The terminal block is a kind of connector and it is an important component in the electrical industry. It plays an irreplaceable and non-negligible role. Because the engineers and technicians first check the interface during the inspection, that is, the terminal, the terminal block The design is particularly important.
Product design is based on: a comprehensive design of product standards, materials, structures, electroplating, certification, molds, and manufacturing processes. Terminals are no exception.
(1) The product standard serves as a general guideline. Almost all considerations are based on it. Our terminal design standards are based on UL and CSA first, but some electrical parameters can also be based on other criteria, such as Low temperature test. (2) The choice of materials directly affects the performance of the entire product and is the key to the design. Take plastic materials as an example: if the flame retardance of UL94 and V-0 is the design basis, we must carefully review the technology of each material property table. Whether the parameters can meet the product's standards, such as the impact resistance voltage and aging test can pass, in the hardware material is mainly TP's tablet material selection is particularly important, because the tablet must meet a certain conductivity (current) To have a certain degree of flexibility, it has brought difficulties to our engineers in selecting materials. It is precisely in this respect that connector manufacturers are pursuing the trend toward flexible components. Many manufacturers of manufacturing hardware materials are working hard in this direction to conduct electricity. The rate directly affects the temperature rise and the contact resistance. The elasticity is related to the chemical element, elastic modulus, hardness and tensile strength of the material. The selection of the elastic modulus is calculated using the fourth strength theoretical formula of the material mechanics. The greater the conductivity of the material, the lower the contact resistance. The lower the temperature rise, the relationship between the insertion force and the contact resistance becomes a quadratic curve, and the contact resistance is mainly divided into the compression resistance, the film resistance, and the volume resistance (the resistance of the conductor itself). . Among them, the film resistance accounts for 70-80% of the total resistance, which is also the main factor that affects the service life of the connector. It should be given full attention. It is compared with the terminal gold plating and silver plating. Although the conductivity of silver is higher than that of gold, its chemistry The stability is not good, and the film resistance caused by the film is far greater than the gold plating. Therefore, to clarify the relationship between the above has guiding significance for the selection of materials, and it is a prerequisite for product design.
(3) The design of the product structure is also very important. This is entirely an experience and there is no shortcut. In this aspect, each series has its own characteristics, such as: the screw is prevented from falling off, the spliced ​​product is curved before and after, and is long. Deformation of digits, shrinkage caused by uneven wall thickness, etc. The following are available for the prevention of screws: Three ribs are prevented from falling out, the hoops are prevented from being thrown out, the neck is prevented from being detached, and the punching is prevented, due to the influence of the technical process. At present, there are not many necks used to prevent them from falling out. Most of them use the neck to prevent them. The realization of the above structure is based on the premise that plastic material is PA66. Here, it is necessary to explain how to prevent the neck from falling off. Take the screw M3 as an example. The actual outer diameter of M3 screw is φ 2.90mm, so the size of the shell neck should be designed in: φ2.5 ~ φ2.6, the thickness of the shell neck should be 0.4 ~ 0.5mm, and the screw head should be less than a paragraph below The polished rod on the neck of the shell can ensure that the screw can be screwed into the thread smoothly. The production process should also be adjusted accordingly. The following is a statistical and solution solution to the problems in the structure of our company's products. Splicing Growth deformation digit combination products, the main reason is due to the structure caused by an irrational Falcon the uneven two splicing vertically and horizontally back and forth, as shown in the configuration must be designed to direction of the force and deformation of the splicing Falcon.
Second, the screw to prevent the problem, in this regard, I recommend using the neck as much as possible to prevent it, because it is compared with the guard against the mouth to avoid screw screw rod and hoop mouth tolerances caused by the accuracy of the troubles. And structural reliability tolerances are easy to control.
Third, the problem of salt spray test after plating on screws and threaded steel parts, due to the company's current thread plating standards (plating is limited, but how much the thread corresponds to the coating thickness is currently I think still need to be further determined) to solve this problem Problems There are two methods in the normal electroplating process. Choose the right sealer and apply plating multiple times. Both of these methods cover the voids that the screws can't see with the naked eye. It is recommended that the first method be used because the cost of electroplating with multiple platings is higher. The key to this method is the study of the sealer formulation.
Fourth, the problem of insertion force, this area involves more content, it is related to materials, electroplating, structure and applied industries, is an important mechanical performance requirements of the connector industry, plug-in terminals Even more so, the choice of material is limited by the conductivity (current) and contact resistance and temperature rise in terms of insertion force. The detailed description will not be given here. Plating is mainly affected by the type of plating and whether it is pre-plated. In general, after the pre-plating under the same material and structure, the pressing is performed more than the first pressing and re-plating. Insertion and extraction force should be stable because in the process of post-plating process, the hardware material is hardened in intangible process, and the prior stamping just eliminates this phenomenon. The main consideration in the structure is the contact between the tablet and the needle. The contact between the needle and the tablet is mostly line contact. This causes the sudden appearance of a large moment in the moment of insertion, and then suddenly becomes smaller, to the customer. The use of the process has a very unstable feeling, affecting its life. If the contact between the tablet and the needle is changed to the surface contact in the structure, then the problem of the insertion force is solved and the contact resistance and the temperature are reduced. Rise.
