US3677047A

US3677047A - Forming of tubular metal ducting

Info

Publication number: US3677047A
Application number: US24554A
Authority: US
Inventors: Noel Victor Holyoake; David William Barr
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-04-03
Filing date: 1970-04-01
Publication date: 1972-07-18
Anticipated expiration: 1989-07-18

Abstract

Apparatus for forming spiral lock seamed ducting from flat strip metal material, the apparatus employing or adapting a machine having at least one pair of driven lock forming rollers with cooperating peripheries and which are capable of drawing flat metal strip from a supply source and shaping opposite longitudinal edge portions of said strip so that one edge portion is capable of being interlocked with the other. In the present invention a circular forming head is provided at the output end of the lock forming machine and wit its axis transversely of and angled to the feed path of lock formed strip fed from the machine so that strip fed through an aperture in the forming head will follow a helical path in such forming head to emerge from one open end of the forming head as spiral formed tubular ducting, the angle of the forming head relative to the strip feed path determining the pitch of the helical path and providing that the leading edge portion of one circumvolution and the trailing edge portion of a preceding circumvolution will overlap. The forming head is provided with an inner curved forming member adjacent the strip inlet to the forming head and co-operating with an inner circumferential bearing surface of the forming head and disposed so that the strip passes between the forming member and the said bearing surface. A tuck-in member extends partly into the forming head adjacent the strip inlet thereto and is arranged to tuck or fold one edge portion of the strip into the opposite complementary shaped edge portion of the next circumvolution; in addition there is provided a compression means which can be in the form of a pair of co-operating rollers disposed so that overlapping edge portions of adjacent circumvolutions are passed therebetween and can be compressed to form a locked seam to the tubular ducting formed by the apparatus.

Description

United States Patent Holyoake et al.

[451 July 18, 1972 541 FORMING 0F TUBULAR METAL DUCTING [72] Inventors: Noel Victor Holyoake, 34 The Cresent; David William Barr, 22a Abbot Road, Ngaio, both of Wellington, New Zealand [22] Filed: April 1,1970

[21] Appl.No.: 24,554

3,538,728 11/1970 Trihey ...72/49 2,136,943 1 1/1938 Freeze ..72/49 FOREIGN PATENTS OR APPLICATIONS 1,080,770 8/1967 Great Britain ..72/49 Primary Examiner-Charles W. Lanham Assistant Examiner-R. M. Rogers AttarneyHolman and Stern 57 ABSTRACT Apparatus for forming spiral lock seamed ducting from flat strip metal material, the apparatus employing or adapting a machine having at least one pair of driven lock forming rollers with co-operating peripheries and which are capable of drawing flat metal strip from a supply source and shaping opposite longitudinal edge portions of said strip so that one edge portion is capable of being interlocked with the other. in the present invention a circular forming head is provided at the output end of the lock forming machine and wit its axis transversely of and angled to the feed path of lock formed strip fed from the machine so that strip fed through an aperture in the forming head will follow a helical path in such forming head to emerge from one open end of the forming head as spiral formed tubular ducting, the angle of the forming head relative to the strip feed path determining the pitch of the helical path and providing that the leading edge portion of one circumvolution and the trailing edge portion of a preceding circumvolution will overlap. The forming head is provided with an inner curved forming member adjacent the strip inlet to the forming head and co-operating with an inner circumferential bearing surface of the forming head and disposed so that the strip passes between the forming member and the said bearing surface. A tuck-in member extends partly into the forming head adjacent the strip inlet thereto and is arranged to tuck or fold one edge portion of the strip into the opposite complementary shaped edge portion of the next circumvolution; in addition there is provided a compression means which can be in the form of a pair of co-operating rollers disposed so that overlapping edge portions of adjacent circumvolutions are passed therebetween and can be compressed to form a locked seam to the tubular ducting formed by the apparatus.

