Inappropriate selection of the hole diameter of the screw can easily lead to slippage. The processing range of the large diameter d1 value of Tapping screws is 4.22~4.04mm, and the processing range of the small diameter d2 value is 3.10-2.95mm, so the value of the hole diameter of the Tapping screws must fall between 4.22-2.95mm. In order to increase the occlusal force between the screw thread and the steel plate, and at the same time consider the influence of the increase in the thickness of the steel plate on the screw penetration resistance, the minimum value of the hole diameter is generally 3.1, and the maximum value is generally 3.5. When the matching hole is too large, the occlusion of the screw teeth and the steel plate is too small, and the slippery wire is prone to occur; when the matching hole is too small, the screw is not easy to penetrate, and the screw will break at the same time; therefore, for different thicknesses of steel plates, different thicknesses should be selected. The hole diameter of the screw can avoid the phenomenon of slippage.
The unreasonable design of the screw hole structure can easily lead to slippage. The screw hole structure can be divided into flat holes and flanged holes. Through research, it is necessary to use flanged holes for steel plates with a thickness of less than 1.0mm.
Structural defects of screws can easily lead to slippage. The structural defects of the screw include substandard thread size and diameter, substandard thread pitch, substandard screw angle, unsaturated and incomplete screw teeth, and reverse taper of the thread.
If the major diameter of the screw is too small but the minor diameter remains the same, it will affect the unilateral occlusion of the screw teeth and the steel plate.
The pitch value P of Tapping screws is 1.4mm. When the deviation of this value is large, it means that the helix is elongated, and the length of the screw teeth "bite into" the steel plate is short, which will also cause slippage.
The thread angle of Tapping screws is 60°C; under the condition of constant size and diameter, when the thread angle is too large, the thread is fuller and firmer, which is conducive to the engagement with the steel plate and can increase the screwing torque. However, the wireless can not be too large, so that the screw teeth will become dull and affect the ability to attack. Generally suitable for 60-65°
