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Impellers are critical components of pumps and are responsible for generating fluid flow. There are several manufacturing processes used to produce pump impellers, depending on factors such as the material of the impeller, the required accuracy, complexity of the design, and production volume. Here's a detailed overview of different manufacturing processes for pump impellers, along with their applications and when to use them:

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• Casting: Casting is a versatile process suitable for manufacturing impellers of various sizes and complexities. It is particularly advantageous for producing large impellers with intricate internal features. Cast impellers can be made from materials like stainless steel, cast iron, or bronze. This process is commonly employed when high accuracy, complex geometries, and high production volumes are required. Cast impellers are usually machined on the CNC as shown in below video.

• Machining: Machining involves removing material from a solid block of metal to create the impeller. This process is suitable for small to medium-sized impellers and is known for its precision. Machining is preferred when high dimensional accuracy and tight tolerances are necessary. It is often used for specialized applications that demand superior surface finishes and tight geometric control.

• Welding: Welding is a process where multiple metal components are joined together to form the impeller. This method is typically used for impellers with simple designs and operating conditions that are not excessively demanding. Welded impellers are commonly found in smaller pumps and applications where cost efficiency is important.

• Powder Metallurgy: Powder metallurgy involves compacting and sintering metal powders to create a solid impeller. This process is particularly suitable for impellers made from materials that are difficult to cast or machine. Powder metallurgy enables the production of complex shapes and impellers with high strength and dimensional accuracy. It is often used when specific material properties, such as enhanced wear resistance or corrosion resistance, are required.

• Additive Manufacturing (3D Printing): Additive manufacturing, or 3D printing, is an emerging technology that offers design flexibility and the ability to produce complex impeller geometries. It is commonly used for prototyping and small production runs. Additive manufacturing is advantageous when rapid design iterations, customization, or the production of highly intricate impellers are needed. However, it may not be suitable for high-volume production or when specific material properties are critical.

When selecting the appropriate manufacturing process, it's essential to consider factors such as the impeller's material, type, size, complexity, required accuracy, production volume, and cost considerations. Each manufacturing process has its strengths and limitations, and choosing the right method ensures that the impeller meets the required specifications and performs optimally within the pump system.

Impellors are a fundamental component of turbomachinery; they use flow deflection to convert mechanical energy into pump power output. Depending on the application, machined impellors are mass-produced or specifically created for a unique piece of machinery. But which type of impellor does Secomak use in their industry-leading products?

Different manufacturing processes are used to produce impellors, such as CNC machining (a type of machining process), casting, 3D printing, or forging Each fabrication method has its advantages and disadvantages, affecting factors such as cost, efficiency, safety, reliability, longevity, and performance.

Other factors that determine the type of impellor needed include the application (e.g., pumping, compressing, air movement, or mixing), the impellor materials, its type (e.g., open, shrouded, radial, peripheral, or axial), and other required features. For example, it might need to be anti-static or corrosion-resistant. Read on to learn about the various differences between machined impellors.

Different Types of Machined Impellors

An impellor is a fundamental gas booster, compressor, fan, and blower component. We know there are different ways to manufacture impellors; the best method depends on the application. However, before we compare their differences, let’s consider the characteristics of impellors, which can help determine what type of manufacturing process is best:

Material

Impellors can be machined from various materials, including metals (e.g., stainless steel, aluminium, bronze, and titanium), plastics, and composite materials. The choice of material depends on factors like the pumped fluid or gas properties, temperature, pressure, corrosion resistance, and mechanical strength requirements.

 

Design and Geometry

An impellor’s design, including its shape, number of blades (or vanes), blade curvature, and blade angle, is tailored to the specific application and the intended airflow characteristics. For example, impellors in centrifugal pumps will have a different design from those in axial compressors.

• Impellors are designed to rotate clockwise or anti-clockwise,
• They can have one vane (or blade), or multiple vanes,
• The vanes must be smooth to promote the efficient flow of matter,
• The vanes are accommodated on a disc called a back (or inner) shroud, and
• Closed impellers have a front (or outer) shroud that covers the vanes.

Size

Impellors can range from tiny sizes used in microfluidic devices to large industrial-scale ones used in power plants or aviation turbines. The size directly affects performance and manufacturing complexity.

Performance Characteristics

Impellors are designed to meet specific performance characteristics, such as flow rate, pressure head, efficiency, and NPSH (Net Positive Suction Head) requirements.

Application

Different applications require different impellers. For example, those used in fans generate high airflow, while those in centrifugal compressors may prioritise pressure rise.

