hand paste forming process of FRP mould:
The hand paste forming process of FRP mould is to first apply a layer of release agent on the model, then apply the resin mixture to the model with a scraper or brush, and then lay the cut fiberglass cloth or other reinforcing material on it. Force the resin into the glass cloth with a scraper or brush, discharge bubbles, and after the resin is soaked in the reinforcement material, lay the second layer of reinforcement material, so repeatedly painting the resin and laying the reinforcement material until the required number of design layers is reached. Then curing, demoulding and finishing are carried out.
selection of raw materials for FRP moulds:
The raw materials of FRP hand paste molding mould are mainly resin, reinforcement material and auxiliary material and so on. Reasonable selection of raw materials is an important link to ensure product quality and reduce cost. When selecting raw materials, the following conditions must be met:
Meet the performance requirements of product design;
Adapt to the characteristics of hand paste molding process;
The price is cheap and the supply is abundant.
At present, the main raw materials are: resin, reinforced fiber (glass fiber cloth, short cut felt, surface felt), rubber coat, curing agent, accelerator, release agent, pigment, toughening agent, filler (quartz powder, diamond powder, cast asbestos powder, asbestos powder) and so on.
1. Selection of resin:
The selection of resin varieties for hand paste molding is very important, which is directly related to product quality and production process. Therefore, the variety of resin must be determined according to the product performance, application conditions and process requirements.
1.1 Product performance considerations, pay attention to:
1.1.1 curing shrinkage of resin: low shrinkage resin should be selected.
1.1.2 fracture elongation: the resin with good extensibility should be selected to improve the cracking strength of FRP.
2.1 from a technological point of view, vinyl resins should meet:
2.1.1 good wettability. The infiltration of resin to fiber is not only an important factor to ensure the quality of FRP, but also a prerequisite for hand paste process. If the infiltration is not good, it will not only make the molding of FRP products difficult, but also cause bubbles between resin and fiber.
2.1.2 appropriate viscosity. When the resin viscosity of hand paste forming is too low, the flow glue phenomenon will appear, the viscosity is too large, and it will be difficult to infiltrate the molding.
2.1. 3 can be gelled and cured at room temperature or low temperature, and no low molecular weight is required to be cured.
2.1.4 non-toxic or low-toxic;
2.1.5 the price is cheap and the supply is abundant.
At present, the most commonly used resins in hand paste molding process are unsaturated polyester resin and epoxy resin, but phenolic resin is rarely used alone.
2. Selection of reinforcement materials:
Fiber varieties are generally selected according to the use conditions and process design.
2.1 from the use conditions, the use temperature, strength, toughness, specific gravity, insulation and other factors should be taken into account.
2.2 from a technological point of view, it is required to have the following characteristics:
2.2.1 easy wettability: easy to be soaked by resin;
2.2.2 coating deformability: when pasting products with complex shape, fiberglass products are required to adapt to the change of mold shape and have certain deformation properties.
At present, the commonly used glass fiber products are untwisted roving, short cut fiber felt, surface felt, untwisted roving, composite reinforcement materials and so on.
3. Selection of release agent:
In the process of producing fiberglass products, in order to prevent the products from bonding with the mold, the release agent is coated on the mold before hand paste forming. There are many kinds of release agents, which can be divided into three types: thin film type, mixed solution type and oil wax type.
When selecting release agent, many factors should be considered, such as mold material, resin type, curing temperature, product appearance and structure, production cycle, economic benefit and so on.
4. Selection of rubber coat resin:
There are many kinds of rubber coat resin, which are generally selected according to the conditions of use. At present, the rubber coat resins are polyester and vinyl and so on.
(三) hand paste forming steps and matters needing attention for FRP products:
1. Preparation of fiber reinforced materials:
Hand paste forming cloth or felt, to be pre-treated surface treatment, as far as possible to select the pre-treated fiber reinforced materials, no matter what kind of fiber and products, must be kept dry before use, do not touch the oil. The tailoring design of reinforced materials is very important and should be concentrated in order to improve efficiency and save cloth.
When clipping, you should pay attention to:
1.1 the warp and weft strength of the cloth is different, it should be laid alternately vertically and horizontally according to the design requirements. For the products with directional strength requirements, one-way cloth can be used to strengthen.
1.2 for products with large surface fluctuations, the fiber cloth should be cut partially, but as little as possible, and attention should be paid to staggering the opening.
1.3 the lap length of the reinforced material is generally 50 mm, when the thickness requirement is strict, butt joint can be taken, but attention should be paid to the wrong joint.
1.4 the size of the cut glass cloth shall be determined according to the size, performance requirements and ease of operation of the product. There are many small pieces of joint, low strength, if the construction is convenient, as far as possible to use large pieces of cloth paste.
2. Preparation of resin glue:
The technological indexes of resin glue include three indexes: viscosity, gel time and curing degree.
2.1 viscosity of resin:
Resin viscosity, also known as fluidity, is an important index in hand paste molding. Too high viscosity will make it difficult to coat glue, and it is not easy to soak the reinforcing material. If the viscosity is too low, the flow glue phenomenon will appear, which will affect the quality.
