2. Read one more text on the problem and do the tasks. Wood-Based Panels. Oriented Strand Board

A. OSB (Oriented Strand Board) was first developed in Germany but was then massively developed in the North American market as a structural board to replace the lower grades of plywood. In America OSB technology developed from the production of large particle boards known as waferboards or flakeboards. These boards used almost square wafers up to 75 mm long and approximately 0,4 to 0,6 mm thick cut tangentially from the wood. Commonly aspen, grown for only 10 years to take full advantage of its fast growth rate, was used for waferboard. Waferboards lost their market with the development of OSB. Aspen continues to be used in North America for OSB but in Europe where in 1994 there were two manufacturers with further plants planned, higher quality wood, such as Scots pine forestry thinnings, is preferred. The OSB particles are laid into a three ply structure with the strands oriented as they form the mat. The surface plies are equal in thickness, with the strands running basically parallel to the length of the mat and the core strands, accounting for up to 50% of the volume, are transversely aligned and randomly laid. Boards thickness range between 5 and 25 mm with densities of 550 to 750 kg/m³. Surface quality is achieved by sanding.

2. Fibreboards is a genetic name for seven different board types with widely differing densities and properties. They may be categorized by density and manufacturing process. Raw material, normally softwood forestry thinnings, is chipped and mechanically reduced to basic wood fibre. The chips are steamed under high pressure to soften the lignin, the natural gluing agent in the wood. In the more modern process the fibrous mass is conveyed in an air stream to the mat forming station. The fibres must be coated with resin to achieve good bonding. The mat may be up to 500 mm thick and is then pre-stressed between steel belts to remove air. Cut lengths are hot pressed into sheets giving two very finely finished surfaces.

C. Wood-based panels overcome some of the deficiencies of natural timber in that they have a lower degree of variability, lower anisotropy and higher dimensional stability in the plane of the board, they are available in very much larger sizes and provide a wide range of finishes. The variability is reduced by the random distribution of the components into a more even consistency. The reduction in variability increases as the size of the components decreases. Dimensional stability in the plane of the board is relatively constant. As a consequence sheet materials are ideal where large widths are required such as in flooring and wall sheathing.

D. Fibreboards, particle boards and OSB are relatively new structural materials. They are efficient in their use of waste or low quality timber and small diameter logs. As composites their properties may be developed to suit their end use and they are now able to replace solid timber and plywood, in many situations. Board development is on going and not all boards have their characteristic structural properties defined. Thus alternative methods of specifications are sometimes necessary to enable them to be used in structural situations, typically in flooring, roofing and wall sheathing.

Task 1.

Define which of the statements are:

A- true B- false C- not mentioned in the text

1. The main species preferred for OSB in Europe is Scots pine.

2. OSB contributed to the development of waferboard market.

3. The surface quality of OSB is achieved by sanding.

4. The strength properties of wood-based panels are extremely high.

Task 2.

Which paragraphs (A,B,C,D) express the following ideas?

1. Fibreboards are produced from softwood thinnings.

2. Wood-based panels have certain advantages over natural timber.

Task 3.

Answer the question. Make the right choice.

What are the fibres in fibreboards coated with resin for?

It is necessary _____.

A. to increase moisture content

B. to achieve good bonding

C. to reduce strength

D. to lower hygroscopisity

Task 4.

Finish the sentence in accordance with the text.

Dimensional stability in the plane of board makes it _____.

A. suitable for decorative purposes

B. suitable for the production of paper

C. ideal for railway sleepers

D. an ideal material for flooring and wall sheathing

Task 5.

Answer the question.

Why is aspen commonly used for the production of OSB in America?

A. It grows fast.

B. It has got high strength.

C. Its moisture content is low.

D. No other trees are available.

Task 6.

What is the main idea of the text?

1. New structural materials are of no value in woodworking.

2. New structural materials are very efficient in the use of waste and low quality timber.

3. New structural materials find no application in modern life.

4. New structural materials have many disadvantages over natural timber.