On a narrow conveyor, air knife length is usually easy to decide. The blade covers the product, the bracket has enough space, and the operator can see the drying result across the full width. Wide production lines are different. A small sizing mistake can leave wet edges, dry only the center, or force the team to run the blower harder than needed.
The common mistake is to match the air knife length only to the nominal product width. A 1,000 mm sheet gets a 1,000 mm air knife. A 1,200 mm conveyor gets a 1,200 mm air knife. This looks logical on a drawing, but drying coverage is not only a dimension. It is the useful air curtain that reaches the wet surface with enough force, at the right angle, before the water escapes to an edge or low spot.
For wide lines, air knife length should be selected from the actual wet width, product tracking variation, edge bead behavior, mounting angle, working distance, and airflow balance inside the air knife body. The longer the blade becomes, the more important inlet configuration and internal pressure distribution become.
The first sizing question is simple: what area must be dry after the air knife? The answer is not always the full conveyor width. In sheet, panel, glass, metal strip, PCB, textile, and packaging lines, the wet area may be wider or narrower than the product itself.
A flat product may carry water on the top surface, on both edges, and sometimes under the edge where droplets wrap around. Bottles and containers may need coverage across a row pattern, not across a flat sheet. A web or strip may wander from side to side. If the air knife only covers the average product position, the line will dry well during setup and fail during normal production.
A practical rule is to define three widths before choosing length: the product width, the maximum lateral movement during production, and the moisture travel zone. The moisture travel zone matters because water rarely moves straight down. The air curtain pushes it toward the side, toward the trailing edge, or into a drain path. If the blade ends too close to the wet surface, water can collect at the edge and leave a visible bead.
Wet edges usually come from one of four causes. The air knife may be too short. The air curtain may be weaker near one end. The product may be moving outside the expected path. Or the air knife may be mounted so the air pushes water toward an edge without giving it a clean exit path.
Length is the easiest cause to see, but it is not the only one. A long air knife with poor inlet balance can still leave one side wet. On wide lines, air has to travel inside the plenum before it exits the slot. If one inlet feeds too much of the blade and the opposite end receives less pressure, the center and far end may not dry at the same rate.
This is why edge drying should be checked under real line conditions, not only during a short static test. Run the conveyor at normal speed. Use the actual rinse, wash, coolant, coating, or liquid load. Watch the first 50-100 mm near each edge. If the center dries but one edge carries droplets forward, the line has a coverage or balance problem.
For many wide flat products, the air knife should extend beyond the wet product width. The overhang gives the air curtain room to carry water off the surface instead of stopping exactly at the edge. It also protects against small product tracking changes.
The needed overhang depends on the line. A stable panel line may only need a small allowance. A web, textile, belt, or row of containers may need more because the product path changes during operation. PCB wet processing often uses a minimum overhang beyond the board width, especially where water can sit at the board edge or inside holes. For general wide-line drying, it is safer to discuss the real edge behavior instead of copying a fixed number from another machine.
Oversizing also has a cost. A blade that is much longer than the required wet width consumes air across unused space. That extra air may create splash, disturb light products, or increase noise. Good sizing is not simply the longest possible air knife. It is enough length to cover the working zone and edge movement without wasting air outside the process.
A single long air knife gives a clean, continuous air curtain. It is easier to align and easier to guard. It also avoids the small weak zones that can appear between separate knives if they are spaced poorly. For many sheet, panel, and conveyor applications, one properly designed long air knife is the preferred layout.
Multiple shorter air knives can make sense when the machine frame has cross members, maintenance doors, sensors, or product guides in the way. They can also help when different zones need different angles or when a very wide line must be fed from separate blower branches. The risk is overlap. If the knives do not overlap correctly, a narrow wet line may appear between them. If they overlap too much, the crossing jets can create turbulence and push water back onto the product.
The choice should be made from the machine layout and drying result, not from catalog convenience. On a 1.5 m or 2 m line, a custom long knife with balanced inlets may be cleaner than several small catalog blades. On a line with many obstructions, two or three shorter knives may be easier to install and service.
Long air knives need stable internal pressure. If the inlet is too small or placed poorly, the blade may have strong airflow near the inlet and weaker airflow farther away. Operators often try to fix this by increasing blower pressure. That can dry the weak side slightly better, but it may over-blow the strong side and waste energy.
QXY Machinery uses single-inlet and dual-inlet configurations depending on length and application. As a general reference, QXY standard aluminum air knives use one inlet for knives up to 600 mm and two inlets for knives over 600 mm. For wide lines, the inlet diameter, inlet quantity, inlet position, and manifold layout should be considered together with blade length.
A balanced Y-split duct, similar hose length on both sides, and enough blower capacity help the full air knife length work as one drying tool instead of two uneven zones. The goal is not simply more air. The goal is a useful, even air sheet from one end of the blade to the other.
The following values are useful starting points when discussing a wide production line with QXY Machinery. Final sizing should still be based on product width, conveyor speed, liquid load, air source, mounting space, and required dryness after the station.
Reference point | QXY value or recommendation |
Standard lengths | 150, 300, 450, 600, 800, and 1000 mm |
Custom length | Available up to 6,000 mm for wide lines |
Slot gap | 0.5-2 mm standard; set at the factory according to order |
Airflow uniformity | Factory calibration target of +/-5% across knife length |
Inlet configuration | Single inlet for <=600 mm knives; dual inlet for longer knives |
Typical blower pressure | 2-6 psi (0.14-0.42 bar) for blower-driven systems |
Working distance | 20-50 mm for many drying applications |
These values are reference points, not automatic guarantees. A 2,000 mm line drying a thin water film at moderate speed is not the same as a 2,000 mm line carrying heavy coolant, chemical rinse, or viscous residue. Line speed, surface texture, liquid viscosity, and drainage direction all change the required setup.
