Key knowledge of steel structure

- Dec 13, 2017 -

1, Steel structure system has the advantages of light weight, easy installation, short construction period, good seismic performance, fast investment recovery, less environmental pollution, good plasticity and toughness, good impact resistance.
2, the types of steel are: according to the thickness of different sub-sheet (thin steel thickness < 4mm), the board (medium thickness 4-20mm) and thick plate (thickness 20--60mm) is more than 60 thick. The strip is included in the steel plate.
3, the difference between ordinary bolts and high-strength bolts?
Ordinary bolts generally made of ordinary carbon structural steel, without heat treatment, high-strength bolts are generally made of high-quality carbon structural steel or alloy structural steel, the need to undergo heat treatment to improve the overall mechanical properties. High-intensity is divided into, 8.8, 10.9, 12.9.
From the intensity level: high-strength bolts commonly used 8.8S and 10.9S two strength levels. Ordinary bolts generally have 4.4, 4.8, 5.6, 8.8.
The prestress force is applied from the high-strength bolt of the bearing force and the external force is transmitted by the friction force. The common bolt transmits the shear force by the shearing force of the bolt rod and the pressure of the hole wall.
4, according to the characteristics of force is divided into: friction type and pressure type
Friction-type high-strength bolts are based on the friction between the connected components to transfer external force, when the shear force is equal to friction, extremely friction-type high-strength bolt connection design limit load. At this time Lianzhong rod does not occur relative slip, the bolt rod is not shear, the bolt hole wall is not pressure.
Pressure-type high-strength bolts and ordinary bolts similar to the shear force can be more than friction, the connection member will be relatively slip between the moment, the bolt rod and the hole wall contact, the connection depends on the friction and bolt rod shear pressure Common force transmission.
Large deformation of high-strength bolts, not suitable for direct bearing structure of dynamic load connection.
5, several types of electrodes
There are about a dozen: carbon steel electrode, low alloy steel electrode, molybdenum and molybdenum molybdenum heat-resistant steel electrode, low temperature steel electrode, stainless steel electrode, surfacing electrode, cast iron electrode, nickel and nickel alloy electrode, copper and copper alloy electrode, Aluminum and aluminum alloy electrodes and special purpose electrodes.
6, weld defects:
(1) Impermeable: The blunt edges at the center (X groove) or root (V, U groove) of the parent metal joint are not completely fused together and the local unfused remains. Impermeability reduces the mechanical strength of the welded joints, creating stress concentrations at the notched notches and ends, which can easily lead to cracking when the welded parts are subjected to loads.
(2) Unfused: Partial fusion between solid metal and filler metal (between weld bead and base metal), or between filler metal (between weld beads or between weld beads) during multi-pass welding or In spot welding (resistance welding) between the base metal and base metal are not fully fused together, sometimes accompanied by slag often exist.
(3) Porosity: During the fusion welding process, the gas in the weld metal or the gas intruded by the outside world does not have time to overflow before the molten metal is solidified and cooled, leaving holes or voids formed in or on the surface of the weld metal. Morphology can be divided into single stomata, chain stomata, dense stomata (including honeycomb stomata) and so on. Especially in arc welding, due to the short time of metallurgy process, rapid solidification of the molten pool metal, the gas generated in the metallurgical process, Gas absorbed by the liquid metal, or solder flux damp and decompose at high temperatures to produce gas, even in the welding environment, the humidity is too high will decompose at high temperatures, and so on, these gases will precipitate when the formation of porosity defects. Although porosity is less stress concentrated than other defects, it destroys the denseness of the weld metal and reduces the effective cross-sectional area of the weld metal, resulting in reduced strength of the weld.
7, Non-destructive testing is a test method for inspecting the surface and internal quality of the tested components without damaging the working status of the workpiece or raw materials.
Common nondestructive testing methods:
Ultrasonic flaw detection: the use of ultrasound can penetrate the depths of metal materials, and from one cross-section into the other cross-section, reflected at the edge of the interface features a way to check for defects, when the ultrasonic beam from the part surface from the probe to Metallic interior, when encountering the defect and the underside of the parts, reflected waves occur respectively, forming a pulse waveform on the fluorescent screen, and determining the position and size of the defect according to the pulse waveforms.
Radiography (X-ray, γ-ray): Detection method of using ray to penetrate objects to discover internal defects of objects.
Magnetic particle inspection: is used to detect the surface of ferromagnetic materials and near-surface defects of a detection method. When the workpiece is magnetized, if there is a defect on the surface of the workpiece, magnetic leakage will occur due to the increase of the reluctance in the defect and a local magnetic field will be formed. The shape and position of the defect will be displayed here to judge the existence of the defect.
8, parts processing procedures: preparation, correction, lofting, cutting, bending, hole making, assembly, welding, testing, rust, painting.
9, metal surface rust methods are: manual processing, mechanical processing, chemical treatment and flame treatment of four.
(1) manual processing
Handle the main tool with a blade, wire brush, emery cloth, cut hacksaw and other tools, by hand knocking, shoveling, scraping, brushing, sand to achieve the removal of rust, which is the painter's traditional rust removal method is the easiest way , Without any environmental and construction conditions, but due to poor efficiency and effectiveness, only a small range of rust treatment.
(2) mechanical descaling method
Mechanical rust method is to use some of the main electric, pneumatic tools to achieve the purpose of removing rust. Common electric tools such as electric brush, electric grinding wheel; pneumatic tools such as pneumatic brush. Electric brush and pneumatic brush is the use of special round wire brush rotation, by the impact and friction to rust or oxide scale clean, especially for the surface rust, the effect is better, but the deeper rust is difficult to remove. Electric grinder is actually portable grinder, you can move freely in the hand, the use of high-speed grinding wheel to remove rust, the effect is better, especially for the deeper rust, its high efficiency, construction quality is good, easy to use, is a Desirable rust tools. But be careful in the operation, do not puncture the metal skin.
(3) sand blasting, shot peening method
Sand blasting, shot peening method with the previous section to remove the old coating usage. (4) flame treatment method Flame treatment method is the use of gas torches on a small amount of hand-hard to remove the deeper rust spots, red burn, so that high-temperature rust rust oxide chemical composition to achieve the purpose of rust. Use this method, be careful not to burn through the metal surface, and to prevent the deformation of a large area of the surface heat.
(5) chemical treatment method
Chemical treatment method is actually pickling rust method, the use of acidic solution and metal oxide (rust) chemical reaction, generating salts, and from the metal surface. Commonly used acidic solution: sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid. During operation, the acid solution is applied to the metal rust site to slowly remove the chemical reaction with the rust. Rinse with rinsing after rust removal and neutralization reaction with weak base solution, then rinse with water and dry, drying, to prevent rust soon.
The pickled metal surface to be roughened or phosphating treatment, mainly to increase the adhesion of metal surfaces and primer. Dilute the concentrated sulfuric acid, sulfuric acid should be slowly poured into the container of water, and constantly stirring, not the opposite operation, so as to avoid sulfuric acid spill wounding.
10, common lifting equipment: gantry crane tower crane crawler crane truck crane wheel crane mast crane jacking machine gourd bridge crane.

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