The general process of hand lay up molding for fiberglass molds is to first apply a layer of fiberglass release agent on the mold, then mix the pre prepared resin, brush it on the model, and then lay cut fiberglass cloth or other reinforcement materials on top of it. Use a brush to force the resin into the fiberglass cloth, eliminate bubbles, wait for the resin to fully penetrate the reinforcement material, and then lay the second layer of reinforcement material. Repeat the above process to brush the resin and lay the reinforcement material repeatedly until the required number of layers are reached, and then proceed with curing, demolding, and finishing.
The raw materials for fiberglass hand lay up molds mainly include resin, fiberglass release agent, and reinforcement materials. Reasonable selection can ensure the quality and quantity of raw materials, and reduce costs. But when choosing raw materials, the following conditions must be met:
① Meet the performance requirements of the product design itself;
② The raw material prices are cheap and the supply is sufficient, so try to purchase as close as possible;
③ Capable of adapting to the characteristics of hand lay up molding process.
1. How to choose resin?
Good resin is crucial in hand lay up molding process as it directly affects product quality and production process. Therefore, the variety of resin must be determined based on the product's usage conditions, process, and performance.
From the perspective of resin performance, attention should be paid to:
① Resin fracture elongation: Choosing resin with good elongation performance can improve the strength of fiberglass molds when they crack
② Resin curing shrinkage problem: choose low shrinkage resin
From the perspective of resin technology, it should meet the following requirements:
① Non toxic/low toxic;
② It can be cured at room temperature or low temperature, and gel is produced without low molecular substances;
③ Appropriate viscosity, if the resin viscosity is too low during the hand lay up molding process, there will be a phenomenon of glue flow; But if the viscosity is too high, there may also be difficulties in forming infiltration;
④ Resin prices are cheap and the supply is abundant;
⑤ Good wettability, resin fiber infiltration is an important factor in ensuring the quality of fiberglass products and is also a crucial condition for the hand lay up process. If infiltration is not good, it not only causes difficulties in forming fiberglass products, but also leads to a large number of bubbles between resin fibers.
At present, the most commonly used hand lay up molding processes are epoxy resin, unsaturated polyester resin, and phenolic resin, but phenolic resin is rarely used alone.
2. How to choose reinforcement materials?
Reinforcement materials are generally selected based on process design and usage conditions.
For example, from a process perspective, the following characteristics must be met:
① Deformability is inevitable in hand lay up processes when encountering products with complex shapes. In this case, we need to require fiberglass products to be able to adapt to changes in mold shape and have a certain degree of deformability;
② Easy to infiltrate, the selected reinforcement material must be easily impregnated with resin,
For example, factors such as strength, toughness, temperature, insulation, and specific gravity can be considered based on usage conditions. At present, we commonly use glass fiber products, short cut fiber felt, surface felt, untwisted roving, untwisted coarse gauze, composite reinforcement materials, etc.
3. How to choose fiberglass mold release agent?
In the process of hand pasting, in order to prevent the mold from sticking to the product, it is generally necessary to apply a layer of release agent that can separate the mold first. There are many types of release agents, including oil-based release agents, water-based release agents, solvent based release agents, etc. When choosing a release agent, one should first consider the mold material (fiberglass mold/metal mold), followed by the resin type (epoxy resin/unsaturated polyester resin/phenolic resin), curing temperature (room temperature/high temperature X ℃), product appearance structure (conventional/complex), production cycle, and other factors.
At present, the commonly used hand pasted fiberglass release agent brands include Diva release agent, Kentian release agent, Henkel release agent, etc. These release agents are widely used in the market.
