In the field of mechanical equipment, flanges serve as versatile and critical components for connections and sealing, widely used in various applications such as power transmission, medium conveyance, and component assembly. Their core functions include enabling "removable connections," ensuring "reliable sealing," and facilitating "load transfer." When selecting flanges for specific mechanical equipment applications, it’s essential to flexibly choose their structure and material based on the equipment’s operating conditions—such as pressure, temperature, medium type, and vibration intensity. Detailed explanations can be provided by focusing on the following key categories of machinery:

1. Power Machinery: Designed to handle high-load and vibration conditions, ensuring stable power transmission

Power machinery—such as diesel engines, gasoline engines, gas turbines, and electric motors—are the "power sources" for industrial and civil equipment. Flanges are primarily used at power output ends, as well as in cooling systems and fuel/lubrication systems, making them critical components that must effectively withstand "high vibration," "high temperatures," and "load impacts."

• Engine block connected to accessories The connections between the engine block and components like radiators (cooling system), oil coolers (lubrication system), and exhaust pipes (exhaust system)—whether for diesel or gasoline engines—are all achieved using flanges. For instance, the exhaust pipe flange on a diesel engine must withstand high-temperature exhaust gases ranging from 400°C to 600°C. As a result, materials such as heat-resistant cast iron (e.g., HT300) or heat-resistant steel (e.g., 1Cr18Ni9Ti) are commonly selected. The sealing surface typically features a flat face design, paired with a metal-asbestos gasket that offers excellent resistance to both high temperatures and aging, effectively preventing leaks of hot exhaust gases. Meanwhile, the connection flange between the engine and the oil cooler, where the medium is engine oil (ranging from ambient temperature up to 120°C), can be made from cast steel (such as ZG230-450). Here, the sealing surface adopts a male-and-female configuration, complemented by a nitrile rubber gasket that ensures reliable oil resistance and tight sealing, thus avoiding oil leakage and subsequent lubrication failure.
• The electric motor is connected to the transmission components. : In scenarios involving the connection between the output end of high-power electric motors (such as industrial or marine motors) and reducers or couplings, flange-type connections—commonly referred to as "flange couplings"—are often employed. These flanges are typically "rigid flanges," made from high-quality 45# carbon steel for its excellent strength and ease of machining. The flange faces are securely fastened together using bolts, ensuring both efficient torque transmission from the motor and precise alignment of the drive system. Meanwhile, for smaller motors, the end cap is usually connected directly to the motor housing via a mating flange, which is typically crafted from gray cast iron (e.g., HT200). This simpler, cost-effective design primarily serves to seal the windings inside the housing while providing effective protection against dust and water ingress.

2. Fluid Machinery: Focusing on medium sealing and pressure matching to ensure leak-free conveyance

Fluid machinery—such as pumps, compressors, fans, and centrifuges—is the core equipment in industry for "transferring fluids (liquids and gases)." Flange applications are primarily concentrated at fluid inlets and outlets, shell joint connections, and links to auxiliary systems. The key requirements include "pressure resistance," "resistance to media corrosion," and "compatibility with fluid characteristics."

