JPH04500782A - How to monitor gasket compression force when tightening fasteners - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] How to monitor gasket compression force when tightening fasteners One bean standing! The invention is in the field of mechanical engineering, and more particularly in the field of pressurized fluids. In physical systems, bolt tightening sometimes monitors gasket compression force. A typical application of the present invention relates to a method of preventing fluid leakage by Used in power plants or other equipment with high internal pressure and where the effects of leakage are significant. It is a piping system used for large-scale application equipment.

1 bean stand and 1 Piping systems containing high pressure and/or corrosive liquids or gases. systems, pressure vessels, pumps, and pulp are typically flanged and bolted. It is closed by fitting and sealed with a special gasket. Traditionally, such attire The bolts used in the installation are tightened by using a torque wrench. However, a different method is now used.

One alternative method of tightening bolts uses a special device called a hydraulic fastening tool. be done. One form of hydraulic fastening tool uses hydraulic pressure to pull the bolt end. With the bolt in tension, the nut with no load is tightened.

Bolt fastening tools are disclosed in U.S. Pat. Nos. 3,749,362 and 4.249.718. , No. 4.438.901, and No. 4.433,828.

In many of these cases, bolt tightening tools are more effective than torque wrenches. Although easier, more convenient, and more accurate to use, such fastening tools There are still devices that monitor the compression force of a gasket by simply applying force. I don't have a method.

In U.S. Pat. No. 3,643,501, Pauley Tightening applied to a fastener becomes a power strain when the force begins to exceed the elastic limit of the fastener. A differential inoculation (differentiator) to stop the problem is described.

This tightening force range is much greater than the tightening force according to the present invention, and Pauly's invention is based on a different physical effect than the present invention.

In U.S. Pat. No. 4.102.182, Brown et al. In addition, tightening in which a limit on the slope of the torque-angle curve is used is described with respect to the procedure. states.

In U.S. Pat. No. 4,400,785, Wallace et al. and others use a microprocessor to sequentially calculate the lower part of the torque-angle curve. The area is measured to determine whether the tightening has reached the strength standard.

In U.S. Pat. No. 4,228,576, Eshghy torque or tightening using Kerr angle curves to monitor or tighten fasteners. It's in control.

All of the above-mentioned patents provide a method for tightening that takes into account the unique requirements of pressure-sealing gaskets. does not provide a method. In contrast, the present invention allows gasketing to specific limits desired. The conditions under which the gasket compresses and the bolt tightening that causes that particular gasket compression are determined by the force It is only concerned with the identification of

l bean stand l top The present invention relates to a type of flap in which the degree of gasket compression is limited by a metal compression stopper. Intended to use bolting tools for bolted and bolted connections It is something. The compression stop is either part of the gasket or part of the flange. It may be. The present invention allows the user to install bolts that produce appropriate gasket compression. Tightening allows the user to determine the force and whether the gasket is Check that the bolts have the correct density and that the bolts are properly preloaded. possible.

High-pressure sealing gaskets vary in size, shape, and color, even if they have different densities. may be difficult to tell apart, unless proper gasket operation is verified. It cannot be verified that the connections are properly tightened.

If the gasket is too flexible, the gasket should be tightened too little. The force is fully compressed to the compression stop, no matter how much additional bolt tightening is applied. It will leak no matter how much you try. If the gasket is too dense, remove all bolts. Tightening forces the force onto the gasket surface, so complete gasket compression is In this latter condition, large bolt tightening will not occur even in force. Subsequent gasket relaxation reduces bolt tightening force. This condition also causes the bolt to undergo increased fatigue loads, which would result in leakage. Proper tightening is necessary to avoid force Full gasket compression (up to compression stop) must occur and this Additional bolt tightening is required to withstand even more fluctuating internal and external loads. Added. This keeps the gasket properly loaded and under pressure. The contracting flanges are firmly joined metal to metal and sufficiently preloaded to prevent movement of the connection. This minimizes the load fatigue of bolts.

Therefore, the main objective of the present invention is that bolt tightening is performed when the force is increased. Monitor the gasket compression and check the force for tightening at full gasket compression. As a result, metal-to-metal bonding is achieved.

