Porcelain is a material famous for its visual appeal, durability, and versatility. It is a kind of ceramic material made by heating constituent elements in a kiln at very high temperatures – 1,200 to 1,400 degrees F. These constituents often contain kaolin, also known as china clay. Porcelain is most commonly used for making tableware and tiles.
While it is possible to weld two porcelain parts or join this ceramic material to metals, the process is energy-intensive and requires a careful selection of metals. Several techniques have been used, and many new welding processes are being patented to weld ceramic materials.
Laser welding is the best technology to weld porcelain. While ceramics generally can be welded, gluing or brazing are better joining methods for porcelain due to thermal shock induced by any welding process.
Before discussing these welding methods for porcelain, let’s understand more about the characteristics of this novel material.
Properties of Porcelain
Porcelain can be classified into three different types: soft paste, hard paste, and bone china. The classification is based on the composition and the temperature at which the material is made.
Porcelain ceramics are famous for their white color and for their strength. This material is considered a superior ceramic and is more difficult to manufacture compared to stoneware and earthenware. Porcelain is hard, impermeable, and has high resistance to chemical and thermal shocks. It is also strong and translucent.
There are different subtypes of porcelain, including alumina porcelain, feldspar porcelain, and vitro porcelain. The properties of these materials differ from one another, as do their functions. Porcelain finds applications in building materials, electrical insulation, medicine, laboratory materials, and even in art and decoration.
Porcelain is harder than glass, extremely durable, and non-porous. However, despite all these attractive physical properties, the material is brittle in nature. Although porcelain is crack- and chip-resistant, it can break if not handled properly or if it undergoes extreme temperature changes.
Difference between Porcelain and Other Ceramics
Porcelain differs from other ceramics but is fruit from the same tree. The factors that make it different are the type of clay used, the water content, the firing temperature, the duration of firing, and the additives mixed with the clay.
Some of the differences between porcelain and other ceramics are:
- Porcelain contains a high percentage of kaolin clay, which is refined and white, while the amount of kaolin clay in other ceramics is low.
- Porcelain is also completely vitrified (glossy), while other ceramics mostly remain porous if not glazed.
- Porcelain is more durable compared to other ceramics.
- While other ceramics can absorb more water, the water absorption rate of porcelain is low.
- Porcelain is also heavier (high density) compared to other ceramics.
Why is Welding Porcelain Difficult?
While porcelain exhibits useful mechanical properties, the same properties make the material difficult to weld. Due to its high heat resistance, for example, traditional welding techniques will fail to weld two porcelain parts together. Instead, this type of welding requires precision heating to focus only on the weld area to melt the material efficiently.
It is much easier to weld porcelain with metals that exhibit good plastic flow characteristics, such as aluminum, copper, and lead. However, metals that are resistant to plastic flow or need greater heat to create plastic flow are often challenging to weld with porcelain as they’re likely to induce thermal and mechanical shock and lead to cracking or fractures.
Types of Welding Methods to Weld Porcelain
While welding ceramic materials is a complex and energy-consuming process, the following are some of the popular welding methods being experimented with to weld porcelain successfully. Bear in mind that each technique has its benefits and drawbacks.
Fusion welding is a technique that has been in use since the 1960s. However, its application in welding ceramics and porcelain is very limited. The problem with fusion welding is that it is challenging to match the thermal contraction characteristics and melting temperatures of the different porcelain pieces that are being joined.
This is a method of joining pieces of porcelain together using ultrafast and tightly focused laser pulses. The problem with this technique is that ceramics don’t absorb light. Instead, they’re good at scattering it, which is why research projects are underway to develop lasers that can fire a million pulses in one second, combining two different ceramic pieces with a clean weld.
Glaze bonding is often used to combine larger porcelain pieces or to join different ceramic components. In this method, the joining surfaces are ground flat and are then coated with a glaze slip. These surfaces are then connected and fixed to fuse the glaze and bond the porcelain pieces together. Special glazes are available to bond combinations of metal and ceramics.
Metalizing and Brazing
This method is used to join ceramic to metals. The brazing alloy used in this method makes the joining surfaces wet. While wetting metal surfaces is easy, this is not the case with ceramics. Hence, first, the ceramic material is treated with a layer of compatible alloy, a process that is called metalizing. Once this process is complete, brazing is carried out using conventional alloys.
This is a simpler welding process that does not depend on a vacuum and high temperatures. Instead, this method uses glues and cold-cure resins to join porcelain. Epoxide, acrylic, polyurethane, and phenolic adhesives can be used for adhesive bonding for temperatures up to 200 degrees C. For high-temperature applications, polyamides and other polymers are used for bonding.
It is evident that welding porcelain is a complex process and may not always be efficient and cost-effective. One of the major challenges with this material is that despite being hard and non-porous, it can break easily if not handled properly. Most of the welding methods discussed above are still being experimented with in labs and are not commercially and economically viable.
While we see a reliable and cost-effective method of welding porcelain developed soon, prevention is currently the best approach to porcelain. You should always be extra careful when handling ceramic items, to prevent them from breaking. Also, avoid transferring your porcelain items suddenly from cold to hot temperatures or vice versa, as doing so can induce a thermal shock that can cause cracks to develop.