WO1996015860A1

WO1996015860A1 - Direct coater apparatus for elongated strip articles

Info

Publication number: WO1996015860A1
Application number: PCT/CA1995/000661
Authority: WO
Inventors: Robert Arthur Innes; Carl Wollam
Original assignee: Alcan International Ltd Canada
Current assignee: Rio Tinto Alcan International Ltd
Priority date: 1994-11-23
Filing date: 1995-11-23
Publication date: 1996-05-30
Anticipated expiration: 1997-05-23

Abstract

Apparatus for coating a strip article with a coating of uniform thickness. The apparatus includes a rigid coating head defining an elongated open-sided slot and having an extended surface immediately adjacent to the open side of the slot. In use, the extended surface is arranged at an angle to the surface to be coated to form a converging coating gap. The apparatus further includes a strip feeder for continuously longitudinally advancing the strip article successively past the slot and the extended surface of the head in a direction transverse to the slot; a supply apparatus for supplying liquid coating material under pressure to the slot; and a rigidly mounted load application device for pushing the coating head towards a major surface of the strip article facing the slot while permitting free movement of the coating head in a direction perpendicular to the surface of the strip article. In one form of the apparatus, the coating head is rigidly connected to the load application device with the load application device providing the entire support for the coating head against movement of the coating head in a direction other than a direction perpendicular to the surface of the strip. In another embodiment, a support is provided for the load application device that is movable between an operational position, in which the coating head carried by the piston and cylinder device(s) is positioned at an operational distance from the strip article, and a retracted position, in which the coating head is separated from the strip article by a distance greater than the operational distance for maintenance, repair or the insertion of a new strip article.

Description

DIRECT COATER APPARATUS FOR ELONGATED STRIP ARTICLES

TECHNICAL FIELD

This invention relates to apparatus used for the direct coating of strip articles, such as metal sheet, with paints or plastics to provide surface protection and/or to improve the appearance of the article. BACKGROUND ART

Metal sheet material, and particularly thin aluminum strip used.for beverage can stock and other purposes, is frequently coated with paints or plastics to provide surface protection and/or decorative finishes. The coatings are typically applied by dissolving or suspending polymers and other components in organic solvents, applying the resulting mixtures by roller coater to the strip, and baking the resulting product to remove the solvents and to cross-link the polymer.

An alternative means of applying such coatings is to employ an extrusion die movably connected to a supporting structure and having die lips of a suitable shape arranged around an extrusion opening in the form of an elongated slot extending transversely above the surface of the strip. The die lips are positioned close to the strip and the clearance between strip and die lips is precisely controlled by adjusting the position of the extrusion head relative to the supporting structure. In such apparatus, the thickness uniformity of the coating depends on the precision used in the manufacture and control of the die and the precision of the support roll generally used to support the sheet material during coating, as well as the uniformity of the metal gauge along the strip. As a result, it proves very difficult in practice to produce uniform coatings of the desired thickness. If an attempt is made to improve thickness uniformity by providing the extrusion die with a mechanical spacer that rides on the strip surface in order to maintain a uniform clearance between the die lips and the strip, unsightly marks may be made on the surface of the strip by the spacer and the marks may not be completely hidden by the applied coating.

An apparatus and method suitable for single-sided coating of a sheet material without reliance on mechanical spacers that contact the strip is disclosed in U.S. Patent No. 4,675,230 of June 23, 1987, assigned to the same assignee as the present application. Moreover, a related apparatus and method of two-sided coating of sheet material is disclosed in PCT Patent Application Serial No. PCT/CA94/00291, filed

