ARRANGEMENT COMPLETING A DOOR ACTUATOR AND A FIRE PROTECTION FASTENING DEVICE

Description

[0001] The invention relates to arrangements comprising a door actuator and a fire protection fastening device.

[0002] Furthermore, the invention shows an arrangement comprising a door actuator, a mounting plate and a fire protection fastening device.

[0003] Door operators are used to open and / or close doors. The term "door operator" specifically refers to door closers and door drives. With a door closer, a spring is typically charged by the manual opening motion. The stored energy is then used to close the door. With a door drive, the door can be opened and / or closed automatically, for example, using electromechanical or hydraulic mechanisms.

[0004] Door handles are typically mounted on a surface, such as the door leaf, frame, or wall. It is particularly important to note that fire doors often use flammable fluids, such as hydraulic oils, in their handles. Appropriate measures should be taken to prevent the fluid in the door handle from overheating and potentially igniting in the event of a fire.

[0005] US 2014 / 260929 A1 discloses a device and a method for the detachable fastening of access control components for a door lock to a door. A base element is suitable for mounting on the door. A first wire connector is attached to the base element. A fastener with an attached combustible material is provided. A second wire connector is attached to the fastener, and the second wire connector is detachably connected to the first wire connector to fasten the fastener to the base element. A spring is provided, and a retainer holds the spring in a tensioned state, whereby in the event of a fire the retainer can melt so that the spring force can exert its force on the fastener. Alternatively, the force can be applied by an expanding material.The force causes the wire connecting elements to loosen and the fastening element to be separated from the base element.

[0006] EP 3 064 684 A1 relates to a holding arrangement, in particular for a door actuator for a door, comprising at least one mounting element and an intumescent material which, when an intumescence temperature is exceeded, has a volume that is larger than below the intumescence temperature.

[0007] The object of the present invention is to provide a fire protection bracket for a door operator that enables a reliable fastening of the door operator and simultaneously meets safety-relevant requirements, especially in the event of a fire.

[0008] The problem is solved by the features of independent claims 1 to 3.

[0009] The dependent claims relate to advantageous embodiments of the invention.

[0010] The invention describes an arrangement comprising a door actuator and a fire protection fastening device.

[0011] As mentioned at the beginning, the door operator is a door closer or door drive. The door operator must be attached to a mounting surface. This mounting surface is typically a door, frame, or wall.

[0012] The fire-resistant mounting device comprises a frame. According to one embodiment of the invention, the frame is designed for placement between the door operator and the mounting surface. If a separate mounting plate is omitted, the door operator rests directly against the front of the frame. The rear of the frame faces the mounting surface; in particular, it rests directly against the mounting surface. As will be described in detail below, a mounting plate can be used between the frame of the fire-resistant mounting device and the door operator. In particular, the mounting plate is screwed to the frame of the fire-resistant mounting device, and the door operator is attached to the mounting plate.

[0013] In an alternative embodiment, the frame of the fire-resistant mounting device is an integral part of the door operator. This embodiment will also be explained in detail. For the purposes of describing the invention, a mounting axis is defined. The mounting axis is perpendicular to the frame, in particular perpendicular to the rear of the frame. Furthermore, the mounting axis is perpendicular to the mounting surface. The mounting axis is, for example, parallel to the screws used to attach the frame to the mounting surface. According to an alternative definition, the mounting axis is perpendicular to the output axis of the door operator. The door operator is connected to the door or wall via this output axis, for example, by means of a linkage.

[0014] The frame of the fire protection fastening device incorporates at least one reaction chamber. In a preferred embodiment, the frame has several reaction chambers. In particular, the frame provides two, three, four, five, six, seven, or eight reaction chambers. For the sake of simplicity, the invention is usually described using one reaction chamber as an example, whereby it is always assumed that the multiple reaction chambers are identical. However, the reaction chambers can differ in size, so that, depending on the geometric design of the fire protection fastening device, as many reaction chambers as possible with the largest possible surface area can be used.

[0015] The reaction chamber is fully enclosed by the frame. Its depth extends parallel to the mounting axis. Accordingly, the circumference of the reaction chamber is also defined along an axis parallel to the mounting axis. The reaction chamber is open at the rear and / or the front of the frame. If the reaction chamber is open on both sides, i.e., at the front and the rear, it forms a through-hole in the frame. If the reaction chamber is open on only one side, it forms a pocket within the frame.

