Fire closure shutter
BACKGROUND OF THE INVENTION 
     The invention relates to a fire closure shutter. 
     Especially in the ventilation ducts in ships there is a need for fire closure shutters the purpose of which is to separate, in the event of fire, the area under fire from the other spaces of the ship. The cross-sectional area of this kind of air duct can be about two square meters and the fire closure shutter must form a barrier able to close the whole of this area. For the acceptance of a fire closure shutter a fire test is arranged in which at one side of the closed shutter a temperature corresponding to that of a fire prevails for one hour. Severe thermal stress caused during the fire test generally causes distortion of the elements of the shutter creating non-acceptable gaps in the barrier created by the elements of the shutter. 
     SUMMARY OF THE INVENTION 
     An aim of the invention is to create a fire closure shutter which resists heat well and which is constructed so that even a very severe thermal stress fails to cause any significant gaps to appear in the closed fire closure barrier created by the shutter. 
     A fire closure shutter according to the invention comprises a number of plate elements arranged adjacent to each other and mounted to turn about mutually parallel axes. Shape changes caused by thermal stress usually occur on the edge areas of a plate element where in its closed position it is in contact with the adjacent plate element. In addition shape changes caused by thermal stress usually occur in directions substantially perpendicular to the plane of the plate element. In a construction according to the invention one edge of a plate element is provided with a transverse part extending perpendicular to the plane of the plate element, and because the usual distortion of the edge area of the adjacent plate element caused by thermal stress occurs in the direction of the plane of the transverse part, the clearance between the adjacent plate element and the transverse part does not increase significantly. Thus, the invention is based on the principle that, due to the construction, shape changes caused by thermal stress do not, to any significant extent, cause gaps to appear in the fire closure shutter. 
     The solution provided by the invention can be accomplished in a simple way by fixing (e.g. welding) on one edge of a plate member an L-shaped steel or the like heat-resistant profiled element, one part of which serves as the transverse part and the other part of which is substantially parallel to the plane of the plate element. The use of an L-shaped steel edge reinforcement provides an advantageous solution particularly with regard to costs. Alternatively by bending the edge part of a plate element it is possible to form an integral construction which has both a transverse part and a part parallel with the plate element avoiding the need to weld a separate edge part to the plate element. However, the kind of edge area bending needed require the use of a relative expensive plate bending apparatus because the thickness of the material of the plate element would typically be about 5 mm. 
     The presence of a transverse part could cause a minor disadvantage in the open position of the shutter, because it could reduce the free flow-through area of the shutter opening. However, if the dimension of the transverse part of each plate element can be reduced so that in the direction perpendicular to the plane of each plate element it does not substantially exceed the corresponding dimension of the construction located at the position of the turning shaft for the plate element, the transverse part of the plane element will not per se affect the size of the flow-through area of the shutter opening. 
     In a favored embodiment the turning axis for the different plate elements is located in the central region of each plate element. In this way a balanced plate element is more easily achieved, to which the air flow through the shutter opening does not create a turning force on the plate elements, for example, so that a strong air flow resists a closing of the shutter. 
     In order to keep the distortions of the plate elements caused by thermal stress sufficiently small, the size of the plate elements has to be limited. It has been proved in practice that very wide plate elements should be avoided and that plate elements manufactured to have a pitch between the turning axes thereof which is at the most 30 cm, and preferably is about 20 cm, are advantageous. 
     It is important for good fire resistance of the fire closure shutter that harmful distortions be avoided also in the vicinity of the frame of the shutter. Therefore the frame supporting the turnable plate elements must be rigid and it must not be disposed to thermal distortion. A desirable degree of rigidity is obtained if the width of the frame in the through-flow direction of the open shutter is greater than the pitch between the turning axes of the plate elements. The frame can with advantage be manufactured of U-shaped channel-section members arranged so that the outer bottom surface of each U-shaped member faces the gas flow opening. 
     For turnably journalling of the plate elements in the frame only stub shafts or the like are needed at opposite ends of the plate elements, but the longitudinal part of each plate element located between the stub shafts is suitably provided with a bent area or the like aligned with the longitudinal axes of the stub shafts to make the plate element more rigid. 
     In most cases a thickness of the plate elements and the walls of the frame of about 5 mm has been found to be sufficient. 
     All the components of the fire closure structure must be made of fire resistant material. Preferably, the structural components, including the fire plate elements, the shafts, and the frame are made of steel of other suitable metal. 
