Dacromet exterior six
Dacromet galvanized Grade 8.8 and 10.9 high – tensile B7 hex head bolts and nuts predominantly utilize high – strength alloy steel as the base material.
Description
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Product Material
Dacromet galvanized Grade 8.8 and 10.9 high - tensile B7 hex head bolts and nuts predominantly utilize high - strength alloy steel as the base material. The B7 designation indicates that the material meets specific ASTM A193 standards, which are widely recognized for their mechanical properties and chemical composition requirements in high - stress applications.
For Grade 8.8 bolts and nuts, the alloy steel typically contains elements such as carbon, manganese, and silicon. After proper heat treatment, these components work together to achieve a minimum tensile strength of 800 MPa and a yield strength of 640 MPa. This makes them suitable for general - to medium - heavy - duty applications where reliable fastening under significant loads is required.
Grade 10.9 high - tensile variants, on the other hand, are made from alloy steel with more precise control over the chemical composition and a more rigorous heat - treatment process. They can attain a minimum tensile strength of 1000 MPa and a yield strength of 900 MPa, enabling them to withstand extremely high loads, vibrations, and mechanical stresses. This high - strength grade is often employed in critical structural connections where failure is not an option.
The defining feature of these products is the Dacromet galvanization. Dacromet coating is a high - performance anti - corrosion treatment composed mainly of zinc flakes, aluminum flakes, chromates, and organic binders. When applied to the surface of the alloy steel bolts and nuts, it forms a dense, uniform, and adherent film that provides superior corrosion resistance compared to traditional galvanization methods.
Product Models
The product line of Dacromet galvanized Grade 8.8 and 10.9 high - tensile B7 hex head bolts and nuts includes various models categorized by size, length, and specific application requirements:
Standard Metric and Imperial Models: Available in a comprehensive range of metric and imperial sizes. In the metric system, bolt diameters typically range from M6 to M36, while in the imperial system, they cover from 1/4" to 1 - 1/2". The length of the bolts can vary from 20mm (or 3/4") to 300mm (or 12") or more, depending on the actual needs of different projects. Standard models follow relevant international and national standards for hex head bolts and nuts, ensuring compatibility with standard wrenches, sockets, and other fastening tools.
High - Load - Capacity Special Models: For heavy - duty industrial applications, large - scale construction projects, and critical infrastructure installations, high - load - capacity special models are offered. These bolts and nuts often have larger diameters and thicker hex heads to handle substantial tensile and shear forces. They are specifically designed for use in applications such as heavy machinery assembly, bridge construction, and high - rise building frameworks, where the ability to withstand extreme loads is crucial.
Corrosion - Resistant Enhanced Models: Besides the standard Dacromet galvanization, some models may undergo additional anti - corrosion treatments or use advanced formulations of Dacromet coating. These corrosion - resistant enhanced models are developed for extremely harsh environments, such as offshore platforms, chemical plants, and areas with high levels of air pollution and humidity. They can offer extended protection against severe corrosion, ensuring the long - term reliability of the fastening system.
Manufacturing Process
The production of Dacromet galvanized Grade 8.8 and 10.9 high - tensile B7 hex head bolts and nuts involves multiple precise steps and strict quality - control measures:
Material Preparation: High - quality alloy steel raw materials are carefully sourced to meet the requirements of ASTM A193 B7 and the specific strength grade (Grade 8.8 or 10.9). Rigorous inspections are carried out on the chemical composition, mechanical properties, and surface quality of the steel. The steel bars or rods are then cut into appropriate lengths according to the specified sizes of the bolts and nuts.
Forming: The alloy steel is formed into the characteristic hex head and shank (for bolts) or the hex nut shape through cold - heading or hot - forging processes. Cold - heading is commonly used for smaller - sized bolts and nuts, which is efficient for mass production and can accurately form the shape while maintaining dimensional accuracy. Hot - forging is applied to larger - diameter or high - strength bolts and nuts, where the steel is heated to a malleable state and then shaped under high pressure to achieve the required strength and precise dimensions.
