1. Features of steel structure:
The steel structure system has the comprehensive 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 and so on.
2. Types of steel:
According to the thickness of different plate (thin plate thickness < 4mm), medium plate (medium thickness 4-20mm) and thick plate (thickness 20-60mm), greater than 60 is extra thick, steel strip is also included in the steel plate class.
3. The difference between ordinary bolt and high strength bolt:
Ordinary bolts are generally made of ordinary carbon structural steel without heat treatment, while high-strength bolts are generally made of high quality carbon structural steel or alloy structural steel, requiring quenching and tempering heat treatment to improve the comprehensive mechanical properties. The high strength is divided into 8.8, 10.9 and 12.9 levels.
From the strength grade: high strength bolt commonly used 8.8s and 10.9s two strength grade. Ordinary bolts are generally 4.4, 4.8, 5.6, 8.8.
According to the stress characteristics of high-strength bolts, pre-tension and friction force are applied to transfer the external force, while the shear force of ordinary bolts is transferred by the shear resistance of bolt rod and the pressure of hole wall.
4. High strength bolts are divided into friction type and pressure type according to their mechanical characteristics
The friction type high strength bolt is based on the friction between the parts to transfer external force, when the shear is equal to the friction force, that is, the friction type high strength bolt connection design limit load. At this time, there will be no relative slip of the member of the Union, the bolt rod is not shear, and the wall of the bolt hole is not pressured.
The shear force of pressure-bearing high-strength bolts is similar to that of ordinary bolts. The shear force can exceed the friction force. At this time, relative slip will occur between the connected members.
The deformation of high strength bolts under pressure is large and it is not suitable for the connection of structures under dynamic load directly.
5. The type of welding rod
There are roughly a dozen kinds: carbon steel electrode, low alloy steel electrode, molybdenum and chrome 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 electrode and special purpose electrode.
6. Weld defects:
(1) Incomplete welding: the blunt edge of the middle (X groove) or root (V, U groove) of the parent metal joint is not completely fused together and the local incomplete fusion is left. Underpenetration reduces the mechanical strength of welded joints, and stress concentration points will be formed in the inpenetration gap and end, which will easily lead to cracking when the welds are subjected to loads.
(2) Not fusion: solid metal and filler metal (between the weld and the base metal), or between the filler metal (between the weld or welding layer) local incomplete fusion, or in the spot welding (resistance welding) between the base metal and the base metal is not completely fused together, sometimes often accompanied by slag.
(3) Porosity: in the process of melting and welding, the gas in the weld metal or the gas invading from the outside does not have time to overflow before the cooling and solidification of the molten pool metal and the remaining holes or pores formed in the interior or surface of the weld metal. According to its shape, it can be divided into single porosity, chain porosity, dense porosity (including honeycomb porosity), etc.
Especially in arc welding, the metallurgical process in a very short time, the molten pool of metal solidification soon, metallurgy process of gas, liquid metal absorption of gas, or electrode flux of be affected with damp be affected with damp and decomposition at high temperatures to produce gas, and even in welding environment humidity is too large will be out of gas at high temperature decomposition, etc., these gases to precipitate will form the hole defect.
Although porosity has a less stress concentration tendency than other defects, it destroys the denseness of weld metal and reduces the effective cross-sectional area of weld metal, resulting in a decrease in weld strength.
7. Nondestructive testing is a test means to check the surface and internal quality of the inspected parts without damaging the working state of the workpiece or raw materials.Common nondestructive testing methods:
(1) Ultrasonic flaw detection: Using ultrasound can penetrate into the depths of the metal materials, and consists of a section into another section, on the edge of the interface reflection characteristics of flaws, a method to check the parts when the ultrasonic beam from the surface by the probe through the metal parts inside, encountered defects with parts when the bottom reflection wave respectively occurred in the pulse waveform is formed on the screen, According to these pulse waveforms, the location and size of defects can be determined.
(2) Ray detection (X ray, γ ray) : the detection method of using ray to penetrate the object to find the internal defect of the object.
(3) Magnetic particle testing: it is a testing method used to detect the surface and near surface defects of ferromagnetic materials. When the workpiece is magnetized, if there is a defect on the surface of the workpiece, the magnetic flux leakage will be generated due to the increase of the magnetic resistance at the defect, forming a local magnetic field, and the magnetic powder will show the shape and position of the defect here, so as to judge the existence of the defect.
8. Procedures for parts processing:
Preparation, correction, herding, cutting, bending, drilling, assembly, welding, testing, derusting, painting.
9. metal surface rust removal methods: manual treatment, mechanical treatment, chemical treatment and flame treatment four.
(1) Manual processing:
Manual processing mainly with the shovel knife, steel wire brush, emery cloth, hacksaw blade tools, such as by hand knock, shovel, shave, brush, the method of sand to remove rust, this is the painter's traditional cleaning methods, which is the most simple method, no environment and construction conditions, but because of poor efficiency and effectiveness, can only apply to small range of rust removal process.
(2) Mechanical derusting:
Mechanical derusting is mainly to use some 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 brushes. Electric brush and pneumatic brush are made of special circular steel wire brush rotation, by impact and friction to clean the rust or oxide scale, especially for the surface rust, the effect is better, but it is difficult to remove deep rust.
Electric grinding wheel is actually portable grinder, can be moved at will in the hand, using the high speed rotation of the grinding wheel to remove rust, the effect is good, especially for the deep rust spot, its high efficiency, construction quality is also good, easy to use, is an ideal rust removal tool. But in the operation must be careful not to break through the metal skin.
(3) Sandblasting and shot peening method:
Sandblasting, shot peening treatment with the previous section to remove the use of the old film.
(4) Flame treatment method:
Flame treatment method is to use the gas torch to a small number of manual difficult to remove deep rust spots, red, so that high temperature to rust oxide change chemical composition and achieve the purpose of rust removal. When using this method, care must be taken not to let the metal surface burn through, and to prevent large areas of the surface from heating deformation.
(5) Chemical treatment:
Chemical treatment method is actually pickling rust removal method, using acid solution and metal oxide (rust) chemical reaction, the formation of salts, and away from the metal surface. Common acid solutions are: sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid. In the operation, the acid solution is applied to the rust part of the metal and the rust is slowly removed by chemical reaction. After rust removal, clean water should be applied, neutralization reaction should be carried out with weak alkali solution, and then wipe and dry with clean water to prevent rust soon.
The pickling of the metal surface needs to be roughed or phosphating treatment, mainly to increase the adhesion of the metal surface and the primer.
In the dilution of concentrated sulfuric acid, sulfuric acid should be slowly poured into the water container, and constantly stirring, do not contrary operation, so as not to hurt the sulfuric acid liquid splash.