Chemically resistant encapsulated plates for plating, anodising and rinse tanks, where a bare element would be destroyed by the bath. Epoxy Immersion and Tank Heaters are used for conduction heating from a rigid, flat, sealed plate that holds full contact with the load and survives the chemistry around it, anywhere up to 150 °C. A resistance wire or foil element vacuum-potted in thermally conductive filled epoxy on an aluminium or steel plate. It has real thermal mass, so it is slow to respond and slow to cool, and it is sealed — against moisture, plating chemistry and mechanical damage — in a way no film construction is. This page sets out the industries and assemblies where the construction is specified, what has to be stated on the drawing and the order, how it is installed, and the duties where a different construction is the right answer. This construction is built up to 300 x 800 mm, 8 mm to 20 mm thick to your outline; the full capability table is further down the page. It is rated at 0.3 W/cm² in free air and 2 W/cm² bonded full-area to metal, and the difference between those two figures is the difference between a heater that lasts and one that does not.
Typical Applications for Epoxy Immersion and Tank Heaters
The assemblies and sectors where this construction is specified:
- Laboratory and industrial hotplates: even, slow, stable surface heating where thermal mass is an advantage because it damps the disturbance from putting a cold vessel on the plate.
- Food processing equipment: sealed heated surfaces in washdown areas, where the construction has to survive cleaning as well as heating.
- Freeze protection on valves and manifolds: bolted plates on assemblies that have to stay above freezing outdoors and cannot be wrapped.
- OEM equipment manufacture: designed-in heating on new equipment, specified from the surface, the target temperature and the available power at the design stage rather than retrofitted afterwards.
- Retrofit and equipment upgrades: replacing a failed or unsuitable heater on existing equipment, where the outline, the voltage and the mounting all have to match what is already there.
How to Specify Epoxy Immersion and Tank Heaters for Your Application
- Outline drawing: There is no catalogue size to order from: this part is made to your outline. Send a drawing or a DXF showing the heated area, every hole and cutout, which face is bonded, and where the leads leave the part — the process builds up to 300 x 800 mm, 8 mm to 20 mm thick. Everything else on this list is quoted against that drawing.
- The chemistry, in full, and the level interlock: List the bath chemistry, concentration and temperature so the encapsulation can be selected against them, and specify a low-level interlock. The plate is protected against the bath; nothing protects it against being energised above the liquid line.
- The 150 °C ceiling belongs to the epoxy: The element and the plate would both go far higher; the filled epoxy will not. Specify the duty against 150 °C continuous, and where the process needs more, the construction has to change to silicone, mica or thick film rather than being derated.
- Flatness, fixing and thermal interface: This is a conduction heater whose whole value is full-area contact. State the flatness of both faces, the bolt pattern and torque, and the thermal interface material — an unflat plate bolted to an unflat load contacts on three points and heats them.
- Thermal mass and warm-up time: The plate stores real energy. That is an advantage where stability matters and a liability where the duty cycles: state the acceptable warm-up and cool-down times, because they, not the wattage, are usually what disappoints in service.
- Chemical exposure, in full: For a tank or bath application, list the chemistry, the concentration and the temperature. The encapsulation is selected against that list, and "plating solution" on its own is not a specification.
- Supply voltage: State the supply voltage: this construction is wound or printed for 110-120 V AC, 220-240 V AC or 380-415 V AC, and it is built for the one voltage ordered rather than being switchable between them. At mains voltage the insulation, the earthing or double insulation and the creepage distances become part of the construction, and a low wattage at 230 V means a very fine, very long element that is harder to build reliably than its low-voltage equivalent.
- Wattage and watt density: This construction is rated at 0.3 W/cm² in free air and 2 W/cm² bonded full-area to metal. Those are not two options: they are the same heater under two cooling conditions, and the second figure is only true while the heat has somewhere to go. Design at the bonded figure and then leave the heater unbonded, air-gapped, or stuck to plastic or foam, and the element runs at roughly 7 times the density its own surface can shed — the insulation reaches its limit in minutes and the failure is permanent. Give the wattage you need and what the heater is bonded to in the same sentence, and the watt density can be checked against the construction before anything is built.
- Temperature limit: The continuous limit is 150 °C, and it belongs to thermally conductive filled epoxy rather than to the element. Nichrome, Inconel and fired resistor pastes all survive far beyond it; what fails first is the material holding them, and no derating of the wattage moves that number. State the maximum temperature the assembly can reach under fault as well as the working set point, because it is the fault case that has to stay inside this number.
- Control and protection: This construction does not limit itself in any way. At rated voltage into a surface that has lost contact, run dry or lost its coolant, it goes on taking full power until the insulation fails, so a thermostat or a thermal cutoff sized to the assembly — not to the heater — belongs in the design and in the schematic. Where a fault must not be allowed to repeat itself, a one-shot thermal cutoff goes behind the resettable device, because a bimetal thermostat cycling on a genuine fault will cycle for as long as the power is on.
- Mounting: This construction is bolted to the load. State the bolt pattern, the torque and the thermal interface material, and state the flatness of both faces — a conduction heater delivers through its contact patch and nothing else.
- Sensor and where it sits: A sensor can be built into the part rather than fitted next to it: NTC, PT100 or PT1000, a thermocouple, or a bimetal device. Say which, and mark its position on the drawing — a sensor under the densest part of the circuit, a sensor at the coldest corner and a sensor next to the load are three different control schemes, and the drawing is where that gets decided.
