Blockboard is one type of engineered compound plywood board where softwood strips are joined edge to edge and bonded together machining often a sandwich structure placing hardwood between them. Block board is usually found in different sizes and thickness. 2440 x 1220 x 30mm is the normal size of block board.
Technical Properties of Blockboards
- Modulus of elasticity long
- Bending strength
- Bending strength cross
- Formaldehyde emission
- Modulus of elasticity cross
- Fire safety category
- Thickness tolerance
- Length and width tolerance
Types of Blockboards
The classification of block boards depend on different properties such as quality, use, raw wood used for the core. Followings are the type of blockboard:
- Depending on quaity and use:
- Depending on the raw wood used in the core:
Different aspects of these types are briefly discussed below:
Interior Grade Blockboard
These grades are made for indoor uses which are resistant to moisture and called MR (Moisture Resistant) eg. Furniture, door, window shutter.
Exterior Grade Blockboard
This variety of blockboard is manufactured for outdoor uses. These are called BWP (Boiling Water Proof) or as BWR (Boiling Water Resistant). This high quality of resistance is because of the adhesives used here are also good in quality.
Softwood Block board
Solid blocks of wood are used to make each blockboard sheet those are attached together using glue. The sheets are called strips or battens. The surface is covered with hardwood veneers.
Hardwood Block board
Hardwood is dense, heavy, costly, strong as the core is made from hard sheets. The coating is also by hardwood.
Processing of Blockboard
Followings are the steps of blockboard processing:
The logs of timber are sliced at first for making the raw of blocks. Strips may be 25 mm.
2. Rotary Cutting
For outer layer, logs are cut at rotary cutting. Thus veneer for coating is obtained.
To attach the slices glue or adhesives are used eg. Urea formaldehyde, Phenol formaldehyde which is called plastic resin. Exterior grade block board requires phenol formaldehyde. Gluing is done under high pressure.
The blocks are dried to reduce the moisture as well as water content left inside blocks. For drying the blocks are kept before the sun. The moisture content is reduced to 10-12%. After proper drying, they are ready for making a sandwich.
Blocks are attached together used softwood or hardwood as required for interior or exterior grade required.
Final finishing giving lamination, a coating is done.