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| Thick Film Heating Technology |
| Q |
What is a thick film heater? |
| A |
A thick film heater is produced by layering several different film coatings onto a carrier substrate. After each layer is printed, it is dried to evaporate solvents, then fired at high temperatures. This firing cycle bonds the multiple layers together and to the base material; it melts glass frit materials into multiple cohesive dielectric layers; and allows metal oxides present to form the conductive lattice that carries the current and generates heat.
Watlow utilizes different dielectric and resistor ink combinations depending upon thermal expansion and electrical conduction characteristics of the substrate material. The material chosen is determined by the process, compatibility, operating temperature and cycle rates.
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| Q |
How do I know if thick film heaters are right for an application? |
| A |
If you are having a problem with an application where the current heater is not adequately solving the problem, then it would be worthwhile to look at thick film heating technology. Following are some additional differentiators:
- Possibly the most significant indicator is if you have the need for even heat distribution or very high thermal uniformity across a heated surface. By better distributing the heater film, more heat can be put in certain areas to meet the needs of the application.
- Space saving is another important advantage because thick film heaters offer a low profile. This is especially true with applications where the voltage/wattage combination would require a tubular style heater's resistance wire gage to be very small.
- Very fast heater response can be achieved due to low heater mass. We can provide heaters with ramping capabilities as high as 80°C (176°F) per second.
- Annual unit volumes range from one to 10,000. Note that engineering and tooling charges can make small quantity orders expensive on a per unit basis.
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| Q |
What base or substrate materials are available? |
| A |
430 Stainless Steel, Aluminum Oxide, Aluminum Nitride, and Quartz substrates provide low thermal expansion, high temperature tolerance, lower dielectric constant, rigidity and dimensional stability; while accommodating mounting holes and notches. |
| Q |
What are the benefits of a thick film heater? |
| A |
Thick film heaters are low profile and compact in size. They have a fast response with low thermal mass and maintain an even thermal profile to ±2°C (±5°F). High watt densities range from 5.4 to 19.4 W/cm² (35 to 125 W/in²) dependent upon application and temperature. Maximum operating temperature can reach 550°C (1025°F) depending upon application demands and substrate material. Thick film heaters are corrosion resistant and have a longer heater life. Application-specific distributed wattages are available. |
| Q |
How do I know which substrate materials to use? |
| A |
Substrate material is usually chosen based on compatibility with the process, operating temperature, cycle rates, etc. Stainless Steel is the lowest cost option; while Quartz and Ceramics have very good conductivity characteristics at a higher cost. Please consult factory for recommendations.
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| Q |
What termination options are available? |
| A |
We can provide a contact pad for spring probes, welded stud terminations (our most robust option), welded lead wires or soldered and epoxied lead wire connections. Overmold terminations and mechanical compression assemblies are also available for specific types of thick film heaters. |
| Q |
What is the Watlow warranty on thick film heaters? |
| A |
All Watlow thick film heaters carry the standard warranty of 12 months for material and workmanship from date of shipment. |
| Q |
Do we have thick film heaters in stock for immediate delivery? |
| A |
Yes. We have a wide selection of conduction heaters, quartz modules and nozzle heaters in stock. These stocked heaters have been designed based on common market needs. Please consult factory for current stock inventory. |
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| Thick Film Conduction Heaters |
| Q |
Are there any thick film conduction heaters carried in stock for immediate delivery? |
| A |
Thick film stock conduction heaters are stocked for immediate delivery. These heaters are designed for clamp-on applications and are supplied as a multi-part assembly; heater, mica insulator, clamping plate and mounting hardware. Stocked shapes include disc, square and rectangle (refer to current thick film conduction heater (HAN-TFCH) literature for current stocked dimension) of a variety of sizes. |
| Q |
What are the watt densities of the thick film conduction heaters? |
| A |
The wattage densities of the standard products vary between 3.2 W/cm² (20 W/in²) and 6.6 W/cm² (40 W/in²). Custom applications can be designed up to 15.4 W/cm² (100 W/in²).
