Sunrod Split Sheath Miniature Cartridge Heaters

• Small footprint, high heat
• 1/8 inch and 4MM diameters
• 3 - 240 volt operation
• Hundreds of sizes In stock
• Heaters as short as 1/2"

Sunrod split sheath cartridge heaters have a novel, innovative design that removes the failure points of conventional miniature heaters. The design includes a continuous resistor packed in maximum density insulation and welded to the heater connections. Lead wires exit through the insulation with a temperature rating of 500 degrees Fahrenheit. Insulation with a temperature rating of 900 degrees Fahrenheit is also available.

In contrast to typical cartridge heaters, which have cold areas throughout their length and unheated sections at each end, Sunrods generate heat continuously for the whole length of the heater. The even heat dispersion of Sunrod ensures more uniform temperatures for your process. 

Sunrods have a unique hot tip that allows you to reach any part of your operation that requires heat. 

When activated, the split sheath design of SunRod forces its opposing legs to extend into contact with the surrounding bore for optimal heat transfer resulting in reduced operating temperature and an extended operating - by up to five times! 

SunRod elements contract when de-energized, breaking contact with the bore and allowing slide-out removal. SunRods are never going to seize! 

You may now apply heat whenever you want! Drill a small bore to the area that requires heating and insert a hot tip SunRod.

Contact BCE for more information about Sunrod split sheath miniature cartridge heaters. Call 510-274-1990 or visit https://bcemfg.com.

BCE Cartridge Heaters

 

BCE manufactures a wide range of cartridge heaters for a variety of industrial applications, and can provide you with heaters manufactured to your exact specifications. Cartridge heater size, sheath, leads, terminals, wattage and voltage can all be adapted to meet your exact needs.

Low to Medium Watt Density Cartridge Heaters

BCE precision cartridge heaters provided localized heat to restricted work areas requiring close thermal control. Dies, platens, and a variety of other types of processing equipment are efficiently heated and can be closely controlled. Part work temperatures of up to 1250ºF are obtained by a combination of heater location and proper wattage output. Basic heater designs are readily adaptable to a wide variety of special requirements, sizes, or ratings. Heating element wires are constructed just beneath outside surface for optimum heat transfer and minimum core temperature, resulting in faster part heating.

The maximum power densities for low to medium watt density cartridge heaters is computed at 60 watts per square inch of heated surface. With proper fit in a heat sink, long life can be expected. Consult BCE for higher watt density applications. Lower watt density will result in longer life. Standard voltages are either 120V or 240V. Other voltages are available.

High Watt Density Cartridge Heaters

The useful life of a Cartridge heating element is determined by how quickly the heat generated in the internal resistance wire can be dissipated to the outside sheath. BCE high watt density cartridge heaters are design and constructed in a way that accelerates the transfer of heat from the resistance wire to the sheath. This is accomplished by relocating the wire so that it is closer to the sheath; and swaging the outside diameter of the heater, thereby compressing the magnesium oxide filler so that it becomes an improved conductor of heat from the wire while maintaining its dielectric properties. By improving the heat transfer rate, it is possible to manufacture elements of higher densities because the differential between the wire temperature and the sheath temperature has been minimized.

Common applications for high watt density cartridge heaters are dies, heat sealing machines, hot melt adhesive equipment, plastic molding machines, platens, and shoe machinery.

Optimizing Performance and Operating Life of High Watt Density Cartridge Heaters

Cartridge Heater Fit

High watt density heaters require careful fit to insure optimum performance and long life.  BCE recommends that installation holes not be drilled and reamed over .002” or larger than the nominal hole size required. 

Cartridge Heater Cycling

Rapid cycling of heaters from very low to very high temperatures shortens their life considerably. It is recommended therefore, that care be taken to compute the correct wattage for any given installation. Optimum wattage should result in a 50/50 off/on cycle.

