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Drying of the boards
Softwood- boards are dried down to a moisture content of approx. 12 % and then planed.
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Strength-grading
The planed dried boards are strength-graded either visually or mechanically. For the outer lamellas of the glulam additional requirements concerning the outward-appearance of the glulam are taken into account.
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Cutting off knots and other wood-defects
Board sections with wood-defects having significant influence on the strength or the outward appearance such as knots, resin- or bark-pockets are cut out off the boards dependent on the strength class and the surface-class. The boards are jointed together lengthwise to a theoretically infinite lamella using fingerjoints (glued connection between the edges of two boards which have a shape similar to a hand).
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Planing of the lamellas
After the fingerjoints have been hardened the lamellas are planed to thicknesses of up to 45mm.
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The glue is applied on the broader edge of the lamella. |
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Pressing
At least three lamellas are stacked and pressed in an either straight or curved press.
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Planing of the glulam
After the gluelines are hardened the raw glulam is usually planed and chamfered.
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Factory assembly and further detailing
In most cases the glulam members are cut to their final size and joints are fixed in the plant. If necessary the members are given preservative treatment or temporary coating against the influence of direct weathering during construction and the members are wrapped with packing material.
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Glue lines are very thin. The portion of glue in a glulam-member is less than 1%.
Glulam is strength-graded and refined by lamination. Therefor its permissible bending strength is up to 50% higher than the permissible bending strength of the usually used solid-wood.
As a result of the production-procedure glulam members are deformed less through shrinkage and have a higher resistance to cracking. As the single lamellas are very flexible unless bonding together, it is very easy to produce curved glulam members. Spatially curved or twisted members require greater efforts.
