Study on Thermal Insulation Mechanism of Casting Technology for Rudder Arm Casting Steel Castings Zhang Huimin, Xie Jingpei, Wang Aiqin, Wang Wenbiao, Li Luoli (School of Materials Science and Engineering, Henan University of Science and Technology, Luoyang, Henan 471003, China). The results show that the high-temperature thermal conductivity of GLI-type covering agent is small, and the number of people is 0.1366W/(mK). After high-temperature sintering, the inside is lamellar, and the porous hole has good expansion and good thermal insulation performance.
And measuring 3 table 1 GLI type cover agent formula w (%) fly ash low carbon graphite expanded perlite aluminum silicon iron powder acidified graphite 41 23 ~ 30 circumferential edge every 120 with a vernier caliper to measure a thickness, and then take the average as The calculated thickness of the sample.
~157t, the wall thickness of the casting changes greatly, almost all the surfaces are curved, the shape is streamlined, and the dimensions of each section are different, which is easy to produce shrinkage during casting production. So the study of high-quality insulation materials and insulation mechanism, improve the riser feeding effect has important significance to improve the quality of castings. Production practice has shown that 55% of the total heat of the riser during solidification is lost by the top surface radiation of the riser. In this paper, the microstructure and physical properties of GLI-type covering agents were studied, and the thermal insulation mechanism was discussed.
1 Test method 1.1 Sample preparation GLI type covering agent, the color is grayish black, the main raw materials are low carbon graphite, acidified graphite, expanded perlite, aluminum silicon iron powder and fly ash.
The formulation and chemical composition are shown in Table 1 and Table 2. A round sample of about 20 mm. After drying, the sample and the high-aluminum lightweight pad are placed in a dry box and dried at 110~120C to a constant amount. In the sample collection date: 2006 fund project: Henan Province outstanding talents funded project number 4Y flat plate thermal conductivity heating furnace heated to 1200C insulation for 3h, measuring the thermocouple thermocouple halo value and the central calorimeter The amount of water flowing at the nozzle for 1 min was repeated twice and the thermal conductivity was calculated.
In the box-type electric furnace SX816 the covering agent are heated to 550C for 1h holding furnace cooled to room temperature, samples were taken at the surface thereof by vacuum deposition of platinum particles FC 1600 type sputtering apparatus, scanning electron microscopy with SM5610LV arranged thereon microscopic EDAX The hot surface temperature of the ti sample; t2 the cold surface temperature of the sample.
2 Analysis of test results and analysis of physical parameters of the thermal conductivity calculation formula: K constant calculated as 0.088; V center calorimeter water temperature millivolt value; the amount of water W 1min center calorimeter; S a - test the thickness of the sample; table 3 measurement results for the thermal conductivity of the coating agent, the average value of the thermal conductivity is measured: = 0.1366W / (mK). The thermal conductivity of the commonly used insulating material such as floating beads is 0. K). Fourier's law from heat transfer Q=A (AtF/ knows: Under the same conditions (ATF/S) is relatively stable, the smaller the thermal conductivity A is, the less heat dissipation. The thermal conductivity of GLI-type covering agent is lower at 1200 C. With good thermal insulation properties.
The measurement of the thermal conductivity of the coating agent is shown in Table 3. The number of hot surface temperatures of the factory C cold surface temperature factory C 1min water flow rate / g sample thickness / mm measurement voltage / mV U ten value / after cooling the sample thickness expansion is 45. 3mm, is More than twice the initial thickness, indicating that the expansion effect is better, the covering agent can be quickly deployed on the top surface of the riser, which can provide a good covering effect.
After high temperature sintering topography scanning electron microscope of the microstructure analysis 2.2.
Under 1550C, the covering agent is formed into a black hard block, and the internal porous hole not only reduces the heat dissipation speed, but also effectively reflects the radiant heat, thereby playing a double heat preservation effect. At 1200C, more black lumps with holes are formed, which is beneficial to the insulation of the insulation layer. The lamellar shape of the 1550 Cf covering agent is more obvious than that at 1 200 C. This is because after the high temperature reaction, the graphite can be expanded at a very high speed and fully expanded, and distributed in a lamellar shape, rapidly covering the molten steel to form a slag liquid layer.
Is a spectrum covering agent, of (a) can be seen, the rear cover 1550C by high temperature sintering agent composition of the matrix in line with the chemical composition listed in Table 2, in which the SiO2, Al2O3, Fe2O3 and CaO content is high. (B) is the spectrum of the circular large particles, showed mainly made of SiO2, (c) is the spectrum of circular small particles, mainly composed of SiO2 and Fe2O3. SiO2 acts as a high temperature resistant skeleton, and the presence of large and small particles forms a porous structure, which effectively serves as a heat preservation.
2.3 Mechanism of insulation riser top heat radiation plays a very important role in the quality of castings. The covering agent should make the top surface of the riser close to adiabatic, reduce the radiation and convective heat transfer, reduce the heat dissipation rate of the molten steel, and prolong the solidification time. Therefore, the covering agent must have three thermal effects of heat preservation, heat generation and expansion. GLI-type coating agent mainly formed of insulating material, heating the material, set of ink residue liquid material, with the molten steel chemical reaction heat is generated, and because a large number of low-carbon graphite contains SiO2, Al2O3, CaO and Fe2O3, and steel coating agent The liquid interface will generate liquid slag, and the flow of the slag will drive the covering agent to cover the top surface of the entire riser to form a protective layer with extremely poor thermal conductivity and low melting point, that is, a liquid slag layer, so that the covering agent few components immersed in the liquid steel. The second layer is the thermal insulation layer, and the slag liquid shape formed on the upper surface of the slag liquid layer is a low carbon stone hingm state multi-A hole, which prevents radiant heat loss and prevents convective heat loss. . The second layer is a heating layer, the GLI-type coating agent in the heat generating agent is sendust, coating agent enables rapid temperature increase, alleviate heat loss of the top of the riser.
2.4 industrial application CITIC Heavy Machinery Company in 2005 produced rudder horn 4 by mass of 80t or more, are used GLI-type coating agent. The surface of the rudder arm is smooth, and all of the ultrasonic flaw detection and magnetic particle inspection are qualified, meeting the technical requirements. The use of GLI-type covering agent reduces the size of the riser, and the process yield is increased by 3%.
3 Conclusion The thermal conductivity of GLI-type covering agent is 1200C/(mK) at 1200C, which is lower than the thermal conductivity of general thermal insulation material. The GLI-type covering agent is lamellar at high temperature and has a porous hole inside. It has good expansion. , thermal insulation performance is better.
The fly ash in the GLI type covering agent is industrial waste, which is used for the thermal insulation covering raw materials, which not only eliminates pollution, but also turns waste into treasure.
(Finish)
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