Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Reexamination Certificate
2002-03-04
2004-11-30
Lechert, Jr., Stephen J. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
C264S040700, C264S101000, C264S112000, C264S118000, C264S122000, C264S138000, C264S308000
Reexamination Certificate
active
06824715
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 For
02 Mar. 2001
Forming A Laminated Sheet
Material By A Spattering
PR3478
Coatings For Building Products
02 Mar. 2001
The present invention relates to a method and apparatus for forming a sheet material, and in the preferred form, a laminated sheet material.
The invention has been developed primarily for use in the formation of fibre reinforced cement (“FRC”) sheeting, from cementitious slurry through a modification to the “Hatschek” process, for use in the building industry. It will therefore be described primarily with reference to this application. It should be appreciated, however, that the invention is not limited to this particular field of use, being potentially applicable to other materials, other manufacturing processes, and other industries.
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. Sheet material, and in particular FRC sheet material, is widely used in the building and construction industries in a variety of applications including cladding, lining, framing, flooring, roofing, dooring, window framing, insulating, waterproofing, decorative trimming and the like. Depending on how the material is used in different situations, advantage is taken of its unique structural, aesthetic, acoustic, thermal, and weather resistant properties. It is typically manufactured in different sizes, shapes, thicknesses, densities and with various special purpose additives, in conjunction with other materials, so as to take optimal advantage of its functional characteristics in different applications.
FRC sheet was initially manufactured using modified paper making machinery, from cementitious slurries incorporating fibrous asbestos for reinforcement. Later, fibrillated cellulose fibre was substituted as an alternative to asbestos, and the manufacturing equipment was progressively developed more specifically to the FRC industry.
As a culmination of this development work, one of the most common manufacturing processes currently used in the industry is now known as the “Hatschek” process. In this process, a cementitious slurry is initially formed from water, cellulose fibre, silica, cement and other additives selected to impart particular properties to the product according to its intended application. The slurry is mixed in an agitator and delivered to a feed sump from where it is pumped through a series of vats. A sieve cylinder is immersed in the slurry within each vat and these cylinders rotate as they are progressively driven by the bottom run of an overlying belt, formed from a specially formulated felt material. A typical Hatschek machine in a large scale production environment will incorporate a series of three or four vats, and a corresponding number of associated sieve cylinders. The number of vats and cylinders may vary, however, and there need not be a one to one correlation between them in the sense that several cylinders could be immersed in a single vat.
In the process, the relatively dilute slurry in the vats filters through wire mesh screens fitted to the respective sieve cylinders. As the slurry filters through this mesh, it deposits a layer of cellulose fibre on the underside surface of the wire, which acts as a filter medium to trap the other particulate materials in the feed slurry. By this mechanism, a thin film of material having a thickness of around 0.3 mm is quickly built up on the surface of the sieve. This process thickens the slurry from a concentration of around 7% solids in each vat to a concentration of around 70% solids in the film. The excess water passes through the sieve wire as filtrate and exits from the end of the sieve cylinder, so that the residual solids may be recovered and recirculated.
The film formed on the surface of each sieve cylinder is transferred upon contact to the outer surface of the overlying belt. This transfer process takes place by virtue of the fact that the felt is less porous than the sieve, as a consequence of which atmospheric pressure facilitates the transfer.
As the felt passes over each successive vat in the series it picks up a corresponding series of sequential layers of film from the associated sieves and thereafter passes over a vacuum box positioned along the top run of the belt where the accumulated layers of film on the belt have their moisture content reduced.
The layered film then passes between a tread roller, which also provides the driving force to the belt, and an adjacent accumulation or “size” roller in the form of a relatively large diameter drum. The tread and size rollers are positioned such that further water is pressed out of the film while it is transferred to the size roller by a mechanism similar to that by which it was previously transferred from the sieve cylinders to the belt. The size roller accumulates a number of layered films according to the number of turns allowed before the film is cut off. Thus, the formation of a thicker sheet is achieved by allowing a larger number of turns before cutting the film. In the cut off process, a wire or blade is ejected radially outwardly from the surface of the size roller to cut longitudinally the cylinder of layered film material that has cumulatively formed on the surface of the roller.
Once cut, the sheet of material peels off the size roller to be removed by a run-off conveyor. The material at this stage has the approximate consistency of wet cardboard, and therefore readily assumes a flat configuration on the run-off conveyor. To complete the process at the wet end, the felt is cleaned as it passes through an array of showers and vacuum boxes, before returning to the vats to pick up fresh layers of film. It will be appreciated that the quality and characteristics of sheet material produced from the Hatschek process are dependent upon a wide range of variables associated with the slurry formulation and the various settings at the wet end of the machine.
Further down the process line, the “green” sheet is roughly trimmed to size at a green trim station using high pressure water jet cutters, after which it proceeds as individual sheets to a stacker. At the stacker, the green sheets are picked up by vacuum pads and formed with interleaving sheets into autoclave packs.
After partial curing, and optionally a further compression process to increase density, the sheets are loaded into an autoclave unit for final curing under elevated temperature and pressure conditions. In the autoclave, a chemical reaction occurs between the raw materials to form a calcium silicate matrix which is bonded to the cellulose reinforcing fibre. This process takes around 12 hours and at its completion, the sheets emerge fully cured, ready for accurate final trimming, finishing and packing.
One of the major limitations with the Hatschek process, and other known processes for the manufacture of FRC sheet, is that because of the way in which the layers of film are progressively formed from a cementitious slurry, and because the composition of the slurry itself is critical to the formation process, it is difficult to form sheet material accurately in multiple discrete layers having substantially different material compositions. This is desirable for a number of reasons, primarily to permit a greater degree of flexibility in tailoring the structural, aesthetic and other properties of the material, so as to optimise its performan
Brunton Greg
Cottier John Sydney
Lyons Robert
James Hardie Research PTY Limited
Knobbe Martens Olson & Bear LLP
Lechert Jr. Stephen J.
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