This invention relates to apparatus for stripping excees coating liquid from continuous strip material.

It is commonplace to strip excess coating liquid from continuous strip material, as it rises out of a dipping bath or other coating station, by directing gas streams or jets on to the coated surfaces laterally thereof and in a direction which iβ substantially normal thereto. The gas is usually air, superheated steam or other suitable me ^d ia. The coating liquid may be paint, glue, molten

10 metal or other common coating liquid, and the strip (to which the particular coating must, of course, be appropriate) may for example be paper, metal or other strip material pliant enough for reeling and amenable to production in long runs; for example, lengths running to thousands of metres .

Although the present invention is applicable to jet stripping in the general sense indicated above, it is primarily concerned with excess coating removal near the edges of steel strip during the stripping of excess

20 molten coating metal as the strip emerges substantial _l y vertically from a molten metal bath ^" , and the invention is described hereinafter mainly in terms of that particu _l ar use.

In continuous hot dip metal coating processes, one of the generally preferred methods of the prior art, to remove excess metal from the steel βtrip, is to arrange for the coated strip, as it leaves the molten metal coating bath to move vertically through a zone containing

the jet stripping means and, once the coating has solidified and the coated strip cooled, the coated strip ^• is then reeled.

The jet stripping means comprises essentially a pair of linearly extending gas nozzles disposed substantially horizontally on either side of the strip, at a distance above the surface of the coating bath such that the coating on the strip iβ still molten upon arrival in the stripping zone. The lateral span of the stripping jets is normally greater than the width of the strip passing between them. There may be substantial variations in the shape and design of nozzles, the jet span and gas pressure employed. The stripped matter simply flows downwardly from the stripping zone back to the bath. Jet stripping apparatus of the kind indicated above is hereinafter referred to as being "of the type described"

A common occurrence in the use of apparatus of the type described is that a thicker coating remains on or near the edges of the strip than on the remaining area of the strip. In extreme cases the thicker coating may extend in from the edges by up to 30 millimeters but is normally confined to a marginal area 5 or 6 millimeters from the edge.

This problem has hitherto been overcome by the use of devices described in the specifications of Australian Patents No. 453,826 and 543,722, However, it has been found that when the strip speed is less than a certain critical speed those devices are not totally effective.

The critical speed is dependent on the composition of the coating liquid and is in the range 10 to 60 øetres/ in.

It is an object of the present invention to provide a stripping device which overcome the abovementioned problem of edge coating defects when even when the strip speed is less than the critical speed.

Accordingly the present invention consists in apparatus for stripping excess coating liquid from an upwardly and vertically moving strip, of the kind comprising: means for directing a gas stream extending laterally of a coated surface of a strip onto said surface in a direction which is substantially normal thereto, a baffle plate at the region of impingement of said gas stream having a vertical portion presented to the edge of said strip and a non-vertical remainder portion below said vertical portion and trended away from said edge, a carrier plate having said baffle plate fixed along one edge of it, a carriage movable towards and away from said strip edge and having said carrier plate suspended from it, means urging said carriage to approach said strip edge and means to maintain a minimum spacing between said strip edge and said vertical portion so as to produce a substantially uniformly thick coating over the width of the strip? characterised in that an eductor is provided fixedly attached to said carrier plate with its intake end interrupting said vertical portion of said baffle plate adjacent said non-vertical remainder portion.

A preferred embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings in Which;

Figure 1 is a perspective view of part of the apparatus of the present invention;

Pigure 2 is an end elevation taken on line 2-2 of figure l;and

Figure 3 is a section taken on line 3-3 of figure 2;

Referring firstly to figures 1 and 2 there iβ shown a steel strip 1 which is rising vertically from a continuous hot dip coating bar and carrying an excess of coating liquid. The strip 1 passes between a pair of linearly extending gas nozzles on either side of the strip for the removal of the excess coating in conventional fashion. Such nozzles are well known and so are not shown in the drawings.

At each side of the moving strip 1 there is provided in accordance with the invention, a baffle 2 functioning to modify the flow of the stripping jets at the edge of the strip. Only one of the two baffles and its associated assembly is shown.

The baffle 2 consists of an elongate strip of sheet steel and has a straight vertical portion 3A and a non-vertical portion comprising a straight bottom 3B and an arcuate transition portion 3C.

The baffle 2 is fixedly attached to the edge of a carrier plate 4. The carrier plate 4 is suspended on two hangers 5 having their upper ends fixed to a truck 6.

