WO1996001984A1

WO1996001984A1 - Method and apparatus for measuring tension in a moving strand

Info

Publication number: WO1996001984A1
Application number: PCT/GB1995/001632
Authority: WO
Inventors: Boris Tchostkovski; Sergei Georgievich Shipilov
Original assignee: Hes Optical Fibres (Uk) Limited
Priority date: 1994-07-11
Filing date: 1995-07-11
Publication date: 1996-01-25
Also published as: AU3556795A

Abstract

A method of measuring tension in a moving strand (11, 21, 31) comprising the steps of: causing the strand to pass along a working path (X, P1) between first (A) and second (B) locations: directing across the strand at a predetermined position (P, 8, 14) a jet of gas (Q; Q'; Q1, Q3, Q2, Q4; F) to displace the strand (11, 21, 31) from the working path (X, P1) to a displaced path (ADB, D', P2); measuring the lateral displacement (H, D) of the strand (11, 21, 31) from the working path (X, P1) to the displaced path (ADB, D', P2); using the value of lateral displacement (H, D) and the distances (I1, I2) of the predetermined points along the strand (11, 21, 31) to the first and to the second locations to establish the tension (F) in the strand: characterised in that the velocity of the jet of gas (Q; Q'; Q1, Q2, Q3, Q4; F) is periodically varied. Typically the velocity of the gas jet is varied either by varying the gas flow speed through a nozzle (13; 2, 3; 2, 5, 3, 6; 16) defining the direction of the jet or alternatively the velocity of the gas jet (F) can be varied by varying the radial direction of the gas jet (F) relative to a predetermined location (14) on the working path (P1). The invention is further directed to apparatus for carrying out the method and product achieved by use of the method or apparatus.

Description

METHOD AND APPARATUS FOR MEASURING TENSION IN A MOVING STRAND

TECHNICAL FIELD

This invention relates to a method and to apparatus for tension measurement. It is particularly, but not exclusively, concerned with non-contact measurement of tension in a strand in a process where the strand is being drawn in a direction along its length. The term 'strand' is used as a generic term to cover items in the form of a filament, fibre, thread or suchlike and whether in the form of a mono filament or several filaments twisted, woven, plaited or otherwise drawn together to provide the required strand.

In the production of strand in the form of an optical fibre a preformed glass mass is placed in a furnace where it starts to melt. A glass fibre is drawn from a tip of the melting mass, passed through a region where it solidifies and is then passed into a coating bath where the fibre receives a protective coat of synthetic plastics material.

In drawing the fibre through the region where it solidifies it is necessary to measure the tension and when necessary make operating adjustments say to the furnace temperature so as to keep the tension within given tolerances during the drawing process. In practice the fibre moves at very high speed through the region where it is extremely thin and fragile prior to coating. Measurement of tension in such circumstances presents considerable difficulties. Typically any method of tension measurement involving contact with the fibre is impractical.

BACKGROUND ART

Known systems make use of non-contact tension measurement. In UK Patent 2127544 there is shown a device and a method wherein the value of strand tension is calculated by using an electrodynamic sound generator to generate a sound wave in the thread and measuring its velocity relative to the speed of sound in air. The disclosure is particularly concerned with fabric fibres. There are disadvantages in this system. Typically the measuring system is of large size (typically 900 mm high) which is not conveniently mounted on the drawing system. The excitation of the strand by the sound wave tends to disturb the drawing process and to affect strand quality. European Patent Application 0 549 131 (AT&T) with a priority date of 23rd December 1991 discloses a process of contactless monitoring the tension in a moving strand, such as during the process of drawing optical fibres from preforms, and a non-contacting tension gauge which allows measurement of strand tension at line speed. The process includes the steps of sensing an initial position of a moving optical fibre, applying a gas jet onto a section of the optical fibre in a direction transverse to the direction of movement of the fibre so as to cause deflection of the moving fibre axially of the gas jet, sensing the magnitude of deflection of the fibre relative to the initial position, and, depending on the magnitude of deflection, adjusting the tension in the fibre so as to cause the change in the magnitude of deflection to a preselected value, the monitoring is said to be especially suitable for monitoring the tension in an optical fibre being drawn from a heated preform, the tension being adjusted by adjusting the temperature of the fibre drawing furnace.

This describes the use of a fixed single gas jet to laterally displace a drawn strand from its drawn path and the use of a simple relationship between displacement and tension used to identify the strand tension.