Location of temperature Sensor and Cartridge Heater

When thermostats are used, the sensing element ought not to be placed further than 1⁄2" away from the heater wherever possible.

For more information about cartridge heaters, call BCE at 510-274-1990 or visit their website at https://bcemfg.com.

New! Product Builders for BCE Cartridge Heaters and Mini Clean Flow Heaters

BCE is pleased to introduce two new online product configuration tools that allow you to build an electric cartridge or a fluid heater from a selection of pull-down menus and text field entries.

Cartridge Heater Product Builder
(click for larger view)

The BCE "Mini Clean Flow Heater Builder" and the BCE "Cartridge Heater Builder" are easy to use web-based applications that offer users the ability to design a heater specifically for their application.

The user interface consists of an onscreen product drawing which is updated as each element of the design criteria is chosen. Once designed, it provides a finished drawing and allows the user to submit a pricing quotation request to BCE.

Mini Clean Flow Heater Product Builder
(click for larger view)

The product builders are intended to save customers time by providing an easy and convenient way to choose heater options and get a fast, accurate price quote.

See the "Cartridge Heater Product Builder" and "Mini Clean Flow Heater Product Builder" here.

For more information, contact BCE. Call them at 510-274-1990 or visit their website at https://bcemfg.com.

The Top Four Reasons Why Cartridge Heaters Fail

Cartridge heaters fail because either the heat generated in the internal resistance wire is not efficiently dissipated or moisture (or a foreign substance) seeps inside the protective sheath, creating a short circuit.

Inadequate heat dissipation results in an elevated internal temperature, which can rapidly breakdown the heating element. Inadequate heat dissipation occurs for several reasons: when machined tolerances are outside of an accepted range (improper fit); if the watt density is too high; or when powered by too high a supply voltage.

1) Loose Fit

Loose fit is the most common cause of premature cartridge heater failure. The bore hole within which they are inserted must be held to tight tolerances. High watt density cartridge heaters are even more sensitive as the internal temperature of the heater can rise rapidly and jeopardize the life of the heating element. To ensure adequate thermal dissipation, the recommended hole diameter is no more than 0.002 in. greater than the nominal diameter of the heater.

Typical allowable watt densities for swaged cartridge heaters are based on fit and operating temperature.

Max. allowable watt density vs. fit. Click image for larger view.
Graph courtesy of Backer Hotwatt.

2) Too High a Watt Density

The watt density of the heater is vital to its performance. This is a measure of thermal power density and the higher the watt density, the greater the needs are for thermal dissipation. High watt densities can lead to premature failure when thermal dissipation needs are not met, as the internal temperature of the heater will exceed the limits of the resistive heating element.

3) Too High a Supply Voltage

In a resistive circuit, since the resistance is fixed, when the voltage is doubled, the current doubles as well as quadrupling the wattage output. Incorrectly specifying the supply voltage can lead to premature heater failure, as voltage has a dramatic effect on the wattage and the amount of heat generated as can be seen in the following formula.

Voltage calculation. Courtesy of Backer Hotwatt.

4) Moisture or Contaminant Ingress

Even when cartridge heaters feature heliarc-welded end caps, they are prone to failure when the air surrounding the heater contains impurities or has a high moisture content and the heater’s leads are not adequately sealed. This is due to the nature of MgO insulation: it is a highly hydroscopic white powdered mineral, and when the heater undergoes thermal cycling a vacuum is created, drawing in moisture or other contaminants such as oil, which can result in internal shorting.

Watt Density Selection and Thermal Cycling

Suggested watt density is based on several factors including the fluid medium to be heated, the desired operating temperature and process variables such as flow rate. In general, operating temperature is inversely related to the suggested watt density. Additional considerations are taken when heating a fluid to a point near its boiling point, as phase changes drastically reduce its heat transfer capabilities. Highly viscous fluids or fluids that tend to coke or carbonize also require a low watt density. Highly corrosive solutions also need a low watt density, as the increased watt density increases the potential for corrosion, drastically reducing the life of the heater’s sheath.

