Green sand determines the casting quality of vertical molding lines(2)

3 Production application
3.1 Sand mixing process
Sand mixing process should be done firstly to mix sand, bentonite, water and additional materials evenly; in kneading various materials to make the clay film evenly wrapped around the sand particles. The order of adding materials is generally the first dry materials mixed, and then add water wet mix. But after observation, the sand after loose sand is always some like small rice size hard sand mass wrapped in the sand, its composition is actually bentonite and sand sinter and clay ball, the sand mass open when it meets water. Therefore, the sand mixing process is recommended to be changed to add sand and then add water to wet mix and dissolve the sticky sand mass, and then add other powders. Old sand + new sand + water (preferably atomized water); wet mix 15s, add bentonite + coal powder + additives, mix 120 ~ 150s. sand mixing time is not too long, otherwise the sand heat reduced fluidity, strength is affected.
3.2 Molding
Before molding should be preheated template (especially in the cold winter season), so that its temperature is higher than the sand 5 ℃ is appropriate, when the mold does not stick, the surface is not dry, the surface of the mold is bright and clean.
3.3 Sand inspection
First, strict incoming inspection of raw materials (including raw sand, bentonite, coal dust, etc.); second, strengthen the online detection of sand, regular testing of sand performance, timely detection of problems and timely resolution.
3.4 Judgment of good and bad sand
Some companies believe that "the value of wet compression strength" instead of "effective bentonite value" to determine the amount of bentonite added to the sand mixer, this view is not valid. Simply put, both the bentonite and the dead clay in the sand produce wet compressive strength, and increasing the amount of dead clay increases the value of wet compressive strength while the compactness remains the same, so the wet compressive strength is misleading. The results of other properties and the effective clay and clay content are also considered when considering the wet compressive strength. The "effective clay content test" is the only method that can determine the bentonite content of a sand. Under the premise of ensuring the effective clay content, the sand mixing site should focus on controlling the compact rate of the sand, so that the proportion of bentonite and moisture in the sand is moderate, giving full play to the bonding effect of bentonite, avoiding the phenomenon of free water due to excessive moisture in the sand.
3.5 Pouring
It should be fast, high temperature, continuous pouring, fast filling; otherwise, it is easy to produce cascading, sand rushing, the formation of water migration (commonly known as cannon), resulting in sand damage, casting scrap.

4 Main defects analysis and countermeasures
4.1 Trachoma
Trachoma is caused by sand particles falling out of the pouring system or type or by scattered sand particles falling out of the wall due to the scouring of the iron liquid. If the sand mixing position is far away from the molding line, the wet sand type in the belt conveying process, the sand surface dehydration strength drops sharply, the northern weather dry season "wind dry" phenomenon is more serious, should draw attention and attention. In addition, if the old sand is used repeatedly, the ash and mud content in the sand is too high, which will lead to low toughness and brittleness of the sand, poor mold performance, so that the corners and edges of the sand broken, causing trachoma defects.
Measures to prevent trachoma
4.11 Use high-quality bentonite, according to the season (dry, wet, etc.) changes, reasonable control of sand moisture, improve the strength of the sand.
4.12 Mediate the old sand dust removal equipment, control the mud content of the old sand to less than 12%, and increase the compactness of the sand at the molding to 34%-38% and the water content to 3.2%-3.8%, so that the ratio of compactness to water content is within the range of 10-12.
4.13 Add a small amount of starch to the sand to improve the toughness of the sand, reduce the frictional resistance of the starting mold and enhance the surface air-drying strength.
4.14 Adjust the core sand content in the old sand in time, and extend the mixing time appropriately.
4.2 Sticky sand
Sticky sand is a surface defect caused by the penetration of iron into the casting mold.
The countermeasures taken are
4.21 Adopt raw sand with fine particle size and moderate distribution, improve the fluidity and compactness of the mould sand (mould hardness is controlled at about 90), and reduce the voids on the surface of the mould.
4.22 Use high efficiency and high quality pulverized coal, control the effective pulverized coal content in the sand, i.e. volatile matter, reduce the oxidation of the surface of the iron liquid and the wetting and penetration of the surface of the sand.
4.23 Appropriately reduce the pouring temperature and reduce the pressure of ferrofluid.
4.3 Porosity of ductile iron parts
Porosity prevention.
4.31 Improving the air permeability of the type sand.
4.32 Control the amount of coal dust added to the molding sand and the content of moisture and core sand to reduce the amount of air emission from the molding sand.
4.33 Reasonable arrangement of exhaust slots on the template to facilitate the outward escape of gas from the casting mold.
4.34 Appropriately increase the pouring temperature (1380℃) and speed, and sprinkle cryolite powder on the liquid surface of the pouring ladle.

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