无缝钢管厂为天津拖拉机制造厂试制一种“铁牛—45”型拖拉机中间轴用管,规格为76×19.5毫米,用45号钢制造。钢管外径偏差为+1.25%,-1.0%;内径偏差为+0,-4毫米;壁厚不均不得大于3.5毫米。这种钢管属于小直径特厚壁钢管,按照“140”自动式轧管机组的现行生产工艺,须采用直径较大的管坯走减径生产。试制中实际采用的工艺过程:用直 Seamless Steel Tube Plant trial for the Tianjin tractor manufacturing plant a “Tieniu -45 ” type tractor intermediate shaft with a size of 76 * 19.5 mm, made of 45 steel. Steel pipe diameter deviation of +1.25%, -1.0%; diameter deviation of +0, -4 mm; wall thickness shall not be greater than 3.5 mm. This kind of steel pipe belongs to the small-diameter extra-thick wall steel pipe. According to the current production technology of the “140” automatic pipe rolling unit, the pipe with larger diameter is required to be reduced in diameter. Trial production process actually used: with straight