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Heading shield
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Patent number 4,420,278
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Issue date Dec 13, 1983
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Dowty (South Africa) (Proprietary) Limited
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Andrew J. Walker
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E21 - EARTH DRILLING MINING
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Mobile mine roof support system
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Patent number 4,307,982
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Issue date Dec 29, 1981
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Mining Machinery Development Corp.
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Robert C. Nelson
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E21 - EARTH DRILLING MINING
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3902324
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Patent number 3,902,324
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Issue date Sep 2, 1975
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E21 - EARTH DRILLING MINING
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3890792
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Patent number 3,890,792
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Issue date Jun 24, 1975
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E21 - EARTH DRILLING MINING
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3877717
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Patent number 3,877,717
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Issue date Apr 15, 1975
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E21 - EARTH DRILLING MINING
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3823566
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Patent number 3,823,566
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Issue date Jul 16, 1974
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E21 - EARTH DRILLING MINING
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3811290
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Patent number 3,811,290
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Issue date May 21, 1974
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E21 - EARTH DRILLING MINING
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3621661
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Patent number 3,621,661
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Issue date Nov 23, 1971
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E21 - EARTH DRILLING MINING
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3138933
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Patent number 3,138,933
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Issue date Jun 30, 1964
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E21 - EARTH DRILLING MINING
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3115754
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Patent number 3,115,754
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Issue date Dec 31, 1963
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E21 - EARTH DRILLING MINING
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2795936
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Patent number 2,795,936
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Issue date Jun 18, 1957
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E21 - EARTH DRILLING MINING
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2795935
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Patent number 2,795,935
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Issue date Jun 18, 1957
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E21 - EARTH DRILLING MINING