方管也就是边长相等的的钢管。是带钢经过工艺处理卷制而成。一般是把带钢经过拆包，平整，卷曲，焊接形成圆管，再由圆管轧制成方形管然后剪切成需要长度。方管打包标准一般是50根每包。

A square tube is a steel pipe with equal side lengths. It is made by rolling steel strip through process treatment. Generally, the strip steel is unpacked, flattened, curled, welded to form a circular tube, then rolled into a square tube and cut into the required length. The packaging standard for square tubes is generally 50 pieces per package.

　　方管根据生产工艺的不同将方管分成不同的种类，方管在施工的过程中会出现下列的问题，你是否遇到了呢？

According to the different production processes, square pipes are divided into different types. During the construction process, the following problems may occur with square pipes. Have you encountered them?

　　镀锌方管60*60*4.75，材质Q235（此工程为幕墙工程）, 方管与5#角钢，对接焊接后，在方管焊接处周边（方管管体）有裂纹开裂现象。经检验，方管材质合格。

Galvanized square tube 60 * 60 * 4.75, material Q235 (this project is a curtain wall project). After butt welding between the square tube and 5 # angle steel, there are cracks and cracks around the welding point (square tube body) of the square tube. After inspection, the material of the square tube is qualified.

　　针对上述问题，测化学成分没太大意义，方管的材质肯定合格，现在问题主要集中在三个方面:

Regarding the above issues, measuring the chemical composition is not very meaningful. The material of the square tube is definitely qualified. Currently, the problems mainly focus on three aspects:

　　1、产品选择的是镀锌方管，所以在焊接前将待焊区域的镀锌层全部打磨干净了吗？锌的存在就容易使焊缝出现裂纹，即使焊后暂时看不到，也会由于钢结构的内应力，从而扩展延伸，直至整个断裂。你一定见过汽车挡风玻璃上的裂纹吧，没有裂到一半停止了的，而是慢慢延展到整个玻璃。

1. Has the galvanized square tube been selected as the product, so have all the galvanized layers in the area to be welded been polished clean before welding? The presence of zinc can easily cause cracks in the weld seam, even if it is temporarily invisible after welding, it will expand and extend due to the internal stress of the steel structure, until the entire fracture occurs. You must have seen cracks on car windshields, they didn't stop halfway, but slowly extended to the entire glass.

　　2、如果工程是在冬季施工的，按施工规范，一般环境低于0度就要采取一定的措施了，比如焊前要进行预热处理，起码起弧处100mm范围内要预热到50度左右吧。

2. If the project is constructed in winter, according to construction specifications, certain measures should be taken when the environment is generally below 0 degrees Celsius. For example, preheating treatment should be carried out before welding, and at least within a 100mm range of the arc starting point, preheating should be done to around 50 degrees Celsius.

　　3、一般方管都是通过拉拔或轧制而成的，在加工过程中是有内应力的，成形后要进行退火消应力。这与方管生产厂家的实力有很大的关系，正规厂家生产的大型H型钢，可能是规格太大了，消应力也不好消，在冬季气割时，焊前不预热，都能开裂了。

3. Generally, square tubes are made by drawing or rolling, and there is internal stress during the processing. After forming, annealing is required to relieve stress. This is closely related to the strength of square tube manufacturers. Large H-shaped steel produced by legitimate manufacturers may have too large specifications and difficult stress relief. During winter gas cutting, without preheating before welding, it can crack.

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