Coating apparatus – Projection or spray type
Reexamination Certificate
2002-03-04
2004-02-17
Crispino, Richard (Department: 1734)
Coating apparatus
Projection or spray type
C118S429000, C239S219000, C239S220000
Reexamination Certificate
active
06692570
ABSTRACT:
FIELD OF THE INVENTION
This application claims priority from the following Australian provisional patent applications, the full contents of which are hereby incorporated by cross-reference.
Application No.
Title
Date Filed
PR3474
A Composite Product
02 Mar. 2001
PR3475
Spattering Apparatus
02 Mar. 2001
PR3476
Additive For Dewaterable Slurry
02 Mar. 2001
PR3477
A Method And Apparatus
02 Mar. 2001
For Forming A Laminated Sheet
Sheet Material By A Spattering
PR3478
Coatings For Building Products
02 Mar. 2001
The present invention relates to an applicator for a fluent substance, and in the preferred form to an apparatus for applying a slurry to a substrate, by spattering.
The invention has been developed primarily for use in relation to the production of fibre reinforced cement (FRC) sheet from cementitious slurry, and will be described primarily with reference to that application. However, it will be appreciated that the invention is not limited to this particular field of use.
BACKGROUND OF THE INVENTION
The following discussion of the prior art is intended to present the invention in an appropriate technical context and allow the significance of it to be properly appreciated. Unless clearly indicated to the contrary, however, reference to any prior art in this specification should not be construed as an admission that such art is widely known or forms part of common general knowledge in the field.
Various apparatus for applying liquids to substrates are known. For example, one process makes use of a spray bar whereby a liquid coating, such as a paint or primer, is squirted and atomised through spaced apart nozzles, so as to coat the substrate which typically passes progressively beneath the spray bar on a conveyor. One problem with devices of this type is that the relatively fine nozzles required to achieve the degree of atomisation necessary for uniform coating are readily clogged, particularly in the case of slurries containing a solid component in suspension. This results in inconsistent application, and requires frequent cleaning which is time consuming, costly and disruptive to the production process. Atomisation is also problematic in the case of more viscous liquids and slurries.
Another known device is a curtain coater, which makes use of a sheet or curtain of flexible fabric material which drapes over the moving substrate and applies a coating by means of a direct wiping action. However, curtain coaters are prone to inconsistent application, are not well suited for use with slurries, are limited in terms of the speed at which they can operate effectively in a production environment, and are not well adapted to applying relatively thick coatings.
Another known form of applicator is usually referred to as a flood coater, which essentially operates by forming a pool of liquid on the substrate, and spreading the pool over the surface with air jets. Again, however, there are limitations with this technique in terms of the uniformity of application, the viscosity of the liquid or slurry that can be used, and the thickness of the layer or coating that can be applied.
Generally, therefore, these known forms of apparatus are subject to a variety of limitations including susceptibility to clogging, inconsistent application, limitations in speed, limitations in the width of sheet material that the coating can be applied to, limitations in the consistency of the liquid or slurry that can be applied, or some combination of one or more of these shortcomings. They are also typically adapted to apply relatively thin outer surface coatings, as distinct from intermediate layers of substantial thickness as part of a laminated sheet. These limitations render such prior art devices generally unsuitable for use in the manufacture of sheet materials, and particularly FRC sheets, of substantial size and at relatively high speed.
Another known form of apparatus is a spatter coater, which makes use of a rotating roller incorporating a radial array of flexible filaments or bristles to spatter a coating onto a substrate. Spatter coaters are used, for example, to apply surface coatings to clay or masonry tiles, on a production line. Spatter coaters are able to some extent to overcome some of the deficiencies of the other known forms of coating apparatus, especially in terms of clogging. However, in the context of the production of sheet material, known spatter coaters are also subject to inherent limitations.
In particular, known spatter coaters are not able accurately to stop and restart the application process on an intermittent basis, in order to permit precisely controlled coating or laminating. This is especially so with the types of slurries typically used in the production of FRC sheet, because of the relatively runny consistency required to ensure “self-levelling”, and the consequential tendency for excess slurry to drip onto the substrate, even if the slurry supply is shut off or the spattering roller is temporarily stopped.
This precise control over intermittent stopping and starting of the application process is particularly important in a high speed production environment where different batches of sheets, having different layers, thicknesses or properties, may be required to run back to back through the coating apparatus and inaccurate transitional control can result in patchy application, or the coating for one batch running over into the following batch of product.
A further difficulty arises due to the fact that, in the manufacture of FRC sheet or other products using cementitious slurries, it is desirable not to stop the supply of slurry to the apparatus itself, as this can result in the stagnation or accumulation of slurry in the apparatus or in upstream parts of the process. This, in turn, can result in overflows, changes in slurry consistency or concentration, settling or sedimentation, or undesirable variations in other process parameters.
Known spattering apparatus do not provide for the precise interruption of the slurry application process, and also do not allow for interruption without stopping the supply of slurry to the apparatus. They are therefore not effective in enabling an accurately controlled intermittent application process, especially in a high speed production environment for sheet materials.
It is an object of the present invention to overcome or ameliorate one or more of the disadvantages of the prior art, or at least to provide a useful alternative.
SUMMARY OF THE INVENTION
Accordingly, the invention provides an apparatus for applying a slurry to a substrate, the apparatus including:
a delivery surface disposed to support a layer of slurry;
spattering means adapted to be positioned closely adjacent the delivery surface and being movable so as to spatter the slurry from the delivery surface onto the substrate; and
regulation means for selectively varying or interrupting the flow of slurry from the delivery surface onto the substrate.
The terms “spatter”, “spattering” and the like as used herein, are intended to encompass any application technique whereby the slurry is deposited onto a surface or substrate in droplet, globule, particulate or atomised form, whether produced by brushing, flicking, rotating, spraying, agitating, atomising or other dispersion means, and whether propelled by mechanical, electrostatic, hydrostatic, hydrodynamic, gravitational or other means.
Unless the context clearly requires otherwise, throughout the description and the claims, the words ‘comprise’, ‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.
Preferably, the apparatus includes a reservoir to contain slurry upstream of the regulation means. Preferably, the reservoir includes an inlet to direct slurry from a supply source and an outlet associated with the regulation means.
The regulation means preferably include a pair of barrier elements selectively movable to define an intermediate clearance space of variable effective cross-sectional flow area
Cottier John Sydney
Curran Chris
Dow Geoffry
Crispino Richard
James Hardie Research Pty Limited
Knobbe Martens Olson & Bear LLP
Lazor Michelle Acevedo
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