Operating Conditions

The operating conditions (e.g., temperature, pressure, and fluid or gas properties) influence the materials chosen and the design features. For instance, Secomak’s heaters can operate at temperatures of up to 400°C (752°F).

Balancing

Impellors must be precisely balanced to avoid excessive vibrations, ensure smooth operation, and prevent damage to the machinery. The balancing process may vary depending on the component’s size and complexity, rotational speed, intended use, as well as its manufacturing process.

Cost

The cost of manufacturing impellors can differ significantly depending on the type of impellor, the complexity of its design, the materials used, and the manufacturing process used.

It’s essential to consider these characteristics carefully when selecting an impeller for a specific application to ensure optimal performance and reliability. Engineers and designers often work closely with manufacturers and use computer simulations and 3D iterations to optimise impellor designs for specific use cases, e.g., customised products.

CNC Machined Impellors

Computer Numerical Control (CNC) machines are used to shape an impellor from a solid billet of material, e.g., metal, using a subtractive process. These machines are equipped with a built-in workpiece and tools for drilling and cutting, which are guided by a computer and specific software.
This method of making impellors is suitable for small to medium production volumes and creating prototypes.

Advantages and Disadvantages of CNC Machined Impellors

Below are some of the advantages and disadvantages of making impellors using a CNC machine:

Advantages

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• CNC-machining is an accurate way to produce a precision impellor
• These machines take much less time to produce a product.
• If any iterations of an impellor are required, it only requires a change to the CNC program.
• CNC machines can function 24 hours a day, as opposed to relying on shifts and manual labour.
• Impellor designs and prototypes are stored on the CNC machine’s software, so production isn’t limited to only one operator.
• You can make impellors from different metals, depending on the application.
• CNC-machined impellors are energy-efficient as they have a smoother, more polished finish that allows for improved flow of matter.
• These impellors are more robust as they were machined from a solid piece of metal.

Disadvantages

• CNC machines are costly to install.
• They have limits as to how large a product can be.
• While these machines are accurate and precise, it is possible for an operator to make an error.
• Depending on the impellor design, there could be a lot of material waste compared to casting.
• CNC machines should only be operated by a trained engineer or operator.

Cast Impellors

Casting is a cheaper way of making impellors and allows for increased production. However, producing impellors this way is time-consuming and less precise than with a CNC machine. Here’s an outline of how cast metal impellors are made using sand for the mould:

• Temporary moulds are made in frames, most commonly with a mix of sand and clay compressed around solid forms, which are then removed.
• Additional elements or moulds might be included depending on the impellor’s design.
• The frames and corresponding moulds are stacked atop each other, with an inlet area where molten metal is poured from above. Together, the partial moulds will make up one solid impellor.
• The molten material is poured into the moulds and left to cool until it becomes solid.
• Once the moulded metal has cooled, the excess sand is washed off, and irregular pieces of metal are chipped off.
• The impellor must then be polished smooth, checked for irregularities, and balanced.

Advantages and Disadvantages of Cast Impellors

The advantages and limitations of cast impellors are summarised as follows:

Advantages

• It is more cost-effective to make cast impellors.
• This method is suitable for producing large quantities.
• The process can be manual, automated, or a combination of both.
• Depending on the material used, some moulds are reusable.

Disadvantages

• The quality of the impellors may vary and are subject to human error.
• The process is more time consuming and requires physical labour and monitoring.
• Impellors made this way must still be polished and smoothed using machinery.
• Cast impellors are less energy efficient than CNC machined ones.
• They might be less precise and accurate than CNC machined impellors.
• If the impellor design changes, it might be necessary to change the mould or tools.

3D-Printed Impellors

Another way of making impellors is by using an additive manufacturing process like 3D printing. To do this, you would need a design program, a 3D printer, and the best type of filament for the impellor’s application. Once the design is sent to the printer, it gets to work by melting the filament and layering it in the designed format from the bottom up.

Then, when the impellor is completed, it can be polished to remove layer lines and make it smoother.

Advantages and Disadvantages of 3D-Printed Impellors

The advantages and disadvantages of 3D-printed impellors are discussed below:

Advantages

• 3D printers can function 24 hours a day.
• They can produce high volumes of smaller impellors.
• Only an operator is required to supervise the printing process.
• Reiterations of an impellor design are quickly done.
• They are helpful for creating prototypes and testing design efficiency and functionality before manufacturing starts.

