The core feature of blackened Type B pins is the dual advantage of "standardized structure + blackening anti-corrosion", which complement each other and establish its core position in the fastening field. Structurally, different from Type A without a cotter pin hole, Type B pins are reserved with a standard cotter pin hole at the end of the rod, which can be used with cotter pins or R-type pins to achieve reliable anti-loosening locking, effectively avoiding the risk of falling off under vibration conditions. This design makes it particularly suitable for scenarios bearing alternating transverse forces. The size specifications strictly comply with national standards, with the nominal diameter ranging from 3mm to 100mm and the tolerance level precisely controlled. Among them, the nominal diameter tolerance is h11, the head diameter tolerance is h14, and the pin hole diameter tolerance is H13, ensuring the interchangeability and fitting accuracy with supporting components, which can be directly assembled without additional processing.
Blackening treatment is the core surface process of blackened Type B pins, also known as bluing treatment, which is a classic anti-corrosion method for carbon steel and low-alloy steel. Its process principle is to put the derusted and degreased pins into a mixed solution of concentrated alkali and oxidant at 130-150℃ for heating, so that a layer of ferroferric oxide film with a thickness of 0.5-1.5 microns is formed on the surface, showing a blue-black or dark black color, which has both anti-corrosion and decorative effects. This treatment process is low-cost and easy to operate, and does not change the internal material and dimensional accuracy of the pin. It only isolates air and moisture through the surface oxide film to effectively delay rust. At the same time, after oil immersion treatment, it can also improve surface lubricity and reduce friction loss during assembly and use. Compared with galvanizing, Dacromet and other treatment methods, blackening treatment is more suitable for application scenarios with high requirements on dimensional accuracy, cost sensitivity and non-strong corrosion environment.
Material selection and heat treatment process determine the bearing capacity and service life of blackened Type B pins. The mainstream materials are mainly 45# steel and 40Cr alloy structural steel. 35# steel can be selected for light-load scenarios, and high-strength alloy steel such as 35CrMo can be used for heavy-load scenarios. The yield strength and tensile strength of the material are strictly matched with the load requirements, and the hardness is controlled between 125HV and 245HV, balancing strength and toughness, and can effectively bear shear force and extrusion force. During the production process, the pins need to go through quenching and tempering heat treatment, and some heavy-duty models will also undergo high-frequency quenching strengthening to further improve surface hardness and fatigue resistance, ensuring that they will not bend or break under long-term alternating loads. For example, blackened Type B pins used in construction machinery can reach a surface hardness of HRC58-62 and a tensile strength of ≥980MPa, which can easily meet the needs of heavy-load operations.
The application scenarios of blackened Type B pins cover many industrial fields, becoming a "key hub" connecting various mechanical components. In the field of construction machinery, it is widely used at the articulation of the boom and bucket rod of excavators and loaders, undertaking the functions of power transmission and component positioning, adapting to harsh working conditions such as mines and infrastructure, and can resist dust and muddy water erosion after blackening treatment; in the field of automobile manufacturing, it is used for the connection between the control arm of the suspension system and the steering knuckle, bearing alternating transverse forces to ensure driving stability; in the fields of rail transit and agricultural machinery, it is adapted to the connection of coupler buffer devices and tractor components, relying on anti-loosening design and anti-corrosion performance to improve the reliability of equipment operation; in addition, in fields such as precision instruments, food machinery and amusement facilities, different specifications of blackened Type B pins are selected according to load requirements, balancing accuracy and practicality.