Home > Knowledge > Content

What is difference between vacuum process and hand lay up processs for unsaturated polyester resin ?

Jan 23, 2019

The process of introducing vacuum into the resin is to spread the “dry” reinforcing material (glass fiber, carbon fiber, sandwich material, etc., different from the vacuum bag process) on the mold, then vacuum the bag and withdraw the vacuum in the system in the mold cavity. Forming a negative pressure, using the pressure generated by the vacuum to press the unsaturated resin into the fiber layer through the pre-laid pipe, allowing the resin to infiltrate the reinforcing material and finally filling the entire mold. After the product is solidified, the vacuum bag material is removed and obtained from the mold. The required product, VIP uses a single-sided mold (like the usual hand lay-up and spray mold) to establish a closed system, the vacuum introduction process has been published for a long time, this process appeared in the patent record in 1950, however, knowing the near It took only a few years to develop. Since this process is introduced from abroad, there are various names in the naming, vacuum introduction, vacuum infusion, and vacuum injection. Vacuum introduction resin process.

The hand lay-up process is an open mold process and currently accounts for 65% of glass fiber reinforced polyester composites. His advantage is that there is a great deal of freedom in the shape change of the mold, the mold price is low, the adaptability is strong, the product performance is recognized by the market and the investment is small. It is especially suitable for small companies, but also for the marine and aerospace industries, which are usually one-off large parts. However, the process also has a series of problems, such as excessive emission of volatile organic compounds (VOC), great impact on the health of operators, loss of personnel, limited use of materials, low product performance, waste of resin and large amount of consumption, especially The product quality is unstable, the glass fiber and resin ratio of the product, the thickness of the part, the manufacturing rate of the layer, and the uniformity of the layer are all affected by the operator, and the operator is required to have better technology, experience and quality. The resin content of the hand lay-up product is generally from about 50% to about 70%. The VOC emission of the mold opening process exceeds 500 ppm, and the volatile amount of styrene is as high as 35% to 45% of the amount used. The national regulations are all 50-100PPm. At present, most of the foreign countries have switched to cyclopentadiene (DCPD) or other low styrene release resins, but styrene as a monomer has not been a 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) The product has excellent performance and high yield. In the case of the same raw material, the strength, rigidity, and other physical properties of the vacuum resin introduction process molding member can be increased by 30% to 50% or more as compared with the hand lay-up member. After the process is stable, the yield can be close to 100%. Increased glass fiber content for higher strength and lighter weight, VIP has many advantages over traditional processes. (2) The product quality is stable and the repeatability is good. Product quality is less affected by the operator, whether it is the same component or a high degree of consistency between the components. The fiber content of the product has been put into the mold according to the specified amount before the resin is injected. The component has a relatively constant resin ratio, generally 30%-45%, so the uniformity and repeatability of the product performance is better than the hand lay-up process product. Many, the defects are much less, the resin infiltrates the glass fiber in a vacuum environment, and there are few bubbles in the product compared with the conventional manufacturing process. (3) The anti-fatigue performance is improved, and the structural weight can be reduced. Due to the high fiber content, low porosity, high product performance, especially the improvement of interlayer strength, the fatigue resistance of the product is greatly improved. In the case of the same strength or stiffness requirements, the product made by the vacuum introduction process can reduce the structural weight. It is possible to minimize the loss of the resin and, more importantly, to save costs. (4) The environment is friendly. The vacuum resin introduction process is a closed mold process in which volatile organic compounds and toxic air pollutants are confined to a vacuum bag. There is only a trace amount of volatiles when the vacuum pump is vented (filterable) and the resin barrel is opened. VOC emissions do not exceed the standard of 5PPm. This has greatly improved the working environment of the operators, stabilized the team of laborers, and expanded the range of available materials; (5) The product integrity is good. The vacuum resin introduction process can simultaneously form the reinforcing ribs, the sandwich structure and other inserts, thereby improving the integrity of the product, and thus can manufacture large-scale products such as a fan hood, a hull and a superstructure; (6) reducing the use of raw materials and reducing labor. When the same layer is applied, the amount of resin is reduced by 30%. Less waste, the resin loss rate is less than 5%. High labor productivity, saving more than 50% of labor compared to hand lay-up. Material and labor savings are even more impressive when forming large and complex geometries of sandwiches and reinforced structural members. The smooth and flat products on both sides can be obtained with only one mold, which can better control the thickness of the product. Save mold manufacturing costs and time. For example, in the vertical rudder manufacturing of the aerospace industry, the cost of fasteners is reduced by 365 by 75% compared with the conventional method, the weight of the product is unchanged, and the performance is better. (7) The precision of the product is good. The dimensional accuracy (thickness) of the vacuum resin introduction process product is superior to that of the hand lay-up product. Under the same layup, the thickness of the general vacuum resin diffusion technology product is 2/3 of that of the hand lay-up product. The product thickness deviation is about 10%, and the hand lay-up process is generally 20%. The flatness of the surface of the product is better than that of the hand lay-up product. The inner cover of the hood product of the vacuum resin introduction process is smooth, and the surface naturally forms a resin-rich layer, and no additional top coat is required. Reduces labor and materials for the grinding and painting process.

The resin vacuum introduction process also has certain disadvantages; (1) The preparation process is long and complicated. Requires proper layup, laying of diversion media, draft tube, effective vacuum sealing, etc. Therefore, for small-sized products, the process time is more than the hand lay-up process. (2) The production cost is high and more waste is generated. Auxiliary materials such as vacuum bag film, flow guiding medium, release cloth and guiding tube are all used once, and at present, quite a lot of imports are dependent on, 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 auxiliary materials that can be used multiple times in the current research are a development direction of the process. (3) There are certain risks in process manufacturing. Especially for large and complex structural products, once they fail in resin infusion, the products are easy to be scrapped; therefore, there must be better 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 to increase the material cost, but this part can reduce the balance of the resin dosage. In addition, the skill requirements of the operator are higher. Each process is carefully followed by steps to enter the next step, otherwise it will cause irreversible losses. However, people have a large demand for higher performance materials, vacuum introduction process is being recognized and adopted by more and more people.

Neweco 二维码QuanZhou Neweco High Polymer Material Co.,Ltd.


Neweco is one of the leading unsaturated polyester resin manufacturers and  suppliers,widely used in automobiles, ships, rail transit, wind power  generation, pipe cans, heat and corrosion protection, building  materials, stone repair, sanitary ware, artificial stone and other  industries. Suitable for hand lay-up, spray, pultrusion, winding,  molding, vacuum introduction / RTM, casting and other molding processes. Neweco Resin is committed to excellence and focuses on the application  of composite materials to provide customers with comprehensive  solutions.

TEL:   86-595-22639779