The function of the sheath is to prevent the power cord from directly contacting the housing and reduce the damage of the power cord sheath. The jacket needs to be made of elastic insulating material with good elasticity and a certain thickness of rubber. The use of recycled rubber to produce and relatively thin-walled sheaths are soft to the touch, lack sufficient elasticity, and are prone to aging. They are easily broken during the test and do not protect the power cord. The jacket should be tightly fitted with the tool housing so that no displacement will occur during the bending process, no additional force will be generated on the power cord, and the failure rate of the bending test can be reduced.

Tool inlet structure. The main damage points of the power cord and rubber sheath are at the position of the pressure line and the entrance of the sheath. The main problems of the inlet structure are as follows: (1) The distance between the fixed pressure plate of the power line and the inlet is too close, and the bending at the inlet is under great stress. Therefore, the broken part of the power line is often located here. (2) The power cord and sheath should be straight at the entrance, and no twisting phenomenon can occur. This can avoid pre-bending and reduce additional stress, which can significantly improve the qualification rate of bending. In particular, the position of the pressure plate directly affects the unevenness of the power line and the sheath.

For a reasonable entrance structure, an unreasonable entrance structure, the power cord and sheath have been bent. Therefore, in the structural design of the production plant, the positional relationship among the pressure plate, inlet port, and jacket should be considered. (3) The shell at the inlet of the sheath shall be provided with a plastic guard ring, which can fix the sheath and reduce the damage rate of the sheath.

The pressure of the power cord fixed platen should be appropriate. In order for the manufacturer to install the power cord securely, the screws are often tightened too tightly, resulting in a deformation of the power cord, which also reduces the qualification rate of bending. The weight of the tool itself is large, and the weight of the tool is increased, resulting in an increase in the rate of failure of the bend.

Problems to be noted in the test process: Equipment: After a long period of operation of the bending tester, the bending angle will form a certain deviation. Sometimes one side is too large and one side is too small, and both sides may be too large or too small at the same time. Happening. The increase in the deflection angle will greatly increase the rate of failure of the power cord bend.

The measuring period of a bending tester is generally one year (six months for regular use), and the deflection angle has often changed before the next metering period has arrived. Therefore, the inspection period should be shortened. Generally, an intermediate inspection of the equipment is performed every 1 to 2 months in order to find out the deviation of the equipment in time and improve the accuracy of the test.

Clamp: The clamps vary according to the mechanical structure of the different power tools. Some tool handle faces are perpendicular to the sheath (such as angle grinder and electric drill). The power line and casing are easy to maintain vertical when installed; but some tool handles have a certain degree of arc (such as electric circular saw, electric hammer, etc.), reasonable If the entrance structure of the entrance is not reasonable, the structural part of the entrance can not be guaranteed to be perpendicular to the plane. When clamping, ensure that when the bending tester is in the middle position, the power cord is down vertically and does not bear any bending stress.

Environment: The laboratory ambient temperature should be maintained at 23 °C ± 2 °C. The power cord and sheath are sensitive to temperature. The higher the temperature, the higher the elongation rate, and the power cord is not easily broken.

The hidden dangers of the sheath and the power cord not only affect the service life of the power tool, but also may cause safety accidents such as electric shock and fire. Therefore, the production plant should strictly follow the standard for design and production. After the product passes the test, do not arbitrarily change the design, especially the structure that affects the product safety, the power cord and the jacket material.