An object of the present invention is to provide a continuous non-contact measurement of strand tension during a drawing process which avoids shock excitation or vibration of the drawn strand while providing for rapid and accurate tension measurement and to ensure effective feedback for stable control of strand tension.

DISCLOSURE OF INVENTION

In what follows the term 'velocity' is used in relation to gas flow to refer to a vector. That is to say an entity having both amplitude (referred to as 'speed') and direction relative to some datum direction. The term 'speed' is used to refer to an entity characterised only by amplitude.

According to a first aspect of the present invention there is provided a method of measuring tension in a moving strand comprising the steps of: causing the strand to pass along a working path between first and second locations; directing across the strand at a predetermined position a jet of gas to displace the strand from the working path to a displaced path; measuring the lateral displacement of the strand from the working path to the displaced path; using the value of lateral displacement and the distances of the predetermined points along the strand to the first and to the second locations to establish the tension in the strand: characterised in that the velocity of the jet of gas is periodically varied.

According to a first preferred version of the first aspect of the present invention the method is characterised in that the velocity of the jet of gas is varied by varying the gas flow speed through a nozzle defining the direction of the jet. Typically the gas jet flow speed is varied at a period of between 0.5 to 5 seconds.

According to a second preferred version of the first aspect of the present invention the method is characterised in that the velocity of the gas jet is varied by varying the radial direction of the gas jet relative to a predetermined location on the working path.

According to a first embodiment of the second preferred version of the first aspect of the present invention the method is characterised in that radial direction is varied by supplying the jet in turn from one of a plurality of nozzles disposed radially about the working path.

According to a third preferred embodiment of the first aspect of the present invention the second preferred version or the first embodiment thereof is characterised in that the gas jet serves to define a displaced path in the form a spiral about the working path.

According to a fourth preferred version of the first aspect of the present invention the method of the third preferred version is characterised in that the direction of the gas jet is caused to rotate about, while being directed towards, the working path so as to cause a point on a strand drawn through the region to follow a helical path relative to the working path.

According to a fifth preferred version of the first aspect of the present invention or any preceding preferred version thereof the method is characterised in that the measurement of displacement involves a lateral dimension of an envelope defined by a locus of a point on a strand drawn through the region while in the displaced path. According to a second aspect of the present invention there is provided apparatus for undertaking continuous measurement of tension of a strand during a drawing process comprising: means defining a region through which the strand is caused to pass along a working path; a nozzle directed across the working path; means for directing a gas jet through the nozzle so as to displace a strand initially passing along the working path from the working path to a displaced path; a sensor for detecting the displacement of the strand from the working path to the displaced path; and means for determining from the displacement of the strand the tension in the strand in the displaced path characterised by means for varying the velocity of the gas jet.

According to a first preferred version of the present invention the apparatus is characterised in that the means for varying the velocity of the gas jet serves to vary the gas flow speed through the nozzle.

According to a second preferred version of the present invention the apparatus is characterised in that the velocity of the gas jet serves to do so by varying the direction of the gas jet relative to a datum direction such as the working path.

According to a third preferred version of the second aspect of the present invention the apparatus is characterised by a pair of gas nozzles used in horizontally opposed alignment on opposite side of, and perpendicular to, the working path and flow means provide for a gas jet to issue from each nozzle of the pair in turn to displace the strand.

According to a first embodiment of the third preferred version of the second aspect the apparatus is characterised by at least one further pair of gas nozzles in horizontally opposed alignment on opposite side of, and perpendicular to, the working path and flow means provide for a gas jet to issue from each nozzle of the further pair in turn to displace the strand; the or each further pair being located at a predetermined angle relative to the pair of nozzles. Typically the predetermined angle is a right angle.

According to a third preferred version of the second aspect of the present invention or any preceding preferred version thereof the apparatus is characterised in that the sensor is located perpendicular to the working path and in juxtaposition with the gas nozzle or nozzles. According to a third aspect of the present invention there is provided a strand manufactured by means of a production process characterised in that it incorporates a method of measuring tension according to the first aspect.

According to a fourth aspect of the present invention there is provided a strand manufactured by means of a process characterised by the use of apparatus according to the second aspect.

