Guide to Cartridge Heaters
A cartridge heater is an industrial heating element that uses conductive heat to precisely control temperatures. They are widely used in manufacturing processes that require direct and localized temperature control.
How Cartridge Heaters Work
Cartridge heaters have a ceramic core with a resistance wire wound around it in a specific manner which will transmit thermal heat in the desired application period. This dielectric assembly is then encased in a steel or stainless steel sheath, which absorbs the powered heat from the coil and radiates it to the surrounding environment or processes to be heated. Typically, cartridge heaters are inserted directly into the item or process to be heated. However, the entire heating assembly can be manufactured with more than one power zone for multiple heat transfer points.
Cartridge heaters are also designed with an insulating material, such as magnesium oxide, placed between the casing and the resistance wire, and the metal tube is compressed to fit the diameter and tolerance required of the machine or process. The maximum heat transfer, efficiency, and service life of the cartridge heater are determined by the proximity of the resistance wire to the metal sheath and how tightly compacted the internal insulation is.
Advantages
Imperial or metric cartridge heaters are preferred over other heaters in some industrial applications, including plastic molding, laminating presses, medical equipment, and hot runner molds. This is because they offer many advantages, including, but not limited to:
- Uniformity: Cartridge heaters can uniformly heat in multiple power zones, and there are fewer cold spots due to their continuous coils.
- Customizable: They can be customized to fit unique heating profiles.
- Versatility: Imperial and metric cartridge heaters are available in many power specs and sizes.
- Costs: They are generally more cost-effective than mica heaters.
- Ease of Use: Cartridge heaters are easy to install, maintain, and replace.
Disadvantages
Many of the disadvantages associated with cartridge heaters have to do with their suitability for the application or process in which they are used. Other disadvantages are inherent to the design and include:
- Operating Temperature: Cartridge heaters will run at temperatures up to 1,400°F provided the correct setup is in place.
- Heat Dissipation: The heat sink must be thicker in the cartridge heater for efficient heat dissipation.
- Bore Hole Fit: They require a bore hole fit with tighter tolerance for maximum heat transfer.
- Risk of Bore Seizing: A cartridge heater with an overly tight fit in the bore is at a higher risk of seizing. Please note that some manufacturers offer anti-seize coating to help reduce this risk.
Common Causes of Failure
Environment: Premature failure or cartridge heaters can occur when the environment doesn’t support efficient thermal dissipation or when the surrounding air holds too much moisture or contaminants. The hygroscopic nature of magnesium oxide can draw in these vapors that can result in an internal short circuit. High-quality cartridge heaters may be waterproofed and sealed to reduce these complications.
Loose Bore Hole Fit: The most common cause of cartridge heater failure occurs when the bore hole fit is too loose to ensure adequate thermal dissipation. The bore hole must be held to a tight tolerance to avoid an improper fit, especially when the component is a high-density cartridge heater.
Incorrect Supply Voltage/Watt Density: Finally, an incorrect supply voltage or the wrong watt density can result in a shortened heater life due to the internal temperature of the heater exceeding the limits of the resistive heating element.
Types & Applications
Some industries use mica heaters, which may provide convective and radiant heating. Generally, for most applications, the benefits of high-density cartridge heaters outweigh the disadvantages.
There are many types of standard and metric cartridge heaters that are available in various sizes, lengths, shapes, and power wattage to meet a wide range of localized heating requirements. They are primarily split into three sub-categories: high-density, low-density, and split-sheath.
High-Density
High-density cartridge heaters are designed to absorb shock and vibration, perform in high operating temperatures, and overcome expansion and contraction due to temperature cycling, making them ideal for rugged environments.
High-density cartridge heaters are primarily used to deliver high heat for tempering metallic parts with closed structures such as die blocks and plastic injection molds. Other industries that benefit include food service equipment, hot stamping, semiconductors, and hot runner molds.
Low-Density
Low-density cartridge heaters are typically constructed of nickel chrome resistance helically-wound wire placed in an insulating body. These heaters are more economical and are used in lower-temperature operations with little or no impact or vibration. These heaters are often selected to meet the demands of specific applications, such as heating fluids, printing, packaging, and heating molding press platens.
Split-Sheath
Split-sheath cartridge heaters are designed for outward and independent expansion along each half of the heater for maximum metal-to-metal contact, which results in maximum heat transfer. Also, higher-grade magnesium oxide is used and more tightly compacted to increase heat transfer and dielectric strength away from the coil.
Split-sheath heaters are designed for equipment with bore holes that are poorly drilled and are more commonly used for platen, die, or mold industrial heating applications.
How to Choose the Right Cartridge Heater
Factors to consider when selecting a heater include:
- Whether the application is vacuum sealed
- The likelihood of rapid temperature fluctuations
- The number of standard temperature zones that must be heated
When choosing a cartridge heater, design specifications such as material, shape, and maximum temperature are primary considerations. You will find cartridge heaters in a wider array of performance specs, and they can be custom-built to supply heat to independent zones without cold spots.
Have Questions? Contact Hi-Watt Today!
Founded in 1979, Hi-Watt is an established regional supplier of custom cartridge heaters. We carry high-quality products from brands we know and trust, including Watlow, Tempco, Chromalox, and Dalton Electric. Visit our website to learn more about our products, or contact us today if you need help selecting the right cartridge heater.