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Views: 21 Author: Site Editor Publish Time: 2021-02-22 Origin: WOOD168.NET
In high-quality plywood manufacturing, mastering the thickness of the wood veneer is a critical, yet often misunderstood, process. The thickness of the finished plywood product is the result of a series of complex changes that the veneer undergoes. This guide breaks down the science and practical steps behind achieving precise veneer thickness, from the initial rotary cutting to the final product, ensuring product integrity and minimizing waste.
To understand the final product, it's essential to measure the veneer's thickness at four key stages. Using the same screw micrometer at consistent measurement points is crucial for accuracy.
Nominal Veneer Thickness: The target thickness specified for the peeling process.
Actual Peeling Thickness: The thickness measured directly after rotary cutting.
Veneer Thickness After Drying: The thickness after the veneer is dried to its target moisture content (8%-12%).
Finished Product Veneer Thickness: The final, compressed thickness of the veneer within the completed plywood panel.
The veneer's thickness is not static; it changes at each stage of production. Ignoring these factors can lead to significant deviations in the final plywood panel.
Peeling Rebound: After being compressed by the pressure ruler during rotary cutting, the veneer undergoes an elastic rebound, causing its thickness to slightly increase.
Drying Shrinkage: As moisture is removed in the dryer, the veneer shrinks, resulting in a reduced thickness. It is important to measure the specific shrinkage rate for your process, as it differs from the general shrinkage rates of uncompressed wood.
Gluing Expansion: The application of adhesive introduces moisture, causing the veneer to expand and increase in thickness before pressing.
Hot Pressing Compression: During the hot pressing stage, the veneer is compressed under high heat and pressure, which significantly reduces its thickness to form the final panel.
To achieve the desired finished thickness, the nominal peeling thickness must account for all these changes. The formula for the nominal veneer thickness is:
The peeling machine must be precisely calibrated to produce the specified nominal thickness. This involves setting the feed amount (the distance the rotary knife advances per rotation) while also accounting for the compression applied by the pressure ruler.
Adjusting the Feed Amount:
The feed amount is determined by the nominal thickness. However, due to machine tool accuracy and other factors, the actual thickness may deviate.
To correct this, you must adjust the feed amount based on real-time measurements. For example, if a nominal thickness of 1.20mm is required, the feed amount might be set to 1.10mm to compensate for machine-specific inaccuracies. This trial-and-error adjustment is best performed at the start of a log to minimize wood waste.
Controlling Pressure Ruler Compression:
The pressure ruler's compression rate must meet specific technical requirements to ensure a smooth, high-quality veneer.
To verify and adjust the compression:
Measure the thickness of an uncompressed veneer sample.
Measure the thickness of a veneer peeled with the pressure ruler applied.
Calculate the compression rate and compare it to the required specification.
Adjust the gap width of the knife accordingly to achieve the desired compression.
The production of high-quality plywood relies on a deep understanding of veneer thickness at every stage. By meticulously accounting for factors like rebound, shrinkage, expansion, and compression, manufacturers can accurately set the nominal peeling thickness. Precise rotary cutting machine calibration and continuous quality control are essential to producing consistent, high-quality plywood and minimizing material loss.
