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Author: Site Editor Publish Time: 2025-09-12 Origin: Site
In numerous fields, including industrial manufacturing, building renovation, and home appliance assembly, fasteners (fasteners) are core elements for connecting various components. Self-drilling screws, with their efficient, integrated "drilling + fastening" capabilities, have become a highly practical fastener. Bi-metal self-drilling screws, with their unique material combination and superior performance, have broken through the application limitations of traditional self-drilling screws, demonstrating irreplaceable advantages in complex working conditions. This article will comprehensively analyze this innovative fastener from the perspectives of its definition, core advantages, structural features, application scenarios, purchasing tips, and industry development trends. This will help practitioners and buyers gain a deeper understanding of the value of bi-metal screws and accurately select the appropriate self-drilling screw solution.
Bi-metal Self-Drilling Screws: Redefining the Value of Self-Drilling Screws in Fastener Applications
In numerous fields, including industrial manufacturing, building renovation, and home appliance assembly, fasteners (fasteners) are core elements for connecting various components. Self-drilling screws, with their efficient, integrated "drilling + fastening" capabilities, have become a highly practical fastener. Bi-metal self-drilling screws, with their unique material combination and superior performance, have broken through the application limitations of traditional self-drilling screws, demonstrating irreplaceable advantages in complex working conditions. This article will comprehensively analyze this innovative fastener from the perspectives of its definition, core advantages, structural features, application scenarios, purchasing tips, and industry development trends. This will help practitioners and buyers gain a deeper understanding of the value of bi-metal screws and accurately select the appropriate self-drilling screw solution.
Bi-metal self-drilling screws are a special type of self-drilling screw. Their core feature is the composite construction of two metal materials with different properties. They typically use high-strength steel as the screw body and a high-hardness alloy (such as high-speed steel (HSS)) as the drill bit. A special process achieves a tight bond between the two metals. This "strong combination" of materials retains the efficient advantages of traditional self-drilling screws—direct drilling and fastening without pre-drilling—while also addressing the shortcomings of single metal materials in terms of hardness, toughness, and corrosion resistance through the complementary properties of bimetal. Bi-metal self-drilling screws have become "efficient connection experts" in the fastener field, adapting to complex connection requirements.
Within the fastener system, self-drilling screws have become a widespread replacement for conventional self-tapping screw and bolt combinations by simplifying the installation process and improving installation efficiency. Bi-metal self-drilling screws (Bi-metal screws) take this concept a step further. Addressing the challenges of traditional self-drilling screws, such as easy wear of the drill bit, inability to penetrate high-hardness substrates (such as thick steel and galvanized sheet metal), and susceptibility to rust in humid environments, Bi-metal screws achieve breakthroughs by utilizing differentiated materials for the drill bit and screw shaft, achieving both hardness and toughness, and high efficiency and durability. For example, in steel structures, traditional self-drilling screws are prone to bit breakage when drilling through steel plates thicker than 8mm, while the high-speed steel drill bit of Bi-metal screws easily handles this issue. In outdoor photovoltaic rack installations, the corrosion-resistant properties of the bi-metal structure also extend the fastener's lifespan and reduce ongoing maintenance costs.
Compared to conventional self-drilling screws and other types of fasteners, bi-metal screws offer multiple advantages in performance, efficiency, and applicability, making them a preferred connection solution across multiple industries.
One of the core advantages of bi-metal screws is that their drill bits are made of high-hardness high-speed steel (such as HSS 4341 and HSS M2), achieving a Vickers hardness of 800-1000 HV, significantly higher than the carbon steel drill bits used in conventional self-drilling screws (hardness approximately 500-600 HV). This high hardness allows Bi-metal Screws to easily penetrate high-hardness substrates that traditional self-drilling screws struggle with, such as cold-rolled steel sheets, galvanized steel sheets, and aluminum alloy profiles over 10mm thick. The drill bit is also less likely to become dull or crack during the drilling process.
In actual construction, for example, when installing color-coated steel sheets in a steel structure factory building, conventional self-drilling screws take an average of approximately 15 seconds per screw to penetrate 6mm thick galvanized steel, and the drill bit needs to be replaced after approximately every 50 screws. Using Bi-metal Screws, drilling time can be reduced to under 8 seconds, and a single drill bit can continuously penetrate over 200 screws while remaining sharp, significantly improving construction efficiency and reducing consumable replacement costs. This high efficiency gives it a significant advantage in large-scale industrial installation scenarios, such as automotive production lines and home appliance assembly lines.
