GB2499818A

GB2499818A - Intumescent seal for fire damper blade

Info

Publication number: GB2499818A
Application number: GB1203540.8A
Authority: GB
Inventors: Michael Backham; Matthew Beavington; Emil Schmidt; Derek Ward
Original assignee: BSB ENGINEERING SERVICES Ltd
Current assignee: BSB ENGINEERING SERVICES Ltd
Priority date: 2012-02-29
Filing date: 2012-02-29
Publication date: 2013-09-04
Anticipated expiration: 2032-02-29
Also published as: GB2499818B; GB201203540D0

Abstract

A damper blade 5 for a fire damper is disclosed. The damper blade comprises a seal element 13a, 13b for forming a seal, in use, between the damper blade and a damper casing 1, the seal element comprising a first layer of non-flammable material impregnated with an intumescent material. The blade preferably consists of two steel discs 10a, 10b with two fibre glass seals impregnated with intumescent material. The blades may be held together by rivets 11a-11n which are positioned such that at least a region of the blade elements are movable and are forced away from each other when the intumescent material swells with increased temperature. The damper may be movable between open and closed positions, and may be retained in an open position by a temperature sensitive retainer. Above a predetermined temperature, the retainer releases the damper which is then urged to the closed position by a biasing member 8.

Description

1

DAMPER BLADE

This invention relates to a damper blade for a fire damper.

Fire dampers are used in air-flow ducting, such as is used in heating ventilation and air-conditioning (HVAC) systems, to prevent the spread of fire in a building 5 along the ducting. There is a wide variety of different types of fire damper available. One type that is commonly used in HVAC systems falls comprises a tubular casing for installation in a length of ducting and circular blade within the body. The casing and blade are typically made of steel. The damper blade pivots between open and closed positions on an axle supported centrally within 10 the damper casing.

Such dampers are typically installed in a duct where it passes through a wall or floor. In the event of a fire, the heat causes the damper blade to close, thereby maintaining fire integrity where the duct passes through the wall or floor.

Prior to 1991, fire dampers were straightforward to manufacture because the 15 requirement of the relevant standard (BS476 part 20) at that time were not onerous. When fire tested, a damper was considered satisfactory provided that a 6mm diameter rod could not pass between the damper blade and casing over a gap along the perimeter of the damper blade of 150mm or more and that a 25mm diameter rod could not pass between the damper blade and 20 casing at any point around the perimeter of the damper blade. Thus, it was sufficient to manufacture a fire damper in which the damper blade was simply of slightly smaller diameter than the interior diameter of the damper casing.

The currently applicable standard (EN1366-2) sets a more complicated test, involving creating a difference in air pressure across the fire damper and 25 measuring the leakage of air past the damper blade. This measurement is performed both under normal conditions and conditions simulating a fire.

One way of meeting the requirements of this test is to provide a seal around the perimeter of the damper blade. The seal is made from a non-flammable material such as fibreglass cloth and is sized to engage with the interior

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surface of the damper casing when the damper blade is in the closed position. However, the lifespan of this seal is limited under fire conditions because it becomes brittle, which can quickly cause it to become frayed and disintegrate, destroying the fire integrity of the seal. Furthermore, the fibreglass material is 5 porous and allows a significant amount of air leakage when the damper blade is closed.

In accordance with a first aspect of the invention, there is provided a damper blade for a fire damper, the damper blade comprising a seal element for forming a seal, in use, between the damper blade and a fire damper casing, 10 the seal element comprising a first layer of non-flammable material impregnated with an intumescent material.

The presence of an intumescent material in the seal element has two effects. Firstly, the intumescent material swells, as a result of the heat of a fire, to fill the gaps between the damper blade and the fire damper casing to improve the 15 initial integrity of the seal. Secondly, the intumescent material improves the longevity of the seal by binding the non-flammable material together and slowing the disintegration. The seal is effectively formed by the engagement of the non-flammable material with the fire damper casing (e.g. by wiping across it as the blade moves to a closed position) and the swelling action of the 20 intumescent material as it heats up. The intumescent also makes the seal relatively impermeable, improving its air leakage performance.

The seal element preferably further comprises a second layer of nonflammable material impregnated with an intumescent material.

The non-flammable material is typically a woven material.

25 Normally, the non-flammable material is fibreglass. A suitable material is Envirograf 400g glass cloth impregnated with fine graphite available from Intumescent Systems Limited of Envirograf House, Barfrestone, Dover, Kent, CT15 7JG, United Kingdom. The same company also manufactures a suitable intumescent material under the name Envirograf Multigraph No. 4.

