Impact steel pipe surface quality factors and improvement measures

Abstract: With the increasing precision steel pipe, in order to ensure its normal operation, extending its life, you need to strictly control surface quality. Strict quality control, each assembled parts of the steel pipe must go through a strict qua

Boston, Aruba (prHWY.com) September 5, 2012 - Impact steel pipe surface quality factors and improvement measures
 
Abstract: With the increasing precision steel pipe, in order to ensure its normal operation, extending its life, you need to strictly control surface quality. Strict quality control, each assembled parts of the steel pipe must go through a strict quality audit, to avoid all possible factors of the steel pipe occurred. This paper analyzes the factors that influence the surface quality of the steel pipe, summarizes improvements to improve the surface quality of the steel pipe.

Keywords: steel pipe processing, surface quality factors and improvement measures
With the development of human society and the people required to further improve the quality of products, many of the important parts of working in a special environment such as high temperature high pressure. Overloaded surface under great stress and the corrosive effect of the surrounding medium, the surface of the part of any a subtle defects are likely to result in damage to the parts. Product work performance, such as the reliability of durability of the good or bad, depends largely on the quality of the main parts of the surface. Research steel pipe machined surface quality and its influencing factors, grasp the variation is of great significance to improve the surface quality of steel pipe processing and product use performance.
1, 1. Cutting
(1) the nature of the workpiece material impact
Parts of the surface roughness to increase one of the reasons is that since the tooling plastic material will be plastically deformed, together with the tool on the interested part during machining of a tearing effect. Usually workpiece better the toughness, its plastic deformation is greater the more rough machined surface. If the workpiece is a brittle material, after cutting chips into crushed granular. After cutting, on the surface of the parts of the processing will be many of its roughness increases pitting.
(2) the impact of cutting the amount of
Improve the speed of processing of the plastic material, reduce the feed amount of the cutting, it is possible to improve the machining surface finishing degree, or vice versa.
(3) grinding surface roughness
Machining in the surface of the pipeline the metal geometric factors of the machined surface and the plastic deformation of the metal directly affect parts abrasive machining surface roughness. Which is the most important influence: the feed rate of the particle size and hardness of the grinding wheel itself. Grinding finishing speed. Processing the feed rate of the surface of the part and the part surface processing.
(4) processing surface layer the physical steel pipe performance influencing factors
Under the cutting force and the action of heat, the surface of the parts processing in the cutting, the physical steel pipe of the metal properties will produce a certain degree of change, including change of microstructure and residual stress generated.
2 surface layer of cold hardening
(1) Evaluation Parameters
Due to the role of the cutting in the surface processing step of the process, appears to cause lattice distortion. Distortion of the plastic deformation. Between the grains and the grains due to shear slip, will appear which is elongated. Fibrosis, and even the grains appear broken, so that the higher the strength and hardness of the surface of the metal, this phenomenon is the cold hardening . Strengthen the surface after the metal layer, the deformation resistance is gradually increased, but the ductility will be reduced, while the surface of the metallic state gradually stabilized, this phenomenon is the weakening. While the size of the metal weakening effect mainly by the temperature and temperature duration. Strengthening control. Surface metal processing by the thermal and mechanical process, the final nature of the metal surface layer is mainly determined by the enhancement. The consolidated results of the weakening. The hardness of the metal microstructure (ie metal microhardness measurement). Actual depth of the hardened layer. Assessed based on the degree of cold hardening.
(2) the impact of cold hardening factors
Obtuse cutting edge radius increases proportional to the the cold hardening strength and processing surface metal extrusion pressure is proportional to the plastic deformation; chilled layer depth is inversely proportional to the cutting speed and tool proportional to the time of the workpiece surface interaction, and plastic deformation is proportional to the extended depth. Chilled degree proportional to the speed of the cutting, and cutting heat is inversely proportional to the actual duration of action of the parts machined surface; the Chilled role is proportional to the strength and the amount of feed, cutting force increases, the plastic deformation of the surface metal will accelerate intensified.
3 microstructure material changes in the surface layer
(1) grinding burn
Phase transition temperature when the grinding temperature is higher than the expected part of the processing of the surface layer, the strength and hardness of the surface of the metal will reduce the microstructure material has changed, and accompanied by a certain amount of residual force, when it reaches a certain degree, or exceed prone to micro-cracks, and this phenomenon is the grinding burn. The time of the grinding of hardened steel, the main tempering quenching annealing three kinds of burns form.
(2) grinding burn path to improve
Grinding heat source of grinding burn, to improve the grinding burn need to do: minimize cutting heat generated under the conditions allowed; improve machined surface cooling conditions, to avoid more heat into the workpiece . When using a grinding wheel, to improve the cooling conditions of the premise is a reasonable amount of cutting.
4. Residual stress of the surface layer
(1) parts on surface residual stress generated
â'  in the parts for cutting the metal expansion in volume is due to an increase in the specific volume of the - OCTG pipe surface metal . Hematocrit produced only in the surface of the metal, plastic deformation of a certain relationship, plastic deformation occurs, the hematocrit will increase the surface hematocrit increases the metal layer would be connected to the inner metal layer of hinder, thereby processing The metal layer in the surface will produce residual stress, the inner tensile residual stress will be generated.
