GB1602731A

GB1602731A - Removal of excess liquid coatant from skip

Info

Publication number: GB1602731A
Application number: GB18013/77A
Authority: GB
Original assignee: British Steel Corp
Current assignee: British Steel Corp
Priority date: 1977-04-29
Filing date: 1977-04-29
Publication date: 1981-11-18
Also published as: ZA782226B; SE7804918L; FR2388605A1; FI781304A; DE2818620A1; ES475992A1; NO781500L; BR7802685A; BE866501A; ES469210A1; LU79566A1; CA1091994A; NL7804630A; IT7867976A0; JPS549122A

Description

(54) IMPROVEMENTS IN THE REMOVAL OF EXCESS LIQUID COATANT FROM STRIP (71) We, BRITISH STEEL CORPORATION, a Corporation incorporated and existing under the Iron and Steel Act 1967 whose principal office is at 33 Grosvenor Place, London SW1 do hereby declare the: invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention is concerned with improvements in the coating of strip and particularly with devices commonly known as fluid or gas knives which remove excess liquid coatant from a strip moving upwardly from a bath containing the coatant.

In the coating of strip, particularly the galvanising of steel strip, the strip is introduced into a molten bath of the zinc to form the coating of the strip. Generally the strip coated in this manner has an excessively thick and uneven coating of zinc. To remove the excess zinc and provide a uniform zinc coating, it is the conventional practice to subject the strip, at a position just above the surface of the bath where the zinc is still molten, to the action of two jets of fluid, for example, air or steam on opposed surfaces of the strip transversely of the strip width. The air or steam jets issue from devices known conventionally as fluid or gas knives, which comprise elongate nozzles with a slot through which the jets of air or steam emerge. The jets form barriers tending to cause the excess zinc to run back towards the bath of molten zinc.

To ensure that the complete width of the strip is subjected to the action of the jets, the nozzle is normally dimensioned to extend beyond either longitudinal edge of the strip so that the fluid jet also extends beyond the edges. Unfortunately, this gives rise to a significant and usually unacceptable noise problem caused by the impingement upon each other of the opposed fluid jets at the regions beyond the edges of the strip.

It is therefore an object of the present invention to provide a device in which the degree ofjet impingement is at least reduced so as to lower the noise level inherent in the use of these devices.

According to one aspect of the present invention, a device is provided for removing excess liquid coatant from a strip moving upwardly from a bath containing the liquid, the device comprising a cylindrical header having a pair of lips defining an elongate nozzle having a slot for directing a fluid jet onto the strip surface, together with at least one hollow part-cylindrical baffle nesting within the header and dimensioned to close off all but a portion of the nozzle from the header, the baffle being so shaped that axial rotation thereof varies the length of the open nozzle portion and thereby the width and alignment of the fluid jet transverse to the strip.

Preferably two baffles are provided, one at each end of the header so that all but an intermediate portion of the nozzle is closed off from the header and baffle is suitably provided with a portion having a circumfer-ential edge following a helical path.

Suitably a movable side seal is provided for the or each baffle, the or each side seal being located within the space between the nozzle lips and the baffle, the or each seal being located adjacent the point or points where fluid from the baffle or baffles enters the nozzle and the or each seal being effective substantially to limit the width of the fluid jet issuing from the slot to that of the open nozzle portion.

Conveniently the or each baffle and the or each seal are motor driven, and preferably the or each seal and its corresponding baffle are coupled together by gearing in such a manner that the linear vector of baffle movement and that of the seal are coincident.

An embodiment of the invention will now be particularly described by way of example only with reference to the accompanying drawings in which: Figure 1 is a front view in elevation of a device in use during the galvanising coating of steel strip emerging from its coating bath; Figure 2 is a side view in section along lines II-II of Figure 1; Figure 3 is a perspective view of a side baffle; Figure 4 is a sectioned front view showing the coupling between a side baffle and its drive gear; Figure 5 is a top view of an end section of two fluid devices at opposite sides of a steel strip, and Figure 6 is a sectioned front view of a bottlejack for driving a baffle sealing member.

Referring to Figure 1, the device shown generally at 1 comprises a cylindrical header 2 which is mounted by an elongate support bracket 3 above a bath 4 containing in this case molten zinc 5. The device 1 also comprises a nozzle assembly shown generally at 6 (to be described more fully later) which is horizontally disposed adjacent a steel strip 7 which emerges upwardly from the zinc 5 via the rolls 62, 63 the strip 7 thereby having a molten coating of zinc. The excess zinc is stripped away by the action of an air jet issuing from the nozzle assembly 6 of the device 1. A similar device 10 is disposed on an opposite side of the strip 7 as shown in Figure 5 to strip excess molten zinc from that side of the strip 7.

Referring to Figure 2, the nozzle assembly 6 comprises a pair of upper and lower lips 8 and 9 which are angled towards each other and define at their strip-facing ends an elongate slot 11 through which a flat jet of air can issue onto the strip 7. Each lip 8,9 is held at two positions by screws 12, 13 to plates 14, 15 which are welded to the circumference of the header 2. Within the header 2 nests at either end thereof part-cylindrical side baffles 16 (only one shown) which are rotatable to close off from the header 2 the nozzle lips 8, 9.

