WO2000006285A1

WO2000006285A1 - Laminar flow frame

Info

Publication number: WO2000006285A1
Application number: PCT/SE1999/001315
Authority: WO
Inventors: Bertil Larsson
Original assignee: ABB Fläkt AB
Priority date: 1998-07-27
Filing date: 1999-07-26
Publication date: 2000-02-10
Also published as: SE9802627D0; AU5661199A; SE9802627L; SE512715C2

Abstract

A laminar flow frame intended for use in clean rooms, comprises mounting sections (2) connected together, for a laminar flow screen (18). Each mounting section has an open groove running in longitudinal direction with the groove opening facing outwards from the frame. The groove is designed to firmly retain a longitudinal locking element (20) of resilient material inserted in the groove, said element having a cross section that fits the shape of the groove. The locking element extends along substantially the whole length of the groove in order to secure the screen to the section by clamping it between the wall (16) of the groove and the locking element (20). At least one reinforcing section (26, 28), adjustable in length, is arranged between two opposing sections to brace the frame to exactly the desired shape after the screen has been clamped in the frame.

Description

L A M I N A R F L O W F R A M E

The present invention relates to a laminar flow frame intended for use in clean rooms, comprising mounting sections connected together, for a laminar flow screen, each mounting section having an open groove running in longitudinal direction with the groove opening facing outwards from the frame, which groove is designed to firmly retain a longitudinal locking element of resilient material inserted in the groove, said element having a cross section that fits the shape of the groove and said locking element extending along substantially the whole length of the groove in order to secure the screen to the section by clamping it between the wall of the groove and the locking element.

To achieve good parallel flow after HEPA filters used for the supply of air to "clean rooms", for instance, it is known to use a very thin, fine-meshed screen, known as a laminar flow screen, after the filter. A pressure difference of 20 Pascal may typically prevail across the screen, resulting in a uniform flow rate across the whole surface of the screen. The screen is usually made of polyester, polyamide, polyvinyl difluoride (PVDF), nylon or similar material having long, resilient fibers. Hitherto the screen has often been glued to a steel frame attached to the filter and provided with a special device for stretching the screen. Such a screen is preferably installed above machines and similar equipment in clean rooms in order to achieve laminar air flow.

US 4 898 087 describes a frame for a screen of the type described above. In this frame the side sections are joined together by special corner pieces so that the corner angles are somewhat greater than 90°, i.e. the side pieces, which are resilient, assume a convex, outwardly curved shape before mounting of the screen. When the screen is then stretched over the frame the sides of the frame should be straightened out by the elastic deformation caused by the tension in the screen. Suitable tension is thus maintained thereafter in the screen. This previously known frame has a number of drawbacks. The construction with the special corner pieces is complicated and expensive and it is extremely difficult, if not impossible, to mount the screen on the frame with exactly the right tension for the frame to assume the intended rectangular shape.

The object of the present invention is to provide a laminar flow frame with which the above-mentioned drawbacks of the previously known technology are eliminated.

This is achieved with a laminar flow frame as claimed in claim 1.

The present invention thus provides a laminar flow frame of simple construction that makes it possible in a simple manner to ensure an absolutely tetragonal, preferably square frame when the screen has been fitted. The reinforcing sections prevent the frame sections from bending or, if the sections have bent, this can easily be rectified by adjustment of the reinforcing sections. Furthermore, the screen always stretches during use and the frame according to the invention also allows simple compensation for this stretching so that the desired tension is maintained in the screen over an extended period. Another advantage of the frame according to the invention is that there is very little screening-off of the flow area.

In accordance with an advantageous embodiment of the frame according to the invention the groove in each section is substantially circular, the groove wall extending over a sector of slightly more than a half circle, and in that the locking element has a substantially circular cross section that fits the groove. By shaping the section in this way, with an open cylindrical groove, a locking effect is achieved when the resilient locking element is inserted. Since the locking element is elastic a certain variation in the groove opening can be accepted. However, the actual opening sector must always be somewhat smaller than a semi-circle to ensure that the locking element is retained in the groove. The locking element also serves to seal the screen to the section and also as sealing when the mounting section is screwed to another section, for instance. It is also simple to fit and remove the screen, for washing or replacement for instance, and the screen is automatically stretched upon being fitted in the frame according to the invention, built up of such sections. According to another advantageous embodiment of the frame according to the invention the locking element has a rough outer surface in order to achieve high friction between locking element and screen. A reliable grip is thus ensured between locking element and screen, so the screen is automatically stretched upon installation in the frame and the need for expensive tensioning means is eliminated.

