Carriage bolt
Hot Dip Galvanized HDG Dacromet Geomet Mushroom Head Square Neck Carriage Bolts primarily utilize carbon steel as the base material, commonly in grades like 4.8, 8.8, and 10.9.
Description
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Product Material
Hot Dip Galvanized HDG Dacromet Geomet Mushroom Head Square Neck Carriage Bolts primarily utilize carbon steel as the base material, commonly in grades like 4.8, 8.8, and 10.9. Lower - grade 4.8 carbon steel provides basic strength, making it suitable for general - purpose fastening tasks where load requirements are not extremely high. Higher - grade carbon steel, such as 8.8 and 10.9, can undergo heat treatment to enhance its tensile strength, hardness, and toughness, enabling the bolts to withstand heavier loads and more demanding working conditions.
To further enhance corrosion resistance, these bolts incorporate multiple protective layers. The hot - dip galvanizing (HDG) process applies a thick layer of zinc on the surface, which acts as a sacrificial barrier, corroding preferentially to protect the underlying steel. Additionally, the Dacromet or Geomet coating, consisting of zinc flakes, aluminum flakes, chromates, and binders, is applied on top of the galvanized layer. This coating forms a dense, uniform, and adherent film, providing superior corrosion resistance far beyond that of traditional zinc - based coatings. It can endure hundreds of hours of salt - spray testing, making the bolts highly durable in harsh environments.
In certain specialized applications where non - metallic properties are necessary, such as in electrical insulation or medical equipment, alternative materials like nylon or engineering plastics may be used for parts of the bolt or as supplementary components. However, for the main body of the bolt in most structural applications, the combination of carbon steel with HDG and Dacromet/Geomet coatings remains the standard due to its excellent strength - corrosion resistance balance.
Product Models
The product range of Hot Dip Galvanized HDG Dacromet Geomet Mushroom Head Square Neck Carriage Bolts encompasses various models categorized by size, length, thread type, and strength grade:
Standard Model: The standard bolts are available in a wide array of metric sizes, with diameters typically ranging from M6 to M36 and lengths varying from 20mm to 300mm. They feature the characteristic mushroom - head shape, which provides a larger bearing surface for even pressure distribution, and a square neck that prevents the bolt from turning when the nut is tightened. Standard bolts usually have a coarse - thread pitch, suitable for general - purpose fastening in construction, furniture making, and light - machinery manufacturing.
High - Strength Model: Engineered for heavy - duty applications, high - strength bolts are made from higher - grade alloy steel, often with a strength grade of 12.9. These bolts have larger diameters and longer lengths to handle significant tensile and shear forces. They are indispensable in industrial settings for securing heavy machinery, large - scale structural components, and equipment operating under high loads and vibrations. High - strength bolts typically display visible strength grade markings on their nuts or shanks for easy identification.
Special - Feature Models:
Fine - Thread Model: With a smaller thread pitch compared to standard bolts, the fine - thread model offers increased adjustment precision and enhanced resistance to loosening. It is commonly used in applications that demand fine - tuning, such as in precision machinery, optical equipment, and high - end furniture manufacturing, where a more secure and accurate fastening is crucial.
Long - Length Model: Designed for applications requiring longer fasteners, such as in thick structural members or multi - layer assemblies, long - length bolts can have lengths exceeding the standard range. These bolts ensure a secure connection through multiple layers of materials, providing stability and strength in complex structures.
Custom - Coated Model: In addition to the standard HDG and Dacromet/Geomet coatings, some models may receive custom - applied supplementary coatings. For example, a Teflon - based coating can be added to reduce friction during installation, while a specialized anti - abrasion coating can further protect the bolt in high - wear environments.
Manufacturing Process
The production of Hot Dip Galvanized HDG Dacromet Geomet Mushroom Head Square Neck Carriage Bolts involves a series of precise steps and stringent quality - control measures:
Material Preparation: High - quality carbon steel bars are sourced and carefully inspected for chemical composition, mechanical properties, and surface quality to ensure compliance with production standards. The steel bars are then cut into appropriate lengths according to the specific bolt size requirements.
