EP1273410B1

EP1273410B1 - Laser treatment method of the surface of granite slabs or similar

Info

Publication number: EP1273410B1
Application number: EP20020380152
Authority: EP
Inventors: Juan Maria Pou Saracho; Ramon Francisco Soto Costas; Fernando Lusquinos Rodriguez; Mohamed Boutinguiza Sidahmed-Larosi; Felix Quintero Martinez; Mariano Jesús PEREZ-MARTINEZ Y PEREZ-AMOR
Original assignee: Digafer Sa; Universidade de Vigo
Current assignee: Digafer Sa; Universidade de Vigo
Priority date: 2001-07-06
Filing date: 2002-07-05
Publication date: 2013-01-23
Anticipated expiration: 2022-07-05
Also published as: PT1273410E; ES2180450B1; EP1273410A1; ES2180450A1

Description

OBJECT OF THE INVENTION

The invention refers to a treatment method of granite slabs by means of a laser radiation application, permitting the superficial modification of granite slabs for using in both facades and floorings, obtaining a bushhammered-type surfacing, in other words a surface with a rough surfacing giving the impression of being more rustic and natural.
By means of the method of the invention, it is possible to bushhammer thin granite slabs with thicknesses of less than 20 millimeters, practically eliminating the risk of breaking them, permitting obtaining different types of surfacing with the same equipment without needing to change tools.

BACKGROUND OF THE INVENTION

Granite has been used for a long time in constructing large public works, buildings, etc., although granite is currently widely used as a decorative element, in other words as a facade siding of large buildings and as both indoor and urban flooring.
Regardless of the different handling stages of granite, up to its definitive surfacing, the most frequently used surfacings in the case of granites are the following:

Bushhammered: it is the oldest superficial treatment of rocky materials for outdoor sidings and artisan works. The rock surface is struck with a special hammer whose head is provided with small, pyramid shaped teeth. This mechanism permits obtaining different grain sizes on the worked surfaces.
Buffed: with this treatment, a shiny surface is obtained due to the high degree of crystallinity of the granites it is applied to.
Sawn: it is the surfacing obtained by means of using machines for sawing the blocks. The surface is marked with parallel gutters produced by the strips.
Flamed: a flame is applied to the surface of the granite, which provokes the release of small sized rocks and chips. This treatment gives the rock a rough and glossy appearance with typical chromatic effects, and it increases the stability of the granite against atmospheric chemical alteration.

In the past few years, using granite for siding detached single-family homes or townhouses and for floorings (both indoors and in the urban setting) and a certain aesthetic change in the siding of large buildings (a certain "boredom" with buffed granite) have significantly increased the demand for slabs with a rough superficial surfacing.
As we have just explained, the alternative to buffed granite is the bushhammered or flamed surfacing since the sawn surfacing is too rough for some applications.
The bushhammered granite can successfully be applied to practically all granite varieties and it gives the stone a more rustic and natural surfacing. There are two fundamental types of machines on the market dedicated to these tasks: the mechanical bushhammer machines and those that bushhammer by means of a jet of water.
The drawbacks of the mechanical bushhammer machine are the following:

The hammering of the bushhammers on the stone introduces an enormous amount of stresses on it that break the granite slabs on numerous occasions.
The noise in these facilities is deafening (120 dB).
Enormous amounts of dust are released.
The bushhammering machines are more expensive than the merely flaming machines.
The wearing of the bushhammers is very great. They must be regularly sharpened and frequently replaced.

Flaming consists of a thermal treatment of the surface by means of oxyacetylene burners applied at a 45º inclination with the surface and an approximate flame temperature of 2,800º C. The drawbacks of flaming are the following:

It is a fairly slow process.
Not all granite varieties can be flamed with commercially acceptable results.
It is necessary to cool the rock by means of water immediately after applying the flame so that it does not burst.

These drawbacks are the reason the bushhammered surfacing is the most extended rough surfacing.
Recently, bushhammering machines by means of a jet of water have been developed. These machines solve some of the drawbacks of the mechanical bushhammering machines:

It is possible to bushhammer thinner slabs (of up to 10 mm thick) without breaking the rock.
Noise reduction.
Dust elimination.

