英语翻译

英语翻译
Chock
In a chock support,the canopy is a solid piece and the base may be either a solid piece or two separate parts connected by steel bars at the rear and/or the front ends.In both cases a large open space is left at the center for locating the double-acting hydraulic ram which is used to push and pull,respectively,the chain conveyor and the chock in a whole unit.This setup is also used in the shields and chock shields.
Again,all hydraulic legs are installed vertically between the base and the canopy.The number of legs ranges from 3to 6,but the four-leg chocks are by far the most popular ones.In most chock supports,there are hinge joint connections between the legs and the canopy and between the legs and the base.But in order to increase the longitudinal stability,it is reinforced mostly with a box-shaped steel frame between the base and each leg.A leg restoring device is installed around each leg at the top of the box-shaped steel frame.
The chocks are suitable for medium to hard roof.When the roof overhangs well into the gob and requires induced caving,the chocks can provide access to the gob.
Shield
Shields,a new entry in the early seventies,are characterized by the addition of a caving shield at the rear end between the base and the canopy.④The caving shields,which in general are inclined,are hinge-joint to the canopy and the base making the shield a kinematically stable support,a major advantage over the frames and the chocks.⑤
The hydraulic legs in the shields are generally inclined to provide more open space for traffic.Because the canopy,caving shield,and base are interconnected,it can well resist the horizontal force without bending the legs.Thus unlike the solid constraint in the frame/chock supports,the pin connections between the legs and canopy and between the legs and the base in a shield support make it possible that the angle of inclination of the hydraulic legs varies with the mining heights.⑥Since only the vertical component of the hydraulic leg pressure is available for supporting the roof,the actual loading capacity of the shield also varies with the mining heights.
Chock Shield
The chock shield combines the features of the chocks and the shield.As such it possesses the advantages of both.⑦
If all of the four or six legs are installed between the canopy and the base,it is called a chock shield.There are regular four-or six- leg chock shields in which all legs are vertical and parallel.Others from V or X shapes.Some canopies are a single piece and some are two pieces with a hydraulic ram at the hinge-joint.
The chock shield has the highest supporting efficiency.They are suitable for hard roof.