Five Critical Requirements of Caul Materials
Lightweight but strong, aluminium has been the material of choice for caul plates in the manufacture of plywood, fiberboard, hardboard, and particle board, as well as plastic-and veneer-faced furniture. Aluminium has certain characteristics which make it eminently suitable for this application. As a result of their commitment to quality and value, Arconic is the world’s leading producer of aluminum sheet and plate products.
Caul plates must have sufficient compressive yield strength at elevated temperatures of up to 350°F (176°C) to resist buckling and edge waves from friction constrained thermal expansion. The compressive yield strengths of Arconic’s 2024-T81 and 6061-T6 provide excellent resistance to buckling. The 2024-T81 alloy is more forgiving of gaps between adjacent panels which are cured at the same time. This allows for the use of wider cauls.
The ideal caul material should provide rapid heat transfer from press plate to the load in order to speed resin curing, thereby shortening the process cycle time. Typically, aluminum thermal conductivity for 2024 and 6061 is approximately 1100 BTU in/ft2hr F° which is roughly 36% higher than sheet steel.
Aluminium has a naturally occurring thin and transparent oxide layer which provides its well-known corrosion resistance. To further enhance corrosion performance, this oxide layer can be artificially thickened by anodizing. This has been shown to be an effective way to increase the life cycle of aluminium caul plates. Arconic will drop-ship material to the anodizer of your choice, or provide a finished anodized product at customer request.
Imperfections, such as nicks, gouges, scratches, slivers, etc. cannot be tolerated on cauls used for pressing hardboard or applying impregnated paper overlays, because they will be transferred to the final product. Arconic’s Davenport Works is the world’s leading supplier of surface critical products, such as aircraft skin sheet and bright anodized sheet for automotive, appliance and architectural applications. This capability enables Arconic to provide a superior surface on their caul plate products.
Caul plates need to be light weight for ease of handling in and out of the press. Aluminum weighs about 35% as much as steel by volume: 170 lbs. per cubic foot of aluminium, versus 490 lbs. per cubic foot of steel.