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Mold temperature changes during every die casting cycle.
Molten metal transfers heat into the die. Cooling circuits then remove part of this heat. Mold spraying, cycle interruptions, and factory conditions create further temperature changes.
These shifts affect:
Metal flow
Cavity filling
Solidification
Surface quality
Casting dimensions
Cycle time
Mold service life
A cold mold may cause incomplete filling or visible flow marks. An overheated mold may increase sticking, soldering, and cooling time. Uneven temperatures can also cause local shrinkage or dimensional variation.
A Temperature Control Unit, commonly called a TCU, manages this thermal balance.
It circulates water or thermal oil through channels inside the die. The unit heats or cools the fluid according to a defined setpoint.
Passive cooling cannot provide the same level of control. It cannot preheat a cold mold before production. It also responds poorly to changing thermal loads.
A TCU therefore does more than cool the mold. It actively regulates heat transfer throughout the production cycle.
This guide explains:
The Temperature Control Unit working principle
How a TCU controls mold temperature
How the heating and cooling cycle works
Which TCU components regulate the process
How different fluid circuits operate
Why flow rate and turbulence matter
How operators troubleshoot unstable temperature
Longhua provides integrated Temperature Control Unit solutions for die casting production lines.
Note: A TCU regulates heat transfer throughout the mold circuit, not only fluid temperature.
A Temperature Control Unit is an industrial thermal management system.
It adds or removes heat from a manufacturing process. In die casting, it regulates the operating temperature of molds, cores, and cooling circuits.
The unit circulates a heat-transfer fluid between the TCU and the mold. Water is commonly used at moderate temperatures. Thermal oil supports higher operating temperatures.
Longhua’s current mold temperature controller has a published working range of 50°C to 300°C. Its water-based configuration covers 50°C to 120°C. The oil-based configuration covers 50°C to 300°C.
A TCU primarily controls the circulating fluid temperature.
The fluid then transfers heat to or from the mold steel. This process influences cavity temperature, core temperature, and solidification conditions.
Operators may monitor:
Supply-fluid temperature
Return-fluid temperature
Mold-surface temperature
Cavity temperature
Fluid pressure
Fluid flow rate
The controller display normally shows fluid temperature. It may not represent every mold surface.
Local temperatures vary because of:
Casting geometry
Cooling-channel position
Wall thickness
Metal heat input
Spray distribution
Core and cavity design
For critical castings, engineers should compare fluid measurements against actual mold temperatures.
A cooling-water pump only moves fluid.
It does not automatically measure temperature or adjust heating and cooling output.
A Temperature Control Unit combines:
Fluid circulation
Heating
Cooling
Temperature sensing
Feedback control
Pressure protection
Alarm monitoring
These functions allow it to maintain a controlled process window.
A standard industrial chiller mainly removes heat.
It uses refrigeration to produce cold utility water. This water may supply several machines or factory systems.
A TCU performs a different role.
It can heat a cold mold during startup. It can also cool the circulating fluid during production. Many TCU configurations use water from a chiller or cooling tower.
Equipment | Main Function | Heating Capability | Typical Role |
|---|---|---|---|
TCU | Regulates process temperature | Yes | Controls mold circuits |
Chiller | Produces cold utility water | Usually no | Removes process heat |
Cooling tower | Releases heat outdoors | No | Supports central cooling |
A TCU and chiller can work together. They do not perform the same function.
The TCU sits between the mold circuits and plant cooling supply.
Hoses connect it to internal channels in the fixed and moving die halves. Separate circuits may control cores, cavities, or local hot zones.
Longhua offers mold temperature controllers in single-circuit and dual-circuit configurations. Its current controller also supports one to six independently controlled temperature zones.
A TCU can be integrated with cold chamber die casting machines, automation systems, and centralized production controls.
Tip: Define the mold circuits before selecting the TCU configuration.
The Temperature Control Unit working principle combines fluid circulation, temperature measurement, and automatic feedback control.
The operating cycle contains seven main stages.
A pump moves water or thermal oil from the TCU.
The fluid travels through a supply hose and enters the mold channels. It absorbs or releases heat while passing through the die.
The fluid then returns to the TCU.
Continuous thermal fluid circulation keeps the mold connected to the heating and cooling system.
Restricted flow reduces temperature-control performance. Blocked channels, small hoses, clogged filters, and closed valves can all weaken heat transfer.
Temperature sensors monitor the circulating fluid.
