Analysis of the causes of small can sealer failures

Common problems of small can sealer products: low partial discharge initial voltage, inter-line sparks, or high-voltage electronic products such as televisions, display line output transformers, automobile and motorcycle ignition devices, which often cause partial discharge (corona), inter-line sparks or breakdown phenomena due to improper packaging process. The high-voltage coil diameter of such small tank sealers is extremely small (usually only 0.02～0.04 mm), and the encapsulation material at the coil gap fails to fully saturate, resulting in a persistent coil gap. Since the gap is much smaller than the dielectric constant of the epoxy resin sealing material, a uniform electric field will be formed under alternating pressure conditions, resulting in partial discharge at the interface, aging of the decomposition material and insulation breakdown.

From a process perspective, there are two reasons for the gaps between wires:

1) The vacuum seal is insufficient and the air between the wires cannot be completely removed, resulting in the material not being fully impregnated.

2) Insufficient preheating temperature before specimen encapsulation prevents the viscosity of the specimen filling material from decreasing rapidly, affecting the penetration effect.

When vacuum sealing or manual packaging is carried out after mixing and degassing, if the material mixing and degassing temperature is too high, the thermal curing process is operated for a long time, or there are too many materials during the application period, making it impossible for small packaged products to enter in time, the viscosity of the material will increase, affecting the coil impregnation. The sealing material of thermosetting epoxy resin composite material has a smaller viscosity when the initial temperature is high, and the viscosity increases more rapidly over time. In order to obtain a good impregnation effect on the coil material, the following points should be paid attention to during operation:

1) The sealing material composite should be kept within the specified temperature range and placed in a suitable environment after use.

2) Heat the sample to the desired temperature before sealing and complete the sealing during the thermal curing process.

3) The vacuum seal meets the requirements of technical specifications.

(2) Problems such as shrinkage, local depression and cracks on the sealing surface. The sealing material shrinks during thermal curing, that is, the phase change from liquid to solid during cooling physically shrinks. During the shrinkage process, the chemical changes during the curing process can be further divided into two categories: The micro-network structure formed by the shrinkage phase produced by the chemical cross-linking reaction after heat sealing is called pre-cured gel shrinkage. The contraction from the gel phase to complete cure is called cure contraction. The shrinkage rates of the two processes are not the same. The former consumes more drastic changes in the physical state of reactive groups during the transition from liquid state to network structure than the latter, and its volume shrinkage rate is also higher than that of the latter. During the gel pre-curing stage (75℃/3 h), the curing reaction of the epoxy groups disappeared at a later stage (110℃/3 h). This is confirmed by the results of the differential thermal analysis (Figure 8-4). The specimens cured to 53% after 750℃/3 hours.

If the specimen seal is cured at high temperature, the two stages of the curing process are too close together, and gel pre-curing and cross-linking curing occur almost simultaneously. This will not only cause excessive exothermic peak damage to the component, but also subject the seal to huge pressure, resulting in product defects inside and outside the small can sealer. In order to obtain excellent components, it is necessary to design and formulate sealing material formulas during the curing process, focusing on solving the problem of matching the curing speed of the sealing material (i.e., the gel time after the A and B components are mixed) with the curing conditions. A common method used in stapling machines is to perform segmented processing on the properties and uses of sealing materials according to the curing process at different temperatures. Color TV Line Output Transformer Splitter Curing at Different Temperatures Heat Release Program and Internal Parts. The temperature of the pre-cured gel seal material in the curing reaction zone increases slowly, the heat of the reaction is gradually released, and the increase in material viscosity occurs in sync with the volume contraction. In the fluid state, the volume shrinkage property level of the phase material continues to decrease until gelation, which can completely eliminate the volume shrinkage stress of the phase. After the gel is pre-cured, gentle heating should also be used during the curing stage. After curing is completed, s

If the specimen seal is cured at high temperature, the two stages of the curing process are too close together, and gel pre-curing and cross-linking curing occur almost simultaneously. This will not only cause excessive exothermic peak damage to the part, but also subject the sealing tape to huge pressure, resulting in product defects inside and outside the small can sealer. In order to obtain excellent components, a sealing material formulation must be designed and formulated during the curing process, focusing on solving the problem of matching the curing speed of the sealing material (i.e., the gel time of components A and B) with the curing conditions. A common method used in stapling machines is to process the properties and uses of the sealing material in sections according to the curing process at different temperatures. The segmented packaging process of color television line output transformers requires curing and exothermic control at different temperatures. The pre-cured gel sealing material slowly heats up in the curing reaction zone, the reaction heat is gradually released, and the increase in material viscosity is synchronized with the volume contraction. The volume shrinkage properties of the phase material in the fluid state gradually decrease until gelation, which can completely eliminate the volume shrinkage stress of the phase. After the colloid is pre-cured, mild heating is still required during the curing stage. After curing is complete, the seal should be slowly cooled and the heating equipment adjusted synchronously to reduce the internal stress distribution through multiple means. The surface of the workpiece should avoid shrinkage, depression or even cracking.

The curing conditions of the sealing material of the small sealing machine also need to be combined with factors such as the layout of the embedded parts, the filling degree and size of the workpiece, the shape, and the sealing ability of the monomer. In the case of internal sealing sites, where there are a large number of monomer seams and fewer parts are to be buried, appropriate pre-curing cooling measures and extended gel time must be taken.