|Title of Invention||
"A HIGH ABRASION RESISTANT GLAZE COMPOSITION"
|Abstract||A high abrasion resistant glaze composition comprising of ball clay, soda feldspar, dolomite, calcite, quartz, zinc oxide, alumina, wollastonite, spodumene andfrit. A process for making a high abrasion resistance tile from the high abrasion resistance glaze.|
|Full Text||Field of the Invention:
The present invention belongs to the field of ceramic tiles. More particularly the invention belongs to a high abrasion resistant glaze composition for ceramic tiles and a method for application of the same.
Background of the Invention:
Man has always desired to create beautiful and durable living spaces Ceramic tiles are an effort in that direction There is evidence of use of the ceramic tiles by man for 4000 years Tiles of various designs and patterns have been found in Egyptian pyramids and Greek cities It is said that the tiles were invented in the east Gradually they moved to Persia and much more vibrant designs were introduced under the Islamic culture In late 12th century Europe was introduced to ceramic tiles and they gained prominence all over the world
The English word 'tile' is a less precise derivative of the Latin word 'tegula' and its French derivative 'tuile' that mean quite precisely a roof tile of baked clay. However tile word can be used for any kind of earthenware slab applied to any surface of a building The word 'ceramic' comes from the Greek word 'keramos' meaning pottery, it is related to an old Sanskrit root meaning 'to burn' but was primarily used to mean 'burnt stuff.
Tiles are a specialized form of covering for use on building surfaces, and since there are three types of building surface - roofs, walls and floors - there are three types of tiles -roofing tiles, wall tiles and floor tiles.
Tiles for walls and floors may be either glazed or unglazed. Generally speaking wall tiles are glazed and floor tiles unglazed, but the rule admits of exceptions.
Simply put tiles are made of clay. Tiles were made by hand, in early days clay bricks made by flattening the clay and cutting pieces into shape - were dried beneath the sun or baked. Later the only mechanical aid was a wooden mould carved in relief, which indented a pattern on the clay slab. The slab was dried and the impression filed with clay, which after further drying was shaved flat. After the formation of the tile body, ceramic tiles go through a firing process in a kiln under very high heat to harden the tile body and to create the surface glaze. Historically, unglazed tile was fired once. Glazed tile was fired twice. The first firing formed a tile body called a 'bisque'. The biscuit firing had the highest temperature at 1060 C that fixed the tiles for size and shape. After glazing the tiles were glost fired at about 1020 - 1240 C. On glaze decoration was fired at 750 C, just before the glaze began to melt. The modern tile industry was advanced by reviving the lost art of encaustic tile making. The industry was further revolutionized in the 1840s by the 'dust-pressing' method, which consisted of compressing nearly dry clay between two metal dies. Dust pressing replaced tile-making by hand with wet clay, and facilitated mechanization of the tile-making industry.
Various decorative techniques have been used in the tile making industry such as unglazed, plain glazes, encaustic or inlaid, mosaic, hand painting, carved and modeled tiles, sgraffito, luster painting, tube lining and transfer printing.
Different schemes of decoration such as tile pictures, single motif and patterns have been used in the art. Tiles have also been set in various shapes and assemblies for ease of setting as well as decoration.
