GB2172359A

GB2172359A - Frame member for air ducts

Info

Publication number: GB2172359A
Application number: GB08512915A
Authority: GB
Inventors: Georg Mez
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-03-14
Filing date: 1985-05-22
Publication date: 1986-09-17
Also published as: DE3509080A1; FR2578948A1; FR2578948B1; JPH058344B2; DE3509080C2; JPS61213434A; GB2172359B

Abstract

A frame member for prefabricated flanges for reducing leakage losses and designed for above-atmospheric and below-atmospheric pressures in air ducts comprises a first longitudinal bead 22 forming the free end zone of an inner longitudinal web 16, an outer end face 23 of the first longitudinal bead being higher than the inner face 24 of the inner longitudinal web by at least one third of the thickness of the sheet metal, the inner longitudinal web having a second longitudinal bead 26 which is embossed into the push-in gap, and which has an arcuate cross-section and in size is embossed outwards to a height corresponding to around one-quarter to around the entire thickness of the sheet metal and areas 38 for pressure connection, eg spot welding, between the outer longitudinal web, a pushed-in sheet metal portion of a duct wall 36 and inner longitudinal web lies in the region between end face and second longitudinal bead. <IMAGE>

Description

SPECIFICATION Frame member for air ducts The invention relates to a frame member according to the preamble to the Main Claim.

Such frame members are produced from coil material on profile shaping machines. The sheet metal used is referred to by the designation It is galvanised on both sides. A main problem of these flanges is that they should be sufficiently tight, in most cases to withstand an above-atmospheric pressure prevailing inside them. They must however also be suitable for negative pressure situations although these are substantially rarer.

Furthermore, the configuration of the flanges should make them suitable both for low pressure ducts and also for medium and high pressure ducts. It would be desirable to be able to use the same configuration for different pressures, because one could then remain with the same system regardless of the pressure and not require special frame members for each situation or at least for extreme cases. At the same time, the frame member should not be so constructed that although it is properly tight at the maximum pressure likely to occur but owes this tightness to the provision of auxiliary expensive complicated measures which alter the system. This would mean that the right expense is laid out for the higher pressures but that money is wasted for the medium and lower pressures, and this would have an adverse effect on costs.Furthermore, as far as possible the frame member should fit into the standard, obviating the need for constantly new standards to be set down, and the less obtrusive the variations from the norm, the better. Such standards are for example the "Specification for sheet metal ductwork" D.W.

142 of the Heating and Ventilator Contractors' Association of 1982. Page 13 for example shows what is understood by the terms low pressure, medium pressure and high pressure duct, where the leakage limits lie, which bases of calculation are applied, etc. Flanges to which the invention could be applied are shown there in Figures 40 and 42. The invention could however also be applied to purely L-shaped frame members which have no supporting web.

As can be seen for example from Figure 42, higher pressures are absorbed by higher flanges and also by the use of thicker sheet metal, ranging from 0.8 mm to 1.25 mm thick. On grounds of economy, sheet metal to thicknesses down to 0.7 mm are already in use.

Naturally, the frame member must continue to be able to fulfil its main task, namely that of connecting two sections of duct to each other. This means that it must be very rigid mechanically. The loadings in this case may be quite high. Many companies run motor cars through the ducts when they have to be inspected. It is however also entirely normal for several men in a repair gang to go through the ducts or walk about in them. An additional loading is the fact that not only must the static pressures be resisted. Instead, the column of air in the air ducts is always in oscillation ranging in frequency from subsonic to super-sonic levels.

Also the spectrum of amplitudes of these frequencies is widely diverse.

In order to increase the sealing-tightness, it is possible for example to create pockets such as shown in Figure 41 of the above-mentioned Standards. Production of these pockets into which then the end zone of a duct section passes, make the manufacture of the frame members expensive although this is a field in which there is a very severe price war battling over tenths of a penny. On the other hand, such pockets can only be manufactured by bending the material over through 180 and then twice through 90 . This repre-sents excessive loading on the sheet metal and it is known from fundamental research that during this bending process the neutral zone travels quite a distance, material is squashed away in the upset zone and material starts to rupture in the traction zone.

