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Principle And Process Of Glass Fiber Reinforced Plastic Resin Crafts

Jul 29, 2020

There are many ways to make glass fiber reinforced plastic resin crafts, such as: hand lay-up molding process, injection molding process, compression molding process and so on. Among them, hand lay-up is the simplest. The following editor will introduce the principle of hand lay-up in detail. And process.


1. The principle of hand lay-up

Hand lay-up molding process, also known as contact molding, is the earliest used and most common molding method in the production of resin composite materials. The hand lay-up process is based on the b glass fiber reinforced plastic resin mixture with curing agent as the matrix, glass fiber and its fabric as the reinforcing material, and hand-laid on the mold coated with the release agent to bond the two together At the same time, a process method for manufacturing FRP products. The matrix resin usually uses unsaturated polyester resin or epoxy resin, and the reinforcing material usually uses alkali-free or medium-alkali glass fiber and its fabric. In the hand lay-up process, less mechanical equipment is used, it is suitable for the production of multi-variety, small-batch products, and is not limited by the types and shapes of products.

  2. Molding process


The hand lay-up process is as follows: first apply a release agent on the cleaned or surface-treated mold forming surface, and after it is fully dried, curing agent (initiator), accelerator, pigment paste and other additives will be added Stir a uniform gel coat or glass fiber reinforced plastic resin mixture, and apply it on the molding surface of the mold, and then lay the cut glass cloth (felt) and other reinforcement materials on it, and pay attention to soak the resin and eliminate air bubbles. Repeat the above layering operation until the design thickness is reached, and then perform curing and demolding.


3. Molding equipment


  The hand lay-up molding process uses less equipment. The equipment for making models includes woodworking lathes, woodworking planers, woodworking circular saws; demolding generally uses air compressors, hoisting equipment, etc.


   The FRP mold making process is a method of making the mold by hand-paste the mold layer by layer by mixing liquid epoxy resin with organic or inorganic materials as the base material, and based on the prototype. The specific process of hand lay-up FRP mold is as follows:

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1.  Parting surface design


   Whether the parting surface design is reasonable or not has a great influence on the difficulty of the process operation, the paste of the mold and the quality of the parts. In general, according to the characteristics of the prototype, the position and shape of the parting surface should be as simple as possible on the premise that the prototype can be demolded smoothly and the installation accuracy of the upper and lower parts of the mold is ensured. Therefore, it is necessary to choose the position of the parting surface and the gate correctly and reasonably, and it is strictly forbidden to have an inverted draft angle, so as not to fail to demold. A smooth wooden board is used to fix the prototype along the parting surface, so as to separate the upper and lower molds. When applying the release agent on the prototype and parting surface, it must be applied evenly and thoughtfully. It must be applied 2 to 3 times. After the release agent applied in the previous application is dry, the next application can be performed.


2.   Brush the gel coat layer


   After the release agent is completely dry, apply the special gel coat brush for the mold twice. The brush should be even. After the first layer has initially set, apply the second layer. The gel coat is black, and the total thickness of the gel coat layer should be controlled at about 016mm. It should be noted that the gel coat should not be applied too thickly to prevent surface cracks and wrinkles.


3. Resin glue preparation


  According to the viscosity of the resin at room temperature, it can be preheated appropriately. Then mix 100 parts of WSP6101 type resin and 8-10 parts (mass ratio) of acetone (or propylene oxide butyl ether) in a clean container. After stirring evenly, add 20-25 parts of curing agent (curing agent). The added amount should be appropriately increased or decreased according to the site temperature), stir quickly, and perform vacuum degassing for 1min to 3min to remove the bubbles in the glass fiber reinforced plastic resin glue. It can be used.


4. Glass fiber paste layer by layer


When the gel coat is initially set and feels soft and not sticky, apply the prepared resin glue to the gel coat, and then spread a layer of chopped felt, and use a brush to laminate the cloth to make it contain glue The amount is uniform and the bubbles are discharged. In some cases, you need to use a pointed object to pick up the bubbles. The laying of the second layer of chopped strand mat must be carried out after the first layer of resin glue has condensed. Afterwards, it can be pasted layer by layer in the form of one cloth and one felt. After each 2 to 3 layers are pasted, after the resin curing exothermic peak has passed (that is, when the resin glue is more viscous, the temperature is generally 20 ℃ 60min or so) before the next layer of paste can be made until the desired thickness. When pasting, the glass fiber cloth must be spread smoothly, and the seams between the glass cloth should be staggered, and try not to overlap at the corners. It is necessary to strictly control the amount of resin glue for each layer, which can fully infiltrate the fibers, but not too much. With high glue content, bubbles are not easy to eliminate, and the curing exotherm is large, and the shrinkage rate is large. Low glue content, easy to layer. After the first mold is cured, remove the excess flash, clean the mold and the debris on the surface of the other half of the prototype, and then apply the release agent to make the gel coat layer, place the injection holes and vent holes, and perform the second mold Paste. After the second mold is cured, cut off the excess flash. To ensure that the mold has sufficient strength, avoid mold deformation. Some supports, fasteners, positioning pins, etc. can be properly bonded to complete the mold structure.


5. Demoulding and trimming


  The mold made by pasting at room temperature (about 20 ℃) will be basically cured within 48 hours, and it can be demolded. When demolding, it is strictly forbidden to hit the mold with hard objects, and use compressed air to blow intermittently as much as possible to make the mold and the master mold gradually separate. After demolding, depending on the requirements of the mold, you can do some drilling and other mechanical processing on the mold, especially in the dead corners where the material is not easy to fill during pouring or injection molding. If there are no reserved air holes, you must drill some air holes. Then carry out the post-treatment of the mold, generally use 400 # ~1200 # water sandpaper to polish the mold surface in turn, and use a polishing machine to polish the mold surface. After all the procedures are completed, the mold can be delivered for use.


FRP resin crafts process


Points to note: 1. The master mold must be smooth, 2. The release agent must be uniform, 3. There must be no bubbles when making the first layer, 4. It must be carefully polished, of course there are many details in the middle, if any Questions can leave a message.

Source:https://www.up-resin.com/

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