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Summary of common casting problems caused by pouring

Views: 223 Update date: Aug 03,2021

1. Common problems of pouring machine

1. Don't understand what is the best pouring? This leads to incorrect evaluation and selection of pouring equipment.

2. Using a vertical parting boxless molding line, but wrongly choose a pouring machine that needs to stop production or low efficiency to replenish molten iron.

3. The vertical parting molding line is used, but the horizontal parting molding line pouring machine is wrongly selected.

4. The non-heated pouring machine is used for pouring gray iron on the horizontal parting and box molding line. This is definitely not an ideal choice, especially when it is used for the production of large and complex parts (such as engine block and cylinder head castings). a mistake.

5. It is wrongly believed that the horizontal moulding line pouring machine must have the function of chasing the bag in order to be able to produce normally.

6. In the high-speed molding line, it is mistaken that manual pouring is more economical than automatic pouring machine.

7. In the production of ductile iron, a non- ductile iron casting machine is wrongly selected.

8. There are a lot of over-pouring and under-pouring, and sometimes over-pouring may even cause damage to the molding line.

9. Confusing the difference between mechanized pouring machine, predictive semi-automatic pouring machine and fully automatic pouring machine.

10. Jetting occurs during pouring, and a large amount of molten iron splashes.

11. There are many waste products with slag holes and stomata, and sand washing is serious.

12. The yield of castings is low.

13. The inoculation effect is not good, and the quality of castings is not high.

14. The temperature loss of the casting machine is too large, and the temperature drop is very large, often reaching 5~8℃/min.

15. The life of the casting machine lining is too low.

16. Too much oxidized slag from the pouring machine makes it difficult to remove.

2. What is the best pouring, are you pouring it right?

Before discussing the pouring machine in depth, we must first discuss what is the best pouring? Many people believe that the best pouring is to accurately pour molten iron into the mold within the specified time. Some people think that the best pouring must be perfect, and there is no pouring defect or waste pouring at all. In fact, neither of these two opinions is correct. We believe that the best pouring refers to people or pouring equipment accurately pouring molten iron into the pouring cup, and keeping the pouring cup full during the pouring process until the end of the pouring. Pouring process.

This is because we believe that keeping the sprue cup full is the best state that can be achieved by pouring. If the molten iron cannot flow into the mold in time due to poor pouring system design, the pouring cannot be completed within the specified time; if the pouring system design is too large, the molten iron cannot fill the pouring cup, causing oxide slag, sand, and gas to enter the mold directly , Cause sand washing, slag inclusion, and pore defects; if the pouring system design problem or the molding sand has poor air permeability, it will cause splashing, etc.; all of this has nothing to do with pouring.

3. Take the horizontal parting box molding line as an example to illustrate how to choose a pouring machine

Horizontal parting and box molding lines are generally divided into domestic simple mechanized molding lines or imported automatic molding lines. The biggest feature of the domestic simple mechanized moulding line is that the moulding speed is generally slow, with dozens of moulds per hour, and the size of the sand box is not too large. This kind of molding line generally adopts manual pouring or mechanized pouring machine (such as teapot pouring machine or fan pouring machine) to meet the needs, and we will not discuss it here. The most important feature of imported automatic moulding lines or some domestically-made air punching lines is: the speed of the moulding line is high, the mechanism is extremely complex, and there are many auxiliary machines. The task of core setting is often heavy. The moulding line is often shut down for a short time due to various reasons. This situation is more complicated, let's briefly analyze it according to different situations:

