Know something about the molding process of composite materials (Ⅱ)

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Hand paste forming process

 

The process flow of hand paste forming is as follows:

 

(1) Production preparation

The size of the working site for hand pasting shall be determined according to the product size and daily output. The site shall be clean, dry and well ventilated, and the air temperature shall be kept between 15 and 35 degrees Celsius. The post-processing refurbishment section shall be equipped with exhaust dust removal and water spraying device.

Mold preparation includes cleaning, assembly and release agent.

When the resin glue is prepared, we should pay attention to two problems: (1) prevent the glue from mixing bubbles; (2) The amount of glue should not be too much, and each amount should be used up before the resin gel.

Reinforcement materials The types and specifications of the reinforcement materials must be selected based on the design requirements.

 

(2) Pasting and curing

Layer-paste manual layer-paste is divided into wet method and dry method two: (1) dry layer-prepreg cloth as raw material, the pre-learn material (cloth) according to the sample cut into bad material, layer-softening heating, and then layer by layer on the mold, and pay attention to eliminate bubbles between layers, so that dense. This method is used for autoclave and bag molding. (2) Wet layering directly in the mold will strengthen the material dip, layer by layer close to the mold, deduct bubbles, make it dense. General hand paste process with this method of layering. Wet layering is divided into gelcoat layer paste and structure layer paste.

Hand pasting tool Hand pasting tool has a great impact on ensuring product quality. There are wool roller, bristle roller, spiral roller and electric saw, electric drill, polishing machine and so on.

Solidify products solidify cent sclerosis and ripe two stages: from gel to trigonal change want 24h commonly, right now solidify degree amount to 50% ~ 70% (ba Ke hardness degree is 15), can demolom, after taking off solidify below natural environment condition 1 ~ 2 weeks ability makes products have mechanical strength, say ripe, its solidify degree amount to 85% above. Heating can promote the curing process. For polyester glass steel, heating at 80 for 3h, for epoxy glass steel, post curing temperature can be controlled within 150. There are many heating and curing methods, medium and small products can be heated and cured in the curing furnace, large products can be heated or infrared heating.

 

(3) Demoulding and dressing

Demoulding demoulding to ensure that the product is not damaged. Demoulding methods are as follows: (1) The ejection demoulding device is embedded in the mold, and the screw is rotated when demoulding to ejection the product. The pressure demoulding mold has a compressed air or water inlet, demoulding will be compressed air or water (0.2mpa) between the mold and the product, at the same time with wood hammer and rubber hammer, so that the product and the mold separation. (3) Demoulding of large products (such as ships) with the help of jacks, cranes and hardwood wedges and other tools. (4) Complex products can use manual demoulding method to paste two or three layers of FRP on the mold, to be cured after peeling from the mold, and then put on the mold to continue to paste to the design thickness, it is easy to take off from the mold after curing.

Dressing dressing is divided into two kinds: one is size dressing, the other defect repair. (1) After shaping the size of the products, according to the design size to cut off the excess part; (2) Defect repair includes perforation repair, bubble, crack repair, hole reinforcement, etc.

 

Jet forming technique

 

Jet forming technology is an improvement of hand paste forming, semi - mechanized degree. Jet forming technology accounts for a large proportion in composite material forming process, such as 9.1% in the United States, 11.3% in Western Europe, and 21% in Japan. At present, domestic injection molding machines are mainly imported from the United States.

(1) Jet forming process principle and advantages and disadvantages

Injection molding process is mixed with initiator and promoter of two kinds of polyester, respectively from the spray gun out on both sides, and will cut off the fiberglass roving, by the torch center, mixing with resin, deposit to the mould, when the deposit to a certain thickness, with the roller compaction, make the fiber saturated resin, eliminate air bubbles, cured into products.

