When the problem with the noise came to Ortviken's knowledge, Charlotta Lindberg, environmental engineer, started a detective work. With assembled forces from the mill, it was found that the nash pumps from paper machine 5 caused the noise. The sound was at a low frequency and the sound of the pump was clearly heard.
“An audio consultant measured the sound at the pipes on the roof and then on the other side of the bay of Sundsvall, in Skönsmon, where the complaint came from, and it was the same frequency. Then we tried with different traditional solutions," explains Charlotta Lindberg.
Mufflers were installed in a pump pit in the basement, the pipes from the nash pumps that go up to the roof of the factory building were redirected, and they also tested to shut down a pump when possible.
Close dialogue with local residents
Charlotta Lindberg always had a close dialogue with the local residents to see if the measures that were implemented had any effect. The production engineers also had contact, especially at night when the sound disturbed the sleep.
“It got a little better, but it wasn't enough. It was then that we decided to try a new solution to noise disturbances that were used successfully in the Husum mill, for example," says Charlotta Lindberg.
The solution implied that a smaller tube with quarter-wave resonators was mounted on the exhaust pipes. The quarter wave resonators take out the unwanted sound waves. They are adjustable and can be adjusted to the right frequency.
“We first tried on one pipe and when it turned out successfully we also mounted on the remaining four," says Lars-Göran Hägglund Rongdén, who works as operator at paper machine 5.
“The result of this work gave very good results. The pump noise could no longer be heard and we got a reduction of 10 dB and satisfied neighbors. One major contributor to the success was that we worked widely with resources from different parts of the business," says Mattias Kling, Block Manager at paper machine 5.
The picture below shows these tubes at the top.