IES74718B2

IES74718B2 - A method for producing woven wire fabric sheet

Info

Publication number: IES74718B2
Authority: IE
Inventors: Michael Redmond Quigley
Original assignee: Wire Weavers R & D Limited
Priority date: 1997-03-03
Filing date: 1997-03-03
Publication date: 1997-07-30
Also published as: GB2322873A; IE980141A1; GB2322873B; IES970132A2; GB9804424D0

Abstract

A method for producing woven fabric sheet (2) from a weaving loom with relatively constant airflow resistance therethrough comprises checking the airflow resistance of the sheet (2) at 40cm intervals as the sheet (2) is being fed from the loom using a portable micromanometer (10). The micromanometer (10) comprises a measuring head (12) having an upstream part (21) and a downstream part (22) between which the sheet (2) is sealably clamped. Air is drawn through a bore (14) extending through the head (12) by a vacuum pump (15). A first differential pressure gauge (47) monitors the pressure drop across an orifice plate (45) for determining the velocity of air through the bore (14), and a second differential pressure gauge (50) monitors the pressure drop across the sheet (2) so that the air flow resistance may be determined.

Description

A method for producing woven wire fabric sheet The present invention relates to a method for producing woven wire fabric sheet with relatively constant airflow resistance within predetermined tolerance limits, and in particular, though not limited to a method for producing woven wire fabric sheet for use in the aeronautical industry.

Noise emission from jet engines is suppressed by the 10 use of acoustic liners, which line the inner surfaces of the housing of the jet engine. Particularly efficient acoustic liners are produced from woven wire fabric sheet. Such woven wire fabric sheet, however, must be manufactured within relatively narrow tolerances, and in particular, it is essential that the airflow resistance through the fabric sheet should be relatively constant over the entire sheet. In general, the airflow resistance should be within relatively narrow upper and lower tolerance limits. Such fabric sheet, in general, is woven on a loom, and it is therefore essential that the weaving process be controlled so that the airflow resistance through the fabric sheet is maintained substantially constant throughout the sheet. In known methods, the fabric sheet is woven on a loom, and is rolled therefrom onto a reel. On completion of a fabric sheet, the reel is removed and placed on an inspection table. The fabric sheet is unwound from the reel, and the airflow resistance of the sheet is checked at a plurality of spaced apart locations as the sheet is unwound from the reel. Parts of the fabric sheet which are found to have airflow resistance values outside the predetermined tolerance limits are cut from the sheet and removed. This, it will be appreciated is relatively wasteful. In many cases, if the relevant settings of a weaving loom were to begin to drift in the early part of a production run, and the drift were not detected, an entire production run of the fabric sheet or a substantial part thereof could well have to be rejected.

There is therefore a need for a method for producing woven wire fabric sheet with relatively constant airflow resistance therethrough which overcomes these problems .

The present invention is directed towards providing such a method, and the invention is also directed towards providing a woven wire fabric sheet woven according to the method.

According to the invention there is provided a method for producing woven wire fabric sheet having a relatively constant airflow resistance therethrough throughout the sheet, the method comprising weaving the fabric sheet on a loom, and periodically monitoring the airflow resistance of the fabric sheet as it is being woven on the loom, and adjusting the loom where necessary for maintaining the airflow resistance of the fabric sheet within predetermined tolerance limits, the airflow resistance of the fabric sheet being monitored by a micromanometer, the micromanometer comprising a measuring head having an elongated bore extending therethrough, a receiving means for receiving and sealably engaging the fabric sheet adjacent the bore with the fabric sheet extending transversely of the bore, so that all the air flowing through the bore flows through the fabric sheet, a means for urging air through the bore, a first measuring means for measuring the velocity of air through the bore, and a second measuring means for measuring the pressure drop in the bore across the fabric sheet for determining the airflow resistance of the fabric sheet.

Preferably, the measuring head comprises an upstream part and a downstream part, the respective parts forming an upstream and a downstream portion of the bore, and a clamping means for clamping the upstream and downstream parts together with the respective upstream and downstream bores aligned with each other, the receiving means being located between the respective upstream and downstream parts.

In one aspect of the invention an orifice plate is 5 located in the bore, the first measuring means comprising a first differential pressure measuring means for measuring the pressure differential in the air across the orifice plate for determining the velocity of air through the bore, and the second measuring means comprises a second differential pressure measuring means for measuring the pressure drop across the fabric sheet, the means for urging the air through the bore comprising a vacuum pump.

Additionally, the invention provides woven wire fabric sheet woven according to the method according to the invention.