Selecting an incorrect watt density can have adverse effects to the response of a thermal system, but it is not the only factor to consider. There are four basic elements to any thermal system, including the thermal load, the heat source, the heat transfer device and the temperature controller.

Thermal power delivered by a heating element is a function of wattage, and a correctly sized heating element will provide an ideal thermal response without rapid cycling of the element. The optimal wattage results in a 50/50 off/on cycle, which prevents or minimizes hunting or temperature overshooting. For more precise thermal control, variable voltage devices or solid-state controllers may be used.

For more information on properly applying cartridge heaters, contact BCE by calling 510-274-1990 or by visiting the cartridge heater section of the BCE website.

Everything You Wanted to Know About Cartridge Heaters ...

Cartridge Heater (Hotwatt Backer)

Reprinted with permission of Backer Hotwatt

WHAT ARE CARTRIDGE HEATERS?
Cartridge heaters originally consisted of a ceramic-supported heating wire inserted into round metal tube, making them look like cartridges (the likely source of their name). They provide localized heat to restricted working areas requiring close thermal control. Their power density is less than 60 W/in2 and they generate temperatures up to 1,200°F. They range in diameter from 1/8 to 2 in. and vary in length from less than an inch to over four feet. Although they are usually round, they can have square or rectangular cross sections. Standard cartridge heaters account for an estimated 20% of all electric heaters made.

Compacted cartridge heaters were developed about 60 years ago and feature inorganic powder tightly compacted onto the heater wire. This increases their power density to nearly 500 W/in2 and maximum temperatures approach 1,800°F. The need for higher quality tubing and precision-fired crushable ceramics makes compacted heaters cost 1.5 to 3 times the cost of a standard cartridge. They are available in diameters from 1/8 to 1 in. and lengths from 1 inch to over 3 feet.

HOW ARE CARTRIDGE HEATERS MADE?

Cartridge Heater Internal View

For standard cartridge heaters, nickel / chromium heating coils are inserted in a ceramic tube inside a metal housing or sheath. Magnesium oxide filler is then vibrated into the hole to fill any voids. This increases heat transfer to the metal exterior. An end cap is welded on the bottom and insulated leads are installed at the opposite end. For swaged cartridge heaters, the nickel / chromium wire is wound around a ceramic core, placing the wire closer to the metal housing. Magnesium oxide is vibrated in and the heater swaged to a specific diameter. This compresses the MgO so it becomes a better conductor of heat while maintaining its dielectric properties. This improves heat transfer and allows for higher watt densities. Swaging also lets the heaters operate at higher temperatures and better withstand vibrations.

HOW CAN YOU GET THE MOST EFFICIENT HEAT TRANSFER AND LONGEST OPERATIONAL LIFE OUT OF A CARTRIDGE HEATER?
There are several steps users can take. On installation, for example, cartridge heaters should be installed in holes drilled and reamed to no more than 0.002 inches larger than needed. The heaters are routinely sized to never be 0.005 less than the nominal diameter and always at least .001 under the nominal diameter for a slide fit. These close fits ensure rapid heat transfer from the heater to the housing and helps keep the heater as cool as possible, which contributes to a long life. Heaters should not be cycled from low to high temperatures as it shortens their life considerably. Instead, designers should calculate the proper wattage for their applications. The best wattage results in a 50/50 off/on cycle. For temperatures over 750°F, off/on control can be replaced by input voltage regulation through variable transformers or proportioning controllers to minimize temperature fluctuations. If a heater is going to be turned off routinely, the air around it should be kept dry and no impurities (oil, gas,) should be in contact with the heater. That’s because the ceramic material used in cartridge heaters is hygroscopic. Every time power to the heater is switched off, it creates a vacuum inside the cooling housing which draws in air and any nearby impurities from the surrounding area. The moisture or impurities, once inside the housing, can cause a short circuit and result in heater failure.