13 Claims, 7 Drawing Figures FORMING OF TUBULAR METAL DUCTING This invention relates to the forming of tubular metal ducting and more particularly relates to the forming of ducting with a spiral locked seam from flat strip metal material. Ducting of this kind has many applications an example of which is the use of such ducting in heating and ventilating systems, the ducting of this nature being usually relatively light in weight and relatively cheap to manufacture as it may be manufactured from thin gauge metal such as galvanized steel strip or such as a light-weight alloy strip material.

Existing machines particularly designed for the purpose of forming such spiral lock-seamed tubular ducting can be expensive to produce and purchase and it is therefore an object of this invention to provide apparatus capable of being manufactured and sold at relatively low cost when compared with most known spiral lock-seamed ducting machines while being efficient in operation and adaptable for use with existing machinery, in particular machinery having lock forming rolls such as are more commonly in use in sheet metal working concerns. Other objects and advantages of the present invention will become apparent from the ensuing description.

According to this invention therefore there is provided apparatus for forming spiral lock-seamed tubular ducting from strip metal comprising an attachment for the output end of a machine having driven lock forming rollers, the attachment including a strip receiving circular forming head arranged for disposition with its axis transversely of and angled to the feed path of lock formed strip from the machine so that strip fed into the forming head will follow a helical path therein so as to emerge from the forming head as spiral formed tubular ducting, the angle of the forming head relative to the strip feed path determining the pitch of the helical path and providing that the leading edge portion of one circumvolution and the trailing edge portion of a preceding circumvolution will overlap, an inner curve forming member adjacent the strip inlet to the forming head and co-operating with an inner circumferential bearing surface of the forming head, the strip passing between said forming member and said bearing surface, a tuck-in member extending partly into the forming head adjacent the strip inlet thereto and arranged to tuck or fold one edge portion of the strip into the opposite complementary shaped edge portion of a next circumvolution, and compression means for compressing the overlapping and tucked in edge portions together in forming a locked seam to the tubular ducting formed.

In a further aspect of this invention, there may be provided apparatus for forming spiral lock-seamed tubular ducting comprising a machine having at least one pair of driven lock forming rollers with co-operating peripheries and which are capable of drawing flat strip metal from a supply source and shaping opposite longitudinal edge portions of said strip so that one edge portion is capable of being interlocked with the other, guide and retaining means to the output side of said lock forming rollers and directing the lock formed strip into an attachment including a strip receiving circular forming head arranged for disposition with its axis transversely of and angled to the feed path of lock formed strip from the machine so that strip fed into the forming head will follow a helical path therein so as to emerge from the forming head as spiral formed tubular ducting, the angle of the forming head relative to the strip feed path determining the pitch of the helical path and providing that the leading edge portion of one circumvolution and the trailing edge portion of a preceding circumvolution will overlap, an inner curve forming member adjacent the strip inlet to the forming head and cooperating with an inner circumferential bearing surface of the forming head, the strip passing between said forming member and said bearing surface, a tuck-in member extending partly into the forming head adjacent the strip inlet thereto and arranged to tuck or fold one edge portion of the strip into the opposite complementary shaped edge portion of a next circumvolution, and compression means for compressing the overlapping and tucked in edge portions together in forming a locked seam to the tubular ducting formed.

In a preferred form of the invention a lock forming and iongitudinal corrugation forming machine is adapted and provided with the attachment for forming the spiral lock-seamed tubular ducting so that the final product can, although constructed from a thin and light weight material, be strong and to some extent flexible so as to be particularly usable in the provision of heating and ventilating systems, the ducting being self-supporting over relatively long spans while being capable of being bent so as to negotiate obstacles and turn corners which might not be easily negotiated or turned when using conventional non-corrugated tubing.