This truck is provided with rollers 7 and 8 so that it may run freely along a pair of opposed rails 9 as best shown in figure 2. The truck 6 carries a yolk 10 for a roller 11 able to ride the edge of the strip 1.

In order to influence the truck 6 towards the strip 1 so that the roller 11 bears against the edge of the strip 1, the tracks 9 are inclined downwardly towards the strip at an inclination at between 5° and 10° degrees from the horizontal. The arrangement hereinabove described is prior art. It has been found that such prior art has been successful when the strip feeds is between the critical speed and 200 metres/min. However, when the strip speed falls below 60 metres/min it has been found that there is a deterioration in the quality of edge stripping. To overcome this problem and in accordance with the invention, an eductor 20 is provided secured to the carrier plate 4 such that the carrier plate 4 extends in a radial direction from either side of the eductor 20. The eductor 20 is positioned so that its intake end opens through the vertical portion 3A of the baffle plate 2, adjacent the transition portion 3C.

The eductor as best shown in figure 3, comprises a length of tube 21 having an intake end 22, an exhaust 23 and a pressure input nozzle 24. As will be appreciated by those skilled in the art, when pressurised gas is provided to the nozzle 24 a flow from the intake 22 to the exhaust 24 of the eductor is generated. Such flow

causes suction at the intake 22. In operation, when the strip speed falls below the critical speed, pressurised air is supplied to the nozzle 24. The resultant suction at the intake end which is disposed adjacent the edge of the strip 1 draws off excess coating metal from the edge of the strip and blows it from the exhaust 23.

The pressurised air supplied to the nozzle 24 is delivered through a pipe 25 which includes a flexible portion enabling the truck 6 to move. In the preferred embodiment the internal con iguration of the eductor 20 includes a rounded intake lip 26 leading smoothly to a first internal bore portion 27 and thence to a second internal bore portion 28 being co-axially aligned with the first bore portion 27 and having a slightly greater internal diameter. A smoothly contoured transitional step 29 interconnects the first bore portion 27 with the second portion 28. The second bore portion 28 leads directly to the exhaust 23.

The arrangement is such that molten coating metal which contacts the walls of the first bore portion 27 is blown over the transitional steps 29 and from there directly to the exhaust 23 without contacting the sides of the second portion 28. It has been found that such an arrangement prevents build up of coating metal within the eductor 20.

In order to provide the requisite suction at the intake 22 a considerable quantity of pressurised air must be provided at the nozzle 24. This provision of course

adds to the cost of running the eductor. Accordingly considerable experimentation has been carried out to ascertain dimensions which provide maximum suction for a given mass flow rate delivered to the nozzle 24.

It will be appreciated that a certain minimum overall length L is required for suction to be induced at the intake 22. This suction initially increases with increase overall length L. However as L increases further, frictional losses which occur within the eductor eventually causes a reduction of the suction at the intake 22.

It has been found that optimum efficiency is attained when the length of the eductor from the nozzle 24 to the exhaust 23 ( ) is within the range 7 D to 12 D where D is the internal diameter of the first bore portion 27. Preferably should be 9.8 D.

It has further been found that the distance from the intake 22 to the strip edge 1 must be in the range from 8 mm to 0.6 D and the optimum distance from the nozzle 24 to the transitional step 29 is in the range 0,5 D to 1 D,

In the preferred embodiment the nozzle 24 is 5 millimeters in diameter, and is inclined backwardly at an angle of 15° from the longitudinal axis of the eductor 20. The distance from the intake 22 to the nozzle 24 is approximately 1.5 D. The gauge pressure supplied to the nozzle 24 is approximately 400 Pa. (Gauge), and D is 24 millimeters.

It is envisaged that the internal cross sectional

shape of the eductor may be other than circular in which case D will be replaced with an hydraulic diameter that is four times the cross-sectional area of the first interval bore portion 27 divided by its peripheral length.

As aforementioned the eductor 20 is utilized when the strip speed falls below the critical strip speed.

It will be appreciated by those skilled in the art that when the strip speed is in excess of the critical strip speed the air supplied to the nozzle 24 is stopped and the stripping apparatus acts in accordance with the prior art. When the strip speed falls below the critical strip speed, pressurised air is supplied to the nozzle 24 and the resultant suction at the intake 22 of the eductor 20 is effective to strip excess molten metal from the edge of the strip 1.

Whereas the eductor of the preferred embodiment includes first and second bore portions a plain bore eductor may be used.