If a thermostat is used to control the temperature, it should be no more than 0.5-in. from the heater. Mounting it any farther away could let the unit run hot and thereby shorten its life. Another cause of failures is too high a watt density. If the heater was incorrectly specified for an application and provides too much heat, the heater will not be able to dissipate the heat and will fail. Similarly, if the heater is designed for 120 V but is being powered by 240 V, the output wattage will be four times greater than it should be, which can, again, lead to failure.

WHAT OPTIONS ARE AVAILABLE ON CARTRIDGE HEATERS?
There are several options and variations available. Heaters may be three-phase or multiple wattage in a single unit. For instance, an application might need quick heat ups and then a standby circuit to maintain a relatively low temperature using different wattages based on changing thermal loads. Heaters can have wattage outputs that vary over their lengths in order to even out temperatures over a platen or a large surface. Heaters can also have built-in thermocouples, usually at the bottom of the heater and type J or K grounded or ungrounded. If a precision fit is needed, companies can supply centerless ground diameters. They can also supply certain heaters at higher voltages (300 to 600 V).
Heaters used in corrosive environments can be Teflon coated or electro-polished. Heaters that need hermetic sealing or will be used in a vacuum application can be ordered with ceramic-to-metal seals that withstand temperatures to 1,000°F.

CAN CARTRIDGE HEATERS BE USED IN LIQUIDS AS IMMERSION HEATERS?
Yes, when applied with a mount- ing fitting. Not all cartridge heaters made as immersion heaters are completely moisture sealed. The heater and bushing are submersible but the termination end is not necessarily sealed. If an application is in a high humidity area, however, the termination area should be sealed. Seals can be silicone rubber or Teflon which are good to 400°F, or epoxy potting which can handle temperatures to 265°F.

WHAT ARE SOME OF THE TERMINATION OPTIONS OFFERED ON CARTRIDGE HEATERS?
There are multiple options for cartridge heaters, almost too many to list. Standard options start with straight internally connected leads. External connections are optional on larger sizes, recommended when repairable leads are required. There are also post terminals available on cartridges 15⁄16-in. and larger. For applications with limited space, manufacturers can supply right-angle leads.

There are also several options for protecting leads. Fiberglass or silicone rubber sleeving, as well as ceramic bead insulation, protect against temperatures up to 1,000°F. Additional protection can be provided using flexible conduit or stainless steel braid.

Have a requirement for cartridge heaters? Call BCE now at 510-274-1990 or visit https://belilove.com

Cartridge Heater Design

All cartridge heaters are not created equal. Some are designed to provide reasonable performance at a reasonable cost. Some cartridge heaters are designed for high performance and long life, but come at higher cost. Neither design is superior or inferior when applied properly. Both designs have their place in the world.

First, it's important to understand a very basic concept when applying electric heating elements. All electric heating elements need to move the heat away from the resistance wire into the surrounding media. This is done through conduction, convection, and radiation. Preventing resistance wires from getting too hot is the goal.

The difference comes down to internal design. 

Low watt density cartridge heater.

From the outside, all cartridge heaters may look the same, but internally they're worlds apart. Lower watt density (lower cost) heaters use a helically wound resistance wire threaded through holes a ceramic bobbin. The nichrome resistance wire and bobbin are then inserted in a metal tube with loose magnesium oxide (MgO) back-filled around the bobbin. The result is a cartridge heater designed for lower operating temperatures and lower watt densities. These limitations are caused the insulating affect of the air surrounding the magnesium oxide grains and placement of the helically wound wire. Loose magnesium oxide provides poor thermal conduction and therefore prevents the resistance wire from conducting it's heat outward. The inability for the wire to shed heat is further complicated by the placement, in relationship to the sheath, of the resistance wire.

High watt density cartridge heater.