The invention will accordingly be described by way of example in this form and with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side elevational view illustrating the general arrangement of a lock forming machine with strip metal being fed to one end and a spiral lock-seaming attachment at the other end, I

FIG. 2 is a diagrammatic plan view of the arrangement shown in FIG. 1,

FIG. 3 is an enlarged sectional view on line III-Ill of FIG. 1 and illustrating a typical metal strip issuing from the lock forming machine and prior to passing through the lock-seaming attachment,

FIG. 4 is a side view of the attachment, as viewed in the direction of arrow IV in FIG. 2 and without the metal strip or formed ducting,

FIG. 5 a rear side view of the attachment, as viewed in the direction of arrow V in FIG. 2 and without the metal strip or ducting,

FIG. 6 is a fragmentary sectional view on line VI-Vl of FIG. 4, illustrating also the joint being formed between adjacent circumvolutions of the strip, and

FIG. 7 is a fragmentary sectional view on line VIlVlI of FIG. 4 illustrating also the compressed and locked seam joint of the finished spiral ducting.

The machine, generally indicated by the arrow 1, may have a plurality of aligned pairs of rollers 2 between which strip material 3 can be passed; and such rollers 2 are shaped so as to progressively increase the number of longitudinal corrugations 3a formed in the strip 3, and provide the appropriately and complementary shaped or lock forming edge portions 3b and 30 to the strip 3 as the strip 3 passes along the machine 1 and between the rollers 2 towards the output end. In the illustrated arrangement the leading peripheral edge portion 3b of the strip 3 is, in cross section, generally V or U shaped and the other or trailing peripheral edge portion 30 is generally an inverted V or U shape. At least one of each pair of rollers 2 are driven so that the flat strip metal 3 is drawn from a supply source, which may be in the form of a reel 4 on a reel holder 4a, and the progressive deformation of such strip 3 provides a smoothly finished product without unsightly crinkles or creases such as could develop if a single pair of rolls formed all longitudinal corrugations 3a and the lock formed longitudinal edge portions 3b and 3c in one operation.

At the output end of the machine 1 the corrugated and lock formed strip 3 may be slidably located between a pair of retaining and

guide plates

5 and 6 which are formed with longitudinal corrugations 7 complementary to the corrugations 3a of the strip 3 and so that the strip 3 is maintained in its correct path and prevented from buckling as it passes into the forming head 8 of the attachment, generally indicated by the arrow 9, which is located at the outer end of the guide plates, 5 and 6. Side rollers or projections 10 may be provided on either side of the guide plates, 5 and 6, and arranged to bear against the longitudinal edges of the corrugated strip metal 3 so as to further guide and retain the strip 3 in its correct feed path. The side rollers or projection 10 may also serve to further turn the lock formed edge portions 3b and 3c in to the desired positions prior to entry of the strip 3 into the forming head 8.

The machine 1 may have a generally horizontal bed with the driven lock forming and corrugating rollers 2 mounted with parallel horizontally disposed axes, the metal strip 3 being thus fed onto and through and from the machine 1 while in a generally flat and horizontal plane.

The forming head 8 may be a hollow cylindrical member, the internal diameter of which defines the diameter of the tubular ducting (generally indicated by the arrow 11 to be formed, and such cylindrical forming head 8 is mounted at the output end of the lock forming and corrugating machine 1 with its axis in a horizontal plane and transversely of and above the feed path of the metal strip 3, but angled so as to determine the pitch of the helical path of the metal strip 3 fed into the forming head 8 and emerging as spiral formed ducting 11. The angle of the forming head 8 is also such that the lock formed edge portion 3b of one circumvolution of the strip 3 will overlap so as to be matable with the complementary opposite edge portion 3c of the next circumvolution of the strip 3.

The cylindrical forming head 8 is located with its axis above the strip feed path so that the strip 3 may be fed tangentially through an inlet aperture or slot 12 in the base part of the forming head 8.

