INVENTION DESCRIPTION

1. FIELD OF APPLICATION

The invention relates to stone engraving process.

In the International Patent Classification, it is classified as Section B - Performing operations; Class B28 - Working stone; Subclass B28D - Working stone (machines, processes), Group B28D 1/22 - Working stone by cutting.

2. TECHNICAL PROBLEM

Precise and quick stone engraving, of various degrees of treatment and depth of cutting, requires also big investments in technical devices. In the present tools, machines and utensils market there are numerous products that, with some energy consumption, enable more or less successful and precise stone engraving, manual or machine or combined. Computer controlled machines have a growing role in this field. Any of these engraving processes requires investments in machines and energy consumption, and their field of operating is limited by dimensions of the very stone engraving machine.

The above mentioned engraving techniques are known in several variants, but the main deficiency of all known methods is the impossibility of serial precise production.

The technical problem that is solved by this invention relates to the process of enhancing the preparations and precise stone engraving, aimed to cutting deep or raised signs in the stone: alphabetic, numeric and figural signs, QR codes, reliefs and Braille alphabet. 3. STATE OF THE ART

The presently known stone engraving methods can be classified into several groups, almost every method having several sub-methods. Thus, the scope of methods being used for stone engraving can be divided into several types:

a) Traditional or manual method, utilising tools such as:

- chisel, file or similar hand tools;

- electric or pneumatic hand turbine.

This method slightly differs from one school to another, same as from one hand to another, but most of them for design preparation use pencil, marker or another device for writing on stone, or a stencil for creating a predesigned image, according to which the stone is then engraved. Different methods are aimed to similar goals. Achieved are contours required for subsequent deep cutting of the stone. The marking devices - pencils differ from each other, but their results are similar. They remain on the stone surface, more or less resistant to the water that is required to cool the stone down when cutting a relief with hand turbine, similar as when an engraving is made by dry method, without cooling the tools, as the case is with water resistant pencils. When cooling the stone with water, a large loss of time is washing and blowing away the stone dust produced when any hand tool is used. The deficiency of such preparation is that while such engravings are being made with a chisel, file or hand turbine, stone disintegrates into fine dust that covers the working surface, thereby preventing a good view of the design made with a pencil, most often at the place that the engraver is most interested in, where the surface is being treated, therefore making the engraver's point of interest. When working with chisel and file, this problem is less present, but still requires often cleaning the stone surface, because otherwise the lines of the first, and for precision the most important, cut in the stone, are to be made blindly. b) Semi-automated methods, utilising stencil controlled machines:

- pantograph.

The main deficiency of this method is that every stone that is being treated, where a sequence of stones are produced - such as in cases of producing long relief decorations - is to be of the same dimensions, which rises the price of the stone that is required to produce the decorative sequence. Another deficiency is the high cost of producing the stencil that indirectly controls such machines. Another deficiency is that the stone working surface area is limited by the machine and the stencil working areas. c) Highly automated method, utilising computer software controlled machines:

- CMC machine.

Highly automated stone engraving methods directed by computer preparation, most often utilising milling machines that cut the stone exactly where required. This method's deficiency is the high price of such technologically advanced machines, large quantities of energy they consume, and the high costs of the milling machine expendable elements. Work of a computer controlled milling machine can be precise, but the milling head diameter prevents precise shaping of angles. Another deficiency is the working area of the stone being limited by the working area of the machine.

- Laser.

Laser affects stone only superficially, slightly entering its structure - depth. This makes writings short lasting, because most often such writings are exposed to atmospheric elements, wherefore after several decades of time it significantly looses its quality and legibility. These makes lasers inadequate for treating lime stone, they are more often used at engraving granite, where its work is more visible. The stone working area is also limited by the laser working area dimensions. d) Etching

Etching is the process of removing material surface by means of corrosive agents. Usually, a part of the surface is protected against corrosion, wherefore it is removed only the unprotected surface. It is being applied in arts, printing and industry. Well known is producing of lithographic stones, utilised as a printing form in lithography, the oldest planographic printing method. Here, stone slab is used as the printing stencil only.

4. ESSENCE OF THE INVENTION

The essence of the invention is stone engraving process by etching enhanced by computer preparation, this process comprises three stages:

Stage one - preparation, of graphical signs for engraving, by means of computer software; Stage two - preparation of stone with graphical signs for engraving by means of etching; and

Stage three - engraving graphical signs on stone by means of etching. Process according to this invention enables:

- production of engraved stone slabs as final products, where the engravings do not require additional manual treatment, and

- production of engraved stone slabs that are not final products, where the engravings require additional manual treatment.

The process makes engraving easier and more precise, enabling fast, easy and low cost engraving of alphabetic, numeric and figural signs, QR codes, reliefs and Braille alphabet, mostly in lime stone.

The process eliminates as much as possible all the deficiencies of semi-automated and highly automated stone engraving methods, and significantly enhances and makes easier manual stone engraving methods.

Computer preparation enhances the stone engraving process by etching thanks to its unlimited possibilities of drawing and cutting graphical signs that are to be engraved by etching in the stone.