High watt density cartridge heaters, capable of higher operating temperatures and long life include a different internal design, incorporating a swaging process and great care to resistance wire placement. High watt density heaters have very precisely wound nichrome resistance wire around the ceramic bobbin, and then, with exact centering and very tight tolerances, vibrate MgO into the metal tube surrounding the bobbin/wire core. Once the MgO is added, the heater goes through a swaging process that reduces the inner diameter of the metal tube. The result is compacted magnesium oxide with rock-like properties and much better thermal conduction from resistance wire to external heater sheath.

Both styles of cartridge heaters have their value and proper application. Using low watt density cartridge heaters on a simple applications like glue pots is fine, and will yield good life and performance. On the other hand, high temperature applications such as plastic injection mold machines require the higher performance and extended life that only a swaged heater will provide.

Contact BCE for more information on electric heating elements. Visit https://www.belilove.com or call (510) 274-1990.

BCE’s Foil and Cartridge Heaters: Braving Extreme Weather Conditions in Rain Gauges

Rain Gauge Heater Combination

Rain gauges are essential in collecting data on precipitation an area receives over a period of time. This information is used by scientists to track biodiversity and develop advanced meteorological instruments aiding notably in aviation.

However, rain gauge performance can be severely impaired in regions where extreme cold weather dominates. In fact, a leading manufacturer of aviation technology solutions approached BCE to develop a means to heat their tipping bucket rain gauges in regions impacted by heavy snowfall and freezing rain. 

In order, for these rain gauges to remain operational, precipitation needed to be melted in the collection funnel, then remain fluid inside the gauge and finally drain with ease after the data had been collected without freezing with exposure to the outside air.

SCOPE

Electric heaters to be incorporated in the rain gauge needed to meet the following specifications:

• All heaters needed to operate at 220V 
• Heater used for collection funnel needed to operate at 160W 
• Heater used for inside of gauge needed to operate at 130W 
• 2 drain tubes required heaters to not exceed operation at 25W each 
• Operating temperatures between -30°C to 45°C 
• Temperature control required for heaters used in collection funnel and inside the gauge 
• Temperature to remain approximately 15°C inside collection funnel 
• Temperature to remain approximately 5°C inside gauge 
• Heater used for collection funnel was not to exceed 8” in height and width 
• Heater used for inside of gauge was not to exceed 11” in height and width 
• Heaters used inside drain tubes needed to operate continuously and not exceed 20” in length 

OUTCOME

BCE proposed foil heaters to heat the collection funnel and the inside of the gauge. These heaters were precisely manufactured to achieve the perfect form and fit needed for the rain gauge components. Not only did they match the exact electrical specifications, the resistance element laminated between aluminum foil shells provided optimal surface heating. Furthermore, each of the foil heaters were also embedded with thermostats for accurate temperature control. For the drain tubes, BCE manufactured cartridge heaters to the desired length and with a robust stainless steel sheath providing continuous operation. These cartridge heaters further ensured maximum heat transfer through the close proximity of the element wire and sheath. This also allowed minimal internal temperatures in the cartridge heaters increasing heater life and preserving excellent dielectric strength, two essential criteria for this application. BCE’s contribution proved to be a huge success in the design and operability of these tipping bucket rain gauges.

Contact BCE for any electric heating design or application. You'll be pleased with BCE's experience, knowledge, and service. Visit them at http://belilove.com or call (510) 274-1990. Download the PDF Application Note here.

Swaged vs. Standard Cartridge Heater Design and Heater Life

Cartridge heaters provide localized heat to restricted work areas requiring close thermal control. Dies, platens and a variety of other types of processing equipment are efficiently heated. Closely controlled work temperatures up to 1400° F (760° C) are obtained by a combination of heater location and proper wattage output.

