Structure

The impeller consists of several dozen forward-curved blades that are shallow in the radial direction and long in the axial direction. The ends of the blades are riveted or welded to the main circular plate and side plate. The side plate and boss are firmly secured with multiple tie bolts, creating a strong structure. Combined with a comprehensive dynamic balancing test, this design ensures durability even at high rotational speeds.

The casing is primarily made of thick plate material, reinforced with structural steel to withstand mechanical and environmental conditions and ensure long-term durability.

The bearings used are typically ball or roller bearings, all of which are designed for long service life.

In addition, special materials such as stainless steel, Hastelloy, titanium, PVC, and high-tensile steel plates are used for heat resistance (up to approximately 1000°C), chemical resistance (acid resistance), and other specific requirements. Special structures, such as double-layer insulated casings, have also been successfully designed and manufactured.

Features and Applications

The multi-blade fan (also known as a Sirocco fan) is suitable for relatively low-pressure applications, with a pressure range of 0.1 kPa to approximately 1.5 kPa.

Its applications include:

• Ventilation for buildings and ships
• Heating, cooling, and air conditioning systems
• Drying applications
• Mine ventilation
• Boiler forced draft and induced draft
• High-temperature gas circulation for furnaces

Key Features

• Compared to other centrifugal fans, it has slightly lower efficiency.
• However, for the same pressure, it requires a lower airflow velocity, allowing for a more compact fan design.
• The pressure variation in response to airflow changes is minimal, making it suitable for systems with multiple inlets or outlets where opening or closing some ports does not significantly affect overall performance.
• On the downside, if resistance decreases and airflow increases, the required shaft power tends to rise sharply, requiring careful consideration during operation.

This type of centrifugal fan is one of the most widely used for stationary equipment on land. It is generally driven by a V-belt, though direct-drive and motor shaft-driven types are also available.

Structure

The impeller consists of 10 to 20 small backward-curved blades made of stainless steel or cast iron, designed to withstand high-speed operation. These blades are either riveted onto the main disk or firmly assembled using a circular wedge-shaped side plate with rivets or welding. This structure is tested for dynamic balance to eliminate misalignment and prevent vibration.

The casing is primarily made of thick plate material to ensure high strength under mechanical and external conditions. Reinforcement ribs are added as needed to further enhance strength, reduce vibration, and minimize external deformation.

Bearings generally use ball or roller bearings, selected for long service life. Depending on conditions, sleeve bearings may also be used.

For lubrication, grease is commonly used, but depending on the operating conditions, oil lubrication, forced lubrication, or water cooling may be applied. The cooling methods include natural air cooling, forced air cooling, and water cooling.

All design decisions regarding fan application and operational conditions are based on our company’s past experience and track record.

Features and Applications

Turbo fans are suitable for relatively high-pressure applications in the range of 0.25 to 10 kPa. Their applications include:

• Forced draft fans for boilers
• Induced draft fans
• Secondary air fans
• Ventilation fans
• Heating and cooling fans
• Dust collection fans
• Gas compression fans
• Air supply fans

Due to their versatility, turbo fans are widely used across various industries today.

One of the key features of this fan is its high efficiency among centrifugal fans, low noise levels, and large airflow capacity. Unlike multi-stage blowers, turbo fans do not have significant limitations on discharge airflow. Additionally, when combined with inlet vane control systems, these fans can efficiently adjust performance under partial loads without major losses.

Furthermore, the change in airflow is minimal, making it ideal for series operation. Compared to other centrifugal fans, turbo fans require less additional power when increasing airflow, making them energy-efficient.

Inlet Vane Control

Inlet Vane Control is a method of controlling airflow by installing adjustable guide vanes at the intake of a fan. These vanes are mechanically linked, as shown in the image, and can open and close to create a swirling airflow in the same direction as the impeller rotation. This reduces the pressure rise and input power of the fan, effectively controlling the airflow.

