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Quality Inspection and Control of Bolt Ball Steel Space Frame

The steel space frame structure is often associated with large public buildings or long-span industrial plants. The quality of its structure is very important, which is related to the life safety of the country and the people. In order to achieve the purpose of quality control, extensive and strict quality testing is required. The bolt ball steel space frame is composed of bolts, bolt balls, steel pipes, pins, sleeves, sealing plates or cone heads and other parts. The steel pipe rods and bolt balls are connected by high-strength bolts to form a space space frame structure . The steel space frame is a high-order super-statically indeterminate structure, and its structural load is jointly borne by the rods, high-strength bolts, and bolt balls. The three most important links in quality control. Let’s talk about the quality inspection and control of bolt balls.

1、Quality inspection and control of bolt balls

2、Stress characteristics of the bolt ball

The stress state of the bolt ball is similar to that of the general nut, the difference is that the steel ball is in a multi-directional stress state.

3、Inspection items of bolt ball

Use a 10x magnifying glass to visually inspect or use magnetic particle inspection to detect surface defects and hidden dangers of steel balls. Once harmful defects such as cracks are found, they should be sorted and inspected one by one to remove the defective bolt balls, and the steel ball threads should be inspected with standard thread gauges. Tolerance and matching accuracy, the spot check ratio is 5% of each specification, and not less than 5 pieces.

4、Quality Control

Bolt balls are strictly prohibited from overburning and cracks. Bolt balls are generally formed by die forging and do not require heat treatment, so the quality of steel balls is easier to guarantee than cast steel balls. Our station has tested thousands of bolt balls in more than a dozen projects, and only found cracks on the surface of the balls in the net frame project of the public waiting station of Changle Airport. Analyzing the reason, it is mainly due to the forging crack caused by the low final forging temperature during die forging. This crack not only exists on the surface of the steel ball, but also can be found inside the dissected steel ball. Since the steel ball acts as a force-bearing joint in the entire space frame, it constitutes a serious hazard to the safe use of the entire space frame. We believe that once this situation is found in the steel ball sampling inspection, the whole batch should be scrapped , because the cracks caused by the forging process not only exist on the spherical surface, but also often have hidden cracks on the sub-surface layer. With the long-term use of the space frame, The crack will gradually expand and eventually break the steel ball.