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北京起重机器厂早期生产的 ＱＹ２０Ｂ型起重机最大起重量为２０ｔ，主吊臂为箱型结构，共有三节伸缩臂，长度１０．２－２４．５ｍ，主吊臂的前端可装设７．５ｍ的副吊臂。在起重作业中，发现起重机在不装副臂的工况下，副卷扬机构不能使用，而实际吊装时，往往在主臂允许的工
Beijing crane factory early production QY20B crane maximum lifting capacity of 20t, the main boom for the box structure, a total of three telescopic arm, the length of 10.2-24.5m, the front end of the main boom can be installed 7.5m Vice boom. In lifting operations, found that the crane is not equipped with jib conditions, the auxiliary winch can not be used, and the actual lifting, often in the main arm allows workers