Disadvantages

• Impellor size will be limited according to the 3D printer’s range of movement.
• 3D-printed impellors are made from a material weaker than most metals.
• The material used in 3D printing is unsuitable for applications requiring high temperatures.
• See how easy it is to make different impellors using a 3D printer. This video shows how fast the process is and how plastic impellors are not ideal for industrial fans and blowers.

Forged Impellors

The last type of machined impellor we’ll look at in this article is the forged kind. Only certain types of impellors can be made using this process due to its limitations, which include high cost, limited materials, and shaping ability. However, due to the heating process, forged impellors often have improved metallurgical properties.

Advantages and Disadvantages of Forged Impellors

Below are some of the advantages and disadvantages of forged impellors:

Advantages

• Forged impellors, when well-made, are a good option for turbomachinery.
• They have improved metallurgical properties suitable for more extreme conditions.

Disadvantages

• The process can be expensive due to the required preparation, tools, and time.
• Only specific impellor designs can be forged due to die limitations.

A Summarised Comparison

Based on the overviews provided, here’s a table to summarise the differences between machined impellers:

Characteristics Machined Impellor Type CNC Machined Impellors Cast Impellors 3D-Printed Impellors Forged Impellors Material Stainless steel, titanium, aluminium, and alloys Stainless steel, iron, bronze, carbon steel, and plastics Filament, which might include additives like carbon fibre or metal shavings. Metals or alloys that are easily deformed Ability to Produce an Intricately-Designed Impellor Yes Possible, but in layers. Possible, but in layers. Not ideal for intricate designs. Size Limited to CNC machine size Unlimited Limited to 3D-printer size Limited to die set Performance High-performance and energy-efficient High performance Low- to medium performance for smaller applications High-performance Application Fans, pumps, and turbomachinery Fans, pumps, and turbomachinery Smaller fans and pumps Fans, pumps, and turbomachinery Operating Conditions Industrial, capable of performing at high RPM and temperatures Industrial, capable of performing at high RPM and temperatures Cooler operating conditions, lower RPM Industrial, capable of performing at high RPM and temperatures Balancing Required Yes, but not as much Yes Yes Yes Polishing Required Possibly. Some CNC machines polish automatically. Yes Yes Yes Cost Mid- to high cost. Cheapest method for metal impellors Probably the most affordable option, depending on the type of filament used They are costly due to the tools requiring regular maintenance. Making Changes and Iterations Quickly done – requires only a change to the programming on the computer software. Not quickly done as a mould must be remade. Quickly done with computer software. Not quickly done as the die casts must be reshaped.

Which Manufacturing Process for Impellors Does Secomak Use?

Secomak is an industry leader in air-moving industrial equipment; the company has been moving and manipulating air for the better part of a century. Their success lies in their expertise, craftsmanship, and use of quality components. As such, they use the best impellors for their fans and blowers, i.e., CNC-machined impellors.

Secomak uses CNC-machined impellors in their products for the following reasons:

• The superior quality of the impellors,
• The low risk of component failure,
• Lower vibration than other impellors at over 15,000 RPM,
• Machined impellors are easier to balance because of the precision and accuracy during manufacturing,
• Impellor strength, stability, and longevity (because they’re formed from a single piece of metal),
• Reduced friction (because they’re smoother),
• Improved airflow and pressure,
• Improved energy efficiency by delivering a higher flow rate with lower input power,
• They perform well and are reliable, and
• Machined impellors are easier to iterate, making it easier to customise a product (requiring only a new design to be loaded onto the program). This is compared to cast impellors that would need new moulds and tools to make an iteration.

Conclusion

Secomak uses CNC-machined impellors for their boosters, fans, and blowers, as this method offers many advantages compared to alternative manufacturing processes such as casting, forging, or 3D printing. Compared to cast or printed impellors, those manufactured using a CNC machine are more precise, accurate, and energy efficient. They also tend to be more robust and durable, making them a preferred choice for industrial purposes.

References

https://en.wikipedia.org/wiki/Impeller

https://gas-boosters.com/

https://secomak.com/

https://secomak.com/products/fans-blowers/

https://secomak.com/products/heaters/

https://www.globalspec.com/learnmore/flow_control_flow_transfer/pumps/impellers

https://www.ksb.com/en-global/centrifugal-pump-lexicon/article/impeller-1116078

https://www.sciencedirect.com/topics/chemistry/impeller

https://www.sciencedirect.com/topics/engineering/forging-process

https://www.sciencedirect.com/topics/engineering/impeller

https://www.youtube.com/watch?v=_W57TWMQ1co&t=31s

https://www.youtube.com/watch?v=mafjVYfFgg4

https://www.youtube.com/watch?v=T2fBDZ0mhiI

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