ã€Abstract】In this paper, the positive and negative analysis methods of interaction and conditions are used to determine the main factors affecting the assembly process of the valve bolt assembly, and then analyze the positive and negative influences of the valve bolt assembly. Finally, the conditions for the positive influence of the valve bolt assembly are analyzed, and the control is favorable. The factors to obtain a relatively optimized bolt assembly method provide suggestions for the improvement of the valve bolt assembly process, and also provide a method for problem analysis and optimization in the industrial production process.
ã€Keywords】 positive and negative analysis method; valve bolt group; lubrication; assembly process 0 Introduction Bolt group plays the role of fastening connection and compression sealing in the valve, in the relevant standards of the valve, the connection bolts of the pressure-receiving part are categorized. Among the pressure parts, it can be seen that the bolt is a very important part of the valve. Using scientific analysis methods to determine the key influencing factors of valve bolt assembly process can effectively control these key influencing factors, and improve these factors to make them have a positive effect. This is of great significance for optimizing the assembly process of valve bolt sets and improving valve performance.
1 Valve Bolt Assembly Process Influencing Factors Analysis of the Main Body 1.1 Valve Bolt Assembly Process Influence Factors Determining the Main Body of the Valve Bolt Group The parts or parts that are in contact during the assembly process are valve flange, nut thread face, screw hole thread face, and tightening wrench , The associated parts have gaskets. The effect of the valve bolt set on the contact and associated parts is defined as a positive action, and the effect of the contact and associated parts on the valve bolt set is defined as a reverse action. By decomposing and analyzing the factors in Table 1, it can be seen that the positive effect of the valve bolt set on the thread surface and the wrench is due to the need to achieve the function of tightening and compressing the seal, so the positive effect can be summarized as tightening and compressing the seal. The reverse action induces the force and rotation of the bolt set. These effects are the influencing factors of the valve bolt assembly process.
Table 1 Positive and negative action analysis of the valve bolt group 1.2 Influence factors of positive and negative influences of the main components of the assembly process of the valve bolt group Define the conditions that can achieve the above positive and negative effects as the basic conditions, and enable the above conditions for positive and negative effects to be optimized. The optimization conditions can make the deterioration condition of the above positive and negative effects be deteriorated conditions. By analyzing the realization conditions of the above effects in Table 2, we can see that the basic conditions are summed up as sufficient force and sufficient strength, and the optimization conditions are summarized as uniform and smooth. The worsening conditions are all negative effects of the associated optimization conditions and have no other influence. The sufficient strength is the category of the bolt group design, and it is not the content discussed in this paper. Therefore, the realization and optimization conditions of the valve bolt assembly process can be summarized as sufficient and uniform force and smoothness. This condition is also the valve bolt assembly process. Positive influence. When the positive influence of the valve bolt group can be achieved, the negative effect does not occur.
Table 2 Valve bolt assembly positive and negative action related condition analysis 2 Valve bolt assembly influence factor main body's positive influence achievement condition analysis 2.1 Sufficient force Want to make the valve bolt group have sufficient force, can realize through two aspects : First, actually increase the tightening force of the valve bolt set to achieve good fastening or compression sealing, and second, improve the factors that can affect the fastening force to achieve a good fastening and pressure sealing. In the first aspect, actually increasing the design fastening force of the valve bolt group can be directly implemented, but this is not an optimized way. The second aspect can be analyzed by calculation. Check GB/T 16823.2-1997 "Fasteners fastening general rules" can be seen, the relationship between the bolt fastening force, see formula (1).
Tf=kFfd(1)
Where Tf - tightening torque;
K - torque factor;
Ff - initial preload or preload
d - nominal diameter of the thread.
According to formula (1), the nominal diameter d of the bolt is determined when the size of the bolt is determined. Therefore, if the torque coefficient K can be reduced at the same tightening torque, a greater fastening force can be obtained.
Check GB/T 16823.2-1997 "General tightening of threaded fasteners," we can see, the relationship between the torque coefficient K see formula (2)
K=1/(2d(P/π+μsd2secα'+μwDw)) (2)
P in the formula - pitch;
Îœs - thread friction coefficient;
D2 - thread diameter;
α' - thread flank angle;
Îœw - bearing surface friction coefficient;
Dw - the equivalent diameter of the frictional torque on the bearing surface.
