How to prevent castings pores?

August 25, 2020

Types of castings pores, causes of casting pores, and how to prevent castings pores.

Automatic sand molding machine manufacturers tell you the prevention of subcutaneous castings pores in the ductile iron part.

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I believe that the majority of business owners will generally encounter the problem of pores in the process of castings, and sometimes they are deeply affected by him. Then the automatic foundry manufacturer Delin Machinery will come to tell you how is going on.

In general, castings pores are divided into three types: surface, subcutaneous and internal stomata. The casting process, casting materials, pouring process operations, etc. may all be the causes of castings pores. Let’s analyze and analyze.

1. Defect analysis and solutions

According to the appearance of castings pores, we judged as subcutaneous stomata and divided into two types, one is subcutaneous stomata with shiny inside, and the other is slag stomata with black inside.

We know that the pores formed by the reaction between molten metal and molds (including sand, sand core, paint, cold iron), molten metal and slag, or certain elements and compounds in the molten metal are called reaction pores.

The pore-like pores are generally located under the surface of the casting, called pinholes or subcutaneous pores. When the ductile iron castings are molded with tidal sand, the gas generated in the pores is H2S, H2, magnesium vapor, etc. This is the reason for the formation of the first type of pores;

As for the second type of slag pores, we analyzed that it was caused by the oxidation of the molten metal. Based on the above analysis, we have conducted a comprehensive analysis of various processes such as smelting and pouring, core making, and treatment, and modeling, and formulated corresponding solutions for the problems found.

2. Melting and pouring process
(1) Reduce the amount of spheroidizing agent, reduce the amount of spheroidizing agent from 1.7% to 1.5% of the molten iron, and strictly control the Mg content, which must be kept at wMg<0.05%.
(2) Strictly dry the ladle and inoculation bag, and properly dry the spheroidizing agent and inoculant to ensure maximum drying.
(3) Use silicon barium inoculant to replace the currently used silicon strontium inoculant, and the addition amount remains unchanged.
(4) Increase the pouring temperature, and increase the pouring temperature from 1360-1370℃ to 1380-1390℃.
(5) Speed up the speed of tapping and unpacking, and minimize the possibility of molten iron being oxidized.

3. Core making process
(1) The sand core of this product only has a thermal core weighing about 4kg. We mainly detect the air volume of the thermal core and control it below 16mL/g. In addition, the gas evolution of the paint is also required to be controlled below 30mL/g, and efforts are made to reduce the gas evolution of the sand core.
(2) Drill vent holes at the position of the core head of the sand core, and control the depth of the vent hole to be about 1/2 of the length of the core head. At the same time, pay attention to check whether there is paint accumulation or blockage of vent holes in the sand core after dipping.

4. Sand treatment process
(1) In order to reduce the chemical reaction at the interface between the molten metal and the mold, we appropriately increased the pulverized coal content in the molding sand to ensure that the cavity is filled with reducing gas.
The basis for judging whether the reducing gas atmosphere is established is that the ignition loss of the molding sand should be greater than the water content of the molding sand.

(2) On the premise of ensuring that the effective bentonite content of the molding sand is about 7.5%, appropriately reduce the compaction rate of the molding sand to reduce the moisture of the molding sand, reduce the air content of the surface of the casting, and reduce the probability of subcutaneous pores. In addition, calculating the AFS of the used sand is 48-50, so we add 1% to 2% of the scrub sand with a particle size of 0.224 to 0.106mm (70/140 mesh) per mill to improve the particle size composition of the molding sand.

5. Modeling process
(1) Under the premise of ensuring that the sand mold horizontal surface hardness is greater than 90 and the vertical surface is greater than 85 (tested by B hardness tester), the compaction pressure of the upper box is reduced to further improve the exhaust efficiency.
(2) Strictly control the Baume degree of the paint between 37 and 39, and standardize the spraying operation method. It is necessary to spray in place without accumulating the paint to ensure the thickness of the paint layer.
For this modeling is relatively strict, our Guangzhou Zhuwang automatic modeling machine fully meets the needs of this aspect in terms of modeling, and the products have become better.

6. Implementation effect
After implementing the above measures, the subcutaneous pore defects of the castings were completely eliminated, and the product quality was guaranteed. Through this process improvement, we found that if there is a little deviation in each link in the production, it will lead to serious quality problems when combined.
This requires us to strictly control, operate carefully, and continuously improve the details in production in order to produce high-quality products.

With the development of society, machinery is to replace manpower. Delin Machinery is a professional manufacturer of fully automatic horizontal molding machines. We have been leading the industry and won more than 10 invention patents. It is more suitable for some customers and better. To solve their problems and more effectively cater to the needs of most foundries, helping them solve their immediate problems. At present, our company’s main automatic horizontal molding machine sandbox specifications are 700mmx600m, 600mmx550mm, 600x500mm, 520mmx420m, various specifications, and can also be customized according to customer needs.

You can click here: automatic sand molding machine to view more machine introduction, and maybe you are interested in machine working video: DL-3040 automatic sand molding machine working process video

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