Advantages and Disadvantages of Prepreg

• Advantages of prepreg

Maximum strength characteristic. A typical manual ply has a lot of excess resin, which increases Brittleness and reduces overall 

Performance. Most prepregs contain about 35% resin, which is ideal for achieving maximum curing performance, which is usually not

possible with conventional manual lamination.

Uniformity and repeatability. The prepreg is of uniform thickness and each part coming out of the mold may theoretically be the same. Vacuum bagging technology still has some errors in processing, but prepreg can greatly reduce these problems.

Reduce curing time.After the thermal curing cycle, no need to wait for the standard 48 hours can be fully cured.

Looks better.Although prepreg processing still requires mold preparation and demoulding, prepreg processing eliminates air bubbles and makes it easier to obtain a smooth, glossy surface.

• Disadvantages of prepreg

High Cost. In view of the material characteristics and processing technology and other factors, the cost of preg is always high.

Shelf life. HIGH-PERFORMANCE PREPREGS can be stored at room temperature (75 ° F) for up to six months, but their shelf life is shortened once they are heated and cured and stored at higher temperatures.

Necessary Heat Cure. In order for the Preg to cure, it must reach a minimum temperature of 270 ° F and be kept at that temperature for at least four hours, so many advanced manufacturers use autoclaves.

• How to process the prepreg?

In order to fully cure the PREG, heating and pressure are required. Although a press can be used to obtain pressure, a more typical method is vacuum bagging. After the parts are placed, they must be packed in a vacuum bag with all the commonly used components, with a stripping layer to keep the bags from sticking to the parts, and then a breathable cloth to absorb the excess resin.

Although prepreg is cured in a variety of ways, the ideal curing environment is a autoclave with temperature and pressure control functions. Heat requirements usually require an oven to control temperature rise and fall, and to maintain a controlled uniform temperature for a certain duration.

• How to use prepreg?

First you need to prepare the mold, and in order to get a smooth finished part, you must have a waxed and PVA coated flawless mold. The prepreg is between the two linings and the fabric needs to be peeled off before it can be put into the mold. Because the surface of the prepreg is very sticky, it is necessary to place the material carefully into the mold. Unlike dry fabrics in manual lamination, prepreg can not be repositioned without a release agent.If the PREPREG is partially cured, it can be trimmed, pleated, and formed with a knife or scissors. The prepreg is easy to handle, and because of its viscosity, it will fit snugly into the mold. After the layers are placed in the mold, the preg must be compressed to bond to remove residual air between the layers and squeeze out excess resin. Although the resin content in the prepreg is controlled, the resin will naturally dilute as the temperature increases and there will be resin flow before the resin is fully cured.

Use a press to achieve the desired compression, but do not select a press unless the part is completely flat. As a result, parts are usually packed in vacuum. One of the advantages of prepreg is that, after curing and cooling, an additional layer can be laid on the part without scratching or additional surface treatment. Again, up to a quarter of an inch can be placed at a time, taking into account the need not to trap air between the layers. After stacking, the vacuum bag is closed and sealed, and then the vacuum is ready to be evacuated and the heating cycle begins.

All curing cycles begin with an increase in temperature and end with a decrease in temperature. The difference is the target temperature and the time required to fully cure. Continue to rise at a rate of no more than 5 ° F per minute until the target temperature is reached. The target temperature is maintained throughout the curing cycle and then lowered to at least 150 ° F at a rate of less than 5 ° F per minute before being removed from the oven.

Let the part cool to room temperature, remove the vacuum packaging material, and then remove the part from the mold. There are a few caveats when determining the time and heat to use. First, if you are not in a hurry, you can place the part at high temperatures for up to 24 hours without damaging the part. Second, in determining the temperature and curing cycle, consider the quality and conductivity of the mold, if it is a thin metal, it will be heated rapidly and will not interfere with the curing cycle; finally, the quality of the mold and the temperature limits of the mold material must be considered if the mold is thin and made of a typical polyester/glass fiber material, may deform when heated.