• Pump equipment (centrifugal pumps, plunger pumps, gear pumps) The connections between the pump’s inlet and outlet pipelines, as well as between the pump body and pump cover, must be designed as detachable seals using flanges. For instance, in centrifugal pumps handling clean water, the inlet and outlet flanges are typically flat-welded flanges made of materials like cast iron (e.g., HT200) or stainless steel (e.g., 304, suitable for mildly corrosive environments). These flanges usually operate at pressure ratings ranging from PN1.0 to PN2.5, with a raised-face sealing surface paired with low-cost yet highly effective rubber gaskets. On the other hand, for corrosion-resistant pumps used to convey strong acids (such as sulfuric acid) or strong bases (like sodium hydroxide), the inlet and outlet flanges must be crafted from 316L stainless steel, featuring a tongue-and-groove sealing surface along with PTFE gaskets—materials that offer exceptional resistance to severe corrosion and can withstand temperatures up to 260°C—thus preventing corrosive media from leaking and damaging equipment or contaminating the environment. Finally, for high-pressure plunger pumps—such as hydraulic pumps—where operating pressures can reach 10–30 MPa, welded flanges made of 40Cr alloy structural steel are employed, paired with metal-jacketed gaskets that provide excellent high-pressure performance and reliable resilience, ensuring the seal remains intact even under extreme conditions.
• Compressor and Fan The flanges connecting the air compressor’s cylinder to the air receiver tank and cooler must be capable of withstanding compressed air pressures ranging from 0.8 to 1.6 MPa. The recommended material is Q235B carbon steel or 20# steel, with a raised-face sealing surface paired with flexible graphite gaskets—these gaskets offer excellent temperature resistance and are well-suited to handle condensation that may occur during the compressed air cooling process. In contrast, the flange connections at the centrifugal fan’s inlet port to its associated ductwork and fan housing are designed for handling primarily atmospheric air under normal pressure and ambient temperature. As a result, the flange structure here is simpler, typically made from thin steel plates such as Q235A. After being joined by bolts, these flanges require only basic sealing—such as applying sealant—to ensure proper airflow guidance and secure positioning.

3. Heat Exchange and Separation Machinery: Addressing temperature fluctuations and multi-medium contact while balancing sealing performance with corrosion resistance.

Heat exchange machinery (such as heat exchangers and condensers) and separation equipment (such as filters and centrifuges) are critical devices in industrial processes for "temperature control" and "media purification," respectively. When selecting flanges, it’s essential to consider factors like "adaptability to temperature fluctuations," "compatibility with the process medium," and "ease of maintenance."

• Heat exchangers (shell-and-tube, plate-type) The connections between the tube box and shell, as well as the shell and head of the shell-and-tube heat exchanger, must be made using flanges to ensure a detachable design—this facilitates easy cleaning of either the tube side or shell side later on (e.g., disassembling and cleaning after fouling occurs). If the heat exchanger is used for heating water (temperature ≤150°C, pressure ≤1.6 MPa), the flange material should be Q235B carbon steel, with a male-and-groove sealing surface paired with an asbestos-rubber gasket. For applications involving cooling high-temperature oil (temperature range 200–300°C), the flange material must be 15CrMo low-alloy heat-resistant steel, featuring a raised-face sealing surface along with a metal-jacketed gasket designed for high-temperature resistance and excellent resistance to oil swelling. In cases where the heat exchanger handles corrosive media (such as seawater), 316L stainless steel flanges are recommended, paired with PTFE gaskets to prevent seawater-induced corrosion of both the flange and sealing surfaces.
• Separation machinery (filters, centrifuges) The connection between the filter cartridge housing and end cap for industrial precision filters (such as liquid filtration or gas dust removal) typically uses small-sized flat-welded flanges (DN50–DN200), with the material selected based on the medium being processed—cast iron for filtering water, cast steel for oil filtration, and stainless steel for corrosive liquids. The sealing surface features a flat design, paired with an O-ring made of durable rubber for easy installation and reliable sealing, making it convenient to periodically open the end cap for filter element replacement. For horizontal centrifuges, the connecting flanges between the drum and the machine casing, as well as those linking to the feed pipe, are designed to withstand vibrations and loads caused by centrifugal forces. Therefore, these flanges are fabricated from 45# steel or 20CrMnTi alloy structural steel. Additionally, high-strength bolts (such as Grade 8.8) are used for the flange fasteners, while the sealing surface employs a raised-face design, complemented by oil-resistant rubber gaskets tailored to handle the oily sludges, suspensions, and other media commonly processed in centrifuges—effectively preventing material leakage.

4. Heavy and Special Machinery: Designed to handle high loads and complex operating conditions, with enhanced structural strength.

