Experiment § Reasons for shrinkage of molded resin
Many heavy electrical facilities use epoxy resin to provide insulation properties, such as current transformers, voltage transformers, and transformers. We occasionally receive this kind of customer feedback about the uneven surface of the epoxy resin after curing. Analysis of the reasons can often be attributed to the shrinkage of epoxy resin. During the curing process, the resin changes from liquid to solid, so there will be a shrinkage phenomenon of volume reduction. We can add appropriate inorganic powder (for example quartz powder) to the resin to reduce the proportion of organic resin so that shrinkage can be reduced. Another factor that causes shrinkage is related to the baking temperature. The resin solidifies directly at high temperature (>110°C) and shrinks more severely after cooling to room temperature. If it is baked at a low temperature (80~90℃) first, and then the temperature is increased to increase the reaction rate, the shrinkage of the latter process will be smaller. In addition to affecting the appearance of molded resin shrinkage, special attention should be paid to the performance of the molded product. The thermal expansion coefficients of metal materials and epoxy resins in heavy electrical equipment are different, and the reaction of thermal expansion and contraction will be different. Rapid and dramatic changes in temperature often cause resin cracking, or peeling between two materials, and destroy the electrical properties of the product. Slowly cooling down after baking can reduce the shrinkage stress between the two and avoid this phenomenon.
─Author: Mrs. Yun-Xian Liu, Assistant R&D Engineer Everwide Chemical
Activity § The sub-assembly process in the cleanroom
During the manufacturing process, impurities may be mixed into the product due to unclean raw materials or the manufacturing environment. Generally, we will use filter mesh or filter bag to filter to remove impurities in the product. For some precision electronic applications, we will carry out the final filtration and packaging in the cleanroom to completely eliminate dust pollution. The current cleanroom of Everwide is 100,000 class. We use a multi-tube filter element to filter the product, and after the product is repackaged, use light to carefully check whether there are impurities in the hose. Through everyone's efforts and the installation of clean rooms, many of Everwide's products have met the strict requirements of the electronics industry, and many cases have proved that we can provide the most "clean" materials with the smallest particles in the market.
Knowledge § What are the principles of defoamers and wetting agents?
1. The principle of defoamer: There are often some foam-stabilizing substances in the resin, which will increase the strength of the bubble liquid film and cause the bubbles to be stable and not easy to burst. Most defoamers are substances with very low surface tension, which are easy to spread on the surface of the liquid, absorb the foam-stabilizing substances, and make the liquid film of the bubbles thin locally, causing the bubbles to burst. The most common defoamers are silicone or copolymers of silicone and other structures. Since the role of the defoamer occurs on the surface of the liquid, the compatibility of the defoamer and the liquid is the key to the defoaming performance. When the compatibility between the defoamer and the liquid is good, the defoamer is not easy to run on the surface of the liquid, so the defoaming performance is not good. A system with poor compatibility will have better defoaming properties, but it may cause other defects such as surface defects, oily surfaces, and difficulty in adhesion coating after the resin is cured. The principle of defoaming is very simple, but it takes a lot of experimentation to choose an appropriate defoaming agent. 2. The principle of the wetting agent is that the liquid with high surface tension cannot spread on the solid surface with low surface tension. In order to improve this phenomenon, some surfactants can be added to the liquid to reduce the surface tension. And this kind of surfactant is called a wetting agent. The molecule of the wetting agent is composed of two segments of high polarity and low polarity. The high polarity segment is compatible with the liquid, and the low polarity segment points to the external environment, which can achieve the purpose of reducing surface tension. The method of evaluating the wettability is very simple, as long as a specific weight of liquid (for example 50mg) is dropped on the surface of the substrate to be evaluated, and after a certain period of time, the maximum surface area (in cm2/g) of liquid diffusion is measured. The larger the diffusion area, the better the wetting capacity.
Living § "Self-assessment": the master's tricks
Boss Chen told me that a student's score in the joint entrance examination depends on his performance when he walks out of the examination room. He said that students with average grades think that they will solve many problems in the exam, but the fact is that their results are not ideal. This kind of student usually needs to see the answer to know that they have done a wrong question and have deducted five points, and finally send out the transcript to find that the test result is far less than expected. What about students with good grades? When they write the test papers, they will have intuition. They will feel that the answers to many questions are weird. They also need to check the test papers to prevent blank spaces. Once they walk out of the test room, they feel that they have done a lot of wrong questions and they feel that they will fail the exam. Usually, students with this kind of performance have good scores in the entrance exam, because only those who are good at exams can have a delicate intuition and quickly know whether their exam results are good or not. Boss Chen said that this method of predicting the results of the entrance exam was his own personal experience, as well as observations of a large number of relatives, friends, and younger generations. My own two entrance exam experiences and Boss Chen’s comments are quite consistent. My junior high school grades are intermediate. According to the school mock test, I may not be able to pass the first two choices and I can only pass the fourth choice. Surprisingly, on the day of the senior high school entrance examination, the test paper felt like a godly help. The next day I read the answers published in the newspaper and was generally good. I thought I could get admitted to Taipei Municipal Chien-Kuo Senior High School by luck. When I saw the list, I returned to reality, and I only passed the fourth choice. When I was in the third grade of high school, my grades were always in the second or third place in the class. In theory, I could pass the university entrance exam steadily. However, during the entrance exam, I always felt that my writing was not good enough. Especially for the first math test, I knew when I was writing that there was a problem set that was incorrectly calculated, but there was not enough time to recalculate, and my mood for the test was greatly affected. I felt that the three years of hard work were in vain. Only after I received the transcript did I know that I was doing pretty well in the exam. From another perspective, I am too strict with myself. Yes, high-level people mostly adopt stricter standards, repeatedly "self-evaluate" and spur themselves to reflect on their progress, so they can achieve better results. People with low ability have relatively loose "self-assessment" standards and low frequency of self-assessment, because when they simply self-identify as qualified, of course, many of them have unsatisfactory performance. This is true for exam experience, and so is work experience.
─Author: Dr. Ming-Xu Li, Everwide Chemical
