A Review of Centrifugal Air Compressors

Over the last few months, my EXAIR colleagues and I have blogged about several different types of air compressor types including single and double acting reciprocating, rotary screw, sliding vane and rotary-scroll air compressors. You can click on the links above to check those out. Today, we will examine centrifugal air compressors.

The types of compressors that we have looked at to date have been of the Positive Displacement type.  For this type, an amount of air is drawn in and trapped in the compression area, and the volume in which it is held is mechanically reduced, resulting is rise in pressure as it approaches the discharge point.

types of compressors

The centrifugal air compressors fall under the Dynamic type. A dynamic compressor operates through the principle that a continuous flow of air has its velocity raised in an impeller rotating at a relatively high speed (can exceed 50,000 rpm.) The air has an increase in its kinetic energy (due to the rise in velocity) and then the kinetic energy is transformed to pressure energy in a diffuser and/or a volute chamber. The volute is a curved funnel that increases in area as it approaches the discharge port. The volute converts the kinetic energy into pressure by reducing speed while increasing pressure. About one half of the energy is developed in the impeller and the other half in the diffuser and volute.

Centrifugal Compressor
Centrifugal Compressor Components

The most common centrifugal air compressor has two to four stages to generate pressures of 100 to 150 PSIG.  A water cooled inter-cooler and separator between each stage removes condensation and cools the air prior to entering the next stage.

Some advantages of the Centrifugal Air Compressor-

  • Comes completely packaged fort plant air up to 1500 hp
  • As size increases, relative initial costs decrease
  • Provides lubricant-free air
  • No special foundation required

A few disadvantages-

  • Higher initial investment costs
  • Has specialized maintenance requirements
  • Requires unloading for operation at reduced operational capacities

EXAIR recommends consulting with a reputable air compressor dealer in your area, to fully review all of the parameters associated with the selection and installation of a compressed air system.

If you would like to talk about air compressors or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Super Air Knife Replaces a Blower-type Air Knife and Saves Money Annually

Sheet washing system

A sheet metal company made thin stainless steel sheets in their process.   Before the sheets were rolled up, it went through a washing system.  Two blower-type air knives were mounted after the wash cycle to remove the residual water from the surface.  They purchased the blower-style air knives under the belief that they would save money by not using compressed air.  They found out quickly that it was not a true statement especially when it comes to the total cost of ownership.

With the dirty environment at their facility, the inlet filter on the blower was getting plugged.  The blower motor would heat up from the filter being restricted.  After eight months of service, the blower motor failed due to excessive heat.  The replacement was very costly, and it created a production stoppage for an entire day.  The manufacturer of the blower-type air knife recommended that the filter should be changed every month instead of quarterly.  This recommendation increased the monthly budget for the blower system, but they did not want to replace the blower motor again.  Instead of a quarterly stop in production for maintenance, the washing system had to be stopped every month for filter change-out.   They decided to contact EXAIR to see if their concept of “saving money” with the blower-type air knife was valid.

To better explain the concept, I divided the comparisons into different categories explaining the details between the Super Air Knife and the blower system.

  1. Initial Cost:
    • Blower System – They are an expensive set up when you have to include a blower, ducting, and a knife. To have any flexibility, a control panel with a VFD will be needed.
    • Super Air Knife – It is a fraction of the cost. With their system above, we were roughly 1/4 the cost.  A capital expense would not be required for ordering two Super Air Knives to remove the water from the stainless steel sheets.
  1. Maintenance:
    • Blower System – The intake filter had to be changed every month, and the customer estimated a cost of $150.00 each. The motor and belt also had to be checked quarterly as a preventive maintenance.  Being that the blower motor is a mechanical device, the bearings and belts will wear and have to be replaced.  Without proper maintenance, things can break prematurely.  This customer had to already replace the motor in their system.
    • Super Air Knife – They do not have any moving parts to wear out, and they are not affected by the dirty environment. Only compressed air is needed to operate.  The maintenance requirement is to change the compressed air filter once a year.  The annual price for the replacement filter is less than $35.00.
  2. Compressed air usage:
    • Blower System – This device does not require any compressed air to operate, but it does use an electric motor. For this customer, they had a 7.5KW blower motor.  With the inherent designs of blower-type air knives, they have reduced blowing forces and turbulent air flows.  This combination required maximum power output on the 7.5KW blower motor.
    • Super Air Knife –With their unique design, it has one of the highest efficiencies in the market place. It can entrain 40 parts of ambient “free” air with every 1 part of compressed air.  With laminar flow and the power of compressed air, the Super Air Knives can be used at a much lower air pressure.  To compare with the electric blower motor above, the Super Air Knives only required 11KW of compressor power to operate.
  3. Noise:
    • Blower System – With the turbulent air flow, the blower units are very loud. It can have a sound level near 93 dBA.  If operators are working near the system, they would require PPE for hearing.  The cost for proper hearing equipment and the training for the operators will add more cost with using blower systems.
    • Super Air Knife – These units are very quiet. Even at an elevated pressure, the sound level is only 72 dBA at 100 PSIG.  This level is below the maximum noise exposure for hearing safety as marked in OSHA 29CFR 1910.95(a).

