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The related processes of vacuum introduction with silicone rubber

Writer:adminSource: Date:2020-06-30

With the development of society, various kinds of carbon fiber products also emerge as the times require because of their high strength, light weight and good performance. Compared with other processes in mechanical properties, the principle of vacuum import composite material processing method has obvious advantages. Next, the production process of vacuum import process is briefly introduced.

Aiming at the glass fiber reinforced plastic (FRP) vacuum lead-in process, the manufacturing process of composite materials is constantly improved and innovated. From the beginning, hand paste has developed to mechanized spraying, pultrusion, molding, and then to the current vacuum introduction process. The related processes of vacuum introduction include resin transfer molding (RTM), vacuum assisted RTM (VARTM), vacuum bag pressing, scrimp, SRIM (structural reaction molding), RTI (resin film infiltration). Each process has its own special features. Today, we only introduce vacuum induction

1. Vacuum infusion process (VIP)

Vacuum leading in process, referred to as VIP, is to lay reinforcing materials (glass fiber, carbon fiber, sandwich material, etc.) on the mold, and then lay the vacuum bag, and use the vacuum to extract the air in the system to form a negative pressure in the mold cavity, and use the pressure generated by the vacuum to press the unsaturated resin into the fiber layer through the pre laid pipeline After curing, remove the vacuum bag material and get the required products from the mold. VIP uses a single side mold (like the usual hand paste and spray mold) to establish a closed system.

Vacuum lead-in technology has been patented since 1950 (according to the records of relevant books on the Internet), and it has not been widely used. It has only been developed in recent years. This process was introduced from abroad. There are many names for this process: Vacuum introduction, vacuum infusion, vacuum injection, etc.


2. Vacuum introduction theory

Vacuum induction process can be widely used. Its theoretical basis is Darcy's law

Darcy's law) t = ℓ 2H / (2 KDP), t is the introduction time, which is determined by four parameters; H-resin viscosity.

From the formula, it can be seen that the lower the viscosity of the resin used, the shorter the lead-in time is required. Therefore, the viscosity of the resin used in vacuum introduction should not be too high. To make the resin quickly fill the whole mold. ℓ - injection length refers to the distance between the resin feed port and the outlet port. The distance is long and the time required is also long. DP - pressure difference, the greater the pressure difference between inside and outside the system, the greater the driving force on the resin, the faster the resin flow rate, of course, the shorter the lead-in time. K = permeability, which refers to the parameters of glass fiber, sandwich material and so on. If K value is high, it means that the infiltration is good. For example, multi-directional felt is more likely to be infiltrated by resin than that of gabion. Therefore, in order to make the resin more convenient to fill the system when the reinforcing material is compacted, people usually set up some diversion grooves, such as punching holes on the sandwich foam.


3. Advantages of vacuum introduction

In the usual hand lay up process, the reinforcement material is placed in the mold, and the reinforcement material is soaked manually by brush, roller or other methods. In this process, the improved method is to use a vacuum bag to suck out the excess resin in the layer. With the increase of glass fiber content, higher strength and lighter products can be obtained. VIP has many advantages over the traditional process, such as hand paste, vacuum bag and vacuum import. In terms of mechanical properties, vacuum induction has obvious advantages.

From this we can see the advantages of vacuum introduction

A higher quality products: resin impregnated glass fiber in vacuum environment, compared with traditional manufacturing process, there are few bubbles in the products. There is no extra resin left in the system, and the glass fiber content is very high, which can reach 70% or even higher. The product has lighter weight and higher strength. It is also very stable between batches.


B less resin loss: with VIP process, the amount of resin can be accurately estimated. For hand paste or spray process, it will be difficult to control due to the variability of operators. VIP can minimize the loss of resin, and more importantly, it can save cost.


C uniform distribution of resin: for a product, the pressure produced by different parts of vacuum is the same, so the infiltration rate and content of resin on glass fiber tend to be consistent. This is critical for FRP parts with stable weight requirements.
D process less volatile: there is no brush or roller in the production process, which will not cause the phenomenon of resin splashing or dripping, and there will be no large amount of odor. Therefore, it can provide a clean, safe and friendly working environment to protect the physical and mental health of operators.
E use of single side mold: only one side mold can get smooth and smooth products on both sides, which can better control the thickness of products. Save mold manufacturing cost and time.
Because of the advantages of the products made by VIP technology, they were first used in aerospace and other special fields, and then slowly applied to high requirements of civil products.
Application fields of VIP process
1) Shipbuilding industry - hull, deck, rudder, radar shield
2) Wind energy - blade, hood
3) Sports leisure - helmets, windsurfing
4) Automotive industry - all kinds of roof, windshield, carriage
5) Construction field - building roof components, building formwork
6) Agriculture and Horticulture - barn round cover, agricultural machinery protective cover
4.1 VIP materials
4.1.1 resin
When preparing to start the vacuum lead-in test, it is necessary to select the appropriate resin, epoxy resin or unsaturated polyester resin. The resin for vacuum induction process can not be replaced by ordinary resin. It has special requirements for viscosity, gel time, exothermic peak, wettability and so on, which can be consulted specifically by resin supplier.
4.1.2 curing system
If it is epoxy resin, its corresponding special curing agent should be used; the commonly used curing agent for unsaturated resin is methyl ethyl ketone peroxide. The quality of different manufacturers is different, so the evaluation of the selection should not affect the quality of the whole product because of the small amount of materials.
4.1.3 reinforcing materials
Glass fiber and carbon fiber are commonly used as reinforcement materials. For example, compound seam felt, single cloth, etc., should be designed according to mechanics. When selecting, it is better to do some experiments, how about the permeability, because the size of the fiber used in the manufacturing process, the different adhesive, the infiltration of resin will be different, resulting in the mechanical properties of the final product will be very different.
4.1.4 sandwich materials
Commonly used are carbon fiber, glass fiber, Balsa wood, PVC foam, PUR/PIR foam, felt and so on. According to the needs of the products, select the appropriate sandwich materials.
4.1.5 equipment and auxiliary materials
Vacuum pump, interface, pressure gauge, guide pipe, demoulding cloth, guide cloth, vacuum bag, etc. The materials used in vacuum lead-in process can not be used casually. Each kind of material should be confirmed by experiment to judge whether it is applicable.
To sum up, a key step of vacuum introduction is the need for a vacuum bag as an auxiliary accessory. How is the vacuum bag made?
In the past, the film was used as a vacuum bag in the process of operation. To the present development, more and more liquid silica gel is selected as the vacuum bag production in the vacuum introduction. Shenzhen hongyejie Technology Co., Ltd. has the requirement of high temperature resistant liquid silica gel compound. Please consult for detailed operation!

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