According to formula (2), the nominal diameter d, pitch P, median diameter d2, thread flank angle α′, and equivalent diameter Dw of the bearing surface friction torque of the bolt are determined when the bolt size is determined. Under this condition, the torque coefficient K is only related to the thread friction coefficient μs and the bearing surface friction coefficient μw. In consideration of the looseness of the bolt, the surface roughness of the bearing surface should not be raised too much, so the bearing surface friction coefficient μw is relatively constant. It can be seen that reducing the thread friction coefficient μs can reduce the torque coefficient K. Reducing the thread friction coefficient μs can be achieved by increasing the surface roughness of the thread and increasing the lubrication between threads.
2.2 smooth to achieve smooth requirements involves three aspects: First, the size of the tolerances with a reasonable, and second, the surface roughness of the thread contact surface is better, the third is to increase the lubrication between threads. At present, the valve thread fit tolerance according to the mechanical design manual is usually selected 6g/6H, this tolerance fit is applicable to the general requirements of tightness and strength, and other mating tolerances are not experimentally studied here; the surface roughness of the thread contact surface can be adjusted by thread Machining parameters or technological process of adding grinding after threading are realized; lubrication can be achieved by using lubricant.
Relative to the increase of the surface roughness of the contact surface, increasing lubrication is more economical and efficient. The choice of lubricant should be based on the different types of valve threading components. For the bolt and nut screwing, the lubricant with slightly higher viscosity can be selected. For the threaded blind hole, lubricants such as light oil or graphite powder can be selected to prevent the screw contact surface from being filled with oil film to form a closed space. Caused difficulty in bolt installation and accidental pressure in the closed air at the bottom of the screw hole. For stainless steel bolts, molybdenum disulfide lubricant should be selected to ensure that it can effectively prevent the contact thread from being seized while providing lubrication.
2.3 Uniform assembly of valve bolts The requirements for a uniform assembly involve the evenness of the bolt assembly sequence and the strength of each bolt. At present, the industry research on the assembly sequence of the bolts shows that: the simultaneous loading is better than the diagonal loading, and the diagonal loading is better than the sequential loading. However, consider the type and size limitations of the valve flange. According to the following principles, the bolt loading method can be selected:
(a) Where the tool permits, the method of simultaneously loading valve bolts is adopted for blind flange covers with sufficient operating space;
(b) In the case of simultaneous loading of tools due to flange type and size limitations, the use of diagonally loaded valve bolts;
(c) Avoid the use of sequential loading of valve bolts.
To obtain uniform tightening force for each bolt, a constant torque wrench can be selected as a tightening tool for the valve bolt set. Of course, in order to improve efficiency, you can also choose electric or pneumatic torque tools to tighten the valve bolts.
3 Conclusion Positive and negative effects analysis and positive and negative effects of positive and negative analysis methods, relatively reliable and comprehensive analysis of the valve bolt group of the influencing factors and specific impact. This method is used to analyze and determine the main factors affecting the assembly of the valve bolt assembly, analyze the positive and negative influences of the main factors affecting the assembly of the valve bolt assembly, and analyze the positive influence of the main factors affecting the assembly of the valve bolt assembly. Appropriate lubrication of the thread contact surface can reduce the friction coefficient of the bolt fastening, and then obtain a greater fastening force under the same tightening torque; a relatively uniform tightening can be achieved through simultaneous loading or diagonal loading; Torque tightening tools give each bolt a uniform force. When designing the valve bolt assembly process, select a reasonable method of proofreading, control the factors that affect the bolt set, convert these factors into optimized conditions, and thus produce a positive effect, which can effectively improve the valve bolt assembly assembly process.
ã€references】
[1] Gao Junfeng, Wu Shuji. Selection of Large Diameter Flange Connection Gaskets for Pressure Vessels [J]. Pressure Vessels, 2012.19(10):67-70.