The pressure rise and power input of the fan are proportional to (U₂C₂ – U₁C₁), as shown in Figure 7 (velocity triangle diagram). By imparting a swirl in the same direction as the impeller rotation, the C₁u component increases, thereby reducing the energy required to move the air. When the swirl direction is adjusted with vane openings, the pressure rise and power input can be efficiently controlled.

Advantages Compared to Other Control Methods

Figure 8 illustrates the advantages of inlet vane control compared to other control methods. The key benefits include:

• Wider control range compared to damper control
• Higher efficiency than speed control in certain ranges (10% to 70% of rated flow)
• Energy savings when combined with other control systems
• Compact and simple mechanism
• Reduced noise and vibration

Since inlet vane control mechanisms can be operated manually or automatically, they allow for seamless integration with automation systems, providing immediate operational effects.

Application Example in Boiler Draft Fans

Figure 9 shows an example of an inlet vane control system used in boiler draft fans. The mechanism employs a unique spherical-link system, which ensures smooth movement and minimal wear. For high-load applications, oil-free metal bearings are used to reduce friction and enhance durability.

In cases where high-temperature airflow, corrosive gases, or heavy dust loads are present, the external movement type mechanism is used to prevent damage.

Inlet Vane Control

Inlet Vane Control is a method of airflow regulation that involves the installation of movable guide vanes at the intake of a blower. As shown in the image, these vanes are mechanically linked and open or close in unison, inducing a swirling airflow in the same direction as the impeller rotation. This reduces both the pressure rise and power input, effectively controlling the airflow.

The pressure rise and power input of the blower are proportional to (U₂C₂ – U₁C₁) (refer to Figure 7, velocity diagram). By imparting a swirl in the same direction as the impeller rotation, the C₁u component increases, thereby reducing the energy required to move the air. The degree of swirl can be adjusted by opening or closing the vanes, allowing precise control of pressure rise and power input.

Advantages Compared to Other Control Methods

Figure 7 – Velocity Diagram

Figure 8 highlights the advantages of inlet vane control over other airflow regulation methods. The key benefits include:

• Wider control range than damper-based control
• Higher efficiency than speed control in certain operating ranges (approximately 70% to 100% of rated airflow)
• More economical operation, especially when combined with other control systems (e.g., system C)
• Simpler structure and lower equipment costs
• Ease of operation and compatibility with remote and automated control systems
• Instant response, meaning there is no delay between operation and effect, making automatic control highly effective

Example of a Structure Used by Osaka Blower

Figure 9 illustrates a specific inlet vane control system structure adopted by Osaka Blower. This system features:

• A unique spherical-link mechanism that enables smooth movement
• All sliding components in full surface contact to ensure proper lubrication
• Use of oil-less metal bearings in locations where lubrication is difficult
• Minimized operating torque and reduced wear, ensuring long-term durability

The standard system shown in the image features an internal drive mechanism. However, in cases where the mechanism is exposed to hot airflow, abrasive environments, or corrosive gases, an external drive system is used to prevent damage.

Performance Characteristics of Inlet Vane Control (Figure 10)

The curve in Figure 10 represents performance changes for different vane opening angles. For convenience, the rated airflow, pressure, and power input are normalized to 100% at the standard operating point.

As shown in the figure, the effect of the inlet vanes begins to become significant at approximately 60 to 70–80 degrees of vane opening. Due to this, the typical operating range of inlet vanes is from 0 degrees to about 70–80 degrees.

For large-capacity fans, fans with frequent or significant partial-load operation, or applications where power consumption is restricted, inlet vane control is highly recommended for efficient performance and energy savings.

Figure 10

A blower for operating steam turbine engines

• The Forced Draft Fan is a blower that supplies combustion air to the boiler of a steam turbine engine.
• In a steam turbine engine, the boiler burns combustion air and boiler off-gas to generate steam, which drives the turbine. The generated power is then transmitted to the propeller to propel the ship.
• If the Forced Draft Fan fails, the turbine, which is the power source of the ship, cannot operate. Therefore, high reliability of the Forced Draft Fan is essential to support the ship’s operation.
• Since operating a large ship requires immense power, the Forced Draft Fan must be a large-capacity blower that supplies a massive airflow to the boiler. To meet these demands, we have built an advanced in-house testing facility and manufacturing system.
• As the only domestic supplier of Forced Draft Fans, we support the operation of ships worldwide. Additionally, to ensure safe operation for our customers, we dispatch supervisors globally to provide technical support.

