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Bolt Tightening 1 2019.02.01（13:51:53） TECHNICAL DATA TECHNICAL DATA 2-1 Various Tightening Methods Torque and Tension 2 2019.02.01（13:51:53） Various tightening methods 34 Why tighten screws? Screw tightening is carried out in order to stop 2-2 Screw and Torque objects from moving (to fix them). Followings are major objectives of the screw tightening. Relation formula between screw and torque 35 Bolt Tightening 1. For fixing and jointing objects Bolt Tightening 2. For transmitting driving force and braking force 2 2-3 Torque Coefficient 3. For sealing drain bolts, gas and liquid Formula of torque coefficient （1） 36 The fixing force at this time is called the axial （2） The torque coefficient is not stable 36 tension (tightening force), and the target of screw tightening is to“apply an appropriate axial tension.” （3） Even when the torque is stable, axial tension may vary 36 Bolt Tightening Although axial tension control should normally be carried out, because axial tension is difficult to 2-4 Method for Determining Tightening Torque measure, torque control is used for its substitute （1） Applying appropriate tightening torque 37 characteristics that allow tightening administration and operations to be carried out easily. （2） Methods for determining tightening torque 37 （3） Standardize the tightening torque 38 （4） Standard tightening torque 40 Axial tension 2-5 Tolerance of Tightening Torque Tolerance of tightening torque 42 2-6 Tightening of Tension Stability Figure 2-1. （1） Zigzag tightening 43 Enhance reliability with （2） Two steps tightening 43 combination of fixing, （3） Two times tightening 43 transmitting, preventing leakage and others. （4） Stabilized tightening 43 32 TOHNICHI TORQUE HANDBOOK Vol.9 Technical Data 33 四校TOHNICHI_00_02 2019.02.01（13:51:53） TECHNICAL DATA TECHNICAL DATA 2-1 Various Tightening Methods Torque and Tension 2 2019.02.01（13:51:53） Various tightening methods 34 Why tighten screws? Screw tightening is carried out in order to stop 2-2 Screw and Torque objects from moving (to fix them). Followings are major objectives of the screw tightening. Relation formula between screw and torque 35 Bolt Tightening 1. For fixing and jointing objects Bolt Tightening 2. For transmitting driving force and braking force 2 2-3 Torque Coefficient 3. For sealing drain bolts, gas and liquid Formula of torque coefficient （1） 36 The fixing force at this time is called the axial （2） The torque coefficient is not stable 36 tension (tightening force), and the target of screw tightening is to“apply an appropriate axial tension.” （3） Even when the torque is stable, axial tension may vary 36 Bolt Tightening Although axial tension control should normally be carried out, because axial tension is difficult to 2-4 Method for Determining Tightening Torque measure, torque control is used for its substitute （1） Applying appropriate tightening torque 37 characteristics that allow tightening administration and operations to be carried out easily. （2） Methods for determining tightening torque 37 （3） Standardize the tightening torque 38 （4） Standard tightening torque 40 Axial tension 2-5 Tolerance of Tightening Torque Tolerance of tightening torque 42 2-6 Tightening of Tension Stability Figure 2-1. （1） Zigzag tightening 43 Enhance reliability with （2） Two steps tightening 43 combination of fixing, （3） Two times tightening 43 transmitting, preventing leakage and others. （4） Stabilized tightening 43 32 TOHNICHI TORQUE HANDBOOK Vol.9 Technical Data 33 四校TOHNICHI_00_02 Bolt Tightening Bolt Tightening 2019.01.28（17:16:04） TECHNICAL DATA TECHNICAL DATA 2-1 Various Tightening Methods 2-2 Screw and Torque Various tightening methods Relation formula between screw and torque Table 2-1. Various tightening methods Figure 2-3. Formula of screw (1) 2 Detail drawing Relational drawing Reference literature: "Theory and calculation of threaded fasteners" 2 2019.01.28（17:16:04） Tightening method Description Advantages and disadvantages Akira Yamamoto (Yokendo Co., Ltd.) Bolt tightening is controlled by specific It is reasonable way for tightening control and operation. Friction on the α Torque control torque value. Tightening torque is not influenced by the bolt length so β bearing surface 50% d μ n method This is the most widely used method. easy to standardize. The Bolt efficiency will be low due to Tension Ff ² d 10% T= Ff + tanβ +μn ÷1000 wide tolerance of the tension. 2 cosα 2 The tightening is managed by rotting Tightening within plastic zone gives lower dispersion of axial Bolt Tightening Friction on the threaded portion Tension Ff Friction on the bearing surface Bolt Tightening angle which start from the seating tension and easy the operation. Rotation angle ｄ2 point of the bolt head. Since tightening conducts beyond the yield point, there is method Friction on the Tightening is conducted by specific limitation for additive load to the joint or difficulty for re- ｄ threaded portion Example: For a M8 bolt at Ft = 8000 [N], the tightening torque is angle from the snug torque. tightening. It is difficult to define the tightening angle. 