Metal hose is a new type of material used for wire and cable protective sleeve, belonging to flexible metal hose, which can be used for open and concealed laying and cast-in-place concrete laying in various occasions. Because of its light weight, good strength and insulation, it can be bent at will (without tools), and it is equipped with various accessories, which is very convenient for construction and can greatly improve work efficiency, so it has been widely used in electrical installation engineering.
1, composition of metal hose 1. 1 metal hose
It can be divided into metal hoses and plastic-coated metal hoses. The outer layer of the metal hose is hot-dip galvanized steel strip (or copper strip), the middle layer is cold-rolled steel strip, and the inner layer is waterproof electrical paper, which is coiled into a spiral shape and the outer wall threads itself; Plastic-coated flexible metal wire protective sleeve is a layer of plastic (PVC) coated on the outer layer of metal hose. Its specifications range from 10 # to10/#, and its inner diameter ranges from 9.2 mm to 100.2 mm, with specifications of *** 12.
1.2 metal hose fittings
Junction box connector: the metal hose is connected with the junction box (box) waterproof; Direct joint: metal hoses are connected with each other to be waterproof; Non-threaded connector: used to connect metal hose with steel conduit or steel pipe; Hybrid connector: used to connect metal hoses and threaded pipes, which is waterproof at 90 degrees and waterproof at 45 degrees; Grounding card: used for grounding metal hose.
2, the characteristics of metal hose
Convenient construction and superior performance. The pipe is light in weight, convenient to carry, free from mechanical bending and cutting, easy to bend and move, simple to connect (without buckle), and equipped with various corresponding accessories. Because the steel strip adopts a special hot-dip galvanizing process, it has superior moisture resistance and corrosion resistance. It has good strength and insulation. It has a wide application range and can replace common galvanized steel pipes. There are basic, anti-corrosive, explosion-proof and heat-resistant types, and the corresponding pipes and fittings can be selected according to different occasions.
3, metal hose construction application technology
Before pipeline laying, the appearance of metal hose should be carefully checked, and the requirement is that the coating of casing should not fall off, rust or have spots; The PVC layer of plastic-coated metal hose should be free of bubbles and damage. There is no protrusion or damage on the inside and surface of the shell, and the cutting surface is smooth and burr-free.
3. 1 Bending and cutting
Metal hoses can be bent freely by hand according to the requirements of bending direction without any tools, and the bending angle should not be less than 90 degrees. The bending radius of the exposed pipe should not be less than 3 times of the outer diameter of the pipe; The bending radius of the pipe should not be less than 6 times the outer diameter of the pipe when it is used in the place where it cannot be disassembled; When embedded, the bending radius of the pipeline shall not be less than 10 times of the external diameter of the pipeline. When cutting metal hoses, tools such as vises are not needed. When cutting the hose, hold it by hand or put it on the workbench. Use a special sleeve to cut the blade, and align the threaded groove of the pipe at a right angle as much as possible. You can also cut it with a hacksaw. After cutting, remove the burr at the nozzle in time to make the cutting surface smooth.
3.2 Pipeline connection
Interconnection of metal hoses. When metal hoses need to be connected in the middle of laying, straight heads with threaded joints are used for interconnection. First, check whether the pipe end is burr-free, then screw the direct head into the pipe end of the metal sleeve by hand, and then screw the other end of the metal sleeve into the other end of the direct head. The counterpart connecting the metal sleeve should be in the center of the direct head. Connection between metal hose and steel pipe. The connection between metal hose and steel pipe can be divided into two types: threaded and unthreaded. The threaded connection adopts a hybrid joint. Firstly, the hybrid joint is screwed into the threaded end of the steel pipe to make the nozzle of the steel pipe match the threaded inner opening of the hybrid joint, and then the metal sleeve is screwed into the threaded end of the hybrid joint sleeve. Alternatively, the mixing joint can be unscrewed and decomposed first, and then screwed to the metal sleeve and steel pipe respectively. Then screw the mixing joint into a whole. The unthreaded connection adopts the unthreaded connection joint. First, screw the metal sleeve into the threaded end of the sleeve of the unthreaded joint. When the end of the metal sleeve is consistent with the inner opening, plug the steel sleeve end of the unthreaded joint with a steel pipe. After the insertion depth meets the requirements, tighten the two compression bolts on the joint with a screwdriver or wrench. Connection between metal hose and box (box). The metal hose is connected to the box (box) with a box connector. Screw the metal sleeve into the threaded end of the metal sleeve of the box connector, insert the other end of the connector into the ejection hole of the box (box), unscrew the fastening nut of the connector and put it on the inner wall of the box (box), and then tighten the fastening nut of the connector with a wrench.
3.3 Technical Requirements for Pipeline Laying
When metal hoses pass through equipment and building foundations or may be subjected to obvious mechanical impact, protective measures such as adding protective pipes should be taken, and compensation devices should be installed when they pass through settlement joints or expansion joints. When metal hoses are exposed, they should be arranged neatly, fixed firmly, and the fixed points should be evenly spaced. The distance between the pipe clamp and the terminal, the turning midpoint and the edge of the electrical appliance or equipment is
150mm~300mm, the maximum distance between the fixed pipe clamps in the middle of the pipeline is 0.5~ 1m, and the spacing between the fixed points should be uniform, with the allowable deviation not greater than 30 mm; the allowable deviation of levelness or verticality of metal hoses laid horizontally or vertically is plus or minus 5%, and the total length deviation should not be greater than12 of the internal diameter of the pipeline. When the metal hose is concealed, it should be laid along the nearest route and reduce bending. The minimum distance between the metal casing buried in the building and the surface of the building should not be less than15 mm; When laying in cast-in-place concrete, it should be fixed with steel bars, and the fixed spacing should not be greater than 500mm. When the pipe passes through the metal hose, the total cross-sectional area of the conductor in the pipe, including the insulation layer, should not be greater than 40% of the empty cross-sectional area in the pipe. When the metal hose is long or bent, in order to prevent the wire from being damaged due to excessive resistance during threading, the distance between two junction boxes or cable boxes is specified: no more than 30m when there is a bend, no more than 20m when there are two bends, no more than15m; When there are three bends, it shall not exceed 8m. If the above requirements are exceeded, cable boxes (junction boxes) should be installed or the diameter of wiring pipes should be increased. The metal shell of the metal hose shall be reliably grounded, and the pipeline shall not be connected with the grounding wire by welding. A special grounding card shall be used for grounding, and the metal hose shall not be used as an electrical grounding wire.