The forming inner diameter standard for armour rod repair strips is strictly regulated in the industry. From a production perspective, controlling the helical pitch diameter of armour rod in transmission line to be slightly smaller than the outer diameter of the conductor is based on a comprehensive consideration of material mechanics and geometry. This dimensional fit directly determines the gripping performance and long-term operational stability of the pre-stretched fitting.

Mechanical Basis for Preload Formation

Engineering Design of Inner Diameter Difference

The inner diameter of forming armor rods conductor is set to be slightly smaller than the outer diameter of the conductor. This "negative tolerance" design allows the material elasticity to naturally generate a radial compressive stress pointing towards the conductor axis when armor rod preformed is wound onto the conductor. This uniform compressive stress is the source of subsequent friction.

Coordination of Pitch and Helix Direction

The helical pitch of preformed armour rod must match the outer layer twist pitch of the conductor. The helical direction also follows the principle of consistency with the outer layer of the conductor. This geometric uniformity allows the armor rods to "hold" the conductor more tightly when under tension, distributing the tensile load along its length.

Tolerance Control in Actual Working Conditions

Physical Changes During Installation

At the installation site, workers unwind the pre-stirred wire and wind it around the conductor. Due to the factory-preset small pitch diameter, the pre-stirred wire generates a continuous restoring force, attempting to shrink back to its original diameter. This restoring force translates into a persistent gripping force on the conductor, preventing it from easily loosening even after long-term wind vibration and temperature changes.

The Auxiliary Role of the Coefficient of Friction

Typically, a certain particle size of diamond abrasive is adhered to the inner wall of the pre-stirred wire. When the pre-stirred wire elastically deforms and presses tightly against the conductor surface, the diamond abrasive increases the coefficient of friction of the contact surface. Combined with the aforementioned radial pressure, both constitute a reliable friction gripping system, preventing the conductor from slipping out of the clamp under tension.