Tile manufacturing/Production Process
In this article, We are going to see the Tile Manufacturing/Production Process. Ceramic tiles are economical to produce because of the raw materials used are easily available mined ceramic minerals. The Primary raw material for the tile production is Clay, Quarts and Feldspar.
Steps in the Tile manufacturing Process are:
- Batching is the initial step in the tile manufacturing process
- During batching the raw materials are included in a formulated percentage known as composition or in other the composition decides the amount of raw material to be taken to the manufacturing process.
- The raw materials are plastic raw materials and non-plastic raw materials and additives
- The plastic raw materials provide strength and plasticity to the green compact
- The non-plastic raw materials provide the liquid phase needed for verification and also provides strength to the fired body. feldspar is a non-plastic material.
- The raw materials are taken in a ball mill and them grinded with water for certain hours. The grinding media is usually alumina because it has good wear resistance and good density. This process is known as wet grinding.
- The raw material will be obtained in a slurry form at the end of the wet grinding process. The slurry is stored in a slip tank
- The slurry is continuously rotated in order to prevent the setting of the slurry.
- The slurry is taken to spray drying unit through the conveyors.
- In a spray dryer, the slurry is converted into powder through the atomizer and the hot air.
- The function of the atomizer is to spray the slurry into fine droplets. The basic principle behind the functioning of the atomizer is Bernoulli’s principle.
- the sprayed slurry is made to contact with hot air, during which liquid associated with the slurry gets evaporated and the remaining solid substance is obtained in a powder form
- During this process, more than 90% of the liquid in the slurry is evaporated.
- Depending upon the position of the atomizer and the hot air entry port the spray dryer is classified into three types.
- If the hot air zone and atomizer are at the same end of the dryer then it is called co-current flow dryer. It produces a lot of dust. To overcome this problem, there is a bed combined along with the dryer. This bed clumps the small dust particles to form a bigger sized particle, thereby reducing the problem with this type of dryer. The liquid gets evaporated by utilizing the heat from the hot air.
- If the hot air zone and atomizer are at the opposite ends of the dryer, then it is called counter-current flow dryer. The hot air is thrown against the direction opposite to that of the sprayed slurry, mostly the atomizer will be at the top and the hot air entry port will be at the bottom. The counter-current flow dryer has more efficiency than that of the co-current flow dryer.
- There is another type called a mixed flow dryer in which the mechanism of both co-current flow dryer and the counter-current flow dryer is combined together.
- Based on the cycle of the hot air the spray dryer is of two types. They are open cycle dryer and the closed cycle dryer.
- In an open cycle dryer, the air is withdrawn from the atmosphere. It is heated, processed and then it is let out into the atmosphere.
- In closed cycle dryer, the air is not let out, it is recycled and it is used again and again.
Crushing and Milling
- In this process, the raw is crushed and grounded and mixed together.
- There are various crushing machines which perform the crushing such as jaw crushers, gyratory crushers and pig mill.
- In jaw crusher, there will be a movable jaw and a stationary jaw. The movable jaw moves and then it crushes the raw materials against the stationary jaw.
- In gyratory crusher, the rotating cone throws the material against the shell by which the materials get crushed
In pig mill, there is a hammer shaft and rotor. Due to the rotating oh hammer, the material is ground and gets powdered.
- There are many mills which powder to fine powder. The example is a hammer mill and muller mill
- The crushed powder is then taken to screening and it is stored in silos.
The wetting machine is a consists of hollow structure inside. The material flows from top to bottom inside this structure. The water is sprayed by tubes to the material and thus it gets required moisture content.
Advantages of Dry process
- Spray dryer could be eliminated
- Power supplied and water supplied to spray drier could be avoided.
- Initial capital is less compared to wet process
Dis-Advantages of Ball mill
- The product will be of low strength when compared to wet process.
- The finishing will not be as good as product obtained in wet process.
Tiles Green ware Formation:
The Tiles green ware production usually consists of two methods.
- Pug milling and Extrusion
- Powder pressing
Clay is mixed to get a plastic state.
- The Pug mill usually consists of a augar blades (or) knifes in the rotating shaft.
- It cuts and blends the clay with water.
- In some cases, there will be a de-airing chamber before blending.
- It removes the air from the mass which increases the plasticity of the clay mass.
- At the end of a pug mill a plastic mass which has good plasticity is obtained.
The shaping of plastic mass is done by extrusion.
- The plastic mass from pug mill is taken to a extruder.
- The extruder consists of a pressuring chamber and a die.
- The die has a thin rectangular cross section.
- The pressuring chamber pressurizes the clay into a die through which a flat, slafs of continuous tile green ware emerges.
Cutting tile green ware:
- In this process, sharp blades are used to cut the continuous greenware into a required shape. Then the shaped tile greenware is taken to the drying process.
- In this process, there is a hopper, mould cavity, top plunger and a bottom ejector.
- The hopper pours the material which is in powder form into the mould cavity.
- Then the top plunger moves into the mould cavity and pressurizer the powder present in the cavity.
- After pressing, the bottom ejector moves up and pushes the tile greenware into the conveyor.
- The conveyor takes the change of the tile greenware, which takes it to the drying process.
The most commonly used process is powder pressing.
- In this step, the powder produced by spray drying is fed into the mould cavity.
- Then the top punch moves down and presses the powder to dry pressed tile.
- The binding component is usually water. In some industries, chemical additives are also used as a binder.
- The pressed tile is ejected by an ejector.
- The dry pressed ware is then taken to the drying chamber through the conveyors.
- Nowadays pressure glazing is a new technique followed. In this method, the powder is pressed and then the glaze which is in powder form is pressed into it.