[0016] Each reaction chamber contains a drive element. The drive element is made of thermally intumescent material. It is designed to push the door actuator away from the mounting surface when thermally activated, i.e., when heated accordingly. Specifically, the thermally activatable material of the drive element is designed to be activatable within a temperature range of 90°C to 200°C.

[0017] The drive element is, in particular, a flat, plate-shaped material that can be cut to any desired size. Since this material is available in certain thicknesses, it is preferably intended that several layers are stacked on top of each other to form the drive element. The multiple layers then together form a single drive element.

[0018] Activating the thermally intumescent material increases its volume, for example, by foaming. Because the drive element is located within the reaction chamber and because the reaction chamber is completely enclosed by the frame, the drive element expands only in a direction parallel to the mounting axis. Expansion of the drive element in a direction perpendicular to this is blocked by the complete confinement of the frame.

[0019] As previously described, the frame can be arranged as an independent component between the door actuator and the mounting surface. A mounting plate may optionally be located between the frame and the door actuator. In this arrangement of the frame, the reaction chamber can be open at both the front and the rear. Crucially, upon thermal activation, the drive element expands in the direction parallel to the mounting axis, thereby pushing the door actuator away from the mounting surface. Whether the frame is also pushed away or remains in contact with the mounting surface is irrelevant to the fundamental function of the invention.

[0020] In the design whereby the frame is an integral part of the door actuator, it is particularly provided that the reaction chamber is open at the rear in order to push the door actuator together with the integral frame away from the mounting surface.

[0021] During the thermal activation of the drive element(s) in the individual reaction chambers, the door actuator is forced away from the mounting surface, potentially breaking the external threads on the screws or the corresponding internal threads. This causes the door actuator to detach from the mounting surface, i.e., the door, frame, or wall. It is assumed that the door actuator is located on the side of the door facing away from the fire. Detaching the door actuator from its mounting surface prevents it from overheating and thus avoids igniting the fluid within the actuator.

[0022] In a preferred embodiment, the fire protection fastening device comprises a piston plate arranged in the reaction chamber. In particular, the piston plate is arranged in the reaction chamber such that the mounting axis is orthogonal to the piston plate. When using multiple reaction chambers, each reaction chamber contains a drive element and, preferably, a piston plate.

[0023] The piston plate is made of a rigid material and serves to be displaced by the drive element when the drive element is thermally activated. It is specifically designed that the piston plate is guided within the reaction chamber.

[0024] The direction of displacement is, in particular, parallel to the mounting axis. The gap between the piston plate and the reaction chamber should preferably be kept as small as possible so that the intumescent material of the drive element does not ooze past the piston plate through the gap. During activation, i.e., during the expansion of the drive element, both the drive element and the piston plate can exit the reaction chamber.

[0025] The piston plate can generally be positioned on either the front or the back of the drive element. Furthermore, it is also possible to position one piston plate on each side of the drive element. Accordingly, two piston plates are then provided per reaction chamber.

[0026] The piston plates can also be called pressure distribution plates or pressure modulator plates, as they ensure that the pressure applied by the actuator is transferred over as large an area as possible. Furthermore, they prevent the actuator from being wasted in cavities, such as the uneven back surface of a door handle, during thermal activation.

[0027] Preferably, the piston plate is made of metal, for example aluminum. This results in a rigid, lightweight, and easy-to-manufacture piston plate.

[0028] However, it should also be considered that in most applications a thermally insulating design of the fire protection mounting device is advantageous. In principle, heat transfer from the mounting surface to the drive element should occur with as little resistance as possible. Any further heat conduction, especially towards the door operator, should be prevented if possible. Therefore, it is preferred that a piston plate arranged between the drive element and the door operator be made of non-metallic, thermally insulating material. Alternatively, the piston plate can also be multi-layered, with at least one layer made of non-metallic, thermally insulating material. Furthermore, it is possible to provide that a piston plate arranged between the drive element and the mounting surface is made of metallic, thermally conductive material.This ensures rapid heat transfer from the mounting surface to the drive element, guaranteeing early expansion of the intumescent material. Therefore, the drive element can be encased by two different piston plates, particularly two piston plates with different thermal conductivities.