5. ILLUSTRATION DESCRIPTIONS

Figure 1 shows two-layer foil with cut letters - front view.

Figure 2 shows two-layer foil from the Figure 1 - top view.

Figure 3 shows two-layer foil from the Figure 1 - left side view.

Figure 4 shows transferring one-layer transparent foil stuck on cut sticker of the two-layer foil - front view.

Figure 5 shows transferring one-layer transparent foil stuck on cut sticker of the two-layer foil - bottom view.

Figure 6 shows transferring one-layer transparent foil stuck on cut sticker of the two-layer foil - left side view. Figure 7 shows sticker with cut letters stuck on the stone slab working surface - front view.

Figure 8 shows sticker with cut letters stuck on the stone slab working surface - bottom view.

Figure 9 shows sticker with cut letters stuck on the stone slab working surface - left side view.

Figure 10 shows an example of stone slab with raised engraved letters - front view.

Figure 1 1 shows an example of stone slab with raised engraved letters - bottom view. Figure 12 shows an example of stone slab with raised engraved letters - left side view. Figure 13 shows an example of stone slab with raised engraved letters, with foil removed from the engraved letters, as a final product - bottom view.

Figure 14 shows an example of stone slab with deep engraved letters - front view.

Figure 15 shows an example of stone slab with deep engraved letters - X-X cross section, bottom view.

Figure 6 shows an example of stone slab with deep engraved letters - Y-Y cross section, left side view.

Figure 17 shows an example of stone slab with deep engraved letters with foil removed from the stone working surface, as a final product - X-X cross section, bottom view.

6. DETAILED DESCRIPTION OF THE INVENTION EMBODIMENT AND FUNCTIONING

Stone engraving process by etching enhanced by computer preparation, according to this invention, comprises three stages:

Stage one - preparation, of graphical signs for engraving, by means of computer software,

Stage two - preparation of stone with graphical signs for engraving by means of etching, and

Stage three - engraving graphical signs on stone by means of etching.

Etching is performed by hydrochloric acid (2CaC0 ₃ + 4HCI→ 2CaCI ₂ + 2C0 ₂ + 2H ₂ 0) of the Ph factor from 0.5 to 1.3, which is used in households.

The process is described and illustrated by the example of a stone slab with raised engraved graphical signs - letters of the words "ART MUZEJ", Fig.10, 1 1 , 12, 13, and by the example of a stone slab with the same letters being deep engraved, Fig.14, 15, 16 and 17.

Process description:

Stage one - preparation of graphical signs for engraving, by means of computer software, comprises following steps:

- computer software aided drawing of the selected graphical signs that are to be engraved in stone;

- cutting by computer controlled machine cutter of the drawn graphical signs on sticker 4 of two-layer foil 2 in the ratio 1 : 1 with the stone working dimensions, Fig.1 , 2 and 3;

- sticking of transparent one-layer transferring foil 5 over cut sticker 4 of two-layer foil 2, Fig.4, 5 and 6;

- separating of transferring foil 5 with cut sticker 4 from carrying layer 3 of two-layer foil 2.

The two-layer foil 2 comprises sticker 4 and carrying layer 3, so that the sticker 4 is stuck with its adhesive side to the carrying layer 3.

The transferring foil 5 is adhesive on one side only.

Stage two - preparation of stone with graphical signs for engraving by means of etching, comprises following steps:

- preparing stone slab 1 of the selected dimensions and with polished working surface, and cooling the stone slab down to the temperature between 10 and 18°C;

- sticking transparent transferring foil 5 with cut sticker 4 onto working surface of cooled stone slab 1 , Fig.7, 8 and 9;

- separating transparent transferring foil 5 from the stone slab 1 working surface, so that on the stone slab working surface remains stuck cut sticker 4;

- removing parts of the cut sticker 4 from those parts of the stone slab 1 working surface that are to be etched by acid. If on the stone slab working surface there are to be engraved raised letters 7, then the cut parts of the sticker 4 are removed from all surfaces of stone slab 1 except from surface with letters, Fig. 0, 1 and 12. If on the stone slab working surface there are to be engraved deep letters 8, then the cut parts of the sticker 4 are removed only from stone slab surface with letters, Fig.14, 15 and 16;

- removing from the stone slab 1 working surface the glue left from the removed sticker 4, to enable direct contact and reaction of stone with acid;

- protecting the stone slab 1 lateral and back side surfaces from contact with acid by means of adhesive tape 6;

- heating the stone slab 1 for several hours, at the temperature of at least 25°C, to make the cut sticker 4, which has remained stuck on the stone surface, well stuck on the stone working surface.

The sticker 4 of the two-layer foil 2 and the tapes 6 that protect the stone lateral and back sides of the stone from being corroded by hydrochloric acid, are made of an inert material, usually of PVC foil, which is not corroded by acid in the etching procedure.

