Heater–Stirrer Device – Design & Fabrication

This heater-stirrer device was designed for my professor, who needed a compact system capable of:

Reaching temperatures up to 500 °C
Providing programmable heating cycles
Controlling stirrer speed between 100–700 RPM

Since I only have photos of the completed device, the following steps summarize the full design and fabrication process.

1. Defining Functional Requirements

The system needed:

A high-temperature heating plate
A closed-loop PID temperature controller
A programmable timer system
A digital stirrer speed controller (100–700 RPM)
A compact, safe, and easy-to-use enclosure

All control logic (PID + timer + stepper-motor speed control) was implemented on a custom PCB, based on the specifications I drafted.

2. Designing the Electronic Control System

I collaborated with an electrical engineer who designed the PCB board according to my technical requirements:

PID temperature control with very high accuracy
Real-time display of PV (process value) and SV (set value)
Motor speed control via stepper driver
Programmable timer system that activates only after the target temperature is reached
Automatic shutdown of heater + motor after timer expiration
Up/down programming buttons, calibrated controls, and safety fuse
Power switching using a relay connected between the heater and PCB

This ensured stable heating without overshoot (critical because some laboratory samples burn with even ±10 °C deviation).

3. Preparing the Metal Enclosure

To speed up fabrication, I used a ready-made metal box as the main enclosure.

I modified it as follows:

Cut a rectangular opening on the top plate to allow heat and wiring to pass through safely
Cut a large rectangular window in the front panel
Designed a black acrylic (plexiglass) front plate with precise cutouts for:
- LCD display
- Control buttons
- On/off switch

This created a professional-looking and durable front control interface.

4. Fabricating the Heating Plate (Hot Plate)

This was the most important mechanical component.

4.1 Machining the Aluminum Heating Block

I machined a solid aluminum block (approx. 20 cm diameter, 5 cm thick).
Then I milled a circular internal cavity (about 2 cm deep) to embed the heating element.

4.2 Installing the Heating Element

I used a coil heating element (nichrome wire heater) inside the cavity.
To secure it and ensure thermal contact, I filled the cavity with a high-temperature refractory mixture (a fire-clay–based insulating cement mixed with water).
After curing, the heater became fully embedded and safely insulated.

4.3 Adding the Stainless-Steel Top Plate

To provide a smooth, clean laboratory surface, I machined a stainless-steel circular plate via CNC to match the outer diameter of the aluminum heater block.
The stainless plate was bolted to the aluminum block for better durability and cleaning.

5. Wiring the Heater and Electronics

The heater terminals were routed through the opening on the enclosure top and connected to the relay on the PCB.
A K-type thermocouple was installed under the hot plate, in the geometric center, for accurate temperature feedback.
A stepper motor was mounted underneath to drive the stirrer shaft.

6. Final Assembly

After mounting:

PCB and electronics
Temperature controller & display
On/off switch
Heater block
Stirrer motor

…I assembled everything inside the enclosure, verified grounding and insulation, and closed the device.

7. Testing & Calibration

I tested the heater for:

Temperature accuracy
Rise time to 500 °C
PID stability (overshoot control)
Stirrer speed range (100–700 RPM)
Timer operation (activation only after reaching set temperature)

Once calibrated, the system performed reliably for laboratory chemical synthesis and mixing applications.