- The advantages of pressure glazing are glaze storage tanks, energy supplied to the rotors which will be agitating the glaze in glaze tanks, separate glaze line could also be avoided
- The sludge which is the waste produced from glaze unit could be absolutely avoided.
- The dryer is commonly employed after pressing. The dryer reduces the moisture content. After drying, the moisture content will be 1-1.5%.
- The dryer process also increases the strength of the green compact. The horizontal dryer or vertical dryer is most commonly used.
- The time, temperature and type of dryer used depend upon the nature of title.
- If drying time is high, say for 90 minutes the one can go for vertical dryer since constructing a horizontal dryer for that length is quite expensive.
- After dryer the dried tile is taken to glaze line
- The water is sprayed over the surface of the pressed tile.
Preparation of Glaze
The important method in glaze preparation is the selection of raw materials.
- The Raw material must be selected in the way that it must fuse homogeneously at the given temperature.
- If it is applied on the dry body then it must get fused at the temperature at which the body is fixed. If it is applied on bisque fired body, then it must fuse at low temperature.
- Another important criteria is thermal expansion. The thermal expansion of glaze should be slightly lower than the expansion of body so that it will be in slight compression which will increase the strength of the tile.
- If there is a big difference on thermal expansion between the body and the glaze, defects such as crazing, peeling occurs. To avoid that, the thermal expansion of the glaze should be suitable of that of body.
The Raw materials commonly used are
- China clay
- Ball clay
- Zinc oxide
- The above raw materials are taken according to batch composition and then it is taken to ball mill. The grinding of material with water occurs in the Ball mill. The grinding media is usually alumina.
- After milling, certain properties of glaze has to be checked they are viscosity, density, residue and pickup weight
- If the determined value matches with the standard, then the glaze is passed through sieves and it is loaded on glazes storage tanks.
- To get coloured glaze, stains are to be added. The stain can be directly added on Ball milling.
- In other method desired amount of glaze is taken in drum, then stains are added to it and then it is mixed.
- Engobe is also prepared in the same method.
Application of Engobe and Glaze
After engobe application, the glaze is applied over it. The following are different methods of application.
In this method, there is bell-like structure which makes the glaze to fall over the surface. It is a predominantly used method which is used to produce defect-free glaze.
In this method, the disc is employed to through glaze over the surface of the body. The quality of glaze produced by this method is quite less.
- In this method, a wet glaze is first applied over the surface of the body.
- Then dry glaze powder is sprayed over that wet glaze.
- On firing, the powder and the wet glaze will fuse together which will produce beautiful designs.
- As previously said, during pressing, a powder is pressed first and then dry glaze powder is pressed over it. It reduces separate glaze line.
- After glaze application, the raw materials are taken to the kiln for firing.
The decoration over the glaze makes the tile pleasing to the eye. The decoration is done by various techniques. Some of the techniques are
- Screen printing
- Digital printing
- The screen printing is done with the help of screen
- The required design is made on the screen
- The required colourant is added on the screen
- The rotating roller is allowed to pass over the screen
- By the action of rollers, the colourant is squeezed or pressed over the screen and it emerges through the design
- By this, the tiles get designed
- This type of printing is done by digital printers
- The ceramic ink is fed into the printers
- Any type of design could be drawn by digital printers.
- The digital printers prints the given design over the tiles
- The kiln is the back tone of the industry.
- The roller worth kiln is most commonly used.
- The temperature of the kiln depends upon the nature of the tile.
- If one wants to increase the time, the speed of the roller could be increased or vice versa.
- The zone is
- Pre-heating zone
- Firing zone
- Cooling zone
In this zone, heating is done by the heated air coming from the firing zone. The is no flame heating in this area.
The green tile gets heated by the hot air coming out of the firing zone.
In this zone, a group of burners is employed to achieve the highs firing temperature. Verification of tiles takes place in this which provides the tiles desired strength, good finishing and also makes the tiles to be pore-free.
In this zone, the air is drawn from the atmosphere, through air fans and is thrown inside the chamber. This cool air interacts with the tile and absorbs the heat. The temperature of the tile gets reduced.
Indirect Cooling Zone
In this zone, the air is withdrawn from the chamber using air pumps. The temperature of the tile gets further decreased. It is termed In-direct cooling because there is no air cooling is involved as in the previous step.
It is like that of the direct-cooling zone. A larger amount of air is sucked from the atmosphere and it is distributed by cooling fans.
The hot air obtained from this area is used as a heat source for dryer. At this end, the temperature of the tile will be in the range of 40°c-80°c
After firing and cooling, the fired tile is taken to quality check and inspection
In quality, check is done to find whether the tile has defects or it is free from tiles
The common defects found is
- Lamination: Sometimes the body gets swells up. It is known as lamination. It is due to the improper moisture content in the pressed powder and improper pressing conditions etc.
- Chipping: When some portion of the body get chipped off or broken, then it is known as chipping. It occurs due to the hitting of tile against objects such as guides on passing through the conveyor
- Crazing: If the thermal expansion is very high than that of the body, the glaze will be in tension. Cracks will develop over the glaze surface. It is known as crazing.
- Crawling: It occurs due to the adhesion problems. The glaze will not get properly adhered to the body. It May also occur due to the high surface tension of the glaze
- Pinholes: The volatile substance in firing gets escaped from the body which causes small hole I the glaze. It is called as pin holes.
- Cracks: The cracks occur at the side of the pressed compact. It is due to the high moisture content in the press powder or pressure variation during pressing.
Sorting & Packing
The inspected tiles are sorted, packed and taken to the storage area.