Author: AKeson

Resin Additives

We already learned about the basic resin system, and will now discuss the resin additives. Additives are used to modify and enhance resin properties for specific applications. The first additives under discussion will be thixotropes. This additive is used to modify the flow and viscosity properties of the resin to gain processing advantages. Especially important on vertical surfaces, the liquid resin must be viscous enough to stay in place while the resin moves into the cure cycle. Polyester resin commonly uses fumed silica. Fillers are inert additives for resin that are mainly used to reduce cost. Some are mixed in during processing, some come loaded into the mix already. Mixing the resin to keep fillers in suspension is very important. Types of fillers include: Mineral fillers, Calcium Carbonate, Calcium Sulfate, Talc, Mica, Wood Flour, Walnut Shells, Corn Cobs, Microspheres, Ceramic spheres, etc. Pigments and colorants can be added to resins and gelcoats for cosmetic purposes and for weatherability. High sheer mixers blend resin and fine pigments to create pigmented gelcoat. Fire Retardants are important for resin systems depending upon their application. Additives such as alumina trihydrate and antimony trioxide reduce flame spread and smoke generation during flame conditions. Fire retardants are required for applications where reducing fire hazards is important, and I have worked with this for applications in public buildings. Other applications include train and airplane parts as...

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Home Workshop Supplies

Sometimes the most difficult aspects of working on fiberglass projects at home is obtaining the proper supplies. Now that we have the internet, this is greatly simplified, and many online stores exist to sell many different types of resin and reinforcement; tools and supplies. One of the problems with this is the cost of shipping the resins as hazardous materials. And actually seeing and handling the reinforcement will help in determining if it is up for your application. Sometimes it is advantageous to buy supplies from a physical store. This saves time and money from shipping, and allows for better inspection of the purchased products. Local sources are not always easy to identify. Many times automotive bodyshop repair stores carry fiberglass resin. I have found that marine repair supply stores carry a more extensive repair supply, including epoxy, polyester, fiberglass sheeting, and even gelcoat and associated chemical additives. When purchasing esins and gelcoats always keep in mind the shelflife. My experience has always been that polyester, vinylester, and gelcoat have about a six month shelflife from when it was manufactured. Be cautious at autobody supply houses that sell low volume amounts of resin and may have some old stock. Epoxy generally has a longer shelflife. A good practice when obtaining new materials is to always do a test run in a small dixie cup, sometimes called a “Gel Test”....

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Alligatoring Causes

One of the challenges of using Gelcoat is the potential for the defect called alligatoring. This is described as a wrinkled surface on the completed part after it is removed from the mold, and results in extensive post-mold repairs to the cosmetic surface of the part. There are four scenarios that may cause this alligatoring to occur. Applying the gelcoat film too thin is the primary cause. This thin layer of gelcoat will lose a larger proportion of monomer to evaporation than thicker layers of gelcoat. The crosslinking process will deviate from the manufacturer”s intended formulation. This undercured gelcoat is then attacked by the laminating resin which wrinkles the gelcoat layer. Applying the manufacturer-specified mil thickness of gelcoat will prevent this condition from happening. Another scenario of alligatoring is caused by laminating on undercured gelcoat that is the correct mil thickness. This undercure may be caused by: insufficient cure time, insufficient cure temperature, initiator problems, and compressed air contamination. Closely following the manufacturer”s Betsson Casino on Suomessa erittain suosittu. specifications with regards to shop conditions, initiators, and proper equipment will minimize these problems. The spraying process is another cause of alligatoring. Keeping a wet edge is important. This means that the new gelcoat is applied over gelcoat that is still wet, which allows for all of the gelcoat to cure at the same time. Fresh gelcoat sprayed over cured...

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Pultrusion Processing

Pultrusion is a continuous process similar to steel or plastic extrusion for creating products with a constant cross section. Examples of these products are rod stock, structural shapes, beams, channels, pipe, tubing, fishing rods, and golf club shafts. High structural properties are created because of the extremely high fiber loading afforded with this process. A resin bath impregnates the continuous strand fiberglass roving, mat, cloth, or surfacing veil before it is pulled through a steel die. This die is responsible for the shape, consolidating the reinforcement, and controlling the fiber/resin ratio. This die is heated to cure the resin as it passes through and out to the pulling mechanism which controls the speed of processing. Advantages of this process include low labor costs due to the ability to automate. It also allows for cross-sectional shapes ranging from simple to very complex. Very high strengths can be achieved due to the high fiber...

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Composites in the Military

The military has been using composite materials for decades. Mostly applied to the aerospace segment, composites are now finding more uses to the traditional armed forces. One of the uses for military ground forces is in the segment of armored vehicles. Metal armor competes with composite armor with metal being less expensive but heavier. This weight advantage has required the use of composite armor for the “upĀ  armoring” of vehicle systems that were already near their max payload. This minimizes the amount of other weight sacrifices being made in order to add armor. Weight and performance are becoming more important as military tactics transition towards fast and nimble. This will create many future applications for composite materials as acceptance and testing open new...

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