Air Motor Applications for Shredders and Choppers

Click For Summary

Discussion Overview

The discussion revolves around the feasibility of using air motors for a shredder designed to process solid recycled plastics, specifically polypropylene (PP) and polyethylene (PE). Participants explore the technical specifications required for the motor, including torque and RPM, and consider the advantages and disadvantages of air motors compared to electric motors in this application.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Cristian seeks advice on using an air motor for a shredder, specifying a need for 75 RPM and over 20 Nm torque.
  • Some participants note that air motors can be suitable due to their ability to tolerate hot environments and handle overloads without damage.
  • Concerns are raised about the noise level of air motors and the need for proper muffling.
  • Efficiency issues are highlighted, with some stating that air motors are generally low efficiency, requiring significant compressor horsepower relative to the motor's output.
  • One participant mentions that achieving 75 RPM from an air motor may require an integral gearbox.
  • There is a discussion about the necessity of filtering the air supply to prevent damage to the motor.
  • Some participants question the applicability of air motors in dental drills, suggesting that their design may prioritize high RPM over torque.
  • A participant suggests reviewing manufacturer catalogs for performance curves and application notes related to air motors.

Areas of Agreement / Disagreement

Participants express varying opinions on the suitability of air motors for shredders, with some supporting their use while others raise concerns about efficiency, noise, and operational requirements. No consensus is reached on the overall viability of air motors for this specific application.

Contextual Notes

Participants mention the importance of ensuring a sufficient air supply and the potential need for additional components like gearboxes and flywheels to maintain performance under load. There are also references to the specific requirements for air quality and pressure.

Who May Find This Useful

Individuals interested in mechanical engineering, recycling technology, or the design of pneumatic systems may find this discussion relevant.

CristianEc
Messages
3
Reaction score
1
TL;DR
Need advice for considerring an air motor to rotate a shaft
Hi everyone!
My name is Cristian and I would like to ask you for advice. I am trying to build a shredder for solid recycled plastics (particularly PP and PE) and I am seeking and motor to rotate the shaft of this device.
Specifically, I require a motor with a 75 RPM speed and over 20 Nm torque and searching in the internet for alternatives to electric motors, I found that certain air motors can match these requirements. However, when going through usual applications of this kind of motors, I could not see any suggestions on using them for shredders or choppers.
So, I would like to know your opinions on the possibility of using an air motor for this purpose.
Thanks in advance!
 
Engineering news on Phys.org
Air motors are specified by torque and RPM. It is your responsibility to decide if a particular motor is appropriate for your application. The exact application is not important. The only concern is the desired torque and RPM, the motor rating, and the ability to supply enough compressed air at the correct pressure.

Some reasons to specify an air motor:
Hot environment. Air motors tolerate hot environments because they get cooler when they run.
Overloads. Air motors can be stalled without being damaged.
Exhaust air is cold: You may have a need for a jet of cold air.

Factors to consider:
Air motors are noisy. You may need to specify a better muffler to protect the operator.
Efficiency. Air motors are low efficiency. It takes roughly 4 compressor horsepower to drive a 1 hp air motor.
Don't forget to make sure that the air supply is dry.
Remember that air pressure drops when flowing. Make sure that you will get the pressure you need at the flow rate you need.
 
  • Like
Likes   Reactions: CristianEc, berkeman and Asymptotic
This shredder must be very tiny. Knife granulators I've worked on seldom were smaller than 50 horsepower.

In addition to what @jrmichler outlined,
Air motor are high speed devices, and to get 75 RPM out of one it must have an integral gearbox of some sort.

Air supply must be filtered to at least 40 micron (or smaller) particle size as well as being dry.

All granulators in my experience have flywheels to keep the cutter spinning during transient overloads typical in this application. Motor rotor mass adds to the flywheel effect, but I don't know whether the same is true of an air motor rotor. If this isn't taken into account, an air motor may be stall prone even though capable of satisfying nominal torque demand.

Take a look through several manufacturer's catalogs, carefully study motor performance curves, and their compressed air recommendations/application notes. Not an endorsement, but Parker-Hannifin's catalog is written clearly.

https://www.parker.com/Literature/Pneumatics%20Division%20Europe/PDE-Documents/Cylinders/Parker_Pneumatic_P1V-M_Air_Motors_Catalogue_PDE2539TCUK.pdf
 
  • Like
Likes   Reactions: CristianEc, berkeman and jrmichler
jrmichler said:
Some reasons to specify an air motor:
Slightly off-topic, but not too far: Why do dentist drills use air motors? Is it because they need high RPM and not much torque?
 
berkeman said:
Slightly off-topic, but not too far: Why do dentist drills use air motors? Is it because they need high RPM and not much torque?

I can't speak to the intent of the people who design dental equipment, but 1 (sometimes) important advantage of air tools is that they are small/light compared to their equivalent electric bretheren - As long as you don't include the compressor in the comparison.
 
  • Like
Likes   Reactions: Asymptotic and berkeman
jrmichler said:
Air motors are specified by torque and RPM. It is your responsibility to decide if a particular motor is appropriate for your application. The exact application is not important. The only concern is the desired torque and RPM, the motor rating, and the ability to supply enough compressed air at the correct pressure.

Some reasons to specify an air motor:
Hot environment. Air motors tolerate hot environments because they get cooler when they run.
Overloads. Air motors can be stalled without being damaged.
Exhaust air is cold: You may have a need for a jet of cold air.

Factors to consider:
Air motors are noisy. You may need to specify a better muffler to protect the operator.
Efficiency. Air motors are low efficiency. It takes roughly 4 compressor horsepower to drive a 1 hp air motor.
Don't forget to make sure that the air supply is dry.
Remember that air pressure drops when flowing. Make sure that you will get the pressure you need at the flow rate you need.
Many thanks for the explanation!
 
Great!
Thanks
 
  • Like
Likes   Reactions: berkeman

Similar threads

How to spec a motor for this floor testing system?
  • · Replies 10 ·
Replies
10
Views
2K
How can I design a gear train to meet specific torque and RPM requirements?
  • · Replies 2 ·
Replies
2
Views
3K
How do I select the right motor and gear ratio for a mid-drive e-Bike?
  • · Replies 2 ·
Replies
2
Views
4K
Torque calculations: Rotating vertical shaft
  • · Replies 5 ·
Replies
5
Views
5K
Torque required to rotate a hollow cylinder containing chips
  • · Replies 5 ·
Replies
5
Views
2K
Expert Tips for Choosing the Perfect Motor - Maximize Your Design's Performance
  • · Replies 2 ·
Replies
2
Views
1K
Electric motors and gears: torque, rpm questions
  • · Replies 5 ·
Replies
5
Views
12K
Class Project: Tennis Ball Launcher
  • · Replies 11 ·
Replies
11
Views
8K
Hydraulic motor efficiency conundrum
  • · Replies 3 ·
Replies
3
Views
8K
High School How to Calculate Power and Torque for a 15kg Load at 15 RPM?
  • · Replies 7 ·
Replies
7
Views
3K