GB2196105A - Ventilation damper blade - Google Patents

Abstract

The invention relates to a blade for use in a fluid damper, the blade being made by bending a sheet metal blank into an elongate U-section channel member and bringing the longitudinal edges (22, 24) of the channel together to form a trailing edge of the blade, in which the longitudinal edges of the channel are of rolled form with one edge (24) being rolled onto the other roller edge (22) to increase the resistance of the blade to bending and twisting stresses while avoiding the necessity for any welding at the blade trailing edge. <IMAGE>

Description

SPECIFICATION Damper blade This invention relates to blades for use in fluid dampers. In particular, it relates to damper blades which are so mounted in a damper as to be rotatable about respective axes extending lengthwise of the blades in order that they move between a position in which the blades close a passage through the damper and a fully open position in which they allow the free passage of air or other gaseous fluid through that passage. Such dampers are widely used in air ventilation systems.

Nowadays it is quite usual for damper blades to be made by bending a sheet of metal-for example, stainless steel-into a U and bringing the edges of the U together to form the trailing edge of the blade. In some forms of blade the two edges of the U are directly spot-welded to each other. In other cases, one of the edges is bent over the other edge prior to the spot-welding operation. Another way of connecting the edges of the U together is by enclosing them in a Vsection strip which is then spot-welded to those edges.

By way of illustration, these three prior methods of welding the edges of the U together are shown in Figures 1-3 respectively of the accompanying drawings. Thus, Figure 1 shows a blade wherein the edges are spotwelded at 10 directly to each other. Figure 2 shows a blade wherein one of the edges is turned over the other at 12 prior to the spotwelding operation and Figure 3 shows a blade wherein the edges are enclosed in a V-section strip 14 which is then spot-welded at 10 as in Figures 1 and 2.

Welded blades of the construction shown in Figures 1-3 have proved satisfactory in use but they are not especiaily resistant to bending or twisting stresses. Accordingly, in GB-A2,153,265 we have proposed an improved damper blade wherein the edges of the sheet of metal which are brought together to form the blade trailing edge are of castellated form, so that they interlock together, with the castellations being bent, turned or rolled over so as to embrace a reinforcing locking rod. The construction of this form of blade is illustrated in Figures 4-6 of the accompanying drawings, the bent-over castellations being shown at 16 and the locking rod at 18.

Such a blade provides a 50% or more increase in resistance to bending or twisting stresses as compared with the blades shown in Figures 1-3. However, the castellations must be accurately stamped and bent over, and this causes manufacturing difficulties.

The present invention is therefore concerned with a better solution to the problem outlined in connection with Figures 1-3, and according to the invention the edges of the sheet of metal which are brought together to form the blade trailing edge are of rolled form with one edge being rolled onto the other rolled edge.

An example of a damper blade in accordance with the invention is shown in the accompanying drawings, in which Figure 7 is a perspective view of a metal strip or blank from which the blade is to be formed; Figure 8 is a perspective view of the blank after it has been bent into a U shape; Figure 9 is a perspective view of the blade with the edges of the blank destined to form the blade trailing edge being in engagement with each other; Figures 7a, 8a and 9a are end views of the blank or blade corresponding to that is shown in Figures 7-9, respectively; and Figure 10 is an enlarged end view of the blank.

The metal blank shown in Figure 7 can be cut or stamped from a strip drawn off a large roll and can be of stainless steel, galvanised sheet steel, aluminium alloy, brass or bronze to name but a few metals which can be used in producing a blade in accordance with the invention. A wide choice of metals is available because the construction of the blade is not dependent on a welding operation. The blank has projections 20 at its ends to permit it to be used in conjunction with retaining means (not shown) for retaining it on a blade support in a fluid damper.

One longitudinal edge 22 of the blank 18 is rolled over into an O-section or C-section as shown at the left-hand side of Figures 7 and 7a, while the other longitudinal edge 24 is bent over into the form of an open hook as shown at the right-hand side of Figures 7 and 7a. The blank is then bent into a U as shown in Figures 8 and 8a, after which the two edges 22 and 24 are brought into engagement with each other so as to permit the hooked edge 24 to be rolled onto the O-section or C-section edge 22. In this way the edge 24 is likewise formed into a C-section and, as such, it tightly embraces the edge 22.

This is illustrated by Figures 9 and 9a.

Figure 10 indicates typical dimensions for a particular blade in accordance with the invention.

The rolling of the edge 24 onto the initially rolled edge 22 produces a very rigid blade trailing edge equivalent to that obtained in the blade shown in GB-A-2,153,265. The manufacture of the present blade is, however, much simpler and causes fewer problems as compared with the blade shown in that prior Application.

It is to be understood that the term "rolled" is not to be interpretted so strictly as to exclude blade edges which are other than 0section or C-section. The edges could, for example, be of box-section, triangular-section or U-section. The invention extends therefore to any blade edges which are bent over, one onto the other, so as to form a double-thickness trailing edge.

Although the invention finds particular application in dampers where the blades are required to rotate through an angle of 360 degrees, the invention is not restricted to that particular use of the blades.

Claims (9)

1. A blade for use in a fluid damper, the blade being made by bending a sheet metal blank into an elongate U-section channel member and bringing the longitudinal edges of the channel together to form a trailing edge of the blade, in which the longitudinal edges of the channel are of rolled form with one edge being rolled onto the other rolled edge to increase the resistance of the blade to bending and twisting stresses while avoiding the necessity for any welding at the blade trailing edge.

2. A damper blade according to claim 1, in which the blade has projections at its ends to permit the blade to be retained on blade end supports in a fluid damper.

3. A damper blade according to claim 1 or claim 2, in which the rolled-over longitudinal edges are of O-section, C-section, box-section, triangular-section or U-section.

4. A damper blade according to claim 1 or claim 2, in which one longitudinal edge is first rolled over into an O-section or C-section while the other longitudinal edge is bent over into the form of an open hook, whereafter the hooked edge is rolled onto the O-section or C-section edge after the blank has been bent into a U.

5. A damper blade according to any preceding claim, in which the longitudinal edges are rolled onto one another throughout their length.

6. A damper blade according to any preceding claim, in which the blank is stamped from a metal strip.

7. A damper blade according to any preceding claim, in which the blade is formed from a blank of stainless steel, galvanised steel, aluminium alloy, brass or bronze.

8. A damper blade substantially as described herein with reference to Figures 7-10 of the accompanying drawings.

9. A fluid damper incorporating blades as claimed in any preceding claim.