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Main measures to prevent shrinkage and shrinkage

UpdateTime  2018-07-09 15:23:11 Foshan jitian casting material co. LTD. Read

Main measures to prevent shrinkage and shrinkage

Solidification using the riser and cold iron

The use of sequential solidification is an effective method to prevent the formation of shrinkage cavities in castings. Sequential solidification refers to the process in which a casting gradually solidifies from one part to another in a prescribed direction.

In the figure, the part I, then the part II and the part III are successively solidified, and finally the riser itself solidifies. Thus, the volume reduction caused by the solidification of the solidified portion I of the casting is supplemented by the liquid metal or alloy of the portion II; the solidification shrinkage of the portion II is supplemented by the liquid metal or alloy of the portion III; and the solidification shrinkage of the final portion III is caused by the liquid metal in the riser. Or alloy to replenish, transfer the shrinkage hole to the riser, remove the riser to obtain a dense casting.

The riser refers to a cavity in the mold for storing the molten metal for casting, and also refers to the metal filled in the cavity.

The position, size and shape of the riser should be such that it will eventually solidify in the mold and, therefore, is generally placed at the highest or thickest part of the casting. Riser is usually divided into two types: the bright riser and the dark riser.

The riser mouth refers to the top riser or the side riser which penetrates the upper type in the height direction. It acts as a venting and collecting slag while supporting the shrinkage, and can also provide whether the molten metal is filled with the cavity. Information; dark riser means that the top of the mold does not extend in the height direction, and all the risers are covered by the sand with the top riser or the side riser. The dark riser dissipates slowly, and the feeding efficiency is higher than that of the same volume.

In addition to the measures to install the riser, there are other auxiliary measures such as placing cold iron, such as placing cold iron. From the animation 2-1-33, it can be seen that the thick part of the casting that is prone to shrinkage is more than one hot knot. It is difficult to ensure that there is no shrinkage hole in the thick part of the bottom only by the top feeder. Therefore, cold iron is placed there to achieve top-down sequential solidification. Cold iron is made of steel, cast iron or copper. Therefore, determining the position at which the casting produces shrinkage or shrinkage is the basis for rationally placing the riser and setting the cold iron. It is usually judged by the "solidification isotherm method" and "inscribed method" as shown in Fig. 2-1-39; the area where the isotherm does not pass or the maximum diameter of the inscribed circle is the hot section.

The cause of shrinkage and the method of prevention:

cause:

1. Poor feeder shrinkage

2. The charge contains too much gas

3. Overheating near the gate

4. Sand type is too much moisture, sand core is not dried

5. Coarse grain of alloy

6. Improper position of the casting in the mold

7. Pouring temperature is too high, casting speed is too fast

Prevention method:

1. Replenishing molten metal from the riser and improving the riser design

2. The charge should be clean and free of corrosion

3. Set the riser at the shrinkage of the casting, and place the cold iron or cold iron with the riser.

4. Control sand moisture, and sand core drying

5. Take measures to refine the grain

6. Improve the position of the casting in the mold to reduce the pouring temperature and casting speed

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