方管也就是邊長相等的的鋼管。是帶鋼經過工藝處理卷制而成。一般是把帶鋼經過拆包，平整，卷曲，焊接形成圓管，再由圓管軋制成方形管然后剪切成需要長度。方管打包標準一般是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.

　　方管根據生產工藝的不同將方管分成不同的種類，方管在施工的過程中會出現下列的問題，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?

　　鍍鋅方管60*60*4.75，材質Q235（此工程為幕墻工程）, 方管與5#角鋼，對接焊接后，在方管焊接處周邊（方管管體）有裂紋開裂現象。經檢驗，方管材質合格。

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.

　　針對上述問題，測化學成分沒太大意義，方管的材質肯定合格，現在問題主要集中在三個方面:

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、產品選擇的是鍍鋅方管，所以在焊接前將待焊區域的鍍鋅層全部打磨干凈了嗎？鋅的存在就容易使焊縫出現裂紋，即使焊后暫時看不到，也會由于鋼結構的內應力，從而擴展延伸，直至整個斷裂。你一定見過汽車擋風玻璃上的裂紋吧，沒有裂到一半停止了的，而是慢慢延展到整個玻璃。

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，按施工規范，一般環境低于0度就要采取一定的措施了，比如焊前要進行預熱處理，起碼起弧處100mm范圍內要預熱到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、一般方管都是通過拉拔或軋制而成的，在加工過程中是有內應力的，成形后要進行退火消應力。這與方管生產廠家的實力有很大的關系，正規廠家生產的大型H型鋼，可能是規格太大了，消應力也不好消，在冬季氣割時，焊前不預熱，都能開裂了。

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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