May 26, 1994, and published on December 8, 1994 as WO 94/27739, and assigned to the same assignee as the present application. The types of apparatus disclosed in this patent and application rely on the hydrodynamics of the coating material as it is applied to the metal strip for control of the film thickness and can readily compensate for variations in the gauge of the strip and the eccentricity of the support roll (when used) . This is achieved by using a coating head having an extrusion slot and an extended surface on the downstream side of the slot forming an angle with the moving strip, thus creating a gap converging in the direction of the strip travel . The coating head is pushed resiliently towards the strip and the extended surface directly contacts the coating material as it is applied to the strip, thus generating hydrodynamic forces that cause the head to "float" on the layer of coating as it is applied to the strip. Direct contact between the strip and the coating head can thus be avoided, and this in turn avoids damage to or defacement of the metal or pre-coated metal surface to which the coating is applied. The types of apparatus disclosed in this patent and application rely on the loading forces under which the coating head is pushed towards the surface of the strip article, as well as the hydrodynamics of the coating material as it is applied to the surface, for control of the coating thickness and can readily compensate for variations in the gauge of the strip or, in the case of a single-sided coater, the eccentricity of the support roll. For this type of device to work effectively, the coating head must be free to move in a direction perpendicular to the coating surface in response to varying imbalances in the opposing hydrodynamic and loading forces. In the device shown in U.S. Patent 4,675,230, this is achieved by attaching the coating head to a fixed, flat supporting plate in such a way that the head can slide back and forth to a limited extent in the desired perpendicular direction. The attachment is achieved by providing the head with elongated slots for receiving hold-down bolts that clamp the head to the plate, but nevertheless allow for sliding of the head in the lengthwise direction of the slots. Loading is applied to the coating head by pneumatic cylinders that are themselves connected to a support arrangement that includes the supporting plate for the coating head. For maintenance purposes, the support arrangement can be rotated around a pivot point, thus swinging the coating head away from the operational position adjacent to the surface of the strip article. The problem with this type of arrangement is that, under the dynamic loading conditions that apply during use of the apparatus, considerable friction may develop between the contacting surfaces of the coating head and the supporting plate and/or between the inner surfaces of the mounting slots in the coating head and the retaining bolts. This friction impedes the desired free movement of the coating head towards and away from the surface of the strip article as coating progresses and may consequently result in the formation of a coating layer of non-uniform thickness. This friction can be minimized by resorting to very precise machining of the contacting surfaces and the use of lubrication, but these solutions are undesirable because of increased cost and operational difficulty, and also the risk of contamination of the coating material with the lubricant. With this type of apparatus, there is also a risk of intrusion of the coating material into the gap between the sliding surfaces, which may significantly increase friction, even if such countermeasures are resorted to.

Variations of this arrangement have been suggested. One such variation involves positioning the coating head in a deep slot in a rigid support so that it can slide into and out of the slot while supported between the slot side surfaces. However, this arrangement suffers from the same disadvantages as the apparatus described above. Another variation involves mounting the coating head on linear ball bearings, but wide coater heads require several sets of such bearings, resulting in difficulties in achieving accurate alignment and the need for a relatively complex design. These bearings are also vulnerable to contamination by coating material.

There is consequently a need for improvements in the way that such coating heads are supported in order to minimize friction during use. DISCLOSURE OF THE INVENTION

An object of the present invention is to simplify apparatus used for direct coating of strip articles.

Another object of the invention is to reduce friction encountered by coating heads in apparatus used for direct coating of strip articles. Yet another object is to simplify the design of apparatus used for coating strip articles so that maintenance may be carried out.

According to one aspect of the invention, there is provided apparatus for coating a strip article, including a rigid coating head defining an elongated open-sided slot and having an extended surface immediately adjacent to the open side of the slot; a strip feeder for continuously longitudinally advancing the strip article successively past the slot and the extended surface of the coating head in a direction of movement transverse to the slot with a major surface of said article arranged at an angle to said extended surface to form a converging coating gap; a supply apparatus for supplying liquid coating material under pressure to the slot; and a load application device for pushing the coating head towards said major surface of the strip article facing the slot while permitting free movement of said coating head in a plane transverse to said direction of movement and substantially perpendicular to said major surface of the strip article; characterized in that said coating head is rigidly connected to said load application device with said load application device itself providing sole support for said coating head against substantial movement of the coating head in a direction other than said transverse perpendicular plane.

