Sanitary ware refers to appliances related to sanitary installations. It usually includes bathtubs, toilets, washbasins, and so on. It is traditionally made of porcelain, which is made of clay and coated with enamel. Today, sanitary ware is made of various other materials such as acrylics, metals, and glass. However, this article will focus on sanitary ware made of porcelain, especially sanitary kaolin.
This type of production is a very large industry in the world and a lot of them are produced in Chaozhou, a small city in Southern China. This city is known for hundreds of factories that focus on producing sanitary ware. However, there are many other countries that also produce sanitary ware with high-developed processes.
Sanitary ware products are made of vitreous china body that is burned above 1200 degrees Celsius. This high-temperature burning is one of the main requirements to obtain industrial and domestic sanitary ware.
Properties and Components of Sanitaryware
Just like any other products, they have to reach a certain standard to maintain their quality. For sanitary ware, the required properties include below 0.5% water absorption, able to withstand 400 kg weight minimum, and glossy surface for easier cleaning.
There are three major components needed to create Sanitary ware, they are clay, quartz, and feldspar. The clay used can be ball clay, or sanitary kaolin. The three raw materials are then mixed, cast and fired in producing sanitary ware. The materials used offered excellent scratch resistance and are able to withstand heavy weight.
What is Sanitary Kaolin?
Sanitary kaolin is the kaolin used in sanitary ware. Kaolin, also known as china clay, is a soft white aluminium silicate that is hydrated and obtained from the Kaolinite mineral. It is a chemically inert material that offers a low capacity of shrink-swell. Due to these properties, this type of clay is excellent for various industries including sanitary ware ceramics.
Kaolin is naturally white, soft and powdery. In nature, raw kaolin usually also contains other minerals such as feldspar, muscovite, anatase, and quartz. Sometimes, crude kaolin also contains pigments of iron hydroxide that caused this clay to be a little bit yellowish. In this case, it is needed to be bleached chemically to remove this pigment, then wash it to remove other minerals in it before using the kaolin to produce ceramics or other products.
Manufacturing Process of Sanitary Ware
Producing sanitary ware requires a few steps from preparation, moulding, and other steps until it reaches the final product. Here is a short description of each step in the sanitary ware making:
1. Body Preparation
The primary thing to do is body preparation by mixing various ingredients which include ball clay, silica, kaolin and feldspar. The combination of these three materials is called the three types of bodies which consists of body former, filler and flux.
Body farming is important to give sanitary ware its strength during the initial casting stage. The filler will strengthen the sanitary ware after firing, while flux is added for the purpose of reducing fusion temperature in the firing process.
2. Glaze Preparation
The next process is preparing glaze for spraying. In this stage, different colored glazes are made. This stage also requires some more materials which include feldspar, calcite, zircon, chica clay, quartz, and zinc oxide.
These materials are grounded in a ball mill and then tested. When the particles are fine enough to pass through the sieve, the next step is sample spraying and firing. These two steps are important to check whether the desired color is achieved or not.
Before using it for the actual spraying, the glaze should be approved by the laboratory from a series of testing before being used. The glaze then mixed with a binder to obtain the desired density, fluidity, viscosity, and frying time.
3. Moulding Preparation
The next step is preparing the mould which is made of a mixture of water and plaster with the ratio of 4:3. When the mould is ready, it is put into a dryer to remove the remaining water. This step is important to increase the mould’s longevity and durability.
The casting process is similar to other casting methods where the body material is prepared then poured into the mould. Then, the excess materials are drained through a hole made for draining and allow the cast to dry.
When the cast is dry, it is released from the mould. In this stage, the ware is called greenware. Once it is released, the greenware is dried again for up to three days at an atmospheric temperature. Before being sent to the dryer, the greenware is checked again and fixed all the cracks and holes if any.
In the dryer, the greenware is dried again through a mechanical process to remove the remaining water. This process usually takes 6.5 to 12 hours to finish. In this process, the ware is dried at a temperature of 110 to 120 degrees Celsius. Once the drying process, the ware will shrink and lose some of its weight.
6. Controlling and Spraying
When the drying is done, the ware will be inspected to see if there is any defect found. If there is no defect found, the ware is sprayed in the desired colors. When it is complete, the ware is left to dry again before printing a logo on it.
The next step is firing the wares in a kiln with a maximum temperature of 1,250 degrees Celsius. The kiln for this production purpose contains three zones. Preheating to remove water, firing to burn the wares to fuse together the materials and glaze evenly, and lastly, cooling zone to create the glossy surface.
When the firing process is complete, the next step is sorting the wares and inspecting them once again to check minor defects. If no defects are found, the sanitary ware is sent to the packing department, but if there is any, it is repaired using a cold fill and sent to the re-firing process once again.
Sanitary ware manufacture is a long process that also requires high-quality material such as sanitary kaolin to produce an excellent product. Only the right materials and preparation will help producers to obtain durable and glossy sanitary ware. That is why it is important to watch every material and step used in this process.