Hand lay-up is a simple, economical and effective FRP molding process that does not require a lot of equipment and capital investment and can achieve a return on capital in a short period of time.
1.Spraying and painting of gel coat
In order to improve and beautify the surface state of FRP products, increase the value of the product, and to ensure that the inner layer of FRP is not eroded and extend the service life of the product, the working surface of the product is generally made into a layer with pigment paste (color paste), high resin content of the adhesive layer, it can be pure resin, but also enhanced with surface felt. This layer is called gel coat layer (also called surface layer or decorative layer). The quality of the gel coat layer directly affects the external quality of the product as well as weather resistance, water resistance and resistance to chemical media erosion, etc. Therefore, the following points should be noted when spraying or painting the gel coat layer.
2.Determination of the process route
The process route is related to various factors such as product quality, product cost and production cycle (production efficiency). Therefore, before organizing production, it is necessary to have a comprehensive understanding of the technical conditions (environment, temperature, medium, load ……, etc.), product structure, production quantity and construction conditions when the product is used, and after analysis and research, in order to determine the molding process scheme, generally speaking, the following aspects should be considered.
3.The main content of process design
(1) According to the technical requirements of the product to select the appropriate materials (reinforcing materials, structural materials and other auxiliary materials, etc.). In the selection of raw materials, the following aspects are mainly considered.
①Whether the product is in contact with acid and alkaline media, the type of media, concentration, use temperature, contact time, etc.
②Whether there are performance requirements such as light transmission, flame retardant, etc.
③In terms of mechanical properties, whether it is dynamic or static load.
④With or without leakage prevention and other special requirements.
(2) Determine the mold structure and material.
(3) The choice of release agent.
(4) Determine the resin curing fit and curing system.
(5) According to the given product thickness and strength requirements, determine the variety of reinforcing materials, specifications, the number of layers and the way to lay the layers.
(6) Preparation of molding process procedures.
4. Glass fiber reinforced plastic layer paste system
Hand lay-up is an important process of hand paste molding process, must be fine operation to achieve fast, accurate, uniform resin content, no obvious bubbles, no poor impregnation, no damage to the fiber and product surface flat, to ensure the quality of products. Therefore, although the gluing work is simple, it is not too easy to make the products well, and should be taken seriously.
(1) Thickness control
Glass fiber reinforced plastic products thickness control, is the hand paste process design and production process will encounter technical problems, when we know the required thickness of a product, it is necessary to calculate to determine the resin, filler content and the reinforcing material used in the specifications, the number of layers. Then calculate its approximate thickness according to the following formula.
(2) Calculation of resin dosage
The resin dosage of FRP is an important process parameter, which can be calculated by the following two methods.
A calculated according to the principle of gap filling, the formula for calculating the amount of resin, only know the mass of the unit area of glass cloth and the equivalent thickness (a layer of glass fiber cloth equivalent to the thickness of the product), you can calculate the amount of resin contained in FRP
B calculated by first calculating the mass of the product and determining the percentage content of glass fiber mass.
(3) Glass fiber cloth paste system
Products with gelcoat layer, gelcoat can not be mixed with impurities, paste before the system should prevent pollution between the gelcoat layer and the backing layer, so as not to cause poor bonding between the layers, and affect the quality of products. The gel coat layer can be enhanced with surface mat. Paste system should pay attention to the resin impregnation of glass fibers, first make the resin infiltration of the entire surface of the fiber bundle, and then make the air inside the fiber bundle completely replaced by resin. It is very important to ensure that the first layer of reinforcing material is completely impregnated with resin and closely fitted, especially for some products to be used in higher temperature conditions. Poor impregnation and poor lamination can leave air around the gelcoat layer, and this air left behind can cause air bubbles during the curing process and use of the product due to thermal expansion.
Hand lay-up system, first in the gel coat layer or mold forming surface with a brush, scraper or impregnation roller and other hand paste tool evenly coated with a layer of prepared resin, and then lay a layer of cut reinforcing materials (such as diagonal strips, thin cloth or surface felt, etc.), followed by forming tools will be brushed flat, pressed, so that it fits closely, and pay attention to the exclusion of air bubbles, so that the glass cloth fully impregnated, not two or more layers of reinforcing materials at the same time Laying. Repeat the above operation, until the thickness required by the design.
If the geometry of the product is more complex, some places where the reinforcing material is not laid flat, bubbles are not easy to exclude, the scissors can be used to cut the place and make it flat, it should be noted that each layer should be staggered parts of the cut, so as not to cause loss of strength.
For parts with a certain angle, can be filled with glass fiber and resin. If some parts of the product are relatively large, can be appropriately thickened or reinforced in the area to meet the requirements of use.
As the fabric fiber direction is different, its strength also has different. The laying direction of the glass fiber fabric used and the way of laying should be done according to the process requirements.
(4) lap seam processing
The same layer of fibers as continuous as possible, avoid arbitrarily cut or spliced, but due to the size of the product, complexity and other reasons of the limitations to achieve, the paste system can be taken when the butt laying, the lap seam shall be staggered until the paste to the thickness required by the product. When gluing, the resin is impregnated with tools such as brushes, rollers and bubble rollers and the air bubbles are drained.
If the strength requirement is high, in order to ensure the strength of the product, the lap joint should be used between two pieces of cloth, the width of the lap joint is about 50 mm. at the same time, the lap joint of each layer should be staggered as much as possible.
(3) Hand lay-up of chopped strand mats
When using short cut felt as reinforcing material, it is best to use different sizes of impregnation rollers for operation, because the impregnation rollers are particularly effective in excluding the bubbles in the resin. If there is no such tool and the impregnation needs to be done by brush, the resin should be applied by point brush method, otherwise the fibers will be messed up and dislocated so that the distribution is not uniform and the thickness is not the same. The reinforcing material laid in the internal deep corner out, if the brush or impregnation roller is difficult to make it fit closely, it can be smoothed and pressed by hand.
When handing lay-up, use the glue roller to apply the glue on the surface of the mold, then manually lay the cut mat piece on the mold and smooth it out, then use the glue roller on the glue, repeatedly roll back and forth, so that the resin glue is immersed in the mat, then use the glue bubble roller to squeeze out the glue inside the mat on the surface and discharge the air bubbles, then glue the second layer. If you meet the corner, you can tear the mat by hand to facilitate the wrapping, and the lap between two pieces of mat is about 50mm.
Many products can also use chopped strand mats and glass fiber cloth alternate layering, such as the Japanese companies paste the fishing boat is the use of alternate paste method, it is reported that the method of production of FRP products with good performance.
(6) The paste system of thick-walled products
Product thickness below 8 mm products can be formed once, and when the thickness of the product is greater than 8 mm, should be divided into multiple molding, otherwise the product will be cured due to poor heat dissipation lead to scorching, discoloration, affecting the performance of the product. For the products with multiple molding, the burrs and bubbles formed after the first paste curing should be shoveled off before continuing to paste the next pavement. Generally speaking, it is recommended that the thickness of one molding should not exceed 5mm, but there are also low heat release and low shrinkage resins developed for molding thicker products, and the thickness of this resin is larger for one molding.
Chongqing Dujiang Composites Co., Ltd.
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Email:marketing@frp-cqdj.com
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Post time: Oct-09-2022