[2]Hua Jun. Analysis of Influence of Thread Lubrication Status Change on Screw-Guided Pretensioning Force[J]. Vehicle Technology, 2014.(6):13-15.
[3] GB/T 16823.2-1997. Fastening of threaded fasteners [S].
ã€Keywords】 positive and negative analysis method; valve bolt group; lubrication; assembly process 0 Introduction Bolt group plays the role of fastening connection and compression sealing in the valve, in the relevant standards of the valve, the connection bolts of the pressure-receiving part are categorized. Among the pressure parts, it can be seen that the bolt is a very important part of the valve. Using scientific analysis methods to determine the key influencing factors of valve bolt assembly process can effectively control these key influencing factors, and improve these factors to make them have a positive effect. This is of great significance for optimizing the assembly process of valve bolt sets and improving valve performance.
1 Valve Bolt Assembly Process Influencing Factors Analysis of the Main Body 1.1 Valve Bolt Assembly Process Influence Factors Determining the Main Body of the Valve Bolt Group The parts or parts that are in contact during the assembly process are valve flange, nut thread face, screw hole thread face, and tightening wrench , The associated parts have gaskets. The effect of the valve bolt set on the contact and associated parts is defined as a positive action, and the effect of the contact and associated parts on the valve bolt set is defined as a reverse action. By decomposing and analyzing the factors in Table 1, it can be seen that the positive effect of the valve bolt set on the thread surface and the wrench is due to the need to achieve the function of tightening and compressing the seal, so the positive effect can be summarized as tightening and compressing the seal. The reverse action induces the force and rotation of the bolt set. These effects are the influencing factors of the valve bolt assembly process.
Table 1 Positive and negative action analysis of the valve bolt group 1.2 Influence factors of positive and negative influences of the main components of the assembly process of the valve bolt group Define the conditions that can achieve the above positive and negative effects as the basic conditions, and enable the above conditions for positive and negative effects to be optimized. The optimization conditions can make the deterioration condition of the above positive and negative effects be deteriorated conditions. By analyzing the realization conditions of the above effects in Table 2, we can see that the basic conditions are summed up as sufficient force and sufficient strength, and the optimization conditions are summarized as uniform and smooth. The worsening conditions are all negative effects of the associated optimization conditions and have no other influence. The sufficient strength is the category of the bolt group design, and it is not the content discussed in this paper. Therefore, the realization and optimization conditions of the valve bolt assembly process can be summarized as sufficient and uniform force and smoothness. This condition is also the valve bolt assembly process. Positive influence. When the positive influence of the valve bolt group can be achieved, the negative effect does not occur.
Table 2 Valve bolt assembly positive and negative action related condition analysis 2 Valve bolt assembly influence factor main body's positive influence achievement condition analysis 2.1 Sufficient force Want to make the valve bolt group have sufficient force, can realize through two aspects : First, actually increase the tightening force of the valve bolt set to achieve good fastening or compression sealing, and second, improve the factors that can affect the fastening force to achieve a good fastening and pressure sealing. In the first aspect, actually increasing the design fastening force of the valve bolt group can be directly implemented, but this is not an optimized way. The second aspect can be analyzed by calculation. Check GB/T 16823.2-1997 "Fasteners fastening general rules" can be seen, the relationship between the bolt fastening force, see formula (1).
Tf=kFfd(1)
Where Tf - tightening torque;
K - torque factor;
Ff - initial preload or preload
d - nominal diameter of the thread.
According to formula (1), the nominal diameter d of the bolt is determined when the size of the bolt is determined. Therefore, if the torque coefficient K can be reduced at the same tightening torque, a greater fastening force can be obtained.
Check GB/T 16823.2-1997 "General tightening of threaded fasteners," we can see, the relationship between the torque coefficient K see formula (2)
K=1/(2d(P/π+μsd2secα'+μwDw)) (2)
P in the formula - pitch;
Îœs - thread friction coefficient;
D2 - thread diameter;
α' - thread flank angle;
Îœw - bearing surface friction coefficient;
Dw - the equivalent diameter of the frictional torque on the bearing surface.
