How to avoid porosity in casting?

Measures to avoid porosity in casting are:

1. Control the gas content of molten metal, and when smelting metal, it is necessary to minimize the dissolution of gas elements into molten metal, which mainly depends on the raw materials used, reasonable smelting operation and suitable smelting equipment.

2. Reduce the gas generation of sand mold (core) during pouring.

3. Adopt certain measures to make the gas generated during pouring easy to be discharged from the sand mold. For example, to ensure that the sand mold has the necessary air permeability, more pores are pierced, thin-walled or hollow sand cores filled with coke in the middle, large planes are avoided in the horizontal pouring position, air outlets are set up, and the pouring temperature is appropriately increased and air entrainment is paid attention to.

4. Improve the resistance of gas into molten metal. For example, to ensure that the sprue has the required height and the rising speed of the molten metal in the mold, and to apply a coating on the surface of the sand core (mold) to reduce the porosity on the surface of the sand mold (core).

5. Ensure uniform heating during pouring. For example, the furan resin binder casting mold is very sensitive to the pouring temperature, less than 1350 degrees will not appear hot subcutaneous pores, and the different degrees of heating of each part of the cavity will also produce hot subcutaneous pores in the hot zone, so the gating system should disperse the molten metal into the cavity to make its thermal field uniform, shorten the flow distance of the molten metal filling, and prevent the local heating of the cavity from being too intense and decompose the furan resin.

Reduce the pouring temperature appropriately.

The sand mold should be dried.

Summary. That's for sure, water vapor appears at the edges, and as soon as you pour it, it is easy to form pores.

Hello. Hello.

Hello, hello, dear friend, I don't know what problem you are having right now, can you take a picture of the mold**?

Since I changed the burner of the burnt eggplant, the furnace body has not dried the surface, there is always water vapor, and the edge of the poured product is always teasing Zen, is it caused by the fact that the shell is not burned through? How to solve this problem.

That's for sure, water vapor appears at the edges, and as soon as you pour it, it is easy to form pores.

Then you can take it outside the oven and wait for a while for the water vapor to evaporate.

It would be a little better that way.

The main thing is that the exhaust is not smooth.

Then why is there no porosity after burning the shell and pouring it in water?

I poured water on the surface, and some of the water seeped into it.

When you pour at high temperatures, the water that seeps in and precipitates out to form pores. This is an invasive form of stomata.

You see, you can add some exhaust holes where there are air holes.

In this way, a part of the water vapor can be discharged when pouring, so that no bubbles will form on the casting.

Kiss, <>

We're glad to answer your questions! Aluminum casting avoids porosity caused by the abrasive cracking products being rolled into the molten metal. These pores are large and numerous, and are accompanied by carbon black.

The control measure is to improve the process, so that the liquid metal flows smoothly during the pouring process, without turbulence, and at the same time improves the pouring temperature and negative pressure and the air permeability of the coating layer. Extended Material 1. Porosity created by abrasive pyrolysis products being rolled into the molten metal.

This type of stomata is large and numerous, and it is old and clever, accompanied by carbon black. The prevention and control measures are to improve the process, so that the flow of molten metal in the pouring process is stable and does not produce turbulence, and at the same time improve the pouring temperature and negative pressure and the air permeability of the coating layer. 2。

Porosity caused by poor drying of the pattern and paint. The pattern is not dry, the water content is more, the coating is not dry or the pattern seam is poorly adhered to infiltrate the paint shall not be dry, and a large amount of gas will be produced during pouring, which is easy to form a backspray, and the answer is the most likely to produce pores in this case. The prevention and control measures are that the pattern is fully dried, the paint layer is poured in time after drying, and the pattern bonding must not leak the bonding phenomenon.

3。Porosity caused by too much pattern binder. There is too much binder, vaporization is slow, and the molten metal gets it into it to form pores.

The prevention and control measures are to choose a binder with low gas generation and fast gasification speed, and the less glue is used under the premise of ensuring firm bonding, the better. 4。Air is rolled in during pouring to form pores.

The prevention and control measures are to ensure the smooth flow of molten metal during the pouring process through the reasonable design of the gating system and not to entrap gas. Hope mine can help you! <>

Choose the right alloy composition.

If the use conditions permit, try to choose the alloy composition with a narrow crystallization temperature. For example, for gray cast iron and ductile iron, the chemical composition should be selected near the eutectic point to help reduce or eliminate the shrinkage porosity and shrinkage porosity of the casting.

The smelting process is effectively controlled, and liquid alloys with good metallurgical properties are adopted.

The stiffness of the mold varies according to the compactness rate of the shape and the different types of the mold, so the mold should be reasonably selected according to the technical requirements of the casting and the actual production situation, and if possible, the stiffness of the mold should be increased to improve the heat dissipation conditions of the mold.

Casting process: Reasonable casting process.

Rationally adopt the introduction position and pouring process of the gating system, comprehensively use the riser, cold iron and subsidy, and add heating agent and heat preservation agent to the pouring cup and riser.

