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Air knife drying system

2016/7/20      view:

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What is an air knife?

An air knife is essentially a plenum or hollow vessel containing a narrow slot. Pressurised air fed into the vessel through one or more inlet ports is expelled through the slot as a high velocity sheet of air. Most air knives have straight slots, but circular slotted knives are also made. Practical slot widths for our low-pressure air knives range from approximately 0.5 to 3 mm (0.02" to 0.125").


Our air knives have fully adjustable slot widths, to allow them to be "tuned" to suit both the application and the blower used to supply air to the knife. Our knives are rugged and corrosion resistant. They are ideal for heavy-duty air knife applications, especially where hygiene is important. Examples air knives are pictured below.

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While air knives can be powered by high-pressure compressed air, our air knives use air supplied from low-pressure blowers. As we will explain, using low-pressure air can produce well worthwhile benefits in many applications. In its simplest form, a low-pressure air knife system consists of an air knife, a length of interconnecting hose and a blower, as illustrated below.


What are air knives used for?

The high velocity sheet of discharged by an air knife can be put to many uses. Some of the more common are:

  • Driving water and other liquids off wet objects, especially off moving objects that would be difficult or impractical to dry by other means (such as wiping or heating). Drying applications include; bottles and cans after washing, metal parts following cleaning or electroplating, conveyor belts after washing, fruit and vegetables after washing, wet plastic packages discharged from hot-water shrink tunnels and so on.
  • Removing dust and other particles. E.g., removing excess flour from pastries and removing machining swarf from conveyor belts, machine slides and machined components.
  • Thickness calibration of fluid films, such as paint coatings.
  • Density separation (winnowing). I.e., separating light components from heavy components.
  • To form an air slide, e.g., to stop products sticking to a conveyor.
  • Separating different atmospheric zones. Quite literally by forming an air curtain between zones, e.g., to keep flying insects from a critical hygiene area.
  • Gentle air-cooling.

Please note that we don't yet have practical experience in all of these applications. We are simply putting air knives forward as possible solutions to a wide range of process problems. Areas where we have had specific experience include:

  • Drying vacuum-packed food products discharged from hot water shrink tunnels.
  • Drying conveyor belts after washing.
  • Removing "sticky" meat cuts from conveyor belts.
  • Removing machining swarf from alloy wheels prior to X-ray.
  • Removing excess lubricating oil from pressed metal plates.
  • Removing water from food cans after pressure cooking.
  • Drying 2 litre Coke bottles.
  • Blowing excess flour from meat pies.
  • Blowing excess paint from pre-painted building panels.
  • Drying plastic produce crates.
  • Density separation of bark and stone
  • Removing water from washed fruit and vegetable products