The inlet for the metal strip 3 is toward one end of the cylindrical forming head 8 and an inner curve forming member which is preferably in the form of a roller 13 of width substantially equal to the width of the strip 3, extends from a mounting 14 at the inlet end of the forming head 8, into the forming head 8 and over the strip 3 passing thereinto at the inlet 12 so that the inner curve forming roller co-operates with the inner circumferential bearing surface 8a of the forming head 8 at that position and commences the spiral rolling of the strip 3 so that the strip 3 will be turned and curved to following the helical path prescribed within the forming head 8. The inner curve forming roller 13 will have its axis generally horizontal but substantially at right angles to the line of the strip 3 and thus angled relative to the axis of the cylindrical forming head 8.

A tuck-in roller 15 may be located below and at the outer end of the inner curve forming roller 13 and disposed with its axis inclined to the vertical, for example at about 40 to the vertical, so as to be capable of engaging the lower or outer side of the leading longitudinal edge portion 3b of the strip 3 and tucking or folding such edge portion 3b into the inverted channel part of the opposite longitudinal edge 3c of a preceding circumvolution of the strip 3. The tuck-in roller 15 may extend into and through an aperture 16 in the base of the cylindrical forming head 8 and from a mounting l7 therebelow. The tuck-in roller 15 may be provided with an annular groove 15a towards its upper free end and which can mate with the said leading peripheral edge portion 3b of the strip 3.

The compression means for compressing the overlapping and tucked in edge portions 3b and 3c of the circumvolutions may be in the form of co-operating rollers, 18 and 19, close to the inner curve forming roller 13 and tuck-in roller 15 but on the side remote from the strip inlet 12 to the forming head 8. One compression roller 18 is rotatably mounted on a mounting 20 outside the cylindrical forming head 8 but has a peripheral portion extending through an aperture 21 in such head 8 in the path of a helically formed seam of the circumvolutions, the axis of such first compression roller 18 being generally at right angles to the line of such seam. This outer roller 18 preferably has an annular peripheral projection 18b which is locatable in a longitudinal corrugation, 3a of the strip 3 adjacent the leading longitudinal edge 3b thereof and the second roller 19 of the compression means is located within the forming head 8 and is arranged to have its peripheral edge portion bear on the mated edge portions 3b and 3c of adjacent circumvolutions and thus, in co-operation with the outer roller 18, to compress such mated edge portions 3b and 3c and form a locked seam to the tubular ducting 11 formed. The inner roller 19 may extend from the mounting 14 at the inlet end of the forming head 8 but in a preferred arrangement, and as illustrated, both

compression rollers

18 and 19 extend from a common mounting 20 which is detachable engageable with the forming head 8 from the inlet end thereof. The axis of either compression roller, 18 or 19, can be angled slightly relative to the other to assist in forming a neat compressed seam to the ducting 11.

Various adjustment means can be provided for the spiral locked seam ducting attachment 9 and by way of example either or both

compression rollers

18 or 19 can be mounted eccentrically of their

mounting shafts

18a and 19a extending through an aperture in their mounting 20 at the inlet and of the forming head 8 so that partial rotation of either such mounting shaft, 18a or 19a, may vary the distance between the co-operating peripheral surfaces of the inner and

outer compression rollers

19 and 18, respectively, and may thus be adjusted to suit various thicknesses of metal and formed joint. The outer ends of both

shafts

18a and 19a may extend beyond their mounting 20 and be shaped to be engaged by a key or spanner for adjustment purposes and a locking means such as an Allen screw or a stud 22 for each mounting shaft, 180 and 19a, can be provided in the mounting 20 so that when tightened onto such shafts, 18a and 19a, they are prevented from turning.

Similarly, (but not illustrated) the inner curve forming roller 13 can be mounted eccentrically on a shaft, extending through a similar aperture in the mounting 14 at the inlet end of the forming head 8 so that partial rotation of this shaft can effect variation or adjustment of the inner curve forming roller 13 relative to the co-operating inner circumferential bearing surface 8a of the forming head 8 to accommodate various thicknesses of metal and accommodate metal strip 3 with or without corrugations 3a or with corrugations 3a of different depth. However, in a preferred form of the invention (and as illustrated) the inner curve forming roller 13 is rotatably mounted on a shaft 13a which spring influenced so that the curve forming roller 13 is normally biased onto the inner face of the strip 3 being fed into the forming head 8 but in a manner permitting some trans-axial movement of the roller 13 to prevent jamming of the strip 3 occurring, as could happen if the location of the roller shaft 13a were fixed relative to its mounting l4 and the forming head 8. In the illustrated arrangement the shaft 13a extends from a block 14a slidably located in a vertical slot 14b of the mounting l4 and influenced by at least one compression spring within such slot 14b.

