AIR KNIFE SYSTEMS

1. WHAT IS AN AIR KNIFE?

An air knife is a device that delivers a controlled ‘blade’ of air – blowing moisture, debris or excess coatings off products as they move along a production line conveyor belt. These can come as a Straight Air Knives system, but also include Ring Air Knives systems

Air knives initially appear very simple. They comprise just a plenum (blade), some tubing, a blower and a housing. But expert technical advice is essential if you are to specify the right air knife system for your application – ensuring optimum performance and lower energy bills.

Simply ordering an air knife off-the-shelf – without having it configured to your precise requirements is a false economy. It will almost certainly underperform and waste energy. But a correctly specified and properly installed air knife system will pay for itself in months.

It is vitally important to ensure that your air knife system delivers the correct:
• laminar airflow – a smooth ‘blade’ of air with no turbulence
•. air entrainment – ‘free’ air that is drawn into the blown airstream as part of the process
• air balance – with no high or low spots.

You will discover much more about laminar airflow, air entrainment and air balance further down this page – along with the key considerations you must take into account when specifying an air knife system.

2. TYPES OF AIR KNIVES

STRAIGHT AIR KNIVES 

Each air knife system we manufacture and supply to customers typically comprises a centrifugal air blower, ducting and air delivery method.

Straight air knife blades are based on three standard profile heights/widths:
• 50 mm with 2”/50.8 mm inlet(s) – up to 3,500mm long
• 76 mm with 3”/76.2 mm inlet (s) – up to 3,000mm long
• 100 mm with 4”/101.6 mm inlet(s) – up to 4,000mm long.

Custom air knives are also available based around the following heights/widths:
• 150 mm (6”/152.4 mm inlet)
• 250 mm (10 ”/254 mm inlet)
• 300 mm (12 ”/304.8 mm inlet).

Air knives are available in aluminium and stainless steel (304, 316). Anodised aluminium air knives are best suited to industrial applications. They are robust, light and more cost-effective than stainless steel. Download the full list of specifications and options for aluminium air knives.

Stainless steel air knives are aimed at harsh and corrosive environments. They are a must for the food and beverage industry, where cleanliness and hygiene are paramount. Download the full list of specifications and options for stainless steel air knives.

Straight air knives are recommended only for production lines that are <1 metre wide. For lines >1 metre, we recommend chevron air knives.

View our full range of air knives: stainless steel, aluminium, shaped (chevron, ring, square).

Chevron Air Knives

Chevron air knives are a highly effective method of drying because they cut through surface moisture like a snowplough – halving the distance that the water droplets need to travel. This speeds up drying, saves energy and enables faster line speeds.

Find out more here about ACI air knife system components.

Ring/Circular Air Knives

Ring air knives encircle the product, providing a balanced 360-degree airflow for applications involving cables, tubing or lines.

Getting the right airflow – with no inefficient low spots or energy-wasting high spots – depends on specifying the correct ring diameter, hole diameter, number of inlets, the size of the air discharge slot and the air pressure entering the ring.

Ring air knives are available in two forms:
• a solid ring
• two-part hinged ring that opens to allow easy placement or removal of a long product such as a cable.

Specify ring air knives in stainless steel. Two grades are available as standard: 304 or 316L (for food and beverage production, bottle/can drying and the dairy industry).

Sizes range from 50 mm to 700 mm hole diameter. Square air knives are also available. The number of air inlets required for your air knife will depend on its hole diameter and the size of the air discharge slot required for your specific application.

Case Study: How ACI ring air knives helped Global Marine Group to dry cables during subsea deployment

JetPlates: Twice As Powerful As Normal Air Knives

ACI’s unique JetPlates deliver twice as much high-pressure air as normal air knives. They replace the side walls on your conveyor systems – delivering powerful air jets within millimetres of the passing bottles, cans and jars.

Sandwiched between two JetPlates, the bottles and cans are dried quickly, precisely and cost-effectively as they run the gauntlet of clean, blower-driven air.

JetPlates give you optimum drying performance without the need for pitch adjustment.