 

I tabulated the annual cost comparison and shared it with the customer to better explain the total cost of ownership.  After reviewing the information, they decided to try two pieces of the model 110230 Super Air Knife Kits.  When they replaced the blower-type air knives, the customer did share some additional information.  First, they were amazed at the ease of installation.  The blower-type air knives had to be electrically wired; floor space was sacrificed for the blower; the connection hoses were large and bulky; and the mounting was cumbersome.  The customer also noticed the amount of power that was created by the Super Air Knives.  They were able to increase the feed rates of the stainless steel sheets if they wanted and still keep the surface dry.  This gave them flexibility in their production system.  And of course, the maintenance time and cost were practically eliminated.  Compressed air is expensive, but if you use EXAIR products, you can use the compressed air very efficiently.  As noticed in the tabulation above, the total cost of ownership is very expensive for the blower-type air knives as compared to the Super Air Knives.  You can contact an Application Engineer at EXAIR if you want to discuss further the benefits of using the Super Air Knives.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Eliminating False Image Readings Using The Gen4 Stay Set Ion Air Jet

I was recently contacted by a medical device manufacturer who was interested in implementing a Static Eliminator in their production process. They have a manually operated vision station where a plastic substrate, about the same size as a credit card, is placed into a nest then a small amount of liquid is deposited onto the surface. An operator takes a picture of the liquid and substrate and the image is analyzed. The part is stationary in the nest until the image is taken.  When the station is done, the plastic part is manually removed from the nest.

After some internal testing, they determined that static build up on the plastic part was causing the liquid to move, or “bounce” as they placed it, which was leading to a significant drop in their manufacturing yield due to faulty readings. The cycle time from taking the initial  image and the analysis results is roughly 2 seconds so they were needing something that would quickly remove the charge on the plastic part.

The customer was able to email some photos and after further review, EXAIR recommended they use our Gen4 Stay Set Ion Air Jet in the process. The Gen4 Ion Air Jet is a compact ionizer delivering a quiet, focused ionized air stream to quickly eliminate the static charge on the surface of a material or object. Operating at 20 PSIG, the Gen4 Ion Air Jet is capable of dissipating a 5kV charge in 0.45 seconds while maintaining a low sound level of only 67 dBA. The Ion Air Jet entrains ambient air at a rate of 5:1 and the airflow can be adjusted from a “blast” to a “breeze” simply by increasing or decreasing the inlet pressure. The Gen4 Stay Set Ion Air Jet includes our 12” Stay Set Hose which holds position until it is physically repositioned and a magnetic base for easy installation.

If you have an application that requires a concentrated, ionized airflow or for help with selecting the best product to fit your need, give me call at 800-903-9247 for assistance.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

Fluidics, Boundary Layers, And Engineered Compressed Air Products

Fluidics is an interesting discipline of physics.  Air, in particular, can be made to behave quite peculiarly by flowing it across a solid surface.  Consider the EXAIR Standard and Full Flow Air Knives:

Compressed air flows through the inlet (1) to the Full Flow (left) or Standard (right) Air Knife, into the internal plenum. It then discharges through a thin gap (2), adhering to the Coanda profile (3) which directs it down the face of the Air Knife. The precision engineered & finished surfaces serve to optimize the entrainment of air (4) from the surrounding environment.

