Patent Application
20130047408
The present invention generally relates to the tightening of bolted joints, and more particularly, to the uniform and accurate tightening of bolted joints formed with multiple fasteners.
The joining of components in any of a variety of industries often requires the development of bolted joints for effectively securing the components to each other. This can include any of a variety of complex assembly procedures for properly securing a series of fasteners associated with an assembled component or combination of components. Examples of such procedures can include applications such as the joining of cylinder head assemblies to cylinder blocks, which is common practice in the automotive industry, the joining of pipe flanges, having applicability to any of a number of industries, and the complex assembly procedures that are prevalent in the aerospace industry, among others.
Irrespective of the application involved, the overall goal is to achieve a substantially uniform load in all of the fasteners associated with a particular bolted joint being produced, in order to provide a proper connection of components, while performing the required tightening sequence in the least amount of time possible. Although the problems in achieving such a result have been known for some time, numerous attempts at solving such problems have not been entirely successful.
As an example, and for applications involving the connection of flanged joints, U.S. Pat. No. 5,278,775 (Bibel) discloses a method for tightening the threaded fasteners associated with the flanged joint in an effort to achieve a substantially uniform load in all of the fasteners associated with that joint. The disclosed method attempts to solve problems noted in Bibel, G. D., “Tightening Groups of Fasteners in a Structure and the Resulting Elastic Interaction”, Handbook of Bolts and Bolted Joints, Chapter 24, Marcel Dekker Inc. (1998), which recognizes that when a group of fasteners is tightened to form a joint, elongation of the individual fasteners causes structural interaction with the assembled joint which is being compressed, and that subsequent tightening further compresses the joint, reducing the preload in the previously tightened fasteners. Such effects are commonly referred to as “elastic interaction” or “bolt cross talk”. Another effect to be taken into consideration, which is commonly referred to as “rocking”, is where the load increases in a fastener diametrically opposite to the one being tightened. Such rocking can occur in a flange joint when the gasket outer diameter is smaller than the bolt circle diameter, which is often the case.
In an effort to accommodate such conditions, the method disclosed in U.S. Pat. No. 5,278,775 initially tightens each of the fasteners associated with the flanged joint system to a predetermined initial load or stress, in a first pass, and the final load, stress, strain or elongation is measured in each of the fasteners after all of the fasteners have been tightened. As used herein, a “pass” refers to a tightening procedure in which all of the fasteners for developing an assembled joint have been tightened once. Interaction coefficients representative of elastic interactions occurring between the fasteners in the system are thereafter calculated, and are used to predict an initial fastener strain value or load for each fastener in the system. These predicted values, together with the calculated interaction coefficients, are then used to tighten the threaded fasteners in a subsequent pass, whereupon the calculations and predictions are updated to achieve a desired tightening of the flanged joint.
Nevertheless, and even with load indicating fasteners such as the “I-Bolt®” fasteners which are available from Load Control Technologies of King of Prussia, Pa., it has not previously been possible to reliably achieve a satisfactory flange joint having substantially uniform stress on each of the fasteners without employing a significant number of passes in which each of the series of fasteners is sequentially tightened in a predefined pattern, resulting in a significant amount of time to produce the desired flange joint.
While the foregoing discusses problems associated with the joining of flanges, similar problems are presented in other complex assembly procedures. Moreover, such problems can further be complicated by the use of various different gasket materials for developing gasketed joints.
Such problems are solved in accordance with the present invention by establishing predefined procedures for performing a multi-step assembly of a desired joint using a dynamically controllable assembly tool. In joints such as flange joints, load indicating studs are used as the fasteners and access to both ends of each of the studs is made possible, and predefined procedures are established for performing a multi-step assembly in which there is simultaneous or parallel measurement of the load in all of the studs during the assembly operation. Other fasteners can be used to tighten other types of joints, using load indicating fasteners, or using conventional fasteners in which load, torque or other suitable measurements can be made to determine the degree to which such fasteners have been tightened, including fasteners which can only be accessed from one end. In any event, the operator is guided through a tightening sequence and the fastener target loads are modified based on the results of the measurements being made.
The preferred assembly tool includes a pneumatic tool coupled with an electronically controlled air pressure regulator for reducing the tightening rate, or the load increase per impact in the case of an impact or impulse tool, so that the tool can be stopped precisely at a specified stopping load or torque. The predefined procedures for performing the desired tightening operation are established in a controller coupled with the electronically controlled air pressure regulator, for dynamically controlling the pneumatic tool. As alternatives, electric or hydraulic tools can also be used.
The resulting system can then be used for the fast and accurate assembly of joints involving multiple fasteners and which are subject to elastic interaction between the fasteners, rocking, or joint relaxation.
The foregoing improvements are further described with reference to the detailed description which is provided hereafter, in conjunction with the following drawings.
