Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
  • B25B—TOOLS OR BENCH DEVICES NOT OTHERWISE PROVIDED FOR, FOR FASTENING, CONNECTING, DISENGAGING OR HOLDING
  • B25B23/00—Details of, or accessories for, spanners, wrenches, screwdrivers
  • B25B23/14—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
  • B23P19/00—Machines for simply fitting together or separating metal parts or objects, or metal and non-metal parts, whether or not involving some deformation; Tools or devices therefor so far as not provided for in other classes
  • B23P19/04—Machines for simply fitting together or separating metal parts or objects, or metal and non-metal parts, whether or not involving some deformation; Tools or devices therefor so far as not provided for in other classes for assembling or disassembling parts
  • B23P19/06—Screw or nut setting or loosening machines
  • B23P19/065—Arrangements for torque limiters or torque indicators in screw or nut setting machines
  • B23P19/066—Arrangements for torque limiters or torque indicators in screw or nut setting machines by electrical means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
  • B23P19/00—Machines for simply fitting together or separating metal parts or objects, or metal and non-metal parts, whether or not involving some deformation; Tools or devices therefor so far as not provided for in other classes
  • B23P19/04—Machines for simply fitting together or separating metal parts or objects, or metal and non-metal parts, whether or not involving some deformation; Tools or devices therefor so far as not provided for in other classes for assembling or disassembling parts
  • B23P19/06—Screw or nut setting or loosening machines
  • B23P19/069—Multi-spindle machines