The present invention is based on the discovery that strand tension in a region between the furnace and the coating apparatus can be quantified from the transverse displacement of the strand caused by a displacing gas flow directed across the drawn strand. The gas flow displaces the strand from its normal path in a given period. The gas flow can be directed across the strand in a various ways: typically one nozzle can be used or a pair of horizontally opposed nozzles or two pairs of horizontally opposed nozzles.

The required gas flow rates are achieved using conventional flow regulators but at rates according to a pre-determined law. The displacement of the drawn strand from a displaced path by the gas flow is detected by an optical sensor which generates a signal which is passed to a processor which calculates the amount of displacement and thereafter establishes the strand tension.

BRIEF DESCRIPTION OF DRAWINGS

Exemplary embodiments of the invention will now be described with reference to the accompany drawing of optical strand drawing installations in which:

Figure 1 is a diagram relating to tension measurement in a strand;

Figure 2 shows a vertical section of a first strand drawing system using a pair of horizontally opposed gas nozzles;

Figure 3 shows a vertical section of a second strand drawing system utilising two pairs of horizontally opposed gas nozzles;

Figure 4 shows a perspective diagrammatic view of a drawing system utilising the nozzle arrangement of Figure 3;

Figure 5 is a side view of components in a further embodiment;

Figure 6 is a perspective view of a component of Figure 5; and

Figure 7 is a lateral section on section VΗ-VII of Figure 6. MODES FOR CARRYING OUT THE INVENTION

Figure 1

A strand of glass strand 11 is drawn from a melting preformed glass mass in a furnace (shown diagrammatically as a block GF) in the general direction of arrow W through a work region 12 into a coating bath shown as a block CB.

The strand 11 follows a working path X which leaves the melted preform at point A and passes into the coating bath at point B. Gas nozzle 13 is off set from, and is directed perpendicularly across, the working path X at a predetermined region P. The nozzle 13 is supplied with a regulated supply of compressed air by inlet pipe 14.

Point C on working path X corresponds to an initial position of strand 11 in the predetermined region P when there is no gas flow through the nozzle 13.

On the provision of a gas flow Q through nozzle 13 in the direction J the strand 11 is displaced by a force G. For as long as the gas flow Q is maintained the strand 11 thereafter no longer follows working path A C B but rather a displaced path A D B. The distance along strand 11 from point A to point C is II. The distance along strand 11 from point D to point B is 12.

Given a resultant tension F in the strand the displacement H is calculated from the identity:

H = C * d * (II * I2)/(I1 + I2) * Q² * 1/F (1)

where

C is a coefficient dependent on functional parameters of the nozzle 13; d is the diameter of the strand 11;

II, 12 are the distances from A to D and from D to B respectively;

Q is the gas flow rate through the nozzle 13. Q is related to the gas flow speed and so the value of the force G displacing the strand 11.

Relationship (1) gives that the measurement of displacement H, for example by means of a non-contact optical device located in the predetermined region P, it is possible to calculate tension F relatively easily.

In a simple embodiment it is possible to use a constant gas flow Q so providing for strand displacement along the displaced path A D B throughout the drawing process. However this presupposes a stable geometry throughout the strand system and in particular stability of the points A, B. In practice such stable geometry cannot be expected. The tip preform point A moves slowly transverse the path X during the drawing process due to the drawing off point on the melting glass mass not remaining laterally fixed. In addition the position of point B can also move laterally due to movement of the coating bath under the control of a regulator which acts to ensure that the coating applied to the strand is applied concentrically about the strand in passing through the coating bath.

Both these additional factors of displacement at A and B cause additional displacement of the strand 11 when subject to a single constant direct gas flow and this additional displacement could be interpreted as a strand tension change. To overcome this possible source of error the present invention uses a varying gas velocity instead of a constant one in two ways as will be described hereafter.

By using a variation in flow velocity a number of benefits are achieved over and above a constant velocity displacement. It provides for the avoidance of any shock effect of gas flow on the strand 11 so providing for smooth strand displacement in a direction transverse the strand path. With a single gas jet arrangement with varying velocity the strand is periodically displaced in the transverse direction to its displaced path by means of the gas flow and then returns to its working path when the gas flow is periodically terminated. The displacement amplitude H is determined during each period as the distance between the working path and displaced path positions.