Similarly the tuck-in roller 15 may be adjustable axially by any suitable means for use with various thicknesses and shapes of metal strip 3.

In a preferred form of the invention the inner wall of the forming head 8 is provided with a detachable circumferential bearing surface strip 8a within which the first circumvolution is formed. By this arrangement the forming head 8 is stepped in internal diameter thus permitting slight expansion of the circumvolutions after forming and freedom of movement without binding within the remainder of the forming head 8 prior to emerging therefrom as formed tubular ducting 11. Also, by making such bearing surface 8a replaceable it may also act as a wearing surface so that it is not necessary to remove or replace the entire forming head 8 when undue wear takes place through use.

A lubricant may be fed to the forming head 8 through a conduit 23 connected to a suitable supply source, the lubricant being fed between the spiral duct 11 being formed and the inner wall of the forming head 8.

The attachment 9 including the forming head 8 and associated parts may be provided with such as a clamp mounting whereby it may be easily and quickly clamped onto, or subsequently detached from, an existing lock forming machine so that such machine may be readily available for normal uses when spiral formed ducting is not required. It is to be appreciated however that a lock forming machine can be adapted and permanently or semi-permanently converted to spiral duct forming apparatus in accordance with the invention.

Thus, by this invention, the smaller manufacturing concerns may be readily able to purchase a low cost spiral duct forming attachment for use temporarily or permanently with an existing lock forming machine and thus can save the considerable expense of a large machine particularly designed only for the manufacture of spiral lock form tubular ducting.

Particular forms of the invention have been described by way of example but it will be appreciated that other variations of and modifications to the invention may take place without departing from the scope of the appended claims.

We claim:

1. Apparatus for forming spiral lock-seamed tubular ducting from strip metal comprising an attachment for the output end of a machine having driven lock-forming rollers, the attachment including a strip receiving circular forming head arranged for disposition with its axis transversely of and angled to the feed path of lock formed strip from the machine so that strip fed into the forming head will follow a helical path therein so as to emerge from the forming head as spiral formed tubular ducting, the angle of the forming head relative to the strip feed path determining the pitch of the helical path and providing that the leading edge portion of one circumvolution and the trailing edge portion of a preceding circumvolution will overlap, a tuck-in member extending partly into the forming head adjacent the strip inlet thereto and arranged to tuck or fold one edge portion of the strip into the opposite complementary shaped edge portion of the next circumvolution, and compression means for compressing the overlapping and tucked in edge portions together in forming a locked seam to the tubular ducting formed, and wherein an inlet aperture or slot for the metal strip is provided towards one end of the cylindrical forming head and an inner curve forming member in the form of a roller of width substantially equal to the width of the strip extends from a mounting at the inlet end of the forming head, into the forming head and over the strip passing thereinto at the inlet so that the inner curve forming roller cooperates with the inner circumferential bearing surface of the forming head at that position and commences the spiral rolling of the strip so that the strip will be turned and curved to following the helical path prescribed within the forming head; the inner curve forming roller having its axis generally parallel with the plane of the strip but substantially at right angles to the line of the strip so as to be angled relative to the axis of the cylindrical forming head.