Definitions

• the invention relates to a method for pretensioning a settling joint containing two or more threaded fasteners to an intended clamping load by applying simultaneously a torque delivering tool on each fastener.
• the invention concerns a method for pretensioning a joint which contains two or more threaded fasteners and which is apt to settle during an initial stage of the axial load application, thereby causing a relaxation of one or more of the threaded fasteners and a loss of axial clamping load obtained in the joint.
• a previously known method for pretensioning a joint of the above described type is based on a torque related tightening of the fasteners. This means that the actual torque applied on each one of the fasteners is measured continuously during the entire tightening process, and that occurring settlements in the joint at the intended pretension level is met by a continuous maintenance of the predetermined torque level applied on the fasteners for a certain time interval, meaning rotation as well as stand still condition in the fasteners as be required to maintain the predetermined torque level .
• the main object of the invention is to solve the above mentioned problems and to substantially improve the resulted joint clamping load accuracy by referring to the actual axial load in each fastener during the entire pretensioning process .
• the joint pretensioning process is based on the determination of the axial load variations on each fastener via a determination of the variations in the fasteners length by measuring the variations in transit time for ultra-sonic waves induced in the fasteners .
• Fig. 1 shows a joint including four threaded fasteners, and a tightening device for simultaneously and individually tightening the fasteners.
• Fig. 2 shows a longitudinal section through a torque delivering spindle with a nut socket and a sound wave inducing electrode for engagement with a threaded fastener.
• Fig. 3 shows a diagram illustrating tightening one of the fasteners of a joint to be pretensioned in accordance with the invention.
• Fig. 4 shows a diagram similar to Fig. 2 and illustrating tightening of a second fastener comprised in the same joint .
• Fig. 5 shows a diagram illustrating tightening of one of the fasteners of a joint in a two-step pretensioning process .
• a joint comprising at least two fasteners.
• the example shown in Fig. 1 comprises a joint 10 formed by a main structure 11 and an attached upper part 12.
• the joint 10 comprises a gasket 13 for accomplishing a tight connection between the two parts 10,11.
• a common application of this type of joint is the attachment of the cylinder head on an engine block of a combustion engine.
• the invention is as well applicable on joints without gaskets but including one or more parts making the joint apt to settle during pretensioning.
• the main thing is that the joint has such properties that the clamping load in the joint tends to decrease under an initial tightening stage, provided no specific measures are being taken.
• the joint illustrated in Fig. 1 comprises four threaded fasteners 15 a - d in the form of head screws entered through the upper part 12 and threaded into the main structure 11 or in the form of studs secured in the main structure 11 and nuts engaging the upper ends of such studs .
• Fig. 1 there is also illustrated a multiple nutrunner 18 having four individually rotated and controlled output spindles 19 a - d which are intended to engage simultaneously the threaded fasteners 15 a - d and to apply a tightening torque thereon.
• each one of the nutrunner spindles 19 has a splined end 22 for carrying a fastener engaging nut socket 23.
• Each spindle 19 is axially displaceable and biassed into engagement with the respective fastener 15 by a spring 24.
• Each one of the spindles 19 are also provided with ultra-sonic wave generating and detecting means 25 for abutting engagement with the end surface 26 of the fastener 15.
• the ultra-sonic wave generating and detecting means 25 comprises an electrode 27 disposed concentrically in the spindle 19 and a piezo-electric transducer 28 inseparably attached to the rear end surface 26 of the fastener 15.
• the electrode 27 is connected to a control unit (not shown) located in the multiple nutrunner 18 or at a location remote therefrom, and the tip of the electrode is axially biassed by a non-illustrated spring into contact with the transducer 28.
• Figs. 3 and 4 illustrate the clamping load F and the rotation angle ⁇ in relation to time for two of the fasteners of the joint 10.
• the tightening response of the other two non-illustrated fasteners are about the same, but for clarity reasons the description is limited to just two of the fasteners.
• the described and illustrated pretensioning process is just one example of method according to the invention in which the intended final clamping load level F ⁇ in the joint is accomplished directly, i. e. this process does not involve any intermediate steps where the joint is pretensioned to one or more lower load levels.
• the invention is not at all limited to the described process but may as well include intermediate steps ending at one or more load levels below the intended final clamping load level F ⁇ .
• the joint 10 as a whole as well as each one of the fasteners 15 a - d are intended to be pretensioned to a predetermined clamping load target level F ⁇ .
• This is obtained in that the spindles 19 a - d of the nutrunner 18 are brought into engagement with the fasteners 15 a - d, and a tightening torque is applied simultaneously on all of the fasteners 15 a - d until the intended target load is reached. Then, this nutrunner spindle is stopped.
• the axial load F in the fastener which is illustrated by a continuous line in the diagram in Figs. 3 and 4, increases directly from zero to the target level F ⁇ .
• the joint 10 After still another rest period, the joint 10 has settled further, and the nutrunner spindle is restarted a third time at point t 6 to re-establish the intended axial load level F ⁇ in the fastener. This is obtained at point t 7 .
• the axial load remains constant, i.e. no further settlement influencing this fastener occurs.
• the pretensioning process is interrupted.
• the other three fasteners of the joint 10 are tightened in a similar way.
• One of these is illustrated in the diagram in Fig. 4.
• the initial rotation of this fastener results in a direct pretensioning to the target load level F ⁇ at a point t x .
• the fastener has reached an angular position ⁇ 1# and after four additional re- tightenings at the points t 2 , t 3 , t 4 and t 5 , adding rotational angles to the fastener from ⁇ ⁇ to ⁇ 2 , ⁇ 3 , ⁇ 4 and ⁇ 5 .
• the tightening process is interrupted at t ⁇ where the axial load F has remained unchanged at the target load level F ⁇ for a certain time interval.
• the tightening restarting points occur at different occasions in the two fasteners, i.e. no one of the points t x - t 7 of the first illustrated fastener has to coincide with any one of the points t 1 - t 5 of the second fastener.
• the final process interruption point t ⁇ is common to both spindles, though.
• FIG. 5 An alternative embodiment of the invention is illustrated in Fig. 5, namely a two-step pretensioning process, wherein the joint is initially pretensioned to a preliminary clamping load level corresponding to an axial load F p in each one of the fasteners. As this preliminary load level is safely maintained in all of the fasteners, the process is continued by pretensioning the fasteners to the target load level F ⁇ corresponding to the desired clamping level in the joint.
• the two-step pretensioning process is carried out by initially tighten each one of the fasteners 15 a-d to the preliminary load level F p . This is obtained at a point of time t x , wherein the fastener has been rotated to an angular position ⁇ 1 . After some time, there has been a settlement in the joint 10, which calls for a re-application of the tightening torque at point t 2 . The preliminary load F p in the fastener is regained at ⁇ 2 . After another settlement in the joint, the tightening torque is again re-applied on the fastener at a point t 3 to again maintain the axial load in the fastener at F p .
• the second pretensioning stage is commenced at point t 6 .
• a tightening torque is re-applied on each fastener at point t 7 , and when, within a certain final time interval, no further settlements are detected, the process is completed and the power nutrunner 18 is shut off. Then, the illustrated fastener has reached its final angular position ⁇ 7 .
• the pretensioning process may be carried out in more than two stages.
• An uneven settling of such a joint may cause different degrees of relaxation of the fasteners and also require tightening to more intermediate levels to obtain an even final pretension of the joint.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Details Of Spanners, Wrenches, And Screw Drivers And Accessories (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=20413899

Family Applications (1)

Country Status (4)

Cited By (2)

Families Citing this family (4)

Family Cites Families (8)

• 1998
  • 1998-12-29 SE SE9804588A patent/SE515974C2/sv not_active IP Right Cessation
• 1999
  • 1999-12-28 EP EP99965696A patent/EP1146993A1/en not_active Withdrawn
  • 1999-12-28 JP JP2000590817A patent/JP2002533225A/ja active Pending
  • 1999-12-28 WO PCT/SE1999/002487 patent/WO2000038879A1/en not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events