Replacing a Broken Plastic Rotor for 30 m/s Industrial Air

Replacing a Broken Plastic Rotor for High-Speed Air

A customer builds cooling systems for wet, harsh spaces. Meanwhile, they needed a custom aluminum cross flow impeller. At first, they bought a standard plastic rotor. Therefore, this old part measured 180 mm wide by 700 mm long.

The maker built it from a mix of plastic and glass fiber. However, the system needed a much faster air speed. The customer wanted to push air at 30 m/s. In practice, to hit this mark, the aluminum cross flow impeller had to spin at 3000 RPM.

The old plastic part could not spin that fast. Instead, it only reached an air speed of about 25 m/s. Pushing it to 3000 RPM caused big problems. First, the high speed caused severe balance issues.

The outward spinning force was just too strong for the plastic. Next, the plastic blades started to break apart. Over time, the blades pulled away from their weld spots. Finally, the ultrasonic welds failed completely.

Furthermore, the machine works in a very wet space. The parts must resist rust and rot. Therefore, the customer asked us to design a new version. They needed a strong metal fan that would not break.

In short, we had to make 14 test units fast. After testing, they planned to order a batch of 200 parts. The new design had to hit 3000 RPM safely. It also had to resist water perfectly. We followed ISO 5801 test methods to check the airflow.

Choosing Metal for the Aluminum Cross Flow Impeller

We looked at the broken plastic parts from the field. The glass fiber plastic could not hold up to the speed. First, we thought about making the plastic welds thicker. However, we rejected that idea quickly. Thick plastic still bends at high speeds. A 700 mm long rotor bends too much in the middle. So, we had to change the material completely. Instead, we decided to use solid metal.

Stopping Centrifugal Force

The spinning force at 3000 RPM is massive. It pulls the blades away from the center hub. Therefore, we designed a custom aluminum cross flow impeller. Aluminum has very high tensile strength. It holds its shape under heavy stress. Furthermore, it is light enough for the drive motor to turn easily. A heavy steel part would stress the standard 12 mm motor shaft bearings.

Next, we had to solve the rust problem. The air in this system is always wet. Bare aluminum forms a safe layer on its surface. This natural layer stops rot and rust. By contrast, normal steel would rust fast in this wet air. So, aluminum met both the strength and rust needs perfectly.

Managing Cost and Machine Limits

Changing to metal costs more money up front. The customer had to pay for new metal tooling. However, the higher initial price solved the problem. The parts stop breaking in the field. This saves a lot of money in the long run.

Next, we had to make the long part spin perfectly smooth. A long metal tube can wobble if built poorly. We set strict machine limits to stop this wobble. First, the radial runout must stay under 0.7 mm. Next, the axial runout cannot pass 0.6 mm. Finally, the main shaft runout must stay under 0.2 mm. We also balance the metal part carefully. We keep the unbalance under 0.3g when testing at 1200 RPM. These strict rules keep the whole unit safe. The new LWMI-180×700-01 model runs quietly at 3000 RPM.

Technical Specifications

These rows show the strict limits we set for the part. First, the runout numbers matter most for safety. Keeping the wobble under 0.7 mm stops the metal from shaking at 3000 RPM. Furthermore, the strict balance rule protects the aluminum cross flow impeller bearings over time.

Reference: ISO 21940 covers the test method behind these figures.

Technical Documentation

Mechanical Drawing LW180x700-01
First, this document shows the exact shaft sizes and runout limits. Engineers use it to check the fit with their motor.

Next, this image shows the long metal structure. It helps buyers see how the part mounts to a standard drive block.

Fixing Fan Failures at High Speeds

If your plastic fans break at high speeds, you need a stronger part. You can fix the issue with these simple steps.

• First, check the real wind speed your system needs. If you need 30 m/s, plastic will usually bend or break. You must switch to a metal design.
• Next, define your space and air type. Wet air rots steel parts quickly. Therefore, you should pick an aluminum cross flow impeller to stop rust.
• Finally, check your motor shaft size. Our team matches the new metal hub to your old shaft. This means you do not have to buy a new motor.

Related: Cross Flow Fans.

Common Questions About Metal Fan Rotors

Browse our axial fans range, the AC axial fans section, or EC axial fans.