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| Q |
What if a thick film conduction heater comes close to meeting my needs, but I need a few adjustments? |
| A |
For a small engineering charge, we can adjust the conduction heater to fit a customer's needs. What many customers have done is place a small order (one to five pieces) for a stock conduction heater close to what they feel their need will be. After testing the heater, they are able to work with the factory to fine tune a conduction heater to their specific needs. This can reduce engineering charges from thousands of dollars to a few hundred dollars. |
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| Thick Film Nozzle Heating Technology |
| Q |
What is the substrate material? |
| A |
The substrate is 430 stainless steel (W.Nr. 1.4016) in the form of cylindrical tubing. |
| Q |
What are the dielectric materials? |
| A |
The dielectric glass is a proprietary material that is sintered to the substrate through a firing process. It provides an electrical isolation barrier for 'safety' and minimizes current leakage. |
| Q |
Can the glass dielectric be damaged in normal handling? |
| A |
After annealing the glass dielectric is surprisingly robust and can easily withstand handling and installation. We have taken the precaution of offsetting the dielectric 1/32 inch from the end of the nozzle to minimize stress on the dielectric. However, pounding on the heater with a hammer, pliers, etc., to install it on a dirty nozzle or dropping it from above one meter onto a cement floor will probably crack the dielectric and damage the heater. Cracked dielectric will result in current leakage failure. |
| Q |
What are the resistive ink materials? |
| A |
The resistive ink is a proprietary material. After firing, the ink material bonds to the dielectric and becomes a resistive heater circuit.
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| Q |
How are the thick film materials applied? |
| A |
Note: Manufacturing process specifics are considered Watlow Intellectual Property (IP).
The materials are "deposited" and then sintered through various manufacturing processes that are different for each material marriage and application. |
| Q |
What material used in the termination? |
| A |
The termination overmould in Class II designs is a proprietary, high temperature, thermoset plastic material. During bake out, organic materials are removed leaving ceramic that is forming a strong mechanical bond to the thick film dielectric and lead wire termination. This ring provides a high temperature strain relief for the lead wires.
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| Q |
What is the lead wire? |
| A |
The standard lead wire is stranded, 22-gauge fibreglass rated to 450°C (842°F).
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| Q |
What is the dielectric strength of the nozzle heater? |
| A |
All the nozzle heaters are tested to verify that they meet the UL® standard of 1,200 Volts plus two times the applied voltage. |
| Q |
When will the heaters have agency approvals? |
| A |
The Class I and Class II thick film nozzle heaters with the molded termination are UL® recognized and conform to CE.
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| Q |
What voltage, wattage and watt density are available on the nozzle heater? |
| A |
The nozzle heaters can be designed in configurations up to 230/240 VAC. The length of the heater and the maximum allowable watt density determine the actual wattage. The maximum allowable watt density is 15.5 W/cm² (100 W/in²). |
| Q |
Can the heater be designed with distributed wattage? |
| A |
Yes, the ability to repeatedly "deposit" the thick film circuit in a multiple zone distributed wattage pattern is one of the major technical advantages of the thick film nozzle heater. |
| Q |
What is the approximate price of a nozzle heater? |
| A |
Consult the factory or your local representative. |
| Q |
What is the design lead time? |
| A |
Current lead time for a new design is six weeks for prototype delivery.
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| Q |
What is the production lead time? |
| A |
Current lead time for production of an existing nozzle heater is five weeks. |
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| Thick Film Quartz Heater Modules |
| Q |
Are thick film heaters designed for applications requiring aggressive chemical heating? |
| A |
Yes. The thick film quartz heater modules are intended for aggressive chemical and deionised (DI) water heating applications. These applications include ammonium hydrochloride, hydrobromic acid, hydrochloric acid, hydrogen peroxide, nitric acid, phosphoric acid, sulphuric acid and TMAH. For a complete list or a specific application, please contact the factory. You can also receive our specification sheet HAN-TFQM via a request through our web page.
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| Q |
Can quartz modules be mounted either horizontally or vertically? |
| A |
Yes. However, there are limitations when a heater designed for vertical installation is used in a horizontal orientation. It is important to determine and to communicate how the heater will be mounted early in the design phase or when a stock heater is ordered. |
| Q |
What are the flow rates for the quartz heater modules? |
| A |
Minimum flow required for horizontal units is 11.35 liters (3.0 gal.) per minute and for vertical units is 0.95 liters (0.25 gal.) per minute at 0.69 bars (10 psig).
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| Q |
What are the maximum watt densities for quartz heater modules? |
| A |
These heaters can be designed up to 15.5 W/cm² (100 W/in²). The factory will help you determine the best wattage for your application. |
| Q |
Can the quartz heater modules be designed for more than one fluid path? |
| A |
Yes. Depending on your requirements, up to three fluid paths are available. Design and engineering charges may be required for these specific applications. |
| Q |
Do we have any fitting options? |
| A |
Yes. Our aggressive chemical quartz heater modulean be ordered with Flaretek®, FlareLock® compatible and Pillar 300 Series compatible fittings.
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| Q |
Are custom quartz heaters available on flat substrates? |
| A |
Yes. Thick film on quartz can be designed in a variety of shapes and sizes. For your specific application, please contact the factory. |
