The mold gel coat takes two hours to three and a half hours, that is, the ideal time for the mold gel coat is fifty minutes, and the curing time is one hundred minutes. After the second layer of gel coat gel, the base layer can be laid. There are two common lamination methods for making FRP molds. One is the traditional multi-step layup method, and the other is the fast low shrinkage system layup method.
1. Traditional mold layup method
A, raw materials:
1) Mold resin
The mold resin should have a high heat distortion temperature and low shrinkage. A meta-benzene resin, a vinyl resin, and a DCPD resin can be used as the mold resin.
The high solid content and thixotropic properties of the vinyl polyester resin have been promoted to have excellent process properties, low shrinkage properties, excellent mechanical properties, thermal degradation resistance, and chemical resistance. It has excellent strength retention at high temperatures and high heat distortion temperature. It can be used as the first choice for mold materials when manufacturing high-end molds, ensuring that the surface quality of the products depends on the mold gel coat, ensuring the stability and consistency of the product quality, and relying on the performance of the mold resin.
2) Glass fiber reinforced materials
The surface felt is often used as the first layer of reinforcing material because of its fine fiber, convenient wetting and easy defoaming. Chopped mat is an ideal reinforcement for molds because it minimizes the printing of fiber lines.
3) Quality assurance
In order to ensure that the mold resin meets the quality requirements, it is also necessary to perform quality inspection like the mold gel coat. Including: material storage period, testing gel time.
B, operation process
First floor (first layer after spraying gel coat)
The mold layer starts from the first layer of the paste. Depending on the complexity of the shape of the mold, the surface of the first layer can be made of a surface felt, 300 g or 450 g of chopped strand mat. The quality requirements of the first floor are very strict, and it is necessary to avoid re-repair after the mold is completed. In order to ensure the quality of the mold, the laminate should be rolled very carefully to ensure that all the bubbles are ejected, and a reasonable ratio of resin to fiber should be ensured. The resin should be applied by special tools. When the first layer is cured, thoroughly review the laminate thoroughly, including all corners and surfaces, and all possible problems. If bubbles are found, the bubbles must be carefully removed and the damaged surface repaired.
C, thickening the layer
A paving layer for thickening layers is made entirely of fiberglass, which is the most traditional method and is not specifically described here.
Here, I will introduce some new methods.
In the manufacture of the mold, the strong core felt can be selected as the fast thickening layer, which can effectively improve the surface quality of the mold and prevent the printing of the glass fiber or the sandwich material in the mold reinforcement layer. A layer of 450G felt can be laid behind the first layer, a strong core felt, a layer of 450G felt, and three layers of paving at the same time. Such a layup can effectively improve the surface quality of the mold. Since the structure of the strong core felt is organic fibers and microbeads, such a layup can also appropriately increase the rigidity of the mold.
Structurally, the core felt is a composite structure of hollow microspheres and organic fibers. It is a thin core material commonly used in the FRP industry. With this material, the stiffness of the FRP can be increased in an appropriate amount, and Can effectively improve the surface quality of the mold or product.
Another type of mold layup is to consider whether a sandwich sandwich structure is used during molding. The sandwich structure refers to the use of light wood, PVC and other materials for the glass fiber in the FRP layer.
1) Balsa balsa: It accounts for more than 50% of all sandwich materials. It has been the longest used core material for more than 50 years. Its processability is better than other core materials, the highest compressive strength and compressive modulus, the most economical resin consumption, and the best adhesion to the panel, which can be used as the main structure sandwich.
2) PVC: linear and crosslinked.
Sandwich materials have been widely used in composite structures. For the mold, the sandwich structure can be used to obtain a high-strength, lightweight laminate, while also reducing the requirements for the external structural skeleton.
If the product you are making is relatively thin, the product resin has low heat release or the product cycle is long, there is no problem with the sandwich structure mold. However, if the product is very thick, use high exothermic resin or have a short production cycle, it is best not to use a sandwich mold.
D. Determine the paving plan with the hardness of the hardness
A good way to develop a layup plan is to observe the change in the hardness of the laminate. When the laminated Barcol hardness reaches 80%-90% of the full curing hardness, the next layup can continue to be laid. When measuring the hardness of the laminate using a Barcol hardness tester, be careful to record multiple readings and calculate the average value, and use this value as the hardness value. This approach eliminates data errors due to differences in time due to the time it takes to lay out in this way, which is usually faster than the layup schedule.
E, rapid molding process
The key to this mold forming process is the use of a fast, low-shrinking mold resin system that uses a special resin and filler that shrinks little or no shrinkage during solidification. Therefore, the speed of the laminate can be increased, and the glass fiber jet can be used to obtain higher efficiency. The process can be combined with traditional processes, or combined with the use of strong core felt, balsa core and other materials in the design of the layup.
This high quality resin system produces high quality, non-deformable mold surfaces with stringent temperature and operational requirements. Therefore, the production conditions and methods must be strictly in accordance with the requirements of the resin system supplier.