This can be shown very easily by dipping a flange which has been bent in this way into a salt solution. After a few days, rust will be noted in these over-stressed areas.

It can also happen during these bending operations that the per se ductile galvanising coating becomes cracked and squeezed away by the rollers which produce this pronounced bending to and fro.

If the material of the metal sheets which are already becoming increasingly thinner is so maltreated, then naturally the weakest point will determine the overall quality just as the weakest link in a chain determines its overall quality. Expenditure applied elsewhere is then wasted.

The preamble to the Main Claim is based on German Patent Specification No. 32 07 990 which discloses on the inner longitudinal web two longitudinal beads which serve for sealing purposes.

However, the seal is not achieved by the longitudinal bead within the meaning of the present invention. Instead, these longitudinal beads serve to reinforce the inner longitudinal web and it is hoped as a result to avoid those distortions of the sheet metal material which occur due to the heat of spot welding. This is however quite a different basis of solution. Furthermore, the in-wardly shaped beads encourage leakage losses: these beads can however be regarded as tiny air connecting passages which extend over the entire length of the frame members and which connect to one another like nodal points all the air leakage paths which are present at this height.Viewed statistically therefore such a longitudinal bead joins leakage paths which lead to it from one side but which would not extend completely, to leakage paths which extend to it from the other side but which would not in themselves extent through to form a communicating system.

In the case of the known flange, this undertakes to satisfy the task of providing a seal, as aimed at by the invention, a pocket the sides of which must be bent with a high degree of accuracy so that the edge of the end zone of the pushed-in duct section bears on the top of the pocket rather like a knife edge seal.

The object of the invention is to indicate a way of arriving at substantially lower leakage losses without using such pockets and, in comparison with conventional flanges, achieveing this end in a simple way without weakening the flange and without having to adopt measures which burden the price.

According to the invention, this problem is resolved by the features disclosed in the characterising part of the Main Claim. At the same time, manufacturing conditions must not result in an increase of the tolerances conventional in this field of sheet metal working.

The sealing area formed by the end face is enlarged by the features according to Claim 2.

When the end zone of the duct section is pushed in, the longitudinal webs are spaced apart from each other by a definite distance, namely equal to the thickness of the sheet metal used for the duct section, as a result of the features according to Claim 3.

The effect of the features according to Claim 4 is that also the remaining area of the longitudinal webs are remote from each other#substantially by the same amount when the end zone of the duct section is pushed in.

By virtue of the features of Claim 5, only minimal shaping work is needed to produce the second longitudinal bead and it does not destroy the structure of the steel.

By reason of the features of Claim 6, this more intensely stressed zone is provided with even better material properties without the material there being deformed in a way which would destroy the structure.

In the case of the embodiment of the invention, the features according to Claim 7 produce improvements in sealing-tightness by the values shown in the table which is mentioned in the description.

The same applies to the features according to Claim 8.

By reason of the features according to Claim 9, broad zones of the second bead can serve as a sealing face.

As a result of the features according to Claim 10, this area is reduced in the direction of a knife-edge seal without entailing the drawbacks of a knifeedge seal.

The features according to Claim 11 result in the second bead being very satisfactorily braced by the transition - which of course represents a zone of particular rigidity.

The features according to Claim 12 mean that the tractive force generated by the through-connection (mostly a welding point) favours equally both the end face and also the crest.

The invention will now be described with reference to examples of embodiment shown to scale in the accompanying drawings, in which: Figure 1 is a cross-section through a frame member according to the invention with a pushedin cut corner angle arm; Figure 2 shows the cross-section through a second form of bead, and Figure 3 shows a cross-section according to Figure 1 but with the pushed-in end zone of the duct section and the spot weld.