Also schematically shown in
Similarly, the fasteners 6 shown in
It is to be understood that any of a variety of different types of fasteners, combined with any of a variety of different types of fastener identifying elements, can be used in accordance with the present invention, other than the stud and nut combination which has been shown for illustrative purposes. For example, the fasteners can be implemented as studs or bolts, which can be combined with a backing nut, or which can engage a threaded body. The studs or bolts are preferably provided with an ultrasonic transducer 8 which is permanently coupled with an end of the fastener 6, and an identifying element 9 which is permanently coupled with exposed portions of the fastener 6, although removable components can also be used if desired. If removably coupled with the fastener 6, the ultrasonic transducer 8 can be adhered to, magnetically coupled with, frictionally coupled with, or screwed onto the fastener 6, including direct placement of the ultrasonic transducer on an end of the fastener 6 which is to receive it, by sliding the ultrasonic transducer over the end of the fastener 6 which is to receive it, or by screwing the ultrasonic transducer onto the fastener 6 which is to receive it. A temperature sensor can also be combined with a removable ultrasonic transducer, if desired.
As further alternatives, the fasteners 6 can have a recess 10 in the head of the fastener (
The fasteners 6 are suitably prepared to perform their intended function, which can vary and which will depend upon the combination of structural elements employed. To this end, one or more ends of a standard bolt (or stud) can be made suitable for electronic load measurement using techniques which are themselves known, and used in the industry for purposes of protecting bolts (or studs). For example, a coating compatible with ultrasonic load measurement can be applied to desired surfaces to protect against corrosion and exposure to environmental complications, including exposure to high temperatures. Suitable coatings for accomplishing this include metal plating, paints, polymer and epoxy coatings, and fluoropolymer corrosion coatings. The selected coating is preferably a non-sacrificial metal coating (e.g., chrome) to prevent the potential changes to parameters associated with the fastener which could otherwise result. The fasteners 6 are also pre-calibrated, i.e., pre-qualified and certified for integrity of the ultrasonic measurements to be performed, and appropriately identified, whether or not the fasteners 6 incorporate an ultrasonic transducer.
An identifying element such as a bar code, an RFID device, a magnetic strip, or some other suitable device, can be placed at one or both of the ends, or along the body of the fastener 6. As a further alternative, the identifying element can be coupled with the flange or other body which is to be subjected to a tightening procedure. For example, a label or strap can be applied to a surface of the flange, or other receiving body, either permanently, semi-permanently, or even removably, provided the applied identifying element is suitably prevented from rotating relative to the receiving structure. As an example, a stainless steel label can be used for this, which can further include a black oxide coating for marking purposes, if desired. The identifying element can have one or more bar codes associated with it, to identify any of a variety of parameters associated with the joint being produced, such as identification of the joint, the fasteners used to form the joint and/or parameters associated with the joint and the fasteners. The identifying element can also include a pointer for indicating a particular feature associated with the joint, such as the fastener which is to serve as the starting point for the tightening procedure which is to take place (e.g., to locate the first fastener in the sequence, with the remaining fasteners numbered in a clockwise sequence, resulting in an identification of all of the fasteners in the sequence). Such identification can complement, or serve as an alternative to any identifying elements provided on the fasteners associated with the joint. Multiple identifying elements can be useful in circumstances where damaging elements are present, so that a functioning identifying element remains available even where another identifying element has been compromised. The identifying element can further be provided with coded information in human-readable form, which can be manually entered by an operator in cases where the machine-readable identifying elements have all been compromised.
Referring to
The functions associated with the electronic control 2 can be performed using the “LoadMaster®” portable bolt load unit which is available from Load Control Technologies of King of Prussia, Pa. The functions associated with the fasteners 6 can be performed using “I-Bolt®” fasteners, which are also available from Load Control Technologies of King of Prussia, Pa. The functions associated with the probes 15 can be performed using the “LoadMaster® I-Probe” measurement, data logging and tracking device, which is also available from Load Control. Technologies of King of Prussia, Pa. An example of a system for performing different assembly procedures is given in Appendix 1, which is attached hereto and which is incorporated by reference as if fully set forth herein.
Operation of the system of the present invention will now be described with reference to the conventional high pressure 8-stud flange connection shown in
The electronic control 2, for example, the previously described “LoadMaster®” portable bolt load unit, incorporates a display 20 for purposes of supporting overall system operations, and for displaying data and other information associated with an assembly, identification and/or inspection procedure which is to take place. A typical example of such a display 20 is the screen shown in
The display 20 is accessed using techniques which are themselves known, in order to allow the system to automatically sequence through desired assembly or inspection operations. Such operations are preferably defined in an accessible program text file, an illustrative example of which is given in
Examples of valid operating instructions which can be implemented by the accessed text file, for an illustrative sequence of bolts being operated upon to implement a selected tightening procedure, can include the following:
The “InspectBolt” and “TightenBolt” instructions have parameters for overriding a selected application number and application parameters including joint length, target load, minimum load, maximum load, minimum torque and maximum torque. Such instructions also provide for conditional “Operator Pause” and “GoTo” capabilities based on “OK”, “NOK”, or “Fault” status conditions following the selected operation. “Operator Pause” requires the operator to acknowledge an indicated status condition. The next instruction to be executed can be selected manually, if required, with an appropriate authorization.
