Most of the ceramic industries primarily manufactured wall tiles because they’re economical yet profitable and aren’t complicated to make. The raw materials used in making these ceramic products are abundantly available in nature. Raw materials such as clay, feldspar, and silica are the main component in making ceramic tiles. These raw materials undergo site sampling and are examined to determine its elemental composition using X-ray fluorescence or XRF. Oxide and chemical analysis are also determined to be able to formulate raw material ratio and proportion according to target body properties and standards.
The mixing of different raw materials at a specific ratio and proportion by weight is called batching. Prior to the utilization of these raw materials for batching, moisture content (MC) is determined to obtain the dry weight of each raw material. Heavy construction equipment such as backhoe payloader is used in moving and mixing these raw materials into certain mixing storage. Prior to that, individual raw materials are stored on their corresponding storage for batching. Initial comminution or preliminary particle size reduction are sometimes involved but such a process would just result in downtime in production or unless the process had undergone thorough experimentation which determines manufacturing efficiency.
Right after batching, the mixed raw materials are transported to the ball mill via conveyor and are added with a calculated and measured amount of water then blended, homogenized, and grinned by means of alumina balls (or ceramic pellets) for hours to form a slurry. There is an initial grinding period for this process but no definite grinding duration. The endpoint of this process is when the standard properties of the resulting slurry such as the density, viscosity, and particle size are achieved. QC personnel will obtain samples right after the initial grinding period to determine these properties using specific laboratory equipment. This procedure will be repeated until the standard properties of the resulting slurry are attained.
The slurry is then transferred and stored into a large cylindrical storage tank called a slurry tank. The slurry is then aged for 24 hours prior to its utilization to the next process. Inside the slurry tank, continuous agitation (scientific work for mixing) of the slurry involving the constant rotational speed of mixing paddle is observed. This is to make sure that the slurry is continually homogenized during the aging period.
After aging the slurry for 24 hours, the mixture is then fed into the atomizer or most commonly known as the spray dryer (SD). The spray dryer is equipped with nozzles that spray the slurry into hot air to produced powder. Again, QC personnel determined the powder’s %MC and grain size for the SD operator to be able to adjust the nozzle spraying rate and hot air temperature to produce a powder with standard properties. The resulting powder is stored inside a certain storage called a silo tank. The powder is cured for 12 to 24 hours prior to its utilization in production.
The main manufacturing procedure of these ceramic tiles initially starts during pressing. The preserved powder inside silo tanks is transported into pressing machines’ steel box via conveyor. From the steel box, a precise amount of powder is evenly fed into the press machine’s mold. As the powder had remaining moisture content, a certain pressing force is applied to form an initial solid unfired ceramic body called green tile with a specific length, width, and thickness. Again, QC personnel will make sure that the standard measurements correspond with the set standards.
Right after the initial ceramic body or the green tile is formed, it simultaneously undergoes preheating or drying at 100-400 degrees Celsius for hours or minutes to remove the remaining moisture or the mechanically bond water. This process is necessary and is very important for the green tile to be stable and not experience thermal shock which will result in breakage during the firing process inside the kiln. This will also make sure that the resulting products are strong, durable, and are free of defects.
The glazing procedure happened right after the preheating process. Glazes are primarily made of silica and feldspar and are glass-like substances which act as a vitreous coating to ceramic tiles. Glazes are primarily for decorative purpose only however glazing also covers up pores of the tiles after firing since glaze vitrifies which could also contribute to hardness and durability of the resulting product. Glazes are usually applied to green tiles either by roller glazing, spraying, waterfall, dipping, screening, or dry glazing method. Again, QC inspects grams per tile of glaze to prevent variation of glaze colors after firing.
Firing is the most vital procedure in the entire ceramic tiles manufacturing process. So after the tiles are applied with glaze, a continuous firing procedure follows inside the kiln. There are different types of kilns but the most appropriate and the most efficient kiln for tile manufacturing is the roller hearth kill or RHK. The RHK is a type of continuous firing kiln with ceramic rollers which transport ceramic tiles at different firing temperature with uniform temperature distribution. Usually, the temperature in the inlet of the RHK does not vary significantly with the outlet of the preheating furnace and the RHK’s temperature is usually highest in its 3rd quarter’s section. The temperature of the RHK’s outlet also controls to prevent thermal shock which may result in the breakage of resulting tiles.
We technically have to produce ceramic tiles out of raw materials. After firing, the tiles are transported into the quality assurance department using a forklift for manual inspections. Here, the tiles are manually checked for defects. Although there are already machines that automatically detect these defects, manual checking is still practiced since most defects such as “chip off” occurred during packaging. Sorting and packaging of ceramic tiles then followed. Ceramic tiles are sorted based on the variation of colors and size. Variation of the color of final glaze can happen since glaze nozzles sometimes encounter clogging problems while RHK temperature varies through time. Once the tiles are packed, they are placed in a warehouse for shipping.