Do You Know What Are The Cooling Methods Of Gearboxes?

During the operation of the gearbox, if overheating occurs, the normal function of the system will be restricted. In order to ensure the operation efficiency of the gearbox and give full play to its performance, it is necessary to understand the selection principle of the heat dissipation method of the gearbox and choose the most suitable heat dissipation method according to the actual working conditions.

Heat capacity concept

The heat capacity of the gearbox is also called thermal power, which refers to the corresponding output power value when the gearbox continuously runs to the set oil temperature under certain conditions.
Specific conditions include: installation location, installation method, altitude, ambient temperature, lubrication method, input speed, heat dissipation method, type and viscosity of lubricating oil, etc.

Influencing factors of heat capacity of gearbox

Own factors: mainly the heat dissipation area, heat transfer coefficient and efficiency of the gearbox
Conditions of use: installation location, installation method, altitude, ambient temperature, lubrication method, input speed, working cycle, type and viscosity of lubricating oil, etc.
Heat dissipation method: different heat dissipation methods have different heat dissipation capabilities

The main source of heat for the gearbox

1) The gearbox itself generates heat
Under the ideal model, the heat dissipation calculation only considers the three aspects of gear meshing, bearing rotation and shaft seal heat generation.
However, in actual operation, in addition to load, backstop, overrunning clutch, bearing adjustment, gear accuracy, shaft alignment, lubricating oil performance and liquid level, lubrication method, etc. will all have an impact on heat generation.
2) Transfer of external heat to the gearbox
In some occasions, external heat will be transferred to the gearbox. This part of the heat must be considered when dissipating heat. There are four common situations:
A. Direct sunlight, especially in summer
B. The ambient temperature is higher than the surface temperature of the gearbox (it may be local or short-term), and external heat will be transferred to the gearbox
C. Radiant heat from high-temperature objects, such as rotary kilns, ladle, etc., transfer the heat to the gearbox
D. The output shaft transfers heat from the fluid to the gearbox through high-temperature fluids such as steam

Cooling method of gearbox

Natural heat dissipation from the cabinet

The gear box runs to generate heat, the lubricating oil transfers the heat to the inner wall, the inner wall of the box transfers to the outer wall, and then the paint transfers to the air. In the heat transfer process, due to the low heat transfer coefficient of the heat transfer between liquid and solid, and the heat transfer between non-metal and gas, the lubricating oil inside the tank and the heat dissipation on the surface of the tank are also key areas for strengthening.

The natural heat dissipation method has low cost and simple maintenance, but it is greatly affected by external wind speed and dust on the surface of the cabinet.

Cooling with fan

Fans can usually be divided into five types. One is standard fan, which rotates in both directions, has strong adaptability and is widely used; the other is a fan with explosion-proof requirements, which can meet specific explosion-proof occasions; and the third is an axial fan with air volume and air pressure ratio. The standard fan is higher; the fourth is a dual fan, which has a stronger heat dissipation capacity than a single fan; the fifth is an electric fan, which is not affected by the input speed, has a strong heat dissipation capacity, and is more replaceable and has the actual temperature control energy-saving effect. Compared with the natural heat dissipation of the cabinet, the fan’s heat dissipation capacity is significantly increased, the maintenance is simple, and the application range is wide.

With cooling coil for heat dissipation

Compared with fan heat dissipation, the heat dissipation effect is significantly increased, the explosion-proof effect is good, and the influence of the ambient temperature is small. The underground scraper and H1 model are relatively more used.
The heat dissipation of the cooling coil is greatly affected by the water quality, it is not convenient to replace, the joint installation requirements are high, and the improper installation leads to a high water leakage failure rate.

Shell-and-tube water-oil cooler for heat dissipation

Need to match the oil pump, commonly used flange pump, can also use electric pump. Compared with the heat dissipation with coils, the heat dissipation effect of this method increases significantly, but it is greatly affected by the water quality.
Heat dissipation with plate water-oil cooler
It needs supporting oil pumps, and it is mostly used in the papermaking and chemical industries. Compared with the shell-and-tube water-oil cooler, it has the advantages of small size, high heat transfer efficiency, and high pressure bearing. However, the passage between the plates is small, not easy to clean, the brazing structure cannot be disassembled, and the water side is often equipped with a filter to avoid clogging by impurities.

With water cooling oil station heat dissipation

Water-cooled oil stations can meet the gearbox capacity and monitoring requirements. They are usually large in size and partly replaced by water-oil coolers or air-cooled oil stations.

Wind oil cooler for heat dissipation

It needs matching oil pumps, commonly used flange pumps, or electric pumps. Products with different heat dissipation capabilities are available. Compared with air-cooled oil stations, the structure is more compact, and there is a tendency to be gradually replaced by air-cooled oil stations.

With air-cooled oil station heat dissipation

It can meet the heat dissipation capacity and monitoring needs of the gearbox, and there are products that meet the coal safety standards, and the application is more and more extensive.

Finned tube radiator

Small size, generally use shaft end pump for oil supply, no need to connect to power supply, easy installation and maintenance. At low temperature, the resistance of lubricating oil is large, and the finned tube is required to be equipped with a pressure relief bypass, and the heat dissipation capacity is more than 7kW.

Centralized heat dissipation in petrol stations

Centralized control and easy unified management. The oil temperature of each gearbox can be controlled in an appropriate range by adjusting the flow rate. It is necessary to increase the lubricating oil inlet and outlet pipes and control the flow rate and liquid level. Usually, it is mostly used in the steel, chemical and paper industries.

Box body with water jacket for heat dissipation

Usually used in high ambient temperature occasions, such as continuous casting equipment in steel mills, the gear box adopts a welded box body with a water jacket on the outside, and the heat is dissipated through circulating water. Affected by the water quality, the heat dissipation capacity decreases after scaling. This type of heat dissipation method has fewer applications and can be replaced by a centralized oil supply cooling method.

Selection principle of gearbox heat dissipation method

The selection of the heat dissipation method of the gearbox should follow the four principles of safety, economy, meeting reasonable requirements, and combining theory with practice
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