Terminal blocks are an accessory product used to achieve electrical connections, and are industrially classified as connectors. With the increasing degree of industrial automation and the increasingly stringent and precise requirements of industrial control, the demand for terminal blocks is gradually increasing. The rapid development of the electronics industry has made the use of terminal blocks more and more wide and more types.

01

Classification of terminal blocks

Terminal blocks can be divided into: WUK terminal blocks, European terminal block series, plug-in terminal block series, transformer terminal blocks, building wiring terminals, fence terminals series, spring terminal series, rail terminals series, through-wall terminals series, photoelectric coupling terminals series, 110 terminals, 205 terminals, 250 terminals, 187 terminals, OD2.2 torus terminals, 2.5 torus terminals, 3.2 torus terminals, 4.2 Ring terminals, 2 ring terminals, 6.4 ring terminals, 8.4 ring terminals, 11 ring terminals, 13 ring terminals flag series terminals and sheath series, All kinds of ring terminals, tubular terminals, terminal blocks, copper strip iron strip (2-03, 4-03, 4-04, 6-03, 6-04). wait. At present, the most widely used pcB board terminals, hardware terminals, nut terminals, spring terminals.

The plastic insulation material and conductive parts of the terminals are directly related to the quality of the terminals, and they determine the insulation and conductivity of the terminals respectively. Failure of any one terminal block will result in the failure of the entire system engineering. Needless to say in this regard, there are many warning cases, and Xiaobian will not give them one by one. As an accessory product for precision operation, the quality of motion control terminals is always concerned by customers, and how to effectively check and prevent them has become a topic of concern.

02

Common faults with terminal blocks

From the perspective of use, the function that should be achieved is: the contact site must be conducted, and the contact is reliable. Where the insulation part should not be conducted, it must be insulated reliably. There are three common forms of fatal failure of terminal blocks:

1. Poor contact problem

The metal conductor inside the terminal block is the core part of the terminal that transmits voltage, current, or signal from an external wire or cable to the contact corresponding to the connector that matches it. Therefore, the contact parts must have excellent structure, stable and reliable contact retention and good conductivity. Due to the unreasonable structural design of the contact parts, the wrong material selection, the unstable mold, the processing size is ultra-poor, the surface is rough, the surface treatment process such as heat treatment plating is unreasonable, the assembly is improper, the storage and use environment is poor and the operation is improper, it will cause poor contact in the contact parts and the mating parts of the contact parts.

2, the problem of poor insulation

The role of the insulator is to keep the contact pieces in the correct position arrangement, and to insulate the contact parts from the contact parts and between the contact pieces and the housing. Therefore, the insulation must have excellent electrical properties, mechanical properties and process forming properties. Especially with the high density, the widespread use of miniaturized terminal blocks, the effective wall thickness of insulators is getting thinner and thinner. This puts forward stricter requirements for insulation materials, injection mold accuracy and molding processes. Due to the presence of metal excess, surface dust, flux and other pollution moisture on the surface or inside of the insulator, organic material precipitates and harmful gas adsorption membranes are fused with the surface water film to form ionic conductive channels, moisture absorption, long mildew, aging of insulation materials and other reasons, which will cause short circuits, leakage, breakdown, low insulation resistance and other insulation adverse phenomena.

3. Poor fixation

Insulators not only act as insulators, but often also provide precise alignment and protection for protruding contacts, while also having the function of mounting positioning, locking and fixing on the device. Poor fixation, light affects the reliability of contact caused by instantaneous power failure, serious is the disintegration of the product. Disintegration refers to the abnormal separation between the plug and the socket and the pin and the jack caused by the unreliable structure of the terminal block in the mating state, which will cause serious consequences of the interruption of power transmission and signal control of the control system. Due to unreliable design, incorrect material selection, improper selection of molding process, heat treatment, mold, assembly, welding and other poor process quality, assembly is not in place, etc. will cause poor fixation.

In addition, due to the appearance of poor appearance caused by skin coating, corrosion, bumping, plastic shell edge, cracking, rough processing of contact parts, deformation and other reasons, due to poor positioning locking and matching size, poor consistency of processing quality, excessive total separation force and other reasons, it is also a common disease and multiple diseases. These faults can generally be found and rejected in time during inspection and use.

03

How to detect terminal short-circuit faults

Faults in the wires and terminal blocks can also be caused by short circuits between the harness and the body (ground wire) or inside the switch in question. Before inspection, you should first see if the terminals on the body are secure, and then you can follow the steps below to test.

1. Check the wire on and off

First remove the terminal blocks on both sides of the control computer ECU and the sensor, and then measure the resistance between the corresponding terminals of the terminals. If the resistance value is not greater than 1 ohm, the wire is normal for the next check. When measuring the wire resistance, it is best to gently shake the wire in both vertical and horizontal directions to improve the accuracy of the measurement, and note that for most wire terminals, multimeter bars should be inserted from the rear end of the connector, but for waterproof terminals equipped with waterproof sleeves, the bracelet cannot be inserted from the rear end, because a little carelessness will deform the terminals when inserting.

