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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.

Task

Water flow control

Implementation

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.

Customer benefits

  • Stable furnace behaviour over time
  • Precise cooling contributes to high ingot purity
  • Early detection of water flow interruption
  • Following product families can be used
    Product family FFU
    Non-contact flow measurement
    • Flow sensor for conductive and non-conductive liquids
    • Compact design with no moving parts
    • Process temperature up to 80 °C, process pressure up to 16 bar
    • High chemical resistance due to seal-free sensor design
    • Large display with membrane keyboard
    • Integrated empty tube detection
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