Field of the Invention This invention relates to a method of making a duct member, i.e. a length of duct of which a number can be joined end to end to form tubular ducting for, e.g., air and gas distribution systems. Background to the Invention

WO 2010/094385 ( PCT/EP2010/ 000433 ) published on 26 August 2010 discloses a tubular duct member comprising a plurality of sheet metal panels joined along adjacent longitudinal edges by cooperating folded sheet metal catches. The catches are pushed together such that respective detent surfaces on each catch engage behind one another to retain the edges of the sheets together. In some embodiments, an insulating panel is fixed to the various panels of the duct member.

It is an object of the present invention to provide an improved method of making a duct member. Summary of the Invention

The present invention provides a method of making a duct member comprising feeding sheet metal continuously from a roll, progressively folding the opposite edges of the sheet as it advances to form a respective folded metal catch along each edge, each catch including an upstanding wall defining with the main body of the sheet a shallow tray across the width of the sheet, dispensing a thermal

insulator in flowable form into the shallow tray as the sheet advances so that the thermal insulator spreads out to fill substantially the full width of the tray between the upstanding walls, the liquid thereafter solidifying to form a solid thermally insulating layer, and cutting the sheet transversely into individual panels having a respective catch along each edge for in-use push fit connection to a cooperating catch along the edge of an adjacent panel.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a duct panel produced according to an embodiment of the present invention. Figures 2 and 2 (a) show detailed views of assembled ducting including the duct panels of Figure 1.

Description of Embodiments of the Invention Figure 1 shows a duct panel produced according to an embodiment of the present invention. Figure 1(a) is an underneath plan view of a duct panel 100, Figure 1 (b) is a cross-section on the line B-B of Figure 1 (a) , and Figure 1 (c) is an enlarged cross-section similar to Figure 1 (b) .

As in WO 2010/094385 Figure 8, the panel 100 has male and female catches respectively running along opposite parallel edges. These catches are constructed and operate generally the same as the male and female catches 14', 16' of WO 2010/094385 Figure 8 and, accordingly, the same reference numerals have been applied. The following description will concentrate on the differences from WO 2010/094385, the basic operation of the catches being assumed.

The main difference is that each catch 14', 16' includes a respective upstanding wall 102, 104 formed by additional folding of the sheet metal at each edge of the panel through two 90 degree bends and one 180 degree bend, as shown in Figure 1(c) . These walls 102 and 104, together with the main body 106 of the panel 100 as a base, form a shallow tray across the width of the panel.

The panels 100 are produced continuously from a roll of sheet metal, the edges of the sheet being progressively folded as the sheet advances from the roll to form the catches 14', 16' and the upstanding walls 102, 104, the sheet then being cut transversely into individual panels. However, after the folding of the catches and the

upstanding walls, but before the sheet is cut into

individual panels, a liquid polyurethane (LPU) is

continuously dispensed into the shallow tray formed by the walls 102, 104 and the metal sheet. This flows sideways to fill the full width of the tray between the walls 102, 104 and rapidly cures (within minutes) to form a solid

insulating layer 110. Longitudinal and transverse

strengthening ribs 112 are formed in each panel by pressing before the application of the LPU. Finally, end flanges 118 as shown in the assembly drawing of Figure 2 and the detailed view of Figure 2 (a) , serving the same purpose as the integral flanges 18 in WO 2010/094385 Figures 1 to 4, are riveted (or alternatively spot welded) to the

transverse cut ends of each panel for fixing each panel to an adjacent panel.

In the preceding embodiment a hard polymer lining 114 is optionally sprayed onto the exposed surface of the

foam/insulating layer 110, Figure 1. This has two

advantages. First, it provides a hardened surface which serves to protect the underlying layer 110 when the ducts are being cleaned. Second, although the layer 110 has a certain amount of flame resistance, it can still be

flammable. The hard polymer lining is a flame retardant, and provides a higher fire resistance than the underlying material. The hard polymer layer 114 has a thickness of about 3mm, but could range in thickness from about 0.5mm, in contrast with the layer 110 which is typically 32mm-35mm thick but could be up to around 45mm thick. The flame retardant polymer 114 is preferably of the type produced by BASF under the mark Elastocoat C6325/105; or by Bollom Fire Protection (UK) under the mark BroFlame.

In embodiments of the invention where the assembled

ducting, for example as shown in Figures 2 and 2 (a) , includes an insulating layer 110 possibly coated with a polymer lining 114, a durable and relatively impervious internal lining is provided, by comparison with using for example Rockwool or equivalent as an insulator either within or around the ducting. This layer/lining does not accommodate rodents or harbour or promote the spread of bacteria, such as Legionella as readily as prior art systems. At the same time, the ducting can be transported in flat packed form and when assembled can provide a relatively airtight conduit for use in many applications.

In addition or as an alternative to the layer 114, an antimicrobial layer (not shown) can be added to the insulating layer 110. One suitable coating is produced by General Paints Ltd of Celbridge, Ireland under the mark Hygen

Ultra.

The invention is not limited to the embodiments described herein which may be modified or varied without departing from the scope of the invention.