Unlike the prior art, the present invention provides that the specific applied tightening is determined by the total amount of force. Directly measure the displacement made and the applied tightening for a given increment of force. The point of metal-to-metal flange contact is represented by a sharp change in the rate of displacement.

(In some cases, if further confirmation of metal-to-metal contact is desired, use sound Acoustic propagation (from one flange to the other) confirms the above instructions monitored by the change point in the propagation associated with metal-to-metal contact, which is useful for You may be

The operation of the "bolt" and nut is, for the purposes of this invention, the same as a "shut bolt". The behavior is similar to that of nuts.

The momentary selection is dictated by the geometry of the parts. For further discussion, By understanding that one term applies to the other depending on the purpose of the application. Therefore, the terms "bolt" and "shut bolt" are used interchangeably. The term ``threaded fastener'' is a term used to describe ``bolts'' and ``planted fasteners.'' This includes both "embedded bolts".

Sealing of joints in high pressure joints is typically done on new chassis, bell mounts, etc. A.Flexitallic Ga5ket Company, Inc.) Sketches (spiral wound gaskets) made using J The present invention is particularly well suited for industrial applications using spirally wound gaskets. It is something that

In a preferred embodiment of the invention, the user can ensure that adequate gasket compression occurs. Bolt tighteners get a visual indication of the force and compare that information to the set point. Determine join eligibility. In the example of the separate report, based on the operation of the gasket Connection qualification is determined and final fastener tightening is achieved without user intervention. will be accomplished.

According to a preferred embodiment of the invention, the spacing of the surfaces compressing the gasket is , the applied tightening is measured while the force is increased. gasket compressed When the distance is set, the applied tightening is predictable for each increment of force. amount decreases. However, after the gasket is compressed to the desired limit , metal-to-metal contact between the opposing compressed surface portions occurs, and then, Further tightening will result in an increase in force, which will first cause deformation of the bolt and cause separation of the opposing surfaces. When this metal-to-metal contact occurs, tightening is caused by force, which has little effect on Knowledge of forces and final fastener tightening can be used to properly assess the suitability of the connection. required to be valued.

In the most general form of the invention, changes in compression surface separation (ΔE) and fastening The tightening of the tool is determined by any accurate means of measuring the change in force (∆F) and the gasket. From the ratio ΔE/ΔF measured during compression of the gasket, after the gasket is fully compressed, , distinctly different ratios ΔE/ΔF are measured as a result of the elastic deformation of the metal joint. It may be used to confirm the transition to . This means that the distance measurement is at a convenient location on the device being attached or on the device itself. and thereby facilitate the use of the method of the invention. It is. It also includes the use of some already known tightening devices , which further improves the usefulness of the method of the invention.

The novel features believed to be characteristic of the invention include both the mechanism and method of operation. With respect to the Better from the description below, considered in conjunction with the accompanying drawings, which are explained throughout. It will be understood, however, that the drawings are for illustration and explanation purposes only. It is clear that the invention is not intended to define the scope of the invention. should be understood.

Brief description of the drawing FIG. 1 is a partial representation of a typical pulp configuration in which the method of the invention may be used. Figure 2 is a cross-sectional side view showing means for measuring changes in separation of compressing surfaces;

FIG. 2 shows a partial section of a typical vibe bond in which the method of the invention may be used. Figure 2 is a cross-sectional side view showing means for measuring changes in separation of compressing surfaces;

FIG. 3 shows a typical manway and hole in which the present invention may be used. 1 is a side view in partial section of a pressure vessel with a bar; FIG.

FIG. 4 is a side view, partially in section, of a typical hydraulic bolting tool.

Figure 5 shows the measurement of the displacement of the compressed surface as a function of the travel distance between parts of the fastening tool. 1 is a side view, partially in section, showing a typical hydraulic bolting tool using Ru.

Figure 6 shows the connection between the threaded end of the fastener and the outside of one of the members to be compressed. A typical method using means of measuring the displacement of a surface being compressed as a function of the travel stroke of FIG. 2 is a partially sectional side view showing a hydraulic bolt fastening tool;

FIG. 7 shows a typical operation according to the method of the invention used with a secondary verification device. FIG. 3 is a side view of a partial cross-section showing a hole.

