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What Is Spiral Duct?

Oct 28

The basic component of a ventilation system is the ventilation air duct. Air is transported by ventilation ducts, which deliver fresh outside air while removing stale indoor air. Circular, rectangular, and oval ventilation ducting can be classified based on their shape (a compromise between rectangular and round ventilation ducts).

It can also be distinguished by the material it is composed of, such as stiff spiral pipe, which is typically made of galvanized steel sheet, and flexible ducts, which are frequently made of aluminum, polyester foil, and other similar materials. Rigid spiral ducting and rectangular ducting are by far the most common forms of ductwork used in both residential and industrial ventilation systems.

A spiral duct is a type of duct

Spiral duct is a spirally wound tube made of steel metal, usually galvanized steel, but also stainless steel, aluminum, or copper. Due to the female ends of spiral ducting, a male coupler must be utilized as a connection piece to link two duct sections.

Spiral ductwork, of course, is more than just pipe and fittings; depending on the project, a comprehensive ventilation system may include the following components:

  • Bends, reducers, t-pieces, couplings, end caps, and other ducts and fittings are examples.
  • Air dampers, VAV and CAV regulators, for example, are items that regulate airflow.
  • Sound attenuators, flexible duct connectors, and duct insulation are some examples of sound attenuation goods.
  • Fire and smoke dampers, as well as fire-rated air valves, are all examples of fire-fighting products.
  • Clamps, threaded rod, support brackets, self-drilling screw, rivets, and a sealing tape for duct connections without seals; Suspension and fixing items, such as clamps, threaded rod, support brackets, self-drilling screw, and rivets;
  • Air valves, diffusers, louvres, and other finishing-trim products

What is the process for making a spiral duct?

Spiral ducts are produced from spirally rolled steel sheet metal with widths of 137 mm and 140 mm, and are manufactured using tubeformers, or spiral air duct manufacturing equipment. It is critical for the duct manufacturer to purchase or cut these metal strips to ensure that they have a precise dimension tolerance. A minor margin of error can allow the spiral duct machine to improperly close the lockseam. A slitting machine is a machine that cuts big steel coils into smaller steel strips, such as 1250-1500 mm wide.

SPIRO International machines - tube formers are the most common spiral duct machines in use in the HVAC sector. As a result, many HVAC professionals refer to spiral ducts simply as spiro ducts because SPIRO tubeformers is a well-known brand among spiral duct makers.

On the market, spiral pipe making machines can produce ducts up to 2500 mm in length. Circular ventilation ducts with such huge diameters, however, are rarely employed. We usually pick rectangular ducts when bigger diameters are required. As a result, most spiral duct manufacturers, including ourselves, have forming heads that extend up to 1600mm and offer spiral ducting in sizes ranging from 80 to 1600mm.

Metal sheet

Spiral ducts are built of galvanized steel sheet as a standard, and galvanized ducting is a default not only for us, but for the majority of duct manufacturers. You could inquire, but what kind of inquiry would you like to make? Manufacturers of spiral ductwork typically employ a variety of steel grades. DX51D (often used for spiral ducts), DX53D, and DX54D are the most popular steel grades. In a nutshell, the flexibility or formability of these steel types differs during manufacturing. Furthermore, it's zinc-coated hot-dip galvanized steel.

Coating designations like Z100, Z140, and Z275 are most likely familiar to you. When it comes to spiral ducts, galvanized steel Z275 is believed to be the industry standard, while Z140 and Z100 are also used.

The corrosivity class of a duct is another factor to consider when choosing a ducting type for a certain project. You must first identify which corrosivity category a given facility [environment] belongs to, and then determine how much thickness loss will occur over time using the standard BS EN ISO 12944-2 (see table below). The C1, C2, C3, C4, and C5 classes are defined by the standard.

The nature of the loss can vary greatly. It may be slower or faster depending on the pace of corrosion and the severity of the environment. Because of this, selecting the proper coating thickness is critical for the longevity of ventilation ducting. In a certain corrosive environment, you can calculate how many years the chosen coating will last.

The dimensions of spiral ducts

The ducts are typically offered in 3 m lengths, however circular ducts of any length between 0.5 and 12 m can be manufactured with a tolerance of up to 2 mm.

Spiral ductwork comes in diameters ranging from 80 mm to 1600 mm, with the majority of typical diameters in stock. The diameter and needed pressure in the ductwork determine the duct wall thickness. Spiral ducts are made from metal sheets ranging in thickness from 0.4 to 1.8 mm, with the material chosen based on the system's pressure and mechanical requirements, as well as cost.

Spiral ducts sheet thickness

Corrugation is provided on spiral ducts with a diameter of 160 mm or more for increased stiffness and vacuum strength. For diameters ranging from 250 mm to 1600 mm, corrugations are a regular feature. It is recommended to employ ducts with additional stiffening corrugations while reducing the wall thickness to "relieve" duct suspension components that both secure the ductwork as well as preserve its rigidity.

Airtightness vs. spiral ductwork

The increasing demand for airtight ventilation systems, in order to minimize any leakages, is influenced by the rising trend of energy efficiency. As a result, if our project demands the highest airtightness class, we should seek for ventilation systems that have as few duct connections and joints as feasible, as well as a highly efficient sealing technology. Circular ducts are considerably superior to rectangular ones in terms of ductwork airtightness.

When compared to rectangular ductwork, spiral ducting has significantly fewer "duct-to-duct connections," lowering the risk of leakage. The standard length of a spiral duct is 3 meters, though we can easily manufacture ducts up to 12 meters, while the typical length of a rectangular duct is 1 to 1.5 meters.

If the production processes are perfect, the lockseam, which is the overlap of metal sheet that the spiral duct machine makes, should be airtight. However, if necessary, the lock seam can be sealed again. A sealing compound, such as an EPDM seal or a high-temperature silicone, can be used to seal the spiral pipe's lock seam. For example, one of our clients employed a spiral ductwork system with NBR seals for oil mist applications, which necessitated extra sealing.

Spiral ducts and duct fittings are joined with slide-in connections in airtightness class B, protected against disconnection with sheet metal screws or rivets, and sealed with a 50 + 100 mm wide self-adhesive sealing tape composed of polyethylene (PE) wrapped with fabric.

Spiral ducts and duct fittings in airtightness class D are joined with slide-in connectors and secured with self-tapping screws or tight rivets to prevent separation. EPDM rubber seals are installed at the factory on duct fittings to keep leaks at bay.

The question remains: can high airtightness standards be met with good quality spiral ductwork? Unfortunately, this is not the case. We need to work as a team to achieve airtightness class D, which means a duct manufacturer or wholesaler must supply high-quality ducts and fittings with airtight seals. Following that, these components must be transported and stored in a safe manner to avoid potential harm, such as seal breakage. Finally, when it comes time to install the ducting, it must be done to the highest standards possible.