Forming: Metal bolts are typically formed through cold - heading or hot - forging processes. Cold - heading is commonly employed for smaller - sized bolts, where the steel is shaped into the desired mushroom - head, square neck, and shank form using dies in multiple stages. This process is efficient for high - volume production and can create accurate thread forms and bolt shapes. For larger or higher - strength bolts, hot - forging is used, where the steel is heated to a malleable state and then shaped under high pressure to achieve the required strength and dimensional accuracy.
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 bolt. Specialized threading dies are used to ensure the thread quality, pitch accuracy, and compatibility with corresponding nuts. For bolts with specific thread requirements, such as fine - thread models, additional precision machining may be involved.
Heat Treatment (for high - strength bolts): Bolts made from higher - grade carbon steel or alloy steel may undergo heat treatment processes including annealing, quenching, and tempering. These processes optimize the mechanical properties of the bolts, increasing their strength, hardness, and toughness to meet the specific application requirements.
Hot - Dip Galvanizing: The formed bolts are immersed in a molten zinc bath for the hot - dip galvanizing process. This results in a thick, durable zinc coating that adheres firmly to the bolt surface, providing a primary layer of corrosion protection. The galvanizing process not only coats the outer surface but also penetrates into the pores and crevices of the bolt, ensuring comprehensive protection.
Dacromet/Geomet Coating Application: Following galvanization, the bolts are subjected to the Dacromet or Geomet coating process. First, the bolts are thoroughly cleaned to remove any contaminants, oil, or residues from the galvanizing process. Then, they are immersed in a solution containing zinc flakes, aluminum flakes, chromates, and binders. After immersion, the excess solution is drained, and the bolts are cured at a high temperature, usually around 300°C. During the curing process, the components of the solution react to form a dense, uniform, and highly corrosion - resistant coating on the bolt surface.
Quality Inspection: Every batch of bolts is rigorously inspected. Dimensional checks are performed to ensure that the bolt's diameter, length, thread specifications, head shape, and neck size meet the standards. Mechanical tests, such as tensile strength, hardness, and torque tests, are carried out to verify the load - bearing capacity and durability of the bolts. Coating thickness and adhesion tests are also conducted to ensure the quality of the HDG and Dacromet/Geomet coatings. Visual inspections are performed to check for surface defects, cracks, or improper coatings. Only bolts that pass all quality tests are approved for packaging and distribution.
Surface Treatment Process
The surface treatment of these bolts is a key aspect, involving two major protective processes:
Hot - Dip Galvanizing: In the hot - dip galvanizing process, the bolts are first degreased and pickled to remove any surface contaminants, rust, or scale. They are then fluxed to ensure proper wetting by the molten zinc. After that, the bolts are immersed in a molten zinc bath at a temperature of around 450 - 460°C. The zinc reacts with the iron in the steel to form a series of zinc - iron alloy layers, followed by a pure zinc outer layer. The resulting galvanized coating is thick, usually ranging from 50 - 100 microns depending on the bolt size and application requirements. This thick zinc layer provides excellent corrosion resistance by acting as a sacrificial anode, protecting the underlying steel even if the coating is scratched or damaged.
Dacromet/Geomet Coating: The Dacromet or Geomet coating process starts with a clean, galvanized bolt surface. The bolts are then dipped into a water - based solution containing zinc and aluminum flakes, chromates, and binders. The flakes are dispersed evenly in the solution, and when the bolts are removed, a thin film of the solution adheres to the surface. This film is then cured at high temperature, causing the components to react and form a continuous, dense, and adherent coating. The Dacromet/Geomet coating offers superior corrosion resistance, lubricity, and heat resistance compared to traditional coatings. It can withstand extreme environmental conditions, including high humidity, salt - laden atmospheres, and exposure to chemicals, while also reducing friction during bolt installation and use.