The advantages of jet molding: (1) using glass fiber roving instead of fabric, can reduce the cost of materials; (2) The production efficiency is 2-4 times higher than hand paste; (3) The product has good integrity, no joints, high interlayer shear strength, high resin content, good corrosion resistance and leakage resistance; (4) it can reduce the consumption of flapping, cutting cloth scraps and remaining glue liquid; The product size and shape are not restricted. The disadvantages are: (1) high resin content, low strength products; (2) the product can only do one side smooth; It pollutes the environment and is harmful to workers' health.

Jet forming efficiency up to 15kg/min, so suitable for large hull manufacturing. It has been widely used to process bath tub, machine cover, integral toilet, automobile body components and large relief products.

(2) Production preparation

In addition to meeting the requirements of hand paste process, special attention should be paid to environmental exhaust. According to the size of the product, the operation room can be closed to save energy.

Material preparation raw materials are mainly resin (mainly unsaturated polyester resin) and untwisted glass fiber roving.

Mold preparation includes cleaning, assembly and release agent.

Injection molding equipment injection molding machine is divided into two types: pressure tank type and pump type: (1) Pump type injection molding machine, is the resin initiator and accelerator are respectively pumped to the static mixer, fully mixed and then ejected by the spray gun, known as the gun mixed type. Its components are pneumatic control system, resin pump, auxiliary pump, mixer, spray gun, fiber cutting injector, etc. Resin pump and auxiliary pump are rigidly connected by rocker arm. Adjust the position of auxiliary pump on the rocker arm to ensure the proportion of ingredients. Under the action of air compressor, resin and auxiliary agent are evenly mixed in the mixer and formed by spray gun droplets, which are continuously sprayed to the surface of the mould with the cut fiber. This jet machine only has a glue spray gun, simple structure, light weight, less initiator waste, but because of mixing in the system, it must be cleaned immediately after completion, in order to prevent the injection blockage. (2) The pressure tank type glue supply jet machine is to install the resin glue in the pressure tank respectively, and make the glue into the spray gun to spray continuously by the gas pressure into the tank. It consists of two resin tanks, pipe, valve, spray gun, fiber cutting injector, trolley and bracket. When working, connect the compressed air source, make the compressed air pass through the air-water separator into the resin tank, glass fiber cutter and spray gun, so that the resin and glass fiber are continuously ejected by the spray gun, resin atomization, glass fiber dispersion, mixed evenly and then sink to the mold. This jet is resin mixed outside the gun, so it is not easy to plug the nozzle of the gun.

(3) Spray molding process control

Injection process parameters selection: Resin content spray molding products, resin content control at about 60%. When the resin viscosity is 0.2Pa·s, the resin tank pressure is 0.05-0.15mpa, and the atomization pressure is 0.3-0.55mpa, the uniformity of the components can be guaranteed. (3) The mixing distance of resin sprayed by different Angle of spray gun is different. Generally, an Angle of 20° is selected, and the distance between spray gun and mold is 350 ~ 400mm. To change the distance, the Angle of the spray gun should be high-speed to ensure that each component is mixed in the intersection near the surface of the mold to prevent the glue from flying away.

Spray molding should be noted: (1) the ambient temperature should be controlled at (25±5) , too high, easy to cause the blockage of the spray gun; Too low, uneven mixing, slow curing; (2) No water is allowed in the jet system, otherwise the product quality will be affected; (3) Before forming, spray a layer of resin on the mold, and then spray the resin fiber mixture layer; (4) Before injection molding, first adjust the air pressure, control resin and glass fiber content; (5) The spray gun should move evenly to prevent leakage and spray. It can not go in an arc. The overlap between the two lines is less than 1/3, and the coverage and thickness should be uniform. After spraying a layer, immediately use roller compaction, should pay attention to edges and concave and convex surface, ensure that each layer is pressed flat, exhaust bubbles, prevent with fiber caused burrs; After each layer of spray, to check, qualified after the next layer of spray; The last layer to spray some, make the surface smooth; Clean the jet immediately after use to prevent resin solidification and damage to the equipment.


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