Dispensing Machine Manufacturer: How to Solve Core Fracture Issues?

Question: How to solve the problem of magnetic core breakage in dispensers? The magnetic core always breaks during the cycle after the product is glued. We have tried magnetic cores from many manufacturers, but the breakage still occurs. Is it a problem with the glue or the magnetic core?

Below is the response from the technical staff at Jiuju Automation, hoping to help you!

Response 1: It is best to specify where the glue is dispensed and where the breakage occurs. Generally, if the magnetic core breaks after dispensing, and the cause is the glue, the breakage will occur at the center pillar where glue is applied—especially when hard glue is used, which pulls and cracks the center pillar of the magnetic core. If no glue is applied to the center pillar, or if soft glue is used but breakage still happens, the magnetic core is highly likely to be the cause. Additionally, if the baking temperature is too high, it is recommended to lower the oven temperature. The glue may also be problematic, and an experiment can be conducted to verify: use the same type of glue with the same volume, apply it to magnetic cores from different manufacturers, bake them at the same temperature for the same duration, and check for breakage after taking them out. If all cores break, the issue is unrelated to the magnetic cores; otherwise, the magnetic cores are the cause. Factors that directly affect this problem include the surface tension of the glue after baking shrinkage, baking temperature, cooling method (try not to use a large exhaust fan for rapid cooling immediately after taking the cores out of the oven), and the material of the magnetic cores.

Response 2: After the magnetic core is glued by the dispenser, the glue will shrink in volume during the curing process, which creates residual stress inside the magnetic core. When this residual stress is relatively large, cracks are likely to form and lead to breakage—especially at stress concentration points of the magnetic core (such as the root and corners). Therefore, the damage to the magnetic core is related to both the magnetic core itself and the glue. Common solutions are as follows:

Response 3: Pay attention to controlling the amount of glue dispensed. Slowing down the aging rate and lowering the aging temperature will help improve the situation!

Response 4: Ferrite material is a type of ceramic material, whose thermal conductivity and flexural resistance are both inferior to those of metal materials. Thermal expansion and contraction easily generate stress inside the magnet—especially after the magnetic core is glued. Due to the inconsistent thermal expansion coefficients of the magnetic core and the colloid, the magnetic core expands and contracts unevenly during high-low temperature cycles, which further creates stress inside the magnet. If this stress reaches the limit of the magnetic core's flexural strength, the core will break. Recommended solutions: select glue with a thermal expansion coefficient similar to that of the magnetic core; extend the glue curing time to reduce stress caused by glue curing.

The above are the responses. Has this resolved your confusion? Be sure to pay attention to these issues when using the dispenser for gluing operations.

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