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The Difference Between Unsaturated Polyester Resin Vacuum Introduction Process And Hand Lay-up Process

Jul 13, 2020

The process of vacuum introducing resin is to lay "dry" reinforcement materials (glass fiber, carbon fiber, sandwich material, etc., different from the vacuum bag process) on the mold, then lay the vacuum bag, and extract the vacuum in the system in the mold cavity A negative pressure is formed, and the pressure generated by the vacuum is used to press the unsaturated resin into the fiber layer through the pre-paved pipeline, so that the resin infiltration reinforcement material finally fills the entire mold. After the product is cured, the vacuum bag material is removed and obtained from the mold For the required products, VIP uses a single-sided mold (like the usual hand lay-up and injection molds) to establish a closed system. The vacuum introduction process has been known for a long time. This process has a patent record in 1950. However, it is known that It took only a few years to develop. Since this process was introduced from abroad, there are various names for naming, vacuum introduction, vacuum infusion, and vacuum injection. Vacuum introduction of resin process

The hand lay-up process is a mold-opening process and currently accounts for 65% of the glass fiber reinforced polyester composite materials. His advantage is that he has great freedom in changing the shape of the mold, the mold price is low, the adaptability is strong, the product performance is recognized by the market, and the investment is low. Therefore, it is particularly suitable for small companies, but also for the marine and aerospace industries, where large parts are usually disposable. However, the process also has a series of problems, such as excessive emissions of volatile organic compounds (VOCs), large impact on the health of operators, easy loss of personnel, many restrictions on allowable materials, low product performance, waste of resin and large dosage, etc., especially The quality of the product is unstable. The ratio of the glass fiber to the resin, the thickness of the component, the manufacturing rate of the layer, and the uniformity of the layer are all affected by the operator. The operator is required to have good technology, experience and quality. The resin content of hand lay-up products is generally around 50%-70%. The VOC emission of the mold opening process exceeds 500PPm, and the volatile amount of styrene is as high as 35%-45% of the used amount. The national regulations are 50-100PPm. At present, most foreign countries use cyclopentadiene (DCPD) or other low styrene release resins, but styrene as a monomer has no good substitute.

The resin vacuum introduction process is a low-cost manufacturing process developed in the past 20 years, and is particularly suitable for the manufacture of large-scale products. (1) Excellent product performance and high yield. In the case of the same raw materials, the strength, stiffness and other physical characteristics of the vacuum resin introduction process molding member can be increased by more than 30%-50% compared with the hand lay-up member. After the process is stable, the yield can be close to 100%. The increased glass fiber content results in higher strength and lighter products. VIP has many advantages over traditional processes. (2) The product quality is stable and the repeatability is good. The product quality is less affected by the operator, and there is a high degree of consistency between the same component and each component. The fiber amount of the product has been put into the mold in a prescribed amount before the resin is injected. The component has a relatively constant resin ratio, generally 30% to 45%, so the uniformity and repeatability of the product performance is better than the hand lay-up process product. There are more defects, and there are far fewer defects. The resin infiltrated the glass fiber under the vacuum environment. Compared with the traditional manufacturing process, the product has very few bubbles. (3) The anti-fatigue performance is improved, which can reduce the weight of the structure. Due to the high fiber content, low porosity, and high product performance, especially the increase in interlayer strength, the anti-fatigue performance of the product is greatly improved. In the case of the same strength or rigidity requirements, the products made by vacuum introduction process can reduce the structural weight. Can minimize the loss of resin, more importantly, this can save costs. (4) Environmentally friendly. The vacuum resin introduction process is a closed-mold process, and both volatile organic compounds and toxic air pollutants are confined to the vacuum bag. There is only a small amount of volatiles when the vacuum pump is exhausted (filterable) and the resin drum is opened. VOC emissions do not exceed the standard of 5PPm. This also greatly improves the working environment of the operator, stabilizes the workforce, and expands the range of available materials; (5) The product has good integrity. The vacuum resin introduction process can simultaneously form reinforcement ribs, sandwich structures and other inserts, which improves the integrity of the product, so it can manufacture large products such as fan hoods, hulls and superstructures; (6) Reduce the use of raw materials and labor. In the same layer, the resin dosage is reduced by 30%. Less waste, resin loss rate is less than 5%. The labor productivity is high, which can save more than 50% of labor than the hand lay-up process. Especially when molding large-scale complex geometric cores and reinforced structural parts, the material and labor savings are even more considerable. Only one side of the mold can be used to obtain smooth and flat products on both sides, which can better control the thickness of the product. Save mold manufacturing costs and time. For example, in the manufacture of vertical rudders in the aerospace industry, the price of fasteners is reduced by 365 pieces and the price is reduced by 75% compared with traditional methods. The product weight remains unchanged and the performance is better. The dimensional accuracy (thickness) of vacuum resin introduction process products is better than hand lay-up products. Under the same layer, the thickness of general vacuum resin diffusion technology products is 2/3 of the hand lay-up products. The thickness deviation of the product is about ± 10%, while the hand lay-up process is generally ± 20%. The flatness of the product surface is better than the hand lay-up products. The inner wall of the hood product in the vacuum resin introduction process is smooth, and a resin-rich layer is naturally formed on the surface, and no additional top coat is required. Reduce the labor and materials of the grinding and painting process.

The resin vacuum introduction process also has certain disadvantages; (1) The preparation process takes longer and is more complicated. Requires correct layup, flow guide medium, flow guide tube, effective vacuum seal, etc. Therefore, for small-sized products, the process time exceeds the hand lay-up process. (2) The production cost is higher and more waste is generated. Auxiliary materials such as vacuum bag film, flow-guiding medium, release cloth and flow-guiding tube are all disposable, and currently rely on imports quite a lot, so the production cost is higher than the hand lay-up process. But the bigger the product, the smaller the difference. With the localization of auxiliary materials, this cost difference is getting smaller and smaller. The current research on auxiliary materials that can be used multiple times is a development direction of this process (3) process manufacturing has certain risks. Especially for large and complex structure products, once they fail in resin infusion, the products are easy to be scrapped; therefore, there must be good preliminary research, strict process control and effective remedial measures to ensure the success of the process.

Both the resin vacuum introduction process and the hand lay-up process have their own advantages. At present, a large part of the disposable consumables required for vacuum introduction need to be imported, which increases the material cost, but this part can be balanced by reducing the amount of resin. In addition, the skill requirements of the operator are higher. Each process must be done carefully according to the steps before proceeding to the next operation, otherwise it will cause irreversible losses. However, there is a large demand for higher performance materials, and the vacuum introduction process is being recognized and adopted by more and more people.