Wiring terminal composition
The composition of the terminal is relatively simple. It is a piece of metal enclosed in insulating plastic. There are holes at both ends for inserting wires, or there are screws for fastening / loosening. For example, two wires sometimes need to be connected and sometimes need to be disconnected. Here, terminals can be used to connect them instead of welding or winding them together.
Classification of terminal blocks
As far as the current market is concerned, the terminal can be divided into: European terminal series, plug-in terminal series, transformer terminal series, spring terminal series, rail terminal series, etc. At present, PCB board terminals, hardware terminals, nut terminals and spring terminals are widely used.
Common fault problems of wiring terminal
From the perspective of use, the common faults of the terminal include poor contact, poor insulation, poor fixation, etc. the details are as follows:
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 its matching connector. Therefore, the contact must have excellent structure, stable and reliable contact holding force, and good electrical conductivity.
Due to unreasonable structural design of the contact, wrong material selection, unstable mold, out of tolerance of processing size, rough surface, unreasonable surface treatment processes such as heat treatment and electroplating, improper assembly, poor storage and use environment and improper operation and use, poor contact will be caused at the contact parts and mating parts of the contact.
2. Poor insulation
The function of the insulator is to keep the contacts in the correct position and arrangement, and to insulate the contacts from each other and the contacts from the shell. Therefore, the insulator must have excellent electrical performance, mechanical performance and process molding performance.
Especially with the wide use of high-density and miniaturized terminals, the effective wall thickness of the insulator becomes thinner and thinner. This puts forward more stringent requirements for insulation materials, injection mold accuracy and molding process.
Due to the presence of metal residues on the surface or inside of the insulator, the pollution of surface dust, flux, etc., the organic material precipitates and harmful gas adsorption film and the surface water film merge to form an ionic conductive channel, moisture absorption, mold growth, aging of insulating materials and other reasons, short circuit, leakage, breakdown, low insulation resistance and poor insulation will be caused.
3. Poor fixation
The insulator not only plays an insulating role, but also provides centering and neutralization protection for the protruding contacts, and also has the functions of installation, positioning, locking and fixing on the equipment. Poor fixation, light impact on reliable contact, resulting in instant power failure, and serious product disintegration.
Disassembly refers to the abnormal separation between plug and socket and between pin and socket caused by unreliable structure due to material, design, process and other reasons when the connection terminal is in the plugged state, which will cause serious consequences of interruption of power transmission and signal control of the control system.
Due to unreliable design, wrong material selection, improper selection of molding process, poor quality of heat treatment, mold, assembly, welding and other processes, and improper assembly, etc., poor fixation will be caused.
In addition, the appearance is poor due to peeling, corrosion, bruise, plastic shell flash, fracture, rough processing of contact parts, deformation and other reasons; Poor interchangeability due to out of tolerance of positioning and locking fitting size, poor consistency of processing quality, excessive total separation force, etc. They are common and frequently occurring diseases. These faults can generally be found and eliminated in time during inspection and use.
Solutions to common faults of wiring terminals
In order to ensure the quality and reliability of the terminal blocks and prevent the occurrence of the above-mentioned fault problems, it is suggested to study and formulate the corresponding screening technical requirements according to the technical conditions of the products, and carry out the following targeted reliability inspection for failure prevention.
1. Prevent poor contact
1) Conduction test
There is no such item in the product acceptance test of the general terminal manufacturer, and the user generally needs to conduct conduction test after installation. Therefore, it is suggested that manufacturers should increase point by point conduction test for some key models of products.
2) Instantaneous break detection
Some terminals are used in dynamic vibration environment. The experiment proves that only checking whether the static contact resistance is qualified can not guarantee the contact reliability in the dynamic environment.
Because the connectors with qualified contact resistance still have transient power failure when conducting vibration, impact and other simulated environment tests, it is better to conduct dynamic vibration tests on the terminals with high reliability requirements to assess their contact reliability.
3) Single hole separation force detection
Single hole separation force refers to the separation force of the contact piece in the inserted state from static to moving, which is used to indicate that the pin and the jack are in contact.
The experiment shows that the separation force of single hole is too small, and the signal may be broken when subjected to vibration and impact load. It is more effective to check the contact reliability by measuring the separation force of single hole than by measuring the contact resistance. It is found through inspection that the contact resistance of the jack with out of tolerance single hole separation force is still qualified.
Therefore, in addition to developing a new generation of flexible plug-in contact stable and reliable contact parts, the manufacturer shall not use automatic plug-in force testing machine for multi-point simultaneous measurement for key models, and shall conduct point by point single hole separation force inspection for finished products to prevent the signal from breaking due to the relaxation of individual jacks.
2. Prevent poor insulation
1) Insulation material inspection
The quality of raw materials has great influence on the insulation performance of insulators. Therefore, the selection of raw material manufacturers is particularly important. We should not blindly reduce the cost and lose the quality of materials. We should choose large manufacturers with good reputation. In addition, for each batch of incoming materials, the batch number, material certificate and other important information shall be carefully checked and the traceability data of material use shall be well prepared.
2) Insulation resistance inspection of insulator
By 2012, some manufacturers required that the electrical performance should be tested after assembly into finished products. As a result, the insulation resistance of the insulator itself was unqualified, and the whole batch of finished products had to be scrapped. The reasonable process shall be the process screening in the state of insulator parts to ensure the electrical performance is qualified.
3. Prevent poor fixation
1) Interchangeability inspection
Interchangeability inspection is a dynamic inspection. It requires that the same series of matching plugs and sockets can be inserted and connected with each other, and it is found whether there is any failure to insert, position and lock due to the out of tolerance of the dimensions of insulators, contacts and other parts, missing parts or improper assembly, or even the disassembly due to the rotating force.
Another function of interchangeability inspection is to timely find out whether there are metal residues that affect the insulation performance through plug-in connection such as threads and bayonets. Therefore, the terminal blocks for some important purposes should be inspected to avoid such major fatal failure accidents.
2) Torque resistance inspection
Torque resistance inspection is a very effective inspection method for assessing the structural reliability of terminal blocks. Such as mil-l-39012. According to the standard, each batch of samples should be sampled for torque resistance inspection to find problems in time.
3) General test of crimped conductor
During electrical installation, it is often found that the crimping wires of individual cores cannot be delivered in place, or cannot be locked after being delivered, and the contact is not reliable. The reason is that there are burrs or dirt stuck on the screw thread of individual mounting holes. In particular, several installation holes that have been electrically installed to a plug socket by the manufacturer have to be removed one by one after the defect is found, and the plug socket has to be replaced.
In addition, due to improper selection and matching of wire diameter and crimping aperture, or due to improper operation of crimping process, the crimping end may be unstable. Therefore, before the finished products leave the factory, the manufacturer shall conduct a through test on all the installation holes of the delivered plug (seat), that is, use the loading and unloading tools to simulate the wires crimped with pins or jacks to the position and check whether they can be locked. According to the product technical conditions, check the pulling force of each crimped wire.
