Theoretical analysis is conducted on the characteristics of hand layup process operation and raw materials, and the main factors affecting the surface quality of products are as follows: ① the processability of resin; ② The processability of gel coat resin; ③ The quality of the mold surface.
resin
Resin accounts for approximately 55-80% by weight in hand laid products. The various properties of the resin directly determine the performance of the product. The physical properties of resin in the production process determine production efficiency and product quality. Therefore, when selecting resin, the following aspects should be considered:
1.1 Resin viscosity
The viscosity of hand laid resin is generally between 170 and 117 cps. The resin has a wide viscosity range, which is conducive to selection. However, due to the difference in viscosity between the upper and lower limits of the same brand of resin being about 100cps to 300cps, there will also be significant changes in viscosity in winter and summer. Therefore, experiments are needed to screen and determine the resin that is suitable for viscosity.
This article conducted experiments on five resins with different viscosities. During the experiment, the main comparison was made on the resin impregnation speed of fiberglass, resin foaming performance, and the density and thickness of the paste layer. Through experiments, it was found that the lower the viscosity of the resin, the faster the impregnation speed of fiberglass, the higher the production efficiency, the smaller the porosity of the product, and the better the uniformity of the product thickness. However, when the temperature is high or the resin dosage is slightly high, it is easy to cause glue flow (or control glue); On the contrary, the speed of impregnating fiberglass is slow, the production efficiency is low, the product porosity is high, and the uniformity of product thickness is poor, but the phenomenon of glue control and flow is reduced.
After multiple experiments, it was found that the resin viscosity is 200-320 cps at 25 ℃, which is the best combination of surface quality, intrinsic quality, and production efficiency of the product. In actual production, it is common to encounter the phenomenon of high resin viscosity. At this time, it is necessary to adjust the resin viscosity to reduce it to the viscosity range suitable for operation. There are usually two methods to achieve this: ① adding styrene to dilute the resin to reduce viscosity; ② Raise the temperature of the resin and the temperature of the environment to reduce the viscosity of the resin. Raising the ambient temperature and resin temperature is a very effective way when the temperature is low. In general, two methods are usually used to ensure that the resin does not solidify too quickly.
1.2 Gelation time
The gel time of unsaturated polyester resin is mostly 6~21 min (25 ℃, 1% MEKP, 0 5% cobalt naphthalate). The gel is too fast, the operation time is insufficient, the product shrinks greatly, the heat release is concentrated, and the mold and product are easy to be damaged. The gel is too slow, easy to flow, slow to cure, and the resin is easy to damage the gel coat layer, reducing production efficiency.
The gelation time is related to temperature and the amount of initiator and promoter added. When the temperature is high, the gelation time will be shortened, which can reduce the amount of initiators and accelerators added. If too many initiators and accelerators are added to the resin, the color of the resin will darken after curing, or due to rapid reaction, the resin will release heat quickly and be too concentrated (especially for thick walled products), which will burn the product and mold. Therefore, the hand lay up operation is generally carried out in an environment above 15 ℃. At this time, the amount of initiator and accelerator does not need much, and the resin reaction (gel, curing) is relatively stable, which is suitable for hand lay up operation.
The gelation time of the resin is of great significance to the actual production. The test found that the gel time of the resin is at 25 ℃, 1% MEKP and 0 Under the condition of 5% cobalt naphthalate, 10-18 minutes is the most ideal. Even if the operating environment conditions change slightly, the production requirements can be ensured by adjusting the dosage of initiators and accelerators.
1.3 Other properties of resin
(1) The defoaming ability of resin is related to the viscosity of the resin and the content of defoaming agent. When the viscosity of the resin is constant, the amount of defoamer used largely determines the porosity of the product. In actual production, when adding accelerant and initiator to the resin, more air will be mixed. If the resin has poor defoaming property, the air in the resin before gel cannot be discharged in time, there must be more bubbles in the product, and the void ratio is high. Therefore, the resin with good defoaming property must be used, which can effectively reduce the bubbles in the product and reduce the void ratio.
(2) Color of resin
At present, when fiberglass products are used as high-quality exterior decorations, they generally need to be coated with high-end paint on the surface to make the product surface colorful. In order to ensure the consistency of paint color on the surface of fiberglass products, it is required that the surface of fiberglass products be white or light colored. To meet this requirement, light colored resin must be selected when selecting resin. Through screening experiments on a large number of resins, it was shown that the resin color value (APHA) Φ 84 can effectively solve the color problem of products after curing. At the same time, using light colored resin makes it easy to detect and discharge bubbles in the paste layer in a timely manner during the pasting process; And reduce the occurrence of uneven product thickness caused by operational errors during the pasting process, resulting in inconsistent color on the inner surface of the product.
