Tin bronze produces water porosity defects in the formation of causes and solutions

Causes of water porosity defects

Melting process

Raw material factor: If the raw material used (e.g. copper, tin, etc.) contains high levels of gaseous impurities (e.g. hydrogen) or moisture, these gases will dissolve into the liquid alloy during the melting process. For example, wet metal lumps or metal materials containing oil will release moisture and gases during melting, thus increasing the gas content in the liquid alloy.

Melting Temperature and Time: High melting temperatures or long melting times may result in increased gas absorption into the liquid alloy. When the temperature rises, the solubility of the alloying liquid for gases increases, and prolonged melting causes the alloying liquid to be in contact with the furnace gases for a longer period of time, increasing the chances of gas dissolution.

Pouring process

Improper pouring method: If the pouring speed is too fast, the liquid alloy will produce turbulence in the cavity, which will make the gas in the alloy liquid to escape too late and be involved in the casting, forming gas holes. For example, direct pouring from a high place or pouring port design is not reasonable, resulting in the alloy liquid fall too large, are prone to turbulence.

Poor air permeability of casting: The air permeability of casting also has a great influence on the formation of porosity. If the casting material (such as sand) of the permeability is not good, the gas in the alloy liquid can not be discharged through the casting, will remain in the casting to form pores. In addition, if the casting contains too much water, when pouring, the water is heated into water vapor, will also enter the alloy liquid to form pores.

Solutions

Melting

Pre-treatment of raw materials: Before melting, the raw materials should be sufficiently dried and cleaned. For example, dry the metal blocks in a drying oven to remove surface moisture and oil and reduce gas sources.

Control the melting process parameters: Reasonably control the melting temperature and time. Avoid excessive temperature and time, generally according to the composition of tin bronze and melting equipment, select the appropriate temperature range, such as for common tin bronze melting temperature can be controlled between 1100 - 1200 ℃, and try to shorten the melting time. At the same time, a covering agent can be used to reduce the contact between the alloy liquid and the furnace gas to prevent gas absorption.

Pouring

Optimize pouring process: Adopt reasonable pouring speed and pouring method. For example, bottom injection type pouring is adopted to make the alloy liquid enter the cavity smoothly and avoid turbulence. And control the pouring speed, so that it can not only ensure the casting of the mold, but also let the gas have enough time to escape.

Improve the casting performance: improve the casting permeability. For sand casting, you can choose good air permeability of the sand, or add air permeability enhancer in the sand. At the same time, to ensure that the casting of dry, reduce the moisture content of the casting, such as in the casting before the pouring of the casting of adequate drying treatment.