Flow measurement for controlled cooling in the silicon furnace
Hot silicon ingots must be cooled along a gradual curve (30+ hrs.) or yield and quality will be compromised. The cooling cycle depends on controlling water flow, and the SICK FFU ultrasonic flow sensors provide real-time data for precise control. The IO-Link adds bidirectional update capability, a key automation advantage.
Water flow control
Multi-crystalline ingots are the raw material to produce solar cells. They are produced in casting furnaces. Chunks of polysilicon in a quartz crucible inside the furnace are heated until they melt. The crystallization process then starts. The temperature is slowly reduced from the bottom to achieve a slow crystallization of around 1.5 cm/hour.
During the crystallization process it is essential to precisely control the cooling water flow. A furnace contains 6 or more cooling circuits. Each needs to be controlled independently.
SICK ultrasonic flow sensors are designed to provide a precise and repeatable cooling behaviour. Unlike mechanical flow meters, they contain no moving parts.
- Stable furnace behaviour over time
- Precise cooling contributes to high ingot purity
- Early detection of water flow interruption