If you’ve ever used a leaf blower, or rolled down the car window while traveling at highway speed, you’re familiar with the power of a high velocity air flow.  Now consider that the Coanda effect can cause such a drastic redirection of this kind of air flow, and that’s a prime example of just how interesting the science of fluidics can be.

EXAIR Air Amplifiers, Air Wipes, and Super Air Nozzles also employ the Coanda effect to entrain air, and the Super Air Knife employs similar precision engineered surfaces to optimize entrainment, resulting in a 40:1 amplification ratio:

EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of air from the surrounding environment.

As fascinating as all that is, the entrainment of air that these products employ contributes to another principle of fluidics: the creation of a boundary layer.  In addition to the Coanda effect causing the fluid to follow the path of the surface it’s flowing past, the flow is also affected in direct proportion to its velocity, and inversely by its viscosity, in the formation of a boundary layer.

High velocity, low viscosity fluids (like air) are prone to develop a more laminar boundary layer, as depicted on the left.

This laminar, lower velocity boundary layer travels with the primary air stream as it discharges from the EXAIR products shown above.  In addition to amplifying the total developed flow, it also serves to attenuate the sound level of the higher velocity primary air stream.  This makes EXAIR Intelligent Compressed Air Products not only as efficient as possible in regard to their use of compressed air, but as quiet as possible as well.

If you’d like to find out more about how the science behind our products can improve your air consumption, give me a call.

Dirty Coolant in, Clean Coolant Out – EXAIR’s Chip Trapper Extends Coolant Life

In a machine shop one of the most dreaded tasks is always cleaning out the coolant sumps of the CNC machines. Over time, chips and shavings can make their way up into the coolant lines resulting in a clog. The coolant flow slows down or stops entirely, resulting in premature wear of expensive cutting tools, imperfections in the parts, or unacceptable product finish. When this occurs, if it is even noticed right away, the machine has to be stopped and valuable production time must be spent identifying the location of the clog and removing it.

Another problem, one anyone working around CNC machines can attest to, is the rancid coolant smell that is a result of bacteria building up in the stagnant cutting fluid. Regularly cleaning this oil can reduce this smell, prevent premature tool wear or costly shutdowns, as well as extend the overall life of your coolant.

ctrhlctr_heroi_770x620

There are some machines out there capable of cleaning the oil and removing any chips or shavings, but these tend to be very expensive and not very effective. We tested a few different methods here at EXAIR in our machine shop. As a result of these tests we determined that the best foot forward would be to develop something ourselves. Enter the EXAIR Chip Trapper. Using either a standard or High Lift Reversible Drum Vac to provide the vacuum source, the Chip Trapper is capable of filling or emptying a 55 gallon drum in less than two minutes. It is able to pick up both the liquid coolant as well as any chips or shavings that are suspended in the coolant. The liquid is forced through a filter bag inside of the drum which contains any solid materials while allowing the coolant to filter out into the drum. Switching the knob on the Reversible Drum Vac and the directional flow valve to empty will allow the clean coolant to be pumped back out of the drum and reused.

After implementing the Chip Trapper in our own shop, we were able to increase the life of the coolant by 6x. In addition to the increased coolant life, a process that used to take up to 2 hours per machine now takes less than 10 minutes. The Chip Trapper quickly and easily pays for itself.

The Chip Trapper is available in either 30, 55, and 110 gallon systems. It’ll also come with (2) 5 micron filter bags, other filter bags are also available ranging from 1 micron up to 200 micron filtration. Using a simple detergent, the filter bags can be washed out, cleaned, and reused multiple times. With no motors or impellers to clog or wear out, as well as no electricity requirement or shock hazard, the Chip Trapper comes with our standard 5-year Built to Last Warranty. Do yourself (and your machine operators) a favor and get a Chip Trapper on order today. They’re in stock, ready to ship and start saving you time and money!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD

Protect Personnel from Noise with Engineered Products

Sound can be defined as vibrations that typically travel as an audible wave through mediums that can be a gas, liquid or solid. For this blog we will concern ourselves with sound travelling through a gas (atmosphere) in an industrial setting.