Most systems use resistance temperature detectors or thermocouples. They send temperature readings to the controller.
Sensor placement affects control accuracy.
A supply sensor measures fluid entering the mold. A return sensor measures fluid leaving the mold. The temperature difference indicates the amount of heat transferred during circulation.
A mold-surface sensor provides separate information. It can identify local hot or cold zones.
Damaged or poorly positioned temperature sensors may cause unstable control.
The operator enters a target temperature called the setpoint.
The PID controller compares this setpoint against the measured temperature. It then calculates the required heating or cooling response.
PID represents three control actions:
Proportional control responds to the current temperature error.
Integral control corrects a lasting temperature offset.
Derivative control reacts to rapid temperature changes.
PID temperature control in a TCU reduces repeated overshooting and undershooting.
Longhua’s product page lists PID intelligent control and temperature precision of ±0.1°C. This is a controller specification. It does not mean every mold surface remains within ±0.1°C.
The heater activates when the measured temperature falls below the setpoint.
Electric heating elements transfer energy into the fluid. The circulation pump then carries this energy into the mold.
Heating is especially important during startup.
A cold die can experience severe thermal shock after receiving molten metal. Gradual preheating reduces this temperature difference.
Heating may also operate during:
Low production rates
Long cycle interruptions
Cold factory conditions
Small shot weights
Initial process stabilization
The heating system must match the mold’s weight and thermal mass.
Each casting shot adds heat to the mold.
When the fluid exceeds the setpoint, the controller starts the cooling process. The cooling method depends on the TCU circuit design.
A direct-injection system adds cooler water into the process loop. A closed-loop system transfers heat through a heat exchanger.
A cooling valve regulates utility-water flow. Modulating valves provide smoother control than basic on-off valves.
A standard TCU usually needs an external heat-rejection source. This may be a chiller, cooling tower, or central cooling-water system.
Warmer fluid returns from the mold.
The Temperature Control Unit measures its temperature again. It then heats, cools, or recirculates the fluid without adjustment.
The prepared fluid returns to the mold.
This process creates a continuous closed loop temperature control system:
The pump circulates the fluid.
Sensors measure its temperature.
The controller compares it against the setpoint.
The TCU activates heating or cooling.
The fluid returns to the mold.
The cycle repeats continuously.
Every casting shot changes the mold’s thermal load.
Large castings transfer more heat than small castings. Faster cycles leave less recovery time between shots.
The TCU must respond without causing severe temperature changes.
Stable operation requires enough:
Pump flow
Heating power
Cooling capacity
Heat-exchanger area
Fluid volume
Control response speed
Note: A TCU maintains a controlled thermal window, not one identical temperature across the whole mold.
Several components work together inside a Temperature Control Unit.
The circulation pump provides fluid flow and pressure.
It must overcome resistance from:
Hoses
Valves
Couplings
Filters
Mold channels
Heat exchangers
A weak pump may create insufficient flow. An oversized pump may increase pressure, energy consumption, and seal wear.
Pump selection should consider:
Required flow rate
Circuit pressure loss
Fluid viscosity
Operating temperature
Hose diameter
Channel layout
Centrifugal pumps are common in water-based systems. Specialized systems may use other pump types.
The heater raises the process-fluid temperature.
The cooling system removes excess heat. It may use direct water injection or a heat exchanger.
The TCU pump and heat exchanger function as one thermal circuit. The pump transports the fluid, while the heat exchanger transfers energy.
Heating and cooling capacity must match the actual process load.
An undersized heater creates slow startup. Insufficient cooling causes gradual temperature increases during production.
Temperature sensors provide the feedback needed for automatic control.
The PID controller uses this feedback to regulate heaters, valves, and cooling output.
Modern systems may also provide:
Touchscreen operation
Alarm records
Data logging
Remote monitoring
Communication interfaces
Process trend displays
Longhua’s current mold temperature controller includes touchscreen operation, fault monitoring, and remote data functions.
Sensors should be inspected and calibrated regularly. Incorrect readings can create unstable heating and cooling cycles.
The fluid tank maintains a stable supply.
Thermal oil systems also need expansion space. Oil increases in volume as its temperature rises.
Common safety devices include:
Pressure-relief protection
Low-fluid alarms
Overtemperature alarms
Pump overload protection
Leak monitoring
Emergency shutdown
Tip: Compare safety protection and monitoring functions before comparing equipment prices.
The circuit design determines how the process fluid receives cooling.
