In the casting production process, after the liquid metal is poured into the mold, shrinkage occurs due to cooling, and solidification results in shrinkage and shrinkage in the interior of the casting, resulting in waste products. In order to ensure a sound casting, there must be enough metal fluid to feed it. The most common method is to set up a riser. The conventional process uses an ordinary riser, ie, the same shape material is used for the riser and the mold. Since the solidification speed of the riser and the casting is the same at this time, despite the large geometry of the riser, the effective feeding volume is small. According to the data, only 6% to 10% of the total. The vast majority of metals in the riser is actually a kind of consumption. Especially for steel castings with large body shrinkage, the weight of the riser accounts for about 50% to 100% of the weight of the casting, that is, 1/3 to 1/2 of the molten steel is used for the riser. Although the riser metal can be remelted in the furnace, the cost of the casting is increased due to the large amount of manpower and material resources required to remove and melt this part of the metal from the casting. Therefore, how to minimize the size of the riser on the premise of ensuring the obtaining of dense castings has always been the goal pursued by foundry workers. There are many ways to improve the feeding efficiency of feeders. There are two general categories: First, methods to increase the pressure on feeders, including atmospheric pressure risers, compressed air risers, and pressure rise vents; and second, extend the riser. The method of solidification time includes a heat riser, a heat riser, and a composite heat riser. Among them, the most widely used is the insulation riser. China began researching insulated risers in the 1970s and now has more than 10 kinds of insulated riser products. The most typical insulation risers are expanded perlite products and composite fiber products. However, due to the low strength and damage of the expanded rare earth products, the workers are inconvenient to use, and the composite fiber products have complicated production processes and high costs, which limits their use. The author uses a new type of insulation material - microbeads to make insulated risers and achieve satisfactory results. 1 Insulation Riser Formulation and Production Process 1.1 Microbeads and their properties Microspheres are obtained from the flotation of ash from the thermal power plant through water flotation. It is a small, hollow, thermally stable, high-strength, smooth-surfaced spherical light. The particles are grayish in color, and the less impurities, the higher the degree of whiteness. The mineral composition of the microbeads is mainly composed of an amorphous silicate phase and a glassy phase of a microcrystalline structure and is intermixed with a small number of combinations of quartz, mullite, magnetite, and the like. The specific composition and performance are shown in Table 1 and Table 2. Table 1 Microbeads Chemical Composition Composition Percentage 20~40 Table 2 Physical Properties of Microbeads Particle Size m) Refractive Degree Thermal Conductivity (w/mk) 1.2 Insulation Riser Main Raw Materials Fire Resistant Aggregate. From the role of high-temperature skeleton, generally use SiO2 (purity of 98% or more), granular shape for the polygon, the particle size as small as possible, but consider the cost, suitable can be. Refractory clay. Establish the wet strength of the mixture to meet the modeling requirements, add people to take the lower limit. Hemp fiber. Increase the normal temperature strength, length 10mm ~ 20mm for the use of polyester resin, water glass and phosphate as a binder. should. 1.3 Insulated riser ratio binder. Establish dry strength at room temperature and high temperature strength, can be ratio of insulating riser (see Table 3) Table 3 Insulation riser Formula composition Microbeads Assist Insulation Material Refractory Agglomerate Hemp Fiber Refractory Clay Adhesive Water Containing appropriate m Dry blend 1~ 2 minutes wet mixing 5~7 minutes Binder water 1.4 Mixture mixing process Beads + auxiliary insulation material + refractory aggregate + fireclay + hemp fiber mixed 2~3 minutes Note: When mixing with sand grinder The height of the grinding wheel is adjusted to prevent the grinding of the insulation aggregate 1.5. 1.6 Drying Process After drying, it usually takes 12 hours to dry. Control the temperature of the drying kiln between 180lC~230t: kiln will be made into a heat-reducing riser and then be dried for 45 hours and then out of the kiln. 1.7 Insulated Riser Performance Indicators Insulated Riser Performance Indicators are shown in Table 4. Table 4 Insulated risers Key Features Capacity:! Refractoriness Thermal Conductivity Flexural Strength Remarked Porosity Line Retraction Shrinkage Residual Moisture 2 Insulation Riser Application in Production 2.1 Design Method for Insulating Riser The prerequisite for the action of feeder feeding is to maintain the molten steel in the riser later than the casting. Solidification and sufficient liquid steel to supplement the shrinkage of the casting. According to the theory and practice of solidification, the conditions for solidification of molten steel in a riser after casting are as follows: The above formula states: To ensure feeder feeding, the ratio of the heat capacity of the riser to the heat dissipation area must be greater than the ratio of the heat capacity of the casting and the heat dissipation area. . In practical applications, the general