Production process of plywood

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Production process of plywood

STORAGE AND PRESERVATION OF RAW MATERIAL

Wooden raw material delivered to the factory is being stored partly on the ground storage
unit, partly in the water (river and lake). Storing in the water preserves the wood mainly
from damage caused by biological factors. Raw material kept on the ground is preserved
permanently from early spring until early autumn by a system of sprinklers, which serves
the same purpose as storing in the water.

HYDROTHERMAL TREATMENT

The whole of raw material is treated thermally in the water to soften it. The logs are soaked
in water pools in temperature 40-60°C depending on the type of wood. Soaking time
depends on season, type of wood and log diameter and varies between 30 hours for birch,
alder, pine, spruce and 72 hours for beech.

DEBARKING

Mechanical debarking removes bark from logs, with mineral intrusions accumulated during
life of the wood or acquired in process of cutting or transporting.

PEELING

Block is transported to a rotary peeling machine. Axially fi tted in the machine it starts
rotate around its axis. The peeling knife moves forward and peels a layer of veneer
in the form of a long band. Standard thickness of fi nal veneer is 1.5 mm (we peel other
thickness too: 0.8, 1.2, 2.0 and 2.5 mm).

DRYING

Acquired veneer, with moisture content of 30-120%, is dried in bands
in belt-conveyor dryers or in sheets in roll-conveyor dryers at 160-180°C to a fi nal moisture
content around 4-7%.

VENEER REPAIRS

Veneers with natural defects (e.g. knots) are being repaired by removing defect
areas and inserting in their place inserts from sound veneer in the shape of shims
or patches (plugs). Stripes of veneer are jointed by edge gluing to form whole sheets.

SCARF JOINTING

In order to obtain long grained veneer sheets of bigger sizes e.g. 3000 mm standard size
sheets are scarf jointed.

LAY-UP

Lay-up – it is a selecting of veneer sheets for core and those for outer plies and putting
them together. Usually panels are completed from odd number of veneers placed
at right angle to each other. Glue is applied on both surfaces of every second veneer sheet
on roll spreaders. The type of glue used depends on the type of plywood produced.

PRESSING

 

Assembled piles of veneer are pressed in multi-opening hot presses.

FINISHING TREATMENT

 

Plywood panels are given fi nal sizes by trimming on panel saws and calibrating thickness
and smoothing surfaces by mechanical sanders

SORTING

Plywood panels undergo fi nal quality control and are graded for defects.

PACKING

Sheets of plywood are piled up on single-decked palletes. All packets, depending on client’s
requirements and means of transport, are secured with foil, cardboard or with hardboard
and banded with band.

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