Continuing with the series of articles on the different manufacturing technologies with composite materials, today we bring you a publication on the infusion process and its characteristics.
Infusion is a manufacturing process of FRP composite material with properties superior to manual lamination or wet lay up. Unlike this, the lamination of the reinforcing fibers is carried out dry, impregnating them with the polymer resin later using a vacuum.
Phases of the infusion process
As we have mentioned, the laminate is positioned in a mold, that is, all the fabrics and reinforcing materials that will form the piece. When the geometry that has to be followed is somewhat complicated, a special light spray adhesive for infusion is usually used, which helps the reinforcement stay where it should be.
Once all the fabrics, cores and other reinforcements have been stacked, the infusion bag is prepared with all the necessary materials. These will vary depending on the type of part, its geometry and size. In general we can summarize them as follows, following an order from the last layer of the laminate (face B) outwards from the mold:
– Peel ply: Peel ply is a synthetic nylon fabric on which the resin does not adhere, so once the piece has cured it can be removed. This skin protects the laminate from environmental contamination during the process and leaves a rough and uniform finish on side B. Therefore, it is advisable to use it when it is necessary to subsequently adhere the FRP piece or obtain a decent finish on side B.
– Release Film or Bleeder: This film of plastic material allows the passage of excess resin and air trapped in the laminate, as well as the evacuation of volatiles and solvents thanks to perforations made in the film itself. Depending on the number of perforations per square inch they are found as P0, P3, P31… In addition, it protects the laminate from external contaminants.
– Blanket or breather: The blanket is a glass fabric that distributes the vacuum pressure evenly across the laminate, allowing air to circulate easily. Also, it absorbs excess resin.
– Vacuum bag: Made of an airtight material, it allows a vacuum to be generated between the laminate and the surface of the mold, compacting the material and eliminating air and other gases included inside.
Before closing the vacuum bag against the mold flange with a special airtight tape, the positioning of the vacuum valve and the resin intake must be studied.
From an external tank, the resin will be absorbed and forced by the pressure gradient generated in the part with the vacuum. In this way, the resin will impregnate the laminate and serve as a bonding material for the reinforcement once cured. Therefore, a poor design of the location of the vacuum and resin feed intakes could generate preferred resin channels, leaving areas of the piece without infusion.
Dry fiber will cause critical failures that are difficult to detect and poor mechanical properties, being a phenomenon that is difficult to repair.
Normally it is primed in the middle and the vacuum points are located at the ends or perimeter of the piece. However, each part geometry is completely different and will require its own study. To improve this, open pipes and meshes are added at the priming points to promote the flow of resin throughout the entire piece.
Most used materials
The materials used in the infusion process are diverse. Due to the applicability of this manufacturing method, it is common to find fiberglass and thermostable resins . In particular, non-crosslinked fabrics improve resin flow, while mats tend to slow it down.
As for resins, it is important to have good control of them. First of all, they must have an appropriate viscosity that allows good fluidity (not thixotropic) . Additionally, the curing time must be known, since curing prematurely would block the movement of the resin to infuse the rest of the piece.
It should be taken into account that curing is an exothermic reaction, and curing will be accelerated with increasing temperature. The molds can be heated using resistances to cure the part in it.
Properties and benefits of the infusion
Regarding the mechanical properties of this process, they are higher than in manual lamination, because the curing is carried out with vacuum pressure and the resin/fiber ratio is somewhat more accurate (without being close to optimal yet). In this way, for a piece with the same mechanical properties laminated manually, the weight of the infusion piece will be reduced.
The price of this technology is economical, as long as the process is controlled and studied well . However, the production volume is not too high.
It is very suitable for large geometry and not very complicated shapes of a single part, such as boat hulls, wind turbine blades or paneling.
Another important advantage is that operators do not have to be in direct contact with the chemical elements of the resin, protecting it from external elements and contamination.
As you already know, at Iberia Compositech we are experts in producing composite material parts and we work using various technologies, selecting the most appropriate for each project based on factors such as the technical properties of the part, its final use or the quantity to be produced.
If you want to know all the processes we work with or leave us a specific question, you can take a look at the technologies section or fill out our contact form .