[0029] Especially when manufacturing the piston plate exclusively from thermally insulating material, it is important to ensure that a sufficiently stable material is used to create a rigid piston plate. Suitable plastics are recommended for this purpose.

[0030] In addition to or as an alternative to using the thermally insulating material in the piston plate, it is preferably provided that at least one insulating plate made of non-metallic, thermally insulating material is placed on at least one side of the piston plate. Preferably, the insulating plate is made of a fiber-reinforced composite material.

[0031] When the insulating plate is inserted between the piston plate and the drive element, it is located primarily within the reaction chamber. If the insulating plate is placed on the side of the piston plate facing away from the drive element, it may also be located outside the reaction chamber.

[0032] Each reaction chamber has a cross-sectional area perpendicular to the mounting axis. This cross-sectional area of ​​the reaction chamber is preferably rectangular, as this geometric design allows for the distribution of as many reaction chambers as possible, or reaction chambers with a large area, across the frame. However, other cross-sectional areas are also possible. Preferably, though, the drive element and / or the piston plate and / or the insulation plate extend over the entire cross-sectional area.

[0033] The reaction chamber is preferably open on both sides, i.e., on the front and the back. In particular, the reaction chamber is open across its entire cross-section on both sides. The open back of the reaction chamber has the advantage that the drive element can be in direct contact with the mounting surface. This ensures that the drive element heats up as quickly and sufficiently as possible in the event of a fire. The open front allows the drive element to expand towards the door actuator, or the piston plate to be pushed towards the door actuator.

[0034] The fire-resistant mounting device is designed to be as flat as possible and positioned discreetly between the door operator and the mounting surface. The depth of each reaction chamber is defined perpendicular to the mounting axis. This depth is preferably between 1 mm and 30 mm, and particularly between 5 mm and 20 mm. This provides sufficient space to accommodate the actuator and, if applicable, the piston plate within the reaction chamber.

[0035] The cross-sectional area of ​​each reaction chamber is defined perpendicular to the mounting axis. This is preferably between 400 mm² and 50,000 mm², preferably between 900 mm² and 10,000 mm².

[0036] When using multiple reaction chambers, the sum of all cross-sectional areas is also of interest, since a larger total cross-sectional area allows for the application of sufficient force to push the door actuator away. Thus, the sum of all cross-sectional areas of all reaction chambers is preferably at least 2,500 mm², and in particular at least 5,000 mm².

[0037] According to a previously described embodiment, the frame is not an integral part of the door operator, but is positioned between the mounting surface and the door operator or mounting plate. In particular, the frame is provided with first fixing points for screwing it to the mounting surface. Furthermore, the frame has second fixing points to which the door operator or any mounting plate can be attached. These fixing points are primarily through holes. Specifically, the through holes at the second fixing points preferably have an internal thread. Alternatively, instead of being holes, the fixing points can also be formed, for example, by threaded rods.

[0038] For the dimensioning of the fastening points described here, their centers, i.e., for example the centers of the holes, are relevant.

[0039] Preferably, two nearest first and second mounting points form a pair. For example, two first and two second mounting points are provided on the right side of the frame. Similarly, two first and two second mounting points are provided on the left side of the frame. This results in two pairs on each side of the frame.

[0040] To achieve the most direct force transmission possible when pushing the door actuator onto the mounting points, it is preferably intended that the distance between the mounting points of a pair be as small as possible. In particular, the distance between the first and second mounting points of each pair is at most five times, preferably at most four times, the thickness of the frame. The thickness of the frame is defined parallel to the mounting axis. Preferably, the frame at its thickest point is the determining factor. Alternatively, the average thickness of the frame in the area between the mounting points of a pair is the determining factor. If the distance between the mounting points of a pair is too large, only the frame may deform without the door actuator detaching from the frame.

[0041] The invention further comprises a first arrangement with a door actuator and the fire-resistant mounting device described above, wherein the frame of the fire-resistant mounting device is formed as an integral part of the door actuator. In particular, the door actuator has a housing, for example, made of die-cast material. The housing contains, in particular, at least one hydraulic chamber containing the flammable fluid. The frame is preferably formed on the rear side of the door actuator, in particular on the housing. In particular, it is provided that the frame contains only a reaction chamber with a corresponding drive element. The piston plate can be located on the rear side of the frame.

