GB2252632A

GB2252632A - Apparatus for determining the permeability of a textile fabric

Info

Publication number: GB2252632A
Application number: GB9201882A
Authority: GB
Inventors: Ludwig Kis
Original assignee: Textilmaschinenfabrik Dr Ernst Fehrer AG
Current assignee: Textilmaschinenfabrik Dr Ernst Fehrer AG
Priority date: 1991-02-08
Filing date: 1992-01-29
Publication date: 1992-08-12
Also published as: IT1257308B; GB9201882D0; FR2672685A1; AT394785B; ATA27391A; ITGE920005A0; JPH0599835A; ITGE920005A1; DE4202205A1

Abstract

An apparatus for determining the permeability of a textile fabric to air comprises a testing head (2), which is adapted to be applied to the textile fabric in airtight contact therewith and is connected to an air-conducting line (3) and is operable to suck or blow a stream of air through the fabric in a predetermined area thereof and a measuring device (6), which serves to measure the flow of air in said air-conducting line and comprises an orifice plate (7) in said air-conducting line and a pressure gage, which is connected to the air-conducting line on opposite sides of the orifice plate. To ensure that said pressure gage will measure said pressure drop with the highest possible sensitivity, the orifice plate consists of an iris diaphragm (11) defining an adjustable orifice (13). <IMAGE>

Description

2 '.)., 1 1 - APPARATUS FOR DETMINING THE PERLEABILITY OF A TEXTI=. FABRIC

TO AIR BACEGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus for determining the permeability of a textile fabric to air, which apparatus comprises a testing head, which is adapted to be applied to the textile fabric in airtight contact therewith and is connected to an air-conducting line and is operable to suck or blow a stream of air through the fabric in a predetermined area thereof and a measuring device, which serves to measure the flow of air in said air-conducting line and comprises an orifice plate in said airconducting line a pressure gage, which is connected to the airconducting line on opposite sides of the orifice plate.

2. Descript ion of the Prior Art

The permeability of a textile fabric, such as woven or nonwoven fabric, to air is usually determined by means of a testing head, which is connected to a suction line and is applied to the fabric in airtight contact therewith. To measure the mte at which air is sucked through the fabric under a predetermined suction pressure the pressure drop across an orifice plate included in the suction line is measured and the velocity of flow is calculated from the measured pressure drop and the flow area ofihe orifice plate. Because the pressure gages used for that purpose have a high sensitivity only in a restricted pressure range, the orifice plate must often be changed for an adaptation of the pressure drop to such pressure range. That change of the orifice plate is a timeconsuming operation and will permit an adaptation only in steps so that measurements involving pressure drops near a limit of such preferred pressure ranges will give rise to the.risk t-hat the pressure drop will depart from the preferred pressure range during the measurement of the permeability of a textile fabric consisting of a moving web. In that case the sensitivity of the measurement will be low so that wrong results may be obtained.

SLILWARY OF THEE IME1NTION It is an object of the invention to avoid the disadvanta-es outlined hereinbefore and to provide for the determination of the permeability of a textile fabric to air an apparatus which is so improved by the use of simple means that a departure of the pressure drop from a preferred range ensuring a high sensitivity of the measurement will be avoided so that measurements giving wrong results will be precluded in practice.

That object is accomplished in accordance with the invention in that the orifice plate consists of an iris diaphragm comprising adjustable blades defining an adjustable orifice.

The orifice plate consisting of an iris diaphragm can be used for a continuous adjustment of the orifice so that the pressure drOP across the orifice plate can be adjusted to lie in a pressure range in which the pressure gage has the highest sensitivity. WhEreas in the determination of the permeability of a moving textile fabric web to air a change of the permeability of such web to air will result in a change of the flow of air through the orifice plate, the pressure drop will remain within the preferred range because it can be assumed that the permeability of the moving fabric web to air will not change suddenly in practia-n, Because the dependence of the area of the orifice on the position of the blades of the iris diaphragm is known, an orifice area can be associated with each position of the diaphragm blades so that the velocity of flow of the measuring air stream through the orifice plate can be computed in conventional manner from the measured pressure drop across the orifice plate.

Particularly desirable meauring conditions can be ensured in that the blades of the orifice plate are controlled by a control device in dependence on the pressure drop which is measured by the pressure gage. By that control device the pressure drop across the orifice plate can automatically be maintained at a constant value so that the pressure drop across the orifice plate will always be measured by the pressure gage with the highest possible sensitivity regardless of changes of the permeability of the moving fabric web to air. It will be understood that in such case any adjustment of the orifice plate must be taken into account in the processing of the measured values to determine the permeability of the fabric to air. If the pressure drop across the orifice platcis automatically maintained exactly at a predetermined value, the adjusted position of the orifice plate will constitute in itself a measure of the velocity of flow of the measuring ab stream.

BRIEF DESCRIPTION OF THE DWINGS

Figure 1 is a side elevation which is paitly broken away and shows an apparatus in accordance with the invention for determining the permeability of a moving textile fabric web to air.