FIG. 8 shows that the applied bolt tightening as measured by the apparatus of FIG. 1 is a graph showing displacement as a function of .

FIG. 9 shows the applied voltage as measured by the apparatus of FIGS. 5 and 6. Tightness is a graph showing displacement as a function of force.

FIG. 10 is a schematic block diagram illustrating a preferred embodiment of an apparatus using the method of the present invention. It is.

FIG. 11 shows another embodiment using the method of the invention with a secondary verification device. It is a schematic block diagram showing.

FIG. 12 is a schematic block diagram showing another embodiment using the method of the present invention. Ru.

FIG. 13 is a schematic block diagram showing another embodiment of an apparatus using the method of the invention. It is a diagram.

FIG. 14 is a schematic block diagram showing a modification of the embodiment of FIG. 11.

FIG. 15 shows the algorithm used in the embodiments of FIGS. 13 and 14. It is a flowchart.

stuttering the next day 211 Figure 1 shows a check valve using the method of the present invention (the flapper is not shown). The diameter of the flow path shown is from several centimeters to one meter or Valves can weigh up to several thousand kilograms. for maintenance The passage into and out of the valve is through a lateral duct 10 closed by a bonnet 12. prepared by. The bonnet 12 typically includes stud bolts 16. It is securely fastened to the body 14 of the valve by a stud.

A gasket 18 is compressed between the bonnet 12 and the body 14 to form a seal. There is. Compression of gasket 18 is intentionally limited by annular land 22 . The bonnet is in its sealing position as shown.

During assembly, the gasket 18 is installed in a fixed position and the bonnet 1 2 is placed above it.

Initially, the gasket 18 is only slightly compressed by the weight of the bonnet. In this case, the annular land 22' is not in contact with the bonnet 12, and then the implanted bonnet 22' The fasteners, typically bolt 16, are tightened and the bonnet is brought closer together at all times. It is attracted to the main body 14. The gasket 18 has a land 22 attached to the bonnet 12. They are gradually compressed until they touch. This point where the land touches the bonnet is This is the point where a gasket seal is occurring, and it is usually located between the land and the bonnet. It is referred to as the point at which "metal-to-metal contact" is achieved between the two. further tightening Internal and external damage will not improve the sealing of the gasket. It may be required to provide an appropriate preload to withstand the force λ.

As shown in FIG. 1, according to a preferred embodiment of the present invention, a linear variable differential transformer ( LVDT: 1inear variable differential transformer) 24 is placed on the armrest 28 attached to the main body 14. be done. The L V D T 24 is in contact with the armrest 26 placed on the bonnet 12. In this method, the LVDT is connected to the bonnet and book. An electrical signal relating to the separation from the body is generated on the conductor 30.

Figure 8 shows that the applied stud bolt tightening is the force F and the valve of the check valve of Figure 1. 3 is a graph showing the relationship between the distance E between the net 12 and the main body 14; Assemble When vertically tightening the stud bolt, the initial values of force F and distance E are F and F, respectively. Denoted as E.

During the first stage of fastener tightening, the change in E is mainly due to the amount of gasket compression and It represents the sum of some amount of metal deformation, and the distance E1 increases as the tightening force increases. Decrease rapidly. However, at a certain point 32 in FIG. 8, the land in FIG. 22 makes contact with the bonnet 12. When tightening the stud bolt at point 32, the force is F. , −, and the clamping represents the force when “metal-to-metal” contact occurs; During tightening after metal-to-metal contact is obtained, the change in E+ is small and the deformation of the metal Represents quantity only.

FIG. 2 shows another situation in which the invention is used. Figure 2 shows pies of two different lengths. The two sides 34 and 36 are similar to those in FIG. They are attracted to each other by the similar arrangement of nuts and bolts.

It should be noted that the bond in FIG. 2 has no form similar to the annular land 22 in FIG. It is. To limit the compression of gasket 38, the circumference of gasket 38 is A thin metal ring 40 is provided. Ring 40 is often a compression gauge Alternatively, it is called a compression stop and effectively prevents excessive compression of the gasket 38.

Compression stop 40 is typically supplied as part of the gasket.