However, the bushhammers by a jet of water have other drawbacks:

The surfacing is not always the desired one.
It is necessary to use pure water to prevent the nozzles from blocking up.
The cost of the machine is much higher (two to three times more than a mechanical bushhammer).
Higher maintenance costs.

US-B-6167879 describes the treatment of granite stones by lasers in order to obtain a non-slip floor covering by regularly or randomly distributed depressions (micro-craters) with suction effect, which preferable are lens-shaped, sharp-edged, flat and invisible to the human eye. Invisible means, in this case, that the micro-craters cannot be seen with the human eye from a certain distance due to the eye's resolution. This is far away from the object of the present invention in which a visible rough surface finish is to be obtained.
JP-A-06092754 discloses a method for treating the surface ruggedness of granite capable by irradiating the surface of granite with laser beam at 150-300 cm²/min treating speed per 1KW irradiation output.

DESCRIPTION OF THE INVENTION

The proposed method has been conceived to solve the previously explained drawbacks, being based on a simple yet no less efficient solution, since it is the laser application for treating a natural rock such as granite.
Concerning this, certain clarifications must previously be made in relation to the term "granite", given that geologically, it is an irruptive rock of igneous origin, of coarse grain, fundamentally constituted of quartz, feldspar and micas. This is a scientific definition that does not comprise more than some decorative granites, those which, therefore, would be the only ones that could be called granites in "stricto sensu".
From the commercial point of view, the term "decorative granite" or simply "granite" is used to refer to all igneous rock with a granitoid or porphyroid texture, as well as some metamorphic rocks of a similar structure (gneisses, etc...) (see for example the work: M. Bustillo Revuelta and C. López Gimeno "Recursos Minerales" ("Mineral Resources"). Gráficas Arias Montano, S.A. Madrid (1996 )). In this way, the commercial definition of granite encompasses not only the rocks geologically considered granites (Rosa Porriño, sylvan varieties), but also others such as gneisses (Rojo Guadajira), gabbros (Negro Villar), diorites (Gris Mondariz, Negro Badajoz) etc..., until reaching more than 80 exploited varieties in Spain alone.
Having made these clarifications, the treatment method of the invention is defined in claim 1. It basically consists of the following:

Placing the granite slab or piece to be treated on a support adjusted to its dimensions, on a mobile system, which will be connected to automatic control means of the placement of the piece.
The granite slab or piece located on the support is irradiated by means of a laser beam, the laser beam coming from a laser resonator and driven to the work area by means of mirrors or fiber optic, depending on the system used and the wavelength of the laser radiation.
The irradiated surface of the granite slab or piece is modified by the laser beam, said laser radiation coming from an equipment of any wavelength, such as a laser, for example, from CO₂, CO, N₂, Nd:YAG, Er:YAG, Nd:glass, Ruby, HeNe, HeCd, HeHg, Cu, I, Ar, Kr, diode, chemicals, excimers, alexandrite, emerald, coloring, or any other type of laser.

The basic required condition is that the density of power reached on the granite piece be enough, which is why the most suitable lasers are those from CO₂, CO, Nd:YAG or diode.
In the method, three possibilities are considered concerning the incidence angle of the laser, perpendicular, with a fixed angle with respect to the perpendicular and with a continuous angle modification; with the particularity of it being advisable to use a cooling fluid immediately after the laser treatment, depending on the nature of the granite, and among those to mention are N₂, Ar, He, Ne, CO₂, O₂, compressed air, etc., or a liquid such as water, liquid N₂, or some organic liquid.
Likewise, after the laser treatment, it may be necessary to brush the surface of the granite slab to remove partially released grains, it being possible to brush by means of circular or linear metallic brushes.
The bushhammering or the thus called treatment is carried out by moving either the granite slab or piece against the laser beam or the laser beam in relation to the granite slab or piece, such that, due to the large mass of the commercial granite boards, it is preferable to move the laser beam, the slab remaining stationary, for the purpose of the laser beam sweeping the surface of the granite slab or piece in those areas in which a transformation of the surface condition is desired to be obtained.
It has also been mentioned that the laser incidence to the surface of the granite slab can be perpendicular or form a certain angle with it, such that by varying this angle, the type of surfacing can be modified, it even being possible to carry out a continuous modification of that incidence angle, obtaining a surfacing different from the one obtained by maintaining the fixed beam orientation.
Said method involves a considerable improvement in the work conditions of the operator processing the granite slabs, greatly eliminating the acoustic and environmental contaminants suffered during the traditional granite slab bushhammering methods.
More specifically, among the benefits derived from the method of the invention, the following can be mentioned:

