Making Your Own Prepregs
Composite materials that are used as reinforcements can be impregnated with resin ahead of time, are called prepregs. You use a prepreg in manufacturing different composite parts by cutting it out and laying it onto your mold, shaping as required. Since it has already been impregnated with resin, there are not any concerns with spreading the resin and curing agents on the dry materials while they are in the mold.
Pre-impregnated materials can be purchased from a composites supplier, or they can be made yourself. Woodward Aerospace shows us how.
Carbon Fiber Pipe Wrap
Carbon Fiber can be used to wrap the outside or the inside of pipelines as a way to reinforce and strengthen them. Carbon Fiber is lightweight yet extremely strong. It can be field-installed on pipelines that are clean and non-pressurized.
Repairs to pipelines can be extremely expensive if they need to be dug out of the ground, cut out, and replaced with new sections. This is time-consuming work requiring long shutdowns. Composites repairs can be accomplished by professionals that can access the work area and have a line that is non-pressurized and clean.
These carbon fiber reinforcements help to restore structural integrity that has been lost through age, damage, or other new design requirements. There are many advantages to repairing existing pipelines and other structures rather than replacement.
Interior repair from ABC 10 News in California demonstrates an interior pipeline repair:
An external pipeline repair is shown here in an instructional video. I do have a few concerns about the use of all of the unreinforced resin that is used to cover the carbon fiber wrap. I am not sure what the purpose there is, other than maybe to protect the carbon fiber from future damage.
Compression Molding Large Vehicle Parts
Compression molding with composite resins can yield very durable, strong, and well-engineered parts.
Placing reinforcements (usually fibered glass) and resin in a heated metal mold before compressing it under high temperatures will result in a finished piece with very unique properties. The parts made in these matched metal molds have very repeatable properties, high strength to weight ratios, and are corrosion and chemically resistant. The parts can be painted, and have many positive design attributes.
Ashley Industrial Molding is a company that manufactures such parts. These large parts are made with compression and RIM molding for customer such as John Deere and Case tractors. They have a good video demonstrating their equipment, processes, and finished parts.
Auto Racing Composites
Roush Racing takes us viewers on a tour through their composites shop in a short clip from Roush TV.
Using mostly carbon fiber and kevlar reinforcements, Roush Racing fabricates many different components for the racing industry using epoxy resin systems. Ranging from the front noses for the NASCAR Car of Tomorrow car to drag racecar bodies and small ductwork, Roush Racing’s composites shop does all sorts of fabrication.
The race shop includes two different fabrication processes. Wet layup vacuum bagging is used for some parts, while others are made using prepreg material that goes into an autoclave.
The video tour is well done, and includes everything from the Eastman material cutter to the fabrication process, bagging process, and trim. We also get to see some of the finished parts after they are demolded and trimmed.
These parts are very expensive to manufacture, due to the high cost of materials and labor. Tooling and equipment costs for this type of process are somewhat reasonable, with the exception of the autoclave and the automated cutting table. Composites fabrication of this caliber is labor intensive, but can produce very unique parts that are lightweight and strong.
Use of FRP Composites in Bridges
FRP (Fiber Reinforced Composites) have been successfully used in the construction and repair of transportation bridges in the U.S. for several years. These projects have proven that the materials and work methods are can be successfully used.
FRP rebar can replace steel rebar and provide equal physical strength while eliminating the corrosion problems of having steel embedded in concrete.
Prefabricated bridge decks made of FRP in a factory can be quickly and easily installed in the field to save time and money during the bridge construction project. The large panels are shipped in and laid down, ready to use very quickly. Concrete cure and inspection times are reduced.
Concrete crack repairs can be made to bridges and concrete structures by wrapping them with composite materials to seal these cracks and hold the concrete together, protecting it from further damage.
This technology has been in development for many years, and proper materials, construction techniques, and design guidelines have been established to allow for many successful projects to be completed.
Economics play a considerable role, and this cost comparison constantly changes with the prices of materials on both sides. Composites have the advantage of typically requiring fewer road closures and construction time in the field.
Vacuum Bagging Video
Vacuum bagging is a process that requires unique materials and processes, but can be simple to operation in an ongoing basis.
There are many advantages to vacuum bag molding, a few of which include:
- Improved resin/glass ratio
- More consistency across the laminate and part -to -part as compared to open layup
- Containment of air emissions from the resins
As compared to hand layup and chop layup, there are a few disadvantages, including
- Higher consumable material cost
- Higher capital equipment cost
- Difficulty with superior surface finish
Some parts are more suitable for vacuum bag molding than others. It also depends upon which process it is being compared with.
Vacuum bag molding requires an extremely tight seal between the mold and the bag. Molds with multiple pieces or holes for inserts can be difficult to complete a seal.
Parts that are overly large and complex can present challenges with placing resin and reinforcement before the cure cycle starts. The bag must be completely sealed and under full vacuum before the curing cycle of the resin begins.
The basic premise of vacuum bag molding is that the air is removed from the bag, allowing the atmosphere (air on the outside of the bag) to push the bag onto the part on the mold, compressing the layers of resin and reinforcement. Many misinterpret the process as “sucking the extra resin out.” We are merely allowing the laminate to be compressed by the weight of the air above us in the atmosphere to consolidate it before cure. The excess resin is usually absorbed by extra layers of sacrificial material inside the bag.
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