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The damper blade may further comprise first and second blade elements separated by the seal element. These blade elements are typically made of a metal such as steel so as to be rigid, fire resistant and non-flammable.

This arrangement of blade elements sandwiching the seal element provides a 5 straightforward way of supporting the seal element, which is typically very flexible, without increasing the thickness of the damper blade. It is important to minimise the blade thickness so that the air-flow impedance of a fire damper comprising the blade is kept to a reasonably low level when the blade is in an open position (i.e. under normal operating conditions). This ensures that the 10 pressure drop through a fire damper comprising the blade is minimised to maximise system efficiency. As an example, for a fire damper size of 100mm diameter, any damper blade thickness much above 5mm will not generally be considered acceptable.

In a preferred embodiment, at least a region of each of the first and second 15 blade elements is moveable away from each other under the influence of the intumescent material as it swells.

This relative movement apart of the damper blade elements allows the length of the seal (in the longitudinal direction of the damper casing) between the damper blade and the damper casing to increase as the intumescent swells. 20 This increases the longevity and general effectiveness of the seal under fire conditions without increasing the thickness of the damper blade (and thus increasing the flow impedance under normal operating conditions).

It is possible that the whole of the first and second blade elements move apart. However, the regions that are moveable are normally outer regions of the first 25 and second blade elements, inner regions of the first and second blade elements within the outer regions being immoveable.

In order to achieve this, the first and second blade elements are typically fastened together at the junctions of the inner and outer regions to render the inner regions immoveable relative to each other, whilst leaving the outer 30 regions free.

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The first and second blade elements may be fastened together by rivets. Alternatively, they may be fastened together by any other form of mechanical fixing, such as screws or bolts.

The seal element may lie between the moveable regions of the first and 5 second blade elements only.

Typically, the first and second blade elements are circular. However, in some embodiments, the first and second blade elements may be square or rectangular.

The seal element may be annular. This is possible because the seal is only 10 required around the periphery of the damper blade. Clearly, it reduces the amount of material required to produce a seal element. Furthermore, the central portion cut out to make the annular shape can be used to make the seal element for a smaller diameter fire damper. This reduces the cost and wastage involved with the production process considerably.

15 When the seal element has a void in its centre, for example, by being annular in shape, a solid core section may be placed in the void. Thus, the solid core section acts as a barrier to prevent the intumescent material migrating into the void, ensuring that it all expands outwardly in the event of a fire and is delivered to the perimeter seal area.

20 In accordance with a second aspect of the invention, there is provided a fire damper comprising a damper casing for installation in a length of ducting; a damper blade according to the first aspect of the invention mounted within the damper casing, the damper blade being movable between open and closed positions; a biasing member, which urges the damper blade into the closed 25 position; and a retention mechanism for retaining the damper blade in the open position, the retention mechanism being adapted to respond to exposure to temperatures above a threshold temperature by releasing the damper blade so that it is urged into the closed position by the biasing member.

5

The retention mechanism may comprise a fusible member that melts on exposure to temperatures above a threshold temperature to release the damper blade so that it is urged into the closed position by the biasing member. Alternatively, the retention mechanism may comprise an actuator and 5 a sensor, the actuator being adapted to drive the damper blade into the open position when the sensor detects a temperature below the threshold temperature and to release the damper blade when the sensor detects a temperature above the threshold temperature.

The open position is that in which the damper blade presents minimum 10 impedance to air-flow through the damper casing, typically by lying substantially parallel with a longitudinal axis of the damper casing. The closed position is that in which the damper blade presents maximum impedance to air-flow through the damper casing, typically by lying substantially perpendicular with the longitudinal axis of the damper casing.

15 The seal element is preferably sized so that it makes contact with the entirety of an interior periphery of the damper body. This is typically done by making the dimensions of the seal larger than the interior dimensions of the damper casing.

An embodiment of the invention will now be described with reference to the 20 accompanying drawings, in which:

Figure 1 shows a sectional view of a fire damper comprising a damper blade according to the invention;

Figure 2 shows an end view of the fire damper of Figure 1;

Figure 3 shows a side view of the damper blade;

25 Figure 4 shows an end view of the damper blade; and

Figures 5a and 5b show a sectional view of part of the damper blade in normal operating and fire conditions.

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A damper casing 1 is shown in Figures 1 and 2. The damper casing 1 is a steel cylinder open at each end. Swages 2a and 2b are formed in the casing 1 close to each end to strengthen the casing 1, help to maintain its round shape, and to act as a stop when fitting connecting ductwork. A flange 3 is welded to the 5 casing 1 to enable the casing 1 to be fixed to a part of a building's structure, for example the wall 4 shown in Figure 1.