According to yet another advantageous embodiment of the invention each section is provided with at least two substantially perpendicular section walls, the groove being arranged on the outside of one wall, with the groove opening substantially in alignment with the other wail and facing outwards from said other wall. The section can thus be turned so that the grooves for clamping the screen will be either on the lower or the upper side of the section. If the groove is on the lower side of the section particularly, the abutment of the screen against the section will be minimal.

In accordance with other advantageous embodiments of the frame according to the invention a T-slot is provided in the section wall opposite said other wall, which slot is designed for assembly of one reinforcing section, or possibly more reinforcing sections arranged separately along the length of the section. Each reinforcing section suitably comprises circular telescopic tubes mounted with T-bolts in said T-slots in the frame sections. The T-slot is also preferably so constructed that a space is maintained between clamped screen and assembled reinforcing section.

in accordance with yet another advantageous embodiment of the frame according to the invention the sections are provided with notches to enable sections to be connected together at the ends at an angle to each other, with L-shaped locking members to form corners. Adjacent sections are thus preferably joined at right angles at the ends and form a closed, tetragonal frame. These locking means thus strengthen the sections at the corners at the same time as the sections are connected at the corners without any surface irregularity. To further explain the invention embodiments of the laminar flow frame according to the invention, selected by way of example, will be described in more detail with reference to the accompanying drawings, in which

Figure 1 shows an embodiment of the mounting section for the frame according to the invention suspended from another section, e.g. one suitable for suspension from a ceiling,

Figure 2 shows the mounting section of Figure 1 on a larger scale in cross section, and

Figures 3 and 4 show two alternative embodiments of the laminar flow frame according to the invention with the mounting section facing in two different directions.

Figure 1 shows an embodiment of the mounting section 2 of the frame according to the invention, which forms a part of a laminar flow frame and is supported by a perforated panel or plate 4 from a section 6 suitable for suspension from the ceiling in a clean room. See also Swedish patent application No. 9802628-9 filed simultaneously herewith.

The mounting section comprises walls 8, 10, 12 at right angles to each other and on the outer side of the wall 8 an open groove is provided running in the longitudinal direction of the section, see also Figure 2. The groove has circular cross section and the groove wall 16 extends over a sector somewhat larger than a half circle. The opening of the slot 14 lies substantially in alignment with the wall 10.

A laminar flow screen 18 is clamped in the section 2 with the aid of an elongated locking element 20 inserted into the groove. The locking element 20 is made of resilient material to allow insertion into the groove 14 and suitably consists of a rubber strip with a cross section to fit the groove. The rubber strip 20 suitably extends along the whole length of the section. When clamping the screen 18 in the supporting frame composed of the mounting section 2, the screen 18 is placed around the rubber strip 20 and this is then pressed into the groove 14. When the strip 20 is pressed into the groove 14 the screen 18 is automatically stretched. Since the wall 16 of the groove extends over slightly more than a semi-circle, the strip 20 pressed into the groove 14 is retained there in a reliable manner.

The strip 20 has a rough surface so that the friction between the strip 20 and the screen 18 is high and a secure grip is guaranteed between screen 18 and strip 20, which eliminates the risk of the screen 18 slipping over the surface of the strip 20.

Instead of the perforated panel or plate 4, a panel or plate provided with nozzles may be preferable for certain applications.

The section 2 is also provided with a T-slot for insertion of reinforcing sections, see Figures 3 and 4.