Heater Life

Cartridge heater life is determined by how efficiently the heat generated in the resistance wire can be conducted away from the wire and into the part being heated.  The efficiency of heat transfer is generally controlled by three factors:

1. Resistance wire watt density
2. Density of insulating material around the wire
3. Fit of the heater into the heated part

There are two basic designs of cartridge heaters - swaged and standard. Although both type heaters look identical, the internal construction is very different.

Standard Cartridge Heater Design

Standard Cartridge Heater Design

Nichrome wire heating coils are inserted in holes formed in ceramic tubes. Pure magnesium oxide filler is vibrated into the holes housing the heating coils to allow maximum heat transfer to the stainless steel sheath. The heater then has a Heliarc welded end cap inserted on the bottom of the heater and insulated leads are installed. The MGO powder is not compacted and heat transfer is a function of the grain-to-grain thermal conductivity to the heater sheath, and then into the heated part. Because of this, the heater wire watt densities must be kept in the low to medium range.

Swaged Cartridge Heater Design

Swaged Cartridge Heater Design

Swaged cartridge heaters wind Nichrome wire around a precision ceramic core and the carefully position the resistance wire and ceramic core uniformly inside the the heater sheath. Pure magnesium oxide (MgO) powder is then vibrated in and the heater is swaged to a specific diameter. Swaging is a process that mechanically forces the heater through a confining die to reduce its diameter and thus compact the powdered MgO to rock-like consistency for greater thermal conductivity. This compressed MGO transfers the heat from the resistance wire much more efficiently. The improved heat transfer allows for higher wire watt densities allowing swaged cartridge heaters to operate at higher temperatures.

Cartridge Heater Fit

The most common cause of cartridge heater failure is an improper fit in the hole into which it is inserted. If the heater is surrounded by air, an excellent thermal insulator, it cannot dissipate it's heat into the part with optimum efficiency. The result is much higher temperatures on the Nichrome wire and failure.  The goal to longer life with cartridge heaters is to accommodate the tightest fit practical for a given application.

In summary, if you want the longest life cartridge heater, choose a swaged heater and make sure you provide a machined, close tolerance fit between the outside diameter of the heater and the inside diameter of the hole.

Why Cartridge Heaters Fail

By understanding the most common reasons cartridge heaters fail, users can take preventative steps in their applications to achieve optimum heater life and lower equipment ownership costs.

Improper Fit
The most common cause of cartridge heater failure is an improper fit in the hole into which it is inserted. If the heater cannot dissipate the heat being generated and produced by contact with the sheath, the temperature inside the heater will continue to rise until the heater fails.

Moisture and/or Impurities
The MGO used in cartridge heaters is hydroscopic. Every time power to electric heaters is eliminated, an internal vacuum occurs which draws in air from the surrounding area. If moisture or impurities (oil, gas, etc.) are present, they can be drawn in to the heater, and cause a short circuit resulting in a heater failure.

Watt Density is Too High
If the watts/square inch is excessive, the heater will not be able to dissipate the heat and the heater will fail.

Incorrect Voltage Applied
The wattage of any electric heater varies as the square of the voltage. If a 120 Volt heater is powered on 240 Volts, the wattage will be 4 times greater than that for the same 120 Volt heater. Under normal conditions, this may result in heater failure.

Frequent Temperature Cycling
Rapid cycling of heaters from very low to very high temperatures shortens their life considerably.

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About BCE

BCE is a recognized leader in manufacturing and applying resistance heating elements in many industries, including medical, analytical, packaging, process, food equipment, and aerospace. BCE's extensive standard and custom product lines include:

• Cartridge heaters
• Immersion heaters - ideally suited for heating various liquids
• Air process heaters - for providing hot air and gas up to 1,400 degrees
• Stainless steel strip and thin strip heaters in various sizes
• Self-contained one-piece assembly coil and rope heaters
• Tubular and finned tubular heaters - specially built to resist impact, vibration corrosion and temperature extremes
• Band heaters for a multitude of applications
• Ceramic and crankcase heaters

For more information, visit http://heater.belilove.com or call (510) 274-1990.

