Functions And Proper Use Of Screw Washers

Screw Washers are not merely load-bearing components; they also govern the retention of preload in bolted joints, the coefficient of friction within the threads, and the integrity of the seal. Incorrect material selection or improper installation can lead to joint loosening under vibration or leakage in fluid systems-failures that rank among the most common field issues for relay, contactor, and circuit breaker assemblies. This article provides OEM engineers and procurement professionals with actionable criteria based on four key aspects: the three primary functions of gaskets, material limitations, selection guidelines, and correct installation procedures.

The core functions of a gasket can be summarized as three-fold: preventing loosening, increasing the coefficient of friction, and preventing leakage.

Preventing loosening is essentially about maintaining preload. After tightening, bolts can gradually lose preload due to fretting wear caused by vibration or cyclic loading. By enhancing the elasticity and friction of the contact surfaces, gaskets retard preload decay and extend the service life of the joint. Spring washers and toothed lock washers are designed specifically for this purpose.

Increasing the coefficient of friction refers to how a gasket alters the frictional state between the threaded assembly and the bearing surface, resulting in a more stable preload value for a given tightening torque. Without a gasket, the friction at the bearing surface is unstable, leading to significant preload scatter; with a gasket, friction conditions are standardized, significantly improving preload consistency.

Preventing leakage is critical in applications involving fluids or gases. Rubber and fiber gaskets create a continuous seal between the bolt head and the flange surface, blocking the escape of liquids or gases through the thread gaps. The effectiveness of the seal depends on the gasket material's ability to withstand the specific medium, temperature, and pressure conditions.

Plastic gaskets are suitable for light-duty connections, commonly found in assemblies involving plastic parts and wood products. Their soft texture improves surface fit, but they lack resistance to high temperatures and heavy loads; prolonged compression causes creep, leading to a loss of preload, so they are not used in load-bearing structural applications.

Metal gaskets are designed for high-temperature, high-pressure, and high-load operating conditions and are typically made of steel, copper, or aluminum. Capable of withstanding high temperatures and corrosion from acidic or alkaline media, they maintain preload over the long term due to their hardness and strength, making them a primary choice for low-voltage electrical equipment, circuit breakers, and high-voltage components in new energy vehicles. Flat washers (corresponding to ISO 7089 / DIN 125) serve to distribute stress on the bearing surface and protect the workpiece surface, while spring washers (DIN 127) and toothed lock washers (DIN 6797) are used to prevent loosening in environments subject to vibration.

Rubber gaskets are used in water and cooling systems, relying on elastic deformation to fill minor surface irregularities and achieve a seal. However, they lack resistance to high temperatures and pressures; excessive heat causes aging and hardening, while excessive pressure leads to extrusion, necessitating strict control of operating conditions.

Fiber gaskets are commonly found in piping connections and automotive applications; made from heat- and pressure-resistant fiber materials, they can withstand corrosion from chemical media. Their sealing performance depends on the correct amount of compression: insufficient compression leads to leakage, while excessive compression damages the sealing surface.

Step 1: Select the right gasket. Determine the material based on temperature, medium, and load, then select the size according to thread specifications; the inner diameter must match the bolt diameter-never substitute a smaller size for a larger one.

Step 2: Clean the surfaces. Before installation, ensure that the bolt bearing surface and the mating surface of the workpiece are clean and dry. Grease, dust, or rust can alter friction characteristics and prevent the gasket from seating effectively, directly leading to inaccurate preload or sealing failure.

Step 3: Position and tighten correctly. Place the gasket beneath the bolt head, insert it into the components to be connected, and then tighten to the specified torque. Spring washers and toothed washers must be oriented correctly to avoid failure due to improper installation. For multi-bolt connections, tighten in a diagonal pattern across multiple stages to prevent localized stress concentration.

Step 4: Inspection and maintenance. After installation, periodically inspect connections for signs of loosening or leakage. If issues are detected, recalibrate the tightening torque or replace the gasket; do not continue operation with compromised components.

The effectiveness of a gasket relies on proper selection and installation. Using materials unsuited to operating conditions, inadequate surface treatment, or uncalibrated tightening procedures can negate the gasket's performance. For mass assembly, it is recommended to incorporate gasket selection, tightening torque specifications, and sampling verification protocols into the assembly process standards, while maintaining batch records to ensure the long-term stability of each connection under vibration, temperature, and pressure conditions.

Submit your Screw Washer and fastener assembly specification sheet now; our precision stamping workshop can validate material compatibility and preload performance for your low-voltage and EV high-voltage projects within 1 working days.