Ceramic tiles have various characteristics that differ as per their application. Ceramic tile are used almost everywhere - on walls, floors, ceilings, fireplaces, in murals, and as an exterior cladding on buildings. Ceramics are defined as products made from inorganic materials having non-metallic properties. Ceramic tiles have a number of outstanding properties, which determine their usefulness. One of the most appreciated is their great durability. This durability can be divided into three types: chemical, mechanical and thermal:
• water absorption
• not affected by oxygen
• abrasion resistance
• impact resistance
• breaking strength
• stain resistance - resistant to almost all acids, alkalis, and organic solvents
It is desirable to have high abrasion resistance tiles for areas where there is heavy human traffic For instance in shopping malls etc there is lot of human movement and hence floor tiles tend to get rough and loose their glaze soon Presently typical life of a floor tile is 5 years, after which it has to be changed This results in additional expenses
Objects and Summary of the Invention:
It is the object of the present invention to overcome the drawbacks of the prior art tiles by providing a tile glazing with high abrasion resistance properties
It is another objective of the invention to introduce such glaze application process in the normal method of making of the tile
To achieve the aforementioned objectives the present invention discloses a novel gla/.e composition which when applied to ceramic tiles makes them much more resistant to abrasion than the tiles being used at present This glaze composition has ingredients chosen specific for external eyes and at the same time are chosen in such a way so as to ensure that it is completely transparent and thereby does not hide the inlaid design pattern
This invention particularly relates to a high abrasion resistant glaze composition comprising of ball clay 5-9% by weight, soda feldspar 38-42% weight, dolomite 7-8% by weight, calcite 14-18% by weight, quartz 5-8%by weight, zinc oxide 2-4% by weight, alumina 5-9% by weight, wollastonite 8-10%by weight, spodumene 6-15% by weigh and frit 5-20% by weight.
BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1 is a flowchart for the slip making process.
Figure 2 is a flowchart showing the full tile making process.
Detailed Description of the Drawings:
A glazed tile consists of two quite different parts, the backing or " body," and the glaze; and naturally the body is made first, and the glaze applied afterwards. This gives us the two main stages of tile manufacture, i.e. the making of the body and glazing.
The body of a glazed tile consists of one or more kinds of clay, usually with an admixture of certain other substances. It is generally composed of two kinds of clay - china clay and ball clay.
Wide ranges of body formulations are used in the tile industry, and this reflects, the wide range of properties of tiles and the availability of raw materials. The key factors governing the choice of body formulations are: - the need to ensure an acceptable fired body
color, and this places restrictions on the iron
contents of the raw materials.
the need to achieve an adequate degree of
vitrification of the body at a firing temp of 1200°C
Body Slip preparation
Next step is to make an intimate mixture of proper proportions of the "body" materials above described. To facilitate this operation they are severally brought to the condition of creamy liquids - or rather that of finely divided particles suspended in water. In the case of the clays this is simple enough. They are placed in a "blunger" - i.e., a hexagonal tub or vat in which powerful arms revolve continuously on a vertical shaft - and slowly churned up with water to a suitable consistency. The other materials are first ground into microscopic size and then carefully determined proportions of the various ingredients are run into a large central vat - the "mixing ark " - in which powerful "agitators" mix them thoroughly together. The mixture thus formed, known as "slip" or "body slip," is next passed through "lawns" or sieves of extremely fine mesh - some 20,000 holes to the square inch - and then over a bed of powerful electro magnets, by which latter any
particles of iron - which would be liable to cause dark specks in the finished tiles - are extracted. From the magnet bed the slip flows into the "finished ark," where further agitators are at work to keep the mixture homogeneous by preventing the heavier materials from settling to the bottom.
The tile body is prepared from the three basic components clays, quartz and feldspar in the proportional range mentioned above. The key considerations in the choice of body slip preparation process are:
- the need to ensure intimate mixing of the body
- the need to obtain the body in the appropriate
physical form for subsequent shaping process.
Once the body is in slip form, it is purified by sieving to remove coarse particle size impurities, and passed through magnetic separators to remove iron-bearing impurities. The slip making process also ensures that the clays are adequately dispersed and thus achieves a homogeneous mixing of the raw materials. This body preparation method is shown in Fig -1.
The body mixture is not yet ready for tile-making, it must first be converted into powdered form. To this end it is pumped under pressure into a filter press consisting of a series of large envelopes of fine canvas held between concave-faced iron plates, with the result that the water trickles away through the canvas, leaving the solid particles behind in the form of large flat cakes of the plastic compound known as potter's clay. As the press is emptied, these cakes, fall into special iron trollies on which they are conveyed into the drying kilns, there to be freed from all traces of moisture. From these kilns the cakes emerge, hard as boards, to be broken up, slightly moistened, and finally ground in pans or mills to the fine powder known technically as "dust," which is automatically conveyed to the department or "shop" in which it will be converted into tiles.