- Certification of the construction: The constructions behind this product are built and tested to UL 499, IEC/EN 60335, RoHS & REACH, CE Marking, IATF 16949. That is a statement about a construction — its insulation system, its creepage and clearances, its earthing, its marking and its tests — and not a claim that a particular made-to-drawing outline carries an approval of its own. Say at the enquiry which standard your end product is certified to, because it constrains the build rather than being added to it afterwards.
- Leads and termination: State the wire type, gauge, length and exit direction, and the termination — bare, ferrule, ring, spade or a specific connector housing. The lead exit is a mechanical design decision: it is where a flexible heater is most often folded during assembly, and the joint behind it cannot be inspected once the part is built.
Control, Protection and What Happens at a Fault
This construction does not limit itself in any way. At rated voltage into a surface that has lost contact, run dry or lost its coolant, it goes on taking full power until the insulation fails, so a thermostat or a thermal cutoff sized to the assembly — not to the heater — belongs in the design and in the schematic. Where a fault must not be allowed to repeat itself, a one-shot thermal cutoff goes behind the resettable device, because a bimetal thermostat cycling on a genuine fault will cycle for as long as the power is on.
- The control device: A sensor on the load and a controller — on/off where the load has thermal mass and a few degrees of swing is acceptable, PID where the set point has to be reached without overshoot. This is what holds the temperature; it is not what protects the assembly.
- The limit device: A bimetal thermostat or a thermal cutoff, sensing the heater or the hottest point of the assembly, wired so that it interrupts the heater regardless of what the controller is doing. It has to be independent of the control sensor: a broken sensor wire that the controller reads as cold is one of the commonest ways a heating assembly ends up at full power.
- The fault case to design against: Ask what happens if the heater loses contact with its load, if the fluid stops, if the fan stops, or if the controller output sticks on. In every one of those the heater goes on delivering full power into a surface that is no longer carrying it away, and the answer has to be a device that acts, not a calculation showing it would take a long time.
- Where the sensor goes: On the surface whose temperature is in the specification, in direct thermal contact with it. A sensor reading the air near a heated part reads a temperature that part passed through seconds earlier, and a loop closed on the lagging measurement overshoots the leading one every time it starts.
Mounting & Thermal Contact Practice
- Bolt in a crossing pattern to the stated torque, with a thermal interface material where the mating face is not ground flat. Contact is the whole heat path — a plate bolted at the corners against a slightly domed load transfers a fraction of its power.
- Support the plate across its area rather than at its edges. A large plate cantilevered from two fixings will distort as it heats, and the distortion breaks the contact patch it depends on.
- Do not machine, drill or grind the encapsulation. The element sits a few millimetres inside it, and there is no way to see where.
- On any tank or immersion application, fit a low-level interlock as well as a temperature cutoff. The plate is protected against the chemistry but not against being run above the liquid line.
- Take the earth connection to the plate seriously in a wet installation, and test insulation resistance after fitting rather than trusting the factory test through an installation that may have scraped the encapsulation.
Common Specification Mistakes with Epoxy Immersion and Tank Heaters
- Specifying the bath by name only. "Nickel plating solution" covers a range of chemistries and temperatures, and the encapsulation is selected against the actual composition.
- Expecting a fast response. This construction is chosen for stability and sealing; a duty that has to reach temperature in seconds belongs in thick film or polyimide, and no amount of extra wattage makes a potted plate behave like a film.
- Running the assembly above 150 °C on the argument that the element can take it. The encapsulant is the limit, and it degrades and cracks rather than announcing itself.
- Immersing without a low-level cutoff. A plate designed to be surrounded by liquid and then run in air is a heater running far above its free-air rating.
- Bolting an unflat plate to an unflat load and then blaming the wattage when the surface temperature is uneven.
- Quoting only one of the two watt density figures in an internal specification. They differ by roughly 7 times on this construction, and a figure copied without the bonding condition attached to it is the single most reliable way to destroy one of these heaters.
- Designing to the working temperature and never checking the fault temperature against the 150 °C ceiling. This construction has less headroom than most of the alternatives, and it is the blocked, covered or dry case that uses it up.
Where Epoxy Immersion and Tank Heaters Are Not the Right Choice
- Not for hydrofluoric acid or strong solvent service, and not for a tank that is regularly run below the heater without an interlock.
- Not flexible, and not thin. The construction is 2.5 to 20 mm of rigid plate; where the surface is curved or the gap is a millimetre, the answer is silicone or polyimide.
- Not above 150 °C continuous. That is a hard property of the filled epoxy, and it is the lowest ceiling of any construction here.
- Not fast. Thermal mass is the reason it is stable and the reason it lags; a duty with a short cycle time will fight it.
- Not for aggressive chemistries outside the list the encapsulation was chosen against — hydrofluoric acid and strong solvents in particular need a different construction, not a thicker coat.
- Not for a curved or irregular surface. This is a rigid construction and it heats what it is in contact with; a surface it can only touch in places is a surface it will heat in places.
- Not as its own protection. This construction has no self-limiting behaviour, so it is never the right answer for a design that has nowhere to put a thermostat or a thermal cutoff.
- Not above 150 °C continuous. That limit belongs to the insulation system rather than to the element, so it cannot be bought back by derating the wattage — above it, the construction itself has to change.