August 4, 2011
Spotting Weaknesses In Solid Wood
Is there a hairline crack in the oak table? Was the window frame glued badly? Ultrasound thermography can reliably identify material defects during the production of wooden items. This allows rejects to be caught quickly and eliminated, and faulty goods to be repaired in good time.
People who buy an expensive solid wooden table or wardrobe want to be certain that their new piece of furniture is absolutely faultless. Pianos "“ whether upright or grand "“ can only produce an opulent tone if their soundboard, bridge and keyboard are made of high-quality materials. And wood that is free of imperfections is also essential in house building and window construction: load-bearing wooden beams need to be of the highest quality, as even the smallest crack can cause them to fail.
"We can spot the imperfections in raw timber. That is crucial for rejecting defective wood before time and money have been invested in processing it," says physicist Peter Meinlschmidt at the WKI. Whether the wood in question is oak, walnut or beech is not important, and neither is the condition of the wood ; defects in damp parts show up on the thermal imaging camera too. The depth to which the wood can be analyzed depends on its thermal conductivity, but up to 20 millimeters are possible. "Our process is especially suited for finding defects in high-quality solid wooden parts and window frame squares and to detect badly glued joints. It's a non-destructive testing method. Applying the ultrasound agitator does leave small pressure marks though "“ but these aren't an issue when you're dealing with raw timber," explains Meinlschmidt. The researchers have even managed to use high-energy ultrasound thermography to detect cracks in ceramics and glass. In laboratory tests, they were able to pinpoint defects in ceramic floor tiles and in glass mouthwash bottles. "In ceramics and glass we can spot defects that are up to 30 centimeters away from the sonotrode," says the research scientist. A demonstrator of the ultrasound generator with thermal imaging camera has already been built.
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