Aframe member 11 has a push-in cavity 12 for an arm 13 of a corner angle not otherwise described in greater detail. Inter alia, it has an outer longitudinal web 14, an inner longitudinal web 16 and, merging into the outer longitudinal web 14 at an obtuse angle and a bend 17, a bracing web 18 which extends at approximately 450 to the horizontal. The outer longitudinal web 14 is flat all the way along and has at its left-hand end zone a short catcher lip 19. Thus far, it has the form of a frame member as already supplied for some long period by Messrs. Georg Mez GmbH & Co. KG of 7410 Reutlingen-2 under Art. No. 117. Also the other dimensions correspond to this known state of the art.

A dash-dotted line 21 extends perpendicularly and shows the location of the bend 17.

At its left-hand end, the inner longitudinal web 16 has a first channel-shaped longitudinal bead 22 which is a full 4.5 mm wide. Its cross-section is approximately circular. It has a free end face 23 which is 0.5 mm higher than the inside 24 of the inner longitudinal web 16. On the left, starting from the dash-dotted line 21, i.e. close to the bend 17, there is a second longitudinal bead 26 which is rolled into the push-in gap 27 which is altogether some 2.5 mm long extending arcuately with gentle transition radii. In the example shown, it is 2.5 mm long and according to the dimensional arrows indicated it projects 0.5 mm higher than the inside face 24. Its crest zone 28 touches the inner face 29 of the outer longitudinal web 14. Therefore, the free end face 23 is just as high above the inner face 24 as is the crest zone 28.

The arrows 31 show the location of the throughconnection which will be applied later. These can be spot welds in the case of sheet steel ducts or may be rivets in the case of aluminium ducts. The invention is naturally suitable also for aluminium frame members and aluminium ducting sections.

The longitudinal bead 22 may be empty or may contain perma-nently plastic sealing material, the upper surface of which will then be higher than the free end face 23.

In the case of the embodiment shown in Figure 2, the second longitudinal bead 32 is more Vshaped, compared with the longitudinal bead 26.

Rolling here has been carried out in such a way that the oppositely disposed rolls produce a higher pressure in the middle zone 33 so that the material in the middle zone 33 becomes compressed. The crest-zone of the longitudinal bead 32 is however not sharp edged but is likewise rounded.

Figure 3 shows the apparatus in a spot welded state. With the invention, the hitherto conventional spacing of spot welds can be maintained. Therefore, the number of spot welds need not be increased. As Figure 3 shows, the free end face 23 bears on the inner face 34 of the duct section 36.

Furthermore, that is where the crest zone 28 rests.

The outer longitudinal web 14 lies substantially flat on the outside 37 of the duct section 36. The spot weld 38 brings the partial zone 39 located between the first and second longitudinal beads 22, 26 up to the inner face 34. As a result, the partial zone 39 bends to an acceptable extent and the free end face 23 and the crest zone 28 are pressed with sealing-tight force against the inner face 34.

If the longitudinal bead 22 has been oversized to a certain degree with a permanently plastic seal, then a part of the oversized volume is located in the wedge-shaped gap 41 because it was scraped off on the left-hand flank of the longitudinal bead 26 (or 32) and an internal pressure in the duct section 36 pushes the permanently plastic material still farther into the wedge-shaped gap 41. The bend helps the outer longitudinal web 14 to be braced against the pressure of the crest zone 28.

Normally, the sheet metal of the duct section is 0.7 mm thick.

The table which is part of the drawings shows what effect at pressures of 500 to 2500 Pascals the invention has compared with flanges 117, 120 and 120 S which are available on the market. What is important therefore is essentially the height of the longitudinal bead 26. Accordingly, the optimum height is 0.5 mm for a pressure of 500 Pascals.

This produces an improvement of 60%, which can be regarded as a jump and, in spite of its slight tolerances, as quite unexpected in the field with which we are concerned. None-theless, at 500 Pascals and with a sealing bead height of 0.3 to 0.7 mm, an improvement of 34% can nevertheless be anticipated, which is likewise substantially more than that which might be expected on average.