As noted above, the extended surface of the coating head is arranged at a small angle to the surface of the strip article during coating to form a coating gap that converges in the direction of movement of the strip. Since this angle is quite small (normally in the range of 0.1 to 5°, or more preferably 0.5 to 1°), virtually any deflection of the coating head is unacceptable since it causes the angle to approach 0°, and the apparatus will not work properly when the coating surface is fully parallel to the strip surface. In general, the deflection of the coating head should preferably be no greater than about 0.005 cm (2 thousandths of an inch) or the angle of the extended surface may be changed to an unacceptable extent. Accordingly, the load application device must be sufficiently robust to prevent such deflection of the coating head without ancillary support.

The load application device used in the present invention may be any device that is capable of delivering a constant force in the perpendicular direction while also providing the required rigid support for the coating head against unwanted non- perpendicular movement. The device must be capable of achieving this rigid support without the need for ancillary support of the coating head, such as a support surface or element, that may generate friction impeding the free movement of the coating head as the head moves in the intended direction towards or away from the surface of the strip article. While sufficiently rigid load application devices such as mechanical springs and electromagnetic mechanisms may be suitable, it is preferable to use robust, limited stroke piston and cylinder devices, most especially pneumatic piston and cylinder devices, configured to minimize free play in the coating direction of the strip article.

By avoiding the need for ancillary support of the coating head, friction that impedes the desired movement of the coating head towards or away from the surface of the strip can be eliminated or minimized, and thus the coating head may rapidly and accurately follow non- uniformities at the surface as it is coated, thus producing a more uniform coating layer on the strip article.

According to another aspect of the invention there is provided apparatus for coating a strip article, including a rigid coating head defining an elongated open-sided slot and having an extended surface immediately adjacent to the open side of the slot; a strip feeder for continuously longitudinally advancing the strip article successively past the slot and the extended surface of the head in a direction transverse to the slot with a major surface of said article arranged at an angle to said extended surface to form a converging coating gap; a supply apparatus for supplying liquid coating material under pressure to the slot; and at least load application device for pushing the coating head towards a major surface of the strip article facing the slot while permitting free movement of said coating head in a direction perpendicular to said surface of the strip article; and a support for said load application device movable between a retracted position, in which the coating head carried by the load application device is positioned at an operational distance from said strip article, and an extended position, in which the coating head is separated from the strip article by a distance greater than the operational distance. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a simplified perspective view of an apparatus according to a preferred form of the present invention;

Fig. 2 is a side elevation, partly in cross- section, of the apparatus of Fig. 1;

Fig. 3 is a transverse vertical side elevation, partially in cross-section, of the apparatus of Fig. 1;

Fig. 4 is a view similar to Fig. 3, showing the coating heads in a retracted position suitable for maintenance; and

Fig. 5 is a simplified schematic view illustrating the operating principle of the rams used in the apparatus of Figs. 1 to 4. BEST MODES FOR CARRYING OUT THE INVENTION The apparatus shown in Figs. 1 to 5 is a two-sided coating apparatus for applying surface coatings simultaneously to opposite sides of an advancing sheet of aluminum or other strip article to be coated. It should be kept in mind, however, that the present invention can be applied equally well to single-sided coating of the type disclosed in U.S. patent 4,675,230 mentioned above. In such alternative apparatus, only one movable coating head would be provided for coating one side of the strip article and the other side would be supported by a suitable rotatable drum or the like. In the illustrated preferred embodiment, the coating apparatus 10 has a pair of rigid spaced supports in the form of thick rectangular metal plates 11, 12 surrounding and supporting a pair of opposed elongated rigid coating heads 14, 14' between which a strip article 15 is advanced (not shown in Figs. 1 and 2 , but see Fig. 3) for double-sided coating. The lower supporting plate 12 is rigidly held in a fixed position by four supporting legs 16, which may be anchored to the floor of the building in which the equipment is located. The upper supporting plate 11 is supported at each of its four corners by hydraulic rams 18 having a lifting capacity capable of raising the upper supporting plate 11 and the equipment carried by this plate, including the upper coating head 14'.

