Electric Heating Elements: Cartridge Heaters

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Cartridge Heater Basics

Cartridge heaters are cylindrical in shape, consisting of an element made of resistance wire wound around a ceramic core. Within a metal sheath tube, the wound core is precisely centered and surrounded by granular magnesium oxide material. This isolates the resistance element from the tube electrically and provides a heat transfer medium to the sheath tube. At one end are electrical terminations. In order to enhance internal heat transfer and electrical insulation characteristics, higher performance, longer-lived cartridge heaters are swaged (a rotary hammer compacting process). Swaging compacts and densifies the granular insulating material, improving its thermal conductivity. Cartridge heaters are commonly used and are produced in a broad range of lengths, diameters, wattages, watt densities, lead agreements, and optional internal sensors.

Cartridge Heater Applications

Specialized Cartridge Heater (BCE)

The following equipment utilizes cartridge heaters: chromatography equipment; medical laboratory equipment, including chemistry analyzers; plastic molds and runners; platens; barrels on extrusion equipment; hot melt glue systems; packaging seal bars; labeling and marking systems; food-warming equipment and steamers; autoclaves; ovens; photographic processing equipment.

Cartridge heaters are capable of operating at elevated temperature as well as high watt density, but care must be taken to apply cartridge heaters at appropriate watt density and sheath temperature levels.

Temperature Capability

A maximum of 1600°F (870°C) sheath temperature is recommended.

Watt Density Capability

A maximum of 400 W/in. and higher under special conditions.  As a rule, cartridge heaters can operate at 1600°F at 40W/in.

Heater Life

Operating at 1600°F internal temperature with modest cycling and with the proper hole fit, a properly designed and constructed cartridge heater will provide approximately a one-year life.

Voltage

Usually 120/240V, with 480V and custom voltages requiring special design or sizing considerations.

Thermal Response/Application

Cartridge heater's thermal response is dependent on conductive heat transfer in most applications.  Optimum conduction requires close fit between the heater and the work to be heated. As heater looseness increases, watt density must be decreased accordingly, to prevent internal overheating. Watt densities of liquid-immersion cartridge heaters vary according to the liquid's viscosity and heat capacity.  When heating liquids, care must be taken to prevent "film boiling" where vapor bubbles create a thermal insulating effect and raise the heaters internal temperatures.

Heater Efficiency

Cartridge heaters are 100% efficient when immersed.

For more information about electric heating elements, contact BCE by calling 510-274-1990 or by visiting https://bcemfg.com.

Electric Heating Element Design: Nichrome Wire

Nichrome wire heating element inside a quartz tube.
(Image courtesy of Wikipedia)

When an electric current passes through a conductive material (a resistor) energy in the form of heat is released. The greater the resistance to electron flow, the greater the heat energy created. The terms resistance and conductance apply to the nature of the conductive material, and it's ability to pass current.

Resistance (measured in ohms and using symbol "R") is defined as the electrical voltage (in volts using symbols "V") divided by the current (in amps, using symbol "I"), or R=V/I. This formula is one variant of Ohm's Law.

The heat, or power, released from the resistor (measured in watts, using the symbol "P") is a function of the supply voltage squared, divided by the conductor resistance. This version of Ohm's Law looks like this: Watts = Voltage squared / Resistance, or P=V²/R.

You can see if the resistance is too high, voltage does not flow, and no heat is produced. For the benefit of simplicity, we'll forego a discussion into superconductors, like those used on MRI machines and mass spectrometers, because their behavior includes complicated magnetic field discussions. Instead, we'll stick to common conductors often used to pass electrical current.

Selecting the right resistive material for a heating element is crucial in order to maximize heat output, heater longevity and energy usage - a conductive material with high resistance that is also easy to work with.

Nichrome alloy, made up of 80% nickel and 20% chromium is by far the most popular resistance heater wire, and is a available in a wide variety of wire gauges and ribbon shapes. It's popularity is performance based - it has high resistance, is easy to apply to many heater configurations, does not oxidize, has a low expansion coefficient and a high melting point. In the design and development of electric heating elements, if you grant that nichrome wire is at the heart of most electric heaters, everything else comes down to packaging and performance.

While there are other materials such as Kanthal (iron / chromium / aluminum) and Cupronickel (copper / nickel), and newer exotic ceramics, the vast majority of electric heaters used in industrial, commercial, OEM, and consumer goods all still rely on the ubiquitous and time proven nichrome alloy.

For more information on electric heating elements, contact BCE by visiting https://bcemfg.com or by calling (510) 274-1990.

Custom Electric Heating Elements Provide OEM Designers Freedom and Flexibility

Custom heater for vacuum
applications with thermowell
and multiple RTD sensors.

