Below, you see a picture of a typical bottle drying setup.
You can see the blower, filter, wye, hose, air knives, mounts, conveyor and bottles. In this illustration, the bottles would be moving from the right to the left. This would cause the air from the air knives to hit the tops of the bottles first and gradually push the water down the bottles as they pass between the air knives. Read the remainder of this entry »
The picture shows a typical setup for drying hanging parts. Imagine the part is a flat sheet of glass. If the air knives were mounted straight up and down, they would blow the water toward the back end of the d be trying to blow the water around the edge and onto the other side of the glassglass. When the back end passed between the air knives, one air knife woul. The other air knife would be doing the same thing. In that situation, there is usually a bead of water left hanging along the entire back edge. If you angle the air knives as shown in the picture, then the air knives sweep the water down along that back edge. If any water is left, it is only a drop on the lower back corner. Read the remainder of this entry »
Below, you see a picture of a typical portable system. This system has a blower, filter and motor starter permanently mounted on a two-wheeled cart. The air knives are pre-mounted on a weighted stand that can be removed from the cart and placed in position beside your production line. Simply wheel it where you want it, plug it in and turn it on.
Air knives are used in many ways in the food processing industry. They can be used to blow the rinse water off of freshly washed fruits and vegetables. They are used to blow excess frost off of freshly frozen food. They are used to remove meat scraps that cling to the conveyors in meat processing plants. Any time the air comes into direct contact with food, there are special requirements that must be met. These requirements are a result of the cleaning processes that are used in these plants. In order to prevent contamination by organisms that cause illness, the processing equipment is cleaned on a regular schedule. If an air knife system is part of the equipment, it must be cleaned. This cleaning is done using strong, sometimes caustic chemical solutions. These solutions will quickly degrade painted steel or aluminum. Almost all the metal equipment in these plants is made of stainless steel. Turbotech stainless steel air knives are a perfect fit for these applications. Read the remainder of this entry »
Some of our competitors offer adjustable air knives in which the exit opening, or gap, can be made wider or narrower. By opening the gap, you can lower the system pressure, making the air knife blow gentler. By closing the gap, you can raise the pressure, making the air knife blow harder. We think adjustable air knives are not a good idea. There are two reasons for this. Read the remainder of this entry »
When we design an air knife system for an application, the first thing we do is to estimate what air velocity will be needed to do the job. This estimate is based on more than twenty years of experience with many different applications. It takes into account many things: the shape of the part, how fast the part is moving, how the part is being held, how close the air knife can be to the part, etc. Once we have settled on a velocity, we calculate the pressure needed to achieve that velocity. This is a straightforward calculation. Knowing the velocity and the size of the air knife opening, we can also calculate the amount of air we will need. Now we have the information we need to specify a blower that will produce that amount of air at that pressure. (Please see also Article #80 “Blower basics”.) There is one more thing we need to account for. As the air travels from the blower to the air knife through tube or hose, some pressure will be lost. If we don’t account for that lost pressure, our air knife system will not give us the velocity we designed for. Read the remainder of this entry »
Almost all air knife suppliers are blower manufactures, from their point of view this is an advantage because it provides them with an opportunity to sell another blower. Their main focus is to sell a blower so the air knife is just an accessory to the blower. The blower sales staff seeks out applications for their blowers. If their blower does not fit the application (even if they choke it or run it into the service factor) they have to walk away from the application. Read the remainder of this entry »
Our competitors all make the same air knife (almost) or at least they make a lot of the same mistakes. Read the remainder of this entry »
Both air sources have a useful place and this is meant to be a simple comparison of the two options. It is also a general comparison and not meant to be absolute to any application or circumstance. Read the remainder of this entry »
Q: What is an air knife?
A: An air knife is a plenum or enclosure with a means to blow air into it and a means for the air to exit. The air is usually blown in through a round tube with a hose attached. The air exits through a long thin slot, or occasionally, a row of holes.
Q: What does an air knife do?
A: An air knife creates moving air with a particular shape. The purpose of the air knife is to optimize that shape to make it as effective as possible.
Q: How are air knives used?
A: The most common use of an air knife is to dry things by blowing liquids off. Air knives can also be used to blow dry debris off of things, to heat or cool things, to control coating thickness, to dry liquid coatings, to remove static, to separate spaces that need to be maintained at different temperatures, to minimize the loss of liquids, to clean conveyors, to remove chips produced by machining, to direct debris into vacuum pickups, and to apply a hold-down pressure.
Q: What makes one air knife better than another?
A: Air knife manufacturers try to achieve two things: 1) minimum pressure loss across the air knife, and 2) laminar air flow. A tear-drop shaped air knife with the exit slot at the point will transmit 95% or more of the inlet pressure to the air exiting the slot. A round tube with holes drilled in it will typically only transmit 60% of the inlet pressure. The pressure loss represents the inefficiency of the exit design. Laminar air flow is air that is all moving in the same direction. Turbulent air flow is air that is moving in many different directions. If you want to sweep water off a flat surface, laminar air flow does that more efficiently than turbulent air flow. Air knife manufacturers achieve laminar air flow by taking advantage of the Coanda effect, which says that air blown against a flat surface tends to stick to that flat surface. This makes it possible to direct air in a more focused way than blowing it out of a round hole.
Q: Why are air knives used?
A: Almost everything that is manufactured must be cleaned before it is packaged or printed on or painted. Prior to 1987, much of that cleaning was done using solvents that contained CFC’s. These solvents would evaporate quickly and leave behind little or no residue. Therefore, there was no need to dry the product. In 1987, the world started to cut back on the use of these solvents because of their negative effects on the health of the atmosphere. Now, most industrial cleaning is done with water-based products. These do not evaporate quickly and can leave a residue behind if they are allowed to evaporate, so there is now a need to dry the products, as well as wash them.
Q: What is velocity pressure?
A: Velocity pressure is the pressure exerted by moving air. If you measure velocity pressure, you can calculate the speed at which air is moving. Air that has been pressurized, but is not moving (as in a compressed air tank) exerts pressure on the walls surrounding it. This is known as static pressure. Air that is blowing into air exerts velocity pressure. Air that is moving in a container, like the hose leading to an air knife, exerts both static and velocity pressures. The combination of these two pressures is called total pressure.
Q: Why is velocity pressure important?
A: There is an upper limit to how fast you can blow air into air. That limit is the speed of sound. At sea level and normal atmospheric pressure, that velocity is approximately 67,700 feet per minute or 770 mph. That velocity happens when the velocity pressure is approximately 10.3 PSI. Most air knife drying applications operate with velocity pressures of 2-5 PSI. One measure of the efficiency of an air knife system is how well static pressure is converted to velocity pressure. Since the velocity pressure can never be more than 10.3 PSI, the higher the static pressure you start with, the less efficient your process is. This is why air knives are typically powered using blowers rather than air compressors. It is easy to specify a blower that produces only as much pressure as you need. All the energy that an air compressor uses to go from the final velocity pressure to 100 or 150 PSI is wasted. In addition, blowers move much more air than an air compressor at the same pressure. It can easily cost four times as much to power an air knife with a compressor instead of a blower.