â'¡ there will be a large amount of cutting heat generated in the machining area.
(3) the density of the different microstructure. Hematocrit is not the same, that would be connected to the metal hampered if the the processing surface layer metal microstructure changes, and therefore will produce residual stress.
(2) The final step of surface processing method selection
Choose the final step of the processing method is critical, and the selection of the final step will lead to the impact of the residual stress on the machined parts. Choice of processing methods, mainly on account of some specific working conditions in parts machined surface and may damage the surface processing concrete form. Under the action of alternating load, the portion of the part is machined surface will appear microscopic cracks, and the tensile stress causes Original crack expanded, resulting in parts completely broken. Angle starting from Part fatigue failure, so the choice of the final step, should be considered a method of residual compressive stress generated in the machined surface.
Second, improve the steel pipe surface quality improvement measures
1. Improve the surface roughness bad
In order to improve the surface roughness worse, is to reduce the area of ​​the cutting of the residue layer. The first is to increase the speed and reduce the amount of feed; followed by primary and secondary declination, nose radius, tool machining high hardness knife.
2 to reduce the plastic deformation of the program
To get a better surface roughness can be obtained through the following means:
(1) in the cutting parameters can increase the cutting speed.
(2) from the material, for the higher parts of the surface roughness, the best in the steel pipe before processing the material tempered.
(3) from the angle of the tool, can be used white blades or welding knives by grinding to obtain a large rake angle and the rear corners of the tool. At the same time to ensure that the tool edge is sharp.
(4) The angle from the heat. Moderate concentration of cutting fluids, cooling fully, as far as possible within the cold for conditional.
3 in the process to reduce the degree of hardening of the program
(1) to reduce the degree of force workpiece processing, reasonable cutting parameters from the tool. Specific programs: frequently changes the tool or increased the tool repair worn frequency to ensure that the tool edge fillet flank wear tiny processing.
(2) to reduce the extent of plastic deformation and the reasonable control of the deformation temperature. The knife its use in good condition, the plastic deformation is mainly affected by the impact of the cutting parameters. The specific programs as follows: to increase the cutting speed, the plastic deformation of the surface can be reduced on the one hand, the other hand can be an appropriate increase in the deformation temperature to the recovery phenomenon, according to the length of processing a reasonable choice of suitable monodentate feed basin.
(3) processing of the material, the surface quality requirements have higher requirements, before processing can be done appropriately modified treatment to improve the processing performance.
4 reduce grinding workpiece surface layer microstructure changes in the degree of specific programs
(1) is a lift-off rotational speed of the workpiece, and to reduce the speed of the grinding wheel can be effective to reduce the degree of deformation of the microstructure, but its side effects is the production efficiency is low, and it is adopted in the case of high-speed operation of the grinding wheel to improve the rotational speed of the workpiece.
(2) reduce the depth of cut, reducing the grinding knife to eat the amount of each feed can also reduce fever grinding inside the processing, in order to ensure that their productivity is not affected, the need to ensure moderate amount of grinding. Specifically suitable feed amount is adjusted according to the specific processing material.
(3) improve the grinding performance of the wheel. For different materials should be selected corresponding thereto grindstone. Also, the the coarse wheel dressing, loose wheel organizations to improve the cooling conditions and reduce the workpiece heating time.
5. Reduce surface residual stress program
Specific programs may make reference to reduce the degree of surface cold hardening program to reduce the degree of change of surface microstructure. For thermoplastic changing specific programs:
(1) Qinhuan the tool or the increase in the frequency of tool repair worn in the process to guarantee Figure corner of the tool edge and flank wear tiny. Guaranteed in the process to obtain lower cutting heat.
(2) In the concentration and pH value of the cutting fluid in the premise of the appropriate range, to ensure sufficient cooling, the cutting fluid injection to guarantee there O.5Mpa pressure. The function of the inner cooling device can be used inside and outside the cold while using.
6. Process in improved surface quality
(1) for a high surface quality requirements piano member. Can be used in process control. Honing, super finishing Finishing as the final processing operations.
(2) subject to high stress, alternating load of parts. Of peening. Rolling. Rolling light can be used to strengthen the process to reduce the surface involved in the stress and cold hardening and reduce the roughness.
In summary, affect the surface quality of the factor in the process is very complicated. To obtain the required surface quality, it must be properly controlled on the processing method, the cutting parameters. Control the quality of the surface often increases the processing costs, the impact of processing efficiency, so the general parts is appropriate to the normal process to ensure the surface quality, do not make excessive demands. Is necessary to control for some direct impact on product performance life and the importance of safety surface
References:http://www.steelpipes.org/steel/steel144.html
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[2] Present Situation Analysis of the quality of the machined surface of the steel pipe [J]. The Hebei Metallurgical, 2006, (04).
[3] Chen Yanhua steel pipe machined surface quality influencing factors [J] new technologies and products in China, 2009, (24)

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