FIG. 3 shows another situation in which the invention is used. Figure 3 shows the pressure vessel wall 8. 3 shows a cross section of the working hole 84 and the circular working hole cover 86. Work hole 84 and work The cover 86 is fitted with holes (some nuts and studs) located around the cover. are therefore attracted to each other, thereby tightening the stud Sometimes the gasket 19 is compressed. As shown in Figure 1, gasket compression It is limited to an appropriate amount by the shaped land 23. Also, similar to Figure 1, Figure 3 is an electric current that measures the change in the value E, which is related to the separation between the working hole 84 and the working hole cover 86. An LVDT 24 is shown generating an optical signal.

One convenient device using the method of the present invention is a hydraulic fastening tool. hydraulic fastening tools One form of this is shown in Figure 4, where fluid pressure compresses the gasket and Used to pull up the bolt, the nut rotates easily and the tightening force is maintained. The fluid pressure is then removed.

In the exemplary example shown, the socket 42 is fitted into the nut 20 and After the dowel bolt 16 has been pulled up, it is used to tighten the nut. Support stand 4 4 is a cover around the socket 42. The support base 44 supports other parts of the hydraulic fastening tool. It is useful for locating the element. The support stand 44 is a hairpin wrench (tommy b). ar) Opening where 52 is inserted to rotate the socket together with the nut Other methods have also been used to rotate the nut, including 54.

A hydraulic chamber cover 46 of the hydraulic fastening tool is located on the support base 44, and the hydraulic chamber cover 46 in the form of an annular groove A ram 48 , including chamber 60 , slidably fits within hydraulic chamber 60 . , are fitted in a sealed state. The tension portion 50 is internally threaded to accommodate the implantable bollard. When the tension part is twisted on the stud 16, and securely secure the ram, chamber enclosure, and support in the positions shown.

Tightening is accomplished by activating hydraulic pump 49. Hydraulic pressure is ducted 58 to the hydraulic fluid within the hydraulic chamber. The hydraulic pressure is against the tension part 50. to push up the ram 48, thereby raising the stud 16. planting While the dowel bolt is in this raised position, against the flange surface 88 To tighten nut 20, socket 42 is rotated.

There is no need to apply any significant torque to the nut 20; It may be manually rotated until it makes positive contact with the flange surface 88. .

When the stud is tightened, hydraulic pressure acts on a constant area of the ram 48. , thus the force F applied to the stud 16 is a function of hydraulic pressure. result Generally, an electrical pressure sensor 47 measures the force F applied to each stud. used for. In some manual applications, electrical pressure sensors A standard pressure gauge is used instead.

According to another embodiment of the invention, as shown in FIG. 26 and 28, and the fixed hydraulic chamber cover 46 and the tension part 50. Measure the mobility E between It is clear that the tension part is against the stud bolt 16. As the tightening force increases, the magnitude of E also increases.

According to another embodiment of the invention, as shown in FIG. 64 and the LVDT (7) probe portion 62 extends to touch the end of the stud 16. is in contact with the part. The LVDT is attached to the top 88 of the flange surface and the stud 16. Measure the change in distance E3 between. The tension portion 50 is connected to the stud bolt 16. As the tightening force increases, the magnitude of E also increases.

FIG. 9 shows the magnitude of the applied tightening, E, and E as a function of the force F. The changes in l and E are the cumulative sum of gasket compression, metal deformation, and fastener elongation. The magnitudes of ml and E, which express the effect of relative increase, but when metal-to-metal contact is achieved at point 32, the rate of increase suddenly increases. deformation of various metal parts, including the elongation of stud bolts. Ru. The rate of change of E2 and E, as plotted in Figure 9, is plotted according to Figure 8. in that stud bolt elongation is not a factor in a fitted arrangement; This is different from the rate of change in El plotted in FIG.

Point 32 is the minimum tightening force required to completely seal the gasket.

Because further tightening will obviously not compress the gasket . However, only an additional prestress is applied to the connection. Once, point 32 Once reached, the movement and movement of the joint to withstand various internal or external loads Even with the appropriate preload applied to minimize bolt load fatigue. good.

