Five Major Defects In Mold Casting
1.Casting shrinkage hole
The main reason is that the alloy solidification shrinkage produces casting shrinkage cavities and the alloy absorbs a large amount of oxygen, nitrogen, etc. in the air. When the alloy solidifies, gas is released to cause casting shrinkage.
(1) Place the gold ball.
(2) Thicken the diameter of the casting track or shorten the length of the casting path.
(3) Increase the amount of metal used.
(4) The following method is used to prevent the formation of depressions in the direction of the casting path.
1) Place a cooling channel at the root of the casting path.
2) In order to prevent the molten metal from vertically impacting the cavity, the casting path should be curved.
3) Place the casting path diagonally.
2. The surface of the casting is rough and not clean
The rough surface of the cavity and the molten metal reacted with the surface of the cavity, mainly reflecting the following conditions.
(1) The embedded material particles are coarse and not delicate after stirring.
(2) After the embedded material is solidified, it is directly placed in a Maofu furnace for roasting, and the water is excessive.
(3) The heating rate of the baking is too fast, and the difference in expansion occurs in different positions in the cavity, so that the inner surface of the cavity is peeled off.
(4) The maximum temperature of the baking is too high or the baking time is too long, so that the inner surface of the cavity is too dry.
(5) The melting temperature of the metal or the calcination temperature of the casting ring is too high, causing the metal to react with the cavity, and the surface of the casting is burned with the embedding material.
(6) The calcination of the mold is insufficient, and when the molten metal is cast, the decomposition of the embedding material is caused, and a large amount of gas is generated to cause pitting on the surface of the casting.
(7) After the molten metal is cast, the local temperature in the cavity is too high, and the surface of the casting is locally rough.
(1) Do not excessively melt the metal.
(2) The baking temperature of the mold should not be too high.
(3) The calcination temperature of the mold should not be too low (the calcination temperature of the phosphate embedding material is 800 to 900 degrees).
(4) Avoid the phenomenon that the structure is concave toward the direction of the casting path.
(5) Apply a liquid to prevent sticking on the wax type.
3. Cracks in castings
There are two main reasons. First, the metal is usually solidified too quickly, causing casting defects (seam); the second is cracking due to high temperature.
(1) For the metal to solidify too quickly, the resulting cast seam can be solved by controlling the casting time and solidification time.
Relevant factors of casting time:
1) The shape of the wax type.
2) The amount of thickness cast.
3) Casting pressure (casting machine).
4) The permeability of the embedded material.
Related factors of solidification time:
1) The shape of the wax type.
2) The highest firing temperature of the cast ring.
3) Type of embedding material.
4) Type of metal.
5) The temperature of the casting.
(2) Cracks due to high temperatures are related to the mechanical properties of metals and embedded materials.
Cracks are easy to occur in the following cases:
1) High casting temperature is prone to cracking;
2) The embedded material with high strength is prone to cracking;
3) Nickel alloys and cobalt alloys with small elongation are prone to cracking.
1) using a low-strength embedding material;
2) Minimize the casting temperature of the metal;
3) Do not use alloys that are less ductile and brittle.
4. Spherical protrusion defects
Mainly caused by the air (bubbles) remaining after the embedding material is mixed and stayed on the surface of the wax type.
(1) The real air conditioner and the embedding material are better after being vacuum-embedded.
(2) Spraying a surfactant on the surface of the wax type before embedding (for example, a castmate of Nisshin Co., Ltd.).
(3) First apply the embedding material to the wax type.
(4) The bubble is extruded by a method of pressure embedding.
(5) Pay attention to the direction of the wax type when embedding, and do not have any depression below the joint between the wax type and the casting path.
(6) Prevent the air bubbles from being mixed in the embedding, and the casting ring and the casting seat and the buffer paper should be closely adhered; the embedding material should be poured along the inner wall of the casting ring (using the vibration machine).
(7) Do not oscillate after filling the casting ring.
5. The flash edge defect of the casting
Mainly due to the cracking of the casting ring, the molten metal flows into the crack of the cavity.
(1) Changing the embedding conditions: using a higher strength embedding material. Gypsum-based embedding materials have lower strength than phosphate-based embedding materials, so care should be taken when using them. Try to use a circle casting. When the ring is not cast, the casting ring is prone to cracking, so it is necessary to note.
(2) Conditions for calcination: Do not directly calcine after the embedding material is solidified (should be calcined after several hours). It should be slowly warmed up. Cast immediately after roasting, do not repeat the roasting of the cast ring.
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