How it is dimensioned...

Phase A1 / PREPARATION OF THE BOARDS

Phase 1 of the production cycle is entirely devoted to the preparation of the boards in such a way as to ensure dimensional stability as well as perfect bonding. The various processing steps that make up this first phase are described below. They are mainly performed by the supplier of the raw
material. Nowadays, large sawmills are equipped with the bulky machines that are needed
in order to cut the boards to length and to prepare them for further processing. The boards that are delivered to a glulam manufacturing plant are thus ready to begin their respective production cycles.

PROCESSING THAT TAKES PLACE AT THE SAWMILL:

• Drying
• Pre-planing of the boards
• Moisture check ( 9 - 12%)
• Strength-grading and marking

Phase A2 / PREPARATION OF THE BOARDS / Dimensional check

This control is necessary in order to guarantee the basic dimensions of the structural element to be manufactured.
ll of the pre-planed boards that are found to exceed the tolerance limits that have been set for the target values are immediately excluded from the production cycle.

Phase A3 / PREPARATION OF THE BOARDS / Moisture check

This second moisture measurement is done in order to find out whether there have been any changes (eg. as a result of the transportation
of the boards from the sawmill to the glulam-manufacturing plant) in the moisture contents previously measured at the sawmill. All the measurements are accurately recorded and stored since they are included in the documentation that is required by the quality certification bodies.

Phase A4 / PREPARATION OF THE BOARDS / Board matching

Although the laminations that make up each structural element are made from one and the same wood species, they may belong to different strength classes. In the case of beams subjected to bending for instance, in which the highest levels of stress are to be found in a limited area
of the cross section, it may be useful to combine material of a high strength class with material of a lower strength class. This matching process may be automatised: an optical reader detects the faulty sections that need to be cut out (these sections having been previously colour-marked during the
strength-grading phase), and the remaining material to be used in the beam layering is then checked by a computer. Once all these steps have been completed, the boards are ready to be transformed into laminations.A questo punto le tavole sono pronte per essere trasformate in lamelle.

Phase B1 / MANUFACTURE OF THE LAMINATIONS / Joint milling and glue spreading

The boards are glued end to end by means of a so-called “finger joint”, which is executed according to the relevant standard.
The shape of this joint is such as to transform longitudinal tensile stress into shear stress along the gluing lines.

Phase B2 / MANUFACTURE OF THE LAMINATIONS / End-to-end pressure gluing

Once the finger joints have been milled and the glue has been spread,the boards are immediately jointed end to end under an appropriate pressure.This processing step must be performed under controlled temperature
and humidity conditions.

Phase B3 / MANUFACTURE OF THE LAMINATIONS / Planing and crosscutting of the laminations

Thanks to the finger jointing technique, the single boards can be combined into laminations of virtually any length. Each lamination is then planed to a uniform thickness and crosscut
to the length of the structural element which is to be manufactured.This technique makes it possible to get around the most important
dimensional constraint imposed by tree stems: length.

Phase B4 / MANUFACTURE OF THE LAMINATIONS / Temporary storage in the “cache”

In order to ensure optimal jointing, the laminations are stored for at least 6 hours in a special area of the plant (the so-called “cache”) under controlled temperature and humidity conditions.

Phase C1 / GLUING AND LAYERING OF THE LAMINATIONS / The adhesive is applied by a glue-spraying machine

Adhesive and hardener are applied separately on one face only by guiding each lamination under nozzles which create a curtain of adhesive or hardener. This must take place within 48 hours of the planing in order to prevent oxidation of the wood surface, a circumstance which might affect curing.
It is also necessary to monitor the dosage according to the type of adhesive used.Bonding quality is a key issue of the whole production cycle since it has a clear impact on the quality of the end product. Bearing this in mind, it is essential to ensure the constant monitoring of all the relevant parameters
(from the preparation of the mixture to the pressing together of the glued laminations). The rooms set aside for gluing are kept at a constant temperature of ≥20°C: the monitoring of the thermo-hygrometric conditions is carried out by means of an automatic device which records any changes
in air temperature and/or humidity.

Phase C2 / GLUING AND LAYERING OF THE LAMINATIONS / Press beds

Since it is necessary to apply pressure on the layered laminations in order to obtain a beam, there needs to be a counteracting surface to which (mechanical or hydraulic) jigs can be fastened. Such a surface is called a “press bed”: it is made up of a series of metal frames that are fixed to the
floor at a distance of 35 to 40 cm from each other. Such jig frames need to be laid out horizontally in such a way as to match the shape of the element that is to be manufactured. When layering the laminations, it is also necessary to pay attention to the orientation of the growth rings: the growth rings of the top
and of the bottom lamination must point in the opposite direction as those of all inner laminations in order to prevent the beam from splitting as a result of shrinkage.

• straight beams: pressure 0.6 ÷ 0.8 N/mm²
• curved beams: pressure 0.8 ÷ 1.0 N/mm²

6 to 20 hours

Phase D1 / BEAM FINISHING / Planing of the beams

Once they have been taken out of the press bed,the glued laminated elements are passed through an automatic planer.This machine removes all the irregularities that have appeared on the outer surfaces of the beams after gluing and trims
each element to its final width. As a rule, this process results in 4 to 5 mm of material being planed off from each side, which means that pre-planed laminations that were 11 cm wide usually end up as 10.0 cm wide beams.

Phase D2 / BEAM FINISHING / End processing and impregnation

The beam finishing phase covers all processing steps that are needed for assembly and installation of the structure according to the working plan. Most of these steps are carried out by CNC machines,with the processing data being directly transferred from CAD and CAM systems. Finally, the beams are impregnated and,
whenever possible, the hardware is inserted and the parts pre-assembled. When the latter job is done at the manufacturing plant, on-site assembly is made easier. As a result, the installation time is shortened and the precision of the execution is increased.