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 loading.
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 another.
Fiberglass Reinforcement
Fiberglass reinforcement materials are a pretty complicated subject and hopefully we can keep it clear. There has been all sorts of nomenclature developed over the years to describe the different weights and styles. When we talk about fiberglass we are really talking about fibers of glass. For the reinforcements we are discussing, they are bundled together to form larger, more workable bundles.
Roving is a ball of continuous filaments wound into a 40 to 5o pound ball. This is commonly used in the fabrication shop with chopper guns and filament winding equipment.
Chopped Strand Mat is the most basic reinforcing materials that comes as a sheet good on a roll. It is fiberglass that is chopped into small pieces and mixed with a binding material to hold it together, before being randomly oriented into a continuous mat.
Continuous Filament Mat uses a continuous fiber nonwoven to itself and contains some sort of binder material. I have also worked with some continuous filament mat that is stitched together to omit the binder.
Surfacing Veils are a non stitched mat product that use very fine glass fibers in random orientation to assist with achieving an improved surface finish. They are intended to keep the coarse fibers away from the gelcoated surface to prevent print-thru.
Woven Roving (Knytex) is a very diverse product that is widely used throughout many applications and processes. It consists of continuous rovings woven in specific directions to each other and then sewn to a Chopped Strand Mat with thread. They come in hundreds of different combinations of directions; including unidirectional, bidirectional, triaxial, and quadriaxial. The Chopped Strand Mat also comes in different weights and sometimes may be substituted with Continuous Filament Mat.
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