The our country multitudinous small and medium plate production plant is still widely used aluminum melting, refining, horizontal continuous casting, cutting, heating, hot rolling, rough, and rolling, annealing process. Fang said this is due to the horizontal continuous casting method has the advantages of continuous operation ingot length is not limited, production efficiency is high, easy operation and equipment and infrastructure investment small. However, Fang aluminum forgings found: defect of the factory in the production process of hot rolling billet surface "bubble" and the cost surface "black pockmark", "skin" and horizontal continuous casting method. Therefore, around the "bubble" and "black pockmark" cause of formation are analyzed and discussed, and put forward prevention measures to put forward their views.

1.1 "bubble" phenomenon

Aluminum forgings, Fang said that appear "bubble" general rule: occasionally appear in bulk in hot rolled billet surface, "bubble" is "bulge" form; number, size; often appear in the blank of a large surface.

1.2 cause analysis

In order to observe the analysis shows that the fundamental reason is because of the tundish, installed on the mould structure is reasonable and it is not conducive to the aluminum melt solidification when the precipitation of gas discharge, stranded in the ingot on the side near the surface caused by. The structure of horizontal continuous casting mold in the field is shown as figure 1. Since the crystallization process is not conducive to the discharge of gas.

Aluminum melt is easy to absorb hydrogen, and with the change of temperature and state, the balance of hydrogen absorption amount varies greatly, the high temperature of an electrolytic aluminum liquid at 950, the equilibrium hydrogen absorption capacity is 2. 9ml/100gAL, 750, 1. 2ml/100g/AL. The melting point of 660 DEG C in liquid aluminum hydrogen absorption capacity balance 0.69ml / 100 gAL, and the temperature of solid aluminum after crystallization is 0. 036mL / 100 gAL, that is, the difference between the two 20 times. Aluminum forgings, Fang said that this shows that continuous casting of aluminum melt in the vicinity of the solidification interface will appear in the hydrogen enriched, its partial pressure increased, enough to nucleation forming "bubble". At this time, due to the asbestos barrier, the "bubble" can not escape through the middle of the body and the body can only remain on the surface of the ingot surface, so that the hot rolling in the gas expansion pressure to form a "bubble"". In the production site in this regard the knife prick force method to eliminate influence their subsequent wouldn do not know the move may be the formation of products of the surface of the "skin", "black" and other defects.

1.3 preventive measures

First is to strengthen the refining effect of the gas, so that the aluminum melt in the mold even the oxygen enrichment is also not up to form "bubble" this level for the direct use of high-temperature electrolysis aluminum liquid as raw materials is particularly important. In the use of effective refining agent and degassing method at the same time, Fang aluminum forgings to remind the strict operation rules is particularly important, in the production of some batches of this defect should be closely related to this, and the other is to improve the structure of the crystallizer. The traditional structure of the small and reasonable structure of the intermediate package, it is necessary to improve the practice of exploration. If you can change the entrance of asbestos baffle into upper and lower side seam, or increase the length of the mould, remove asbestos barrier, so that the melt in the mold is completely connected with the small room.