The reason for first drying and then remoistening the clay cake is that only in this way one can be sure that the dust made from them will contain the right proportion of moisture - just enough to make it bind together properly under pressure and no more. Even a small error in the moisture content of the dust may seriously effect the ultimate product.
The basic principle of the spray drying process are simple. The body slip is projected as a cloud of fine droplets into a stream of hot gas contained within a cylindrical chamber with a conical base. Drying by evaporation from the large exposed surface is rapid, converting the droplets into solid granules, which fall from the gas stream and leave the chamber through a valve situated in the base of the dryer. The vapor driven off is extracted from the chamber via cyclones to atmosphere. The dust in the form of granules is collected and stored in silos.
Making or Shaping or forming
This is the process during which the dust granules is moulded and brought to the final shape under high pressure. The tiles are glazed i.e. decorated with different type of glaze coat, printed and made ready for the final firing where they get hardened. The term "making," covers every part of manufacture, but in the potter's vocabulary it is often restricted to the actual shaping or forming of the article concerned. Tile "making" is done in powerful presses. Of the three main types of press available - the hand, the automatic, and the semi-automatic - the last named has proved the most generally useful. The making procedure is essentially the same in all three types. A steel well or "box" sunk in the bed of the press is filled with "dust," and a heavy steel die descends into it, forcing the dust against another die forming the bottom of the box.
The pressure is such that the dust is knitted into a solid of the required size and shape - a plain tile, for example, a capping, a skirting - hard and strong enough to stand any reasonable handling. As the "green tiles (so called in their unfired state) come from the presses, their edges, to which loose dust may be clinging, are lightly trimmed by hand; in technical language, they are "fettled." They are now ready for firing, but an interval of at
least a few hours, during which they may dry, will elapse before they reach that very important stage of their manufacture.
Nowadays, "continuous" firing is firmly established and rapidly becoming more general. The lies are subjected to varying degree of heats for pre-specified period of time in a continuous heating oven as the need may be.
After their first firing, tiles destined for glazing are known as "biscuit" (sometimes, though mistakenly, "bisque") tiles; and the same term is applied to the first firing itself -"biscuit" firing. After their biscuit firing, then, the biscuit tiles inspected. They are closely examined, and any defective ones - any that are chipped, specked, or fire-cracked, for example - are rejected. This process over, the board with its load is slid over the rollers to the appropriate glazing department or, when that department is at a distance, to the conveyor system connecting with it.
This glaze is simply a form of glass. Here such materials as feldspar, China clay, flint, soda, potash, lime, and oxide of lead are mixed together in carefully determined proportions, applied to the tile and the fired to a white heat. The glaze is in the form of a "slop" or thick liquid. There are many types of glaze - some will fire clear, some opaque, some bright, some matt - but all are based on a frit such as that described. The different colours are obtained by adding to the "slop" glaze certain staining materials, notably certain metallic oxides such as those of copper, manganese, iron, cobalt, and uranium. The purpose of the glaze in tile manufacture is both utilitarian and aesthetic: utilitarian in that it seals the pores of the biscuit, thus providing an article that does not harbour dirt and is therefore hygienic; aesthetic in that it endows the tile with a pleasing - often a very beautiful - finish such as it does not possess in the biscuit state.
Glazing can be done by machines or by hand. One of the types of machine glazing of white tiles is carried out on the "waterfall" principle. Over a horizontal traveling wire belt is placed a vessel at the bottom of which is a long fine slot at right angles to the belt. The vessel is kept constantly supplied with liquid glaze of milky consistency, which escapes through the slot and falls in the form of a thin sheet. Through this sheet the wire belt carries a constant stream of tiles, so that their faces - turned upwards - become coated with glaze. As most of the glaze's moisture is almost instantly absorbed by the porous biscuit, the handling of the newly-glazed tiles, though requiring care, presents no serious difficulty.
Another mechanical - or semi-mechanical - method of glazing is that of aerographing, or air - pressure spraying. Sometimes the color of the pattern being sprayed on through a stencil, and, the stencil removed, a colorless transparent glaze similarly applied over the whole face of the tile.