A direct-injection system uses utility water inside the process loop.
Cooler water enters when the process temperature becomes too high. Excess warm water leaves through a drain or return line.
Its advantages include:
Simple construction
Fast cooling response
Lower initial cost
Fewer heat-transfer stages
However, utility-water quality directly affects the mold circuit.
Scale, corrosion, and contamination may enter the channels.
A closed-circuit TCU keeps the process fluid inside a sealed loop.
A heat exchanger removes heat without mixing utility water into the process fluid.
This design provides:
Cleaner process fluid
Lower fluid loss
Better contamination control
More stable fluid conditions
Closed circuits are suitable for demanding mold temperature control applications.
An isolated system completely separates the process fluid from cooling utility water.
The process fluid passes through one side of the heat exchanger. Cooling water passes through the other side.
The two fluids do not mix during normal operation.
This system is required when using:
Thermal oil
Glycol mixtures
Specialized process fluids
Clean fluid circuits
Circuit Type | Main Advantage | Main Limitation |
|---|---|---|
Direct injection | Simple and responsive | Utility water enters the process loop |
Closed circuit | Cleaner process fluid | Requires a heat exchanger |
Isolated circuit | Supports different fluids | Higher equipment complexity |
Selection depends on:
Target temperature
Process fluid
Water quality
Cooling capacity
Operating pressure
Maintenance resources
Contamination sensitivity
Temperature alone cannot confirm good heat-transfer performance.
The fluid must also move through the mold channels at a suitable rate.
Laminar flow moves in smooth layers.
The fluid nearest the channel wall transfers heat. The inner layers remain partly insulated.
This condition limits heat-transfer efficiency.
Turbulent flow creates irregular mixing and fluid movement. More fluid reaches the channel surface.
This improves:
Heat transfer
Temperature uniformity
Cooling response
Mold-zone stability
The reference material identifies turbulent flow as an important requirement for effective mold temperature control.
Reynolds number helps classify fluid flow.
It depends on:
Fluid velocity
Internal channel diameter
Fluid density
Fluid viscosity
Values above approximately 4,000 commonly indicate turbulent flow. The exact transition depends on the channel geometry and fluid properties.
Insufficient flow may create local hot spots.
Excessive system pressure may damage hoses, seals, or connections. Narrow channels and long hoses also increase pressure loss.
Operators should monitor:
Supply temperature
Return temperature
Flow rate
Supply pressure
Return pressure
Differences between mold zones
A large supply-return temperature difference may indicate high thermal load. It may also reveal insufficient flow.
Tip: Check fluid flow before lowering the temperature setpoint.
Water and oil systems use the same feedback-control principle.
However, their temperature ranges and maintenance needs differ.
Water provides strong heat-transfer performance.
It responds quickly during heating and cooling. It also has a relatively low operating cost.
Longhua lists a working range of 50°C to 120°C for its water-based mold temperature controller.
Operators must manage:
Scale formation
Corrosion
Water quality
System pressure
Seal condition
Freezing risk
Pressurized-water systems can operate above normal atmospheric boiling temperature. Every component must support the required pressure.
Thermal oil supports higher process temperatures.
Longhua lists a working range of 50°C to 300°C for its oil-based controller.
Oil systems require:
Approved heat-transfer oil
Expansion management
Leak prevention
Temperature monitoring
Filter maintenance
Oil-condition checks
Thermal oil may oxidize or degrade under excessive temperatures. It should always meet the TCU manufacturer’s specifications.
Factor | Water-Based TCU | Oil-Based TCU |
|---|---|---|
Heat-transfer response | Faster | Slower than water |
Operating temperature | Moderate | Higher |
System pressure | Can increase at high temperatures | Usually lower at comparable temperatures |
Main maintenance issue | Scale and corrosion | Oil oxidation and leakage |
Typical application | Moderate mold temperatures | High-temperature mold control |
Fluid selection should follow the required temperature, mold design, and system specification.
Stable mold temperature supports predictable metal flow.
Cold cavity areas may cause premature solidification. Excessive heat may increase sticking or soldering.
A balanced die supports more consistent cavity filling.
Cooling rate influences solidification and shrinkage.
Uneven mold temperature may create:
Warpage
Local shrinkage
Delayed cooling
Dimensional drift
Uneven ejection
Multi-zone control helps manage areas carrying different thermal loads.
Repeatable mold temperature supports predictable cooling.
