Grading at the drying line maximizes profit 

Today, high-quality raw material is getting more and more scarce. Veneer is manufactured from wood that has been grown quickly – in about 5-7 years – to its chopping size. This means the wood fiber is poorer than fiber from a wood that has been growing for decades. 

There are huge differences in fiber qualities of different wood species. Even two blocks of the same species can vary in quality, if they have grown in different conditions. With varying qualities of raw material, grading at the drying line helps you make sure your end products are exactly the quality you want them to be. 

If you don’t grade veneer sheets correctly after drying, you may be losing profit. Ask yourself: 

• Are you producing less face veneer than expected? 
• Does your end product quality suffer from faulty face veneer sheets? 
• Do you break a lot of sheets during sorting? 
• Do you produce over-quality just to make sure the product is good enough? 

Why should you grade veneer sheets after drying? 

Wrong sorting decisions at the dryer can have a huge negative impact on your business. If you accidentally send face veneer quality into core veneer stacks, you will lose profit. If you send poor quality sheets into face veneer stacks, they will be used as surface sheets. This means end product quality drops and you will again lose profit. 

Automated grading helps you accurately decide which process to send sheets to after drying. The goal is to assign the best possible quality class to each one, so that:  

• good-quality sheets can be sent to face veneer stacks with or without extra processing 
• core veneer quality sheets can be sent to stacks with or without extra processing  
• sheets that have defects can be sent to patching before they are categorized as face or core veneer sheets 
• poor-quality sheets can be sent to composing, where defects are cut off and good-quality pieces are composed into full-size sheets. 

Visual veneer grading at the drying line 

When humans sort veneer sheets, it takes up a lot of time, is costly and inaccurate – see our previous blog about the faults in veneer visual analyses done by humans. Also, when humans sort and lift dry sheets into stacks, they can cause cracks or even break them. 

Camera-based analyzers bring cost-effectiveness and accuracy to grading: they notice and analyze all cracks and knot holes to the millimeter. Their analyses are reliable and they allow you to automate sheet handling, causing less broken sheets. You can produce more face veneer quality and your mill makes more profit. 

With accurate visual grading, you will know for sure that your face veneer quality is approved by your customer. You can accurately customize end products according to specific requirements or design preferences. This will help you make the most profit and utilize your raw material in the best possible way. 

Moisture-based veneer grading at the drying line 

Moisture content varies a lot between different wood species and can also vary greatly within a single sheet. Some mills utilize handheld moisture meters to analyze veneer sheets after drying. This only analyzes random parts of the sheet and because of the manual labor required, can only be used to analyze a small sample. 

When you use cameras to grade veneer sheets, you can analyze each whole sheet. You will know the total moisture content for each one, recognize their high moisture spikes and notice the areas or sheets that would cause problems in gluing. 

With accurate moisture analysis you don’t need to keep testing and adjusting settings to know how wet sheets you can let through. You will understand exactly how and when to add or reduce drying speed or time to maximize capacity. You will also know which sheets need further drying before delivering them to the following process phase. 

Strength-based grading at the drying line 

In addition to their visual and moisture qualities, veneer sheets can be graded by their strength. This is especially important in manufacturing building materials for beams, walls, floors or ceilings, where certain strength qualities are a must.  

Strength analyses are mainly used by LVL manufacturers, but they are slowly getting more popular among plywood manufacturers, too. 

Strength measurements are taken by analyzing the time it takes for sound waves to pass through the sheet. Based on the results, you can grade the sheets to a number of strength classes, depending on the panel structure you are manufacturing.  

The goal of strength analyses is to optimize panel structure: When you manufacture high-strength beams, you want to mix high-quality sheets with poor-quality ones in the right way to optimize panel strength and cost-effectiveness. On the other hand, if you don’t need high-strength panels, you will want to optimize the use of poor-quality ones. 

The final strength analyses are done after gluing. The panels’ bend and breaking strengths are tested to make sure grading has been done properly, and grading settings can be trusted for continuous manufacturing - with occasional quality checks of course. 

Accurate grading helps tailor products for customer needs 

Whether it's selecting veneer sheets with certain visual properties or making sure they meet specific performance standards, grading provides flexibility to tailor products for diverse market needs. This improves product value and market competitiveness.  

Raute has a full selection of different kinds of visual, moisture and strength analysis tools for veneer drying lines. The best option depends on your automation level, capacity and customer demands for quality – we will assist in selecting the best solution! Check out our Analyzers webpage for more!

> Read more about the whys of grading 

> Read more about grading in the peeling line.