There are several options for making a temperature rise monitoring alarm for ball mill bearing bushes, ranging from simple to complex. Considering the reliability requirements in industrial settings, here are several practical and common methods. You can choose according to your technical capability and budget.

Option 1: Simple Electrical Contact Thermometer Alarm (Classic and Reliable)

This circuit is a classic design and relatively simple to build. Its core component is an electrical contact thermometer (a dial thermometer with an adjustable contact).

• Working principle: Install the probe of the electrical contact thermometer on the bearing bush and set an alarm temperature (e.g., 60 °C). When the bearing bush temperature reaches the set value, the electrical contacts inside the thermometer close, triggering the subsequent audible and visual alarm circuit.
• Fabrication steps:
  1. Prepare core components: Electrical contact thermometer, 12 V power transformer, rectifier bridge, three‑terminal voltage regulator (e.g., 7809 or 7805), relay, transistor (e.g., S9014), LED, buzzer or speaker, etc.
  2. Build the power supply circuit: Step down 220 V AC through the transformer, rectify with the bridge, filter with capacitors, and then regulate with a three‑terminal voltage regulator (e.g., LM7809) to obtain a stable 9 V DC supply for the entire circuit.
  3. Connect the temperature detection and control circuit: Connect the electrical contact thermometer to the transistor, relay, and other components. The thermometer contacts act as a switch to control the transistor’s on‑off state, which in turn drives the relay.
  4. Assemble the audible and visual alarm circuit: Connect one normally‑open contact of the relay in series with the power supply loop of the audible‑visual alarm circuit (consisting of an alarm lamp, a sound chip, a speaker, etc.).
  5. Debug and set: After verifying the circuit is correct, apply power and bring a heat source near the thermometer probe to test whether the alarm triggers correctly at the set temperature.
• Extension: If you need to monitor multiple points (e.g., the inlet and outlet ends of the mill), simply equip each bearing bush with its own electrical contact thermometer and detection circuit, sharing a common audible‑visual alarm circuit.

Option 2: Alarm System Based on a Temperature Controller (Easy to Install)

This option uses a ready‑made temperature controller (e.g., XMT‑2002 series) with a temperature sensor. It is very convenient to install and set, making it suitable for quick retrofits.

• Working principle: Attach a thermocouple or RTD (e.g., PT100) to the surface of the bearing bush and connect its signal wires to the temperature controller. Set the alarm temperature directly on the controller panel. When the temperature reaches the set value, the internal relay contacts of the controller actuate, triggering an external audible‑visual alarm.
• Fabrication steps:
  1. Purchase off‑the‑shelf components: Buy a digital temperature controller with alarm output function, along with a matching temperature sensor (e.g., PT100 RTD).
  2. Install the sensor: Firmly fix the temperature sensor at the measurement point on the bearing bush. For better accuracy, it is recommended to install one sensor on each side of the bearing bush.
  3. Connect and set: Follow the controller manual to connect the sensor and power supply, and set the alarm temperature on the panel (generally 60 °C for alarm and 65 °C for trip).
  4. Connect the alarm: Connect the alarm output terminals of the controller in series with an audible‑visual alarm device (e.g., an electric bell + indicator light).

Option 3: Infrared Non‑Contact Temperature Measurement Alarm (Non‑Destructive Installation)

This option uses an infrared temperature probe to measure the temperature of the hollow shaft without contact, requiring no modification to the equipment.

• Working principle: Aim the infrared probe at the surface of the hollow shaft. It converts the radiated temperature into an electrical signal, which is amplified, processed, and compared with the set value. If the temperature exceeds the set value, an alarm is triggered.
• Key fabrication points:
  1. Core components: Requires an infrared temperature probe (including optical system and photodetector) and a signal processing circuit.
  2. Installation and debugging: Fix the probe so that its field of view is aimed at the hollow shaft surface. During debugging, note that the hollow shaft surface temperature is typically 10–15 °C higher than the bearing bush surface, so the alarm set point must account for this temperature difference.
  • Nota: This option involves relatively complex circuitry and may require some electronics background.

Option 4: Advanced System Solutions (For Large or Critical Equipment)

For large or critical ball mills, more comprehensive systems can be considered.

• PLC control system: Use a programmable logic controller (PLC) as the core. It can interface with multiple temperature and vibration sensors to achieve precise monitoring, logical decision‑making, automatic shutdown, and remote alarming.
• Off‑the‑shelf intelligent protector: You can directly purchase ready‑made products, such as a ball mill bearing bush measurement and control two‑stage alarm protector, which integrates temperature measurement, two‑stage alarming, and automatic shutdown; or a ball mill bearing bush temperature alarm, which uses a thermocouple to directly measure the temperature of the bearing alloy layer for fast response.

Precautions for Fabrication and Use

• Sensor installation position: This is critical. The probe should be placed as close as possible to the Babbitt alloy layer of the bearing bush, or inserted into a small hole drilled into the alloy layer (on a non‑loaded surface) to obtain the truest temperature reading.
• Alarm value setting: As a rule of thumb, 60 °C is generally recommended as the alarm value and 65 °C as the trip value, but the exact values should be fine‑tuned based on actual equipment operating conditions.
• Power supply and safety: Ensure a stable power supply for the alarm, and take measures for waterproofing, dustproofing, and vibration resistance. High‑voltage sections must be strictly insulated to ensure safety.

Summary Recommendations:

• For simplicity and low cost: Prefer Option 1 (electrical contact thermometer) oppure Option 2 (temperature controller).
• For non‑contact, non‑destructive installation: Try Option 3 (infrared).
• For large or critical equipment: It is recommended to use Option 4 (PLC or off‑the‑shelf protector).