A blower for safely operating tankers

The inert gas blower is a blower that injects inert gas into a tanker’s tanks.

During tanker operation, crude oil inside the tanks can vaporize and fill the space, creating a risk of ignition due to static electricity or other sources. To prevent this, non-combustible inert gas (inactive gas) is introduced into the tanks to reduce oxygen concentration and minimize the risk of ignition.

Inert gas is generated by cooling and cleaning exhaust gases from the ship’s boiler. The impeller (fan wheel) rotates at a high speed of 3600 min⁻¹, requiring precision manufacturing to ensure that even the slightest imbalance (weight deviation) is not tolerated. Additionally, due to the adhesion of fluid particles to the impeller, a mechanism for easy maintenance has been adopted to prevent imbalance and ensure superior durability.

As the only domestic supplier of inert gas fans and a leading global company, we have gained absolute trust not only from our customers but also from end users worldwide.

A blower for operating diesel engines

The auxiliary blower is a blower that supplies air to the cylinders of a ship’s two-cycle diesel engine during low-speed operation, mainly when entering and leaving ports.

Currently, to save fuel, continuous low-speed operation is becoming the norm. As a result, auxiliary blowers are now required to operate 24 hours a day, demanding high durability and a fast maintenance response system.

As a top manufacturer of auxiliary blowers in Japan, our company has a proven track record of supplying domestic diesel engine manufacturers and has earned significant trust from end users.

Blowing and ventilating for painting in large facilities

This is a blower for large-scale paint ventilation, designed to enhance explosion protection and safety.

In large shipbuilding painting facilities that handle flammable liquids such as thinner, there is a risk of fire and explosion, making proper ventilation essential.

Our company manufactures large-scale paint ventilation fans that prevent spark dispersion during operation and comply with explosion protection and safety enhancement measures.

We primarily supply these fans to shipyards within Japan.

A genuine high-temperature ceramic fan capable of handling gases exceeding 1000°C

Solid Oxide Fuel Cell (SOFC) High-Temperature Blower

• We have completed the development of a compact, high-speed (50,000 min⁻¹), high-temperature (1000°C) fuel cell blower, and we are expanding sales in collaboration with CAP Co., Ltd.
• For inquiries, please contact CAP Co., Ltd.
• ※ Both the high-temperature ceramic fan and the SOFC blower can be optimally designed to match customer specifications.

To guide exhaust gases to the chimney (IDF)

• This is a blower that draws exhaust gas from a combustion chamber or boiler and directs it to the chimney.
• We offer optimal designs tailored to your specifications, from high-pressure, low-air-volume fans with thin impellers that are difficult to manufacture to large-diameter impellers for low-pressure, high-air-volume fans.
• Our production range includes motor capacities from as small as 15 kW to as large as approximately 720 kW.
• In recent years, high-pressure and large-scale induced draft fans have become mainstream due to customer requests. The main applications include the steel and environmental industries.
• Additionally, we have received high praise from customers facing issues such as low-frequency noise affecting workers, fan vibrations in specific operating ranges, and performance changes due to surging.

A Blower That Reliably Supplies the Necessary Air for Combustion Burners

OSAKA BLOWER  offers optimal designs tailored to your specifications, from high-pressure, low-air-volume fans with thin impellers that are difficult to manufacture to large-diameter impellers for low-pressure, high-air-volume fans.

This product range includes motor capacities from as small as 15 kW to as large as approximately 720 kW.

Main applications include the steel industry and environmental industries. In recent years, due to customer requests, high-pressure and large-scale combustion air fans have become mainstream.

Additionally, OSAKA BLOWER has received high praise from customers who face issues such as low-frequency noise affecting workers, fan vibrations in specific operating ranges, and performance changes due to surging.