2. Apparatus for forming spiral lock-seamed tubular ducting comprising a machine having at least one pair of driven lockforming rollers with cooperating peripheries and which are capable of drawing flat strip metal from a supply source and shaping opposite longitudinal edge portions of said strip so that one edge portion is capable of being interlocked with the other, guide and retaining means to the output side of said lock-forming rollers and directing the lock formed strip into an attachment including a strip receiving circular forming head arranged for disposition with its axis transversely of and angled to the feed path of lock formed strip from the machine so that strip fed into the forming head will follow a helical path therein so as to emerge from the forming head as spiral formed tubular ducting, the angle of the forming head relative to the strip feed path determining the pitch of the helical path and providing that the leading edge portion of one circumvolution and the trailing edge portion of a preceding circumvolution will overlap, a tuck-in member extending partly into the forming head adjacent the strip inlet thereto and arranged to tuck or fold one edge portion of the strip into the opposite complementary shaped edge portion of the next circumvolution, and compression means for compressing the overlapping and tucked edge portions together in forming a locked seam to the tubular ducting formed; and wherein an inlet aperture or slot for the metal strip is provided towards one end of the cylindrical forming head and an inner curve forming member in the form of a roller of width substantially equal to the width of the strip extends from a mounting at the inlet end of the forming head, into the forming head and over the strip passing thereinto at the inlet so that the inner curve forming roller cooperates with the inner circumferential bearing surface of the forming head at the position and commences the spiral rolling of the strip so that the strip will be turned and curved to following the helical path prescribed within the forming head; the inner curve forming roller having its axis generally parallel with the plane of the strip but substantially at right angles to the line of the strip so as to be angled relative to the axis of the cylindrical forming head.

3. Apparatus as claimed in claim 1 wherein the lock forming machine is provided with a plurality of aligned pairs of rollers between which the strip material can be passed and such rollers are shaped so as to progressively form a number of longitudinal corrugations in the strip in addition to forming complementary shaped or lock forming edge portions to the strip as the strip passes along the machine and between the rollers towards the output end, at least one of each pair of such rollers being driven.

4. Apparatus as claimed in claim 1 wherein a pair of retaining and guide plates are provided towards the output end of the machine and between which the strip may pass prior to entry into the forming head, the retaining and guide plates having a cross-section complementary to the cross-section of the strip passing therethrough.

5. Apparatus as claimed in claim 4 wherein side rollers or projections are provided on either side of the guide plates and arranged to bear against the longitudinal edges of the strip metal so as to further guide and retain the strip in its correct feed path as it leaves the guide plates and passes into the forming head.

6. Apparatus as claimed in claim 1 wherein the tuck-in member is in the form of a tuck-in roller located in juxtaposition with the outer end peripheral part of the inner curve forming roller and is disposed with its axis angled relative to the axis of the inner curve forming roller so that the tuck-in roller is capable of engaging the outer side of the leading peripheral edge portion of the strip and tucking or folding such edge portion into an inverted channel part of the opposite longitudinal edge of a preceding circumvolution of the strip, the tuckin roller extending into and through an aperture in the cylindrical forming head from a mounting exteriorly of the forming head and the periphery of the tuck-in roller being shaped so as to be matable with the said leading peripheral edge portion of the strip on which it can bear.

7. Apparatus as claimed in claim 1 wherein the inner curve forming roller is mounted eccentrically on a shaft extending through an aperture in a mounting at the inlet end of the forming head so that partial rotation of this mounting shaft can effect variation or adjustment of the inner curve forming roller relative to the co-operating inner circumferential bearing surface of the forming head.

8. Apparatus as claimed in claim 1 wherein the inner curve forming roller is rotatably mounted on a shaft which is spring influenced so that the curve forming roller is normally biased onto the inner face of the strip being fed into the forming head but in a manner permitting some trans-axial movement of the roller.

9. Apparatus as claimed in claim 8 wherein the shaft of the inner curve forming roller extends from a block slidably located in a slot of a mounting and such block is influenced by at least one compression spring within such slot.

10. Apparatus as claimed in claim 1 wherein the forming head is provided with a detachable circumferential bearing surface strip within which the first circumvolution is formed.

