Materials and Selection of Rotary Joint for Water Media

Rotary joint is commonly used mechanical sealing devices in industry, capable of effectively transporting various fluids from stationary pipelines to continuously rotating equipment. They are widely used in various rotating equipment in industries such as papermaking, textiles, chemicals, and metallurgy.

How Should Materials be Selected for Rotary Joint Conveying Water?

When the transmission medium is water, the corrosion resistance of the rotary joint material is the primary consideration. Generally speaking, "copper material will not rust when exposed to water, while iron rusts easily." While this statement points out the core issue, the actual situation is not so simple and the internal structure needs to be taken into account.

Q Type Rotary Joint

The selection of iron rotary joint for water and steam is different. The internal structure of the steam rotary joint consists of a tube ball, screw, housing, ball ring, and cylindrical ring. The ball ring is a sealing ring, and the cylindrical ring is a support ring. The R face of the ball ring is pushed by the spring force to push the spherical surface of the tube ball to seal. Most iron rotary joints designed for water use mechanical seal components, which consist of two rings pushed by a spring to create a planar friction seal. With iron housings, rust does not affect the seal, so conveying water poses no issue. However, the spherical surface of the nipple in a steam joint is made of iron; if used for water, it would corrode, and damage to the spherical surface would inevitably compromise the seal. Thus, the statement that iron joints are unsuitable for water is not contradictory to the fact that iron rotary joints can convey water; the distinction lies in the sealing structure and internal components.

HRD Rotary Joint

The copper joint, also called the H type rotary joint, has a shaft made of stainless steel. Its sealing mechanism relies on spring pressure to push a flat gasket against an O-ring; this compresses the O-ring so that its outer surface fits snugly against the housing's interior, while its inner surface seals against the outer wall of the H-ring's tapered section. The plane of the shaft seals against the plane of the H ring. Consequently, if the sealing section did not utilize a copper housing, internal wall rust would inevitably lead to leakage. There are distinct advantages to using iron for the front bearing section: it allows for the drilling of holes to secure the rotary joint. In contrast, a copper housing is too thin and lacks sufficient toughness for drilling, making it difficult to mount fixing devices. Rotary joint featuring a copper housing typically employ mechanical seals.

How Do You Choose a Rotary Joint?

• The first step is to determine the connection method of the equipment: Before selecting a rotary joint, you need to understand the connection method of the equipment. Common connections include flange connection, threaded connection, and welded connection. Different connection methods correspond to different rotary joint models.

• The second step is to determine the rotation direction: Rotary joints typically rotate in two directions, clockwise and counterclockwise. Rotate the corresponding rotary joint according to the rotation direction of the equipment to ensure that the medium can flow smoothly when the equipment is running.

• The third consideration is the equipment's rotational speed: the equipment's rotational speed directly affects the service life and performance of the rotary joint. High-speed equipment requires rotary joints that can withstand high speeds, while low-speed equipment can choose relatively simple rotary joints. Understanding the equipment's rotational speed range allows for better selection of matching joints.

• The fourth step involves considering the type of medium: the medium type is a key factor when selecting a rotary joint, as different media may possess varying chemical properties and physical states (such as corrosiveness, viscosity, and temperature). Based on the medium's characteristics, select a rotary joint with the appropriate resistance to corrosion, high temperatures, or pressure.

• The fifth step is to consider the temperature of the medium: the temperature of the medium also has a direct impact on the performance of the rotary joint. High-temperature media require high-temperature resistant rotary joint, while low-temperature media require rotary joint that can adapt to low-temperature environments. Ensuring the rotary joint is compatible with the medium's temperature range is crucial for the proper operation of the equipment.

• The sixth step is to consider installation space and cost: When selecting a rotary joint, you also need to consider the installation space and budget cost of the equipment. Choosing a rotary joint with an appropriate size and reasonable cost allows you to meet equipment requirements while optimizing the overall return on investment.