It is possible to treat thin granite slabs with thicknesses of less than 20 mm, practically eliminating the risk of breaking.
It is possible to obtain different surfacings with the same equipment without needing to change the tool.
The noise produced during processing is drastically reduced in comparison to the most widely used method, the mechanical bushhammering.
The granite piece or slab undergoes no wearing nor corrosion as no contact between the piece and the tool is established, for this reason, it is not necessary to sharpen or replace said tool.
The vibrations of the granite slab being treated are eliminated, likewise reducing the amount of dust released in the environment.

Regarding said treatment, it can be carried out directly after extracting the block from the quarry, although the best results are obtained once the granite slab or piece has been cut to the desired thickness.

PRACTICAL EMBODIMENT EXAMPLE

Bushhammering by means of a laser beam was experimentally carried out on granite slabs of the "rosa porriño" variety, these bushhammerings being by means of a , high-powered diode laser (λ= 940 nm), working in continuous wave mode, with an optic system of a 100 mm focal distance, focusing on the slab surface in normal incidence, without any gas contribution and with a 900 W power. With these conditions, the surface of said granite slabs was bushhammered at a speed of 10 mm/s, the use of a cooling fluid not being necessary.
Different types of surfacings on the same piece were obtained without needing to change the equipment or tool, it only being necessary to modify the processing parameters.
It is worth mentioning the fact that a continuous variation of said processing parameters (power, frequency, pulse width, focal distance, relative beam/piece speed) can be carried out without needing to stop the bushhammering process, obtaining gradually varying surfacings on the granite piece.

Claims

A laser treatment method of the surface of granite slabs or the like, for obtaining a bushhammered-type surfacing, i.e. a surface with a rough surfacing giving the impression of being more rustic and natural, which comprises the following operative phases:
- Positioning the granite slab to be treated on a support adjusted to its dimensions;

- Irradiating the granite slab located on the support by means of a laser beam;

- Modifying the surface of the granite slab irradiated by the laser beam up to obtaining a bushhammered-type surfacing,
wherein the laser is a high-powered diode laser working in continuous wave mode, has a wavelength of 940 nm and a power of 900 W, is operated at a speed of 10 mm/s and is focused on the slab in perpendicular incidence by an optic system having a focal distance of 100 mm.
A laser treatment method of the surface of granite slabs or the like according to claim 1, characterized in that after the laser treatment, the surface of the granite slab is brushed by means of circular or linear metallic brushes in order to remove partially released grains.
A laser treatment method of the surface of granite slabs or the like according to anyone of the previous claims, characterized in that the support on which the granite slab is located on is mobile and is connected to plate positioning control means.
A laser treatment method of the surface of granite slabs or the like according to anyone of the previous claims, characterized in that a cooling of the granite slab is used, capable of being gas or liquid, any chemical composition.
A laser treatment method of the surface of granite slabs or the like according to anyone of the previous claims, characterized in that the mobile means for the support on which the granite slab to be treated is placed, associated to plate positioning control means, consist of a robot, any type of coordinates table, or a combination of both systems.
A laser treatment method of the surface of granite slabs or the like according to anyone of the previous claims, characterized in that the granite slab can have any shape, be of any variety, type, chemical composition and dimensions, and it is bushhammered following any trajectory.
A laser treatment method of the surface of granite slabs or the like according to anyone of the previous claims, characterized in that the laser beam is applied to the granite slab forming a continuously modified incidence angle.