Composites Overview
Composites processes are generally low cost with regards to tooling and equipment costs, depending upon what process is used for comparison. The flip side is that the processes are labor intensive and the quality is operator dependent. The room-temp cure resins allow for working time windows that must be monitored so that the work is complete before the resins get hard. It is one of those things where you only get one chance to get everything in place and the resins and glass consolidated before things are locked together permanently.
The forgiveness is that there are ways to repair the laminate with additional time and money. There will be grinding and dust and reworking something that could have been done better from the first time. Repairing will not look as nice, nor perform as well as a properly planned and completed first attempt.
Safety is something that needs lots of attention. The processes are very operator dependent and we are working with chemicals here, so workers must be protected. Many of these chemicals are regulated by several government agencies. This is why these chemicals are generally difficult to obtain on the street.
The styrene-based polyesters and vinylesters require respiratory protection and skin protection, as styrene is considered by some (California) to be a possible carcinogen. There is a time weighted average for breathing the esters, specific to the percentage of styrene in the mixture. Excessive inhalation can lead to headaches, sinus irritation, and watering eyes. Skin contact is permissible, but can be difficult to remove and can enter the bloodstream.
The epoxy-based resins are more forgivable with regards to respiratory issues, but dermal protection is much more important. Short term occasional exposure is not serious, but can develop into allergic reactions.
Reinforcement to resin ratio
Reinforcement and resin are mutually beneficial to each other. The reinforcement is the strength in the system and the resin is the binder that holds the reinforcement together and shapes the product. The ratio is important in creating the optimal characteristics of cost, quality, and weight of the final product.
The reinforcement may consist of glass fibers (fiberglass), carbon fiber, kevlar, as well as a myriad of other natural and manmade fibers. The resin may consist of thermoset polyester, thermosetvinylester, thermoset polyurethane, epoxy, as well as any thermoplastics. As these are combined to create a product, the ratio used can create a wide range of properties.
The process used and processing goes a long way towards the actual resin to reinforcement ratio. Hand layup is extremely operator dependent where a good, careful laminator can achieve a 30-40% glass loading depending on the design of the glass and the time allowed.
Sprayup processing will allow for glass loading up in the 25 to 35% range. This process is usually a faster pace production process where more advanced equipment is used, though it is generally hand-operated and again operator dependant.
Resin Infusion processing can achieve reinforcement ratios towards 60% depending upon the reinforcements used and the processing. Some reinforcements have voids in them for the resin flow, which remain full at cure and lower the reinforcement ratio.
Infusion processing will have a ratio that is more consistant across the entire part because of the lower interaction with operators and the application of resin.
Vacuum Bagging processing will allow for the highest of ratios, which may reach 75% especially with autoclave operations. Taking very much more resin from the laminate will allow the reinforcement to separate itself and lead to failure.
There are also several more closed mold processing operations including thermoset injection molding, thermoplastic injection molding, compression molding, etc. that I will not get into here.
Energy Conservation
Composites are such a great material for energy conservation. Their superior stiffness to weight ratio allows for them to replace other materials in sectors like transportation in order to gain weight savings. These weight savings of course require less energy to move and stop the vehicles.
This of course comes back to the horsepower to weight ratios which are no secret formula. They were discovered decades ago by racers of all kinds who made their vehicles as light as possible to gain advantage, many times using fiberglass. The sailboat guys know it too; the lightweight carbonfiber masts reduce weight versus aluminum to gain a weight advantage. Drag car bodies made of lightweight fiberglass instead of sheetmetal or aluminum. Circle track cars with fiberglass hoods, noses, and bumpers.
Examples of conserving energy with composites, and the racers got it right a long time ago!
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