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FRP Mold Production Process And Inspection Standards

Jun 10, 2020

1. The process of hand lay-up molding of glass fiber reinforced plastic mold

FRP mold hand lay-up process is to first apply a layer of release agent on the model, and then apply the prepared resin mixture to the model with a spatula or brush, and then lay the laid glass cloth or other reinforcing materials on it. , Use a spatula or brush to force the resin into the glass cloth to expel the air bubbles. After the resin is saturated with the reinforcement material, lay the second layer of reinforcement material, so repeatedly paint the resin and lay the reinforcement material until the desired design layer is reached , And then curing, demolding and trimming.


Second, the choice of glass fiber reinforced plastic mold raw materials

The raw materials of glass fiber reinforced plastic molding are mainly resin, reinforcement materials and auxiliary materials. Reasonable selection of raw materials is an important link to ensure product quality and reduce costs. When selecting raw materials, the following conditions must be met:


①Meet the performance requirements of product design;


② Adapt to the characteristics of hand lay-up molding process;


③The price is cheap and the supply is sufficient.


The current raw materials mainly include: resin, reinforced fiber (glass fiber cloth, chopped mat, surface felt), gel coat, curing agent, accelerator, release agent, colorant, toughening agent, filler (quartz powder, diamond powder , Cast stone powder, asbestos powder), etc.


1. The choice of resin: It is very important to choose the type of resin used for hand lay-up molding, which is directly related to product quality and production process. Therefore, the variety of resin must be determined according to product performance, use conditions and process requirements.


⑴ Product performance considerations, pay attention to:


① resin curing shrinkage problem: low shrinkage resin should be used.


② Elongation at break: Resin with good extensibility should be selected to improve the strength of FRP when cracking.


⑵ From the perspective of process, vinyl resin should meet:


①Good infiltration. The resin infiltration of the fiber is an important factor to ensure the quality of FRP, and it is also a prerequisite for the hand lay-up process. If the infiltration is not good, it will not only make the FRP products difficult to form, but also make bubbles between the resin and fibers;


② Appropriate viscosity. The resin viscosity during hand lay-up molding is too low, there will be glue flow phenomenon, the viscosity is too large, and it will make the molding infiltration difficult;


③ Can be gelled and cured at room temperature or low temperature, and no low molecular matter is required during curing;


④ Non-toxic or low-toxic;


⑤ The price is cheap and the supply is sufficient. At present, the most commonly used resins in the hand lay-up molding process are unsaturated polyester resins and epoxy resins, while phenolic resins are rarely used alone.


2. Selection of reinforcement materials: fiber varieties are generally selected according to the conditions of use and process design.


(1) Considering the conditions of use, factors such as the temperature, strength, toughness, specific gravity, and insulation of the product should be considered.


⑵ From the perspective of technology, it is required to have the following characteristics:


①Easy to wet: easy to be penetrated by resin;


② Deformability of cladding: when pasting products with complex shapes, glass fiber products are required to adapt to changes in the shape of the mold and have certain deformability.


At present, the commonly used glass fiber products include untwisted roving, chopped fiber mat, surface felt, untwisted roving cloth, and composite reinforcement materials.


3. Selection of release agent: In the process of producing FRP products, in order to prevent the product from sticking to the mold, before the hand lay-up molding, the mold is coated with a layer of separation material-release agent. There are many types of release agents, including film type, mixed solution type and oil wax type.


Factors such as mold material, resin type, curing temperature, product appearance structure, production cycle, and economic benefits should be considered when selecting a release agent.


4. Selection of gel coat resin: There are many types of gel coat resins, which are generally selected according to the conditions of use. The gel coat resins currently used include polyesters and vinyls.


Third, the steps and precautions of glass fiber reinforced plastics hand lay-up

1. Preparation of fiber-reinforced materials: cloth or felt for hand lay-up should be surface-treated in advance, and fiber-reinforced materials that have been pre-treated should be selected as much as possible. Grease. The cutting design of reinforced materials is very important. Generally, cutting should be concentrated to improve efficiency and save cloth. Please note when cutting:


① The warp and weft strength of the cloth is different, and it should be laid alternately in vertical and horizontal directions according to the design requirements. For products with directional strength requirements, unidirectional cloth can be used for reinforcement.


②For products with large surface fluctuations, the fiber cloth should be cut locally, but as few cuts as possible, and the opening should be staggered.


③ The lap length of the reinforcing material is generally 50 mm. When the thickness requirements are strict, butt joint can be adopted, but pay attention to the wrong seam.


④ The size of the cut glass cloth should be determined according to the product size, performance requirements and ease of operation. There are many small pieces of joints and low strength. If it is convenient to construct, use a large piece of cloth to paste.


