Characteristics and Design of Hydraulic Seals for Construction Machinery

Construction machinery, also known as construction machinery, is mainly used for mechanical and electrical equipment for the construction, renovation and maintenance of various buildings. Widely distributed in industrial and civil construction, urban construction, national defense construction projects, transportation construction, mining and other raw material industrial construction and production, agriculture, forestry and water conservancy construction, sanitation and environmental protection industries. It contains a wide range of types, such as excavators, loaders, cranes, pump trucks, pile drivers, hydraulic breakers, pavers, graders, rock drills, etc.

Although construction machinery looks extremely complex, the common characteristics that can be summarized are:

Usually work outside

Worksites are constantly changing, and some can move on their own.

The working environment is often dusty or stained.

Nowadays, construction machinery generally adopts hydraulic transmission, because hydraulic transmission has the following obvious advantages compared with mechanical transmission:

Large power-to-volume ratio, easy placement

Infinitely variable speed

Easy to implement overload protection

Less shock, vibration and noise

However, hydraulic transmission also has disadvantages compared with mechanical transmission:

Easy to leak, not environmentally friendly

High manufacturing precision

less efficient

Transmission ratio is not fixed

Due to the special working environment of construction machinery, its hydraulic system has the following characteristics:

Irregular working hours, sometimes working continuously for a long time,

The working environment is outdoors, the working temperature difference is large, and the working environment is dusty;

The machine itself walks. Due to the limitation of volume and weight, the hydraulic oil tank is generally relatively small.

Due to the volume and weight, the working pressure of the hydraulic system is high, usually above 20MPa, and the highest is about 40MPa.

Construction machinery sealing system requirements:

High and low temperature resistance

Because of continuous work for a long time, if it is outdoors in summer, the hydraulic oil temperature of the machine may exceed 100°C, which requires the seal to be resistant to high temperature. If it is outdoors in winter, the temperature may be around -40°C when it is just turned on, and the seals are required to be resistant to low temperatures. Therefore, the sealing system is required to withstand a wide temperature range.

stain resistant

The machine itself walks. Due to the limitation of volume and weight, the hydraulic oil tank is generally relatively small.

Due to the volume and weight limitations of the system, it is impossible to install an ideal filtration and cooling system. High temperature, high pressure, and high speed cause the hydraulic oil to deteriorate easily, and the mechanical parts are also prone to erosion and stains.

There are many stains and impurities in hydraulic oil, but it cannot be thoroughly filtered, which is the aspect of endogenous stains.

All kinds of dust in the working environment may be very large, and it will inevitably enter the hydraulic system in multiple ways, causing oil pollution, which is an external stain.

Therefore, the sealing system is required to be resistant to stains.

good sealing performance

Because the system works outdoors, there is no leakage oil recovery system, and the working medium will directly pollute the environment after leakage, so external leakage requirements are strict. At the same time, for the requirements of hydraulic oil heating control, pressure maintaining or maintaining position, the internal leakage requirements are also very strict.

High pressure

The working pressure of the hydraulic system is high, usually above 20MPa, and the highest is about 40Mpa, which is higher than the general industrial hydraulic system pressure, so the sealing pressure resistance requirements are high.

High pressure

Because the system pressure is high, the temperature is high, and the wear is particularly serious, the seal is required to have good wear resistance.

High pressure

For construction machinery such as excavators and pump trucks, the hydraulic system pressure is high, the cylinder moves fast, and the seal wear is particularly serious. Therefore, the friction coefficient of the seal must be low, so that the seal has good wear resistance and a suitable life. .

Key points of engineering mechanical seal design:

Select a reasonable sealing scheme, focusing on the above requirements.

First of all, the dustproof performance must be good. More than 80% of the failures of the hydraulic system are directly or indirectly derived from the stains in the system.

Choose good seals

For seals of the same structure, the product quality of each company varies greatly. On the whole, the quality of large foreign seal companies is relatively stable, but the probability of encountering fakes is too high. Sometimes the so-called direct supply is not reliable. In terms of domestic seals, most of them are not very good, but at present, some manufacturers' products have been chasing or even surpassing imported products, with stable and reliable quality, such as tetrafluoroethylene and rubber seals produced by Damson Sealing.

Choose the right sealing material

There are many types of sealing materials, including many metals, plastics and rubbers. The same material has different performances from different companies. On the other hand, the same seal has different performances in different working conditions or different sealing schemes, so it must be carefully considered when choosing.

Note: Be sure to consider seals under the premise of a reasonable sealing scheme, then consider the sealing material, and then consider the seal manufacturer. If there is not enough sealing experience, the priority should be given to the sealing company, and the sealing company should consider the sealing scheme and other issues, such as Damansson sealing.

Key points for the use of engineering mechanical seals:

There must be a dust-free site during installation to prevent dust from being brought into the system during installation

All installation parts must be clean, iron filings, rust, paint, welding slag, etc.

Prevent dust from entering from the fuel tank port, etc. (such as refueling).

Replace the filter element on time. When working, the hydraulic system will have internal stains, which must be removed by replacing the filter element.

The hydraulic oil will gradually deteriorate and oxidize during operation, and the hydraulic oil must be replaced on time.

When replacing oil pipes or other parts at the work site, special attention should be paid to dust prevention and pollution prevention.

Introduction of typical construction machinery seals:

1. SPGW

SPGW seal, applied to the bidirectional seal of the piston, has high and low temperature resistance, strong extrusion resistance, low friction coefficient, small installation groove and small static leakage. It is an ideal engineering mechanical seal. The main disadvantage is that special tooling is required for installation.

2. SPGO

SPGO seal, applied to the two-way seal of the piston, has high and low temperature resistance, strong extrusion resistance, and extremely low friction coefficient. The main disadvantage is that special tooling is required for installation, and the static leakage is large.

3. RSJ

RSJ seal, applied to one-way seal of piston rod, has high and low temperature resistance, strong extrusion resistance, low friction coefficient and small installation groove. It is generally used as a buffer seal and is widely used in hydraulic cylinders of construction machinery. The main disadvantage of this type of seal is that if it works alone, there will be a large amount of leakage, so generally only a buffer seal is used.

4. KZT

KZT seal, also known as anti-fouling ring, is installed at the outermost ends of both sides of the piston seal. Its main function is to prevent the stains in the hydraulic oil from entering the main seal position of the piston, causing (strain) damage to the main seal, and secondly to prevent gas Entering the main seal, causing gas explosion or Diesel effect burns to the main seal. Commonly used in construction machinery and metallurgical machinery cylinders.

5. WR

The WR guide ring is installed at both ends of the piston seal or the front end of the piston rod seal. Its main function is to guide the movement of the piston and the piston rod, to prevent the metal parts from directly contacting and straining; to prevent the eccentricity of the piston rod and the piston, and to keep the seal reasonable Extrusion gap; isolation of gas explosion to seal damage and other protection. The main advantage of this type of guide ring is that it has a large bearing capacity, but the disadvantage is that the friction coefficient is much larger than that of the tetrafluoroethylene-filled guide belt; it is easy to age and become brittle and crack at high temperature.