KIA ES05227-00 Bolt / Nut Tightening Standard Torque

Developed by Hyundai-Kia Motors, the oldest motor vehicle manufacturer in Korea, the “KIA ES05227-00 Bolt/Nut Tightening Standard Torque” standard is an engineering standard that specifies the standard tightening torque for bolts and nuts. This specification provides guidance on tightening bolts and nuts and a decision regarding tightening torque, excluding the tightening of special parts. Tightening methods vary, including torque tightening, angle tightening, torque-angle tightening, yield strength tightening, and plastic zone tightening, but this standard only specifies torque tightening.

The tightening of the bolt is to fix an external thread such as a bolt and a machine screw with an internal thread formed into a nut or a clamping part, and to connect two or more clamping parts with a fixed strength. Therefore, the axial part of the bolt passing through a clamping part expands and the clamping part shrinks, and the balance between the pulling force and the pressing force is achieved.

When assembling bolts, the pressing force is called a tensile force or a compressive force against a clamping member. The compressive force is usually set in the range of 70% to 90% of the normal bolt yield point in the elastic range. The figure given in the standard shows the axial graph of tightening versus bolt elongation. The definitions of terms and symbols related to bolt tightening are given in the tables given in the standard.

For the purposes of this standard, the following terms and definitions apply:

• A clamping member is a member or part that is joined by bolting.
• The clamping force is a tensile force applied to the axial portion of the bolt or a pressing force applied to the clamping part during tightening.
• Tightening torque is the torque required to turn a nut or bolt to produce a compressive force.
• The torque coefficient is the proportional constant that represents the relationship between the tightening torque and the clamping force.
• The torque at the engaged part of the teeth is the torque at the engaged part between the internal flange and the external flange.
• The torque on the bearing surfaces is the torque on the bearing surface of the nut or bolt and the torque on the bearing surface of the clamping piece.
• The coefficient of friction between the teeth is the coefficient of friction between the internal flange and the external flange.
• The coefficient of friction between the bearing surfaces is the coefficient of friction between the bearing surface of the nut or bolt and the surface of the clamping part.
• The yield compression force is the value of the compression force when the compression force reaches the yield point during squeezing.
• The yield tightening torque is the tightening torque value when the tightening force reaches the yield point during tightening.

The reference thread shapes and formal and reference dimensions of commonly used metric coarse screw threads and metric fine screw threads are given in the tables given in the standard. Similarly, the strength of commonly used bolts is given in the table titled “Strength classification of bolts (KS B 0233)” and the minimum connection length values ​​of bolts according to the commonly used material are given in the table titled “Minimum joint connection length of bolts”.

The bolt with a smaller root diameter than the nut is weaker against shear and bending stress, so a nut and a bolt should have similar strength, or a bolt should be stronger than a nut. In order for the bolt to have the target compression strength, the test load of the matching nut should be considered, and the detailed specifications should be defined for each case. The recommended combination according to the strength grade of the bolt is in the table under the title “Recommended combination according to screw strength”.

The friction coefficient of the tooth and the friction coefficient of the bearing surface are important variables in calculating the tightening torque, and the friction coefficient by surface treatment is shown in the table given in the standard.

Tightening torque is divided into four types according to the allowable torque range as shown in the table. The tightening torque range is adjusted by tightening the important part and the overall tightening, and appropriate tools are needed according to the allowable torque range.

Tightening torque is calculated according to this standard by the following method:

• Understanding screw information (pitch, nominal diameter, strength)
• Selection of friction coefficient of bearing surface
• Selection of friction coefficient of maximum tightening torque value
• Calculation of tightening torque range according to torque range

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