With the vigorous development of the electronic industry, all kinds of electronic products and electric products have gradually become indispensable tools for people to use, and the batteries closely related to them have gradually attracted people’s attention. Among them, the safety of the battery itself is the focus of attention. A battery with potential safety hazards will become a time bomb around people at any time, endangering people’s lives. There are many factors affecting the safety of the battery, and the high temperature and high pressure generated in the battery are directly related to the heat generation factors. There are many heat generating factors. A certain impact test will generate heat inside the battery, and it can also detect the impact resistance of the battery and its subsequent stable state. Therefore, the heavy impact test is an important test item in the battery safety detection.
1.Test Standards
In the process of battery safety test, UL 1642, UN 38.3, IEC 62133-2012, SJ / T 11169-1998, YD 1268-2003, SJ / T 11170-1998 and other test standards have different specific test requirements for the impact resistance test of the battery, but the principle is basically the same. Two heavy impact test hammers (10 kg and 91 kg respectively) are mainly used to conduct free falling impact test on the battery.
After the battery is fully charged according to the test method specified in the standard, it is placed on the surface of the platform, and the metal rod with a diameter of 158 + 0.2 mm or 8 mm is placed on the upper surface of the geometric center of the battery. A weight with a mass of 9.1 + 0.1 kg or 10 kg is used to impact the surface of the battery with the metal rod from a height of 610 mm ± 25 mm, and observe whether it explodes.
The heavy impact test has two meanings. One is that the potential energy of 9.1 kg hammer from 610 mm height is converted into kinetic energy after free falling and applied to the battery, that is, the round rod with diameter of 158 mm will hit the battery instantly after gaining kinetic energy, and the positive and negative electrode pieces inside the battery will be squeezed instantaneously. If the separator cannot effectively isolate the positive and negative electrodes at this time, it will cause a short circuit in the positive and negative electrodes, which will trigger an exothermic reaction inside the battery, thus causing insecurity. Another meaning is to examine whether the battery will deform.
The weight of the heavy hammer in each standard is mostly 9.1 kg, and only the standard YD 1268 is 10 kg. The impact height is also free falling from the height of 610 mm, and the diameter of the metal rod is about 158 or 79 mm. The observation time is generally 6 h.
2.Design Requirements
The design requirements of the heavy impact tester include the following points:
First, the impact process removes the resistance of the rope, and the accuracy of the lifting height removes the resistance of the rope;
Second, the electromagnetic device sucks, lifts the heavy hammer, the lifting height of the heavy hammer is controllable, and the remote control operation, etc
Third, safety protection device, explosion-proof function, automatic smoke exhaust device, etc. Since the impact of heavy objects is mainly to observe whether the lithium battery explodes, it is easy to cause explosion injury during the test. Therefore, it is necessary to design explosion-proof and observation functions; Fourth, the system requires simple composition, low cost and good popularization.
3.Design and Technical Scheme
In the process of heavy impact test on the battery, it is necessary to lift a certain weight to a certain height. After a series of processes such as rapid separation, free fall and straight impact are realized, the change phenomenon of the battery after impact is observed to determine the safety performance of the battery.
The traditional heavy object impact test device is mostly completed by rope traction. The heavy object is lifted to a certain height by motor traction, and then the traction rope is quickly disconnected. The heavy object falls relatively freely with the traction rope to impact the battery. The new heavy weight impact tester uses electromagnet to absorb the heavy weight, lifts the heavy weight through the screw rod, and then cuts off the power to demagnetize, so that the heavy weight can be quickly separated and completely fall down to impact the battery sample.
3.1 Test Structure and Principle
The main body of the host is composed of a frame, a box, a control box and lifting components. The box is made of explosion-proof materials, and an observation window is left on the front explosion-proof door. The rack includes a bottom plate, a top plate and a lifting guide rod, and the top plate is fixed above the bottom plate through the lifting guide rod: the bottom plate is provided with a placing part for placing the battery to be tested; the box is provided with a weight for testing the impact of the battery, and the test assembly installed on the rack for sucking and releasing the weight is provided with a weight, A lifting assembly arranged above the test assembly and a straightening assembly arranged above the placing pipe at the bottom of the rack: the lifting assembly is installed at the top of the rack; the test assembly is arranged between the lifting assembly and the straightening assembly, and its up and down movement is controlled by the lifting assembly; The test assembly, lifting assembly and positive assembly are all connected with the control box and controlled by the control box.
The tester uses electricity and air pressure as the power source, and the laboratory generally has electricity and air source. Using electricity and air source as the power source can reduce the cost and have environmental protection.
The specific operation process is as follows: press the suction button, the weight will be sucked by the electromagnet, press the lifting button, the weight will be lifted to the specified height, press the “release” button on the control panel, the electromagnet will be powered off, and the weight will be released: the weight will fall freely into the test area, at this time, the weight will tilt and cannot be sucked again, and it needs to press the “car upright” button, Press the “down” button on the control panel to lower the lifting structure to the height where the weight can be sucked. Then press the “suck” button again, the electromagnetic iron will be energized and the weight will be sucked again for test.
3.2 Safety Design
(1)Safety device against falling outside the weight hammer. When it is confirmed that the heavy hammer has been sucked, the safety clamp shall be clamped to prevent the heavy hammer from falling off accidentally in case of unexpected power failure or other unprepared conditions.
(2) Limit protection design of proximity switch and travel switch. When the height of the hammer rises to the specified height, it will automatically stop when it touches the proximity switch. The impact height is determined by adjusting the position of the proximity switch. If the lifting height is too high, the lifting device will press the travel switch on the device, and then the lifting device will stop to protect the motor.
3.3 Innovation Points of Equipment
The innovation points include the following two aspects: on the one hand, the new heavy object impact tester has the characteristics of “electromagnetism”, “cordless traction” and “automatic reset”;
On the other hand, the system can be clamped by pneumatic safety clamp to prevent the hammer from falling off in case of sudden power failure.
4.Conclusion
After the equipment is made, the convenience and accuracy of the battery weight impact test can be further improved. When the equipment is designed, the danger during the battery test is fully considered. Therefore, the safety of the equipment is the focus of this design. The equipment adopts safety protection in several methods, with simple structure, simple processing technology and easy operation. This equipment has been granted a patent, and the impact test in the actual detection has proved that it has strong practicability and has a good reference value in mechanical inspection and application.