Significance of prevention

The plastic insulation and conductive parts of the terminals are directly related to the quality of the terminals, which determine the insulation and electrical conductivity of the terminals. Failure of any of the terminals will result in failure of the entire system engineering. The painful lessons that have taken place at home and abroad in this regard are very profound.

Prevention is the purpose and analysis is the foundation. In a sense, preventing failure is more important than analyzing failure. It has a more realistic meaning for ensuring the quality and reliability of the terminals.

From the point of view of the use of the terminal, the function that should be achieved is that the contact area must be conductive and the contact is reliable. The place where the insulation is not to be turned on must be insulated and reliable. There are three common types of fatal faults in terminal blocks:

 

Poor contact

The metal conductor inside the terminal is the core part of the terminal that transfers the voltage, current or signal from the external wire or cable to the corresponding contact of the mating connector. Therefore, the contact member must have an excellent structure, stable and reliable contact retention and good electrical conductivity. Due to the unreasonable design of the contact structure, the wrong selection of materials, unstable mold, poor processing dimensions, rough surface, unreasonable surface treatment process such as heat treatment plating, improper assembly, poor storage and use environment, and improper operation, will be in the contact parts. Contact and fitting parts cause poor contact.

Poor insulation

The function of the insulator is to keep the contacts in the correct position and to insulate the contacts from the contacts and the contacts from the housing. Therefore, the insulation must have excellent electrical properties, mechanical properties and process forming properties. In particular, with the high density and wide use of miniaturized terminals, the effective wall thickness of the insulator is getting thinner and thinner. This puts more stringent requirements on insulation materials, injection mold precision and molding processes. Due to the presence of metal excesses on the surface or inside of the insulator, surface dust, flux and other pollution are damp, organic material precipitates and harmful gas adsorption film and surface water film fuse to form ionic conductive channels, moisture absorption, mildew, insulation material aging and other reasons, It will cause short circuit, leakage, breakdown, low insulation resistance and other insulation problems.

Bad fixation

The insulator not only acts as an insulator, but also provides precise centering and protection for the extended contacts, as well as mounting and locking to the device. Poor fixing, light contact affects reliable momentary power outage, and serious product disintegration. Disintegration refers to the abnormal separation between the plug and the socket between the plug and the socket caused by the unreliable structure due to the material, design, process, etc., and the power transmission of the control system is caused by the disconnection of the terminal. The serious consequences of signal control interruption. Due to unreliable design, incorrect material selection, improper selection of molding process, poor quality of heat treatment, mold, assembly, welding, etc., assembly failure, etc. will result in poor fixation.

In addition, due to coating peeling, corrosion, bumping, plastic shell flashing, cracking, rough processing of contact parts, deformation and other reasons caused by poor appearance, due to the positioning of the locking fit, the processing quality is poor, the total separation force Poor exchange caused by a large number of reasons is also a common disease and frequently-occurring disease. These kinds of faults can generally be found in the inspection and use process in time.

Reliability screening test for prevention of failure

In order to ensure the quality and reliability of the terminal block and prevent the occurrence of the above-mentioned fatal fault, it is recommended to study and formulate the corresponding screening technical requirements according to the technical conditions of the product, and carry out the following targeted reliability test for preventing failure.

1. Prevent contact failure

1) Conduction detection

In 2012, the general terminal manufacturer's product acceptance test did not have this project, and the user generally needs to conduct continuity test after installation. Therefore, it is recommended that manufacturers should increase the point-by-point conduction test by 100% for some key models.

2) Instantaneous detection

Some terminals are used in dynamic vibration environments. The experiment proves that it is only qualified to check whether the static contact resistance is qualified, and it cannot guarantee the reliable contact in the dynamic environment. Because the connector with good contact resistance often exhibits instantaneous power failure during vibration, shock and other simulated environmental tests, it is better to test the dynamic vibration test of some high reliability terminals. Contact reliability.

3) Single hole separation force detection

The single-hole separation force refers to the separation force in which the contact member in the engaged state changes from static to moving, and is used to characterize that the pin and the socket are in contact. Experiments show that the single-hole separation force is too small, which may cause signal transients when subjected to vibration and shock loads. It is effective to check the contact reliability by measuring the single hole separation force to measure the contact resistance. Check that the single hole separation force is too poor, the measured contact resistance is still qualified. To this end, in addition to the development of a new generation of flexible plug contacts with stable and reliable contact parts, the production plant should not use the automatic insertion force tester for multi-point measurement of key models, and 100% point-by-point processing for finished products. Hole separation force check to prevent signal breakage due to slack in individual jacks.

2. Prevent insulation failure

1) Insulation inspection

The quality of raw materials has a great influence on the insulation properties of insulators. Therefore, the choice of raw material manufacturers is particularly important, not to reduce the cost and lose the material quality. Should choose the reputable big factory materials. And for each batch of materials to be carefully checked the inspection lot number, material certification and other important information. Traceability information on the use of materials.

2) Insulation insulation resistance inspection

By 2012, some of the production plants were required to test the electrical properties after assembly into finished products. As a result, the insulation of the insulator itself was unqualified, and only the entire batch of finished products was scrapped. A reasonable process should be 100% process screening in the state of the insulator parts to ensure electrical performance.

3. Prevention of poor fixation

1) Interchangeability check

Interchangeability checks are a dynamic check. It requires that the same series of plugs and sockets can be mated to each other, and it is found that there is no difference in the size of the insulators, contacts, etc., the missing parts or the assembly is not in place, etc., which cannot be inserted, positioned and locked. Even under the action of the rotating force, it causes disintegration. Another function of the interchangeability check is to find out whether there are metal surpluses that affect the insulation performance by plugging and unplugging the threads and the bayonet. Therefore, the connection terminals for some important purposes should be 100% checked to avoid such major fatal failures.

2) Torque resistance check

Torque resistance inspection is a very effective inspection method to assess the reliability of the terminal structure. Such as the US military standard MIL-L-39012 standard. According to the standard, each batch should be sampled for torque resistance inspection, and problems should be discovered in time.

3) General measurement of crimped wires

In the electrical installation, it is often found that the individual core crimping wires are not in place, or cannot be locked after being sent to the position, and the contact is unreliable. The reason for the analysis is that there are burrs or dirt stuck in the screw holes of the individual mounting holes. In particular, the last mounting holes of the factory have been electrically mounted to a plug socket. It is found that after the ills, the other crimped wires of the other holes have to be unloaded one by one, and the plug holder is replaced again. In addition, due to the improper matching of the wire diameter and the crimping aperture, or due to the operation of the crimping process, the crimping end is not secure. To this end, the manufacturer shall pass all the mounting holes of the sample of the plug (seat) of the delivery before the finished product leaves the factory, that is, use the loading and unloading tool to simulate the wire crimped with the pin or the jack to the position, check whether Locked. According to the technical requirements of the product, the pull-out force of the crimping wires is checked one by one.

Without reliable terminals, there is no reliable system engineering. Failure and reliability are two aspects of a contradiction that are corresponding and interconnected. Through the reliability screening of terminal blocks, various failure modes and failure mechanisms are found, which can lead to a lot of lessons and eliminate various hidden dangers, and provide scientific basis for improving design, process, inspection and use. It is also important to revise and formulate the technical conditions of terminal blocks. in accordance with. Finding the measures to prevent failure and transforming from failure to reliability is the ultimate goal of failure analysis.