The key to spring cabbage cultivation is to prevent vernalization bolting, and to mention the morning market. After years of exploration, the vegetable farmers in this area have basically grasped the growth pattern of spring cabbage, and generally they can grow successfully and obtain high yields. The key measures are as follows:
1, choose the appropriate variety. Generally can choose to use Japanese spring general, South Korea strong, Chunhui and other varieties, these varieties are strong in winter, the growth period is short, resistant to bolting, high ball uniformity, disease resistance, and concentrated harvest, suitable for spring cultivation.
2, sowing early. Because of the cultivation in the greenhouse, the temperature in the greenhouse is relatively high, so it can be sowed early, so that it can be sown in the middle and early March, and early in the middle of February. Early sowing can cause early bolting, too late sowing, and harvesting. The high temperature in the shelter can cause soft rot and other rotten vegetables, affecting the quality of listing.
3, improve the method of raising seedlings. The use of small sheds in the pipe shed to cover the heat preservation seedlings and raise the seedbed temperature. Seeds are sown directly in plastic nutrients or clods. Before sowing, the nutritious bauxite should be filled with water, each seed should be sown. After sowing, a thin layer of nutritious soil cover is used to cover the seed without mulch film, and the small ring shed film is heat-insulated, and the electric heating line is laid under the ramie. Electricity, increase the temperature, promote seedlings. During the seedling management, attention should be paid to improving the ground temperature and temperature of the seedbed to maintain it at a temperature of 10°C or higher, preventing vernalization, and 25 to 28 days for seedlings.
4, early colonization. Planted in tube sheds in mid-March. Planting sheds to apply basic fertilizers, usually 250,000 to 3,000 kilograms of organic fertilizer applied in Mushi, 50 kilograms of fertilizer for vegetables, or 350 to 400 kilograms of organic fertilizer for Mushi basal fertilization, full plough layer fertilization, 6 metre wide standard shed for 3 畦Each row is planted with 4 rows, spacing 30-35 cm, and covered with plastic film. When planting, Chinese cabbage seedlings have three leaves and one heart. After planting, take a small ring to cover the film. When the temperature is low, cover the non-woven at night when the temperature is low. Cloth insulation.
5, field management. In addition to strengthening insulation after planting, focus on good management of fertilizer and water, small greenhouse film can cover about 20 days after the cover can be removed, after planting live trees top dressing 1, with 0.5% urea water pouring root, before the application of heavy fertilizer 1 Times, the general point of urea 15 kilograms of urea, with a knife Chen into the root, then water soluble fertilizer. In the shed, due to the lack of rainwater, water should be taken care of. During the ball stage, the soil should be kept moist and there should be no shortage of water. Watering should be stopped 7-10 days before harvest. It was found that the locusts and green worms should be treated with drugs in time.
6, timely harvest. Spring cabbage early maturing varieties can generally be harvested in mid-to-late April. Generally, harvesting is completed at the beginning of May, and the harvesting period is relatively concentrated. At this time, Chinese cabbage is in short supply. The market is relatively easy to sell, and the average yield per mu can be achieved. 3000-4000 kg.
February 5, 2006
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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