Here is why;
Line size – they can be powered by a ¼”, 3/8” or even a ½” line size. Blowers will require from a 1”up to in some case 6” line sizes. Once you go past the 4” line size requirement you will be dealing with custom designed airknives specific to your environment and requirements.
Control – Compressed air is much easier to automate which allows you to integrate optical eyes and only blow air when a part is in the airknife section. If you can justify the cost to add the controls to a line this could be a low cost alternative. This would be a case if you are only blowing air say 25% of the time or less. Because compressed air can be stored you typically are operating from the reservoir tank. Blowers do not allow for this and they must keep air moving through them for proper cooling. If blowers do not have enough air passing through them for cooling you will shorten the bearing life.
They also claim that compressed air is “dirty air”. They are referring to the fact that plant air compressors are typically oil lubricated and must incorporate expensive oil mist coalescing filters on the discharge. If this filter is not properly maintained and changed regularly you will have oil migrate past the filter and work its way through the entire air stream passing through the airknife and onto the product being airknifed. Should this be metal that needs to be painted you will now end up with “fish eyes” in your paint.
Along with oil in the airstream we cannot forget about condensation! This is a known as we have some moisture saturated into the air we breathe every day. As we know, a small amount or low relative humidity is great you still must be able to handle the high humidity days. (This will be addressed again on a future drying blog). When you compress saturated air the moisture in the air condenses out and becomes water. Except now it is worse! Remember that there is also oil in the air. They do not mix but they both carry through an air system. Condensation is dealt with at many locations through your compressed air system. From the compressor reservoir all the way to the compressed air line drops. At the end of each drop you would find a FRL or just an FR unit (filter, regulator & lubricator) pending on if you are using air tools which require lubrication. The airknife drop should only have the filter / regulator.
So as you can see we have pointed out some the pros and cons of each system. When looking at an airknife system it is best to understand all options that are available to you and look at the total operating cost for the future.
]]>Compressed air people say they are the only efficient airknife on the market because of the following statements:
These are all an attempt to mislead you into thinking that they are the lowest cost way of getting into and operating an airknife system. Though these are true statements let’s look at each one!
So you have a compressor! Do you have plenty of excess compressor capacity? I am sure every company has more air available than they know what to do with. Here is the rule of thumb – 1” of compressed airknife consumes 4 cfm @ 80 – 125 PSI. Even if you can dry your part at 80 PSI, you paid to compress your air to 125 PSI. That was not free!
Air is amplified: wow, there is a statement. It’s pretty hard to measure that. Of course it is amplified. Have you looked at the new “bladeless” fans where air is discharged from what is basically a gap that is on the outer edge of the fan circle. (Think airknife). This occurs with all air that discharges from a higher pressure to a lower pressure (atmosphere, in this case). Even the lower pressure blower powered airknives operate with the same principle. One thing to note, some shapes work better which will be addressed in future blogs.
Maintenance: this is the real joke! Of course a compressed air airknife does not require maintenance but they are now comparing only their airknife and not the source of the air that powers it! Again, this is a misleading statement. Being an election year you can probably catch this one yourself. I have seen them claim anywhere from $500.00 and up per year for belts and filters required by some of the manufacturers of both the blowers and airknives. True these belts and filter need to be serviced, but so do the belts and filters on a plant air compressor. But the companies making these style airknives DO NOT MANUFACTURE THE COMPRESSOR! Do you know the average cost to maintain a plant air compressor is about $90.00+ / HP / YR!
Replacement of blower air ends: yes this is required. With today’s technologies companies have developed some great ceramic bearing. The blower manufactures utilizing this technology will tell you to expect 20,000 hours of service. This is pretty accurate. However 1 shift per day times 52 and you are looking at 2,080 per year. If you are running 24/7/365 you are looking at 8,736 hours. So how come many users of these blowers do not get the full life expectancy from the blowers?
Here are some factors that you need to add to the equation:
If you are a steel mill and utilize anything but a robust blower you are asking for trouble.
So looking at the combination of the above mentioned problems you can understand why you may not be getting the hours of service you were expecting. But here is the icing on the cake, every couple of years the salesman has to tell you how great his product is so you can buy a new or remanufactured air end to the tune of about $3,500 & up pending size / model. Yes, you may have figured it out. These manufactures have created a very expensive razor blade. Keep in mind that these blowers could be the BEST option for your application and it truly is a cost of doing business. The biggest advantage of the high speed centrifugal blowers is their compact size. You get a lot of air out of a very compact blower. The cost of doing this is a costly blower to maintain.
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AIRSTRIKE AIRKNIVES are designed to be powered by low pressure air. A typical air pressure requirement for AIRSTRIKE airknives is 2 to 6 PSI pending the application. By utilizing low pressure airknives where possible a company can lower their compressed air usage for that application by up to 80%!
The low pressure airknives gained popularity in the late 1980’s when many companies were regulated to stop using VOC in their parts cleaners due to the damage that was being caused to our environment. Parts washers were now being designed as aqueous washers and they needed the assistance of either airknives or heat to dry the parts. By utilizing the air you are able to have a part dried spot free with no residue if designed properly. (The heat option is typically the most expensive to operate over the life time of the washer). Please note that in some cases we may recommend heaters or even high pressure airknives where they can be operated efficiently.
Airknives are designed to supply a uniform sheet “knife” of air which can be used to blow off water, debris, excess coatings or even cool a part if needed. The air from an airknife is vary uniform and is referred as laminar air flow. Pending the design, gap and operating pressures, discharge velocities can reach as high as 40,000 FPM. Note that not all applications will require velocities of this magnitude. Many applications operate at 20,000 FPM or less.
Because the airknife utilizes basic math where you have a known gap area of the airknife, a known target operating pressure we can calculate the airflow required to best effectively achieve the target results. Once we know this we can select the best blower for the application. As the airknife can be powered by any brand / type of blower it is best to have a basic understanding of these. These will be covered in future forums.
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