oval of the coal pillars between rooms or chambers to regulate the subsidence of the roof. Also termed "bridging back" the pillar, "drawing" the pillar, or "pulling" the pillar.Pinch- A compression of the walls of a vein or the roof and floor of a coal seam so as to "squeeze" out the coal.
Pinch�C A compression of the roof and floor of a coal seam so as to "squeeze" out the coal.
Pinning- Roof bolting.
Pitch- The inclination of a seam; the rise of a seam.
Plan- A map showing features such as mine workings or geological structures on a horizontal plane.
Pneumoconiosis- A chronic disease of the lung arising from breathing coal dust.
Portal- The structure surrounding the immediate entrance to a mine; the mouth of an adit or tunnel.
Portal bus- Track-mounted, self-propelled personnel carrier that holds 8 to 12 people.
Post- The vertical member of a timber set.
Preparation plant- A place where coal is cleaned, sized, and prepared for market.
Primary roof- The main roof above the immediate top. Its thickness may vary from a few to several thousand feet.
Primer (booster)- A package or cartridge of explosive which is designed specifically to transmit detonation to other explosives and which does not contain a detonator.
Prop- Coal mining term for any single post used as roof support. Props may be timber or steel; if steel--screwed, yieldable, or hydraulic.
Proximate analysis- A physical, or non-chemical, test of the constitution of coal. Not precise, but very useful for determining the commercial value. Using the same sample (1 gram) under controlled heating at fixed temperatures and time periods, moisture, volatile matter, fixed carbon and ash content are successfully determined. Sulfur and Btu content are also generally reported with a proximate analysis.
Pyrite- A hard, heavy, shiny, yellow mineral, FeS2 or iron disulfide, generally in cubic crystals. Also called iron pyrites, fool's gold, sulfur balls. Iron pyrite is the most common sulfide found in coal mines.
R
Raise- A secondary or tertiary inclined opening, vertical or near-vertical opening driven upward form a level to connect with the level above, or to explore the ground for a limited distance above one level.
Ramp- A secondary or tertiary inclined opening, driven to connect levels, usually driven in a downward direction, and used for haulage.
Ranks of coal�C The classification of coal by degree of hardness, moisture and heat content. "Anthracite" is hard coal, almost pure carbon, used mainly for heating homes. "Bituminous" is soft coal. It is the most common coal found in the
��һҳ[1][2][3][4][5]��һҳ