Electric Heaters 101: Get the Heat Out of the Heater

Internal view of swaged cartridge heater.

Metal-clad electric heating elements share one very common and very important requirement for optimal performance - get the heat away from the resistance wire and into the work as efficiently as possible.

At the heart of most resistance type electric heaters is a nichrome alloy wire, or ribbon, referred to as the heating "element". It acts as a resistor to the electrical current and gives off heat. With sheathed heaters, the heating element is then wrapped in some sort of electric insulating material such as mica or magnesium oxide (MgO), and then encased in a metallic sheath. Unfortunately, both the electric insulator and the metallic sheath act as heat insulators to some degree, which cause the nichrome wire to get very hot. Nichrome wire has a melting point of 1400 deg. C (about 2500 degrees F). While this sounds high, the wires and ribbons can easily exceed these temperatures in normal operation when not allowed to adequately conduct heat.

Very often electric heater failure can be directly attributed to poor conductivity between the heating element and the process medium. Whether it be a cartridge, strip, band, duct or immersion heater the principle is the same - lower resistance wire temperatures equal longer heater life.

When applying cartridge heaters, special care has to be taken to the bore tolerance of the hole where the heater is inserted. The tighter the bore tolerance, the more efficiently the high internal wire temperatures are conducted away.  Tolerances of several thousandths of an inch can change the life expectancy of a cartridge heater significantly.

Strip and band heaters require tight, full surface area clamping to maximize life and performance, while duct heaters and immersion heaters require circulation to transfer heat away from the element, and keeping resistance wire temperature within reasonable operating limits.

Internal view of band & strip heater.

Any situation where the heater is exposed to a stagnant air gap (or stagnant fluids) will most likely result in over temperature of the wire and failure at that point.  With this in mind, anyone applying traditional resistance type, electric heating elements must be very aware of maintaining very intimate contact between the heating element and the item or process being heated.

Whenever applying electric heating elements, the consultation of an applications expert is always recommended. They will be able to consider many other operational factors such as wire watt density, conduction properties, control scheme and overall thermal system dynamics.

Electric Heating Element Types and Selection Guide

The following, courtesy of Hotwatt,  is a good reference for selecting an electric heating element for both OEM and process heating applications.

Included are all types of industrial electric heaters - cartridge, band, tubular, immersion, duct, circulation and cable.

OEM & Industrial Electric Heating Element Catalog by Hotwatt from Belilove Company-Engineers

Cartridge Heaters

Styles of Cartridge Heaters

A cartridge heater is a cylindrical electric heating element constructed by tightly winding nichrome wire around a ceramic bobbin, and inserting the wound bobbin into a metallic tube (sheath). The tube is then backfilled with magnesium oxide (MgO) powder to electrically insulate the nichrome wire from the sheath. The heater diameter is then reduced (swaged) to compact the magnesium oxide for better dielectric, while at the same time improving thermal conductivity.

Cartridge heaters come in many diameters and lengths. They vary in voltages, wattages and watt densities. Sheath materials are typically Stainless Steel of Incoloy 800. The electrical leads terminate from one end of the heater and vary in length and insulation material, depending on application and operating temperatures.

Most cartridge heaters are used in some form of die or platen heating. A close tolerance hole is drilled into a metal block, and the proper diameter heater is then inserted in to the hole. It is best to make sure the diameter of the heater is just a few thousands of an inch less than that of the hole, so that maximum surface contact, thus thermal conductivity, can be achieved. A loose fit will cause the internal temperatures of the cartridge heater to climb and the heater will fail prematurely.

Common die heating, or platen heating, applications are:

• Injection mold platen heating
• Heating medical equipment components
• Compressor sump heating
• Bolt heating
• Extruders
• Packaging equipment
• Sealing equipment
• Analytical equipment

Looking for an excellent source for stock cartridge heaters? Check out his link.