10/13/2020

Go with the grain - 10 tips around sanding

HOMAG gives ten practical tips for optimum results on the wide-belt sanding machine

An article from BM, 06/2020  
https://www.bm-online.de/wissen/technik/volles-korn-voraus/

"Perfectly sanded surfaces contribute significantly to added value. We provide tips for selecting the sanding material, the cutting speed, the sanding pressure, the appropriate grain and for quality assurance."  
Torben Hellmann, Product Manager, Surface

 

With these ten tips for sanding on the wide-belt sanding machine, you can achieve optimum processing results:

• The type of grain and the spread pattern used in final sanding are based on the wood to be processed. The aluminum oxide grain type is used for sanding wood in 90% of cases. For lubricating woods such as pine and teak, an open pattern is recommended. For hard woods such as beech, maple or cherry tree, a closed pattern is used.
• The optimum storage temperature for sanding belts is 20–22°C at a relative humidity of 45–65%. Paper belts are particularly sensitive to a relative humidity that is too high or too low. They tend to become deformed, becoming warping or buckling. Sanding belts should also not be stored on the floor, as they can also draw in moisture here.
• Like tools, after long periods of use, sanding materials lose their sharpness. New belts are sharp and remove wood fibers completely. This means that after priming, the surface is not as rough and there is a better stain pattern. In contrast, blunt sanding belts merely press the wood fibers into the surface, creating a poor sanding result.
• The level of sanding pressure and the sanding speed must be selected optimally. An increased sanding force may lead to a higher removal rate but it also increases the sanding (belt) temperature, causing the sanding material to wear more quickly. Therefore, the rule of thumb is that from a surface temperature of 100°C, scorch marks appear on the surface of the wood.
• Narrow sanding elements increase the life of the sanding material and lower the sanding (belt) temperature. Wide sanding elements bring more sanding grains into play. This leads to greater removal but also to a higher temperature and more wear.
• If the pressure beam or sanding pad is used, the following chain of rules should be observed. If too much material is removed: reduce the cutting speed, increase the feed speed, use a softer sanding element, use a narrower sanding element. If not enough material is removed: increase the cutting speed, reduce the feed speed, use a harder sanding element, use a wider sanding element.
• Cross-sanding is used when processing veneer or solid wood. The more frequently the cutting direction is changed, the better the surface will be after staining and lacquering and the fewer fibers it will have — for example, by changing the sanding sequence from crosswise to longitudinal and then to longitudinal with a lamellar pressure belt.
• For water-based lacquers and oiled surfaces, the grain size should be no rougher than P 180. Where conventional solvent-based lacquer systems are used, the grain should be no rougher than P 150.
• For calibration sanding, the cutting speed at the contact roller is set as high as possible and the feed as low as possible. If the feed is doubled, this also doubles the power consumption of the sanding belt drive unit for removing the same material thickness. The grain should not be selected such that it is too fine. The finer the grain of the sanding material, the lower the material removal. Fine grains also clog more quickly, which means that the sanding belt has to be replaced.
• To ensure quality, good lighting conditions are essential when assessing surfaces. In particular, good lighting should be ensured at the outfeed of the sanding belt — for example, a strip light. The color temperature 6500 K (daylight white) has proven particularly useful here.

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