Adopt a reasonable smelting process.

Reduce the gases and oxides in the metal, improve its fluidity and replenishment capacity. The casting mold is placed in the pressure tank, and the pouring hole is quickly closed after pouring, so that the casting solidifies under pressure, and the microscopic shrinkage is eliminated and the casting structure is reasonably improved.

Casting structure.

Reasonably improve the structure of the casting, strive for uniform wall thickness, reduce the hot joint or make the wall thickness change of the casting conducive to sequential solidification.

Summary. Causes of porosity in ductile iron castings:

1. The main influencing factor of subcutaneous pores is the moisture content of the molding sand: within a reasonable range of 3 5% (to ensure the wet performance of the molding sand), it should be controlled as low as possible.

2. The second main influencing factor is S content. The S in the molten iron and the MG in the nodularizing agent react to form MGS, which is reduced by the water in the molding sand to form H2S gas, and if the cooling rate of the casting is fast and it is not completely discharged, it will produce subcutaneous pores under the surface of the casting. Therefore, first, we should try to use ball pig iron with low sulfur content; Second, after spheroidization, the slag should be quickly scraped, and the slag should be cleaned to prevent sulfur return.

3. The third influencing factor is the rationality of the gating system: there are many ways to form pores, such as roll-in pores, immersion pores, etc. If the gating system is not reasonable, equal air will be involved in the pouring process, and due to the paste solidification method of ball milled cast iron, or if the wall of the casting is thin and solidified, it will be difficult to exhaust the air and cause subcutaneous pores.

Causes of porosity in ductile iron castings:

Causes of porosity in ductile iron castings: 1. The main influencing factor of subcutaneous porosity is the moisture content of the molding sand: within a reasonable range of 3 5% (to ensure the wet performance of the molding sand), it should be controlled as low as possible.

2. The second main influencing factor is S content. The S in the molten iron and the MG in the nodularizing agent react to form MGS, which is reduced by the water in the molding sand to form H2S gas, and if the cooling rate of the casting is fast and it is not completely discharged, it will produce subcutaneous pores under the surface of the casting. Therefore, first, we should try to use ball pig iron with low sulfur content; Second, after spheroidization, the slag should be quickly scraped, and the slag should be cleaned to prevent sulfur return.

3. The third influencing factor is the rationality of the gating system: there are many ways to form pores, such as roll-in pores, immersion pores, etc. If the gating system is not reasonable, equal air will be involved in the pouring process, and due to the paste solidification method of ball milled cast iron, or if the wall of the casting is thin and solidified, it will be difficult to exhaust the air and cause subcutaneous pores.

4. Aluminum content in nodularizing agent and pig iron: the dangerous residual aluminum content of wet ductile iron is there, and subcutaneous pores will occur at this time. The addition of the above aluminium to the pouring ladle (without affecting the metallographic structure) can eliminate the subcutaneous porosity of ductile iron castings.

5. Pouring temperature: The appropriate pouring temperature should be selected according to the main wall thickness of the casting, so that the gas in the body fluid can be discharged before the molten iron solidifies. If the wall thickness is less than 10, the pouring temperature should be controlled at 1380 1430;If the wall thickness is greater than 10, the temperature can be controlled at 1320 1380.

Specifically, it should be practiced according to the main wall thickness of your casting. 6. If the casting is a machined piece, some small subcutaneous pores are also allowed, which should be controlled within a reasonable processing range. Otherwise, to completely avoid subcutaneous stomata, strict multi-party measures are required, which may outweigh the costs in terms of cost; If the finished part is required for a cast surface, then it is necessary to make great efforts to avoid subcutaneous porosity.

1. Causes and influencing factors. First of all, the pyrolysis gas generated by the foam film during pouring cannot be discharged smoothly, and it enters the casting to cause porosity. The second is that the model and coating are not dried well or the model adhesive is too much, which causes the water evaporation of the model and coating during pouring, and the excessive gas volume of the adhesive and invades the casting.

Again, it is the air encapsulation during pouring, and if the sprue cannot be poured full, it will be involved.

gas, castings may produce porosity.

2. Preventive measures (1) Use low-density foam plastic film. Lost foam aluminum alloys are used with a density of grams of cubic centimeters. Cast steel and cast iron should be made with gram cubic centimeters.

2) The gas generation of the paint should be small and the air permeability should be high. (3) The pattern and coating should be dry. (4) The amount of adhesive should be small, and the amount of adhesive should be as small as possible.

5) Properly design the gating system. The sprue should not be involved in the gas, the pouring cup should have enough volume, and it should be in a full state during the pouring process, and the molten metal should be smoothly advanced after entering the casting model, replaced layer by layer, without turbulence. (6) The negative pressure should be appropriate.

If it is too small, the pyrolysis product of the model will not be eliminated smoothly, and if it is too large, the mold block will be wrapped in the molten metal, causing casting defects. (7) Master the correct pouring method Refer to the casting network.