The RTM process has good moldability, wide composite freedom of the reinforcing material and the matrix resin, and can improve the operating environment and the like, and there is no problem of volatilization of the organic solvent and the glass fiber. However, due to the process method, the reinforcing material used must be pre-formed before it is placed into the forming die, so that the process method is popularized relatively late. In order to solve the problem of preforming of reinforcing materials, various preforming technologies are being developed abroad, and even RTM methods that do not require preforming have been developed. These improved RTM methods can not only greatly improve operability, but also further improve the operating environment. This article will introduce an improved RTM method developed by the Institute of Industrial Technology, Toyama Prefecture, Japan, which can increase production capacity.
The principle of the improved RTM method is to use the reinforcing material braid to have better flexibility. After the mold is closed, the reinforcing material can self-elongate in the cavity and be closed and fixed, so as to achieve the purpose of reinforcing the material preform. Reinforcing materials such as glass fiber, aramid fiber, and carbon fiber have good reinforcement and low elasticity. However, since the knitted fabric itself has stretchability, a low-stretchable fiber can be used to weave a stretchable fabric. If the fabric is to be added, it is placed on the female mold of the mold and then the ends are fixed. After the male mold is closed, the reinforcing material is stretched and formed in the cavity, and then the resin is injected and cured. With this method, the reinforcing material can be closed and fixed in a forming mold of any shape, the preforming apparatus can be changed without changing the forming mold, and a glass steel product with a relatively complicated shape can also be produced.
In general, the structure of the fiber bundles of the braid has a great influence on its stretchability. According to the direction of the fiber bundles, the braids can be divided into two major categories, horizontal and vertical. The knitting machines commonly used in the family are flat knitting machines, and sweaters, socks, etc. are all of horizontal knitting fabrics. Longitudinal preparation requires the preparation of warp yarn, and the production machine is large. A factory with a certain scale can produce it. Compared with the horizontal knitting, its productivity is higher.
At present, the speed of production of the fastest knitting machine is 2,000 rpm (normal knitting machine is 1.2 rpm). With vertical weaving, there is no problem with the unwrapping of lines like the horizontal knitting.
For the woven fabric used in the RTM process, both horizontal and vertical woven fabrics are acceptable. The modified RTM method uses a vertical weave. The knitting machine can weave fabrics with a thickness of a few millimetres up to 50 millimetres. These braids can be used as RTM reinforcements. Since this type of woven fabric no longer requires a lamination, it can be formed using a single woven fabric, so that there is no delamination phenomenon of the reinforcing material. The knitted fabric is composed of a table, an inner code, an intermediate layer, and the like. The strength, stretchability, and directionality of the knitted fabric vary depending on the composition conditions.
When molding RTM, first prepare the mold. When the mold is closed, it is necessary to fix the end of the reinforcing material to the female mold so that the reinforcing material does not separate from the inside of the mold. When fixing, pin-like clamps can be used, or pins can be placed directly on the female mold. The size of the pin and its configuration must take into account the degree of expansion and end tension of the reinforcing material. From the operation point of view, when the pins are arranged with the female film, the mold is easily closed, and the mold release property after the resin is cured is also good. When a semi-three-dimensional structure is used, it is difficult to remove the air in the intermediate layer after injecting the resin. Therefore, after in-mold vacuum degassing, it is preferable to inject resin or pressurize the injected resin.
The principle of the improved RTM method is to use the reinforcing material braid to have better flexibility. After the mold is closed, the reinforcing material can self-elongate in the cavity and be closed and fixed, so as to achieve the purpose of reinforcing the material preform. Reinforcing materials such as glass fiber, aramid fiber, and carbon fiber have good reinforcement and low elasticity. However, since the knitted fabric itself has stretchability, a low-stretchable fiber can be used to weave a stretchable fabric. If the fabric is to be added, it is placed on the female mold of the mold and then the ends are fixed. After the male mold is closed, the reinforcing material is stretched and formed in the cavity, and then the resin is injected and cured. With this method, the reinforcing material can be closed and fixed in a forming mold of any shape, the preforming apparatus can be changed without changing the forming mold, and a glass steel product with a relatively complicated shape can also be produced.
In general, the structure of the fiber bundles of the braid has a great influence on its stretchability. According to the direction of the fiber bundles, the braids can be divided into two major categories, horizontal and vertical. The knitting machines commonly used in the family are flat knitting machines, and sweaters, socks, etc. are all of horizontal knitting fabrics. Longitudinal preparation requires the preparation of warp yarn, and the production machine is large. A factory with a certain scale can produce it. Compared with the horizontal knitting, its productivity is higher.
At present, the speed of production of the fastest knitting machine is 2,000 rpm (normal knitting machine is 1.2 rpm). With vertical weaving, there is no problem with the unwrapping of lines like the horizontal knitting.
For the woven fabric used in the RTM process, both horizontal and vertical woven fabrics are acceptable. The modified RTM method uses a vertical weave. The knitting machine can weave fabrics with a thickness of a few millimetres up to 50 millimetres. These braids can be used as RTM reinforcements. Since this type of woven fabric no longer requires a lamination, it can be formed using a single woven fabric, so that there is no delamination phenomenon of the reinforcing material. The knitted fabric is composed of a table, an inner code, an intermediate layer, and the like. The strength, stretchability, and directionality of the knitted fabric vary depending on the composition conditions.
When molding RTM, first prepare the mold. When the mold is closed, it is necessary to fix the end of the reinforcing material to the female mold so that the reinforcing material does not separate from the inside of the mold. When fixing, pin-like clamps can be used, or pins can be placed directly on the female mold. The size of the pin and its configuration must take into account the degree of expansion and end tension of the reinforcing material. From the operation point of view, when the pins are arranged with the female film, the mold is easily closed, and the mold release property after the resin is cured is also good. When a semi-three-dimensional structure is used, it is difficult to remove the air in the intermediate layer after injecting the resin. Therefore, after in-mold vacuum degassing, it is preferable to inject resin or pressurize the injected resin.
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