Several defects of quick-drying silica sol lost wax casting technology and their solutions

2020-04-17 10:46:10 1272


Disadvantage 1: important precautions for forging break holes are that alloy condensation and a large amount of oxygen and nitrogen in the atmosphere lead to the interruption of castings during alloying, and gas release during alloy condensation leads to the shrinkage of castings. Preparation for disposal: 1) Place a storage ball. 2. The diameter of the rough forging groove is roughly reduced by the length of the forging groove. 3) Reduce the amount of metal. 4) The following measures shall be taken to prevent the micro sag structure depression in the forged channel target. A. Place the cooling channel at the root of the forging channel. B. To prevent molten metal from directly impacting the die cavity, the forging channel should be twisted. C. Place the forging groove diagonally.






Disadvantage 2: Rough surface of casting and unpolished surface Disadvantage Rough and solidified metal on the cavity surface will respond to the cavity surface, which reflects the following situation. 1) The embedded particles after mixing are thick and not sharp. 2) After curing, the embedded materials will be baked directly in the oven, with too much moisture. 3) The baking and heating speed is too fast, and the uncommon parts are retained and separated, thus causing the internal surface of the cavity to fall off. 4) If the maximum firing temperature is too high, the firing time may be too long, thus making the inner surface of the mold blunt. 5) For forged rings, the solidification temperature of the metal may be too high, causing the metal to react to the mold cavity, and the casting surface is discarded and stuck to the embedded material. 6) Insufficient baking of crystallizer. When pouring metal, it will lead to the synthesis of embedded materials, more gas emission and hemp spots on the casting surface. 7) After forging the metal, the local temperature in the mold cavity is too high, and the surface of the casting is locally rough. A. Preparation for disposal: do not solidify too much metal. B. The calcination temperature of the mold shall not be too high. C. The calcination temperature of the mold should not be too short (the calcination temperature of the material embedded with phosphate is 800-900 ℃). D. Prevent the microstructure from deforming to the forging channel target. The liquid coated with wax can prevent it from being extinguished and adhering.






Disadvantage 3: Cracking of castings






There are two notices. One is that the casting defects (seams) often occur due to the rapid metal condensation there; The other is cracking due to low temperature.






1) For the casting joint with metal agglutination too fast, the casting time and agglutination time can be controlled to deal with the punishment. The relevant component of casting time: wax shape. The thickness of the casting. Casting pressure (casting machine). Air permeability of the embedded material. Coherent component of agglutination time: wax shape. The maximum baking temperature of casting ring. Type of embedded material. Type of metal. Temperature of casting.






2) Cracking due to low temperature is related to the mechanical properties of metal and embedded materials. The following scenes are easy to crack: high casting temperature is easy to crack; The embedding material with high strength is easy to crack; Nickel alloy and cobalt alloy with small ductility are easy to crack.






Solution:






Embedded materials with low strength; The casting temperature of falling metal as far as possible; Do not make the ductility small. Brittle alloy.






Disadvantage 4: bulging defect






The main assumption is that the residual air (bubble) after the mixing of the embedded material stays outside the wax form.






2) Radiate the surfactant outside the wax type before embedding (such as Castmate of Rijin)






3) First coat the embedding material on the wax mold.






4) Receive and receive pressurized embedded body style, and extrude bubbles.






5) The tendency of wax pattern is preferred during embedding, and there shall be no depression below the junction of wax pattern and casting path.






6) Prevent bubbles from mixing during embedding. Casting ring and casting seat. The buffer paper shall be sealed; The embedded material shall be poured along the inner wall of the casting ring (running the vibrator).






7) Do not vibrate after the casting ring is filled.






Defect 5: flash defect of casting






The main assumption is that the molten metal flows into the crack of the mold cavity due to the crack of the casting ring.






Solution:






1) Modify the embedding conditions: use the embedded materials with high strength. The strength of gypsum type embedded materials is lower than that of phosphate type embedded materials, so they should be used carefully. As far as possible to exercise the ring casting. When casting without ring, the ring is easy to crack, so it needs to be noted.






2) Baking conditions: Do not directly bake the embedded material after curing (it should be baked several hours later). The temperature shall be gradually increased. Cast the ring quickly after baking, and do not bake the ring repeatedly.


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