A damper blade 5 is shown in Figures 1 and 2 in the closed position (i.e. the position that presents maximum impedance to air-flow through the casing 1). The blade 5 rotates between the open position (i.e. the position that presents 10 minimum impedance to air-flow through the casing 1) and the closed position on a shaft 6 to which the blade 5 is fastened. The shaft 6 is rotatably mounted on the casing 1. The blade 5 is urged into the closed position by a torsion spring 8 wound around the shaft 6. In normal operating conditions, a retaining mechanism (not shown) holds the blade 5 in the open position against the 15 torque produced by the torsion spring 8. However, during a fire, the heat causes a fusible member in the retaining mechanism to melt, which releases the blade 5, allowing the torsion spring 8 to cause it to close. The shaft 6 terminates in a ninety degree bend, thereby forming a handle 9 for manual operation of the damper blade 5, as may be required for example during 20 testing and servicing.

In a variant of this embodiment, the handle 9 is not present, and the shaft 6 instead extends to couple with a motorised (electric or pneumatic) actuator. The motorised actuator drives the blade 5 to the open position when a thermal sensor probe inserted through a hole in the casing 1 indicates that ambient 25 temperature is normal. If the probe detects an elevated temperature, power (or air supply) to the motor is cut and a spring causes the blade 5 to move to the closed position.

The damper blade 5 comprises a pair of steel discs 10a, 10b riveted together by fourteen rivets 11 a-11 n. Six of the rivets 11c, 11 d, 11 i, 11j, 11m, 11 n also 30 serve to affix brackets 12a-12c to the disc 10a. The brackets 12a-12c secure the disc 10a to the shaft 6. Twelve of the rivets 11 a-111 are arranged in a ring

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at a predefined diameter that is less than the diameter of the discs 10a, 10b. This ring of twelve rivets 11 a-111 separates the discs 10a, 10b into an inner region within the ring of rivets 11 a-111, in which the discs 10a, 10b are relatively immoveable, and an outer region outside the ring of rivets 11 a-111, in 5 which the two discs 10a, 10b are able to move apart as will be described below. The two steel discs 10a, 10b have a diameter slightly smaller than the inside diameter of the damper casing 1, typically by about 6.5mm.

The ring of rivets 11 a-111 will be placed on a circle whose diameter will depend on the overall diameter of the two steel discs 10a, 10b. The following table 10 provides examples of a suitable diameter for the circle on which the ring of rivets 11 a-111 could be placed against the overall diameter of the two steel discs. The two diameters are measured from the same centre so that the ring of rivets 11 a-111 and two steel discs 10a, 10b are concentric.

Diameter of ring of rivets 11 a-111 Diameter of steel discs 10, 10b

42.4mm

93.5mm

64.5mm

118.5mm

88.2mm

143.5mm

97.9mm

153.5mm

137.0mm

193.5mm

186.5mm

243.5mm

236.1mm

293.5mm

251.0mm

308.5mm

Two layers 13a, 13b of woven fibreglass cloth impregnated with an intumescent material are sandwiched between the pair of steel discs 10a, 10b. 25 The two layers 13a, 13b are annular in shape and approximately 0.5mm thick. The annular layers 13a, 13b are larger than the inside diameter of the damper casing 1 for which the blade is intended to be used, typically by about 10mm. The layers 13a, 13b of woven fibreglass cloth create a seal that wipes against or sweeps the inside of the damper casing 1 as the damper blade 5 rotates 30 from the open to the closed position to seal the blade 5 to the damper casing 1 and provide a fire barrier. This type of seal is very flexible, which ensures that it

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offers a low resistance to closure whilst maintain low leakage characteristics. An annular shape is used because there is no need to provide the fibreglass cloth in the centre of the blade 5. The discs cut out from the inside of the annuli can be used to make seals for smaller diameter fire damper blades. The 5 central void of the annular discs 13a, 13b is filled either completely or partially with a layer of intumescent material. The layer of intumescent material may be circular or annular in shape. Alternatively, or in addition, a steel core section may be present in the central void of the annular discs 13a, 13b. As discussed above, this prevents migration of the intumescent material into the void and 10 ensures that it all expands outwardly in the event of a fire.