The strand position is detected with an optical sensor and a processing unit then establishes the displacement H and calculates tension F. The displacement H in this arrangement is substantially independent of any slow drift arising in the points A, B as discussed earlier since the relatively short time needed to make the repeated measurements of periodic displacement is negligible compared with the drifts associated with points A and B. Suitable periods of gas flow change in relation to glass strand have been found to lie in a range between 0.5 and 5 seconds.

The displacement of the strand from its working path ACB to its displaced path ADB effectively increases the length of strand and this has an effect on the drawn strand diameter. With periodic displacement of the strand the strand diameter can be modulated along the length of the strand.

Figure 2

This shows the use of a pair of nozzles 2, 3 located in a horizontally opposed configuration on opposite sides of strand 21. The strand 21 is shown passing through working volume 22 of an optical sensor 4 which by way of sensor heads 4A and 4B senses the displacement of the strand 21 from its working path X. Position D of strand 21 corresponds to the displacement caused by the action of gas from nozzle 2 with no gas flow from nozzle 3. Position D' of strand 21 corresponds to the displacement caused by the action of gas from nozzle 3 with no gas flow from nozzle 2. Typically with a strand diameter of 0.125 mm a suitable displacement has been found to lie in the range 0.05 to 0.150 mm (say 4 to 12% of the strand diameter). Less displacement is required with a pair of jets than arises with the use of a single jet. A reduced displacement appears likely to have less influence on the strand diameter as it passes through the measuring region.

Optical sensor 4 continuously detects the current position of strand 21 and passes the information to processor 23 which from the limiting position D, D' establishes the value of displacement H and so the tension F of the strand 21. In practical terms it is difficult to locate the sensor 4 and the gas nozzles 2, 3 in one and the same plane. Nevertheless a minimum separation is to be preferred.

Figure 3

The removal of the modulation effect on the strand diameter due to periodic displacement discussed earlier can be achieved with the use of additional nozzle pair. The nozzles 2 and 3 are horizontally opposed to create a first nozzle pair. A second nozzle pair made up of nozzles 5, 6 are located in a horizontally opposed relationship at right angle to the first pair. Both pairs of nozzle are equidistant form working path X of strand 31. The nozzles 2/3 and 5/6 are supplied with air at a selected rate so as to provide what amounts to a single jet of gas being rotated in steps about the work path of the strand. Effectively this stepped rotation results in a change in velocity of the gas jet relative to the passing strand. This change in velocity is independent of any change in speed of the gas jet. Nozzles 2, 3 provide gas flows, respectively Ql(t), Q2(t) in accordance with a harmonic sine law. The phase shift between Ql and Q2 is 180°. Nozzles 5, 6 provide gas flows, respectively Q3(t), Q4(t) in accordance with a harmonic sine law. The phase shift between Q3 and Q4 is 180°. The phase shift between Ql and Q3 is 90°.

As a result what is in effect a radially rotating gas jet is generated by way of the flows from the nozzles 2, 5, 3, 4 on the strand 31 causing the strand in the predetermined zone to rotate about the working path X on a displaced path D in the form of a circle centred on the working path. The diameter of the circle D is 2 * H where H is related to the tension in the strand 31 in accordance with relationship (1) above.

Figure 4

This shows a practical embodiment of the arrangement discussed in relation to Figure 3. The gas nozzles are broadly indicated as a block 8 (broken outline) and include the four nozzles 2, 3, 5 and 6 which are connected through pipelines 9 with a gas supply and regulating unit 10. The nozzles 2, 3, 5, 6 are operated as described in relation to Figure 3 to cause what amounts to a radially rotating gas jet to act of the strand 31. The resulting motion of the strand 31 is detected by the optical sensor 4 which feeds the detected displacement H to a processor 11.

Any strand diameter sensing device which also serves to detect the strand displacement can be used in relation to this embodiment such as BETA or ANRITSU sensors.

The processor unit 11 uses the signal relating to strand displacement from the sensor 4 to determine the diameter of the displacement circle D as a difference between values of displacement signal during one period of the strand circling . Displacement H is determined by the diameter of the strand circle D from which the tension can be determined.

The processor 11 can be incorporated on a circuit board along with a micro¬ processor for handling the various signals and to calculate the strand tension in accordance with a suitable algorithm.

Ideally the four nozzles would be located in the same plane perpendicular to the strand path. However it is virtually impossible in view of interaction between the various the gas flows. In addition the location of the optical sensor and the gas nozzles in one and the same plane is not feasible. Consequently for practical purposes the device shown in Figure 4 has certain structural features:

1 The nozzles 2, 3, 5, 6 are positioned at different levels along the strand 31 to avoid mutual interaction between the four possible gas flows as the Ql(t), Q2(t), Q3(t) and Q4(t) as the gas jet radial change occurs.