They also prevent water recontamination on your line because their slot design directs air moisture down and away from the conveyor.

Discover the benefits of JetPlates, and get the full specifications.

3. KEY CONSIDERATIONS

How big or small are the target objects that require an air drying/blowing solution?

What are your expectations?

What do you need to achieve?

Do you need to comply with any industry standards?

What is your actual or target production line speed? How fast will the target objects be moving?

How much space is available on your production line for the air knife system?

Are there any other potential integration issues?

What are your energy saving requirements?

What is the geographical location for your required solution?

How high above sea level is your factory/facility? (This affects the air density.)

What is the climate like?

How big is the spread of temperatures?

4. SPECIFYING THE RIGHT AIR KNIFE

Select an industry from the accordion below

5. ARE YOU WASTING MONEY ON EXPENSIVE COMPRESSED AIR?

Far from being the ‘free fourth utility’, compressed air is very expensive and inefficient. It also carries significantly higher health and safety risks.

But our engineers still come across compressed air systems, usually where the customer has tried to create a DIY solution to an urgent drying issue.

Replacing your old compressed air dryer with a proper air knife system is a guaranteed way to cut your costs.

Compare advanced ACI blower-driven air knives vs costly compressed air. You will discover:
• the downsides of compressed air
• payback analysis – how much money you could save.

6. WHY YOU NEED A SPECIALIST AIR KNIFE PARTNER

Why ‘DIY’ Air Drying Systems Fail
Companies with excess moisture on their production lines will often construct their own air drying systems in a bid to solve the problem. These DIY systems never work well.

They waste costly energy – especially if you use compressed air. DIY systems comprising a tube and some hastily drilled holes also have a nasty habit of trapping dirt and dust due to the Coandă effect (the tendency of air to follow the curve of a convex surface).

Buying off-the-shelf air knives can also be a false economy. Without expert advice on specifying, configuring, installing and testing the equipment, you again risk compromising performance and/or wasting money in higher energy costs.

Every customer, every application is different. So ACI air knife systems are tailored to your specific requirements for optimum performance – but based on standard components to ensure maximum cost efficiency.

All ACI air knife systems are guaranteed to perform as specified and tested. ROI is guaranteed. We can forecast very accurately when your new air knife will start paying for itself – and it’s usually within months.

7. WHY EXPERT TECHNICAL ADVICE ON AIR KNIVES IS ESSENTIAL

Air follows the path of least resistance. It is vital to get the air balance right to avoid:

• high spots – which waste energy
• low spots – which sap performance.

Ensuring correct air balance depends on a series of interconnected relationships in the air delivery system. They include the:

• Length, width and design of the pressurised air knife plenum (blade).
• Number and width of the air discharge holes or slots in the blade. Many have just one continuous slot. These air discharge slots are adjustable but we recommend that you leave them at the settings selected for your application.
• Angle of attack and the ‘roll’ of the blade(s).
• Proximity of the blade to the products requiring drying, cleaning, decontamination, deionisation or blowing away of excess coating(s).
• Position and configuration of other air nozzles and reciprocators.
• Number of air inlets, their diameter and spacing.
• Position and configuration of inlet manifolds.
• Pressure of air being supplied by the blower.
• Geographical location of the site – air temperature, climate, seasonality, humidity.
• Height above sea level (which affects air density).
• Position of the air knife system in the building, sources of air turbulence.

Air balance is particularly important for enrobing applications in the food processing industry. The airflow must be well balanced to ensure consistency when blowing away excess chocolate, batter, breadcrumbs and other coatings.  

ACI air knife systems have a uniform slot design that projects an uninterrupted sheet of precisely controlled, high-velocity air – supplying a powerful flow across the entire surface of the product being processed.

8. LAMINAR AIRFLOW AND AIR ENTRAINMENT

Why Laminar Airflow Matters In Air Knife Performance

Laminar airflow is air which flows in the same direction and velocity within a designated space. It is airflow that is free of turbulence.

This makes an important difference to the performance and operating cost of your air knife system – especially in applications involving deionisation and food enrobing.