Heavy machinery—such as cranes, excavators, and rolling mills—and specialized equipment—like marine machinery and ground testing systems for aerospace devices—operate under far more demanding conditions. In these applications, flanges not only connect components but also must efficiently transmit heavy loads, withstand impact forces, or adapt to challenging environments, such as marine settings or extreme cold temperatures.

• Heavy construction machinery : The hydraulic oil tank of excavators, connected to the hydraulic pump via a flange, and the boom joint flanges of cranes (particularly in some larger models), must withstand both high-pressure and mechanical loads. For these applications, the hydraulic system flanges are made from either 20# steel or 45# steel, with pressure ratings ranging from PN16 to PN40. These flanges are paired with high-pressure hydraulic gaskets—such as copper-clad gaskets—to prevent any risk of high-pressure oil leakage. Meanwhile, the crane boom joint flanges, which need to transmit lifting loads ranging from tens to hundreds of tons, are crafted from Q345B low-alloy, high-strength steel. The flange design features a "rigid flange with reinforcing ribs," and 10.9-grade high-strength bolts are used. Precise control of bolt torque ensures that there is no movement at the joint, thereby guaranteeing safe lifting operations.
• Marine and Offshore Machinery The connecting flange (referred to as a "marine flange coupling") between the ship's main engine (diesel engine) and the propeller drive shaft must withstand seawater corrosion, vibration, and impact. Materials typically used include marine-grade weathering steel (such as CCSB) or stainless steel (e.g., 316), with the flange surfaces treated with anti-corrosion measures like galvanizing or application of protective coatings. For the ship’s seawater cooling pumps and ballast water system flanges—components that are in constant contact with highly corrosive seawater—the materials must be either 316L stainless steel or copper alloys (such as naval brass). The sealing surfaces should feature tongue-and-groove designs, paired with neoprene gaskets that offer excellent resistance to seawater and aging, effectively preventing seawater leakage and protecting the hull from corrosion.

V. Core Technical Features of Flanges in the Machinery and Equipment Sector

Compared to industries like petrochemicals and natural gas, flange applications in the mechanical equipment sector are far more "versatile" and "diverse." The core technological features can be summarized into three key points:

1. Structural adaptability takes priority. : Choose the appropriate flange type based on the installation space and removal requirements of the mechanical components—use a flat-welded flange in compact spaces (for its simple structure), opt for a butt-welded flange when heavy loads need to be transmitted (to ensure high strength), select a loose-type flange for vibrating equipment (to absorb movement), and employ a threaded flange for smaller components (eliminating the need for welding). This approach strikes a balance between "installation convenience" and "structural integrity."
2. Material and Medium / Operating Condition Matching : No need to overly pursue high-grade materials—instead, "choose according to your needs." For ambient temperature and pressure conditions with non-corrosive environments, use cast iron or carbon steel; for oil-resistant applications, opt for cast steel paired with oil-resistant gaskets; in corrosive settings, select stainless steel combined with PTFE gaskets; and for high-temperature scenarios, rely on heat-resistant steel along with metal gaskets. This approach ensures performance while keeping costs under control.
3. Sealing and maintenance combined : Many mechanical devices require regular maintenance—such as filter cartridge replacement and component cleaning—so flange connections must be "easy to disassemble." Gasket sealing is often preferred over welded seals due to its ease of replacement and lower cost (e.g., rubber or asbestos gaskets), while ensuring reliable performance even under the vibrations and operational loads experienced during machine operation. This approach strikes a balance between "sealing reliability" and "maintenance convenience."

In summary, the application of flanges in mechanical equipment fundamentally revolves around "connecting, sealing, and transmitting loads," with the key consideration being to select flange solutions that are cost-effective, easy to maintain, and highly adaptable to the specific operating conditions of different machines. The performance of these flanges directly influences the operational stability, maintenance efficiency, and service life of mechanical equipment, making them indispensable foundational components in both the assembly and operation of such systems.