2.2 Gel time:
After the resin glue is prepared, the time to start heating, sticking and losing fluidity is called the gel time. It is generally hoped that the glue will stop for a period of time after the paste is finished. If the gel time is too short, the quality will be affected by the viscous impermeable fiber in the construction. On the contrary, if there is no gel for a long time, it will cause the loss of resin glue and the volatilization of cross-linking agent, so that the curing is incomplete and the strength is reduced.
The gel time of glue is generally shorter than that of products. The gel time of resin glue is related to formula, environmental temperature, humidity, product thickness and so on.
The gel time of polyester glue is generally controlled by adjusting the amount of curing agent and accelerator.
2.3 degree of curing:
Complete curing is an important condition to ensure the quality of products. From the point of view of process, the curing degree is divided into demoulding strength and service strength. The former is to ensure that the product has demoulding strength, so that the product is not damaged from the mold, while the latter requires the product to achieve the use strength.
The curing degree in the production process is generally controlled by adjusting the formula. For hand paste products, it is hoped that it can be controlled in 24 hours of demoulding, again a long time, will affect the production efficiency. When the room temperature is lower than 15 ℃, appropriate heating or heat preservation measures should be taken.
3. Glue paste preparation:
The glue coat paste is used to make the surface glue coat layer, its function is to improve the weather resistance, water resistance and chemical corrosion resistance of the products, and prolong the service life.
Because the rubber coat resin has thixotropy, it should be fully stirred when it is used, the thickness of the coating should be controlled at about 0.25 mm and 0.4 mm, and when the glue coating begins to gel, the FRP will be pasted immediately and removed after complete curing. When using rubber coating resin layer, it should be prevented from contamination or infiltration of small bubbles between rubber coating layer and FRP.
4. Preparation of hand paste forming tools:
The most commonly used hand paste forming tools are scissors, brush, scraper, circular mill, polishing machine, electric drill and so on.
5. Formulation of forming process route:
The correct selection of process route is the guarantee to complete the task according to quality. Before organizing production, it is necessary to have a comprehensive understanding of product performance, structural characteristics and construction conditions, and formulate a feasible process route on the basis of analysis and research, which should be considered from the following aspects:
5.1 according to the product performance requirements, reasonable selection of fiber types, resin formulations and pasting methods.
5.2 according to the shape, size and strength requirements of the product, select the mold material and forming method.
5.3 choose the curing method according to the climatic conditions and tasks. When curing at room temperature above 15 ℃, it takes 24 hours to demoulding, and when the task is urgent, the thermal curing process can be used.
5.4 according to the requirements of glue content control, select the molding method.
5.5 determine the molding mode according to the surface requirements of the product.
6. Paste construction:
Pasting is an important process of hand paste forming, which must be carefully operated. Before pasting, check whether the mold is missing or not. When there is a glue layer, check whether the glue layer is gel (to achieve soft without sticking hands) and so on. Check qualified, and then start to spread paste, to brush glue, and then spread, pay attention to the discharge of bubbles, until the design thickness. When laying the first and second layers of cloth, the resin content should be higher, which is conducive to soaking the fabric and expelling bubbles.
When scraping, the bubbles should be driven away from one end (or from the middle to the two ends) so that the glass cloth can be closely fitted and the glue content is distributed evenly.
When pasting products with inserts, metal inserts must be pickled and deoiled in order to ensure a strong bond with the products. In order to make the geometric position of metal inserts accurate, it is necessary to locate them on the mold first.
Hand paste products are often cured at room temperature, and the normal curing process can be divided into three stages: gel, curing and aging. Products gel, cured to a certain strength, can be demoulded. Such as polyester FRP products, generally have to be cured 24 hours after molding to achieve demoulding strength. After demoulding, the product can not be used immediately, but should be solidified above 15 ℃ for one week in order to achieve the use strength. However, it often takes a year to stabilize the strength of polyester FRP.
In addition to measuring the strength, the curing degree of FRP can also be tested by Bacall hardness tester. In general, when cured to a Bakol hardness of 15:00, it can be demoulded. By increasing the ambient temperature and accelerating the curing speed, the production efficiency can be improved and the mold turnover can be accelerated. The optimum ambient temperature for hand paste forming is 25 ℃ and 30 ℃. For polyester FRP products with large exposed area, it is not suitable to be heated before resin gel, otherwise the cross-linking agent will evaporate and never solidify. In order to shorten the production cycle of FRP products, post-curing process can also be used.
8. Demoulding, trimming and assembly:
After the product is solidified to a certain strength, it is best to use wooden or aluminum tools to prevent scratches on the mold and products. Large products can be demoulded with the help of jacks or cranes, but avoid excessive force or gravity.
For some products with large size and complex shape, the method of pre-demoulding can be adopted.
Products need to be processed in time after demoulding, remove rough edges and flying thorns, and repair surface and internal defects.