2 The nozzle 3 is located above or beneath the optical sensor 4 relative to the strand but with minimum vertical separation between them.

3 The nozzles 2, 3, 5, 6 have outlets of rectangular cross section. The width is more than the maximum possible diameter of the circle D that can be established by strand 31.

The method embodied in the apparatus described in relation to Figures 3 and 4 includes: forming a gas flow acting on the strand with a velocity which changes in direction according to a periodic law; causing the strand to be displaced on a circular path by the gas jet applied perpendicular to the axis of the strand; observing the current strand position with optical sensing devices; determining the transverse displacement of the strand; and calculating the tension of the strand in accordance with the relationship:

F = k * l /H (2)

where k = C * d * (II * I2)/(I1 + 12) * Q²

The relationship (2) is obtained from the relationship (1). Once the tension F is established the processor 11 can be used to provide a control signal such as to the furnace to adjust the furnace temperature so as to maintain the tension value within a given working range during the drawing process.

Figures 5 to 7

Figure 5 shows a strand of glass strand 11 being drawn down from a melting tip 12 of glass extending from a furnace 13 in the general direction of arrow A through a work station region 14 before entering a first coating station 15. The undisplaced working path for the strand is a straight line PI.

Workstation 14 is now considered in more detail in relation to Figure 6 and 7.

A gas nozzle 16 is mounted on an annulus 17 which is rotatably mounted on a carrier 18 which has an internal passage 19 surrounding the path PI. Rotation of the annulus 17 in direction B about a centre located on path PI results in the nozzle 16 rotating about an orbit 16A where the nozzle 16 is always directed towards the strand 11. The gas velocity established by way of nozzle 16 is thus periodically varying relative to the path PI though the gas speed through the nozzle may be held constant. As a consequence the nozzle 16 directs a flow of gas F which displaces the strand 11 away from the nozzle 16 and causes the strand to follow a path P2. While path P2 is circular as viewed along path PI it represents the locus of a point on the strand 11 as it moves through the work station 14 and when acted on by the gas flow F, is caused to follows helical path P2 about path PI.

In the region of the nozzle 16 displacement D for an optical strand with a diameter of 0.125 mm is envisaged as being about 0.2 to 0.3 mm that is to say the displacement D amounts to about 160 to 240% of the strand diameter.

The annulus 17 rotates freely on carrier 18 which has an internal chamber 21 into which a compressed inert gas, typically nitrogen, is fed by way of inlet pipe 22. Annulus 17 is caused to rotate by means of cogged wheel 23 driven by electric motor 24. The motor is powered by way of lead 25. Pressurised gas from internal chamber 21 flows into nozzle 16 by way passage 26 in the annulus 17 and from thence out of nozzle 16 as gas flow F. Other powering means may be used based on pneumatic or hydraulic sources. An optical scanner 27 is located to measure the displacement D of the strand path P2 from the undisplaced path PI. In a steady state condition with constant drawing speed and unvarying tension the displacement D will remain constant. In the event that the displacement D is detected by the scanner as changing from a steady state output then appropriate corrective action can be taken either by means of control loop of which scanner 26 is a part or by control inputs applied to the system directly by an operator. Such corrective action could be to means applying tension to the strand. In an alternative embodiment the scanner can be housed in the carrier 18.

INDUSTRIAL APPLICABILITY

The described embodiments disclose method and apparatus for measuring strand tension in the course of manufacture without adversely effecting the physical characteristics of the drawn strand. The embodiments are particularly useful where as in the present case a relatively delicate product is travelling at high speed from a source of molten material to a coating bath for the solidified material. The methods and apparatus enables changes in the tension of the material to be determined rapidly and for any necessary corrective action to be applied swiftly. The embodiments make use of a velocity changes in a gas jet impinging on the drawen strand. The velocity changes can be generated by varying the speed or the amplitude (or the speed and the amoplitude) of the, or each, gas jet. By providing more than one gas nozzle around the laterally undisplaced strand path it becomes possible to provide for the issue of gas from each nozzle in turn so that the effect is of a single jet moving around the path of the strand.

