Why and how should you grade veneer sheets?

Whether you want to manufacture veneer sheets that can be formed into furniture, good-looking wood flooring or ceilings, or you want to replace concrete with strong LVL, wood quality matters. 

The secret to producing veneer sheets that are best suited for their end use is grading: sorting each veneer sheet based on its visual, moisture and strength qualities.  

The better you handle your sheets in earlier manufacturing stages, the more benefits you get later in production: you can save up to 10% of energy in drying, free up to 20% of dryer capacity and produce exactly the end-product quality your customer wants. 

In this article we explain how visual and moisture analyses help optimize veneer manufacturing processes – more than you might think. 

Quality of wood matters in veneer manufacturing 

Traditionally, veneer sheets are categorized by operators who observe their surface quality. When a fault is noticed, operators decide which end-use the veneer sheets can be used for, and what is their next processing phase.  

However, human eyes are not the best at analyzing veneer quality, so your mill may run into one or more process issues. Ask yourself: 

• Do you get varying results with your current veneer grading methods?
• Does your peeling line constantly produce more sheets than you can dry?
• Do you want to reduce energy consumption or costs in drying, but it seems difficult?
• Do your panels delaminate in hot pressing?  
• Are there splits and waviness in the veneer sheets? 

 Human performance in visually grading veneer sheets is variable

As humans we are only able to grade visual veneer qualities. We cannot see all faults in the sheets at all, and are not accurate or efficient with our analyses: 

1. It is difficult for humans to concentrate for long periods of time, so we make mistakes in analyzing the sheets:  
   • Bad quality sheets can be accepted as higher quality than they actually are. This results in lower-quality end products.  
   • Good quality sheets are categorized as lower quality to make sure they are good enough. This means the end product quality is too good and you cannot produce as much high-quality end product as you should. 
2. Accurate grading requires a lot of training.  
   • Even if you train people the same way, they do things differently. The quality or grading is not constant between different people. Quality also changes depending on the time of day or the level of a person’s tiredness. 
   • The availability of skilled labor is constantly decreasing, while labor costs are higher. If you invest in training your people and they decide to leave the company, you have to start the costly process all over again. 

When you use machine-based tools for visual analysis, your grading is accurate and consistent. This helps you use resources efficiently and optimize production. 

Without moisture grading you lose raw material, energy and capacity 

You can also sort veneer sheets by their moisture content. This is something humans cannot do. If you skip moisture-based grading, your dry veneer sheets will most often be either too wet or too dry.  

Uneven moisture quality causes problems in later stages of production:

1. Too wet veneer sheets that are glued and pressed together can blow up in pressing. This means you end up losing valuable raw material to waste.  
2. To avoid blowing up, you might use longer pressing time in the sheets to make sure the moisture inside the panel equalizes. This reduces the capacity of the pressing line.  
3. If you dry the veneer sheets longer than necessary you use excess energy, worsen the sheet quality, cause excessive shrinking, more and bigger splits and more dropped knots. Fragile sheets break or shatter later in the process.  

When veneer sheets are dried optimally, the following process phases are easier and more efficient to handle – no matter what the end use for the veneer sheets is.  

Strength-based grading of veneer sheets 

In addition to their visual and moisture qualities, veneer sheets can also 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. We will talk about this more in the blog post that discusses grading in the drying line.   

Automated veneer grading keeps quality consistent and optimizes the process  

Automated veneer grading uses analyzers to determine the visual qualities and moisture class of each veneer sheet.  

But why should we rely on machines to do grading for us?  

1. Machines always work in the same way, so the quality of their work is consistent. As a result, production is consistent and easier to forecast. 
2. Machines are quicker than humans and can increase production throughput. 
3. Machines notice even the smallest changes in quality with high accuracy.  
4. Higher automation level minimizes need for labor.

Reducing waste and increasing production with automated grading turns to cost savings and improved profitability. 

In the next two blogs we will guide you through grading in peeling and drying lines. Read more to understand the principles and benefits of visual and moisture grading in peeling and drying! 

> Read more about grading in the peeling line.

> Read more about grading in the drying line.

Raute has a full selection of different kinds of visual and moisture analysis tools for veneer manufacturing. 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!