A brief discussion on the production of veneerable oriented strand board without formaldehyde addition

Oriented strand board (OSB) restructures the wood grain structure, offering superior mechanical properties, durability, moisture resistance, and dimensional stability compared to conventional particleboard. Its advantages include low expansion coefficient, minimal deformation, excellent stability, uniform material quality, and high screw-holding strength, making it unmatched by traditional particleboard, plywood, and blockboard. Shouguang Luli Wood Industry Co., Ltd. primarily produces formaldehyde-free and veneerable OSB, with an annual output of 300,000 m³.

1. Product structure of veneerable oriented strand board

The veneerable oriented strand board is based on ordinary oriented strand board, with fine material pressed on the upper and lower surfaces. It effectively utilizes the scraps and small firewood from wood processing, saves production costs, improves resource utilization, and makes up for the defect that oriented strand board cannot be directly veneered due to the exposed large particles.

The veneerable oriented strand board uses a graded (diamond roller) paving machine to evenly spread the fine material on the upper and lower surfaces of the slab, making the board surface smooth and flat, with strong decorative properties; the core layer is made of multiple layers of large wood particles oriented together, so it has the characteristics of oriented strand board and can meet various finishing processing requirements.

2. Process flow of veneerable oriented strand board

2.1 Preparation

1) The wood is transported to the drum debarking machine via a chain loader.

2) The peeling machine adopts variable frequency speed regulation. According to the peeling condition of the wood, the drum speed is adjusted to ensure the peeling quality.

3) The peeled bark is transported to the thermal energy plant as fuel. After peeling, the wood enters the long material shaving equipment through a belt conveyor, a chain loader, and a horizontal wood puller to shave oriented strands. The quality of the shavings plays a decisive role in the quality of the veneerable oriented strand board.

4) The scraps and small firewood from wood processing are chipped and shaving to produce fine shavings.

2.2 Drying

1) The wet shavings produced by the long-length flaker are transported to a 460 m3 wet shavings silo for storage to ensure uninterrupted subsequent production.

2) The wet wood chips are dried in a single-channel dryer that is 30 m long and 6 m in diameter. The drying medium is hot flue gas from a thermal power plant imported from the American company GTS. The plant uses fully automated control and is interlocked with the drying system control. This can accurately control the heat of the hot flue gas to ensure the qualified moisture content of the wood chips, while also providing stable high-temperature heat transfer oil for the hot pressing system.

2.3 Screening

After being dried by the drying system, the shavings enter the belt conveyor and are transported to the drum screening machine for screening. The shavings are screened into three specifications. The large shavings with a length of 30 to 160 mm, a width of 10 to 80 mm, and a thickness of 0.4 to 1.0 mm enter the surface dry material bin as surface shavings, and the smaller shavings with a length of 15 to 120 mm, a width of 5 to 50 mm, and a thickness of 0.4 to 1.0 mm enter the core dry material bin as core shavings. The fine shavings are screened again through the swing screen, and then enter the grinder for grinding and stored as the fine material surface layer in the fine material cylindrical silo.

2.4 Gluing

1) The surface and core layer dry shavings stored in the dry material bin are measured by a belt scale and then enter the surface and core layer drum-type glue mixer for glue mixing. The fine material shavings enter the fine material glue mixer for uniform glue mixing.

2) The wood chips after mixing with glue enter two surface dry wood chip metering silos and one core dry wood chip metering silo through scraper chain conveyor and screw conveyor respectively, and the fine wood chips enter two fine material metering silos through belt conveyor.

2.5 Paving

5 metering bins automatically and evenly control the amount of shavings discharged, and 5 paving heads are used to lay the shavings with high precision. Fine shavings are evenly laid as fine materials on the upper and lower surface layers, the two middle layers of long and large shavings are arranged vertically, and the core layer shavings are arranged horizontally. This criss-crossing shavings gives the veneerable oriented strand board extremely high dimensional stability and static bending strength. Both the board surface and the board edge have strong screw holding force. At the same time, the wood texture structure is reorganized, eliminating the influence of wood stress on processing, and has good processing performance.

2.6 Hot Pressing

1) After paving, the slab enters the pre-pressing machine for pre-pressing after longitudinal edge alignment. The pre-pressed slab enters the continuous hot press.

2) Before entering the continuous press, the slab is weighed by a high-precision slab scale, and a mobile density scanner is used to detect the density distribution of the slab, thereby ensuring the stability of the product's bulk density.

3) The slab is hot pressed under the simultaneous action of temperature and pressure using a continuous flat pressing method.

2.7 Plain board processing

1) The hot-pressed blank board is edge-trimmed and then sawn horizontally.

2) The uncut boards are inspected and monitored by online bubble detectors and thickness gauges. The qualified boards after horizontal sawing are cooled by the board turning machine and then longitudinally sawed in the middle, and then enter the stacking machine for stacking.

3) The online installed inkjet printer can automatically and continuously print on the board surface and board edge, and the printing content can be flexibly adjusted according to user needs.

4) The size of the veneerable oriented strand board can be flexibly adjusted according to user needs, and longitudinal middle sawing is not required. The maximum width is 2,550 mm.

5) Sanding is performed according to the different uses of customers. The sanding machine uses Sufuma high-precision sanding machine. The thickness deviation of the plate after sanding is ±0.05 mm.

3. Characteristics of veneerable oriented strand board

Environmentally friendly. The use of isocyanate (MDI) adhesives in the production process of veneerable oriented strand board does not contain aldehydes, benzene, or other substances that are harmful to the human body, ensuring that the veneerable oriented strand board has excellent health and environmental performance.

Good dimensional stability. The veneerable oriented strand board has a 5-layer structure, with fine material on the upper and lower surface layers, the core layer of particles arranged horizontally, and the middle layer of particles arranged vertically, which has good impact resistance and bending resistance.

Good waterproof performance. Isocyanate (MDI) is insoluble in water. The veneerable oriented strand board produced with isocyanate has good waterproof and moisture-proof properties.

The veneerable oriented strand board has a wide range of uses and can be widely used in home decoration, furniture manufacturing, finishing processing, etc., and has a promising market prospect.

Author: Guo Zhiwu

Unit: Shouguang Luli Wood Industry Co., Ltd.

Source: China Wood-Based Panels, Issue 12, 2018

Introduction: This paper introduces the product structure, process flow and characteristics of veneerable oriented strand board.