2. Preparation of resin glue: The process indicators of resin glue include: viscosity, gel time and curing degree.


①Resin viscosity: Resin viscosity, also known as fluidity, is an important indicator in hand lay-up molding. Too high viscosity will cause difficulty in gluing, and it is not easy to soak the reinforcement materials; too low viscosity will cause glue flow phenomenon, affecting quality.


②Gel time: After the resin glue is prepared, the time from the beginning of fever, stickiness and loss of fluidity is called gel time. Generally, it is desirable to stop the gel for a period of time after the paste is finished and then gel. If the gel time is too short, the quality will be affected due to the sticky and impervious fibers of the glue during construction. Conversely, if it does not gel for a long time, it will cause the loss of resin glue and volatilization of the crosslinking agent, resulting in incomplete curing and reduced strength. The gel time of the glue solution is generally shorter than the gel time of the product. The gel time of the resin glue is related to the formula, ambient temperature, humidity, product thickness, etc. The control of the gel time of polyester glue is generally achieved by adjusting the amount of curing agent and accelerator.


③ Degree of curing: Complete curing is an important condition to ensure product quality. From the process point of view, the degree of curing is divided into release strength and service strength. The former is to ensure that the product has demolding strength, so that the product can be removed from the mold without damage, and the latter requires the product to reach the strength of use. Generally adjust the formula to control the degree of curing in the production process. For hand lay-up products, it is hoped that it can be controlled to release within 24 hours. Any longer time will affect the production efficiency. When the room temperature is lower than 15 ℃, heating or heat preservation measures should be taken appropriately.


3. Gelcoat paste preparation: Gelcoat paste is used to make the surface gelcoat layer, its role is to improve the weather resistance, water resistance and chemical resistance of the products, and extend the service life.


Due to the thixotropy of the gel coat resin, it must be fully agitated during use; the thickness of the coating should be controlled at about 0.25 to 0.4 mm; when the gel coat layer starts to gel, immediately paste the glass fiber reinforced plastic and release it after complete curing; use gel coat When the resin layer is used, it is necessary to prevent contamination or small bubbles from entering between the gel coat layer and the FRP.


4. Preparation of hand lay-up forming tools: The most commonly used hand lay-up forming tools are scissors, brushes, scrapers, scrapers, circular grinders, polishing machines, electric drills, etc.


5. Forming of molding process route: The correct choice of process route is the guarantee to complete the task according to quality. Before organizing production, we must fully understand the product performance, structural characteristics and construction conditions, and formulate a practical process route on the basis of analysis and research. Generally, we should consider the following aspects:


①According to product performance requirements, choose the fiber type, resin formula and spreading method reasonably.


②Choose mold material and molding method according to product shape, size and strength requirements.


③Choose the curing method according to the climatic conditions and task conditions. At room temperature above 15 ℃ curing, it takes 24 hours to release the mold; when the task is urgent, the thermal curing process can be used.


④Choose the molding method according to the requirements of glue content control.


⑤ Determine the molding method according to the product surface requirements.


6. Spreading construction: spreading is an important process of hand lay-up molding, which must be carefully operated. Before pasting, first check whether the mold misses coating. When there is a gel coat layer, it is necessary to check whether the gel coat layer is gel (it should be soft and not sticky to the hand). After passing the inspection, start to spread the paste. Brush the glue first, then spread the cloth, and pay attention to the air bubbles until it reaches 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 air bubbles.


When coating, it is necessary to force the air bubbles from one end (or from the middle to both ends) to make the glass cloth fit tightly, and the glue content is evenly distributed.


When pasting products with inserts, the metal inserts must be pickled and degreased to ensure a firm bond with the product. In order to make the geometric position of the metal inserts accurate, the mold must be positioned first.


7. Curing: Hand lay-up products are often cured at room temperature. The normal curing process is divided into three stages: gel, curing and curing. The product can be demolded only when it gels and solidifies to a certain strength. Such as polyester glass fiber reinforced plastic products, it usually takes 24 hours after molding to cure to reach the release strength. The product after demoulding cannot be used immediately, but it should be cured for a week in an environment higher than 15 ℃ to reach the strength of use. However, the strength growth of polyester glass fiber reinforced plastics often takes one year to stabilize.


To judge the degree of curing of glass fiber reinforced plastics, in addition to measuring the strength, it is still possible to check with the Bacol hardness meter. Under normal circumstances, when cured to Bakur hardness 15, it can be demolded. Increasing the ambient temperature will accelerate the curing speed, which can improve production efficiency and accelerate mold turnover. The best ambient temperature for hand lay-up molding is 25~30℃. For polyester fiberglass products with a large exposed area, heat treatment should not be performed before the resin gel, otherwise the cross-linking agent will be volatilized, resulting in never curing. In order to shorten the production cycle of FRP products, post-curing treatment process can also be used.