According to a preferred embodiment of the invention, point 32 in FIGS. 8 and 9 is located in FIG. This can be easily determined using a device. By using LVDT, An electrical signal is generated representing a change in one of the variables EI%E1% and El. is designated by E for ease of understanding. Another electrical signal, bolt tightening. A fitting force Fl is generated by the bolt fastening tool 66. Signal F is These signals, which may be obtained from the pressure sensor of the hydraulic bolting tool, are applied to the vertical and horizontal axes of block 68 and shown in FIGS. 8 and 9. Provide a graph like this.

According to the embodiment of the invention shown in FIG. The tightening force is increased when the The user observes the slope of the curve provided do. For small values of F, the observed slope is will correspond to the slope calculated based on the theory that the plot is compressed. , pay particular attention to changes in slope, point 32 in Figures 8 and 9. A sharp change in slope, shown as , indicates that metal-to-metal contact has been achieved. Tightening primarily results in metal deformation and fastener elongation, resulting in poor bonding. Once the desired predetermined pressure has been applied, The user must stop further tightening with the bolt tightening tool and Tighten the nut until the butt makes firm contact with the supporting surface. After that, the user When tightening a bolt, release all hydraulic pressure and remove the bolt tightening tool from the bolt. The desired tightening is commanded by the connecting tool and forces the nut to hold the connection.

Under some conditions, the secondary accuracy of bolt tightening at full gasket compression Methods using acoustic propagation may be desirable for this confirmation. used for.

According to the embodiment shown in FIG. 7, an acoustic transmitter 81 is arranged on one flange. , an acoustic pickup 82 is placed on the other side. Is the gasket fully compressed? When the flanges are clamped metal-to-metal, direct acoustic transmission occurs through the compression stop. Those acoustic devices should be placed as far away from the fasteners as possible so that the feed path is visible. Ru.

According to the embodiment shown in FIG. 11, the bolt tightening as a function of force is , the acoustic propagation T from one flange to the other is plotted. Tighten Signal components corresponding to the acoustic transmission path through the fitting are filtered out. the remains Acoustic propagation through gasket materials or air gaps has a high resistance. and the gasket is completely compressed and no metal-to-metal contact occurs. When tightened, there is a sharp increase due to propagation from one flange to the other. Occur. This sharp increase in acoustic propagation caused point 32 to be reached. It is useful to check. Erdman In Basadena, California Form Acoustic manufactured by Industries Incorporated A "propagation-via" device may be used for this application.

The use of acoustic propagation as a means of determining complete compression of a gasket is primarily In addition, it can be considered as a way to confirm the results of the method used to measure E. because, This is because measuring E provides a more complete picture of the interaction of the joined parts.

FIG. 12 shows a modification of the embodiment shown in FIG. is the force-related electrical signal F, is an ultrasonic extensometer rather than a bolt fastening tool. Obtained from 80. Such equipment is manufactured by Ray of Middletown, Conn. Manufactured by ond Engineering.

13 and 15 show another embodiment of the invention, in which the bolt Fastening tool 66 is operated under computer 700 control. In this example In this case, the tightening applied by the bolting tool increases the force and Therefore, tightening at predetermined regular intervals increases the magnitude of E for each increment of force (ΔF). is read by the LVDT 24 and sent to the computer 70 in the form of an electrical signal. be done.

As shown in FIG. 15, this sensed value of E is stored in the computer; The tightening force is further increased. After a further increase ΔF is made, the following The reading of E is read by the LVDT and stored in the computer. 1st As shown in step 72 of Figure 5, successive values of E are subtracted by the computer. be done. This calculated increment ΔE is divided by ΔF and the slope of the corresponding curve M x is calculated. This incremental slope M, is compared with a predetermined stored value M, and the absolute value of their difference is compared with a predetermined value d. "MB" The value of rdJ is described below.

The value of MB means that the gasket is completely compressed and the flanges are metal to metal. This is the slope of the curved portion that occurs after contact occurs. The slope MB is the change in the metal part. It is a result of the shape, and its expected value can be calculated. Alternatively, MB is a gas will be determined experimentally by pre-assembling the bond without a socket.

Alternatively, MB may be obtained from a previous or similar assembly. The expected value of B is first stored in the computer.

