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How much do you know about composites
Composites are made from various raw materials including resins, fibers, core materials, etc. As they have different strength, stiffness, toughness, thermal stability and other performance, their costs and outputs are also different. However, the final performance of the composite as a whole is not only related to the resin matrix and fiber (and the core material in the sandwich structure), but also closely related to the structural design and manufacturing process.
10 Common composite forming processes
Resin: polyester is mainly used
Fiber: thick glass fiber yarn
Core: needs to be combined with laminate separately
Spray molding: Chopped-fiber reinforced materials and resin systems are sprayed into the mold at the same time, and then cured into thermosetting composites under normal pressure.
Typical application: simple fences, low-load structural panels, such as convertible bodies, truck fairings, bathtubs and small boats
Hand paste molding
Resin: no special requirement, epoxy, polyester, polyvinyl ester, phenolic resin are all desirable
Fiber: no special requirement, but hand paste molding and infiltration is difficult to achieve for aramid fiber with a larger basis weight
Core: no special requirement
Hand paste molding: The resin is manually infiltrated into the fiber. The fiber can be reinforced by mechanical weaving, manual weaving, stitching or bonding, etc. The hand paste molding process is usually completed with a roller or brush, and then the resin is squeezed into the fiber with a rubber roller. The laminate is cured under normal pressure.
Typical application: standard wind turbine blades, mass-produced boats, architectural models
Vacuum bag molding
Resin: epoxy and phenolic resins are mainly used, polyester and polyvinyl ester are not applicable, because they contain styrene which volatilizes into the vacuum pump
Fiber: no special requirement, even fibers with a larger basis weight can be infiltrated under pressure
Core: no special requirement
Vacuum bag molding: It is an extension of the above-mentioned hand paste molding process, that is, a layer of plastic film is sealed on the mold to vacuumize the hand-pasted laminate, and an atmospheric pressure is applied to the laminate to achieve the effect of exhausting gas and then improve the quality of the composite material.
Typical application: bonding of core materials in large-size yachts, racing parts and shipbuilding processes
Resin: no special requirement, such as epoxy, polyester, polyvinyl ester and phenolic resin, etc.
Fiber: no special requirement, directly use the fiber bundle of the spool holder, no need to weave or stitch into fiber cloth
Core: no special requirement, but the skin is usually a single-layer composite material
Filament winding: The winding process is basically used to manufacture hollow, round or oval structural parts, such as pipes and grooves. The fiber bundle is wound on the mandrel in various directions after being infiltrated by the resin, and the process is controlled by the winding machine and the speed of the mandrel.
Typical application: chemical storage tanks and pipelines, gas cylinders, firefighter breathing tanks
Resin: usually epoxy, polyester, polyvinylester and phenolic resin, etc.
Fiber: no special requirement
Core: not commonly used
Pultrusion molding: The fiber bundle drawn from the spool frame is dipped and passed through the heating plate, where the resin is infiltrated into the fiber and the resin content is controlled. Finally the material is cured into the required shape. The cured product with a fixed shape is mechanically cut into different lengths. Fiber can also pass through the heating plate in directions other than 0 degrees. Pultrusion is a continuous manufacturing process. The cross-section of the product usually has a fixed shape, allowing small changes. The pre-dipped material passing through the heating plate is fixed and laid into the mold to be cured immediately. Although this process has poor continuity, it can change thecross-sectional shape.
Typical application: beams and trusses of house structures, bridges, ladders and fences
Resin transfer molding
Resin: epoxy, polyester, polyvinyl ester and phenolic resin usually used, bismaleimide resin can be used at high temperature
Fiber: no special requirement, stitched fibers are more suitable for this process, because the fiber bundle gap can help transfer the resin, specially developed fibers can promote resin flow
Core: honeycomb foam is not suitable, because the cells of the honeycomb structure will be filled with resin, and pressure will also cause foam collapse
Resin transfer molding: Lay dry fibers in the lower mold and apply pressure in advance to make fibers fit the mold shape as much as possible and bond them together. Next, fix the upper mold on the lower mold to form a cavity, and then inject the resin into the cavity. Generally, vacuum-assisted resin injection and fiber infiltration are used, that is, the vacuum-assisted resin injection process (VARI). Once the fiber infiltration is completed, the resin introduction valve is closed in order to cure the composite material. Resin injection and curing can be done at room temperature or under heating condition.
