With the fixed u_g,the descending bubble size was 30%~40% less than that of rising one in the centre of the column and the descending bubble velocity was about 55% less than that of the rising one when the axial height was 0.

The forming reasons of the skin blowhole in welding gas cylinder steel HP295 are analyzed.

For bearing steel GCr15,by using low times test and making an observation and analysis of microstructure,it can be seen that the surface crack of billet results from skin blowhole and nonmetal lard.

It is suggested that the inclusions,the content of oxygen and the subcutaneous bubble emerged after rolling are the main reasons which result in bend crack of strip steel.

It is suggested that this defect is originated from the internal crack and the subcutaneous bubbles of billet,as well as unreasonable pass design of roughing mill.

The result showed that the crack forming was due to the billet metal in the subcutaneous blow holes were oxidated during heating process and could not be sticked.

By commenting on the relevant references, the forming reason and distribution of the subcutaneous blow hole in the continuous cast slab was discussed.

The subcutaneous blow hole existing in ingot was the main reason by analysis.

A comparison experiment between the common flue-cured house with air descend and the improved close flue-cured house was conducted to investigate the flue-cures cost and economic benefit.