There are many types of hook structure of tension spring, among which the more commonly used ones have been included in the national standard. The end shape of the tension spring is mainly hook and loop, which are formed by bending the end spring coil or steel wire. When designing or selecting the end structure form, the installation method, installation space, load property and other factors of the spring in the hook shall be mainly considered. On the premise of meeting the requirements, the simple structure shape shall be selected as far as possible.
1. Semicircular hook and loop, which is formed by bending half of the spring coil at the end of the spring, is used in occasions where the air space is limited.
2. The torsion circular hook and loop is formed by bending and twisting the spring coil at the end of the spring to the center, and high stress is formed at the bending and twisting position. It is suitable for springs with large winding ratio and small load.
3. The eccentric circular shackle is formed by bending the end spring coil. The shackle is located at the tangent position of the edge of the spring coil. Due to the eccentricity of the load and the 90 degree bending of the shackle root, the steel wire bears large additional stress. This end structure is suitable for springs with medium winding ratio of 8-15, small load or unimportant load.
The center of the circular hook ring located in the middle of the spring coil is also formed by bending and pressing the end spring coil to the center. Compared with the eccentric circular hook ring, it can avoid the eccentricity of the load and is relatively safe and reliable. It is widely used for springs with a winding ratio of C < 20 and bearing higher loads.
LV and LM are long arm shackles with complex processing, which are generally avoided as far as possible. All shackles formed by bending process produce relatively large stress concentration at the bend of the steel wire. Therefore, the end structure of shackles formed by bending process is recommended to be applied to springs with material diameter less than 4mm. However, due to the simplicity of this method, it is sometimes used for springs with a material diameter of about 10 mm. In order to reduce stress concentration, additional hook and loop structure can be adopted, such as adjustable structure. The cylindrical plug with spiral is screwed into both ends of the spring for 1.5-2.5 turns, and a screw is added on the cylindrical plug. This structure is applicable to springs with material diameter greater than 5mm. The end of the spring can also be made into a conical closed end, and a rotatable hook ring can be added. The relative positions of the shackles at both ends can be on a straight line or at 90 degrees to each other, or at any angle required.