Technology advances rapidly and new discoveries in material science, medicine, pharmacology, biology and semiconductors are being made every day. Along with these advancements in  technology comes new treatments, medicines, materials, and processes.

Original equipment manufacturers (OEM's) of analytical, semiconductor, biomedical, life-science, and aerospace equipment continually design new equipment to apply and leverage these discoveries. Pressure to produce new machines offering greater efficiencies, compactness, and greater production is always present. Each item in the precedent design undergoes scrutiny and very often has be modified to a new fit, form, or function.  New components are needed to meet the new design requirements.

The application of localized electric heating elements is one area that OEM design engineers find themselves navigating in unchartered waters. Very logically, they often attempt to use an off-the-shelf cartridge, silicone rubber, or mica heaters for their specialized heating requirement. Unfortunately this approach leads to compromises in layout, packaging, and performance. A much better alternative is considering a custom heating element, developed in consultation with an experienced custom heater manufacturer.

Custom semiconductor wafer
chuck heater. Highly uniform heat
with no brazing or casting. 

Experienced custom electric heater designers provide many important benefits throughout the entire product development cycle. For instance:

• Front-end, practical design review to optimize manufacturability.
• Timely prototype development.
• Partnerships and alliances with platers, brazers, casters and heating element manufacturers.
• Single source responsibility.
• Testing, calibration, and QC.
• Inventory management.
• Value-added assembly.

APCI Heater/Capillary Source Heater
400 deg. C, connector
plug, and internal RTD sensor.

The heater manufacturer partner provides critical guidance in areas such as material selection, power requirements under load, temperature vs. time data, watt density and packaging. With their help, high performance, precise fit, and long heater life are better ensured.

By choosing a custom electric heating element design, the OEM gets exactly what they need in terms of form, fit, and function plus scores of other benefits derived from the heater vendor's tacit knowledge and past experiences.

Experience is Key When Applying Custom Electric Heating Elements

Heater design expertise is
readily available from your
Technical Sales Rep

Designing and applying custom electric heating elements are best completed and accomplished through the proper application of the right resources. One of the most available and important sources of high level technical knowledge is a vendor's local Technical Sales Rep. Their assistance is readily available and their consultative value is very high.  Bringing in a Technical Sales Rep will have a big bearing on a successful task or project completion.

Many Technical Sales Reps are degreed engineers. If they don't have an engineering degree, you'll find they have years of empirical application knowledge from working on many, many projects. You'll also find that many have worked at manufacturer's factories and know the in's and out's of production as well as anyone.

Consider these elements the Technical Sales Rep brings to your thermal system design project:

Watt densities? Thermal profiles?
Distributed wattage?
There's a lot to know.

Product and Application Knowledge: Your Technical Sales Rep has probably seen hundreds, if not thousands, of custom heating requirements. They deliver a mental encyclopedia of product offerings, application insights, and broad spectrum of capabilities. They also have information regarding what products are in development that can give you the competitive edge. Much of this information resides in the Reps head, and is not generally accessible to the public via the Internet.

Experience: As a project engineer, the selection and incorporation of a new heater design may be all new to you. You may be treading on fresh ground with little or no experience in the nuance of electric heaters. There can be real benefit in connecting to a knowledgeable source, with years of past design and application experience, that will save you time, money, and effort.

Access: Technical Sales Reps work closely with a variety of manufacturers, and may even have in-house prototyping or manufacturing capabilities at their own companies. This gives you, the design engineer, a connection to “behind the scenes” manufacturer contacts with essential information not publicly available. The technical sales rep knows people, and makes it his/her business to know the people that can provide answers to your electric heating and custom thermal system application questions.

So, in this age of doing your own research and self-educating on the Internet, let's not forget the importance of a face-to-face visit with someone who can really help - your Technical Sales Rep. You'll be very pleased with the information they can provide to make your job easier and the quality of your product better.

Have a custom heater job? Contact BCE now!
www.belilove.com(510) 274-1990

Engineered Thick Film Heating Elements

Thick film heating elements were developed as an outcropping of long-time technology used for production of printed circuit boards and hybrid circuitry. The term “thick film” refers to the resistance circuit (or heating element) that is deposited by a screen printing process, typically 0.0005” thick and deposited on a ceramic or metal substrate.

A thick film heating element provides precise layout of the resistance element exactly where the heat is required. Additionally, intimate contact of the heating element to the substrate is guaranteed delivering maximum heat transfer by eliminating any air gap there between between the heating element and the substrate.

Thick film heaters give engineers broad design flexibility of the heating circuit itself. Designers can precisely distribute heat where its required and also dictate the uniformity in temperature distribution. This design flexibility can be applied to curved and irregular shapes, as well as flat, to accommodate custom heating applications.