Stage three - engraving graphical signs on stone by means of etching, comprises following steps:

- pouring the etching hydrochloric acid of the Ph factor between 0.5 and 1.3 into a plastic vessel of adequate size and leaving it for a few minutes to stabilise in order to produce a precise and quality engraved product;

- immersing the stone slab with pieces of the cut sticker 4 into the previously prepared plastic vessel containing hydrochloric acid so that the acid exceeds 2-5 cm above the stone surface being corroded;

- keeping the stone plate in the plastic vessel containing hydrochloric acid for 2 to 15 minutes, depending on the type of lime stone and the desired etching depth, wherein the result of engraving graphic signs is usually from at least 0.2 mm in depth for more precise - fine engravings, or up to 5 mm in depth for less precise - larger engravings;

- taking the stone slab out of the plastic vessel after being etched with hydrochloric acid and removing parts of the sticker 4 from the upper surface of raised letters 7, Fig.13, or removing parts of the sticker 4 from the working surface of the stone slab 1 that was protected from the acid corrosion process, in the case of engraving deep letters 8, Fig.17, and removing the adhesive tape 6 from the lateral and back sides of the stone slab 1 ; and - pouring cold water over the stone slab, to stop the acid reaction and wash acid residues.

Hydrochloric acid can have effect precisely on the upper and the lateral sides of the stone immersed in the plastic vessel with acid, while at the back side not, because of the bubbles and flow produced by the reaction. Therefore, the stone with parts of the cut sticker 4 has to be immersed into plastic vessel with hydrochloric acid with the parts of the cut sticker 4 being on the upper side of the immersed stone.

In miniature - smaller engravings of greater precision, keeping the stone in reaction with the acid for too long can cause undermining below the sticker 4 and, thereby, unwanted affecting the areas not intended for this.

Keeping the stone in the acid for too short may produce engravings shallower than wanted.

The process according to this invention enables:

- producing engraved stone slab as a final product, where the engravings require no additional manual treatment because the wanted engraving quality is achieved by the very acid reaction, and

- producing engraved stone slab which is not a final product, where the engravings require additional manual treatment, because in this case the etching is just a preparation for further manual treatment, where the engraving made by previous etching makes a guide for guiding the manual treatment tools.

In cases where the above described process of engraving by etching is only a preparation for further manual and deeper treatment, in the computer preparation on graphical signs there are drawn canal contours of around 0.3 - 0.5 mm in width. Once the cut sticker 4 is removed from the stone surface where canal contours of the above stated width are drawn, on the stone remain canals between the remaining parts of the sticker, that are affected by the acid. In reaction with the acid, canal is hollowed out to the depth of around 0.3 - 0.5 mm and widened along the edges by around 10-15%. Thus prepared canals between the remaining parts of the stickers make precise preparation for further treatment with chisel, file or hand turbine, because now the engraving pattern is not just drawn on stone, but it is hollowed into stone to the required depth. During further manual treatment, the sticker parts remaining outside the canals make good contrast with the canal in the stone, making the line that is to be engraved well visible. In the traditional manual stone treatment, impurities and dust produced in the process decrease visibility and may cause errors in engraving or slow the process down. The canal created after etching enables the first cut in the stone not to be done blindly. A canal that is to be deepened by, e.g. a hand file, makes itself a palpable guide that guides bore bits, which is very helpful in achieving precision. Once the engraving is sufficiently deep or when the engraving is complete, the remaining parts of the sticker are removed and glue is cleaned from the stone.

The process according to this invention eliminates deficiencies of the known stone engraving methods: manual, semi-automated and highly automated, and significantly enhances and makes manual stone engraving easier.

The process makes engraving easier and most precise, enabling quick, easy and low costing engraving of alphabetic, numeric and figural signs, QR codes, reliefs and Braille alphabet, firstly in lime stone.

The process has no limits in dimensions of the stone slab which is to be engraved, except the limit in the weight of the stone slab.

The process enables serial precise engraving of several stone slabs of smaller dimensions.

The process rises general standards in precision of engraving relieves in stone.

The process has significant potential in production automation, and is costing less than any other known stone engraving method.

MEANINGS OF NUMERIC REFERRAL MARKS IN ILUSTRATIONS AND DESCRIPTION:

1 - stone slab

2 - two-layer foil

3 - carrying layer of two-layer foil

4 - two-layer foil sticker (adhesive at one side only)

5 - transparent one-layer transferring foil (adhesive at one side only)

6 - adhesive tape for protection of the stone slab lateral and back sides

7 - raised letters engraved on stone slab

8 - deep letters engraved in stone slab 7. INVENTION APPLICATION

Application of the stone engraving process by etching enhanced by computer preparation, according to this invention, is very wide in producing stone slabs with engraved alphabetic, numeric and figural signs, crests, QR codes, reliefs, Braille alphabet, etc. It is particularly applicable for engraving stone plates with information on important historic facts, cultural heritage monuments and other things of public interest.

The invention produces final product, long lasting, legible and easy to maintain, in all sorts of engravings. Where a deeper relief in stone is to be produced manually, this process, because of its advantages, can make an irreplaceable part of preparations for such relief production.