Rigidly attached at their upper ends to, and depending from, the lower surface of the upper supporting plate 11 are five pneumatic piston and cylinder devices 20 arranged in evenly spaced relationship in a single row along the central longitudinal axis of the upper supporting plate. Collectively, in use, these devices form a load application device for pushing the upper coating head 14' towards the strip article 15 (and for pushing the flexible strip article 15 in turn towards the lower coating head 14) . The lower ends of these devices (formed by piston rods 20a extending from cylinders 20b) are attached to the upper coating head 14', so the upper coating head is supported entirely and solely by the piston and cylinder devices and are movable in a direction towards or away from the upper supporting plate 11 according to the movement of pistons 20c in the cylinders 20b (see Fig. 2) . The attachment of the piston rods 20a to the upper coating head 14' is a rigid attachment created by bolts 22 extending upwardly from the coating head 14' and threaded axially into the lower ends of the piston rods 20a.

While the upper coating head 14' is free to move in the manner indicated above, i.e. in a vertical plane at right angles to the direction of advancement of the strip article 15, movement of any other kind is constrained by the rigid attachment of the coating head 14' to the piston rods 20a, which are in turn free to move only in the desired direction by virtue of their rigid attachment to pistons 20c that are vertically slidable in cylinders 20b. The cylinders of the devices 20 are in turn rigidly attached to the upper supporting plate 11 and movement of the upper supporting plate is itself prevented, except for optional vertical movement to be explained later, by its rigid attachment to the hydraulic rams 18 that are themselves rigidly connected to the lower supporting plate 12.

The only movement of the coating head 14' that is possible, except for the stated movement in the vertical plane, is that allowed by virtue of free play that may exist between the pistons 20c and cylinders 20b within the devices 20 since free play in hydraulic rams 18 is prevented, when the apparatus is in normal operation, for the reasons explained later.

As shown in Fig. 2, the sides of piston 20c within the cylinders 20b do not directly contact the inner walls of the cylinders. Instead, the pistons are each provided with two O-rings 20d (i.e. piston rings made, for example, of Buna-N elastomer) , one at the top and one near the bottom of each piston 20c. These 0-rings are interposed between the pistons and the inner cylinder walls and allow minimal free play.

In order to maximize rigidity in the direction of the strip travel within the devices 20, the diameter of the piston rods 20c is made large (e.g. 7.6 cm (3 inches) in diameter, compared to 2.5 cm (one inch) that is normal in conventional devices) to minimize flexing of the rods and the resulting deflection of the compressible O-rings, and the pistons operate with a short length of travel (stroke) compared to their overall length, e.g. of only about 1 cm, to ensure a rigid support by lengthening the lever arm between the piston and the rod seal compared to the distance between the rod seal and the coating head. While the stroke may be short, the devices are preferably made quite long (e.g. 20 cm (8 inches)) to permit less lateral movement due to the fulcrum effect (n.b. a given amount of free play at the upper ends of the pistons 20c translates into a lower amount of free play between the piston and the cylinder at the lower end as the piston is increased in length and the stroke is reduced) .

The illustrated arrangement has the desired effect of allowing the upper coating head 14' to "float" freely under the countervailing effects of the load applied by the piston and cylinder devices 20 and the hydrodynamic effects of the layers of coating material applied by the coating heads 14 and 14' on the opposite sides of the strip article 15, without bearing against any stationary ancillary support, thus easily and rapidly accommodating any irregularities of the gauge of the strip article or variations in the dynamics of the coating layers. Since the movable coating head 14' does not contact a stationary surface, no friction is developed by the coating head to impede the required vertical movement. Nevertheless, movement other than that in the desired transverse vertical plane is substantially prevented by virtue of the indicated rigid connection of the coating heads within a stable rigid frame formed by the supporting plates 11 and 12 and the rams 18.

