1、 Principle of expansion screw

The fixation of the expansion screw is to use the pull out angle to promote the expansion to produce friction binding force, so as to achieve the anchoring effect.

2、 Embedded depth of expansion screw

Generally, the embedded depth of expansion screw is calculated based on 4 times of the diameter of the bolt used for fixing. Of course, the deeper the embedded screw is, the greater the tensile force shear force it can bear. However, due to factors such as material anchorage, etc., the manufacturer needs to consider when designing.

3、 Reference for use of expansion screws

（1） Strength of concrete

（2） Strength of fixing screw (calculated by material)

（3） Strength of expansion screw (designed by manufacturer)

4、 Strength of expansion screw

Expansion screw (including the strength test, used to be pressurized by hydraulic pressure, in the most Large force is its tensile strength. The disadvantage of this test method is that it fails to measure the displacement of the screw leaving the cement. In other words, we can know that the elastic stress of the expansion material is within a few Newtons. Therefore, the new testing instrument draws the tension displacement in coordinates, Y-axis is tensile force, x-axis is displacement (as shown in the figure). When the tension rises, the displacement will follow Increase until the cement breaks the expansion screw is pulled out broken. The highest point of this curve is the ultimate tensile strength. In addition, when the tensile force rises to a certain point, such as after removing the tension, the displacement can still return to its original position. This point is the yield point of the expansion screw itself, which is also the proportional load we need in our design.

The displacement curve of common expansion screw can be divided into 5 minutes.

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