[0042] Furthermore, the invention comprises a second arrangement with a door operator and the described fire protection fastening device, wherein the door operator can be attached directly to the frame, in particular by screwing it on. The frame of the fire protection fastening device, in turn, is preferably attachable directly to the mounting surface, in particular by screwing it on.

[0043] Furthermore, the invention comprises a third arrangement with a door operator and the described fire-resistant mounting device, as well as an additional mounting plate. The mounting plate is positioned between the fire-resistant mounting device and the door operator. The mounting plate is attached to the frame of the fire-resistant mounting device, in particular by screwing it on. The frame of the fire-resistant mounting device is, in turn, screwed to the mounting surface. The door operator can be connected to the front of the mounting plate in the usual manner, in particular by screwing it on. Upon thermal activation, the mounting plate is pushed away from the mounting surface. The door operator is released along with the mounting plate.

[0044] The advantageous embodiments and dependent claims described in connection with the fire protection fastening device according to the invention find correspondingly advantageous application for the three arrangements.

[0045] The invention will now be described in more detail using exemplary embodiments. These will show: Fig. 1 shows an arrangement according to the invention with a fire protection fastening device according to a first embodiment, Fig. 2 shows an exploded view of Fig. 1 , Fig. 3 a frame of the fire protection fastening device according to the invention in the first embodiment, Fig. 4 the in the Figure 1 and 3 Section AA, Fig. 5, is an exploded view of an arrangement according to the invention with a fire protection fastening device according to a second embodiment, Fig. 6 is an exploded view of an arrangement according to the invention with a fire protection fastening device according to a third embodiment, and Fig. 7 is a detail of Fig. 6 .

[0046] The following are examples of embodiments of the invention. Identical or functionally identical components are designated with the same reference numerals in all embodiments.

[0047] All embodiments show an arrangement 100 with a door actuator 102. In these embodiments, the door actuator 102 is designed as a hydraulic door closer. The door actuator 102 has an output shaft 103. The door actuator can be connected to a door or frame, for example, via a linkage, using this output shaft 103.

[0048] The door operator 102 is attached to a mounting surface 101. The mounting surface 101 is formed, in particular, by a door, frame, or wall. A mounting axis 2 is perpendicular to the mounting surface 101.

[0049] A fire-resistant fastening device 1 is used to attach the door operator 102 to the mounting surface 101. The fire-resistant fastening device 1 comprises a frame 3. In the first two embodiments according to the Figures 1 to 5 This frame 3 is a separate component. In the third embodiment according to the Figure 6 and 7 The frame 3 is an integral part of the door actuator 102.

[0050] The frame 3 has at least one reaction chamber 4. The reaction chamber 4 accommodates a drive element 7 and a piston plate 8. Insulation plates 9 are also used in some cases.

[0051] The side of the frame 3 facing the mounting surface 101 is referred to as the back 5. The opposite side is referred to as the front 6.

[0052] The Figures 1 to 4Figure 1 shows the fire protection fastening device 1 of the arrangement 100 according to the first embodiment. The frame 3 is attached to the mounting surface 101 with its rear side 5. The door operator 102 is mounted directly onto the front side 6 of the frame 3.

[0053] As the Figures 2 and 3 To illustrate, frame 3 has four reaction chambers 4. Each reaction chamber 4 contains a sandwich of drive element 7, piston plate 8, and insulation plate 9. The insulation plate 9 can be, as shown in the section in Fig. 4 shows that it is located outside reaction chamber 4.

[0054] The drive element 7 is formed here from two layers of the thermally intumescent material. The piston plate 8, for example made of aluminum, is arranged between the insulation plate 9 and the drive element 7.

[0055] How in particular the cut in Fig. 4As shown, the individual reaction chamber 4 is open on both sides. The drive element 7 rests directly against the mounting surface 101. Upon thermal activation of the drive element 7, the piston plate 8 is pressed towards the door actuator 102. Because the drive element 7 and the piston plate 8 are located in the reaction chamber 4, the swelling material of the drive element 7 does not spread into the uneven back surface of the door actuator 102, but rather the pressure is applied directly to the door actuator 102 via the piston plate 8.