While the devices 20 are preferably pneumatically operated for rapid response to changes in net forces encountered by the head 14', similar devices operated hydraulically could be provided instead but steps must then be taken to ensure that the same rapid response is achieved. For example, the hydraulic device could be coupled to a load cell for detecting the required force response (e.g. to a variation in the thickness of the sheet) . The load cell would sense the need to apply more or less force and almost instantaneously cause a valve in the hydraulic mechanism to feed in more fluid or, conversely, to release fluid from the cylinder. Alternatively, a piston-in-cylinder device or other device could be operated by a mechanical spring. Such devices have the advantage over hydraulic devices that response times to coating gap variations are faster and thus no such load cell or equivalent pre-sensing device is required.

The coating heads 14, 14' may be generally the same as those disclosed in U.S. Patent No. 4,675,230 and in WO 94/27739. The heads are in the form of hollow elongated rectangular rods that are supplied with liquid or molten coating material from suitable conventional supply apparatus 17 (shown only in simplistic form in Fig. 2) via inlet ports 24, 24'. The heads face each other across a narrow gap 25, for receiving the strip article 15 to be coated, and are each provided with an elongated open-sided slot 26, 26' penetrating the heads within the gap 25 so that the coating material may be extruded from the interior of the coating heads onto each major face of the strip article as it advances through the gap. The heads are also provided with extended surfaces 27, 27' on the opposed surfaces of the heads within the gap 25. These surfaces are formed adjacent to the slots 26, 26' on the downstream sides of the opposed surfaces and, as indicated above, serve the function of controlling the thickness of the coating material as it is applied to the strip article through the slots. The surfaces each form gaps between the coating heads and the adjacent strip surfaces that converge slightly in the direction of travel of the strip article. The forces exerted on these extended surfaces by the coating material in the gaps cause the upper coating head 14' to move up or down when such forces are out of equilibrium with the loading force applied by the load application devices 20.

The strip article 15 is advanced through the gap 25 by a suitable sheet strip feeder, e.g. driven rolls 19, 19', from a coil (not shown) of the strip article.

After passing through the apparatus, the strip article 15 usually traverses an extended run before being recoiled, the run being long enough to allow for drying or solidification of the coating material forming layers on the opposed surfaces of the strip article. This extended run may, if desired, pass through a baking oven (not shown) to accelerate the drying of the coating material .

From time to time it is necessary to separate the heads 14, 14' by a greater distance (e.g. up to 15 cm) than the operational gap 25, e.g. when feeding in or splicing a new strip article or when carrying out maintenance or repair (see Fig. 4 showing the apparatus in this extended position) . This is done by operating the hydraulic rams 18 at the corners of the apparatus to raise the upper supporting plate 11 (and thus the piston and cylinder devices 20 and the coating head 14') from a retracted (operational) position to an extended position. This process is shown in simplified schematic form in Fig. 5 of the drawings. Each ram 18 (only one of which is shown in Fig. 5) has upper and lower oil chambers 18a and 18b, respectively provided above and below a piston 18c. The plate 11 can be raised by feeding hydraulic fluid from a suitable pump 18d into the lower chamber 18b and withdrawing it from the upper chamber 18a through piping provided with valves 18e and 18f. For lowering of the plate 11, this process is reversed. In the fully retracted (operational) position, both of the valves 18e and 18f are closed so that hydraulic fluid remains trapped in each chamber 18a and 18b, thus preventing any up or down movement of the piston 18c. The plate 11, and hence the upper coating head 14', is consequently held motionless on the incompressible hydraulic fluid within these chambers.

As seen best in Figs. 3 and 4, the upper parts of the hydraulic rams on the supply side of the apparatus carry fixed plates 30 that extend down below the level of the strip article 15 and support an elongated element, in the form of a roller 31, that extends beneath the lower surface of the strip article. As the upper supporting plate 11 is raised by the rams 18, the plates 30 and the attached roller 31 are also raised. At the maximum separation of the coating heads 14 and 14', the roller contacts the lower surface of the strip article 15 to support it at the height of the lower coating head 14. This prevents the strip from sliding on the lower coating head surface with metal-to-metal contact. As the upper supporting plate 11 is lowered, the roller 31 descends out of the way and no longer contacts the strip article 15.