Typical application: small and complex space shuttles and auto parts, train seats
Other infusion processes-SCRIMP, RIFT, VARTM
Resin: epoxy, polyester, polyvinyl esterresin mainly used
Fiber: any common fiber can be used. stitched fibers are more suitable for this process, because the fiber bundle gap accelerates the resin transfer
Core: honeycomb foam is not applicable
Other infusion processes:
Fabrics are laid up as a dry stack of materials as in RTM. The fiber stack is then converted with peel ply and a knitted type of non-structural fabric. The whole dry stack is then vacuum bagged, and once bag leaks have been eliminated, resin is allowed to flow into the laminate. The resin distribution over the whole laminate is aided by resin flowing easily through the non-structural fabric, and wetting the fabric out from above.
Typical application: trial production of body panels for small boats, trains andtrucks, wind turbine blades
Autoclave prepreg processing
Resin: epoxy, polyester, phenolic resins are usually used, high temperature resistant resins such as polyimide, cyanate ester and bismaleimide can also be used
Fiber: no special requirement, fiber bundle or fiber cloth is suitable
Core: no special requirement, but the foam needs to resist against high temperature and high pressure
Autoclave prepreg processing: The fiber or fiber cloth is pre-impregnated by the material manufacturer with a resin containing a catalyst, and the manufacturing process is conducted with the use of high temperature and high pressure method or solvent dissolution method. The catalyst is latent at room temperature, so that the material has a shelf life of several weeks or months at room temperature. Cold storage conditions can extend its shelf life. The prepreg can be placed on the mold surface by hand or machine, then covered with a vacuum bag and heated to 120-180°C. After heating, the resin can flow again and finally solidify. An autoclave can be used to apply additional pressure to the material, usually up to 5 atmospheres.
Typical application: space shuttles’ structural parts (such as wings and tails), F1 racing cars
Out-of-autoclave prepreg processing
Resin: usually only epoxy resin is used
Fiber: no special requirement, the same as traditional prepreg
Core: no special requirement, but the use of standard PVC foam requires special attention
Out-of-autoclave prepreg processing: Low-temperature cure prepreg fabrication process is exactly the same as that of autoclave prepreg, except that the chemical properties of the resin allow it to be cured at 60-120°C. For curing at a low temperature of 60°C, the working time of the material is only one week. For a high-temperature catalyst (>80°C), the working time can reach several months. The fluidity of the resin system allows only the use of vacuum bags to cure, avoiding the use of autoclaves.
Typical application: high-performance wind turbine blades, large racing boats and yachts, rescue aircraft and train parts
Semi-preg SPRINT/SparPreg out-of-autoclave processing
Resin: epoxy resin is mostly used, other resins can also be used
Fiber: no special requirement
Core: most materials are suitable, but the use of standard PVC foam requires special attention at high temperature
SPRINT/SparPreg out-of-autoclave processing: When we use the prepreg in thicker structures (>3mm), it is difficult to discharge air bubbles between layers or overlapping layers during the curing process. In order to overcome this difficulty, pre-vacuum is introduced into the layering process, but it significantly increases process time. The semi-preg SPRINT has a sandwich structure which is composed of two-layered dry fibers and one-layer resin film. After the material is placed into the mold, the vacuum pump can completely drain the air before the resin heats up to soften and dip the fibers, and then the curing process can be conducted. The SparPreg is an improved prepreg which can easily remove air bubbles from the bonded two layers of materials when cured under vacuum condition.
Typical application: high-performance wind turbine blades, large racing boats and yachts, rescue aircrafts
Nantong Synasia New Material Co., Ltd. can produce a variety of epoxy resins for composite materials. Welcome all customers to call us and we will serve you wholeheartedly!
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