The invention is also applicable to other types of strand given that the strand can be displaced from a working path to a displaced path by an amount of displacement which can be related to the tension in the moving product.

Claims

1 A method of measuring tension in a moving strand comprising the steps of: causing the strand to pass along a working path between first and second locations; directing across the strand at a predetermined position a jet of gas to displace the strand from the working path to a displaced path; measuring the lateral displacement of the strand from the working path to the displaced path; using the value of lateral displacement and the distances of the predetermined points along the strand to the first and to the second locations to establish the tension in the strand: characterised in that the velocity of the jet of gas (Q; Q'; Ql, Q2, Q3, Q4; F) is periodically varied.

2 A method as claimed in Claim 2 characterised in that the velocity of the gas jet (Q) is varied by varying the gas flow speed through a nozzle (13) defining the direction of the jet (Q).

3 A method as claimed in Claim 2 characterised in that the gas jet (Q, Figure 1) flow speed is varied at a period of between 0.5 to 5 seconds.

4 A method as claimed in Claim 1 characterised in that the velocity of the gas jet (F, Figure 7) is varied by varying the radial direction of the gas jet F relative to a predetermined location in the working path (PI).

5 A method as claimed in Claim 1 characterised in that the radial direction is varied by supplying the jet (Ql, Q3, Q2, Q4) in turn from one of a plurality of nozzles (2, 3, 5, 6) disposed radially about the working path (X).

6 A method as claimed in Claim 4 or Claim 5 characterised in that the gas jet (F; Ql, Q3, Q2, Q4) serves to define a displaced path (P2; D) in the form a spiral about the working path (PI; X).

7 A method as claimed in Claim 4 characterised in that the direction of the gas jet (F) is caused to rotate about, while being directed towards, the working path (PI) so as to cause a point on a strand (11) drawn through the region (14) to follow a helical path (P2) relative to the working path (PI). A method as claimed in any preceding claim characterised in that the measurement of displacement (H; D) involves a lateral dimension of an envelope defined by a locus of a point on a strand (11) drawn through the region (12; 22; 14) while in the displaced path (ADB; DD'; HH; D).

Apparatus for undertaking continuous measurement of tension of a strand during a drawing process comprising: means defining a region through which the strand is caused to pass along a working path; a nozzle directed across the working path; means for directing a gas jet through the nozzle so as to displace a strand initially passing along the working path from the working path to a displaced path; a sensor for detecting the displacement of the strand from the working path to the displaced path; and means for determining from the displacement of the strand the tension in the strand in the displaced path characterised by means for varying the velocity of the gas jet (Q; Q'; Ql, Q2, Q3, Q4; F).

Apparatus as claimed in Claim 9 characterised in that the means for varying the velocity of the gas jet serves to do so by varying the gas flow speed through a nozzle (13) defining the direction of the jet (Q)..

Apparatus as claimed in Claim 9 characterised in that the velocity of the gas jet serves to do so by varying the radial direction of the gas jet F relative to a predetermined location in the working path (PI)..

Apparatus as claimed in Claim 9 characterised by a pair of gas nozzles (Figure 2: 2, 3) are used in horizontally opposed alignment on opposite side of, and perpendicular to, the working path (X) and flow means provide for a gas jet (Q') to issue from each nozzle (2, 3) of the pair in turn to displace the strand (21) from the working path X to a displaced position (D).

Apparatus as claimed in Claim 12 characterised by at least one further pair of gas nozzles (Figure 3: 5, 6) in horizontally opposed alignment on opposite side of, and perpendicular to, the working path (X) and flow means provide for a gas jet (Q3, Q4) to issue from each nozzle (5, 6) of the further pair in turn to displace the strand 21); the or each further pair (5, 6) being located at a predetermined angle relative to the pair of nozzles (2, 3). Apparatus as claimed in Claim 13 characterised in that the predetermined angle is a right angle.

Apparatus as claimed in Claim 9, 10, 11, 12, 13 or 14 characterised in that the sensor (4; 27) is located perpendicular to the working path (X; PI) and in juxtaposition with the gas nozzle or nozzles (Figure 2: 2, 3; Figure 3: 2, 5, 3, 6; Figure 7: 16).

A strand manufactured by means of a production process characterised by a method of measuring tension as claimed in Claims 1 to 8.

A strand manufactured by means of a process characterised by the use of apparatus as claimed in Claims 9 to 14.