During the construction of particle board in the extrusion pressing process, what is the orientation of the wood particles with respect to the plane of board?
Try it first: pick an option, then read the explanation.
Manufacturing Particle Board
Particle board is an engineered wood product made from wood chips, sawmill shavings, or even sawdust, mixed with a synthetic resin or another suitable binder. This mixture is then pressed and extruded. The method of pressing is crucial as it determines the internal structure and properties of the board.
- Platen Pressing: Pressure is applied perpendicular to the face of the board. This orients the particles parallel to the board's surface (0°), creating a stronger board.
- Extrusion Pressing: Pressure is applied along the edge of the board, pushing the material through a die. This is the process described in the question.
Detailed Analysis of the Options
(a) 45°, (b) 30°, and (d) 0°
An orientation of 0° (parallel to the plane) is characteristic of flat-platen pressed boards, not extruded boards. Other specific angles like 30° or 45° are not the primary orientation resulting from the extrusion process. The forces involved in extrusion lead to a distinct perpendicular alignment.
(c) 90°
This is the correct answer. In the extrusion pressing process, the mixture of wood particles and resin is forced through a die. The pressure is applied parallel to the length of the board being formed. This force causes the wood particles to align themselves predominantly in a direction perpendicular (at a right angle or 90°) to the plane (face) of the board. This results in a board that has good dimensional stability but is generally weaker than platen-pressed boards.
Particle Board Pressing Methods
| Pressing Method | Direction of Pressure | Resulting Particle Orientation |
|---|---|---|
| Platen Press | Perpendicular to the board face | Parallel to the board face (0°) |
| Extrusion Press | Parallel to the board length (along the edge) | Perpendicular to the board face (90°) |
Study Tips
- Extrusion = Pushing Out: Think of extruding something like toothpaste from a tube. The force is along the length. In board making, this lengthwise force turns the particles sideways.
- Platen = Pressing Down: A platen press works like a giant flat stamp, pressing down on the face of the board. This flattens the particles, aligning them with the face.
- 90° for Extrusion: This is the key association to remember. The extrusion process results in particles oriented at a right angle to the board's surface.