Application Of Cartridge Heaters
Cartridge heaters are most frequently used for heating dies, platens, molds and other metal parts by insertion into drilled holes. For easy installation, the heaters are made slightly undersized relative to the nominal diameter of the drilled hole.
When low and medium Watt density cartridge heaters (60W/in2 or less) are used in a low temperature application (600°F [315°C] or less), general purpose drills are usually adequate for drilling holes. Typically, drilled holes are .003" to .008" over the nominal size of the drill, resulting in fits of .009" to .014". Of course, a much tighter fit is preferred from a heat transfer standpoint, but a somewhat looser fit aids in the installation and removal of the cartridge heaters, especially heaters with long sheaths. Holes drilled completely through the part are also recommended to facilitate removal of the heater if necessary. After drilling, clean or degrease the part to remove cutting lubricants and any particles that remain from the drilling process.
At high watt densities, a close fit is much more important. The holes for high Watt density cartridge heaters should be drilled and reamed, rather than being just drilled with a general purpose bitl. For example, a nominal 1/2" diameter OMEGA cartridge heater is actually .496" ±0.002. If this heater is placed in a hole which has been drilled and reamed to a diameter of .500", the maximum fit is now .500"- .494" = .006". With a tighter fit, the heater will run cooler and have a longer life expectancy in the application.
Learn more about Temperature Sensors and Controllers
Temperature Sensors and Controllers for Cartridge Heaters
The sensor for the control of part temperature is an important factor in application design. Sensors should be placed between the working surface of the part and the heaters. Measuring the temperature of the part approximately 1/2" away from the heaters is generally recommended. Note that this value was used to develop the Fit Graph that is commonly used in the election of the maximum allowable Watt density (see Frequently Asked Questions on the next page). Depending on the application, there are a variety of other temperature sensors and controllers that can be used.One of the more popular sensor types used for cartridge heater applications are surface mount sensors. Thermocouples,RTDs and Thermistors are available with either an adhesive backing or the ability to be cemented to the surface being heated. There are also bolt on and magnetic surface mount type sensors available.
Control of power is also an important consideration, particularly in high Watt density applications. Inexpensive on-off controls are frequently utilized, but they often result in wide excursions in the temperature of the working parts and the heaters which can significantly shorten their life. Thyristor power controls and other digital temperature controllers are valuable in that they effectively eliminate on-off cycling which substantially extends the life of high Watt density heaters, they come in many different sizes with many output and input choices. Thermocouple and RTD inputs are the most popular with a DC pulse output. DC pulse outputs allow the user to use larger relays to switch the heater load.
Temperature Controllers and Related Products
Cartridge Heaters - Product Specifications
OMEGALUX PREMIUM CIR Series Cartridge Heaters - Specification Sheet
OMEGALUX™ CIR Series high watt density cartridge heaters are manufactured to the highest industry standards using only premium materials. They have been designed to last longer and outperform any other brand cartridge heater in both industrial and laboratory applications. Their heavy duty construction provides high dielectric strength as well as shock and vibration resistance. The Incoloy® 800 sheath material allows Working Temperatures up to 1400°F (760°C) . Maximum sheath temperature is 1600°F (870°C).
HI-DENSITY Series Cartridge Heaters - Specification Sheet
Hi-Density Series cartridge heaters provide Maximum Processing Temperature Capability in most Commercial, Industrial and General purpose applications. These Multi-purpose Cartridge Heaters are an excellent solution to OEM or Maintenance applications. Standard sheath material is 321 Stainless Steel. This alloy provides high temperature strength for Working Temperatures up to 1050°F (565°C) with good thermal conductivity and resistance to corrosion and scaling. Maximum sheath temperature is 1200°F (650°C). For higher operating temperatures or corrosive environments, Incoloy® 800 is available. Consult OMEGA for availability and price.
LOW DENSITY Series Cartridge Heaters - Specification Sheet
Low Density Series cartridge heaters are economical and reliable cartridge heaters for both Laboratory and Industrial applications where lower operating temperatures and Watt densities may be used. The sheath material is Alloy 304 stainless steel. This alloy provides high temperature strength, good thermal conductivity and resistance to oxidation for Working Temperatures up to 1050°F (565°C). Maximum sheath temperature is1200°F (650°C).
Frequently Asked Questions
What is Watt Density?
The term "Watt density" refers to the heat flow rate or surface loading of the cartridge heater sheath. It is the number of Watts per square inch of the heated surface area. For calculation purposes, stock cartridge heaters typically have a 1/4" unheated length at each end. Thus, for a 1/2" x 12" heater rated 1000 Watts, the Watt density calculation would be as follows:
Watt Density = W / (Π x D x HL)
W= wattage = 1000 W
Π = pi (3.14)
D= diameter = 0.5 inch
HL = Heated Length = 11.5 inch
Watt Density = 1000/(3.14 x .5 x 11.5) = 55 W/in
What is Fit and How is it Determined?
The difference between the minimum diameter of the cartridge heater and maximum inside diameter of the hole it is installed in is called the "Fit" All cartridge heater sheath materials have a maximum recommended operating temperature. Fit is a very critical factor in that it determines the rate at which heat energy is being transferred from the cartridge heater sheath to the product being heated. The tighter the fit, the better the heat transfer from the cartridge heater sheath material to the block or product that the heater is installed in and the lower the temperature of the sheath material in the application.
The temperature of the sheath material in any particular application is based three variables, the heat flux of the heater (watt density), the rate heat energy is transfered to the product being heated and the operating temperature of the process. Since it is normally very difficult in most applications to measure the temperature of the cartridge heater sheath, the Graph at right, based on empirical data of various fits, provides a universally recognized guide for the selection of a heater for a specific application.
For more information on cartridge heater applications, design calculations & installation see the "Cartridge Heater Information" site referenced below.
What is the Life Expectancy of a Cartridge Heater?
The life expectancy of a cartridge heater is determined by the operating temperature of the resistance wire. The higher the operating temperature of heater sheath (watt density), the higher the temperature of the internal resistance wire and the shorter the life of the heater.
For that reason the temperature gradient between the resistance wire and sheath of the cartridge heater should be kept as low as possible. It is better to use more heaters with a lower watt density spaced close together than fewer heaters with higher watt density spaced further apart.
Applications and Installation
Watt Density and Fit
Recommendations for Application, Installation and Selection of Cartridge Heaters. Includes Definitions of Watt Density and the Determination and Importance of Proper Fit.
Other Cartidge Heater Products
Heavy Duty Cartridge Heaters
OMEGALUX™ C Series heavy duty cartridge heaters are especially suited for use in applications involving hot plates, molds, dies, platens and container heating.
CSS and CSH Series
Stainless Steel Sheath Cartridge Heaters, Standard and High Watt Density Construction.
CHSA, HTRC and SCB Series
Cartridge Heater Sleeve Adapters, Heat Transfer and Release Coating, Unique Space Heater SCB Series
8 mm (0.315") Diameter Round Heater with Sealed End and Single End Termination
Electric Stud Heaters
CBH Series heaters are constructed of rugged metal sheathed tubular elements homogeneously combined with a metal sleeve that has been accurately dimensioned to provide a proper clearance and ease of inserting into standard drill hole sizes so large bolts or studs may be rapidly expanded and tightened with a wrench, providing ''shrink fit tightness" when cool. Useful in assembly of large compressors, presses, turbines, die blocks, cylinders, engine heads, pressure vessels, etc. Quick heat-up heat up is important to avoid heat drain-away of surrounding metal. CBH heaters are generally used in sets to permit uniform tightening of mating parts.
Cartridge Heater | Related Products
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