The use of the hydraulic rams 18 in this way to separate support elements forming a rigid frame carrying the coating heads and load application device provides a very convenient way of separating the coating heads 14, 14' without affecting the rigid support of these heads during normal operation. Incidentally, this type of arrangement may be used in otherwise conventional equipment, e.g. of the type using coating heads movably supported on a fixed plate. In such a case, the coating head, fixed plate and non-supporting piston and cylinder device of, for example, U.S. patent 4,675,230, would all be mounted directly or indirectly on the movable frame rather than on the pivot disclosed in the paten . The apparatus described above with reference to

Figs. 1 to 5 could be modified for single-sided coating by replacing the lower coating head 14 with a support drum rigidly mounted for rotation within the lower supporting plate 12 or an equivalent fixed supporting structure. In such an apparatus, the strip article 15 would ride over the upper surface of the support drum and would receive coating material from the coating head 14' positioned opposite to the highest point of the drum. EXAMPLE

The lever arm ratios at fully extended and at retracted (operational) extensions of the piston rods was calculated as follows for a device as illustrated in Figs. 1 to 5 having a piston diameter of 7.6 cm (3 inches) , an overall available stroke (with the piston rods fully extended) of 10.8 cm (4.25 inches), and an operational stroke (the extension when coating a strip article) of 0.64 cm (0.25 inches) :

1. For the retracted (operational) stroke: The vertical distance from the coating head surface (the surface opposite to the strip surface) to the lower piston seal was 7.3 cm (2.87 inches) (including the 0.64 cm (0.25 inches) of stroke) . The vertical distance from the upper piston seal to the lower piston seal was 13 cm (5.13 inches) . Therefore, for the 7.6 cm (3 inch) diameter piston:

Lever Arm Ratio = 2.87/5.13 = 0.56 2. For the fully extended stroke:

Lever Arm Ratio = (2.87 + 4)/l.l3 = 6.08

When a force of approximately 45.4 kg (100 lbs.) was applied first to the coating head with the pistons extended 10.8 cm (4.25 inches), and next to the same head with the pistons extended 0.64 cm (0.25 inches), the following lateral deflection was measured:

PISTON EXTENSION DEFLECTION cm (inches) cm (thousandths of an inch) 10.8 (4.25) 0.038 (15)

0.64 (0.25) 0

As already noted, in order to maintain the required angle of the extended surface of the coating head for proper operation, the deflection of the coater head during operation should preferably be no greater than about 0.005 cm (2 thousandths of an inch), and the lever arm ratio should preferably be no greater than about 0.60 or less for a 7.6 cm (3 inch) diameter piston.

It will be understood that the present invention is not limited to the features and embodiments specifically set forth above, but may be carried out in other ways without departing from the spirit of the invention.

Claims

CLAIMS :

1. Apparatus for coating a strip article, including a rigid coating head defining an elongated open-sided slot and having an extended surface immediately adjacent to the open side of the slot; a strip feeder for continuously longitudinally advancing the strip article successively past the slot and the extended surface of the coating head in a direction of movement transverse to the slot with a major surface of said article arranged at an angle to said extended surface to form a converging coating gap; a supply apparatus for supplying liquid coating material under pressure to the slot; and a load application device for pushing the coating head towards said major surface of the strip article facing the slot while permitting free movement of said coating head in a plane transverse to said direction of movement and substantially perpendicular to said major surface of the strip article; characterized in that said coating head is rigidly connected to said load application device with said load application device itself providing sole support for said coating head against substantial movement of the coating head in a direction other than said transverse perpendicular plane.

2. Apparatus according to claim 1 characterized in that said load application device rigidly supports said coating head to the extent that, during use, said coating head is deflected in the direction of movement of the strip article by an amount no greater than 0.005 cm (2 thousandths of an inch) .

3. Apparatus according to claim 1 or claim 2 for two- sided coating of the strip article, further characterized by a second rigid coating head defining an elongated open-sided slot and having an extended surface immediately adjacent to the open side of the slot, said second coating head.being positioned facing an opposite major surface of the strip article with said extended surface positioned downstream of said slot in the direction of advancement of said strip article and arranged at an angle to said opposite major surface to form a converging coating gap, and supply apparatus for supplying liquid coating material under pressure to the slot of said second coating head.