11. Apparatus as claimed in claim 1 wherein the compression means for compressing the overlapping and tucked edge portions of the circumvolutions of the strip is in the form of a pair of co-operating rollers one of which is rotatably mounted exteriorly of the forming head and has a peripheral portion extending through an aperture in such forming head in the path of a helically formed seam of the circumvolutions, the axis of such first outer compression roller being generally at right angles to the line of the seam, this outer roller having an annular peripheral bearing surface over which the outer surface of the helically formed seam of the circumvolutions can pass and the second compression roller being located within the forming head and having its periphery arranged to bear on the inner surfaces of mated edge portions of adjacent circumvolutions and thus, in co-operating with the outer roller, to compress the mated edge portions and form a locked seam to the tubular ducting formed by the apparatus.

13. Apparatus as claimed in claim 11 wherein at least one of the compression rollers is mounted eccentrically of a mounting shaft extending through an aperture of a mounting at the inlet end of the forming headso that partial rotation of such mounting shaft can adjust the distance between the co-operating peripheral surfaces of the inner and outer compression rollers, there being locking means for securing the mounting shaft in the desired location.

i k i i

Claims

2. Apparatus for forming spiral lock-seamed tubular ducting comprising a machine having at least one pair of driven lock-forming rollers with cooperating peripheries and which are capable of drawing flat strip metal from a supply source and shaping opposite longitudinal edge portions of said strip so that one edge portion is capable of being interlocked with the other, guide and retaining means to the output side of said lock-forming rollers and directing the lock formed strip into an attachment including a strip receiving circular forming head arranged for disposition with its axis transversely of and angled to the feed path of lock formed strip from the machine so that strip fed into the forming head will follow a helical path therein so as to emerge from the forming head as spiral formed tubular ducting, the angle of the forming head relative to the strip feed path determining the pitch of the helical path and providing that the leading edge portion of one circumvolution and the trailing edge portion of a preceding circumvolution will overlap, a tuck-in member extending partly into the forming head adjacent the strip inlet thereto and arranged to tuck or fold one edge portion of the strip into the opposite complementary shaped edge portion of the next circumvolution, and compression means for compressing the overlapping and tucked edge portions together in forming a locked seam to the tubular ducting formed; and wherein an inlet aperture or slot for the metal strip is provided towards one end of the cylindrical forming head and an inner curve forming member in the form of a roller of width substantially equal to the width of the strip extends from a mounting at the inlet end of the forming head, into the forming head and over the strip passing thereinto at the inlet so that the inner curve forming roller cooperates with the inner circumferential bearing surface of the forming head at the position and commences the spiral rolling of the strip so that the strip will be turned anD curved to following the helical path prescribed within the forming head; the inner curve forming roller having its axis generally parallel with the plane of the strip but substantially at right angles to the line of the strip so as to be angled relative to the axis of the cylindrical forming head.

6. Apparatus as claimed in claim 1 wherein the tuck-in member is in the form of a tuck-in roller located in juxtaposition with the outer end peripheral part of the inner curve forming roller and is disposed with its axis angled relative to the axis of the inner curve forming roller so that the tuck-in roller is capable of engaging the outer side of the leading peripheral edge portion of the strip and tucking or folding such edge portion into an inverted channel part of the opposite longitudinal edge of a preceding circumvolution of the strip, the tuck-in roller extending into and through an aperture in the cylindrical forming head from a mounting exteriorly of the forming head and the periphery of the tuck-in roller being shaped so as to be matable with the said leading peripheral edge portion of the strip on which it can bear.

12. Apparatus as claimed in claim 11 wherein the inner and outer compression rollers extend from a common mounting which is detachably engageable with the forming head from the inlet end thereof.

13. Apparatus as claimed in claim 11 wherein at least one of the compression rollers is mounted eccentrically of a mounting shaft extending through an aperture of a mounting at the inlet end of the forming head so that partial rotation of such mounting shaft can adjust the distance between the co-operating peripheral surfaces of the inner and outer compression rollers, there being locking means for securing the mounting shaft in the desired location.