Triangular shaped seals 17 are located within the space defined by the lips 8,9 and the baffles 16 adjacent the points where the air from the baffles 16 enters the nozzle assembly 6. The seals 17 have one concave wall 18 so as to mate with the adjacent baffle wall. The seals 17 like the baffles 16 are a close fit within the space they occupy.

Attached to the lower lip 9 is an elongate buffer means 19 comprising a plate 20 having welded to a front portion within a concave recess a circular steel rod 21 which extends beyond the front strip-facing edges of the lips 8,9. The buffer means 19 prevents the strip 7 from contacting the edges of the lips 8, 9 should the strip 7 veer towards the lips 8, 9 during the coating process. In this way blockage of the slot 10 by solidified zinc is prevented.

Referring to Figure 3, the side baffle 16 has a wall 22 in cylindrical form which extends from a circumferentially flanged end 23 to a point someway along its length. At this point.

the baffle wall 22 is open and has a helical edge 24 tracing towards the flanged end 23 a clockwise path. The ends 25, 26 of the helix 24 are joined via an edge 27 parallel to the axis ofthebaffle 16.

As shown in Figure 3 and in Figure 4, the flanged end 23 of the baffle 16 is toothed to enable the end 23 to mesh with a gear 28 (Figure 4) and so drive and axially rotate the baffle 16.

The flanged end 23 and the gear 28 are located between flanged end portions 29, 30 of the header 2 and a detachable header portion 31 which is bolted to the header 2 via nut and bolt arrangement 32. The flanged end 23 of the baffle 16 is spaced from the flanged end portions 29, 30 by annular bearings 33, 34 while the cylindrical portion of the baffle wall 22 is provided with a sleeve bearing 35. Gear 28 is attached to a shaft 36 which rotates upon bearings 37, 38 disposed within apertures in the flanged end portions 29, 30.

Referring to Figure 5, drive for the shaft 36 is derived from a universal coupling 39 and a gear-box 40. Drive for the gear-box 40 is supplied from an electric motor (not shown).

The seal 17 is driven by a bottle-jack arrangement 41 (to be described later), coupled via a shaft 42, a universal coupling 43, and the gear-box 40 directly to a motor-driven shaft 44. The universal couplings 39 and 43 are each provided with intermeshing gears (not shown) within the gear-box 40.

Referring to Figure 6, the seal 17 comprises two steel plates 45 and 46 spaced from each other by a sealing gasket 47 which abuts the wall 22 of the baffle 16 and the nozzle lips (not shown). The seal 17 is attached to a shaft 48 which forms part of the bottle-jack 41.

The bottle-jack 41 comprises a cylinder 49 which is secured to the header 2. An internally threaded outer sleeve 50 is rotated by the shaft 42 with which the outer sleeve 50 is integral, the shaft 42 being driven by the universal coupling 43. The sleeve shoulders 51 and its ends 52 abut against the flanged ends 53, 54 of the cylinder 49 and the sleeve 50 is spaced from the internal walls of the cylinder 47 by sleeve bushes 55, 56. An inner sleeve 57 is partially threaded on its outer surface and engages with the outer sleeve 50. The inner sleeve 57 is also wholly internally threaded and is engaged with a threaded portion of the shaft 48. Appropriate rotation of the outer sleeve 50 causes the inner sleeve 57 to rotate and move the inner sleeve forward past the flanged ends 53 and the end 58 of the nozzle 6. Since the shaft 48 is engaged with the inner sleeve 57, it too moves forward thereby moving the seal 17 forward. When the externally threaded portion of the inner sleeve 57 engages with the flange 53 of the cylinder 47, movement of the inner sleeve 57 is prevented and further forward movement is provided by the shaft 48 itself. Backward movement of course is exactly the reverse of the above process.

Referring again to Figure 5, axial rotation of the baffle 16 will cause the helical edge 24 to change its position linearly in direct proportion to the amount of angular rotation of the baffle 16. Consequently, by selecting a suitable gear ratio, the linear vector of baffle movement and that of its adjacent seal 17 can be made to coincide. In Figure 5 the baffle 16 has been rotated to a position where the header 2 has been cut off from the nozzle 6 at a point indicated by 59. Thus the flow of gas from the header 2 to the nozzle 6 is confined to that portion of the nozzle 6 lying intermediate point 59 and a distant point defined by the baffle (not shown) located at the other end of header 2. Thus the width of the gas jet issuing through the slot 11 is substantially limited in length to that of the nozzle 6 intermediate point 59 and the distant point defined by the other baffle.

Since in practice air is introduced at both ends of the header 2, air can still be deflected through the nozzle (and thereby its slot) at an outward lateral angle. The seal 17, located adjacent the point where the air leaves the baffle 16, presents a barrier to such deflected air and thereby limits the width of the air jet issuing from the slot 11 to that of the nozzle portion intermediate the baffles 16 located within each header 2. The practice is of course identical in device 10.