Each text file contains a number of installation procedure instructions, which can be written in the following format. Each valid instruction preferably starts with an instruction number, followed by a separator (e.g., “:”), an instruction, and a number of operating parameters. Such fields are preferably separated by commas, and the final parameter is preferably terminated with a carriage return (i.e., <cr>). As an example, an illustrative instruction can be written as follows:
5:TightenBolt,7,Mode=5,AP=1,Load=11.0,MinLoad=9, MaxLoad=13,MinTorque=19,MaxTorque=39,JL=43, IfLO=P Call Supervisor,IfHI=P Call Supervisor<cr>
Such an instruction would be interpreted, and implemented by the electronic control 2, as:
The following Table (Table 1) defines various instruction fields for writing an installation procedure:
The following Tables (Tables 2 to 4) define tightening modes for an installation procedure (for all multiplexer modes, the bolt number corresponds to the channel number):
In each case, the above-listed operating instructions, instruction fields and tightening modes are given as examples of presently preferred variables which can be used for implementing the operating system of the present invention. It is to be understood that other operating instructions, instruction fields and tightening modes can additionally be developed, if desired, to achieve other operating modes.
After entering a desired file name, calling a text file for implementing a desired sequence of operating instructions, the selected sequence of operating instructions is initiated, at 24 in
Upon the initiation of a selected procedure, at 24, the user is prompted to take scheduled actions for accomplishing the selected operating procedure, at 26 in
The preferred embodiment of the present invention further includes the capability of reading an identification, such as a bar code, on the component to be assembled (e.g., a flange). From this reading, the electronic control 2 can retrieve all information relating to the assembly, eliminating the need for the operator to have knowledge of the specific component assembly procedure, and additionally automatically initiating the assembly procedure to be performed. Such information can include, for example, the identification of the component in the plant, for maintenance data logging of assembly operations, the correct fasteners and gasket to be used in the component, and the specified assembly procedure. An example of data retrieved for the 8-stud high pressure flange illustrated in
As an example of the implementation of a selected tightening procedure, reference is made to
Following the numbers assigned to the studs 6, as previously described, steps are taken to apply devices on the nuts at the opposing ends of the studs to prevent the nuts from turning during tightening. Such devices are commonly referred to in the industry as “backup wrenches” or “torque reaction wrenches”, examples of which are commercially available from Torcup of Easton, Pa. and A & W Devices of Brentwood, Calif. While such devices can be used with the present invention, they are in practice either cumbersome to use, and expensive, or lack a retaining feature to allow them to remain in place during the entire assembly process, especially when the flange pipe is vertical and such devices are required to secure the nuts on the underside of the flange. To accommodate this, the preferred embodiment of the present invention further uses an improved backup wrench, which is described below, which is simple and inexpensive to manufacture, and which includes a combined retaining and torque release mechanism for easy mounting and removal.
After the backup wrench 35 has been mounted on the nut of each of the studs (
Prior to issuing a prompt to an operator, electronic control 2 first switches the multiplexer 16 to read the next stud in the sequence to be tightened. If the load in the stud is already at the target load for the stud for the current pass, tightening of that stud is skipped, eliminating the need for the tightening prompt and the associated tightening operation. The assembly process then continues until the pass is completed, i.e., all studs have been tightened once, if required. In the preferred embodiment, and after each pass, electronic control 2 measures and stores the load in each stud by sequentially selecting the stud for measurement using the multiplexer 16. During this operation, the display 20 is updated to show the remaining load in each stud after the affect of elastic interaction or rocking from subsequent bolt tightening and gasket relaxation (examples of this are shown in FIGS. 15 and 16). The flange assembly then continues, with additional passes to predefined loads, until all of the studs are at their final specified loads, at which time the assembly procedure is complete. The results of the assembly operation of each stud in the identified flange are automatically logged by electronic control 2 for transfer to a maintenance database.
In the above-described embodiment, the sequence and the loads for each pass are predefined in the programmable installation procedure. It will be appreciated by one skilled in the art that the measurement of loads in all studs after each pass provides the necessary information to determine the elastic interaction, rocking, or other effects of the tightening of each stud on the load of every other stud in the joint, as is described in the above-referenced disclosure of Bibel, G. D., “Tightening Groups of Fasteners in a Structure and the Resulting Elastic Interaction”, Handbook of Bolts and Bolted Joints, Chapter 24, Marcel Dekker Inc. (1998), the subject matter of which is incorporated by reference as if fully set forth herein. Consequently, the electronic control 2 has the data and capability to calculate this interaction after a pass and adjust the target loads for each stud for subsequent passes in order to optimize the assembly procedure to precisely obtain the final load with a minimum of tightening operations.