Traditional self-drilling screws often use high-carbon steel to maximize drill bit hardness, resulting in insufficient toughness in the screw shaft. Slight deformation of the substrate or deviation from the installation angle during installation can easily cause the screw to bend or even break. Bi-metal self-drilling screws, on the other hand, utilize a bimetallic structure: a high-hardness drill bit + a high-toughness screw. The screw body is constructed from low-carbon alloy steel (such as 10B21 or SCM435) that, after heat treatment, exhibits excellent toughness, with an elongation exceeding 15%, making it capable of withstanding minor impact and deformation during installation. High-speed steel in the drill bit ensures sufficient hardness. These two components are tightly bonded together through processes such as friction welding and laser welding to achieve a perfect balance of hardness and toughness. In building curtain wall installations, Bi-metal screws connect aluminum alloy studs to tempered glass frames. If strong winds cause even slight displacement of the substrate, conventional self-drilling screws may break due to insufficient toughness. However, the Bi-metal screw's shank absorbs stress through minimal deformation, preventing breakage and ensuring the stability of the connection. This fracture resistance makes it an ideal fastener for complex working conditions, such as those encountered outdoors and in vibration environments.
In outdoor, humid, and corrosive environments (such as marine engineering, photovoltaic power plants, and chemical plants), the corrosion resistance of the fastener directly determines the service life of the connection. Bi-metal self-drilling screws (Bi-metal screws) enhance their corrosion resistance in two ways: First, the screw body is treated with a surface treatment such as hot-dip galvanizing, Dacromet, or Geomet, creating a uniformly thick anti-corrosion coating that effectively isolates moisture and oxygen. Second, some high-end Bi-metal screws utilize stainless steel (such as 304 and 316) for the screw body, combined with a high-speed steel drill bit, to further enhance corrosion resistance, making them suitable for highly corrosive environments such as coastal areas and chemical plants.
Comparing salt spray test data between ordinary galvanized self-drilling screws and Bi-metal screws: While ordinary screws develop red rust after approximately 500 hours in a neutral salt spray test, Bi-metal screws treated with Dacromet can withstand over 1000 hours of salt spray testing without rusting, more than doubling their service life. This superior corrosion resistance makes them a preferred fastener for applications such as outdoor photovoltaic mounting systems, offshore platforms, and municipal infrastructure. 4. Good Installation Compatibility, Lowering the Installation Barrier
Bi-metal self-drilling screws (Bi-metal screws) are designed with full compatibility in mind with existing installation tools. Their thread specifications and head shapes (e.g., Phillips, Hexagon, pan head, countersunk) conform to international standards (e.g., ISO, ANSI, and GB). They can be directly used with common electric screwdrivers, impact drills, and other tools, eliminating the need for specialized equipment. Furthermore, Bi-metal screws feature optimized drilling depth and thread pitch, ensuring a tight engagement between the threads and the base material after drilling while preventing damage to the base material caused by drilling too deep.
When installing light steel studs for home renovations, non-professional workers using conventional self-drilling screws often deform the studs due to poor control of drilling force. Bi-metal screws, however, feature a sharp drill bit and a tough screw rod, making drilling and tightening easy even for inexperienced users. This lowers the installation barrier and improves the consistency of installation quality.
The superior performance of bi-metal screws stems from their scientific structural design and precise manufacturing process. Understanding their core structure and production process will help you more accurately select and apply this fastener.
Bi-metal self-drilling screws primarily consist of a drill bit, a screw shaft, and a head. The material and structural design of each component are centered around the core requirements of "efficient drilling and stable fastening":
The drill bit is made of high-speed steel (HSS) and features a spiral groove (typically two or three grooves) to dissipate chips generated during drilling. The tip of the drill bit features a sharp blade, with the cutting edge angle adjusted to the substrate (e.g., 120° for steel, 90° for aluminum), ensuring rapid penetration. Screw: Made of low-carbon alloy steel or stainless steel, the screw features a self-tapping thread. The thread profile is typically triangular or trapezoidal, with a pitch designed based on the substrate thickness (large pitch for thick substrates, small pitch for thin substrates). This ensures a tight fit between the threads and the substrate, preventing loosening. Some bi-metal screws feature a breakaway groove in the middle of the screw to facilitate post-installation breakoff, making them suitable for applications requiring a smooth surface.
Head: Made of the same material as the screw, the head shape is designed based on the installation requirements (e.g., a pan head for visible surfaces, a countersunk head for flat surfaces). The head features built-in drive slots (Phillips, hexagonal, etc.) to ensure a stable fit with the tool and prevent slippage.
The manufacturing process for bi-metal self-drilling screws is complex and requires multiple precision steps. The key focus is on achieving a strong bimetal bond and stable performance. The main process includes:
Material Selection: High-speed steel (HSS) and screw steel are rigorously screened to ensure that the material composition meets standards (for example, HSS must contain sufficient tungsten and molybdenum to enhance hardness, while screw steel must contain manganese and chromium to enhance toughness). Raw materials are inspected for defects such as internal cracks and impurities.
Bi-metal Composite: Friction welding or laser welding is used to join the high-speed steel drill bit to the screw body. Friction welding uses heat generated by high-speed rotation to melt the contact surfaces of the two metals, forming a strong metallurgical bond. Laser welding uses a high-energy laser beam to achieve localized, high-temperature welding, resulting in a narrow weld with high strength. Post-weld inspection is required to ensure the weld is free of voids and cracks.