Sound is energy that travels in waves and is measured by its frequency (cycles per second) and amplitude (intensity). A common unit of measurement for sound energy is the decibel. The decibel (abbreviated with dBA) is a unit-less number that is based on the logarithm of a known measured quantity to a reference quantity. Without reciting the equation for every increase of 3 dBA is a doubling of sound energy or twice as loud.

Since our focus is on industrial sound one might question why be concerned at all, after all sound emanates from most machines and devices. The reason for concern is that there are OSHA regulations regarding the amount of time workers can be exposed to different levels of sound in their workday as illustrated below. These limits are in place to protect personnel from Noise Induced Hearing Loss or NIHL. When the damage to anyones hearing is caused by their profession, it is also referred to as Occupational Hearing Loss or OHL.

After monitoring for noise, NIOSH and the CDC next recommend administrative controls to minimize or eliminate the noise hazard (click for their helpful PDF). This would include the use of noise reducing EXAIR products like Super Air Nozzles, Air Knives and Air Amplifiers.

dBA Chart.JPG
OSHA Maximum Allowable Noise Exposure

When considering the many items in an industrial setting that produce loud sounds the list would be exhaustive. Many of them simply produce loud sounds that can’t be eliminated or reduced while on the other hand there are some that can. Some of the noisiest offenders that plants have control over are air powered tools and open tube blow-offs.  Eliminating inefficient methods of part blow off & part cleaning with an engineered solution allows a company to significantly reduce the level of sound in their plant, improve worker safety and save money on compressed air consumption.

Employers are required to provide hearing protection to employees whom are exposed to sounds above 90 dBA on a Time Weighted Average (TWA). Without digressing into the formulas TWA calculates a workers daily exposure to occupational sounds by taking into account the average levels (in dBA) and the time exposed to different levels.  This is the how OSHA assesses workers exposure and what steps should be taken to protect the workers.

To conclude, plants need to be mindful of the OSHA regulations for sound levels, time of exposure and that hearing protectors wear out. Earmuff seals can lose their elasticity and reduce their effectiveness and the soft pre-molded earplugs can wear out in a day and need replaced.  Keep a good supply on hand and OSHA suggests letting workers with noisy hobbies take them home for protection off the clock!

If you would like to discuss reducing noise or any EXAIR product, I would enjoy hearing from you…give me a call.

Steve Harrison
Application Engineer

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When to Use a Receiver Tank for a Compressed Air Application

Recently, I worked with a production engineer at a Tier 1 supplier for the auto industry.  An upcoming project was in the works to install a new line to produce headlight lenses.  As a part of the process, there was to be a “De-static / Blow-off” station, where a shuttle system would bring a pair of the parts to a station where they would be blown off and any static removed prior to being transferred to a painting fixture and sent off for painting.  For best results, the lenses were to be dust and lint free and have no static charge, ensuring a perfect paint result.

The customer installed a pair of 18″ Gen4 Super Ion Air Knives, to provide coverage of the widest 16″ lens assembly, that were staged in pairs.

112212
The Super Ion Air Knife Kit, and Everything that is Included.

The customer was limited in compressed air supply volume in the area of the plant where this process was to occur. 50 SCFM of 80 PSIG was the expected air availability at peak use times, which posed a problem –  the Super Ion Air Knives would need up to 105 SCFM if operated at 80 PSIG.  A further review of the design parameters for the process revealed that the system needed to blow air for only 4 seconds and would be off for 25 seconds to meet the target throughput.

This scenario lends itself perfectly to the use of a Receiver Tank.  Running all of the design numbers into the calculations, showed that the 60 Gallon Receiver Tank we offer, would allow for a 20 second run-time, and require 13.1 seconds to refill.  These figures were well within the requires times, and would allow for the system to work as needed, without having to do anything to the compressed air supply system.

receiver_tank
60 Gallon Receiver Tank

The moral of the story is – if you have a process that is intermittent, and the times for and between blow-off, drying, or cooling allows, a Receiver Tank can be used to allow you to get the most of your available compressed air system.

Note – Lee Evans wrote an easy to follow blog that details the principle and calculations of Receiver Tanks, and it is worth your time to read here.

If you would like to talk about any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
Find us on the Web 
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Twitter: @EXAIR_BB