The reinforcing section suitably comprises circular telescopic tubes 26, 28 attached in opposing mounting sections 2 in a frame by means of T-bolts

30, 32 inserted into the T-slots 22 and attached to one end of the telescopic tubes 26, 28, see Figures 3 and 4. The telescopic tubes 26, 28 are joined by means of a tension screw 34 to enable movement of the telescopic tubes 26, 28 in relation to each other to brace the frame so that it does not bend, or to correct any bending that may have occurred in the frame. In this way an absolutely tetragonal frame, preferably an absolutely square frame, is obtained even after the screen has been clamped in place. It is also possible to simply adjust the correct tension in the screen when using screens of different materials with different tension properties, and when the screen stretches during use.

The T-slot 22 in the section 2 is such that a space is constantly maintained between the screen 18 and the reinforcing section. No part of the screen surface will thus be covered by the reinforcing profile. The reinforcing sections thus cause minimal disturbance in the air flow. To connect the sections 2 at the corners without surface irregularities to form a frame, and at the same time to make the sections more rigid at the corners, notches 36 are provided for the attachment of L-shaped locking sections 38 to hold the sections together at the corners.

Figures 3 and 4 show two alternative embodiments of the frame according to the invention. In the embodiment according to Figure 3 the mounting section is turned so that the groove is at the upper side of the section, and the screen runs over the outside of the walls 10, 12 of the section to cover the lower side of the frame. Figure 4 shows an embodiment with the mounting section 2 turned so that the groove is at the lower side and the clamped screen extends below the frame, directly from the edge of the groove wall 16. In this latter embodiment in particular, the screening-off area from the frame is minimal.

Instead of the arrangement for supporting the laminar flow frame shown in Figure 1 , this can of course be suspended directly from the T-slot in the mounting sections.

Claims

1. A laminar flow frame intended for use in clean rooms, comprising mounting sections connected together, for a laminar flow screen, each mounting section having an open groove running in longitudinal direction with the groove opening facing outwards from the frame, which groove is designed to firmly retain an elongated locking element of resilient material inserted in the groove, said element having a cross section that fits the shape of the groove and said locking element extending along substantially the whole length of the groove in order to secure the screen to the section by clamping it between the wall of the groove and the locking element, characterized in that at least one reinforcing section, adjustable in length, is arranged between two opposing sections to brace the frame to exactly the desired shape after the screen has been clamped in the frame.

2. A frame as claimed in claim 1 , characterized in that the groove in each section is substantially circular, the groove wall extending over a sector of slightly more than a half circle, and in that the locking element has a substantially circular cross section that fits the groove.

3. A frame as claimed in claim 1 or 2, characterized in that the locking element comprises a rubber strip.

4. A frame as claimed in any of the preceding claims, characterized in that the locking element has a rough outer surface in order to achieve high friction between locking element and screen.

5. A frame as claimed in any of the preceding claims, characterized in that each section is provided with at least two substantially perpendicular section walls, the groove being arranged on the outside of one wall, with the groove opening substantially in alignment with the other wall and facing outwards from said other wall.

6. A frame as claimed in any of the preceding claims, characterized in that the sections are substantially tetragonal in cross section.

7. A frame as claimed in claims 5 and 6, characterized in that a T-slot is provided in the section wall opposite said other wall, which slot is designed for assembly of the reinforcing section.

8. A frame as claimed in claim 8, characterized in that the T-slot is so constructed that a space is maintained between clamped screen and assembled reinforcing section.

9. A frame as claimed in any of the preceding claims, characterized in that the sections are provided with notches to enable sections to be connected together at the ends at an angle to each other, with L-shaped locking members to form corners.

10. A frame as claimed in any of the preceding claims, characterized in that the sections are connected together so that the grooves lie in a plane parallel to the clamped screen, with the groove openings directed in parallel with the plane.

11. A frame as claimed in claim 9 or 10, characterized in that adjacent sections are connected at right angles at the ends with L- shaped locking means to form a closed, tetragonal frame.

12. A frame as claimed in claim 11, characterized in that the frame is square.

13. A frame as claimed in any of the preceding claims, characterized in that a reinforcing section comprises circular telescopic tubes mounted with T-bolts in said T-slots of the sections.

14. A frame as claimed in claim 13, characterized in that the telescopic tubes are joined together by means of tension screws to enable exact adjustment of the shape of the frame.