According to formula (2), the nominal diameter d, pitch P, median diameter d2, thread flank angle α′, and equivalent diameter Dw of the bearing surface friction torque of the bolt are determined when the bolt size is determined. Under this condition, the torque coefficient K is only related to the thread friction coefficient μs and the bearing surface friction coefficient μw. In consideration of the looseness of the bolt, the surface roughness of the bearing surface should not be raised too much, so the bearing surface friction coefficient μw is relatively constant. It can be seen that reducing the thread friction coefficient μs can reduce the torque coefficient K. Reducing the thread friction coefficient μs can be achieved by increasing the surface roughness of the thread and increasing the lubrication between threads.
2.2 smooth to achieve smooth requirements involves three aspects: First, the size of the tolerances with a reasonable, and second, the surface roughness of the thread contact surface is better, the third is to increase the lubrication between threads. At present, the valve thread fit tolerance according to the mechanical design manual is usually selected 6g/6H, this tolerance fit is applicable to the general requirements of tightness and strength, and other mating tolerances are not experimentally studied here; the surface roughness of the thread contact surface can be adjusted by thread Machining parameters or technological process of adding grinding after threading are realized; lubrication can be achieved by using lubricant.
Relative to the increase of the surface roughness of the contact surface, increasing lubrication is more economical and efficient. The choice of lubricant should be based on the different types of valve threading components. For the bolt and nut screwing, the lubricant with slightly higher viscosity can be selected. For the threaded blind hole, lubricants such as light oil or graphite powder can be selected to prevent the screw contact surface from being filled with oil film to form a closed space. Caused difficulty in bolt installation and accidental pressure in the closed air at the bottom of the screw hole. For stainless steel bolts, molybdenum disulfide lubricant should be selected to ensure that it can effectively prevent the contact thread from being seized while providing lubrication.
2.3 Uniform assembly of valve bolts The requirements for a uniform assembly involve the evenness of the bolt assembly sequence and the strength of each bolt. At present, the industry research on the assembly sequence of the bolts shows that: the simultaneous loading is better than the diagonal loading, and the diagonal loading is better than the sequential loading. However, consider the type and size limitations of the valve flange. According to the following principles, the bolt loading method can be selected:
(a) Where the tool permits, the method of simultaneously loading valve bolts is adopted for blind flange covers with sufficient operating space;
(b) In the case of simultaneous loading of tools due to flange type and size limitations, the use of diagonally loaded valve bolts;
(c) Avoid the use of sequential loading of valve bolts.
To obtain uniform tightening force for each bolt, a constant torque wrench can be selected as a tightening tool for the valve bolt set. Of course, in order to improve efficiency, you can also choose electric or pneumatic torque tools to tighten the valve bolts.
3 Conclusion Positive and negative effects analysis and positive and negative effects of positive and negative analysis methods, relatively reliable and comprehensive analysis of the valve bolt group of the influencing factors and specific impact. This method is used to analyze and determine the main factors affecting the assembly of the valve bolt assembly, analyze the positive and negative influences of the main factors affecting the assembly of the valve bolt assembly, and analyze the positive influence of the main factors affecting the assembly of the valve bolt assembly. Appropriate lubrication of the thread contact surface can reduce the friction coefficient of the bolt fastening, and then obtain a greater fastening force under the same tightening torque; a relatively uniform tightening can be achieved through simultaneous loading or diagonal loading; Torque tightening tools give each bolt a uniform force. When designing the valve bolt assembly process, select a reasonable method of proofreading, control the factors that affect the bolt set, convert these factors into optimized conditions, and thus produce a positive effect, which can effectively improve the valve bolt assembly assembly process.
ã€references】
[1] Gao Junfeng, Wu Shuji. Selection of Large Diameter Flange Connection Gaskets for Pressure Vessels [J]. Pressure Vessels, 2012.19(10):67-70.
[2]Hua Jun. Analysis of Influence of Thread Lubrication Status Change on Screw-Guided Pretensioning Force[J]. Vehicle Technology, 2014.(6):13-15.
[3] GB/T 16823.2-1997. Fastening of threaded fasteners [S].
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