Figures 5a and 5b illustrate the operation of the damper blade 5. In Figure 5a, the damper blade 5 is in the closed position and the wiping seal between the layers 13a, 13b of intumescent-impregnated fibreglass cloth and the damper casing 1 has been formed. In Figure 5a, the blade 5 is experiencing normal 15 ambient conditions. The two steel discs 10a, 10b lie parallel.

In Figure 5b, the effect of the elevated temperature caused during a fire is shown. The temperature of the fire has caused the intumescent material with which the layers 13a, 13b of fibreglass cloth is impregnated and the inner layer of intumescent material to swell. The ring of rivets 11 a-111 holds the inner 20 portions of the two discs 10a, 10b parallel. However, the outer portions are free to move apart, and the swelling of the intumescent material forces them to do so. As the discs 10a, 10b are distorted apart, the gap between them fills with intumescent material from the impregnated fibreglass cloth and from the layer of intumescent material in the central void of the layers 13a, 13b of fibreglass 25 cloth. This forms a highly resilient fire-proof seal that is long-lasting due to its depth in the direction of the longitudinal axis of the damper casing 1.

Without the intumescent material, the seal would offer much reduced performance in fire conditions. The pressure and heat would cause premature degradation of such a seal, allowing excessive air to flow around the perimeter 30 of the damper blade.

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The depth of the seal shown in Figure 5b is proportional to its duration under fire conditions. Over time, the exposed surface of intumescent material will gradually deteriorate. Thus, by allowing the intumescent material to cause distortion of the discs 10a, 10b, a deep seal can be formed when required in a 5 fire. However, this deep seal does not come at the expense of having a thick damper blade 5. Instead, the thickness of the damper blade 5 is kept, by this design, to an acceptable value.

The use of the fibreglass cloth in conjunction with the expanding seal provided by the intumescent material offers additional advantages in enhancing fire 10 resistance. First, the fibreglass cloth encapsulates the base intumescent material maintaining its density by preventing it from freely expanding and migrating. This ensures a high density of intumescent material, which is proportional to its fire resistance performance. Second, the fibreglass cloth acts as a protective layer between the intumescent material and the fire, 15 reducing the rate at which the intumescent material is eroded by the fire.

In the embodiment described above, the layers 13a, 13b of intumescent-impregnated fibreglass cloth are annular. In alternative embodiments, they may instead be solid discs. Using discs reduces heat transfer from across the blade 5 in a fire. However, it is more wasteful and therefore more costly and 20 more harmful to the environment.

Claims

10 CLAIMS

1. A damper blade for a fire damper, the damper blade comprising a seal element for forming a seal, in use, between the damper blade and a fire damper casing, the seal element comprising a first layer of non-flammable

5 material impregnated with an intumescent material.

2. A damper blade according to claim 1, wherein the seal element further comprises a second layer of non-flammable material impregnated with an intumescent material.

3. A damper blade according to claim 1 or claim 2, wherein the non-flammable 10 material is a woven material.

4. A damper blade according to any of the preceding claims, wherein the nonflammable material is fibreglass.

5. A damper blade according to any of the preceding claims, further comprising first and second blade elements separated by the seal element.

15 6. A damper blade according to claim 6, wherein at least a region of each of the first and second blade elements is moveable away from each other under the influence of the intumescent material as it swells.

7. A damper blade according to claim 5, wherein the regions that are moveable are outer regions of the first and second blade elements, inner regions of the

20 first and second blade elements within the outer regions being immoveable.

8. A damper blade according to claim 7, wherein the first and second blade elements are fastened together at the junctions of the inner and outer regions to render the inner regions immoveable relative to each other, whilst leaving the outer regions free.

25 9. A damper blade according to claim 8, wherein the first and second blade elements are fastened together by rivets.

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10. A damper blade according to any of claims 5 to 9, wherein the seal element lies between the moveable regions of the first and second blade elements only.

11. A damper blade according to any of claims 5 to 10, wherein the first and second blade elements are circular, square or rectangular.

12. A damper blade according to any of the preceding claims, wherein the seal element is annular.

13. A fire damper comprising a damper casing for installation in a length of ducting; a damper blade according to any of the preceding claims mounted within the damper casing, the damper blade being movable between open and closed positions; a biasing member, which urges the damper blade into the closed position; and a retention mechanism for retaining the damper blade in the open position, the retention mechanism being adapted to respond to exposure to temperatures above a threshold temperature by releasing the damper blade so that it is urged into the closed position by the biasing member.

14. A fire damper according to claim 13, wherein the seal element is sized so that it makes contact with the entirety of an interior periphery of the damper body.

15. A fire damper substantially as hereinbefore described with reference to the accompanying drawings.