Hand layup process Production operations - curing and stripping
First, the product of curing
Hand lay-up of FRP products, usually at room temperature curing resin system. Hand lay-up of the operating environment generally requires the following conditions: temperature of not less than 15 ℃, humidity not more than 75%.
Under normal conditions, curing is divided into three phases: gel, curing and heating.
Gels are viscous resins that lose their fluidity and form a soft gel.
Curing can be divided into two stages of curing and curing. Products from the gel to have a certain hardness, so that the product can be taken off from the mold, then the degree of cure of the product can generally reach 50 to 70%, then called the hardening time; The natural environment of natural curing 1 to 2 weeks, so that products have a certain mechanical properties, physical and chemical properties available for use, then become maturation time. At this time the degree of cure can reach more than 85%, the aging is usually carried out at room temperature, but also can be accelerated by post-heating treatment. For example, heat treatment at 80 ° C for 3 hours.
In order to improve the production cycle of FRP own products, improve the utilization rate of mold, and accelerate the hardening time, the heating after-treatment measures are often used.
For FRP, heat treatment temperature should not exceed 120 ℃, generally controlled between 50 ~ 80 ℃, the heat treatment temperature and resin heat temperature, so heat-resistant resin, heat treatment temperature can be higher, Resistant to low temperature resin, heat treatment temperature can be lower.
The degree of curing of the product is proportional to the temperature and the time level. When the ambient temperature is appropriately raised or the product is exposed to sunlight or infrared rays, the curing reaction of the product can be accelerated, the turnover rate of the mold can be increased, and the production cycle can be shortened.
It is important to point out that just before postcure (especially postcure temperatures above 50 ° C), the article should be left standing for at least 24 h at room temperature prior to postcure. Table 4-1 shows the influence of the time interval between the resin gel and the post-curing process on the properties of the product. It can be seen from the table that if the longer time interval between the resin gel and the post-curing treatment is started, The smaller the water absorption, the better the performance of the product used.
When FRP products require the use of higher temperatures, to choose a heat-resistant heat-curing formula, hand layup operation is completed, the product placed under a certain temperature to make it cured. In the post-curing treatment, the slow heating rate is conducive to the formation of resin macromolecule structure, heating rate is too fast, the temperature is too high, can cause the resin agglomeration, affecting the performance of the product.
For some geometric paste system, the assembly accuracy of the higher products, post-curing treatment, should be consistent with the geometry of the bracket support, to prevent deformation, warpage.
Heat treatment methods should be based on product dimensions and mold materials and other factors to be considered to determine the general small FRP products, can be heated in the oven; slightly larger products can be placed in the oven treatment, large products are more use of heating mold or Infrared heating.
If the mold can heat transfer, heating mold can be used for post-curing. The heating methods are: the heat source is arranged in the mold; the heat source is arranged outside the mold; the heat source is placed on the bottom of the mold.
If the mold material does not heat, you can use infrared heating. It is the infrared light installed in the activity of the hood with cover, the infrared light and the distance between products can be adjusted up to a maximum temperature of 150 ℃, but this method of electricity consumption, the power consumption per cubic meter of heating surface The amount of 2 ~ 3kw, 4 ~ 5 times higher than the mold heating.
Second, the product stripping
When the product is cured to mold release strength before demoulding, usually at room temperature more than 24 hours of natural curing. According to the choice of resin curing system to determine the timing of demoulding. If the use of mechanical stripping to pay attention to safety, if the use of artificial demoulding available wood wedge than FRP material stripping less material, stripping should be careful not to damage the mold and products, prohibiting heavy blow or heavy fall mold.
Stripping is a key process in hand lay-up of FRP products. Mold release is directly related to the quality of the product and the effective use of mold. Of course, the demolding is also good or bad depends on the mold design; mold surface finish; release agent and brushing effect; also depends on the demolding technology.
Hand lay fiberglass products generally use gas off, top off, water off and other methods.
(1) air off
Gas off the gas nozzle is pre-installed on the mold, if the gas nozzle connected to the pump through the hose, demoulding through the gas nozzle, compressed air into the gap between the mold and the product interface, with compressed air continue to enter The product comes out. Press the rubber hammer can be used to tap the pores at the moment, so that gas quickly into. This demolding method is very effective for large area products.
The top of the ejection is the top of the paste pieces of the paste in the mold, the mold release screw rotation, the top of the block that is moving outward, which will be the product out. This method is more effective for thick-walled products.
(2) water off
That is injected into the gas nozzle 0.4 ~ 0.6MPa of water, you can also take off the product, because the water can dissolve the release agent, such as the use of polyvinyl alcohol release agent.
Simple structure of the product does not have to be installed demoulding parts, the product cured with a flat shovel gently gently pry off to take off.
Note: The stripping pieces can be installed at the same time a few, but should be installed in a favorable demoulding, non-rigid product appearance unit position.
When stripping do not use a hard hammer beat the mold, because it is easy to product and mold gel coat cracking.