How to solve the problem of shrinkage porosity and porosity of die castings?

Cause: Shrinkage occurs in the solidification process of die castings, and shrinkage porosity or shrinkage porosity is formed due to lack of compensation or insufficient compensation of molten metal.

Ways to eliminate:

Try 1. Reduce the die-casting temperature and reduce the shrinkage of the die-casting.

Try 2, increase the pressurization pressure, enhance the compaction effect, improve the compactness of the die casting, if necessary, vacuum die-casting can be considered (the negative pressure in the mold cavity and the vacuum state in the pressure chamber are also different, the former is limited by the sprue system).

Try 3, improve the sprue system, to prevent the inner intersection from premature solidification, is the pressure is better transmission, but the die casting is solidified or contracted under pressure.

Try 4, strengthen the cooling of the thickness of die castings and most ministries.

Try 5. Improve the structural design of castings.

Fulai die-casting machine Zhou Wei.

The cause of sand inclusion and sand hole phenomenon in castings.

It is that the sand in the sand mold is not clean, and there is residual grit. In the pouring process, it is caused by the molten iron washing the sand of the sprue wall.

Some manufacturers use paint to prevent it, and get a better effect, but there will still be sand inclusion and sand hole in castings. One is that it is more difficult and difficult to paint the gate. The second is that the pouring temperature is high and the erosion is large during the pouring process, and the paint is easy to fall off under the erosion and high temperature soaking.

Causes sand and holes. For a long time, many casting factories did not pay much attention to sprues. The scouring of the sprue wall during the pouring process is neglected.

As a result, the casting is sandhole.

How to solve the phenomenon of sand inclusion and sand hole in castings.

1. Improve the yield of castings, improve the quality of castings, and reduce the total cost of castings.

2. The use of casting gate ceramic pipe, this product is easy to use, with smooth circulation, resistant to molten iron, molten steel washing, no absorption of molten steel, good sawability, etc., can simplify the modeling process, save the difficult work of coating on the inside of the gate, and improve the layout of the gating system, to avoid casting sandwashing, sand hole, sand defects. It plays a great role in improving the quality of castings and the yield of castings, especially in various self-hardening casting molds, the characteristics are more prominent.

Shrinkage porosity and shrinkage porosity usually occur inside castings and are one of the common defects in the formation of aluminum alloy die castings. During dissection or flaw detection, it is found that the holes are irregular, not smooth, and the surface is dark and large and concentrated as shrinkage holes, and small and scattered as shrinkage porosity. Causes of porosity and porosity:

1. The casting cannot be supplemented from the separation of liquid aluminum in the solidification process and forms a hole 2, the pouring temperature is too high, the gradient distribution of the mold is unreasonable 3, the injection ratio is low, and the pressurization pressure is too low 4, the inner gate is thin, the area is too small, and the coagulation is premature, which is not conducive to pressure transmission and molten metal shrinkage 5, there is a hot joint part or cross-section change drastically on the casting structure 6, the amount of molten metal pouring is too small, the residual material is too thin, and the solution to shrinkage porosity and shrinkage porosity in aluminum castings cannot play a role in shrinkage: 1. Reduce the pouring temperature and reduce the shrinkage 2. Improve the specific pressure of injection and pressurization pressure, improve compactness 3, modify the inner gate, make the pressure better transmitted, and have the town of the clan to facilitate the liquid metal shrinkage effect 4, change the casting structure, eliminate the metal agglomeration part, the wall thickness is as uniform as possible 5, speed up the cooling of the thick part 6, thicken the cake, and increase the effect of coarse shrinkage.

Due to the heat absorption of the mold, the metal close to the surface of the cavity quickly drops to the solidification temperature, solidifies into a layer of shell, the temperature drops, the alloy solidifies layer by layer, the solidification layer thickens, and the remaining liquid inside, due to the liquid shrinkage and the solidification contraction of the supplementary solidification layer, the volume is reduced, the liquid level drops, and there are voids inside the casting until the interior is completely solidified, and a shrinkage porosity is formed in the upper part of the casting.

When the casting of the casting that has formed shrinkage porosity continues to cool to room temperature, the contour size of the casting is slightly reduced due to solid shrinkage.

Measures to prevent cratering and porosity:

1. Reasonable selection of casting alloy;

2. Coagulation is carried out in accordance with the principle of directional solidification;

3. Reasonably determine the position of the inner runner and the pouring process;

4. Reasonable application of process measures such as risers, cold iron and subsidies.

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Factors influencing porosity and porosity.

1. Metal properties.

The larger the liquid shrinkage coefficient and the shrinkage rate of liquid and solidification of the metal melt, the larger the volume of shrinkage porosity and shrinkage porosity. The larger the solid-state shrinkage coefficient of the metal, the smaller the volume of shrinkage porosity and shrinkage porosity, and the smaller the tendency of its formation.