[0056] Fig. 3 Figure 1 shows a length 15 and a width 16 of the individual reaction chamber 4. Length 15 and width 16 are measured perpendicular to the mounting axis 2 and determine the cross-sectional area of ​​the reaction chamber 4. Fig. 4Figure 1 illustrates the depth 17 of the reaction chamber 4, measured parallel to the mounting axis 2. In this embodiment, the depth 17 of the reaction chamber 4 also corresponds to the thickness 18 of the frame 2 at its thickest point.

[0057] How Fig. 4 As shown, the individual reaction chamber 4 has a full-circumference rim 10. This rim 10 extends parallel to the mounting axis 2 with a projection 19. The projection 19 is measured from a contact surface 20 between the door actuator 102 and the frame 3. The projection 19 increases the depth 17 of the reaction chamber 4.

[0058] Figures 2 , 3 and 4Show that the frame 3 can have at least one pocket 11 on its front 6. This pocket 11 forms an air-filled space that improves the thermal insulation of the frame 3, thus minimizing heat transfer through the mounting surface 101, through the frame 3, and directly to the door operator 102. Such a pocket 11 can also be arranged on the rear 5 of the frame 3. The pocket 11 can also be filled, at least partially, with a thermal insulating material, particularly a solid one.

[0059] Fig. 3Figure 1 shows that the frame 3 has four first fixing points 12 and four second fixing points 13. The first fixing points 12 are used to screw the frame to the mounting surface 101. The second fixing points 13 are used to screw the door actuator 102 to the frame 3. In the second embodiment, a mounting plate 30 is screwed to the second fixing points 13 instead of the door actuator 102.

[0060] Fig. 3 The first and second embodiments illustrate that a first fastening point 12 and a second fastening point 13, each designed as a hole, form a pair. The distance 14 between two corresponding fastening points 12, 13 is chosen to be as small as possible.

[0061] Fig. 5The exploded view shows the fire protection fastening device 1 on the arrangement 100 according to the second embodiment. Here, the mounting plate 30 is arranged between the door operator 102 and the frame 3. The mounting plate 30 is screwed to the frame 3 via the second fastening points 13.

[0062] In the second embodiment, the frame 3 has five reaction chambers 4. Each reaction chamber 4 contains a drive element 7, again, for example, formed from two layers. A plate is arranged on the front of each drive element 7; this plate can be configured as a piston plate 8 or an insulating plate 9. Furthermore, two plates, namely a piston plate 8 and at least one insulating plate 9, can also be used in a sandwich configuration at this position.

[0063] In the second embodiment, the reaction chambers 4 are also open at the front 6 and the rear 5. At the rear 5, the drive element 7 rests directly against the mounting surface 101.

[0064] Figure 6 and 7 Figure 1 shows the design of the fire protection fastening device 1 in the arrangement 100 according to the third embodiment. In the third embodiment, the frame 3 of the fire protection fastening device 1 is an integral part of the door operator 102. This is particularly evident when considering the rear side of the door operator 102 and Fig. 7 As can be seen, a reaction chamber 4 is formed within frame 3. According to the exploded view, this reaction chamber 4 contains... Fig. 6 the drive element 7 and a piston plate 8. Reference symbol list

[0065] 1 Fire protection fastening device 2 Mounting axis 3 Frame 4 Reaction chambers 5 Back 6 Front 7 Drive element 8 Piston plate 9 Insulation plate 10 Edge 11 Pocket 12 First fixing point 13 Second fixing point 14 Spacing 15 Length 16 Width 17 Depth 18 Thickness 19 Projection 20 Contact surface 30 Mounting plate 100 Arrangement 101 Mounting surface 102 Door actuator 103 Output axis

Claims

1. An arrangement (100) comprising a door actuator (102) and a fire protection fastening device (1) for fastening the door actuator (102), the fire protection fastening device (1) comprising: • a frame (3) with a rear side (5) facing a mounting surface (101), in particular a door, door casing or wall, wherein a mounting axis (2) is defined perpendicular to the rear side (5), • at least one reaction chamber (4) formed in the frame (3), wherein the reaction chamber (4) is fully delimited by the frame (3), and wherein the reaction chamber (4) is open at the rear side (5) and / or at a front side (6) of the frame (3) opposite the rear side (5), • and a drive element (7) which is arranged in the reaction chamber (4) and which is made of thermally intumescent material, which is designed to push the door actuator (102) away from the mounting surface (101) upon thermal activation, • wherein the frame (3) is an integral part of the door actuator (102).