4. Apparatus according to claim 1 or claim 2 characterized in that said load application device comprises at least one piston and cylinder device having opposed first and second longitudinal ends, said first end of said piston and cylinder device being rigidly mounted to a support and said second end of said piston and cylinder device being rigidly mounted to said coating head.

5. Apparatus according to claim 4 characterized in that each said piston and cylinder device is a pneumatic device.

6. Apparatus according to claim 4 or claim 5 characterized in that each said piston and cylinder device is rigidly attached to a support movable between a retracted position, in which the coating head carried by the piston and cylinder device is positioned at an operational distance from said strip article, and an extended position, in which the coating head is separated from the strip article by a distance greater than the operational distance.

7. Apparatus according to claim 6 characterized by at least one hydraulic ram device for moving the support between said retracted and said extended positions.

8. Apparatus according to claim 6 or claim 7 characterized in that said support carries a strip article support element that, in said retracted position, is spaced from the strip article on an opposite side of the strip article from the support and that, in said extended position, contacts and supports said strip article.

9. Apparatus according to claim 4 or claim 5 characterized by a plurality of said piston and cylinder devices orientated vertically and aligned in a direction transverse to a direction of movement of the strip article, said coating head being fixed to lower ends of said devices.

10. Apparatus according to claim 4 or claim 5 characterized in that said piston and cylinder device comprises an elongated rigid piston operating with a short stroke within a cylinder.

11. Apparatus according to claim 10 characterized in that said piston is provided with a plurality of piston rings interposed between said piston and said cylinder at positions spaced axially along said piston.

12. Apparatus for coating a strip article, including a rigid coating head defining an elongated open-sided slot and having an extended surface immediately adjacent to the open side of the slot; a strip feeder for continuously longitudinally advancing the strip article successively past the slot and the extended surface of the head in a direction transverse to the slot with a major surface of said article arranged at an angle to said extended surface to form a converging coating gap; a supply apparatus for supplying liquid coating material under pressure to the slot; and at least load application device for pushing the coating head towards a major surface of the strip article facing the slot while permitting free movement of said coating head in a direction perpendicular to said surface of the strip article; and a support for said load application device movable between a retracted position, in which the coating head carried by the load application device is positioned at an operational distance from said strip article, and an extended position, in which the coating head is separated from the strip article by a distance greater than the operational distance.

13. Apparatus according to claim 12 for two-sided coating of the strip article, further characterized by a second rigid coating head defining an elongated open- sided slot and having an extended surface immediately adjacent to the open side of the slot, said second coating head being positioned facing an opposite major surface of the strip article with said extended surface positioned downstream of said slot in a direction of advancement of said strip article at an angle to the opposite surface of the strip article to form a converging coating gap, and supply apparatus for supplying liquid coating material under pressure to the slot of said second coating head.

14. Apparatus according to claim 12 or claim 13 characterized in that said load application device comprises at least one piston and cylinder device each having opposed first and second longitudinal ends, said first end of said device being rigidly mounted to a support and said second end of said device being rigidly mounted to said coating head.

15. Apparatus according to claim 14 characterized in that each said piston and cylinder device is a pneumatic device.

16. Apparatus according to claim 12 or claim 13 comprising at least one hydraulic ram device for moving the support between said retracted and said extended positions.

17. Apparatus according to claim 12 or claim 13 characterized in that said support carries a strip article support element that, in said retracted position, is spaced from the strip article on an opposite side of the strip article from the support and that, in said extended position, contacts and supports said strip article.

18. Apparatus according to claim 14 comprising a plurality of said piston and cylinder devices orientated vertically and aligned in a direction transverse to a direction of movement of the strip article, said coating head being fixed to lower ends of said devices.

19. Apparatus according to claim 14 characterized in that said piston and cylinder device comprises an elongated rigid piston operating with a short stroke within a cylinder.

20. Apparatus according to claim 19 characterized in that said piston is provided with a plurality of piston rings interposed between said piston and said cylinder at positions spaced axially along said piston.