What are the purification skills of precision casting parts?
In the process of investment precision casting, there are many kinds of residue in the liquid aluminum sucked out from the electrostatic precipitator, so it is required to purify before casting. In industrial production, purification methods such as clear, flux and vapor are mainly used, and some use fixed term solidification and overworry methods to carry out purification.
1. Flux purification Flux purification is the application of participating in liquid aluminum flux composition of a lot of thin liquid, so that the metal oxide in liquid aluminum is wet suction in favor of melting, forming a new liquid rise to the surface, after refrigeration composed of mud removal. The flux used for purification is composed of salt with low dissolution point, small relative density, small surface support force, large vitality, and strong absorption of air oxidation slag. When it is applied, a small piece of flux is first put into the cage, and then stabbed into the bottom of the mixing furnace for round-trip stirring. The alloy steel precision casting parts are removed from the cage after the flux is melted, and the termination is 5~10min. Dregs from the surface can be cast. According to requirements, the flux can also be withdrawn on the surface to cover the effect.
2. Vapor purification Gas purification is a main primary aluminum purification method, commonly used vapor is chlorine gas, nitrogen or chlorine nitrogen mixture.
(1) Chlorine gas purification. Previously, active vapor chlorine gas was used as a purifier (chlorination). In the chlorination process, when chlorine gas is introduced into liquid aluminum, a number of abnormally thin AlCl3 bubbles are formed, which are sufficiently mixed in the liquid aluminum. The hydrogen melted in the liquid aluminum and some of its alloy aluminum precision casting equipment are adsorbed on the AlCl3 bubble, and then discharged when the bubble rises to the surface of the liquid aluminum. When entering chlorine gas, it can also chlorinate some elements that are more negatively charged than aluminum, such as calcium, sodium, magnesium, etc. because of entering chlorine gas and producing corresponding chlorides, which are separated out. Therefore, chlorination is a very effective method for purifying primary aluminum. The amount of chlorine gas used is 500-700g per ton of aluminum. However, because O2 is harmful and precious, in order to avoid gas destruction and reduce the cost of waste aluminum production, it has been gradually used in the contemporary aluminum industry to replace the chlorine method with the rare gas - nitrogen purification method.
(2) Nitrogen purification method. Also known as continuous purification method without smoke, alumina ball (418mm) as the overworry substance. N2 immediately enters the liquid aluminum. Liquid aluminum is continuously sent into the purification furnace, through the alumina ball worry layer, and is washed by nitrogen, so the non-metallic material in liquid aluminum and its dissolved hydrogen are removed, and then continuously discharged, so that the slim nitrogen bubble is evenly distributed in the solved liquid aluminum with purification effect. Nitrogen has zero pollution to the air, and the purification yield is large, each minute can solve 200~600kg liquid aluminum, the loss of aluminum generated in the whole process of purification is relatively reduced, so it is now widely used. But it doesn't remove calcium, sodium and magnesium from liquid aluminum like chlorine does.