Using the techniques disclosed in U.S. Provisional Application No. 60/789,828 and the corresponding International Application, in each of the above-described assembly operations, the pneumatic tool 1 operates to tighten the nut 46 on the stud 6 until a target load specified for the stud 6 (specified in the operating instruction written in the text file) has been reached. The pneumatic tool 1 is automatically stopped when the specified target load is reached, which is monitored through the multiplexer 16 using the probe 15, in conjunction with the ultrasonic transducer 48. The achieved load is displayed for the operator in the window 28 shown in
In the above-described assembly procedure, there remains a risk that the operator will place the tightening tool on the wrong stud and commence assembly while electronic control 2 is monitoring the specified stud. In order to prevent tightening of the wrong stud, electronic control 2 has the ability to detect when the tool is being operated. For a tool with an electrical start switch, this can be done simply by monitoring the state of the switch. For an air tool without an electrical start switch, this is done with a flow switch in the air line. For an electric tool, this is done by monitoring motor current. Should the tool be operated without a corresponding increase in the monitored load, electronic control 2 will immediately shut off the tool, indicating a fault condition.
Any of a number of text files containing any of a variety of instruction sets can be developed for achieving desired complex assembly procedures. This can include complex assembly procedures of the type described above, as well as complex assembly procedures developed for other applications. The various instructions to be implemented, and the manner in which such instructions are combined, can be developed through calculations or empirically, and can be further optimized by the adjustment of developed instructions resulting from experimental activity.
As an example, the instruction set shown in
The display 20 can also be used to display various functions associated with the accessed text file, and the instructions implemented responsive to the accessed text file.
For example, a user can be prompted, at 60 in
Similarly, if data is to be output to a data file, the user can be prompted to enter a data file name (filename.txt), at 62 in
While the foregoing improvements have been described based on certain specific embodiments, incorporating specified components and applied methods, it will be understood that such improvements can equally be employed in any of a variety of alternative applications, having applicability to any of a variety of industries, such as the petrochemical industry, including subsea applications, and the automotive and aerospace industries, referred to previously, or to other industries, including the nuclear and wind power industries.
This can include applications involving both simple and complex joints, employing assembly technologies from uncontrolled tools with low grade bolts to the precision assembly of critical joints with fasteners incorporating load measurement technologies such as those which have previously been described. The quality of the assembly can in any event be improved by significantly reducing operator related assembly errors for all joints through procedure guiding, monitoring and validation of correct assembly operations. This can in each case be accomplished by guiding an operator through an entire predefined assembly procedure, or selected portions of an assembly procedure, through displayed operator instructions or by voice commands, reducing dependency on operator knowledge or judgments, and applying multiple checks to ensure that procedures are followed.
Such improvements are capable of facilitating any of a variety of assembly control or data management requirements, including the monitoring or controlling of torque, hydraulic pressure, electric motor current, drop in air motor speed or angle, or other similar applications, using any of a variety of electronically controllable units suitable to the assembly tool being used and controlled, as well as the parameters being monitored, and are applicable to identification, tracking, assembly procedure guidance, assembly procedure validation and data logging technology in conjunction with any of a variety of fasteners, assembly tools and methods.
It is even possible for such improvements to be used with standard fasteners, without any fastener identification, or responsive only to measurements of torque, without ultrasonic load measurement, using any of a variety of tightening tools, including hydraulic, pneumatic and electric tools, and any of a variety of electronically controllable units, appropriately modified to interface with the previously described components. As an example, hydraulically operated tools, such as hydraulic ratchet tools, can be controlled using known hydraulic pressure transducers in place of the previously described air pressure regulator.
As a further alternative, conventional, removable ultrasonic technology can be used in applications where the use of permanent ultrasonic technology is impractical, for example, in applications where the cost of permanent ultrasonic technology is not justified and the assembly time is not critical, in applications involving the use of very large fasteners, where it is not practical to ship the fasteners for transducer attachment, in high temperature applications where subsequent inspection is required, and in extreme corrosive environments where subsequent inspection is required. The fasteners used in such applications, however, are preferably pre-calibrated, certified fasteners to maximize the results obtainable in such applications.
It will therefore be understood that the present invention further encompasses all enabled equivalents of the components and methods described, and that various changes in the details, materials and arrangement of parts which have been herein described and illustrated in order to explain the nature of this invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the following claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US11/00759 | 5/2/2011 | WO | 00 | 11/5/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61343723 | May 2010 | US | |
| 61400815 | Aug 2010 | US |