Figure 2 is a top plan view showing on a larger scale the means provided in the apparatus of Figure 1 for measuring the flow of air in the apparatus shown in Figure 1.

Figure 3 is a sectional view taken on line III-III in.Figure 1.

DETAILEED DESCRIPTION OF THE PREFERRED EIL1BODIMENT

An illustrative embodiment of the invention will now be described more in detail with reference to the drawing.

The apparatus shown in Figure 1 and serving to determine the permeability of a moving textile fabric web to air comprises a testing head 2, which is mounted in a support 1 for the nioving textile fabric web and is connected by an air-conducting line 3 to the suction side of a fan 45 which is driven by a motor 5 having a constant power so that a constant suction pressure is ensured. Whereas certain advantages will be afforded by the use of a suction air stream for determining the permeability of a moving textile fabric web to air, it will be understood that the permeability to air may alternatively be determined by means of a stream of blast air.

In the operation of the apparatus, the testing head 2 is applied to the moving textile fabric in airtight contact with it around a predetermined area of said fabric and the fan 4 is operated to apply by the testing head 2 a predetermined air pressure to said fabric in said predetermined area to generate an air stream flowing through said fabric, the testing head 2, and the air-conducting line 3.

For the measurement of the velocity of flow of the air which is sucked or blown through the moving textile fabric web, a device 6 for measuring the velocity of flow of the stream of air is associated with the airconducting line 3 and comprises an orifice pMe 7 included in the line 3 and a pressure gage 8, which is connected by two measuring lines 9 to the air-conducting line 3 on opposite sides of the orif ice plate 7.,-Is is apparent from Figure 3 the orifice plate 7 is mounted in a housing, which is incorporated in the air-conducting line and which on each side of the orifice plate 7 contains an annular chamber 10, which communicates with the interior of the air-conducting line 3. From said annular chamber 10 the measuring lines 9 extend to the pressure gage 8. Owing to that arrangement the measuring lines 9 connected to the air-conducting line 3 will not affect the conditions of flow within the air-conducthg line 7i. The orifice plate 7 consists of an iris diaphragm that comprises adjustable blades 11, which can be pivotally moved in unison by means of an adjusting ring 12 for a continuous adjustment of the area of the orifice 13 defined by said blades. The adjusting ring 12 is connected to a gear segment 14, which meshes with a Dinion 16, which is driven by a servomotor 15. The instantaneous angular position of the adjusting ring 12 is detected by an angle encoder 17, which is operatively connected to the pinion 16. A processing stage 18 is provided for computing the velocity of flow of air through the orifice Plate 7 in lpendence on the detected angular position of the adjusting ring 12, i.e., in dependence on the area of the orifice 13, and in dependence on te pressure drop across the orifice plate 7, which pressure drop is measured by the pressure gage 8. The range through which the ad- o justab-1e orifice plate 7 is adjustablEis limited by limit switches 19, which are actuated by a switching lug 20, which is connected to the adjusting ring 12.

Because the area of the orifice 13 can be continuously adjusted, it is possible to maintain the pressure drop across the orifice plate 7 whithin the range in which the pressure gage 8 has the highest sensitivity. This is an essential requirement for an accurde measurement of the permeability of a moving textile fabric web to air. To permit a continual readjustmebt of said pressure drop in response to changes of the permeability of the web to air, it is possible to provide a controller 21 for a continuous control of ite orifice plate 7 so as to maintain a constant pressure drop across the orifice plate 7. For that purpose the actual pressure drop measured by the pressure gage 8 is compared in th-- controller 21 with a set point, which is the pressure drop at which the pressure gage 8 has the highest 0 sensitivity, and in response to said comparison the controller 21 controls the servomotor 15 to eliminate an7 deviation of the pressure drop from said set point. Such an arrangement is schematically shown in Figure 3.

ouim 1. In an apparatus for determining zhe permeability of a textile fabric to air, comprising a testing head, which is adapted to be applied to a textile fabric in sealing contact therewith around a predetermined area ofsaid fabric, an air-conducting line connected to said testing head, means for applying by said testing head a predetermined air pressure to said fabric in said predetermined area to generate an air flow through said fabric, said testing head, and said air-conducting line, and measuring means for measuring said air which measuring means comprise an orifice plate in said air-conducting line and a pressure gage connected to said air-conducting line on opposite sides of said orifice plate and arranged to measure the pressure drop across said orif ice plate, the improvement residing in that said orifice plate consists of an iris diaphragm comprising adjustable blades defining an adjustable orifice.

2. The improvement set forth in claim 1 as applied.to an apparatus for determining the permeability of a moving textile fabric web to air.

3.

wherein a control device is provided for adjusting said adjustable blades in dependence on the pressure drop measured by said pressure gage.

CD Q The improvement set forth in claim 2, 4. wherein said control device is arranged to maintain said pressure drop at a constant value.

The improvement set forth in claim 2, 5. An apparatus for determining the permeability of a textile fabric to air as herein described with reference to the accompanying diagrammatic drawings.