The firing by which the applied glaze is fused to the face of the biscuit is known as the "glost" firing - the firing, that is, of the "glost" (i.e., the glossed or glazed) ware. Here too the tiles are heated in a continuous way over a period of time as the requirement may be.
Glost firing over, the tiles are taken off the trucks and sorted into their different categories according to color, size, shape, etc., the process being greatly facilitated by the use of over-head conveyors and roller sorting tables. This done, the different groups are very carefully looked through, and any tiles that fall short of the high standard of quality are put aside, and either broken up, classed as "seconds," or - in the case of certain types of fault - sent back for retouching with glaze and for refiring.
The veilcraft glaze is a new formulation developed with the aim of getting suitable surface properties considering the extent of reactions during different stages of firing. Below mentioned is the ingredient:
a) Flux (soda feldspar, frit, Wollastonite, zinc oxide) to fuse the raw material at
b) Opacifers (zirconium)
c) Filler (clays, talc, dolomite) component of the blends to act as a
d) Extras (quartz, fused alumina) of controlling the thermal expansion of glaze.
Selection of the raw materials
The several oxides and minerals selected to formulate this glaze is based on the limitations of its melting rate.
During the time when the glaze is at the high temperature during the firing process, all the various raw materials must either melt or dissolve. This time could be as short as 2 to 10 min in a fast fire operation, and hence these processes are the major concern for tile operation. The glaze melting process releases large quantities of gas, which must be eliminated during the firing process. The space between the dried but not fired glaze alone amounts to over 40% of the total volume, and it is but one of several sources of gas. This imposes several limitations. One limitation arises because while gas escapes readily during the initial stages of firing, once the glaze seals over, the only way to eliminate gas is by diffusing it to the glaze surface, where a bubble of gas may burst and the surface heal over. This diffusion process is inherently too slow, hence, there is need to maximize the temperature at which seal-over occurs.
Another limitation is that some raw materials releases substantial amounts of gas on heating. If the temperature of decomposition is not several hundred degrees below the firing temperature, substantial gas may be trapped, producing bubble defects.
Behavior of raw materials during glaze maturing
Behavior of raw materials during glaze maturing may be grouped by their properties. First are the refractories, those materials with high melting points and inertness, with great resistance to degradations either thermally or chemically. Hence, attention to the temperature requirements for an adequate melting rate is required. These raw materials come in two categories: plastic and non-plastic.
Plastic raw materials are those that can be mixed with a little water to form a deformable mass that can be easily worked to form a desired shape. They work because their molecules can attract and loosely bond to water molecules. Hence, they have value in glazes as suspending agents. Such materials used in this glaze are the ball clays TRN-2, and RD-2.These are used in concentration of 7 to 8% to provide slip suspension. During the firing process, they first loose their water of hydration at temperatures of 500°C-600°C. afterwards the remaining materials is an aluminosilicate of moderate refractoriness.
Non plastic materials, such as alumina and silica are of very high melting nature and very resistant to dissolution. When we fire the glaze at high temperature, these materials dissolve in the molten glaze. They also increase the abrasive resistance of the glaze.
Zircon has a solubility in glaze of about 5% at high temperature and 2-3 wt % at room temperature. Thus this is used as an opacifier.
The second group of materials used are the fluxes. These materials were used to provide the glue that would fuse the various other raw materials into a single solid mass.
The flux used here can again be divided into two groups. The first one are those that will melt and provide the initial liquid phase at the firing temperature. Under this group is the soda feldspar and spodumene, which are an alkali-aluminosilicate mineral. The melting properties and the viscosity of the resulting melt of these minerals are such that are found to be suitable for use in the firing of tiles.
As far as lower melting flux are considered, the frits 5535 and 005 is suitably used for the purpose. These were used as a melter and found to work as a good seal over temperature of a glaze.
The other category of fluxes used in this glaze are those materials that do not have low melting points, but are readily attacked by molten firing temperature, and once dissolved, contribute to the reactions forming the final product.