Threading: After forming, the bolts undergo threading operations. Thread rolling is the preferred method as it creates a stronger thread by cold - working the metal, improving the fatigue resistance of the bolts. Specialized threading dies are used to ensure that the thread pitch, profile, and dimensions meet the relevant standards, guaranteeing proper matching with the nuts. For nuts, the internal threads are carefully cut or formed to ensure a precise fit with the corresponding bolts.
Heat Treatment: To achieve the desired Grade 8.8 or 10.9 mechanical properties, the formed bolts and nuts are subjected to a series of heat - treatment processes. This typically includes annealing to soften the steel and eliminate internal stress, quenching to increase hardness and strength, and tempering to adjust the hardness and toughness to the optimal level. The heat - treatment process is precisely controlled to ensure that the bolts and nuts meet the strict strength and performance requirements of their respective grades.
Dacromet Coating Application: First, the bolts and nuts are thoroughly cleaned to remove any contaminants, oil, or scale on the surface. Then, they are either immersed in a Dacromet solution or coated by spraying, which evenly distributes the solution containing zinc flakes, aluminum flakes, chromates, and binders on their surfaces. After coating, the components are cured at a high temperature (usually around 300°C). During the curing process, the components of the Dacromet solution react to form a dense, corrosion - resistant coating with excellent adhesion to the alloy steel substrate.
Assembly and Quality Inspection: Bolts are paired with corresponding nuts. Every batch of products is subject to strict quality inspection. Dimensional checks are performed to ensure that the diameter, length, thread specifications, and head size of the bolts and nuts meet the standards. Mechanical tests, such as tensile strength, proof load, and torque - tension tests, are carried out to verify the load - bearing capacity and performance of the bolt - nut pairs. Visual inspections are also conducted to check for surface defects, proper Dacromet coating coverage, and any non - compliance with appearance requirements. Only products that pass all quality tests are approved for packaging and delivery.
Surface Treatment Process
The Dacromet galvanization surface treatment is a key factor in the superior performance of these bolts and nuts:
Pre - treatment: Before Dacromet coating, the bolts and nuts are pre - treated to ensure good adhesion of the coating. This pre - treatment process starts with degreasing, where the components are cleaned with solvents or alkaline solutions to remove oil, grease, and other organic contaminants. Then, pickling is carried out using an acid solution to remove rust, scale, and inorganic impurities from the surface. After pickling, the bolts and nuts are rinsed thoroughly to eliminate residual acid, and finally, they are dried to prepare for the Dacromet coating.
Dacromet Coating Process: There are mainly two methods for applying Dacromet coating: immersion and spraying. In the immersion method, the pre - treated bolts and nuts are completely immersed in the Dacromet solution, allowing the solution to fully cover the surface. In the spraying method, the Dacromet solution is sprayed evenly onto the surface using spraying equipment. After coating, the components are placed in an oven for curing. During the curing process, the water in the Dacromet solution evaporates, and the zinc flakes, aluminum flakes, chromates, and binders react chemically to form a continuous, dense, and stable coating with a thickness of about 5 - 15 microns.
Post - treatment: In some cases, post - treatment may be carried out after Dacromet coating. This can include passivation treatment with special chemicals to further enhance the corrosion resistance of the coating, or applying a topcoat to improve the abrasion resistance and appearance of the surface. Post - treatment helps to optimize the performance of the Dacromet - coated bolts and nuts and adapt them to different application requirements.
Application Scope
Dacromet galvanized Grade 8.8 and 10.9 high - tensile B7 hex head bolts and nuts are widely used in various critical engineering and construction fields:
Building and Construction: In large - scale building projects, especially high - rise buildings, bridges, and industrial plants, these bolt - nut pairs are used for connecting steel beams, columns, and trusses. Their high strength ensures the stability and load - bearing capacity of the building structure, while the Dacromet galvanization provides long - term protection against corrosion, even in outdoor environments exposed to the atmosphere, rain, and other weather conditions.
