Water glass precision casting process

　　Making wax models

　　1. The mold for pressing wax models should meet the requirements of the product drawings and be used after passing inspection.

　　2. Wax materials should be mixed according to the ratio of paraffin wax: stearic acid = 1:1. After melting, add wax shavings and mechanically stir into a paste, then add it to the wax pressing machine and inject wax into the mold.

　　3. The wax model must be kept under pressure and cooled in the mold before it can be demolded. Deformed wax models should be corrected promptly

　　and cooled in cold water. After complete cooling, remove burrs and trim.

　　4. After inspection and approval of the trimmed wax model, clean the surface oil before welding with the pouring sprue.

　　5. After welding the modules, clean the wax shavings inside and outside before sending them for shell coating.

　　Shell making

　　1. Material selection: The surface layer slurry uses 320-mesh zircon powder, and the strengthening layer slurry uses high-alumina powder or corundum powder and quartz powder above 200 mesh. The binder uses modulus 3.1~3.4, density 1.30~1.40 40# water glass.

　　2. Sand selection: The surface layer uses 80~100 mesh brown corundum, the second layer uses 40~70 mesh quartz sand, the third layer uses 20~40 mesh quartz sand, and the fourth layer and subsequent layers use 10~20 mesh quartz sand.

　　3. Slurry preparation: Surface layer and second layer: Dilute water glass with water to a density of

　　1.28~1.30, then add zircon powder at a ratio of 1:1.1~1.2 (adjust the ratio according to temperature changes), mechanically stir, then add 0.05% cleaning agent and 0.05% defoamer, continue stirring for at least 6 hours, let stand for 4 hours to mature, and then stir evenly before use. The third transition layer uses water glass with a density of 1.30~1.32, adding high-alumina powder and quartz powder at a ratio of 1:0.5:0.5. The strengthening layer is the same as the third layer, with a slightly thicker ratio.

　　4. Slurry viscosity determination: Use a 100ml flow cup to determine the viscosity. The surface layer, second layer, and third layer are 28~35 seconds, and the strengthening layer is 45~50 seconds.

　　5. Coating: Dip the inspected and approved modules into the evenly stirred slurry, move up and down twice, then lift them out, use a brush to pierce and brush the bubbles in the characters and dead corners, remove excess slurry, ensure the entire module is evenly coated without omissions or accumulation, then hang the sand. The entire coating process should not be too long to prevent surface hardening and inability to hang sand.

　　6. Sanding: The sanding action should be quick to avoid slurry dripping and accumulation. Sanding should be even and without blanks. The modules after sanding should be placed in a ventilated place to dry naturally before being put into ammonium chloride solution for hardening. From the third layer onwards, natural air drying and hardening can be omitted, and hardening can be directly put into ammonium chloride solution.

　　7. Hardening: The surface layer hardens for 15 minutes, the second and third layers harden for 15~20 minutes, and the strengthening layer hardens for 40~60 minutes.

　　8. Air drying: Operate according to the actual situation, following the principle of "not wet, not white".

　　9. When the modules are hardening, pay attention to venting and turning over to ensure that every part of the module is fully hardened.

　　10. Hardening agent preparation: Use industrial ammonium chloride with a purity of over 95% and water. The concentration of ammonium chloride solution is 22~28%, the PH value is no more than 7.5, and the temperature is 15~25℃. In winter, it should be above 10℃. When the hardening agent solution has been used for a long time and the concentration has decreased, ammonium chloride should be added in time to increase the concentration. When the PH value is greater than 7.5, concentrated hydrochloric acid should be added to adjust it.

　　Dewaxing

　　1. The coated modules can be dewaxed after standing for three to four hours.

　　2. After cleaning the debris at the gate of the module, put it into the dewaxing frame. When the dewaxing water temperature rises to

　　90℃, put the frame into the dewaxing kettle. Note that the dewaxing frame should be about 100mm away from the bottom of the tank. Then close the gas valve slightly, and keep the water temperature at 90~95℃ to prevent the water from boiling and rolling, bringing debris into the cavity. In order to supplement the hardening of the shell during dewaxing, an appropriate amount of ammonium chloride should be added to the water.

　　3. When the wax no longer floats upwards at the gate of the shell, lift the dewaxing frame out of the water, manually quickly pour out the water in the cavity, and then invert the shell and place it on a clean ground.

　　Firing

　　1. The dewaxed shell should be dried for 4~6 hours before being put into the kiln for firing.

　　2. When firing the shell, the gate should be facing downwards. First, bake at a low temperature, then increase the temperature. The temperature should be controlled at 800~850℃, and kept for 1~2 hours. Cool down to below 500℃ with the furnace before taking it out of the kiln and waiting for pouring. The shell has the highest strength at 400℃. Pay attention to observation and control during pouring.

　　3. During the handling of the shell, the gate should be facing downwards to prevent sand particles or other foreign objects from falling into the cavity, causing defects such as sand inclusion.