The plastic insulating material and conductive parts of the terminal are directly related to the quality of the terminal, and they determine the insulation performance and conductivity of the terminal respectively. The failure of any one terminal will lead to the failure of the entire system engineering.
From the point of view of use, the function that the terminal should achieve is: the place where the contact part is conducting must be conducting, and the contact is reliable. The place where the insulating part should not be conductive must be insulated reliably. There are three common forms of fatal faults in terminal blocks:
1. Poor Contact
The metal conductor inside the terminal is the core part of the terminal, which transmits the voltage, current or signal from the external wire or cable to the corresponding contact of the matching connector. Therefore, the contacts must have excellent structure, stable and reliable contact retention and good electrical conductivity. Due to the unreasonable structural design of the contact parts, the wrong selection of materials, the unstable mold, the excessive processing size, the rough surface, the unreasonable surface treatment process such as heat treatment and electroplating, improper assembly, poor storage and use environment and improper operation and use, the contact parts will be damaged. Contact parts and mating parts cause poor contact.
2. Poor Insulation
The function of the insulator is to keep the contacts in the correct position, and to insulate the contacts from each other, and between the contacts and the housing. Therefore, the insulating parts must have excellent electrical properties, mechanical properties and process forming properties. Especially with the widespread use of high-density, miniaturized terminals, the effective wall thickness of the insulator is getting thinner and thinner. This puts forward more stringent requirements for insulation materials, injection mold precision and molding process. Due to the presence of metal excess on the surface or inside of the insulator, surface dust, flux and other contamination and moisture, organic material precipitates and harmful gas adsorption film and surface water film fusion to form ionic conductive channels, moisture absorption, mold growth, insulation material aging and other reasons, Will cause short circuit, leakage, breakdown, low insulation resistance and other poor insulation phenomena.
3. Poor Fixation
The insulator not only acts as insulation, but also usually provides accurate alignment and protection for the protruding contacts, and also has the functions of installation and positioning, locking and fixing on the equipment. Poorly fixed, the light one affects the reliability of the contact and causes an instant power failure, and the serious one is the disintegration of the product. Disintegration refers to the abnormal separation between the plug and the socket, between the pin and the jack caused by the unreliable structure of the terminal due to material, design, process and other reasons when the terminal is in the inserted state, which will cause the power transmission and Serious consequences of signal control interruption. Due to unreliable design, wrong material selection, improper selection of molding process, poor process quality such as heat treatment, mold, assembly, welding, etc., the assembly is not in place, etc., which will cause poor fixation.
In addition, the appearance is poor due to peeling, corrosion, bruising, plastic shell flashing, cracking, rough processing of contact parts, deformation and other reasons. Poor exchange caused by major reasons is also a common disease and frequently-occurring disease. These kinds of faults can generally be found and eliminated in time during inspection and use.
Reliability screening test for failure prevention
In order to ensure the quality and reliability of the terminals and prevent the occurrence of the above fatal failures, it is recommended to study and formulate the corresponding screening technical requirements according to the technical conditions of the products, and carry out the following targeted failure prevention reliability inspections.
1. prevent poor contact
1) Continuity detection
In 2012, there is no such item in the product acceptance test of general terminal manufacturers, and users generally need to conduct continuity testing after installation. Therefore, it is suggested that manufacturers should add 100% point-by-point continuity detection to some key models of products.
2) Instantaneous interruption detection
Some terminal blocks are used in dynamic vibration environments. Experiments have proved that only checking whether the static contact resistance is qualified can not guarantee reliable contact in dynamic environment. Because the connectors with qualified contact resistance are often subjected to instantaneous power failure during vibration, shock and other simulated environmental tests, it is best to conduct 100% dynamic vibration tests for some terminals that require high reliability. Contact reliability.
3) Single hole separation force detection
The single-hole separation force refers to the separation force that the contacts in the mated state change from static to moving, which is used to indicate that the pins and sockets are in contact. Experiments show that the single-hole separation force is too small, which may cause the signal to be cut off instantaneously when subjected to vibration and shock loads. It is more effective to measure the contact reliability by measuring the separation force of a single hole than to measure the contact resistance. Inspection found that the single-hole separation force is out of tolerance for jacks, and the measurement of contact resistance is often still qualified. For this reason, in addition to developing a new generation of flexible plug-in contacts with stable and reliable contacts, manufacturers should not use automatic plug-in force testing machines for key models to test at multiple points, and should carry out 100% point-by-point orders for finished products. Check the hole separation force to prevent the signal from being cut off due to the relaxation of individual jacks.
2. Prevention of poor insulation
1) Insulation material inspection
The quality of raw materials has a great influence on the insulating properties of insulators. Therefore, the choice of raw material manufacturers is particularly important, and the quality of materials cannot be lost by blindly reducing costs. Should choose the reputable big factory material. And for each batch of incoming materials, it is necessary to carefully check and check the important information such as batch number, material certificate and so on. Do a good job in the traceability of materials used.
2) Insulator insulation resistance inspection
As of 2012, some production plants require that the electrical properties be tested after assembling into finished products. As a result, due to the unqualified insulation resistance of the insulator itself, the entire batch of finished products has to be scrapped. A reasonable process should be 100% process screening in the state of insulator parts to ensure qualified electrical performance.
3. Prevention of poor fixation
1) Interchangeability check
The interchangeability check is a dynamic check. It requires that the same series of matching plugs and sockets can be connected to each other, and it is found whether there is any failure to insert, locate and lock due to the oversize of insulators, contacts and other parts, missing parts or improper assembly, etc. , and even disintegrate under the action of rotational force. Another function of the interchangeability inspection is to detect in time whether there is any metal excess that affects the insulation performance through plug-in connections such as threads and bayonets. Therefore, 100% of the terminals for some important purposes should be checked for this item to avoid such major fatal failure accidents.
2) Torque resistance check
Torque resistance inspection is a very effective inspection method to evaluate the structural reliability of the terminal block. According to the standard, samples should be sampled for each batch for torque resistance inspection, and problems should be found in time.
3) Through test of crimped wire
In the electrical equipment, it is often found that the individual core crimping wires are not delivered in place, or cannot be locked after being delivered, and the contact is unreliable. The reason for the analysis is that there are burrs or dirt on the screw teeth of individual installation holes. Especially when using the last few mounting holes that have been installed in a plug socket by the factory, after finding the defect, we have to unload the crimped wires in the other holes that have been installed one by one, and replace the socket. In addition, due to improper selection of wire diameter and crimping aperture, or due to incorrect operation of the crimping process, an accident that the crimping end is not strong will also be caused. For this reason, before the finished product leaves the factory, the manufacturer should conduct a thorough test on all the installation holes of the delivered plug (seat) sample, that is, use the loading and unloading tool to simulate the wire with the pin or jack to the position, and check whether it can be locked. Check the pull-off force of each crimped wire according to the technical requirements of the product.
Post time: Jul-25-2022