LEDs, photovoltaic cells, jewelry – artificial gemstones such as sapphire crystal are used in the production and development of these products. The crystals are grown in special furnaces. Chinese manufacturers use HBM load cells and amplifiers to monitor the stresses that emerge inside the crystal during this process.
Sapphire crystals are the most important raw material for LEDs. China is now the international center of this industry. The crystals are grown in special furnaces at up to 2,050°C. A principal axis made from a silicon-based material is located in the center of the furnace. An S-shaped HBM load cell connected to the principal axis is attached in the upper section. As the temperature in the furnace increases, the sapphire crystal grows around this axis.
Monitoring the growth of the crystal
The S-shaped HBM load cell is primarily designed for measuring tensile forces. But it can also measure compressive forces, and is therefore perfect for detecting the stresses that arise inside the crystal as it grows.
To ensure high-quality monitoring, the S-shaped load cell is connected to the strain-gauge based RM4220 amplifier from HBM. With an output signal of 4 to 20 mA, the amplifier is ideal for this field of application. It is easy to install, as it is only plugged into standard support rails and enables connection of individual strain gauge transducers.
The crystal growing process developed by the Chinese allows aluminum oxide crystals to form. The product that emerges is similar to corundum, the natural substance from which gemstones such as rubies or sapphires are produced. The development of special furnaces in China will keep this branch of the industry on course for growth. LED manufacturers always endeavor to use increasingly large sapphire wafers, which in turn can only be cut from larger crystals.