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Mining and quarrying, u.Geological survey.Mining and quarrying trends, u.Geological survey.The problem of dust phthisis in the granite-stone industry, by frederick ludwig haffman, published by government printing office, 1922, 178 pp.Previous investigations into the dust hazard of certain trades issued as bulletins nos.79, 82, and 231 of the u.Bureau of labor.
We are a large-scale joint-stock enterprise integrating scientific research, production and sales.Our leading products have crushing equipment, sand making equipment, mobile crusher, etc., Each type of product is with complete specifications. All products have passed ISO9001, CE and GOST international quality system certification.