Air knife length is measured along the blade. Effective drying coverage is what the air curtain actually reaches on the product surface. If the knife is mounted too far away, the jet spreads and loses impact. If the angle is wrong, the air may push water sideways, upward, or back into the process.
For many drying applications, a knife-to-product distance of 20-50 mm is a practical starting range. QXY also uses 15-45 degrees from the product surface as a common impingement angle range, with the airflow angled in the direction of conveyor travel. These settings help the air break the water film and move droplets away from the surface.
On wide lines, the bracket must hold this angle across the full length. A long blade that sags, twists, or sits closer to the product at one end can create uneven drying even when the air knife itself is well made. This is especially important for lightweight frames, long spans, and adjustable brackets that are not locked after commissioning.
The best check is the product itself. After installation, inspect the surface in zones: left edge, left-center, center, right-center, and right edge. Do this at normal speed and normal liquid load. If possible, repeat the check after the line has run long enough for temperature, humidity, pump flow, and product tracking to reach normal conditions.
Look for edge beads, wet stripes, splashback, product movement, and uneven drying marks. If only the edge is wet, the air knife may be too short, too close to the product edge, or pushing water in the wrong direction. If the far end is weak, check inlet balance and duct resistance. If the whole width is wet, the issue may be blower sizing, slot gap, distance, angle, or line speed rather than blade length alone.
A useful commissioning record should include the air knife length, product width, overhang on both sides, slot gap, working distance, angle, inlet pressure, blower model, duct length, and line speed. These notes make later troubleshooting much faster.
When requesting a quotation, do not send only the conveyor width. Send the product width, maximum product movement, wet area, required dryness, conveyor speed, available air source, installation drawing, bracket space, chemical exposure, temperature, and whether the product is flat, round, porous, flexible, or irregular.
For most dry industrial environments, an aluminum alloy air knife is a practical first option because it is lightweight, cost-effective, and suitable for conveyor drying, panel drying, PCB inter-stage blow-off, bottles, glass, metal strips, and general automation. Stainless steel should be considered when washdown, food contact, chemical exposure, or hygienic design is part of the line. PVC or titanium may be needed for more corrosive environments.
Wide production lines reward careful sizing. A correctly selected air knife length gives the process enough coverage at the edges, stable drying in the center, and less need for operators to compensate by raising pressure or slowing the conveyor.
QXY Machinery (Shenzhen Qixingyuan Machinery Equipment Co., Ltd.) is a high-tech enterprise integrating R&D, design, production, and sales, specializing in drying, dust removal, and water-blowing solutions for industrial applications. With over 10 years of focused expertise in the air knife field, QXY Machinery has developed a mature technical foundation and a complete in-house R&D system.
QXY Machinery has independently developed dozens of air knife models spanning aluminum alloy, stainless steel, PVC, titanium alloy, small hole PCB air knives, ring air knives, tornado air knives, and air-to-air configurations. For wide production lines, QXY can provide standard lengths and custom air knife lengths up to 6 m, with inlet configuration, slot width, material, and mounting direction matched to the actual conveyor and drying area.
QXY Machinery operates a complete production system supported by ample raw material supply and strict quality management. Stable processing capabilities and professional technical expertise enable reliable products, precise application support, and efficient after-sales service.
Q: Should the air knife be the same length as the conveyor width?
A: Not always. The better starting point is the real wet width plus allowance for product movement and edge drainage. Matching only the conveyor width can waste air if the product is narrow, or leave wet edges if the wet zone extends beyond the product path.
Q: How much longer should an air knife be than the product?
A: The overhang depends on the process. Stable flat products may need only a small allowance, while moving webs, textiles, containers, or panels with edge beads may need more. The safest choice is based on product tracking, water movement, and the required dry result at both edges.
Q: Can one long air knife dry a very wide line?
A: Yes, if the air knife body, inlet layout, blower capacity, and manifold are designed for that length. Long knives need balanced internal pressure. For QXY standard aluminum air knives, dual inlets are generally used for lengths over 600 mm.
Q: When are multiple shorter air knives better than one long air knife?
A: Multiple knives can help when the machine has frame obstructions, access doors, sensors, or different drying zones. They must be aligned carefully. Poor overlap can leave a wet stripe between knives or create turbulence where jets meet.
Q: Does a longer air knife always need a bigger blower?
A: Usually, longer coverage requires more total airflow, but blower selection also depends on slot gap, pressure, duct losses, line speed, and liquid load. Increasing blower size alone will not fix a poorly balanced inlet or incorrect mounting angle.
Q: Why is one edge still wet even when the air knife is long enough?
A: The cause may be weak airflow at one end, product wandering, bracket misalignment, poor drainage direction, or a working distance that is too large. Check the edge zones under normal production speed before changing the air knife length.
Q: What information should I send QXY before choosing air knife length?
A: Send product width, conveyor width, product movement range, wet area, line speed, liquid type, required dryness, available air source, installation photos or drawings, temperature, material requirements, and any space limits around the drying station.
Shenzhen Qixingyuan Machinery Equipment Co., LTD.
info@airknifecn.com
Building 8, Wanfeng Third Industrial Zone, Xinqiao Street, Bao'an District, Shenzhen, Guangdong, China
