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Noise Reduction of a Pneumatic Rock Drill

Experimental modifications have been made by the Bureau of Mines on standard pneumatic rock drills to reduce the noise of the air exhaust, drill steel resonance noise, and noise radiated by the drill body. A close-fitting case and muffler around the drill body, consisting of a metallic honeycomb skeleton filled with viscoelastic absorber on the inside and a durable outer shell, provide both exhaust and drill body noise muffling and absorption. Drill steel resonance noise is reduced by a constrained-layer treatment consisting of a tubular metal cover bonded to the outside of the rod by a viscoelastic filler. Damping alloy components have been developed to reduce metallic resonance noise. Combined, these modifications have reduced the drilling noise level in granite from 115 dba to 97 dba. Data are presented on the individual and combined effects of these modifications on drilling noise and performance.

Experimental modifications have been made by the Bureau of Mines on standard pneumatic rock drills to reduce the noise of the air exhaust, drill steel resonance noise, and noise radiated by the drill body. A close-fitting case and muffler around the drill body, consisting of a metallic honeycomb skeleton filled with viscoelastic absorber on the inside and a durable outer shell, provide both exhaust and drill body noise muffling and absorption. Drill steel resonance noise is reduced by a constrained-layer treatment consisting of a tubular metal cover bonded to the outside of the rod by a viscoelastic filler. Damping alloy components have been developed to reduce metallic resonance noise. Combined, these modifications have reduced the drilling noise level in granite from 115 dba to 97 dba. Data are presented on the individual and combined effects of these modifications on drilling noise and performance.

Children of Jens Jacob Hansen (c1820-1864) and Anna Marie Kjarvaldsen (1819-1888) in Norway circa 1880.

Standing from left to right are: Andrew Havig Jensen (1861-1930) who married Lena Elaine Olsen (1860-1938) aka Hannah Eline Olsdatter; Hans Gabriel Jensen (1846-?); Jens Julius Jensen (1859-c1903) who married Annie Olsen (1859-?); and Henry Jensen who has a beard. Sitting from left to right are: Katrina Jensen; Anna Marie Kjarvaldsen (1822-1888) who was married to Jens Jacob Hansen (c1820-1864); John Jensen; Anne Marie Jensen (1854-c1895) who married Peter Olsen (1844-1892) and was the mother of Osborne Theomun Olsen (1883-1971); and Tillie Jensen.

Photograph circa 1880. Image from the collection of Arthur Bruce Jensen II (1939- ) from an original photograph in the collection of Sigrid B. Jensen (1895-?) of Williams Bay, Wisconsin.

Jens Jensen:
Jens J. Jensen. Came to America in 1881 from Norway where he was born in Farsund, Mandals and Listers Amt, in 1859, and having been reared and confirmed in the Lutheran faith, was converted in Stavanger in 1877 where he united with the Methodist church, and on coming to Chicago, united with the 1st Norsk-Dansk Methodist Episcopalian church in 1886 tranferring to Maplewood Avenue church where he is now chorister; has been trustee for many years, and was formely S.S. superintendent. His wife, Anna (Olsen), of the same nativity, came with her parents, Soren and Anna Olsen, whose record appears in this volume, to America in 1871, was here converted and is a member of the Ladie's Society of the Maplewood Avenue church. Their children are Jens Arthur and John Sydney, two others Jens Jacob and John Sydney having died in infancy. Mr. Jensen's father, Jens Jacob Hansen, who passed away in Norway in 1864, an adherent of the Lutheran faith, was a talented violinist, the entire family with one exception being musicians. His mother, Anna Marie (Kjarvaldsen) after her husband's death came to America in 1882 and passed away six years later, aged 63 years, having previously embraced the Methodist faith. Mr. Jensen at the age of 14 years left his home for a sailors life, which followed for 3 years, visiting France, Scotland and numerous other countries, on his return home was converted, and about four years later came to America, where he has been one of the most active workers in the Methodist church, also being a member of the Skalden, a musical society.

From left to right are: Leif Jensen (1886-1955); Lena Elaine Olson (1860-1938) aka Hanna Olsdatter; possibly Agnes Hansen (1891-1980) or Maria Elizabeth Winblad (1895-1987); Otto Perry Winblad (1902-1977); and Andrew Havig Jensen (1861-1930) at Williams Bay, Wisconsin on Lake Geneva in 1929. In 1929 Otto Perry Winblad; Marie Elizabeth Winblad; Naida Muriel Freudenberg (1915-1998); and Selma Louise Freudenberg (1921- ) aka Sally Freudenberg, traveled from Jersey City, New Jersey to Chicago, Illinois and then to Lake Geneva, Wisconsin to visit Lena Elaine Olsen (1860-1938) aka Hannah Eline Olsdatter and Andrew Havig Jensen (1861-1930). Lena was the sister of Otto and Mae's mother. Naida later wrote a fictionalized account of the trip and had it published in the Jersey Journal. 75 years later, Richard Arthur Norton (1958- ) flew to Chicago on June 18, 2004 to meet with the descendents of Andrew and Lena. Photograph from the collection of Naida Muriel Freudenberg (1915-1998).

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