I made ice cream with liquid nitrogen today.how do they make it in the ice cream industry?(not with liquid N)?

Not in the same way at least. Very rapid freezing is an important step in high quality ice cream, because smaller ice crystals form, making a smoother ice cream. Therefore, most high end manufacturers use liquid nitrogen air flow to quick freeze the semi-solid product. The first link tells something about the Wells method. (They make Wells Blue Bunny Ice Cream)





BTW, a couple 'kids' from Iowa State have developed a machine to do what you did safely and consistantly in-store. See the second link below.