Failure to deliver laminar airflow is one of the reasons that DIY air dryers perform so poorly – they are usually just tubes with holes so they blast out turbulent instead of laminar air.

ACI air knives feature air discharge slots that are designed specifically to deliver true laminar airflow – preventing turbulence and the Coandă effect (air following the curve of a convex surface).

The Coandă effect is not all bad. Our experienced engineers know how to turn it to your advantage. In one application, we used a curving jet of air to help lift paper so it could be picked up more easily from the production line.

9. HOW ENTRAINMENT MAKES ACI AIR KNIVES MORE EFFICIENT

When air is discharged from a device such as a plenum/blade, it pulls in surrounding air with it. This phenomenon is called air entrainment.   Air entrainment  means you are getting more air for your money. ACI air knives are designed to give you as much entrainment as possible without compromising the true laminar airflow (ie, without causing turbulence).

10. NOZZLES AND RECIPROCATORS

Nozzles: Cap and Neck Dryers

Nozzles play an essential role in directing concentrated jets of air to key areas of the product needing to be dried. They supplement the main airflow coming from the air knife blade.

Applications include:
• blasting out moisture trapped under crown caps in bottling lines
• drying wine bottlenecks so labels will adhere better.

ACI’s nozzles are available in three versions:
• plastic Loc-Line®
• stainless steel
• poly-para-phenylene terephthalamide (the Nylon-like polymer used in bulletproof vests, tyres, aircraft panels, boat hulls and cycle frames).

Spider manifolds with up to 10 nozzles can be used to target problem areas such as the lids and bases of cans to eliminate stress corrosion and to ensure accurate and compliant coding and date stamping.

Find out more cap and neck drying for canning and bottling lines.

Reciprocating Nozzles – More Powerful Than Basic Air Knives

Moving reciprocators deliver more vigorous air movement than a simple, static air knife blade. These banks of flexible nozzles move back and forth to deliver high volumes of air at low pressure.

They are excellent for agitating and blowing away moisture, dust and debris that is trapped in hard-to-reach places. They are particular useful for:

• aerospace – drying complex components
• automotive industry applications – drying bumpers, body sections, driveshafts and interior trim
• drying totes, crates, baskets, bins and cabinet carcasses.

Reciprocating nozzles are available in aluminium as standard or in stainless steel on request. Find out more here…

11. DOWNLOADS

Download Your 22-Page Guide To Air Knife Systems

Download our guide to ACI air knife systems.

You will find information about:
• how air knives are 90% more cost-effective than compressed air systems – as well as being quieter, cleaner and safer
• the ROI, productivity, quality and operational benefits of air knives
• materials, construction and nozzle options
• how we learn your precise requirements before providing a detailed quotation technical drawings of standard ACI air knives and their inlet options (custom designs are also available)
• reciprocating air nozzles (including technical drawings)
• blower-powered de-ionisation air knives (and how they work)
• acoustic enclosures and support frameworks
• modular ducting and flexible hose
• turnkey conveyor systems with integrated air knives
• cable and wire drying systems (with technical drawings)
• spiral drum dryers for small/light components (with technical drawings).

12. REQUEST THE LOAN OF DEMO EQUIPMENT

Decades of experience in supplying bespoke air drying systems have resulted in meticulous testing. So you can be sure that your air knives will perform as specified. This includes:

• scale testing your new system in our laboratory
• loaning you demo equipment so you can test it on-site to prove the technology works
• fine-tuning the completed system to ensure optimum performance.

13. BRING US YOUR CHALLENGES!

Air knives are not just for drying – they can solve lots of other technical challenges too. As this 58-second video proves…

ACI invests heavily in research and development. Our comprehensive test facility provides a simple and effective means of demonstrating how well our systems can solve your challenges.

Whether testing a simple air knife system, a de-ionisation arrangement or a more powerful reciprocator, the test area also has the space to demonstrate larger system assemblies. We can show the effect of blower-powered drying systems on items such as car or truck bodies.

Customers from all over the world send us samples of their products to test. A performance guarantee is given based on the test results.