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Mastercore System Ltd. has invented an efficient, cost-effective process for producing foamed composite profiles/panels that offer significant advantages over the competing materials currently used across a wide variety of commercial applications.
(Published on October - November 2007 – JEC Magazine #36)
ANDREW REKRET, PRESIDENT MASTERCORE SYSTEM LTD.
Mastercore’s new composite material, called “MP” (Mastercore Profile / Panel), is a sandwich construction consisting comprised of an outer shell made of thermoset or thermoplastic impregnated glass-fiber, carbon-fiber, or blended glass- fiber/carbon-fiber matrix, and an inner core of a special CFCfree structural microcell foam material that bonds to the interior of the profile walls.
MP composite panels can be produced in any continuous lineal profile, in any length, and in widths up to 1.20 m. Lineal profile shapes can be designed with sharp corners and a thin or thicker shell for greater impact resistance, rigidity and shear strength. The foam core density can also be adjusted for optimum weight/performance characteristics. With thermoplastic composites it is possible to produce parts for applications requiring cleaner and faster processing such as the trucking industry, while thermosets will dominate parts that require special physical and thermal resistance properties. Thermoplastics will experience much greater growth in the trucking industry.
Mastercore has developed a solvent-free, dry thermoplastic impregnation process. This new patent-pending industrial process is predictable, user-friendly and offers great economical advantages. After impregnation and fibre consolidation, heating under pressure with accurate placement of the thermoplastic foam core provides an automated production method. This method is a natural choice for pultrusion. The company has also developed a method to produce three-directional fabrics with a foam core. This automated production method is best suited for compression moulding or 3-D laminates. Some parts for the trucking industry require filament winding or tape wrapping. The thermoplastic process provides maximum flexibility in design, product fabrication and assembly options. The use of fabrics, tapes or laminates with a foam core also provides opportunities for welding, rapid stamping, co-consolidating and in in-situ tape placement. The main advantage is a significant weight and price reduction, with the opportunity to increase production volumes.
Once the desired profile has been designed using optimizing software, relatively inexpensive dies are designed and built for the different stages of the process.
The injection die is used to wet out the fibres. This eliminates the air trapped in the fibres that could produce voids and reduce impregnation of the fibres by the resin. The injection die is designed according to the specific part shape and wall thickness. The goal is to provide maximum resin penetration to ensure a very good wet out without trapping air or off-gas inside the laminate.
The dies used are shorter than traditional pultrusion dies. The length of a specific pultrusion die depends on many factors such as wall thickness, expected speed, expected surface finish, number of internal ribs, etc. The die length also depends on the time required to bring the composite skins to the expected process temperature. Shorter dies make it possible to heat the die to the expected temperature faster. A shorter pultrusion die reduces the pull force dramatically and proper temperature distribution allows for higher pultrusion speeds.
Foam injection die
A foam die is then used to continue the external skin forming process and to obtain the best surface finish. While the shell is hardening, closed-cell foam (of any desired density) is injected into the hollow portions of the profile. This combination of an outer glass-fibre, carbon-fibre, or blended glass/carbon skin with an expanding and rapidly curing closed-cell foam core that bonds to the interior surfaces of the profile makes the product incredibly strong and light. The use of thermoplastic foam reduces or eliminates the fatigue problems observed with other foams. The foam not only increases the sandwich strength but also provides the high thermal stability required in temperature-controlled environments.
Gel coat die
To complete the process and obtain parts with a superior surface finish, a gel coat is applied in a gel die. This streamlined process enables the MP composite profile to emerge from the die in a finished state. It can simply be cut to any length with a flying diamond-tipped saw-blade, ready for immediate packaging and shipping.
Properties of the final material
The resulting MP profile/panel offers the following characteristics:
The relatively high cost of sandwich composite constructions has long been a barrier to many applications. Combining low-cost glass rovings, mats or veils to produce skins, along with low-cost foam filling, creates the most economical construction material presently available for many types of applications. Generally, by utilizing an MP composite profile, one can expect a 30-50% reduction in raw material costs, while ending up with a product that is lighter and stronger and less thermally conductive than previous profiles. Lower weight brings savings in transportation – the weight translates directly into lower cost. Therefore, when compared to a solid part, the MP product is a very cost-effective approach, reducing long-term operating expenses in every situation.
Once the desired product shape has been established, then it is necessary to design the various aspects of the MP process. The range of potential properties is broad and only limited by the designer's imagination for choices such as fibre material, wall thickness, or foam density. Many standards are taken into account during the computer design process. A number of parameters are considered such as the product’s expected weight, foam quality and density, wall thickness, thickness and geometry of the internal web, thermal performance and surface finish.
A wide range of mechanical properties can be produced through the use of different materials and geometrical designs. The skins are responsible for the strength of the panel. The foam core supports the skins so that they don't buckle and stay fixed relative to each other. The material’s properties and the foam thickness determine the stiffness of a panel or profile. The skins are produced using a material with a high modulus of elasticity and the foam core is designed with an optimum shear modulus. The engineering design focuses on obtaining a balance between skins and foam core so that neither material fails before the other is stressed beyond the design level. Despite its relative lightness, the design of the floor profiles provides significant compressive strength, tensile strength, and shear stiffness in any direction. All the characteristics are well in excess of those necessary for a truck floor. The panel wall system facilitates construction of truck bodies and trailers and the future replacement of damaged panels. Eliminating steel and sheet metal
reduces the weight of the truck, thus increasing gas mileage. Most materials currently used in truck body construction are subject to permanent denting from impacts. The MP panel is dent resistant, far lighter, stronger and requires no assembly rivets, exterior or interior bracing. Its superior properties allow the production of better-looking and longer-lasting roll-up doors.