mill (including fixed reducing the rack, pinch roller rack). Composite tungsten carbide roller is made of cemented carbide and other materials, and it can be divided into tungsten carbide composite roll rings and solid tungsten carbide Composite Roller. Tungsten carbide composite roll rings mounted on the roller shaft; solid tungsten carbide composite roller will be directly cast in the roll axis to form a whole, a large load is applied to the rolling mill.
Tungsten carbide roller production process control
Tungsten carbide rollers produced by powder metallurgy method, the key to its process control is the chemical composition of the material and the mixture was prepared, pressed molding, sintering and deep processing and other preparation process parameters.
1. Preparation of starting material (WC focus quality): As the WC raw material and quality control of the use of different levels of quality may fluctuate, resulting in adverse effects on microstructure.
2. Preparation of the mixture: Mixture preparation is the key to the production process of the roller, the roller of failure modes - trachoma, mainly generated by this procedure.
3. Pressing: roller pressing is an important process of the roller mill.
4. Sintering: roller sintering is to determine the final quality of the roller production processes, use of advanced low-pressure sintering technology, HIP sintering technology can greatly improve the performance of roller.
5. Deep processing: deep processing rollers have a greater impact on the quality and accuracy of the roller surface.
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