Abstract: This invention relates to a joint for risers, and particularly to a telescopic joint suitable for expandably connecting composite-pipe type riser pipes provided internally with tubing pipes. Its structural features reside in that connectors adapted to connect risers in up-and-down relationship are slidably engaged with each other and air cylinders capable of cancelling volume changes of the engaged portions, which volume changes occur due to expansion and contraction movements of the connectors, are communicated to the spacing of the engaged portions, and hydraulic cylinders adapted to cancel volume changes of the engaged portions of an internally-threaded nose portion and an externally-threaded nose portion, which engaged portions serve to communicate the upper and lower tubing pipes to each other, is communicated with the spacing of the engaged portions of the nose portions.

Abstract: A shaft furnace for reducing ores with a gas, wherein the furnace is constructed to destroy the plug-flow state of ores in or above a plug-flow zone where a reduction ratio of the ores is 50 to 70%, in order to prevent the clustering by changing the plug-flow zone into a shear-flow zone. Further, the shaft furnace for reducing ores with a gas is so constructed that a hydraulic radius R (cm) of the furnace in the reduction zone in which the reduction ratio is greater than 50% is selected to be,R.ltoreq.120 exp(8.6-0.009T)wherein T denotes the temperature (.degree.C.) of the reducing gas, in order to prevent the clustering.