2. Short circuit resistance value check

First, remove the wire terminals on both sides of the control computer ECU and the sensor, and then measure the resistance value between the terminal blocks of the connectors on both sides and the body. When measuring, one end of the bracelet is connected to the body, and the other end is measured on the wire connectors on both sides, and if the resistance value is greater than 1 ohm, it means that the wire has no short-circuit fault with the body.

3. Terminal appearance and contact pressure inspection

First of all, each terminal should be removed one by one, check whether there is rust and dirt on the connector terminals, and should be cleaned up for rust and dirt. Then check whether the terminal piece is loose or damaged, whether the terminal is firmly fixed, and the terminal should be free of loose phenomenon when gently pulled. Conversely, if the plug terminal in which housing hole is easier to pull out than the other housing holes, the housing hole may cause poor contact failure in use.

04

How to test for preventive screening

In order to ensure the quality and reliability of terminal blocks and prevent the occurrence of the above fault problems, it is recommended to study and formulate corresponding screening technical requirements according to the technical conditions of the product, and carry out the following targeted reliability inspection to prevent failure.

1. Prevent poor contact

1) Conduction detection

General terminal block manufacturer product acceptance test does not have this project, and the user generally needs to conduct conduction test after installation. Therefore, it is recommended that manufacturers should increase the point-by-point conduction test of some key models of products by 100%.

2) Instantaneous interruption detection

Some terminal blocks are used in dynamic vibration environments. Experiments have proved that only the static contact resistance is qualified, and it does not guarantee the reliability of contact in dynamic environments. Because connectors with qualified contact resistance often still have instantaneous power off phenomenon during simulation environmental tests such as vibration and shock, it is best to assess the contact reliability of some terminals with high reliability requirements for dynamic vibration tests.

3) Single-hole separation force detection

The single-hole separation force refers to the separation force that changes the contact in the insert state from stationary to moving, and is used to characterize the contact between the pin and the jack. Experiments show that the separation force of a single hole is too small, and the signal may be instantaneously interrupted when subjected to vibration and shock loads. The method of measuring the separation force of a single hole is more effective than measuring the contact resistance. Inspection of jacks with single-hole separation force differences, the measurement of contact resistance is often still qualified. To this end, in addition to the development of a new generation of flexible intercalation contact stable and reliable contact parts, the production plant should not use automatic insertion force testing machine for key models multi-point simultaneous measurement, and should carry out 100% point-by-point single-hole separation force inspection of the finished product to prevent signal interruption due to individual jack relaxation.

2. Prevent poor insulation

1) Insulation material inspection

The quality of raw materials has a great impact on the insulating properties of insulators. Therefore, it is particularly important for the choice of raw material manufacturers, and the quality of the material cannot be lost blindly to reduce the cost You should choose a reputable material And for each batch of materials to carefully check the batch number, material proof and other important information Do a good job of traceability of material use.

2) Insulator insulation resistance check

By 2012, some production plants stipulated that the electrical performance would be tested after being assembled into a finished product, and as a result, the entire batch of finished products had to be scrapped due to the unqualified insulation resistance of the insulator itself. A reasonable process should be 100% process screening in the state of the insulator parts to ensure that the electrical performance is qualified.

3. Prevent poor fixation

1) Interchangeability check

Interchangeability checks are a dynamic check. It requires that the same series of matching plugs and sockets can be interpolated and connected, from which it is found whether there is a failure to interpolate, position and lock due to the size of insulators, contact parts and other parts, missing parts or insufficient assembly, etc., and even disintegration under the action of rotating forces. Another role of interchangeability checks is to find out in time whether there are metal excesses that affect insulation properties through plug-in connections such as threads and bayonets. Therefore, 100% of the terminal blocks for some important uses should be inspected in this project to avoid such major fatal failure accidents.

2) Endurance torque check

Endurance torque inspection is a very effective inspection method to assess the reliability of terminal structures. As the U.S. military standard MIL-L-39012 standard stipulates According to the standard, each batch of samples should be sampled for endurance moment check to find problems in time.

3) Pass test of crimped wires

In Denso, it is often found that individual core crimp wires are not in place, or cannot be locked after being sent to the position, and the contact is unreliable. The cause of the analysis is that there are burrs or dirt jamming at the screw teeth of the individual mounting holes. In particular, the last few mounting holes of the factory have been electrically installed into a plug seat, and after finding the defect, the other hole crimping wires that have been installed have to be removed one by one and the plug seat can be replaced. In addition, due to the improper selection of the wire diameter and the crimp aperture, or due to the operation error of the crimping process, it will also cause accidents where the crimp end is not firm. To this end, the production plant should conduct a general test of all the mounting holes of the sample of the delivered plug (seat) before leaving the factory, that is, use the loading and unloading tool to send the wire with the pin or jack to the position to check whether it can be locked. According to the technical conditions of the product, the tensile force of the crimped wire is checked one by one.

05

Write at the end

Terminal blocks are the foundation, and without reliable terminal blocks, there is no reliable system engineering. Prevention and analysis is a necessary process for every enterprise, through the terminal reliability screening to find a variety of failure modes and failure mechanisms, can analyze a large number of lessons learned and eliminate a variety of hidden dangers, to improve the design, process, inspection and use to provide a scientific basis, is to revise and formulate the terminal technical conditions of an important basis, to prevent unnecessary losses to provide technical support.