Author: AKeson

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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Intro to Filament Winding

Filament winding is an open molding process that is automated by using a rotating mandrel as the mold. This mandrel acts as a male mold which allows for the control surface to be on the inside, and the outside diameter size being dependent upon the laminate schedule. The reinforcement to resin ratio can be very high with filament winding because of the automated nature of the process. Very high tensile strengths can be achieved depending upon the use of materials and their orientation. Products that are manufactured include chemical storage tanks, pipes, stacks, pressure vessels, and rocket motors. Lightweight storage tanks have been a real area of growth as of late. The use of these high pressure vessels has been applied to air packs for firefighting as well as Liquid Natural Gas storage devices for alternative fuel vehicles. The process works by feeding continuous strand roving through a resin bath and winding it onto a rotating mandrel. This feed mechanism traverses the length of the mandrel to create a predetermined geometric pattern. After sufficient layers have been applied, the laminate is allowed to cure on the mandrel before the molded part is stripped away to begin...

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Chemistry of Cure

Lets look a little bit closer at the chemistry of curing a polyester/vinylester resin. There is lots of chemistry involved, but it is broken down so it is not too complicated. The initiator is the correct technical term for what some call the catalyst or hardener. This initiator is the additive that begins or speeds up the chemical reaction and becomes part of the crosslinked polymer. Free radical polymerization is the process that occurs during the curing cycle of a polyester resin. The initiator (catalyst) decomposes into free radical molecules, which work to crosslink the polyester and styrene molecules in the resin. The rate of cure can be increased with the addition of more initiator. Selecting the appropriate initiator is important to the control of the chemical reaction. Styrene-based resins use several types of initiators. These include: ketone peroxides, cumine hydroperoxides, acetylacetone peroxides, and benzoyl peroxides. These can also be blended and the initiator package will be recommended by the resin supplier. Methyl Ethyl Ketone Peroxide(MEKP) is the most common and widely used initiator, and is most cost effective and easy to use. It comes in clear or red tinted and can be used as a fine-tuning for resin cure time with the adjustment of its percentage from 1.25% to 3.0%. Cumene Hydroperoxides (CHP) achieve All new Live Dealer games for Blackjack, Baccarat and Roulette have gone down a...

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