An effective way to improve the environmental adaptability of the load cell is to strengthen the protection and sealing technology and process level, and use Teflon shielded cables with strong waterproof and anti-corrosion capabilities and cables with anti-mouse corrosion capabilities. Summarizing the successful experience of protective sealing of domestic and foreign load cell manufacturing companies, potting and welding sealing in blind holes are important process measures to ensure long-term stable and reliable operation of load cells. The protection and sealing of the load cell is divided into multiple processes. The first step is to apply protective glue to the resistance strain gauge attached to the elastic element. The timing of application and cleaning before application are crucial. Generally, it is carried out after the quality of each process of pasting resistance strain gauges, pressure curing, post-curing, quality inspection, pasting terminals, bonding wire bridges and measuring insulation resistance is qualified. That is, the elastic components after overall cleaning are put into the high temperature test chamber as soon as possible. , heat it to 40°C and keep it warm for a certain period of time, take out the elastic element from the box, and apply protective masking tape under dry environmental conditions. Its purpose is to prevent the resistance strain gauge from getting wet during the production process.
And lay the foundation for final protection and sealing. There are many materials used for the protective coating of resistance strain gauges. The representative one is: M-CoatC type protective coating produced by the American VISHAY company. It is a solvent-diluted RTV silicone rubber. After curing, it forms a tough and elastic transparent film with good mechanical, electrical properties and chemical corrosion resistance. The film thickness of its coating is 0.4 ~ 0.5mm. SN-4 type chloroprene rubber and BARRIER-C type non-corrosive silicone rubber produced by HBM Company in Germany. The second step is to apply the protective surface glue on the resistance strain gauge, and then proceed according to the different structures of the elastic components of the load cell.
Surface sealing, blind hole potting or welding sealing are performed. Welding sealing is an effective way to improve the environmental adaptability of the load cell. Electron beam welding and laser welding are most used. The electron beam welding sealing process of the load cell is based on the electron beam
The welding operation is carried out in the vacuum chamber of the welding machine. The welding process is that the welding machine passes current to heat the cathode, making it an electron gun system that can emit electrons. The electron beam with negative charge flies to the load cell housing at high potential at high speed. , the weld where the sealing module and the elastic element fit together. The focusing system of the welding machine focuses the electron beam and impacts it on a very small area of weld at extremely high speed, converting kinetic energy into heat energy. The finer the focus of the electron beam, the more concentrated the energy. It can raise the temperature of a very small area of the weld to nearly a thousand degrees in a fraction of a microsecond, thereby melting the material to be welded and sealing it. The characteristics of electron beam welding are:
(1) The power density is high, the acceleration voltage range is 30 ~ 150KV, the electron beam current is 20 ~ 1000mA, the electron beam focus diameter is about 0.1 ~ 1mm, and the electron beam power density can reach more than 106W/cm2;
(2) Welding is performed in a vacuum chamber with a pressure of 100 to 1000Pa and is not affected by various pollutants;
(3) During welding, the energy is quickly and highly concentrated, the heat affected zone is small, and the welded parts do not deform;
(4) It has a wide range of applications and can weld various alloy steel, stainless steel and non-ferrous metal materials. The minimum welding thickness is 0.1mm;
(5) After welding, the elastic element or resistance strain gauge is in a vacuum of 100 ~ 1000Pa, which is the best sealing state, and the sealing grade can reach IP68;
(6) There is no welding slag and no need to remove the oxide film.
The laser welding sealing process of the load cell uses a high-energy laser pulse beam for welding on a laser welding machine. The requirements for the welding grooves of the elastic components and the sharp corners of the diaphragm are the same as those for electron beam welding. When welding, the pulse laser power supply first lights the xenon lamp to put it in a pre-ignition state. The computer controls the laser power supply to pulse discharge the xenon lamp, thereby forming a light wave with a certain frequency and a certain pulse width. This light is radiated to the laser crystal through the focusing cavity. And make it emit light, and then emit a laser with a wavelength of 1.06μm after resonating in the laser resonator. After beam expansion, reflection, and focusing, the laser is directed to the weld of the welded load cell. The weld absorbs light energy and locally generates high heat. And melting makes the elastic element, diaphragm and shell melt into one. Characteristics of laser welding
yes:
(1) Laser welding is non-contact welding, and the elastic components can be placed in a transparent vacuum cover to achieve vacuum welding sealing;
(2) The energy is concentrated, the heat affected zone is small, and the welded elastic components, diaphragms and shells do not deform;
(3) Can fuse different metals and alloys, and can complete special-shaped welding of different materials, such as metals and ceramics;
(4) There is no welding slag and no need to remove the oxide film. After electron beam welding or laser welding, the load cell is
Implementing a new process of vacuuming and filling with inert gas (nitrogen) has better protective sealing effect and stronger environmental adaptability. It is an effective way to improve the stability and reliability of the weighing sensor.