2. The arrangement (100) comprising a door actuator (102) and a fire protection fastening device (1) for fastening the door actuator (102), the fire protection fastening device (1) comprising: • a frame (3) with a rear side (5) facing a mounting surface (101), in particular a door, door casing or wall, wherein a mounting axis (2) is defined perpendicular to the rear side (5), and wherein the frame (3) is designed for arrangement between the door actuator (102) and the mounting surface (101), • at least one reaction chamber (4) formed in the frame (3), wherein the reaction chamber (4) is fully delimited by the frame (3), and wherein the reaction chamber (4) is open at the rear side (5) and / or at a front side (6) of the frame (3) opposite the rear side (5), • and a drive element (7) which is arranged in the reaction chamber (4) and which is made of thermally intumescent material, which is designed to push the door actuator (102) away from the mounting surface (101) upon thermal activation, • wherein the door actuator (102) can be fastened, in particular screwed, directly to the frame (3).

3. The arrangement (100) comprising a door actuator (102), a mounting plate (30) and a fire protection fastening device (1) for fastening the door actuator (102), the fire protection fastening device (1) comprising: • a frame (3) with a rear side (5) facing a mounting surface (101), in particular a door, door casing or wall, wherein a mounting axis (2) is defined perpendicular to the rear side (5), and wherein the frame (3) is designed for arrangement between the door actuator (102) and the mounting surface (101), • at least one reaction chamber (4) formed in the frame (3), wherein the reaction chamber (4) is fully delimited by the frame (3), and wherein the reaction chamber (4) is open at the rear side (5) and / or at a front side (6) of the frame (3) opposite the rear side (5), • and a drive element (7) which is arranged in the reaction chamber (4) and which is made of thermally intumescent material, which is designed to push the door actuator (102) away from the mounting surface (101) upon thermal activation, • wherein the mounting plate (30) can be fastened, in particular screwed, directly to the frame (3) • and wherein the door actuator (102) can be fastened, in particular screwed, directly to the mounting plate (30).

4. The arrangement according to one of the preceding claims, comprising a piston plate (8) which is arranged in the reaction chamber (4) and which, upon thermal activation of the drive element (7), is displaceable by the drive element (7), in particular relative to the frame and / or door drive.

5. The arrangement according to claim 4, wherein the piston plate (8) is made of non-metallic, thermally insulating material or wherein the piston plate (8) has at least one layer of non-metallic, thermally insulating material.

6. The arrangement according to one of claims 4 or 5, wherein at least one insulating plate (9), which is made of non-metallic, thermally insulating material, is placed on at least one side of the piston plate (8).

7. The arrangement according to one of the preceding claims, wherein the drive element (7) and / or the piston plate (8) and / or the insulating plate (9) extends / extend over the entire cross-sectional area of the reaction chamber (4) defined perpendicular to the mounting axis (2).

8. The arrangement according to one of the preceding claims, wherein the reaction chamber (4) is open on both sides, preferably on both sides over its entire cross-section.

9. The arrangement according to one of the preceding claims, wherein the drive element (7) is exposed at the rear side (5) of the frame (3) for direct contact with the mounting surface (101).

10. The arrangement according to one of the preceding claims, • wherein a depth (17) of the reaction chamber (4) defined parallel to the mounting axis (2) is between 1 mm and 30 mm, preferably between 5 mm and 20 mm, • and / or wherein a cross-sectional area of the reaction chamber (4) defined perpendicular to the mounting axis (2) is between 400 mm2 and 50,000 mm2, preferably between 900 mm2 and 10,000 mm2.

11. The arrangement according to one of the preceding claims, wherein the sum of the cross-sectional areas of all reaction chambers (4) defined perpendicular to the mounting axis (2) is at least 2,500 mm2, preferably at least 5,000 mm2.

12. The arrangement according to one of claims 2 to 11, • wherein the frame (3) has first fastening points (12), in particular designed as holes, for screwing to the mounting surface (101), • and wherein the frame (3) has second fastening points (13), in particular designed as holes, for screwing the door actuator (102) or a mounting plate (30) to the frame (5).

13. A fire protection fastening device according to claim 12, wherein in each case two first and second fastening points (12, 13) lying closest to one another form a pair and the distance between the first fastening point (12) and the second fastening point (13) of a pair is at most 5 times, preferably at most 4 times, the thickness (18) of the frame (3).