For the horizontal parting box molding line, some engineers think that the bottom pouring machine cannot be used, and the large teapot pouring machine must be used. For example, a well-known domestic diesel engine factory produces large-scale mass-produced single gray iron castings such as engine blocks and cylinder heads. They spent nearly 10 million to introduce large teapot pouring machines for pouring. But in fact, in other countries in the world, this is the standard most suitable application for air pressure insulation pouring furnace. As we all know, this kind of large-scale molding line is often composed of many main engines and auxiliary machines, and often has heavy core-setting tasks, and often stops production for various reasons. Using a non-heating pouring machine, even if we do not consider the impact of the reliability of the pouring machine for the time being, the temperature loss of the molten iron in the pouring machine is very large. Once the molding line is stopped for a short time due to various reasons, the casting machine is often caused by the molten iron in the ladle. The temperature is too low to be poured, and the molten iron must be sent back to the electric furnace to heat up. This not only affects the productivity of the pouring machine and the molding line, but also affects the normal production of the electric furnace. Moreover, once the molding line resumes production, the pouring machine may need to be scalded and preheated before it can be used, which greatly affects productivity.

Therefore, for the production of gray iron on a horizontally divided box molding line, it is most suitable to use a heated and heat-preserving pouring furnace. And some foreign foundries, even after using a heat-preserving pouring furnace, directly abolished the holding furnace and changed the production process to a smelting road-heat preservation The process of dual pouring furnace greatly reduces the operating cost and improves the production efficiency of the molding line.

The situation of producing ductile iron on the horizontal parting box moulding line is different. Because ductile iron slag is extremely large, it is very difficult to remove it in the heat preservation pouring furnace. Even if nitrogen protection and other measures are adopted, there will still be a lot of oxidized slag. Affect the use of pouring furnace. In this case, instead, we recommend using an appropriate size non-heating heat preservation ladle. This is because ductile iron is declining due to spheroidization, and generally requires 8 to 10 minutes to replenish the molten iron. If the molten iron cannot be replenished, the molten iron must be returned to the furnace. Therefore, the defects of non-heated ladle are not so obvious here. 

However, in European and American foundries, if complex ductile iron parts are produced, casting furnaces with heating and heat preservation are still often used. This is because they believe that the heated pouring furnace can keep the temperature constant and keep the molten iron pure, which is vital to the production of high-quality castings, even if the heavy slag removal work is worthwhile.

4. Comparison of coreless air pressure pouring furnace and core air pressure pouring furnace

At present, pouring furnaces with heating and heat preservation are divided into core pouring furnaces and coreless pouring furnaces. The common characteristics of the thermal insulation pouring furnace are: the temperature is constant, the pouring temperature can be accurately controlled, which is very beneficial to the improvement of the quality of the casting; secondly, due to the air pressure and siphon principle, most of the oxide slag in the molten iron floats on the surface of the molten iron before pouring. Therefore, the molten iron is relatively pure, and the quality of the molten iron is better; in addition, the capacity of the heat preservation pouring furnace is often large, which has a huge buffer for the production process, and can even replace the heat preservation furnace. And due to the use of nitrogen protection, the spheroidization has a longer time to decline.

The main advantages of the cored pouring furnace are: energy saving, good insulation effect, long lining life, sometimes up to two years, large capacity, strong buffering capacity, if nitrogen protection is used, the spheroidization decline time can be prolonged and so on. The disadvantage is that it must be powered for 24 hours and cannot be cut off. Therefore, it is often required to be equipped with an emergency generator. The molten iron cannot be emptied during production and it is difficult to change the grade of the molten iron.

In response to the shortcomings of cored casting furnaces, coreless casting furnaces have been developed in recent years. In addition to the general advantages of a heat-preserving casting furnace, the coreless pouring furnace can also be powered off and the furnace can be emptied, and the molten iron grade can be easily changed. This completely overcomes the main shortcomings of the cored pouring furnace, which seems very ideal. However, it also brings new shortcomings: more residual molten iron is required, spheroidization is required when producing ductile iron, and the life of the furnace lining is much shorter than that of the cored casting furnace, and the energy consumption is also relatively high.

Prev: Want to improve the performance of ductile iron? Choosing the spheroidization method is the key! Next: Experimental verification of 3 smelting and pouring schemes for ductile iron


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