2. Casting conditions.

The stronger the cooling capacity of the mold, the smaller the volume of shrinkage porosity and shrinkage porosity. Because the casting mold has a strong cooling ability, it is easy to cause the condition that pouring and solidification are carried out almost simultaneously, so that the metal shrinkage is filled by the post-injection molten metal to a large extent, and the amount of liquid metal that actually shrinks is reduced.

3. Pouring conditions.

The higher the pouring temperature, the greater the liquid shrinkage of the metal and the larger the volume of the shrinkage porosity. However, under the condition of having a riser, the high pouring temperature helps to increase the filling capacity of the riser and reduce the volume of the shrinkage porosity. The slower the pouring speed, the longer the pouring time, the smaller the shrinkage porosity.

4. Casting size.

The larger the wall thickness of the casting, the greater the tendency to form shrinkage porosity and shrinkage porosity. Because after the surface layer of the casting is solidified, the temperature of the molten metal inside the thick-walled casting is very high, and the amount of liquid shrinkage is very large, resulting in a large volume of shrinkage porosity and shrinkage porosity.

5. Replenishment pressure.

Applying the shrinkage pressure during the solidification process can effectively reduce the tendency of shrinkage porosity and shrinkage porosity.

Summary. Pro, you can dig out the metal in the defect area, weld the defect area with the same or compatible electrode as the base metal, and repair the flat after welding for post-weld heat treatment.

How to deal with shrinkage porosity in cast steel.

Pro, you can dig out the metal in the defect area, weld the defect area with the same or compatible electrode as the base metal, and repair the flat after welding for post-weld heat treatment.

Dear, when there are some cavities in the place where the cast steel is finally solidified, the large and concentrated holes are called shrinkage holes. Pure metals, alloys with near-eutectic composition are prone to shrinkage porosity. The basic reason for shrinkage porosity is that the sum of the liquid state and solidification shrinkage of the metal is much greater than the solid shrinkage during the solidification and cooling of the casting.

It must be explained that the porosity volume of the casting and the total harvest of the alloy (that is, the sum of liquid shrinkage, solidification shrinkage and solid shrinkage) are not the same concept, but the shrinkage of these three stages can have an impact on shrinkage porosity.

In order to study how to solve the problem of shrinkage porosity, we must understand two problems, first, the solidification characteristics of the alloy and the solidification shrinkage process. Taking cast iron as an example, its solidification characteristics solidify layer by layer, and its general shrinkage process is liquid shrinkage, solid-state shrinkage (coexistence with graphite expansion) and solid-state shrinkage. Second, the influencing factors that determine the shrinkage of cast iron are mainly three aspects; That is, the pouring temperature, the amount of graphite precipitation (chemical formation and method) and the shape stiffness wall movement.

Casting shrinkage porosity solution.

My casting is cast steel, and the shoe mold always has shrinkage holes where the shoe mold is poured?

Dear, I have found a solution for you, suggesting that you refer to 1, reduce the pouring temperature, reduce the amount of shrinkage 2, increase the injection specific pressure and pressurization pressure, improve the compactness 3, modify the inner gate, so that the pressure is better transmitted, which is conducive to the liquid metal shrinkage effect 4, change the casting structure, eliminate the metal agglomeration part, the wall thickness is as uniform as possible 5, accelerate the cooling of the thick part.

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.

Effectively control the disturbance process of the vertical smelting section of the molten plum, and use liquid alloy with good metallurgical properties.

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 grip, 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.

Causes of shrinkage porosity and shrinkage porosity of castings: After the formation of castings, due to the lack of liquid metal or alloy shrinkage in the final solidification area, the concentrated holes that appear in shrinkage are called shrinkage porosity, and the scattered and small pores are called shrinkage porosity. It is often dispersed in the axis area of the wall thickness of the casting, in thick parts, near the root of the riser and near the inner gate.

Measures to prevent cratering and porosity:

1. Reasonable selection of casting alloys, and if the use conditions permit, try to select the alloy components with narrow crystallization temperature.

2. Solidify according to the principle of directional solidification, and effectively control the melting process.

3. Reasonably determine the position of the inner runner and the pouring process;

4. Reasonably apply technological measures such as riser, cold iron and subsidy, and add heating agent and heat preservation agent to the pouring cup and riser.

5. Adopt a reasonable smelting process to reduce the gas and oxide in the metal, and improve its fluidity and shrinkage capacity.

The reason why the shrinkage porosity of the casting is easier to prevent than the shrinkage porosity is that the shrinkage porosity can be solidified sequentially, and the shrinkage porosity can be transferred to the riser by placing the riser, and finally the riser is cut off to obtain a dense casting. However, when shrinkage porosity occurs in castings, the replenishment channel of the riser is blocked due to the well-developed dendrites covering the entire cross-section, so it is impossible to eliminate the riser even if it is placed by sequential solidification.