40% From P.132 Table 8-1. 2 T : Torque ････････[ N・m ] d = 7.188 [mm] The tightening is managed by the Since the dispersion of the axial tension is small, it is possible dn1 = 11.96 [mm] (Hexagon nut style) variation of the torque gradient to design the bolt efficiency large. F : Axial tension ･･･ [N] tan β = 0.0554 Torque gradient against rotating angle at the yield Inspection for the bolt itself is possible even after tightening. d² : Pitch diameter [mm]（See P.132 Table 8-1) point. Tightening is conducted beyond the yield point and the dn : Pitch diameter of bearing surface From P.36 Table 2-2. method The variation is monitored and tightening device is expensive, so it is hard to adopt the μ = μn = 0.15 α = 30゜ carried out arithmetic process by an same method in the service field. ･･････････････････[mm]（See P.132 Table 8-1） electronic device. μ : Friction coefficient of threaded portion T = 8000{ 7.188 ( 0.15 ＋ 0.0554) ＋ 0.15( 11.96 )} ÷ 1000 ･･････････････････（See P.36 Table 2-2） 2 cos30゜ 2 Tightening is controlled by the elongation The dispersion of the bolt is very small. Tightening within the = 13.8［N・m］ Elongation of the bolt, generated by bolt tightening. elastic zone is available. The efficiency of the bolted joint is μn : Friction coefficient of bearing potion measurement Elongation is measured by a micrometer, large. Additive loading and bolt re-tightening are possible. ･･･････････････････（See P.36 Table 2-2） method ultrasonic, or an embedded gauge The bolt end faces must be finished. The tightening cost is a. Hexagon bearing surface (first type nut, bolt) α : Half angle of screw thread · ISO Screw 30° sensor in a bolt. high. 3 3 β : Lead angle [tan β ] ･（See P.132 Table 8-1） 0.608B − 0.524dH By tightening the nut while tensile Axial tension can be directly controlled. dn1 = 2 2 0.866B − 0.785dH Loading load is applied to the bolt, tightening Torsion stress of the bolt is not generated. method is controlled by the generated tensile The tightening device and bolts are specially made. High ■ Formula of pitch diameter B: Hexagon width across flats [mm] Hd : Bearing surface inside diameter [mm] force after releasing the load. cost. of bearing surface (dn , dn) ¹ b. Round shape bearing surface (second, third type nut) Tightening is controlled by the Space and force are not required for tightening. Heating 3 3 variation of the elongation before and There is no clear relation between the heat and axial Figure 2-4. B 2 D − dH method dn = after heating the bolt. tension. Temperature setting control is difficult. dH ・ 2 2 3 D − dH D: Bearing surface outside diameter [mm] dH: Bearing surface inside diameter [mm] Figure 2-2. Tightening control methods Rotation angle method Break point dn1 Torque gradient method Formula of screw (2) T T = K.d.Ff or Ff = Torque control K d method K: Torque coefficient (See P.36 Table 2-2) Yield point d: Nominal size of screw [mm] dn Example: Axial tension to tighten a M20 screw to T = 400 [N・m] Axial tension d =20［mm］ K = 0.2 (See P.36 Table 2-2) dH 400 Elastic zone Plastic zone F = ＝ 100000［N］ D 0.2 × 20 ÷ 1000 34 TOHNICHI TORQUE HANDBOOK Vol.9 Technical Data 35 三校TOHNICHI_00_02 Bolt Tightening Bolt Tightening 2019.01.28（17:16:04） TECHNICAL DATA TECHNICAL DATA 2-1 Various Tightening Methods 2-2 Screw and Torque Various tightening methods Relation formula between screw and torque Table 2-1. Various tightening methods Figure 2-3. Formula of screw (1) 2 Detail drawing Relational drawing Reference literature: "Theory and calculation of threaded fasteners" 2 2019.01.28（17:16:04） Tightening method Description Advantages and disadvantages Akira Yamamoto (Yokendo Co., Ltd.) Bolt tightening is controlled by specific It is reasonable way for tightening control and operation. Friction on the α Torque control torque value. Tightening torque is not influenced by the bolt length so β bearing surface 50% d μ n method This is the most widely used method. easy to standardize. The Bolt efficiency will be low due to Tension Ff ² d 10% T= Ff + tanβ +μn ÷1000 wide tolerance of the tension. 2 cosα 2 The tightening is managed by rotting Tightening within plastic zone gives lower dispersion of axial Bolt Tightening Friction on the threaded portion Tension Ff Friction on the bearing surface Bolt Tightening angle which start from the seating tension and easy the operation. Rotation angle ｄ2 point of the bolt head. Since tightening conducts beyond the yield point, there is method Friction on the Tightening is conducted by specific limitation for additive load to the joint or difficulty for re- ｄ threaded portion Example: For a M8 bolt at Ft = 8000 [N], the tightening torque is angle from the snug torque.
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