Highly machined ceramic parts, with intricate designs, high dielectric properties,  and smooth surfaces are ideal for thick film heating elements. Advanced ceramic's chemically inert, non-porous properties facilitates the careful and exact control of the trace pattern and trace dimensions, thus providing a “heated part” approach to equipment design.

Features of Ceramic Thick Film Heaters:

• High dielectric
• High thermal efficiency
• Very rapid heating
• Uniformity of heated area / pattern
• High watt densities
• Chemically inert
• Custom shapes and sizes
• Custom wattages and voltages
• Embedded temperature sensors

Thick film heating elements are used in many industries today, particularly in advanced technologies such as analytical instruments, medical equipment, aerospace, semiconductor, and research & development.

BCE, located in the San Francisco Bay Area, has decades of experience in consulting, designing, and applying thick film heaters. Their reputation has grown nationally as a premier custom thermal solutions provider.  For more information, contact:

BCE
21060 Corsair Blvd
Hayward, CA 94545
Phone: (510) 274-1990
Fax: (510) 274-1999
E-mail: sales@belilove.com

www.belilove.com

Electric Heaters for Heating Flowing Gases To 1000 F

Examples of air heaters
(click for larger view)

Do you need a small, compact electric heating system that can heat flowing gas or air up to 1000 degrees F.?

You may want to consider an inline "air process heater".

These fabricated (usually custom) electric heaters are self-contained, provide inlets and outlets, wiring,  sensors to measure internal temperatures, and are available in a variety of materials.

Air Process heater provide hot air and gas up to 1000^oF (540^oC) with infinite control by varying the voltage and air velocity supplied.

Units are fitted with a tubing “T” for convenient power lead outlet, while larger diameters can be supplied with post terminals on the sheath for direct electrical connections.

Designs can accommodate male or female NPT threaded fittings, hose adaptors, flanges, or custom fittings to your specifications.

Typical Air Heater Construction

Construction

1. Optional stainless steel bushing. 
2. Ceramic coil support.
3. Resistance element.
4. Stainless steel sheath. 
5. Silver solder.
6. Fiberglass insulated leads. 
7. Epoxy seal.
8. Copper tee.
9. Heliarc weld.
10. Optional brass bushing.

To properly size and select an air process heater:

• Determine the volume of air or gas(SCFM) you will be heating. 
• Determine temperature rise in degrees Fahrenheit(􏰁ToF).
• Calculate wattage required as follows:
• Watts = SCFM x delta-T ^oF / 3

Take into consideration the physical size requirements of your application and determine from the specifications chart for each size, the air heater best suited for your application.

Summary of Features:

• Exit air temperatures to 11000^oF (540^oC).
• Standard pressure rating is 80 psig at room temperature. 
• May be used with recirculating air up to 250^oF (121^oC).
• Designed for horizontal use.
• For use with clean, dry air.

When You Need a Custom Heating Element or Thermal System Design

OEMs often need custom designed heating elements for their equipment. Designing an electric heating element, or a complete thermal system, requires both electrical and mechanical engineering skills. Often, you can save time and money by calling in an expert with the proper experience to assist.

Belilove Company-Engineers has decades of experience developing custom thermal solutions in many industries - from low tech to cutting-edge high tech, from foodservice appliances to semiconductor processing equipment, Belilove has "been there, done that". So the next time you need an electric heating element, temperature sensor, or controller, Think Belilove.

High Purity Fluid Electric Heaters

Transfer Line
Heater Assembly

In many biomedical, pharmaceutical, semiconductor, electronics or R&D laboratory applications, special purpose electric heaters are required for heating high purity fluids. These heaters typically must be ruggedly designed, made from materials immune to process contamination and be vacuum tight. They can be subject to high temperatures, harsh solvents, and corrosive gases. Many times they must maintain a seal for full vacuum, demonstrate a unique or even heating profile and be able to be closely controlled.

The misapplication of screw plug immersion heaters, screwed into a stainless steel welded vessel, offer more problems than solutions due to leaks, material compatibility, poor controllability, and bulky size.

Transfer line
heater assembly

The answer is in a custom high purity fluid heater designed with the process in mind.

Custom electric heating elements are available designed to handle high vacuum, high temperatures, utilize glass liners for ultra-pure gases, offer 316 stainless steel parts, provide internal RTDs for control and can be temperature profiled.

General Specs for these types of custom fluid heaters are:

• Variety of voltages.
• Wide range of watt densities.
• Temperatures up to 350°C.
• Heater length can be profiled to generate a liner temperature profile.
• Vacuum compatible up to 1.0 x 10-8  STD. CC/SEC Helium.
• Can be provided with internal sensors (RTD or thermocouples).
• Can be glass lined for ultra pure gas application.

Careful review of the application is important and the help of an experienced application engineer is required, but the outcome of the test, process or product will be infinitely improved.