8. Demoulding, trimming and assembling: After the product is cured to a certain strength, it can be demolded. It is best to use wooden or aluminum tools to prevent scratching the mold and the product. Large products can be demoulded by jacks or cranes, but avoid excessive force or gravity.


For some products with large size and complex shape, pre-release method can be adopted. After the product is demoulded, it needs to be processed in time to remove burrs and flying thorns and repair surface and internal defects.


4. Relevant inspection standards for model making

(1) The mold forming size is accurately controlled and must meet the assembly size of the product after forming;


⑵Model making must meet the design requirements of product forming process:


①Convenient and simple production operation;


②The product quality is guaranteed and the performance is stable and reliable;


③Meet the needs of mass production.


⑶ Mold shrinkage, sealing, stripping slope, surface finish, mold strength, stiffness, wear resistance must meet the design requirements;


⑷Model creation must fully consider the drawing size of the forming material, and the size of the forming material should be reduced as much as possible while fully meeting the product quality requirements;


⑸ The size, angle, flatness, roundness, fullness and fluency of the sample must be fine and accurate; the product structure design is scientific and reasonable, the operation is convenient, and the performance is stable; at the same time, the product has strong processability and aesthetics;


⑹ After the model is created, relevant personnel must be organized for review, complete inspection records must be filled in, and the next process can be entered after the procedure is completed;


⑺Range: All mold making personnel.


V. Specification of FRP forming process

1. The use and storage of materials are strictly regulated to prevent the occurrence of moisture and mildew;


2. The operation of the formula of the material is strictly related to the relevant specifications. The measuring cup and other measuring tools must be used for the standard ratio. After the use of the related equipment, it must be cleaned, dried and properly stored;


3. The time control, temperature control and thickness control of forming must be strictly executed according to relevant parameters;


4. The compactness and permeability control of the paste must be appropriate;


5. Receiving and using low-value consumables such as hand lay-up tools must be replaced with old ones and the relevant procedures must be strictly followed


6. After the mold is formed by hand lay-up, relevant procedures such as inspection, handover, and storage must be processed, and settlement and man-hour accounting should be carried out based on the storage slip.


6. Inspection standards and requirements of glass fiber reinforced plastic molds

1. Mold appearance should be neat and beautiful, full and smooth;


2. The mold surface must have a high finish;


3. The R angle on the same line of the mold surface must be the same size and the transition is smooth;


4. The forming mold has a suitable stripping slope, and the stripping slope is generally controlled between 1.2° and 2.8°; at the same time, it must have a good edge sealing structure;


5. The surface of the mold cavity is not allowed to be sticky and soft;


6. No wrinkles are allowed on the surface of the mold cavity;


7. Pin holes are not allowed on the mold surface;


8. Poor gloss is not allowed on the mold surface;


9. The surface of the mold does not allow peeling of the gel coat layer;


10. Dry spots are not allowed inside the mold;


11. Layering is not allowed on all levels of the mold;


12. Uneven color phenomenon is not allowed on the mold surface;


13. Spots, fish eyes and depressions are not allowed on the surface of the mold;


14. No fiber exposure is allowed on the surface of the mold cavity;


15. No blistering is allowed on the surface of the mold;


16. Cracking or cracking is not allowed on the surface of the mold;


17. No sink marks are allowed on the surface of the mold;


18. The mold cavity surface does not allow whitening and yellowing;


19. The surface of the mold cavity is not allowed to bulge and deform;


20. The lack of hardness and rigidity is not allowed after the mold is formed.


21. The mold locking bolts are evenly distributed, the distribution line is straight, and the locking position is reasonably designed;


22. The mold floor is welded straight, with good rigidity, high strength, and smooth surroundings;


23. The suction holes of the mold are evenly distributed and the position is reasonable. The distance between the suction holes is maintained at 30±2mm, and the maximum diameter of the suction holes does not exceed ¢1.5mm;


24. The mold must have high reliability and stability to meet the strength and rigidity requirements in the production process;


25. After the mold is formed, it must meet the product design size requirements, precision requirements, quality requirements and performance requirements;


26. Tooling fixtures that match the mold must be light, simple, stable, and reliable, and have high operability.


7. Relevant requirements for the use, maintenance and maintenance of glass fiber reinforced plastic molds

1. Before and after work, the mold must be inspected and maintained;


2. After use, you must fill in the relevant records of mold use;


3. Clean the mold regularly for each shift to ensure that the mold is stable and intact;


4. The mold class must organize personnel to conduct a comprehensive inspection of the mold every other production cycle, and strengthen the supervision of the mold operation status;


5. The production personnel must reset the mold in time after each use of the mold, so that it can be positioned and stored;


6. All molds must be equipped with complete mold signs to indicate the running status, production frequency, model specifications, handover date, etc. of the molds.


Source:www.up-resin.com

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