An overheated die may require longer solidification time. Excessive cooling may create filling problems or higher thermal stress.
Stable TCU operation improves production consistency.
Gradual preheating reduces startup shock.
Stable operation also limits repeated thermal extremes. Controlled shutdown reduces sudden contraction.
Correct mold temperature control supports longer mold life. Longhua also recommends balanced cooling and temperature control to reduce mold deformation and damage.
Learn more about die casting mold temperature control and maintenance.
Note: A TCU reduces defect risks but cannot replace correct gating, venting, injection, and melt-quality control.
Before startup, confirm:
Alloy type
Mold weight
Casting weight
Cycle time
Required temperature
Fluid type
Required flow
Operating pressure
Number of circuits
The TCU must match both the mold and the utility supply.
Use this basic sequence:
Check the fluid level.
Inspect hoses and connections.
Open the required valves.
Fill and vent the circuit.
Confirm pump rotation.
Start fluid circulation.
Preheat the mold gradually.
Allow the system to stabilize.
Begin production at a controlled rate.
Do not begin full-speed production immediately after startup.
Problem | Possible Cause |
|---|---|
Temperature cannot reach setpoint | Weak heater, high heat loss, faulty sensor |
Temperature remains too high | Low flow, blocked channels, weak cooling supply |
Temperature fluctuates | Poor PID tuning, trapped air, unstable utility water |
Low-flow alarm | Pump problem, clogged filter, closed valve |
High-pressure alarm | Blocked channel, small hose, closed return line |
Oil overheats | Low fluid level, degraded oil, weak circulation |
Check the alarms first.
Then confirm:
Fluid level
Pump operation
Sensor readings
Supply temperature
Return temperature
Flow and pressure
Inspect filters, hoses, valves, mold channels, heaters, and the heat exchanger.
Verify the cooling-water supply.
Adjust one major variable at a time. Record the final correction and approved operating settings.
Tip: Never repeatedly reset an alarm without identifying its thermal or mechanical cause.
How does a Temperature Control Unit work?
It circulates water or thermal oil through mold channels. Temperature sensors measure the process fluid. A PID controller compares the reading against the setpoint.
The system then activates heating or cooling.
The complete operating cycle is:
Pump fluid through the mold.
Measure the process temperature.
Compare it with the setpoint.
Activate heating or cooling.
Return and recondition the fluid.
Repeat the cycle continuously.
Effective TCU performance depends on:
Correct heating capacity
Sufficient cooling capacity
Suitable pump flow
Accurate temperature sensors
Stable PID control
Correct fluid selection
Clean mold channels
Proper circuit design
Longhua offers mold temperature controllers covering a 50°C to 300°C working range. Available options include single-circuit and dual-circuit configurations. The system can also support one to six temperature zones.
A TCU does more than heat or cool fluid.
It manages heat transfer across the complete die casting cycle. Correct control supports stable filling, controlled solidification, repeatable dimensions, efficient production, and reduced mold stress.
For projects involving the complete machine, mold, and thermal-control system, explore Longhua’s customized die casting mold and production line solutions.
A: A Temperature Control Unit circulates fluid through the mold, measures its temperature, and uses PID control to activate heating or cooling. This continuous feedback loop maintains the selected process temperature during production.
A: A Temperature Control Unit regulates the supply-fluid temperature entering the mold. It also monitors return-fluid conditions. Heat then transfers between the circulating fluid, mold steel, and molten metal during each casting cycle.
A: A Temperature Control Unit improves mold temperature stability. It supports consistent metal flow, controlled solidification, repeatable dimensions, stable cycle times, and reduced mold thermal stress.
A: Temperature Control Unit costs depend on heating capacity, cooling capacity, pump performance, temperature range, fluid type, circuit design, zone count, safety functions, and control features. Installation, maintenance, and energy use also affect total ownership costs.
A: A closed-loop TCU can add or remove heat to maintain a process setpoint. A standard industrial chiller primarily supplies cooling capacity. The TCU actively controls the mold circuit, while the chiller serves as a heat-rejection source.
A: Common causes include insufficient flow, trapped air, faulty temperature sensors, unsuitable PID settings, blocked mold channels, or unstable utility water. Operators should inspect the complete circuit before changing the temperature setpoint.
Longhua offers mold temperature controllers covering 50°C to 300°C. Buyers should confirm the target temperature, heat-transfer fluid, circuit layout, heating and cooling capacity, and required zone count before selecting a TCU.e instability.
