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Application of the empty import process

Update:06-03-2020
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Abstract: Vacuum introduction is a recently emerging me […]

Abstract: Vacuum introduction is a recently emerging method for processing composite materials. This article introduces the principle of vacuum introduction technology and compares its mechanical properties with other processes. It explains the advantages of products made by vacuum introduction technology, and at the same time, it introduces the production process. The process was briefly introduced. Vacuum introduced PRP glass fiber  Among the current materials, composite materials are widely used because of their light weight and high strength. The manufacturing process for composite materials is also constantly improving and innovating. From the initial hand layup, to the mechanized spraying, pultrusion, molding and other processes, the vacuum introduction process of is now emerging.

The processes related to vacuum introduction include resin transfer molding (RTM), vacuum assisted RTM (VARTM), Vacuum bag pressure, SCRIMP, SRIM (Structural Reaction Molding), RTI (resin film infusion). But there are some differences, which have been introduced in many articles, so I wo n’t repeat them here. 1. Vacuum  infusion process (VIP) Vacuum infusion process (VIP), referred to as VIP, laying reinforcement material on the mold (glass glass fiber, carbon fiber, sandwich material, etc., different from vacuum bag process), and then Lay a vacuum bag and extract the air in the system. 

Create a negative pressure in the mold cavity. Use the pressure generated by the vacuum to press the unsaturated resin into the fiber layer  through the pre-laid pipe to let the resin infiltrate the reinforcing material and finally fill the whole. After the mold and the product are cured, the vacuum bag material is removed to obtain the desired product from the mold. VIP uses a single-sided mold (like the usual hand lay-up and spray mold) to build a closed system. The vacuum infusion process has been known for a long time, and this process was patented in 1950. However, it has not been rampant until recently. Since this process was introduced from abroad, it has various names in terms of name, vacuum introduction, vacuum infusion, and vacuum injection. 2 . Theory The vacuum introduction process can be widely used and has its theoretical basis. This is Darcy ’s Law. T = ℓ 2h / (2 kDP) t is the introduction time, which is determined by four parameters. H- resin viscosity, it can be seen from the formula that the lower the viscosity of the resin used, the shorter the introduction time is required, so the viscosity of the resin used for true introduction is generally not too high.

This allows the resin to quickly fill the entire mold. ℓ-The injection length refers to the distance between the resin inlet and the outlet. The longer the distance, of course, the longer the time is. DP- pressure difference,  The larger the pressure difference between the inside and outside the system, the greater the driving force for the resin, the faster the resin flow rate, and of course the shorter the introduction time. K = Permeability, refers to the parameters of glass fiber, sandwich material, etc., which are good or bad for resin infiltration. A large value of k indicates good wetting, as multidirectional felt is better than gingham, chopped felt is more easily wetted with resin.

Therefore, in order to make the resin easily fill the system when the reinforced material is compacted, some diversion grooves are generally set artificially, such as punching holes in the sandwich foam. 3. Advantages In the usual hand lay-up process, reinforcement material is spread in the mold, manually infiltrate the reinforcement material with a brush, roller or other means. Another improved method is to use a vacuum bag to suck out excess resin in the laminate when sucking out hand layup. In this way, the high glass fiber content is increased to obtain a higher strength and lighter product. VIP  has many advantages over traditional processes. The figure shows hand layup, vacuum bag and vacuum introduction as examples. Vacuum introduction has obvious advantages in mechanical properties.

 

Hand roll vacuum compression bag

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