The preselected threshold level d is predetermined so that the MBQ value is approximated. 8 and 9, and also provides a tolerance for the MB Easily identify sharp changes in slope. Inspection step 74 of FIG. Compare the value of ΔE/ΔF and MB after each increase in plating, and , that is, the bolting tool is operating to the left of point 32 in Figure 8 or Figure 9. There is a computer way to determine whether or not. The fastening tool moves on the side of point 32. If the computer is tightening the bolt, the computer will tell the fastening tool to increase the force by ΔF when tightening the bolt. and the test is repeated. computer bolted If it is determined that the tying tool is operating on the right side of point 32 in Figure 8 or Figure 9, , the program branches to step 78 where the computer Tightening commands the tool to increase the force by a predetermined desired preload amount Ft. . The nut is then tightened and the force of the fastening tool is removed.

FIG. 13 shows the use of a bolting tool that provides a signal Fs, but the first In a modification of the embodiment thereof shown in FIG. 4, the ultrasonic extensometer 80 provides F. used to.

Typically, the bonnet 12 of FIG. 1, one side of the joint 34 of FIG. 2, and the construction of FIG. The hole cover 86 is secured with several stud bolts. of the present invention When performing the procedure, use multiple studs (some or all studs at the same time) A hydraulic clamp of the form shown in Figure 4 from a commonly pressurized hydraulic supply It is possible to provide a tying tool.

Thus, to ensure that the tightening resulted in proper and complete gasket compression. , a method using a bolting tool to monitor the compression of a sealing gasket was described.

Beyond this point a method of secondary confirmation of full gasket compression was also described. Further tightening of may be required to preload the connection, which is Limit joint movement and reduce bolt load fatigue.

The foregoing detailed description is illustrative of several embodiments of the invention; It should be understood that other embodiments thereof can be easily devised by those skilled in the art. It is possible. The embodiments described herein together with those additional embodiments are This is considered to be within the clear range.

engineering, The method of the present invention is an improved method of providing closure for pressurized fluid systems.

This method allows the user to ensure proper gasket operation and proper bolt preload. It makes it possible to monitor the closure member. This method uses pressurized liquid or applications in the manufacturing industry, where the consequences of leakage are very unfavorable. It will be served. Such facilities include nuclear power plants, aerospace bases, and oil refineries. , chemical factories, and hydroelectric power plants.

Fig, 4 (prior technology) E in Figure 5, and international search report

Claims (6)

[Claims] 1. For threaded fasteners that produce a certain limited amount of gasket compression. 1. A method for determining a tightening force, wherein the threaded fastener is a first member. the nut extends beyond the nut and passes through the play hole in the second member; said threaded fastener end by said threaded fastener end; A gasket holds the second member, and a gasket holds the first member and the second member together. The seal is continuously compressed as it is attracted, but the compression is mechanically desired. of the first member and the second member, the sealing portion being limited to an amount that is contained between opposing surfaces; a) a known force between the second member and the end of the threaded fastener; F such that the force F attracts the first member and the second member to each other. The direction is the stage, b) measuring a dimension E that is a function of the separation between the first member and the second member; stages and c) increasing said known force F by a known increment ΔF; d) measuring the size of the dimension E again; and e) measuring the known size in step c). determining the amount of change ΔE in the magnitude of E due to increasing the force F; f) the amount of change ΔE and when the first member and the second member reach the mechanical limit; a step of comparing the amount of change expected in the A method with 2. The threaded end of the fastener extends beyond the nut to form a hydraulic fastener. A tool is attached to the end of the threaded fastener and applies the known force. The step of applying pressure to the hydraulic fastening tool further includes applying pressure to the hydraulic fastening tool. 2. The method of claim 1, further comprising the step of: measuring the hydraulic pressure of the fluid. 3. The step of applying the known force further comprises the step of rotating the nut. The method according to claim 1. 4. Applying the known force to the gasket further comprises: 3. The method of claim 2, further comprising the step of measuring elongation of the fastener. 5. via secondary means, said first member and said second member reach said mechanical limit; The method according to claim 1, comprising an additional and appropriate step for confirming that the Law. 6. an acoustic transmitter attached to the first member for transmitting an acoustic signal; and an acoustic receiver is attached to the second member and receives the transmitted acoustic signal, and further comprising: when the first member and the second member reach the mechanical limit; said sound received to obtain a sudden change in the strength of said signal occurring at 6. The method of claim 5, comprising the step of monitoring the signal.