The most effective material used in this category is the wollastonite. At temperatures above 1050°C -1100°C it is readily attacked by molten oxides. Once dissolved, it is autocatalytic. It lowers the viscosity of the molten oxides, making them more aggressive in dissolving other ingredients.
The other material used as an alternate to wollastonite is the calcite. It has similar behavior and limitations.
Dolomite is also similar in behavior to calcite and is used as a substitute in glaze where MgO was required.
Zinc oxide is attacked and dissolved in molten oxides at reasonable rates at temperature above 1050°C. Once dissolved, it helps to lower viscosity and increase the dissolving power of the melt. Hence this material is used in glaze, since this glaze is formulated to fire at high temperatures.
The glaze compositions were chosen with the compositional range given in table-2
Table 2(Table Removed)This glaze is applied at the 2nd stage of application and in the final stage of application. The role of the glaze is to dissolve the entire glassy mass including the prints into one solid mass, thus protecting the prints from eroding out in period of time.
The above process of tile making is illustrated as a flowchart in figure 2.
Abrasion test results:
This particular glaze is highly abrasive resistant and falls under the class five of the test criteria stipulated by the international standards (ISO 10545-7) Class -5 states as follows:
Floor coverings that are subject to severe pedestrian traffic over sustained periods with some scratching dirt, so that the conditions are the most severe for which glazed floor tiles may be suitable (for example public areas such as shopping centers, airports concourses, hotel foyers, public walk ways and industrial applications).
Test method adopted as per ISO 10545-7
Total load on each test specimen 70.0g of 5mm diameter steel balls 52.5g of 3mm diameter steel balls
43.75g of 2mm diameter steel balls 8.75g of 1mm diameter steel balls 3.0g white fused aluminum oxide of grain Size F80. Water 20ml.
Clamp a metal holder on to the glazed surface of specimen on he abrasion apparatus. Introduce the abrasive load into the holder through a hole in its upper surface. Run he machine till 25,000 revolutions. After abrasion, rinse the specimen under running water and dry in the oven at 110+5C. If the test specimen is stained with iron oxide, they may be cleaned with 10% (v/v) Hydrochloric acid before rinsing under running water and drying.
1. A high abrasion resistant glaze composition comprising of:
- ball clay 5-9% by weight,
- soda feldspar 38-42% by weight,
- dolomite 7-8% by weight,
- calcite 14-18% by weight,
- quartz 5-8%by weight,
- zinc oxide 2-4% by weight,
- alumina 5-9% by weight,
- wollastonite 8-10%by weight,
- spodumene 6-15% by weigh and
- frit 5-20% by weight.
2. A high abrasion resistant glaze as claimed in claim 1, wherein said frit is lower
melting point flux frit 5535 or frit 005.
3. A high abrasion resistant glaze as claimed in claim 1, wherein said ball clay is plastic
raw material that act as suspending agent.
4. A high abrasion resistant glaze as claimed in claim 3, where in said ball clay is TRN-
2 and RD-2.
5. A high abrasion resistant glaze as claimed in claim 1, wherein said ball clay are non-
plastic raw material alumina or silica that have high resistance to dissolution.
6. A process for making a high abrasion resistance tile from the high abrasion resistance
glaze as claimed hi any of the preceding claims, said method comprising the steps of:
i. formulating and preparing the body slip of the tile body, ii. preparing the dust that forms the body of the tile,
iii. shaping or forming the tile from the said dust,
iv. applying the high abrasion resistance glaze v. drying and firing of the tile, and
vi. polishing and cutting of the tile.
wherein said glaze is applied in two stages, one before the printing of design on the surface of the tile and second after the printing of design on the tile surface.
7. A high abrasion resistance glaze composition substantially as herein described with
reference to accompanying drawings.
|Indian Patent Application Number||420/DEL/2005|
|PG Journal Number||05/2009|
|Date of Filing||25-Feb-2005|
|Name of Patentee||SPL Limited|
|Applicant Address||KASSAR, BAHADURGARH, HARYANA 124507, INDIA.|
|PCT International Classification Number||C04B 35/52|
|PCT International Application Number||N/A|
|PCT International Filing date|