QC/T 518-2013Tightening torque for automotive threaded fasteners (English PDF)

1 Scope

This Standard specifies the tightening torque for automotive threaded fasteners.

This Standard applies to fasteners which comply with the following conditions and are tightened using the control torque method.

-- the mechanical properties of external threaded parts comply with grades 8.8, 10.9 and 12.9 as specified in GB/T 3098.1;

-- the mechanical properties of internal threaded parts comply with GB/T 3098.2 or GB/T 3098.4 and have the strength to give full play to the carrying capacity of threaded connecting assemblies;

-- the widths across flats of internal and external threaded parts shall comply with the standard series as specified in GB/T 3104;

-- bolt-nut connecting assemblies and threaded connecting assemblies in addition to bolt-nut;

-- thread is as specified in GB/T 196. The accuracy of thread is not lower than grade 6 as specified in GB/T 197;

-- external threaded parts bear axial tensile loads in tightening;

-- the design tensile force for bolts or screws shall be 90% of tensile point or tensile strength.

This Standard does not apply to the tightening of set screws bearing compressing force in tightening for external threaded parts; self-tapping screws and wood screws threaded by tapping from external threaded parts; threaded fasteners with spring washer or elastic washer; and threaded fasteners of the prevailing torque type.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition dated applies to this document. For undated references, the latest edition of the referenced documents (including all amendments) applies to this document. Ff,min - minimum pretightening force; Ff,max - maximum pretightening force; K - torque coefficient; Kmin - minimum torque coefficient; Kmax - maximum torque coefficient; K1 - torque ratio; m - dispersion; P - thread pitch; Tf - tightening torque; Tf,min - minimum tightening torque; Tf,max - maximum tightening torque;

- yield point of bolts;

- yield strength of bolts;

- thread friction coefficient;

- minimum thread friction coefficient;

- maximum thread friction coefficient;

- friction coefficient of bearing surface;

- minimum bearing surface friction coefficient;

- maximum bearing surface friction coefficient.

4 Tightening torque and pretightening force

4.1 Relation expression of tightening torque and pretightening force […]