(D) the application of the product: mainly used in lighting, communications, security and other industries. The plug-in terminal application industry is the most common, such as frequency conversion, riot control, numerical control panel, access controller, sensors, PLC, instrumentation, power supply, servo drive, these applications industry common to the plug-in terminals The requirements are: the plugging force should be stable, and the contact resistance should be small. It must be able to meet a certain life expectancy and fatigue, so the requirements for the metal shrapnel material are relatively high. This requires that product designers have some experience with the structure and material selection. The main application of the fence terminal is: power supply, relay (especially double-layer terminal), frequency converter, elevator industry (less), air conditioning.
The requirements of this series of terminals are that the torque of the screw is required to be higher when the wire is pressed, the distance from the screw to the highest position is greater than the maximum pressure line range, and the terminal with a long number of digits cannot be warped.
Screws require higher corrosion resistance.
Another: With the beginning of China's 3C certification system, the country has put forward higher requirements for the safety and electromagnetic compatibility of electrical products. The related standards are: GB16836-2003 "General Requirements for the Safety Design of Measuring Relay Protection Devices" , GB/T14598.3-1993 "Insulation test of electrical relays", JB/T 9568-2000 "General technical conditions for power system relays, protection and automatic devices", International Standard IEC 60255-27 (CD:2002) "Measurement relays and The product safety requirements for protection devices, and the safety items related to GB16836-2003, mainly include: mechanical structure, housing protection, insulation coordination, heat generation, fire test, protection against electric shock, safety signs and safety instructions.
1. Safety requirements for mechanical structure The terminals are required to ensure personal safety in terms of chemical and structural materials and charged moving parts, such as the edges and corners of the housing, hardware burrs, and the connection strength of various parts, even under the conditions of sports and other products. Stability, the above are the requirements of the mechanical structure of the terminal in the power industry.
2, the protection requirements of the shell is mainly the JB/T 9568-2000 protection class requirements, it is mainly divided into two kinds, one is the protection level of solid foreign bodies, one is the water caused by the equipment and products.
3, insulation coordination requirements are mainly based on the use of materials, working voltage and environmental pollution levels, to select the electrical clearance and creepage distance, thereby protecting the safety of workers and product work, but also make the product in the over-voltage does not occur insulation damage .
4. The requirements of leakage tracking index, the product in the course of use due to the surface of the solid insulating material in the role of the electric field and the electrolyte, the formation of conductive pathways, so that the insulating properties of the insulation of the shell decline, affecting the safety of the product. If the creepage index is high under the same insulation voltage level, the creepage distance of the product can be reduced. If our products enter the power industry, research and development should pay full attention in this regard.
5, the deformation requirements of thermoplastic materials in the work, it is mainly on the temperature rise and contact resistance of the terminal in the work, it caused by the high temperature deformation of the shell becomes soft, so that electrical short circuit, causing serious accidents, so the terminal load The choice of flow component material is significant.
6, anti-electric shock requirements, the structure of the operating element should not be charged, with the internal connection of the terminal should not be touched, this area is mainly the reliability of the screw torque requirements should be to prevent the screw with the terminal, Unexpected loose wire and short circuit. If grounding terminal requirements: Class I safety products, grounding resistance should not exceed 0.5Ω.
(6) For molds, at least almost all the important components in the connector industry are achieved through molds. High efficiency, good accuracy, and easy maintenance. The main surfaces of the terminals are mainly plastic molds and metal continuous molds, and plastic molds. Aspect: mainly in the design, first of all, the selection of the product parting surface is very important. He decided the design of the mould's own structure, as well as the design of the side pull core (more can be four sides) the inlet and direction of the plastic injection. The system is also a very important item. As for some structures, the design will be affected by the type of plastic material, the uniformity of the insulation shell structure will affect the mold, inserts on the front mold and the rear mold should avoid the plug-in phenomenon, and be a product. If the design engineer only considers the functions and standards of the product, it will lead to the normal production and appearance of the mold. It is necessary to take into account the manufacturing process of the mold and the molding process of the injection molding machine. The influence of this aspect is also very important: the injection temperature and the forming time , clamping force, injection speed and so on.
(seven) other manufacturing processes, the other parts used in the manufacturing process of the parts are: instrumentation, casting, heat treatment. It is not only the understanding of the above processes, but more importantly, it is necessary to accumulate experience, sum up in time, and gradually. Therefore, greatly improving the quality of product project engineers in R&D and increasing the project engineer's responsibility for the management system are the keys to achieving product development.
The above just talked about some of my own experience from the design point of view. If there are any mistakes, please go ahead!
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