US 3864814 A
A method is disclosed by which duct sections made of sheet metal can be joined, especially transversally, and which is based on the known art of providing the edges to be joined with bends, which are held together by a correspondingly bent strip, which is pushed over said bent edges. The improved method of the present invention ensures superior tightness of the seams as well as greater rigidity of the duct entities than before, and it is particularly characterized in that the bends made on the duct edges are half-closed (bent at an angle between 90 DEG and 180 DEG ) as opposed to fully closed (180 DEG ) bends in prior art, that a strip of a packing material is placed in the seam, and the seam is secured with a push-on strip having a substantially triangular cross section. This latter operation is performed with the aid of a special tool, which urges the central part of the strip against the packing and simultaneously supports the lateral components wings of the seam from below or even raises them.
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Description (OCR text may contain errors)
United States Patent [191 Bagge I SEAMING METHOD FOR SHEET METAL DUCTS  Inventor:
 Assignee: Valmet y, Helsinki, Finland  Filed: June 22, 1973 [211 App]. No.: 372,705
John Bagge, Turku, Finland Foreign Application Priority Data July 3, 1972 Finland 1890/72  US. Cl. 29/514, 113/54  Int. Cl. BZId 39/02  Field of Search 29/509, 514, 243.5, 243.56, 29/243.57, 243.58; 113/54, 55, 56; 220/81 Primary Examiner-Richard J. Herbst Attorney, Agent, or Firm-Richards & Geier [111 3,864,814 Feb. 11, 1975  ABSTRACT A method is disclosed by which duct sections made of sheet metal can be joined, especially transversally. and which is based on the known art of providing the edges to be joined with bends, which are held together by a correspondingly bent strip, which is pushed over said bent edges. The improved method of the present invention ensures superior tightness of the seams as well as greater rigidity of the duct entities than before. and it is particularly characterized in that the bends made on the duct edges are half-closed (bent at an angle between and as opposed to fully closed 180) bends in prior art, that a strip of a packing material is placed in the seam, and the seam is secured with a push-on strip having a substantially triangular cross section. This latter operation is performed with the aid of a special tool, which urges the central part of the strip against the packing and simultaneously supports the lateral components wings of the seam from below or even raises them.
Further, optional characteristics specify an advantageous cross section shape of the packing strip and additional bending operations concerning the lateral wings of the seam and intended to impart the completed ducting greater rigidity.
3 Claims, 6 Drawing Figures SEAMING METHOD FOR SHEET METAL DUCTS The present invention concerns a method for seaming sheet metal ducts, especially transversal seaming of ducts, wherein a push strip joint is employed, composed of bends made of the edges of the walls of the ducts to be joined and of a strip to be pushed over these.
The seaming method specified above, wherein the bends provided on the edges of the walls of the duct to be joined are fully closed bends (bent about 180), upon which a push strip equally provided with two fully closed bends is pushed, is generallyemployed especially in transversal joining of sheet metal ducts. This seaming method is very well fit for use, but the tightness of the seam thereby achieved is unsatisfactory in numerous applications. Endeavours have been made to improve the tightness of such seams by means of various paints and fillers, but without success. The rigidityincreasing effect of such seams on the duct also leaves a lot to be desired. The drawbacks mentioned here have restricted the possible applications of the push strip joint, which is otherwise well appropriate for use.
The aim of the present invention is to avoid the drawbacks pointed out and to accomplish a simple seaming method based on the push strip joint. The aims of the invention are achieved in a method which is mainly characterized in that the edges to be joined are provided with half-closed bends, and the seam is provided with a packing and secured with a strip having a cross section of substantially triangular shape, and the seam thus obtained is made tight with the aid of a tool appropriate to this purpose by urging the central part of the strip against the packing, while at the same time supporting and/or raising the seam from under the strip.
The invention is described in detail with reference to certain seams accomplished in accordance with the invention, shown in the figures of the attached drawing. All these figures represent cross sections of seams.
FIG. 1a shows a seam according to the invention, already fitted with a push strip and a packing, prior to its final tightening and closure.
FIG. 1b shows the seam of FIG. 1a, finished to be tight.
FIG. 2a shows a raised seam prior to tightening, and FIG. 2b shows the same seam, finished to be tight.
FIG. 3a shows a seam which is wider than the preceding ones, and FIG. 3b shows the same seam, completed after its tightening and bending operations.
In the push strip joint of prior art both on the edges to be seamed, la and lb, of the duct and on the push strip 2 fully closed bends are used. In the method according to the invention, however, on the duct wall edges Ia and 1b half-closed bends 5a and 5b are used, and corresponding half-closed bends are used on the push strip 2. In this connection, a half-closed bend is understood to mean that the edge has been folded to an angle between 90 and 180 (that is, the bend is intermediate between a straight upright and a fully closed bend). It follows that the push strip will have, prior to its pushing into place and to the seam-tightening operation, substantially the shape of a triangle which is open at one point (FIGS. 1a,2a and 3a). In order to increase the rigidity-inducing effect of the seam, the seam may be provided with a raised ridge 4 (FIGS. and 2b) and/or the seam may be made so wide that (FIG. 3) the wings 2, 5a and 2', 5b of the seam may be bent, for instance, to be substantially perpendicular to the wall of the duct (FIG. 3b).
In the method according to the invention a strip-like packing 3 is used, which has a cross section preferably similar in shape with the push strip 2 (in FIGS. Ia and 2a triangular). However, the shape and material of the packing 3 may vary within wide limits, depending on the particular application.
At the first stage of the seaming process the edges la and lb of the duct sections are provided with halfclosed bends 5a and 5b, the packing 3 is placed into position, and the push strip 2 is pushed over the packing 3 and the bends 5a and 5b in conventional manner. If required, the end of the push strip 2 may be provided with a tongue (not depicted), which is bent at an angle after the push strip 2 has been pushed into position. In this manner the untightened seams of FIGS. 1a, 2a and 3a are produced.
In the second phase of the seaming process a suitable traction tool (not depicted) is used to press the central part of the push strip 2 against the packing 3, while at the same time the tool supportsand/or raises the wings 2, 5a and 2, 5b of the seam, which are directed obliquely outward from the duct wall, by acting upon them in the wedge-shaped space between the wall and the wings. This enables the seam to be efficiently braced during the tightening operation. The same tool, or another tool, may be used to produce the rigidityinducing bends of FIG. 3b. The tool for use in the seaming operation just described may be designed in many different ways. The tool may be of the sliding type and provided with wedge-shaped pressing and supporting projections. Instead of a fixed tool, one may use an equivalent tool provided with rotatable rollers.
After the second phase just described, the seam is fin ished and has the appearance shown in FIGS. lb, 2b and 3b.
1. Method of seaming the opposed edges of sheet metal ducts, particularly for use in transversely seaming ducts, comprising:
providing on the edges to be joined, half-closed bends diverging from each other; placing upon the bends a packing;
uniting the bends with a strip having a substantially triangular cross-section and encircling the bends; and
tightening the seam produced by the above steps by pressing the central part of the strip against the packing and at the same time providing support of the seam under the strip, between the strip and the edges, so that the strip, thus pressed tight, assumes a V-shape projecting from the duct wall from its center towards its margins.
2. Seaming method according to claim 1, comprising partly bending the winds of the seam so that they are substantially perpendicular to the duct wall for additional rigidity.
3. Seaming method according to claim 1, wherein a packing having a substantially triangular cross-section isused.