Let’s look at this in terms of a boat. There are many boats which are made using fiberglass, which begins as a textile—like a long piece of fabric that comes on a roll. The fiberglass is laid into a mold that will create the boat’s hull. In liquid form, a resin is catalyzed and applied to the fiberglass in-mold. Chemically, it will cure and bond to the fiberglass, producing a great deal of heat (called thermosetting). While multiple layers and various techniques are involved, the end result is the boat.
Similar to the boat, composites are popular for a number of reasons, but largely for their combined high-strength for low-weight ration. Generally, they can be tailored to suit different applications, and formed to unique and complex shapes. Also, they are popular for a superior resistance to most environments and can be used by most fabricators without significant investment.
The process of constructing a part within a mold is called molding. Usually, precut reinforcement is placed one layer at a time into the mold and saturated with resin. When the desired thickness and orientation is achieved by the part, it is left to cure. It will have the exact shape of the mold surface once it is demolded.
Originally, laminating referred to applying a thin protective coating of resin and reinforcement over a surface such as wood. The term’s use has since broadened to include virtually any finished composite part, molded or otherwise. A example that is current would be: “The part tested was a 10-ply vacuum bagged laminate.”
The lamination schedule is a list of the individual layers and orientation of the plies used to construct the composite part, and typically specifies the ounce-weight of the reinforcement and the weave style.
The term casting refers to pouring a large mass of resin into a cavity. The cavity can either be a mold when casting parts or the backside filler for a tool when making the mold itself. It is crucial to use specialized casting resins which generate less heat during their cure and thus create less distortion in the final part. To strengthen the casting, fibrous fillers can be added as needed.
Reinforcement Properties and Styles
The physical properties of composites are fiber dominant. This ultimately means, when resin and fiber are combined, their performance remains most like the individual fiber properties. For example, it not satisfactory to merely average the tensile strengths of fabric and resin to determine the panel strength. Fibrous reinforcement is the component carrying the majority of the load, as shown by test data. As a result, fabric selection is critical when designing composite structures. Plant Equipment & Services uses the common reinforcement fiberglass from RPS. Fiberglass comes in various forms and styles, and has many benefits.
Benefits of Fiberglass
Some of the many benefits of fiberglass include:
- great compressive strength
- excellent fatigue resistance
- excellent sanding/machining
- highly heat resistant
- highly moisture resistant
- excellent resin compatibility
Forms of Reinforcement
Fiberglass can be purchased in many different forms and weaving styles. Generally, it is available in tow (pure unidirectional fiber form), veil mats and woven fabrics. It is also offered in a pressed chopped strand mat option.
Tow and Roving
Fiberglass material in this form exhibits the highest properties achievable for a given fiber family. Typically, they are supplied on spools so that they may be fed into filament winders or unrolled and cut as they are needed for selective stiffening. As the resin cures, the fibers must remain in tension or the mechanical advantage is lost. Kinks in tow must first be pulled straight before the fiber will hold a load, once in service. The straighter the initial fabric placement, the better. Using this form of material it is possible to wind extremely strong tubes.
Veil mats are thin plies of continuous strand fibers which are looped randomly throughout a roll of fiberglass. They have the consistency of tissue paper. The veil is held together by a light binder. While they are not intended for structural use, they have two very important functions. Veil mats can be placed in the mold directly behind the surface coat to minimize the print through of the heavier reinforcing cloths applied later. The other use is with sandwich cores. Veil mats can be placed directly over the core to maintain the optimum bond-line thickness. It is also effective at keeping excess resin from draining into the cells of honeycomb cores when a vacuum is not being used.
Chopped Strand Mat
With this material, it is just as the name implies. Typically, the fibers are three to four inches in length and are randomly oriented. While chopped strand mat is not a very strong material because of the short fiber length, it is isotropic, which means that is equally strong in all directions (mat and fillers are the only composite reinforcements exhibiting this trait). Because mat is the least expensive material, it is the most widely used. It is suitable for molds and part production. The fabric print through of gel coats is effectively hidden by the random orientation, and makes molds which are equally stiff in all directions.
Fibers are bundled into yarns oriented in just two directions which makes woven fabrics strong reinforcements. Respectively, the warp and fill yarns run at 0 and 90 degrees. As a result, fabrics are anisotropic, or strong in only two directions. The orientation of the fabrics needs to be as such so the fiber yarns run parallel to the expected loads. Another ply must be added at an angle to the first if extra strength is needed in a different direction. The most common angles are +/- 45 degrees.
These are just a few fundamentals of fiberglass. For more information on fiberglass read our article Fiberglass Repairs Using RPS. PES offers fiberglass repair services using RPS. The RPS Group of Companies designs and manufactures composite corrosion resistant pipe systems and process equipment. From material selection through component design, stress analysis, manufacturing, shipping, installation, and maintenance, PES has the turn key capabilities to ensure you realize the full benefits of your composite installation. Contact us today with the link below for more information!