Forming: The welded blank is formed into a head shape using a cold heading machine, and then the threads are produced using a thread rolling machine. The drill bit is ground to ensure cutting edge sharpness and spiral groove accuracy. Some products also require heat treatment (such as screw tempering and drill bit quenching) to further enhance performance.
Surface Treatment: Anti-corrosion treatments such as hot-dip galvanizing, Dacromet, and Geomet are selected based on the application to ensure uniform coating thickness and strong adhesion. After surface treatment, products undergo salt spray and adhesion tests to verify corrosion resistance.
Finished Product Inspection: Finished Bi-metal Screws undergo dimensional inspection (such as diameter, length, and thread accuracy) and performance testing (such as tensile strength, shear strength, and drilling efficiency) to ensure that each screw meets standard requirements. Unqualified products are rejected.
Due to their excellent performance, bi-metal self-drilling screws have been widely used in various fields, including construction, industrial manufacturing, new energy, home appliances, and transportation, becoming a key fastener for solving complex connection requirements in various scenarios.
In steel structures (such as factories, stadiums, and high-speed rail stations), bi-metal screws are primarily used for connecting color-coated steel sheets to steel purlins and for splicing steel components. Because color-coated steel sheets are often galvanized, and steel purlins are often 8-12mm thick, conventional self-drilling screws are prone to drill bit wear. However, the high-speed steel drill bit of bi-metal screws easily penetrates the steel sheet, and the hot-dip galvanized screw shaft resists corrosion in humid outdoor environments, ensuring long-term stability of the connection structure. In glass curtain wall installation, Bi-metal screws are used to connect aluminum alloy keels to steel frames. Aluminum alloy is relatively soft, and conventional screws are prone to thread stripping. However, Bi-metal screws offer superior toughness, allowing for a tight engagement with the aluminum alloy through a well-designed thread design. This prevents deformation of the keel due to excessive installation force, ensuring the smoothness and safety of the curtain wall.
In photovoltaic power station construction, Bi-metal Screw is one of the core fasteners in ground-mounted photovoltaic mounting systems, connecting steel channels, ground screws, and solar panel mountings. Outdoor photovoltaic mounting systems are exposed to wind, sun, and rain for extended periods, and require connecting steel and aluminum materials of varying thicknesses. Bi-metal Screw offers significant advantages in corrosion resistance and adaptability. The Dacromet-treated screw resists outdoor corrosion, and the high-speed steel drill bit can penetrate the thick steel plates of the mounting system, ensuring the stability of the mounting system and preventing panel tilting or detachment due to fastener failure. In the assembly of energy storage equipment (such as battery cabinets), Bi-metal screws are used to connect battery modules to the metal cabinet. The tight interior of battery cabinets requires quick drilling and fastening during installation. Bi-metal screws' efficient drilling capabilities shorten installation time. Their vibration resistance (the screws are tough and less likely to loosen due to equipment vibration) ensures a stable connection between battery modules, reducing safety risks.
In home appliance manufacturing (such as refrigerators, washing machines, and air conditioners), Bi-metal screws are used to connect metal casings to internal components. Home appliance casings are often made of thin steel or galvanized sheet metal, and production lines require rapid, large-scale assembly. Conventional self-drilling screws' drilling efficiency is insufficient to meet assembly line requirements. Bi-metal screws, however, offer high drilling speed and a long service life, making them suitable for high-speed installation on automated production lines. Their corrosion resistance also extends the lifespan of home appliances (for example, Bi-metal screws in air conditioner outdoor units are resistant to rainwater corrosion).
In automotive manufacturing, Bi-metal screws are used to connect vehicle body accessories (such as door trim panels and underbody panels). Vehicle bodies are made of a complex array of materials, including steel, aluminum alloy, and plastic. Bi-metal screws can adapt to drilling requirements for various materials by replacing drill bits with different blade angles. Their vibration resistance ensures that accessories remain loose while the vehicle is in motion, enhancing driving safety and comfort.
In road guardrail installation, Bi-metal Screws are used to connect guardrail panels and posts. Road guardrails are exposed to the elements for extended periods and must withstand the impact of vehicle collisions. Conventional self-drilling screws are prone to fracture due to corrosion or insufficient toughness. Bi-metal Screws' corrosion resistance and fracture resistance ensure guardrail protection and reduce maintenance frequency. (Traditional screws require replacement every 3-5 years, while Bi-metal Screws can last 8-10 years.)
In the maintenance of municipal facilities (such as light poles and bus stops), Bi-metal Screws are used to repair or replace damaged components. Municipal facility repairs often need to be completed quickly to avoid disrupting traffic and public life. Bi-metal Screws' ability to eliminate the need for pre-drilling shortens repair time. Furthermore, their compatibility with high-hardness substrates makes them suitable for connecting thick-walled metal components like light poles.