The invention will be more clearly understood from the following description of a preferred embodiment thereof which is given by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a plan schematic representation of apparatus for carrying out a method according to the invention for producing woven wire fabric sheet, Fig. 2 is a partly cross-sectional, partly schematic elevational view of a part of the apparatus of Fig. 1, Fig. 3 is a perspective view of a portion of the part of the apparatus of Fig. 2, Fig. 4 is an elevational view of the portion of Fig. 3 of the apparatus of Fig. 1, Fig. 5 is an elevational view of the portion of 10 the apparatus illustrated in Fig. 4, but illustrated in a different position to that of Fig. 4, Fig. 6 is a perspective view of a detail of the portion of the apparatus illustrated in Fig. 3, and Fig. 7 is a perspective view of another detail of the portion of the apparatus of Fig. 3.

Referring to the drawings there is illustrated apparatus indicated generally by the reference numeral 1 for carrying out a method according to the invention for producing woven wire fabric sheet 2 with a relatively constant airflow resistance, and in this embodiment of the invention with an airflow resistance which is constant over the entire sheet within a tolerance of ±10%. The apparatus 1 comprises a weaving loom 5 on which the woven wire fabric sheet 2 is woven.

The sheet 2 is fed from the loom 5 to a reel 6 onto which it is wound to form a roll 7. On completion of weaving, the roll 7 of fabric sheet 2 is removed.

The method according to the invention requires that the airflow resistance through the fabric sheet 2 should be monitored periodically during weaving. The monitoring of the airflow resistance is carried out using a portable micromanometer 10. In this embodiment of the invention the airflow resistance is checked with the micromanometer 10 adjacent a side edge of the fabric sheet 2 at intervals of 40cms as the sheet is being produced. The airflow resistance of the fabric sheet 2 is preferably checked adjacent the side edge which corresponds to the side opposite the side on which the shoot spool of the loom 5 is located, and preferably, at locations on a longitudinal centre line approximately lOcms in from the side edge.

The micromanometer 10 comprises a measuring head 12 through which an elongated bore 14 of constant circular cross-section extends. A means for urging air through the bore 14 comprises a vacuum pump 15 which is connected to the measuring head 12 by a flexible tube 16 which communicates the vacuum pump 15 with the bore 14 for drawing air through the bore 14 in the direction of the arrows A. A throttle valve 18 is located in the tube 16 for controlling the flow rate of air through the tube 16, and in turn, through the bore 14. A control inlet 19 communicates with the tube 16 upstream of the throttle valve 18 through which air may be drawn by the vacuum pump 15, and a throttle valve 20 is located in the control inlet 19 for controlling the rate at which air is drawn into the tube 16 through the control inlet 19 for, in turn, controlling the rate of air flow through the bore 14.

The measuring head 12 is formed in two parts, namely, an upstream part 21 and a downstream part 22, which form an upstream portion 25 and a downstream portion 26, respectively, of the bore 14. The portions 25 and 26 of the bore 14 are aligned. The upstream part 21 is carried on an arm 27, and the downstream part 22 is carried on an arm 28 which is pivotally connected to the arm 27 by a clamping means, namely, a toggle mechanism 29 for clamping the upstream and downstream parts 21 and 22 together. A carrying handle 30 extends from the arm 27 for facilitating carrying and holding the micromanometer 10 during use. The upstream part 21 and the downstream part 22 define respective receiving surfaces 31 and 32, which form a receiving means for receiving and sealably engaging the fabric sheet 2 between the respective upstream and downstream parts 21 and 22 with the fabric sheet 2 extending transversely across the bore 14. A sealing means comprising annular seals 33 located on the respective surfaces 31 and 32 of the upstream part 21 and the downstream part 22, respectively sealably engage the fabric sheet 2 between the upstream and downstream parts 21 and 22 so that all the air drawn through the bore 14 passes through the fabric sheet 2.

The arms 27 and 28 terminate in rings 35 which embrace and secure the respective upstream and downstream parts 21 and 22 to the arms 27 and 28, respectively. The toggle mechanism 29 is secured by screws 36 to the arm 27, and a pivot pin 37 carried in the toggle mechanism 29 pivotally carries a stub arm 38 to which the arm 28 is secured by screws 39. The screws 39 adjustably engage the arm 28 for facilitating adjustment of the clamping pressure exerted on the upstream and downstream parts 21 and 22 by the toggle mechanism 29.

A toggle handle 40 pivotally connected to the toggle mechanism 29 by pivot pins 41 toggles the stub arm 38, and in turn the arm 28 and the arm 27 together. The operation of such toggle mechanisms will be well known to those skilled in the art.

An orifice plate 45 is located in and extends transversely of the bore 14 in the downstream part 22 of the measuring head 12. A first measuring means for measuring the velocity of air through the bore 14 comprises a first differential pressure measuring means, namely, a first differential pressure measuring gauge 47 for determining the pressure drop across the orifice plate 45. Tubes 48 connect the first differential pressure measuring gauge 47 with communicating bores 49, which extend through the downstream part 22 of the measuring head 12 for communicating the first differential pressure gauge 47 with the downstream portion 26 of the bore 14 on respective opposite sides of the orifice plate 45 so that the pressure differential across the orifice plate 45 can be measured for determining the velocity of air through the bore 14, as will be described below.