Application Scope
Hot Dip Galvanized HDG Dacromet Geomet Mushroom Head Square Neck Carriage Bolts find extensive use across multiple industries and applications:
Construction Industry: In construction, these bolts are crucial for fastening wooden beams, joists, and structural components. The mushroom - head design distributes pressure evenly, preventing damage to the wood, and the square neck ensures a stable connection. They are also used in metal - to - metal and metal - to - wood connections in building frameworks, providing reliable fastening for residential, commercial, and industrial buildings. Their excellent corrosion resistance makes them suitable for both indoor and outdoor construction projects, especially in areas with high humidity or exposure to the elements.
Bridge and Infrastructure Construction: For bridge building and other large - scale infrastructure projects, these high - strength and corrosion - resistant bolts are essential. They are used to secure critical structural components, ensuring the stability and longevity of the infrastructure. The combination of HDG and Dacromet/Geomet coatings protects the bolts from the harsh environmental conditions typically encountered in such projects, including exposure to road salts, moisture, and pollutants.
Marine and Offshore Industry: In marine and offshore applications, where exposure to saltwater, high humidity, and harsh weather is constant, these bolts are highly valued. The superior corrosion resistance of the HDG and Dacromet/Geomet coatings ensures that the bolts maintain their strength and integrity over long periods, preventing structural failures due to corrosion. They are used for fastening ship hull components, offshore platforms, and marine equipment.
Industrial Machinery and Equipment: In industrial settings, these bolts are used for assembling and maintaining heavy machinery, equipment enclosures, and conveyor systems. High - strength models can withstand the heavy loads and vibrations in industrial environments, while the corrosion - resistant coatings protect the bolts from industrial pollutants and chemicals, extending their service life and reducing maintenance costs.
Transportation Industry: In the automotive, railway, and aerospace sectors, these bolts are employed for various assembly tasks. Their strength, durability, and corrosion resistance make them suitable for withstanding the vibrations, stresses, and environmental conditions experienced during transportation. For example, they are used in vehicle frame assembly, railway track fastening, and aircraft component installation.
Product Advantages
Exceptional Corrosion Resistance: The combination of hot - dip galvanizing and Dacromet/Geomet coatings provides outstanding corrosion resistance. The thick zinc layer from HDG offers initial protection, while the Dacromet/Geomet coating adds an extra layer of defense, enabling the bolts to endure harsh environmental conditions, such as coastal salt spray, industrial pollution, and high - humidity environments, with minimal corrosion.
High Strength and Load - Bearing Capacity: Depending on the material grade, these bolts can offer excellent strength. High - strength models, made from alloy steel and properly heat - treated, can withstand significant tensile and shear forces, making them suitable for heavy - duty applications in construction, industrial machinery, and infrastructure projects.
Secure and Stable Fastening: The unique mushroom - head and square neck design ensures a secure and stable connection. The mushroom - head distributes the load evenly, reducing the risk of damage to the fastened materials, while the square neck prevents the bolt from rotating when the nut is tightened, eliminating the need for additional anti - rotation devices and enhancing the reliability of the connection.
Versatility: Available in a wide range of sizes, lengths, thread types, and strength grades, these bolts can be easily adapted to different application requirements. Whether it's a light - duty fastening task or a heavy - duty structural connection, there is a suitable model available, providing flexibility in design and assembly across multiple industries.
Long Service Life: Due to their high - quality materials and advanced surface treatments, these bolts have a long service life. The corrosion - resistant coatings protect the bolts from degradation, reducing the frequency of replacement and maintenance, and ultimately lowering the total cost of ownership for projects that use them.
Ease of Installation: Despite their advanced features, these bolts can be installed using standard tools and methods. The standardized design allows for easy tightening and loosening with wrenches or sockets, facilitating assembly, disassembly, and maintenance work in various applications.
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