     For security reasons it is desirable to provide the shutter with an operating system, which turns the plate elements thereof into their closed position by a force generated independently of an external energy source (e.g. a spring force) preferably arranged so that in the closed position of the plate elements some residual force exists for urging the plate elements into the closed position. The result of this arrangement provides the advantage that the fire shutter automatically adopts its closed position and remains tightly closed in the event of a failure of any external energy source provided in the environment (e.g. a loss of electrical, hydraulic or pneumatic power). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which 
     FIG. 1 is a cross-sectional view of the upper part of a fire closure shutter according to the invention, 
     FIG. 2 shows an alternative construction of the fire closure shutter according to FIG. 1, and 
     FIG. 3 is a side view of the fire closure shutter according to FIG. 1. 
    
    
     DETAILED DESCRIPTION 
     In the drawings, 1 indicates fire plate elements and 2 stub shafts thereof. The plate elements 1 are turnably journalled by means of the stub shafts 2 in a rectangular frame 3, which is made of U-shaped channel members 4. The plate elements 1 and the channel members 4 are made of steel plate material, preferably about 5 mm thick. 
     The turning movements of the plate elements 1 from a closed position shown by full lines in FIGS. 1 and 2 to an open position shown by chain lines 15, is shown by arrows 5. The stub shafts 2 of the plate elements are welded to the ends of the plate elements in a channel 6 bent from a central part of each plate element. Fixed along one edge of each plate element is an L-shaped steel member 7 including a plane part 7a and a transverse part 7b. A rim part 3a projects into the gas flow opening of the frame 3 and corresponds to the plane part 7a of the L-shaped member 7 and a transverse part 3b of the frame corresponds to the transverse part 7b of the L-shaped member 7 to ensure good sealing of the outermost plate element 1 to the frame 3. In the lowermost plate element (not shown in FIG. 1) there is no need for a member 7 or the like construction but a rim part similar to 3a can be provided to form a stop element indicating the closed position of the lowermost plate element 1. 
     When the temperature on one side of the fire shutter is extremely high compared to that on the other side, the plate elements 1 may bend due to the temperature gradient, whereby especially at the end of each plate element, having no reinforcing element 7, noticeable shape changes may occur. These shape changes take place, however, substantially in the direction of the plane of the transverse part 7b of the L-shaped member 7, which has no essential effect on the size of the clearance 8 of about 2 mm left between the outer edge of the plate element 1 and the adjacent transverse part 7b. Thus distortion of the edge of the plate element 1 away from the plane part 7a, even though it will result in an increase of the size of the space between the plate element and the plane part 7a of the L-shaped steel member, does not give rise to the creation of a gap because the size of the clearance 8 remains practically the same provided the edge area of the plate element 1 is not distorted so excessively that it moves beyond the outer edge of the transverse part 7b. It is not difficult to ensure this does not occur even where the transverse part 7b is relatively short. 
     There is no need to make the transverse part 7b in the sealing structure between the plate elements very long, indeed it is undesirable to do this because it could have a harmful effect, in the sense that it could decrease the flow-through opening in the open position 15 of the plate elements. Assuming that the total length of the transverse part 7b does not exceed the extent to which the bent area 6 is bent away from the median plane of the plate element, the transverse part 7b will have no reducing effect on the maximum size of the flow-through opening. 
     The embodiments illustrated show the turning axis of each plate element 1 located in the central area of the respective plate elements. This is preferred since in this way each plate element is balanced. 
     The length of the frame of the fire closure shutter in the flow-through direction of the opening is substantially greater than the pitch A between the turning axes of the plate elements, which in the embodiments illustrated is about 20 cm. This arrangement makes the frame particularly rigid and provides the advantage that no part of the turnable plate elements can ever extend outside of the frame, where they could be damaged, whereby transportation of the fire shutter is facilitated. Desirably the frame is of simple construction and as shown is made of four U-shaped channel-section members, the opening to be closed by the plate elements being defined by the bottoms of the four U-shaped members. The thickness of the walls of the frame and the plate elements is 5 mm. 
     FIG. 2 shows an alternative sealing structure between the plate elements, in which the transverse part is provided by bending the plate element 1 as shown in the figure. 
     FIG. 3 shows a suitable operating system for the plate elements. The stub shafts of the plate elements are turnably journalled in bearing housings 9 and a turning lever 10 is fixed to the stub shaft 2 of each plate element at one side of the flow opening (suitably, as shown, in one of the U-shaped channel-section members). The turning levers 10 are turnably fixed to a common operating bar 11, to which an open-holding force, acting parallel to the arrow 12, is applied for example by means of an electrical solenoid device or the like. In the opposite direction (i.e. in the direction of the arrow 13) there acts, for instance, the force of a compression spring 14 or the like, which automatically closes the fire shutter when the open-holding force is removed (e.g. if there is such a disturbance in an external energy system that the open-holding force provided by the solenoid or the like disappears). The spring 14 is designed so that even in the described closed position of the shutter the plate elements are urged further towards the closed position. 
     The invention is not restricted to the embodiment illustrated, since several modifications are feasible within the scope of the following claims.