Heavy Machinery and Equipment Manufacturing: In the manufacturing of heavy machinery, such as construction equipment, mining machinery, and agricultural machinery, these high - tensile bolts and nuts are essential for assembling critical components. They can withstand the heavy loads, vibrations, and shocks generated during the operation of the machinery. The excellent corrosion resistance of the Dacromet coating also protects the bolts and nuts from the harsh working conditions, such as exposure to dirt, moisture, and chemicals.
Automotive and Aerospace Industries: In the automotive industry, Grade 8.8 and 10.9 high - tensile bolts and nuts are used in engine assembly, chassis construction, and suspension systems. The high - strength 10.9 - grade bolts are crucial for securing engine components and ensuring the vehicle's performance and safety under various driving conditions. In the aerospace industry, where strict quality and performance standards are required, these bolts and nuts are used for assembling aircraft components. Their precise manufacturing, high strength, and reliable corrosion resistance are essential for the safety and functionality of aircraft.
Energy and Power Generation: In power plants, including thermal, nuclear, and renewable energy facilities, these bolt - nut pairs are used for fastening equipment, pipes, and structural components. They can withstand the high temperatures, pressures, and mechanical stresses present in power - generation environments. The Dacromet coating protects the bolts and nuts from corrosion caused by steam, chemicals, and other substances, ensuring the long - term reliable operation of the power - generation equipment.
Offshore and Marine Engineering: For offshore platforms, ships, and marine installations, where exposure to saltwater, high humidity, and harsh marine environments is constant, these bolts and nuts are highly valued. The combination of high - strength alloy steel and Dacromet galvanization enables them to withstand the corrosive effects of seawater, preventing structural failures due to corrosion. They are used for fastening various marine components, ensuring the safety and durability of offshore and marine structures.
Product Advantages
Exceptionally High Strength: With Grade 8.8 and 10.9 strength ratings, these bolts and nuts offer outstanding tensile and yield strength. They can firmly connect structural components and withstand heavy loads, vibrations, and shear forces, ensuring the stability and safety of engineering structures in various demanding applications.
Superior Corrosion Resistance: The Dacromet galvanization provides excellent corrosion resistance, far surpassing that of traditional galvanization methods. The unique composition of the Dacromet coating forms a dense protective film that effectively isolates the base metal from the corrosive environment. It can resist the erosion of moisture, salt, chemicals, and other corrosive substances, significantly extending the service life of the bolts and nuts compared to conventional products. This makes them particularly suitable for use in harsh environments where corrosion is a major concern.
Reliable and Secure Fastening: The hex head design of the bolts and the corresponding nuts provides a reliable and secure fastening method. The hexagonal shape allows for easy tightening and loosening with wrenches or sockets, and the precise thread design ensures a tight fit, capable of withstanding different types of mechanical loads. The combination of high - strength material and proper thread engagement ensures that the fastening remains secure even under extreme conditions.
Good Compatibility and Standardization: These bolts and nuts comply with relevant international and national standards, ensuring excellent compatibility across different projects and industries. The standardized dimensions and thread specifications allow for easy replacement and interchangeability, simplifying the procurement, installation, and maintenance processes. This standardization also reduces the risk of errors in assembly and enhances overall project efficiency.
Long - Term Stable Performance: Through strict manufacturing processes, precise heat treatment, and high - quality Dacromet coating, these bolts and nuts maintain stable mechanical and anti - corrosion performance over a long period. They can operate reliably under various complex working conditions without significant performance degradation, reducing maintenance costs and minimizing the risk of unexpected failures. This long - term stability is crucial for ensuring the continuous operation of critical infrastructure and equipment.
Environmentally Friendly: Compared with some traditional anti - corrosion treatments that may produce harmful substances, the Dacromet coating process is relatively environmentally friendly. It contains less heavy metal content and does not produce a large amount of waste during the production process, meeting the requirements of modern engineering construction for environmental protection while still providing high - performance corrosion protection.
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