Production Of Woodbased Boards

Fibreboards. The production of porous wood fibreboards in both a wet and dry production process are described in Chapter 14 (page 280). The processes are similar forsemi-hardand hard products (Figure 15.29).

Chipboard and Oriented strand board (OSB) can be madefrom many types of timber. There is no need for the timber to have its own active glue, as the process includes gluing. Urea-formaldehyde glue is used for both economical and technical reasons, but different melamine glues, phenol-formaldehyde-resorcinol glue and polyurethane glue may be used, and possiblyalsotimber-basedlignin glue and water-glass glue.The manufacturing process of chipboard is as follows:

1.Thetimberisshredded.

2.The shredded timber is ground to small particles or strands, the latter used in OSB boards.

Production of hard and semi-hard wood fibreboards.

Adding water

15.29

Production of hard and semi-hard wood fibreboards.

3.The shavings are dried to a moisture content of about 2%.

4.Glue is added.The amount of glue by weight is approximately 3-12% and is lowest in OSB boards due to the removal of fine particles.

5.The pulp is made into a sheet on a moving band. OSB boards are usually built up in three layers with different strand orientation.

6.Thesheetisthenpressedat180-200 °C.

7.The boards are dried and conditioned to the desired moisture content.

Plywood is produced in different forms and from many different types of timber, including tropical species, by sawing, cutting by knife or peeling. Sawn plywood is mainly used in the production of furniture and is produced by sawing the log along its length in thicknesses of 1.5 mm or more. The other two types of cutting are used on logs that have been boiled or steamed until they are soft and pliable. Cutting by knife is done along the length of the log as with sawing. By peeling, the veneer is peeled offthe rotating log like paper pulled from a kitchen roll. A plywood board is made by gluing several layers of the veneers together. This can be done in two ways, to make blockboard sheeting or plywood sheeting. Blockboard consists of wooden core strips glued together, usually of pine, which are covered on both sides with one or two veneers. Plywood consists purely of different veneer layers glued together. The adhesive used nowadays is usually urea or phenol glue in a proportion of about 2% by weight. Animal, casein and soya glue give good results as well.

Basic info is found in Chapter 10.

Throughout European history plants have been used as roof and wall-cladding; in general, the different types of grasses such as wheat, rye, flax, oats, barley, marram grass, reeds, ribbon grass, greater pond sedge, fern and eelgrass. Plants can be used for thatching as they are, possibly cleaned of seeds and leaves. Several species can also be used to make boards, and oil from the flax plant is the basic raw material for making soft floor coverings of linoleum. In addition to the ordinary conditions a surface material has to fulfil, plant materials often give a high level of thermal insulation and good moisture buffering properties. Many of these materials are flammable and susceptible to rot. However, eelgrass contains salt, lime and silica and is relatively hard to ignite as well as quite resistant to mould.

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