Also with a pressure of 2500 Pascals, and for a sealing bead height of 0.5 mm, the improvement is nevertheless 47% which, viewed in the absolute, must be regarded as outstanding, which also shows that the same measure has an excellent effect over pressure differentials of 1:5.

The improvements are even higher compared with the flange 120. While the flange 117 is made from sheet metal 0.7 mm thick, the thickness of the emtal sheet used for the flange 120 is 0.8 mm.

The flange 120 is a pocketed flange and as can be seen, even without a pocket, the results are quite close to the values attained.

Measurement of the leakage losses of the profile 117 with longitudinal bead 26 was made without adding thermoplastic composition.

Claims

1. Frame member for prefabricated flanges designed to reduce leakage losses from air ducts and capable of withstanding above-atmospheric and below-atmospheric pressures, said frame members being hollow metal profiled sections, with a pushin gap for the end portion of a duct section, said push-in gap being formed by an outer longitudinal web and an inner longitudinal web in the overlapping zone thereof, with a supporting web which merges at an obtuse angle and in one piece into the outer longitudinal web, and with, serving as a seal, two parallel longitudinal beads on the inner longitudinal web, of which the more outwardly situated first bead is directed away from the push-in gap and extends parallel with the frame member, characterised by the following features:: a) the first longitudinal bead forms the free end zone of the inner longitudinal web, b) the outer end face of the first longitudinal bead is higher than the inner face of the inner longitudinal web by an amount equal to a part of the thickness of the sheet metal used for the frame member but is at least one-third of the thickness of the sheet metal; c) the inner longitudinal web comprises the second longitudinal bead which is embossed into the push-in gap and which is situated shortly before the transition between the outer longitudinal web and the supporting web, and which has an arcuate cross-section and which in its sise is pressed out to a height corresponding to roughly one quarter to roughly the entire thickness of the sheet metal;; d) the zone for pressure connection of outer longitudinal web, a pushed-in sheet of a duct wall and inner longitudinal web is located in the region between the end face and the second longitudinal bead.

2. Frame member according to Claim 1, characterised in that the end face of the first longitudinal bead extends parallel with the inner face of the first longitudinal web.

3. Frame member according to Claim 1, characterised in that the crest zone of the second longitu dinal bead, when the sheet metal is not in a pushed-in condition, bears on the inner face of the outer longitudinal bead.

4. Frame member according to Claim 1, characterised in that the inner and outer longitudinal web extend substantially parallel with each other when the sheet metal is not pushed in.

5. Frame member according to Claim 1, characterised in that the arcuate cross-section of the second longitudinal bead has gentle transition radii.

6. Frame member according to Claim 1, characterised in that the second longitudinal bead has more intensely compressed material in the arcuate zone.

7. Frame member according to Claim 1, characterised in that the height of the second bead is 0.7 (-60% t 140%) of the thickness of the sheet metal used for the frame member.

8. Frame member according to Claim 1, characterised in that the height of the second bead is 0.7 (-20% + 80%) of the thickness of the sheet metal used for the frame member.

9. Frame member according to Claim 1, characterised in that the second bead is approximately half-round.

10. Frame member according to Claim 1, characterised in that the second bead has the crosssection of a flat V.

11. Frame member according to Claim 1, characterised in that the second bead starts where the supporting web merges into the outer longitudinal web.

12. Frame member according to Claim 1, characterised in that the zone for the through-connec tion lies in the region of half the distance between the end face and the crest of the second longitudinal bead.

13. Flange using four frame members according to one or more of the preceding Claims.

14. Frame member for prefabricated flanges as claimed in Claim 1, substantially as described herein with reference to and as illustrated by any one of the examples shown in the accompanying drawings.

15 Flange as claimed in claim 13, substantially as described herein.