A second measuring means for measuring the pressure differential across the fabric sheet 2 in the bore 14 comprises a second pressure differential measuring gauge 50. The second pressure differential gauge 50 communicates with ambient air through a tube 51, and communicates the downstream portion 26 of the bore 14 between the fabric sheet 2 and the orifice plate 45 through one of the communicating bores 49 for determining the pressure differential across the fabric sheet 2. By knowing the air velocity through the bore 14 and the pressure drop across the fabric sheet 2, the airflow resistance through the fabric sheet 2 can be determined as will now be described.

In this embodiment of the invention the airflow resistance is measured in centimetre, gramme, seconds, which, is conventionally known as a measure of airflow resistance in Rayls. The relationship between airflow resistance in Rayls and the pressure drop across the fabric sheet 2 and the velocity of air flowing through the bore 14 is as follows: δρ R =... .............................. (1) v where R is equal to the Rayl value in centimetre, gramme, seconds, δρ is the pressure drop in inches of water across the fabric sheet 2 as measured by the second gauge 50, and v is the velocity of air in centimetres per second through the bore 14 which is determined from the differential pressure drop across the orifice plate 45 as measured by the first gauge 47.

In this embodiment of the invention the air velocity is set constant at 105cms per second, and accordingly, with the pressure differential across the orifice plate 45 in inches of water, the above equation reduces to R = 23.723 x Sp ..................... (2) from the above, where δρ is measured in pascals, the above equation reduces to R =----x δρ ....................... (3) .5 In the present method, the orifice plate 45 is sized so that when the pressure differential across the orifice plate is equal to 480 pascals, the velocity of air through the bore 14 is 1.05 M per second. Accordingly, with the micromanometer 10 clamped on to a portion of the fabric sheet 2 as it is being fed from the loom 5, the throttle valves 18 and 20 are adjusted so that the pressure differential across the orifice plate 45 is 480 pascals, thus setting the air velocity through the bore 14 at 1.05 M per second. The pressure differential across the second gauge 50 is recorded, and by substituting the recorded pressure differential from the second gauge 50 in equation (3) above, the airflow resistance in Rayls of the portion of the fabric sheet 2 can readily be determined.

Should the Rayl value of airflow resistance fall outside the predetermined tolerance limits, appropriate adjustments are made to the weaving loom to correct the airflow resistance of the fabric sheet 2.

Periodically, the micromanometer requires calibration, and this is carried out by inserting a standard piece of fabric sheet 2 between the upstream and downstream parts 21 and 22 as already described, and testing the Rayl value of the standard sheet. Should the Rayl value derived from the micromanometer not correspond with the correct Rayl value of the standard sheet, then appropriate adjustments are made to the first and second differential pressure gauges 47 and 50 of the micromanometer.

The invention is not limited to the embodiment hereinbefore described which may be varied in construction and detail.

Claims

1. A method for producing woven wire fabric sheet having a relatively constant airflow resistance therethrough throughout the sheet, the method comprising weaving the fabric sheet on a loom, and periodically monitoring the airflow resistance of the fabric sheet as it is being woven on the loom, and adjusting the loom where necessary for maintaining the airflow resistance of the fabric sheet within predetermined tolerance limits, the airflow resistance of the fabric sheet being monitored by a micromanometer, the micromanometer comprising a measuring head having an elongated bore extending therethrough, a receiving means for receiving and sealably engaging the fabric sheet adjacent the bore with the fabric sheet extending transversely of the bore, so that all the air flowing through the bore flows through the fabric sheet, a means for urging air through the bore, a first measuring means for measuring the velocity of air through the bore, and a second measuring means for measuring the pressure drop in the bore across the fabric sheet for determining the airflow resistance of the fabric sheet.

2. A method as claimed in Claim 1 in which the measuring head comprises an upstream part and a downstream part, the respective parts forming an upstream and a downstream portion of the bore, and a clamping means for clamping the upstream and downstream parts together with the respective upstream and downstream bores aligned with each other, the receiving means being located between the respective upstream an downstream parts .

3. A method as claimed in Claim 1 or 2 in which an orifice plate is located in the bore, the first measuring means comprising a first differential pressure measuring means for measuring the pressure differential in the air across the orifice plate for determining the velocity of air through the bore, and the second measuring means comprises a second differential pressure measuring means for measuring the pressure drop across the fabric sheet, the means for urging the air through the bore comprising a vacuum pump.

4. A method for producing woven wire fabric sheet with a relatively constant airflow resistance within predetermined tolerance limits, the method being substantially as described herein with reference to and is illustrated in the accompanying drawings.

5. Woven wire fabric sheet woven according to the method of any preceding claim.