requirements, when, can guarantee the feeding effect of the feeder. The feeding principle of insulated risers is the same as that of ordinary risers, except that the thermal dissipation rate of insulated risers at high temperatures is lower than that of ordinary risers, which is equivalent to an increase in the thermal capacity of molten steel in risers and a reduction in the heat dissipation area of ​​risers. , thereby extending the solidification time of molten steel. That is equivalent to increase the modulus of the riser, thereby reducing the riser volume and saving molten steel. Usually there are three ways to calculate the insulation efficiency of insulation risers: the modulus of the MR insulation riser. Sand modulus of the riser. The solidification time of the QFP insulation riser The solidification time of the sand riser Aeat, the heat dissipation rate through the insulation riser, which is more commonly used in the increase coefficient method. For example, the volume of the fixed-pillar type sand-common riser is Vc. The volume of the casting part is cm3 Sc. The surface area of ​​the casting is cm2. , Respectively represent the module of the castings and risers, and order: if the same size of the insulated riser, shell IJ: product replacement coefficient) Y - the top surface of the riser correction factor (or apparent area of ​​the top surface of the riser replacement factor ) The amount of solidification time determines the X value is about 0.6 ~ 0.65. Such as the use of dark riser or compound insulation riser, Y can be determined to be 0.7. The riser Y take 2.2 insulation application principles of insulation Insulation riser shape: Insulating risers are generally cylindrical and waist two forms. In the actual application of the Shenyang Steel Mining Plant cast steel factory, the use of open risers is generally limited by the process equipment. Because the process parameters during the casting process are difficult to be constant, the insulation riser is reduced to about 0.8 times the diameter of the normal riser and the twist degree is not changed. Wall Thickness of Insulated Riser: The wall thickness of the insulated riser is an important factor affecting the feeding effect. Too thin to form difficult, and the insulation effect is poor; Too thick has little effect on the insulation effect, and increase the cost. The general wall thickness is 1096~15% of the diameter of the riser, and the thinnest is not less than 20mm. The root of the riser is kept warm: due to the relatively low refractoriness of the insulating riser, the contact surface with the molten metal is not smooth, and it is difficult to remove the riser. Use a method of keeping the height of the riser at the root of the riser. The height of the sand table is generally about 40mm. It is too low to clean up and it is too high to affect the insulation effect. For large risers with a diameter greater than 400mm, the insulation riser is burned more severely, and the internal hanging quartz sand method is used. The thickness is 10 insulation riser specifications: For the convenience of use and management, refer to the commonly used riser size of the cast steel branch. The following 7 specifications were designed (see Table 5). Table 5 Insulation Ties Common Specifications Unit Model Bottom Height Inner Diameter Bo Diameter Inner Diameter 1 Circle 2 Circle 3 Circle 4 Circle 1 Waist 2 Waist 2.3 Insulation Riser Effect Insulation Riser Applied to Shenyang Mining Machine Cast Steel Factory, all tested castings are qualified. At the same time, the molding process is simplified and the quality of castings is improved. Under the current management level, the average savings of molten steel is more than 10%, and the company obtains significant economic benefits. 2.4 Application of Compound Insulated Riser According to thermodynamics point of view, the heat transfer at the upper end of the riser is dominated by radiant heat transfer, which accounts for about 40% of the total heat dissipation of the riser. The heat transfer at the sidewall of the riser is dominated by conduction and heat loss. About 60%. In order to reduce heat loss at the top of the riser, dark risers should be used. If limited by the tooling, a composite insulated riser should be used, ie, an efficient covering agent should be used at the top of the open riser. At this time, the height of the riser riser can be reduced to 0.7 times that of the normal riser, further increasing the feeding efficiency. 2.5 Application of Insulating Board for Steel Ingots Insulating riser formulas are suitably adjusted to produce cast steel ingot insulation panels with good results. 3 Conclusions The insulation riser studied in this paper is characterized by high refractoriness, light weight, high strength, good heat insulation, and stable performance. The actual use of insulated risers should pay attention to: insulation riser should be standardized, serialization; should adopt insulation dark riser and composite insulation riser; insulation riser appropriate control of wall thickness, the root should be left sand table; for large diameter greater than 400mm Riser, high refractory sand should be hung inside. The insulation riser formula and technology studied in this paper save molten steel, improve the quality of castings, and enable enterprises to obtain considerable economic efficiency. Foot Measuring Gauge,Kids Foot Measuring Device,Shoe Measuring Devices,Toddler Foot Measuring Baby Yucheng Weisite Measuring Tools Co., Ltd , https://www.wsttools.com
Research on Insulated Riser for Cast Steel and Its Application