(3) Air dryness
In high humidity or low temperature conditions, it is common for the inner surface of the product to become sticky after solidification. This is because the resin on the surface of the paste layer comes into contact with oxygen, water vapor, and other polymerization inhibitors in the air, resulting in an incomplete cured layer of resin on the inner surface of the product. This seriously affects the post-processing of the product, and on the other hand, the inner surface is prone to adhering dust, which affects the quality of the inner surface. Therefore, when selecting resins, attention should be paid to selecting resins with air drying properties. For resins without air drying properties, a solution of 5% paraffin (melting point 46-48 ℃) and styrene can generally be added to the resin at 18-35 ℃ to solve the air drying properties of the resin, with a dosage of about 6-8% of the resin.
Gelatin coating resin
To improve the surface quality of fiberglass products, a colored resin rich layer is generally required on the surface of the product. Gel coat resin is this type of material. Gelatin coating resin improves the aging resistance of fiberglass products and provides a homogeneous surface, improving the surface quality of the products. To ensure a good surface quality of the product, the thickness of the adhesive layer is generally required to be 0 4-6 mm. In addition, the color of the gel coat should be mainly white or light, and there should be no color difference between batches. Additionally, attention should be paid to the operational performance of the gel coat, including its viscosity and leveling. The most suitable viscosity for gel coating spraying is 6000cps. The most intuitive method to measure the leveling of the gel coating is to spray a layer of gel coating on the local surface of the mold that has been demolded. If there are fisheye like shrinkage marks on the gel coating layer, it indicates that the leveling of the gel coating is not good.
The gel coat must be thoroughly stirred before use, and after adding the trigger system, it must be quickly and evenly stirred to achieve the best use effect. When spraying, if the viscosity is found to be too high, an appropriate amount of styrene can be added for dilution; If it's too small, spray it thin and a few more times. In addition, the spraying process requires the spray gun to be about 2cm away from the surface of the mold, with appropriate compressed air pressure, the spray gun fan surface perpendicular to the direction of the gun, and the spray gun fan surfaces overlapping each other by 1/3. This can not only solve the process defects of the gel coat itself, but also ensure the consistency of the quality of the product's gel coat layer.
The influence of molds on the surface quality of products
Mold is the main equipment for forming fiberglass products, and molds can be divided into types such as steel, aluminum, cement, rubber, paraffin, fiberglass, etc. according to their materials. Fiberglass molds have become the most commonly used mold for hand layup of fiberglass due to their easy molding, availability of raw materials, low cost, short manufacturing cycle, and easy maintenance.
The surface requirements for fiberglass molds and other plastic molds are the same, usually the surface of the mold is one level higher than the surface smoothness of the product. The better the surface of the mold, the shorter the molding and post-processing time of the product, the better the surface quality of the product, and the longer the service life of the mold. After the mold is delivered for use, it is necessary to maintain the surface quality of the mold. The maintenance of the mold includes cleaning the surface of the mold, cleaning the mold, repairing damaged areas, and polishing the mold. Timely and effective maintenance of molds is the ultimate starting point of mold maintenance, and the correct maintenance method of molds is crucial. The following table shows different maintenance methods and corresponding maintenance results.
(1) New molds or molds that have not been used for a long time
Firstly, clean and inspect the surface of the mold, and make necessary repairs to areas where the mold is damaged or structurally unreasonable. Next, clean the surface of the mold with a solvent, dry it, and then polish the surface of the mold with a polishing machine and polishing paste once or twice. Complete waxing and polishing three times consecutively, then apply waxing again, and polish again before use.
(2) Mold in use
Firstly, ensure that the mold is waxed and polished every three uses. For parts that are prone to damage and difficult to demold, waxing and polishing should be done before each use. Secondly, for a layer of foreign objects (possibly polystyrene or wax) that may appear on the surface of a mold that has been used for a long time, it must be cleaned in a timely manner. The cleaning method is to use a cotton cloth dipped in acetone or a special mold cleaner to scrub (the thicker part can be gently scraped off with a tool), and the cleaned part should be demolded according to the new mold.
(3) For damaged molds that cannot be repaired in a timely manner, wax blocks can be used first
Fill and protect the damaged area of the mold with materials that are prone to deformation and do not affect the curing of the gel coat, and continue to use. For those that can be repaired in a timely manner, the damaged area must be repaired first. After the repair, no less than 4 people (at 25 ℃) must be cured. The repaired area must be polished and demolded before it can be put into use. The normal and correct maintenance of the mold surface determines the service life of the mold, the stability of product surface quality, and the stability of production. Therefore, it is necessary to have a good habit of mold maintenance. In summary, by improving materials and processes and enhancing the surface quality of molds, the surface quality of hand laid products will be significantly improved.
Post time: May-20-2024