Thus it will be appreciated that movement of the baffle 16 and its appropriate seal 17, can be varied to confine the position and width of the air jet to the boundary limits defined by the edges of the strip which the nozzle faces. This reduces, or perhaps even eliminates, the ability of the opposed jets from the opposed devices 1 and 10 to impinge upon each other and thus reduces the noize level associated with such devices.

Movement of the baffle 16 and its seal 17 can be automatically controlled as shown in Figure 5. A decibel meter 60 is located adjacent the nozzles of the opposed devices 1, 10 just beyond a strip edge 61. A similar meter (not shown) is located just beyond the other strip edge (not shown).

A signal representative of the noise level reading from meter 60 is compared with a signal representative of a standard or desired noise level reading in a suitable error detector such as a control transformer (not shown). An error signal indicative of excessive noise is then fed back via an appropriate servo-amplifier (not shown) to the motors (not shown) controlling the drive of the baffles 16 and 17 in devices 1 and 10, so as to move the baffles 16 and 17 to a position where the impingement of the opposed nozzle jets is a minimum. As previously explained, this usually occurs when the width of the jet is confined between the boundary defined by the edges of the strip, i.e. the transverse width of the strip.

WHAT WE CLAIM IS: 1. A device for removing excess liquid coatant from a continuous strip emerging from a bath containing the liquid, the device comprising a cylindrical header having a pair of lips defining an elongate nozzle having a slot for directing a fluid jet onto the strip surface, together with at least one hollow part-cylindrical baffle nesting within the header and dimensioned to close off all but a portion of the nozzle from the header, the baffle being so shaped that axial rotation thereof varies the length of the open nozzle portion and thereby the width of the fluid jet transverse to the strip.

2. A device as claimed in claim 1 in which two baffles are provided, one at each end of the header so that all but an intermediate portion of the nozzle is closed off from the header.

3. A device as claimed in claim 1 or claim 2 in which the or each baffle is provided with a portion having a circumferential edge following a helical path.

4. A device as claimed in any of claims 1 to 3 in which a movable side seal is provided for the or each baffle, the or each side seal being located within the space between the nozzle lips and the baffle, the or each seal being located adjacent the point or points where fluid from the baffle or baffles enters the nozzle and the or each seal being effective substantially to limit the width of the fluid jet issuing from the slot to that of the open nozzle portion.

5. A device as claimed in any preceding claim in which the or each baffle is motor driven.

6. A device as claimed in claim 4 or claim 5 in which the or each seal is motor driven.

7. A device as claimed in claim 6 in which the or each seal and its corresponding baffle are coupled together by gearing in such a manner that the linear vector of baffle movement and that of the seal are coincident.

8. A device for removing excess liquid coatant from a continuous strip emerging from a bath containing the liquid, the device being substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. portion of the nozzle 6 lying intermediate point 59 and a distant point defined by the baffle (not shown) located at the other end of header 2. Thus the width of the gas jet issuing through the slot 11 is substantially limited in length to that of the nozzle 6 intermediate point 59 and the distant point defined by the other baffle. Since in practice air is introduced at both ends of the header 2, air can still be deflected through the nozzle (and thereby its slot) at an outward lateral angle. The seal 17, located adjacent the point where the air leaves the baffle 16, presents a barrier to such deflected air and thereby limits the width of the air jet issuing from the slot 11 to that of the nozzle portion intermediate the baffles 16 located within each header 2. The practice is of course identical in device 10. Thus it will be appreciated that movement of the baffle 16 and its appropriate seal 17, can be varied to confine the position and width of the air jet to the boundary limits defined by the edges of the strip which the nozzle faces. This reduces, or perhaps even eliminates, the ability of the opposed jets from the opposed devices 1 and 10 to impinge upon each other and thus reduces the noize level associated with such devices. Movement of the baffle 16 and its seal 17 can be automatically controlled as shown in Figure 5. A decibel meter 60 is located adjacent the nozzles of the opposed devices 1, 10 just beyond a strip edge 61. A similar meter (not shown) is located just beyond the other strip edge (not shown). A signal representative of the noise level reading from meter 60 is compared with a signal representative of a standard or desired noise level reading in a suitable error detector such as a control transformer (not shown). An error signal indicative of excessive noise is then fed back via an appropriate servo-amplifier (not shown) to the motors (not shown) controlling the drive of the baffles 16 and 17 in devices 1 and 10, so as to move the baffles 16 and 17 to a position where the impingement of the opposed nozzle jets is a minimum. As previously explained, this usually occurs when the width of the jet is confined between the boundary defined by the edges of the strip, i.e. the transverse width of the strip. WHAT WE CLAIM IS:

1. A device for removing excess liquid coatant from a continuous strip emerging from a bath containing the liquid, the device comprising a cylindrical header having a pair of lips defining an elongate nozzle having a slot for directing a fluid jet onto the strip surface, together with at least one hollow part-cylindrical baffle nesting within the header and dimensioned to close off all but a portion of the nozzle from the header, the baffle being so shaped that axial rotation thereof varies the length of the open nozzle portion and thereby the width of the fluid jet transverse to the strip.