This article contains everything you need to know about Cartridge Heaters.
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A cartridge heater is a cylindrical heating element designed to deliver accurate and consistent heat to a variety of materials, machinery, and other equipment. In contrast to an immersion heater, a cartridge heater is inserted into a pre-drilled hole within the object that requires heating, supplying internal radiant heat. These heaters are extensively used in manufacturing operations to provide specifically targeted localized heat.
Engineered for easy installation, cartridge heaters ensure uniform heat distribution and feature watt densities tailored for unique applications. Their diameter is slightly smaller than the hole into which they're inserted, ensuring a snug and secure fit for optimal performance.
Cartridge heaters commonly heat metal blocks from the inside at a specified wattage to suit various applications. For this purpose, a hole is drilled into the metal block or die, with a diameter larger than that of the cartridge heater.
The construction of a cartridge heater starts with a ceramic core around which a resistance wire is wrapped. This core and wire are then encased in a dielectric metal sheath, typically made of steel or stainless steel. Heat is transferred from the resistance wire to the sheath and then to the material being heated.
Cartridge heaters can operate at low, medium, or high wattages and are designed to endure temperatures up to 1400°F (760°C). They provide localized, accurate, and precise heat, making them suitable for a wide range of manufacturing applications.
Selection and installation of a cartridge heater are based on its wattage and the specific heating requirements of the application.
The use of a cartridge heater starts with its insertion point. For heavy-duty cartridge heaters, there is a designated insertion port on the device to be heated. In applications involving metal molds or metal blocks, appropriate holes are drilled for this purpose.
For uniformly shaped pieces that need heating, drilling a hole for the cartridge heater ensures even heat distribution. However, for complex machinery and molds, hole placement becomes more intricate and requires careful planning to achieve precise results.
The image below depicts a plastic mixing block featuring an insertion point for a ten-inch cartridge heater with a five-inch heating length.
When placing a cartridge heater, it's crucial to consider the diameter of the heater relative to the placement hole. Generally, the heater's diameter should be 0.004 inches smaller than the hole it is being installed into. As a result, the actual diameter of a cartridge heater will always be slightly less than its labeled size. The chart below serves as a reference guide for matching hole diameters with cartridge heater sizes.
| Cartridge Heater Diameter | |||||
|---|---|---|---|---|---|
| Imperial | Metric | ||||
| Hole Diameter | Actual Maximum Diameter | Actual Minimum Diameter | Hole Diameter | Actual Maximum Diameter | Actual Minimum Diameter |
| 0.125" | 0.124" | 0.120" | 6 mm | 5.97 mm | 5.87 mm |
| 0.16" | 0.155" | 0.152" | 6.5 mm | 6.48 mm | 6.38 mm |
| 0.19" | 0.186" | 0.183" | 8 mm | 7.98 mm | 7.85 mm |
| 0.25" | 0.249" | 0.244" | 10 mm | 9.96 mm | 9.85 mm |
| 0.31" | 0.312" | 0.308" | 12 mm | 11.96 mm | 11.86 mm |
| 0.38" | 0.374" | 0.369" | 12.5 mm | 12.47 mm | 12.34 mm |
| 0.5" | 0.499" | 0.494" | 13 mm | 12.98 mm | 12.85 mm |
| 0.625" | 0.624" | 0.619" | 15 mm | 14.99 mm | 14.86 mm |
| 0.75" | 0.749" | 0.741" | 16 mm | 15.95 mm | 15.82 mm |
| 0.94" | 0.936" | 0.928" | 17.5 mm | 17.47 mm | 17.27 mm |
| 1" | 0.999" | 0.991" | 20 mm | 19.96 mm | 19.76 mm |
| 1.25" | 1.249" | 1.241" | - | - | - |
| 1.9" | 1.910" | 1.890" | - | - | - |
| 2.38" | 2.385" | 2.365" | - | - | - |
The heated length of a cartridge heater is defined as the total length of the heater minus the unheated or cold sections. For optimal performance, the heated length should align with the length of the item being heated. Unheated sections can lead to hot spots and potentially cause heater failure. For high-density cartridge heaters, the standard unheated lengths are 10 mm at the lead end and 6 mm at the disc end. For example, a 152 mm heater would have a heated length of 136.5 mm.
The operating temperature of a cartridge heater varies based on the application. Key factors affecting the operating temperature include watt density, the fit of the heater within the hole, and the thermal conductivity of the material being heated. For high-temperature applications, a specialized electrical terminal is required, and lead wires should be kept below their maximum temperature rating to ensure safety.
Watt density refers to the rate of heat flow or surface loading, measured in watts per square inch of the heated surface area.
It is crucial to keep the leads and the end of the heater free from water, moisture, plastic, or other contaminants. If moisture is present, it can be removed by baking the cartridge heater in an oven.
To prevent overheating, ensure the heater fits snugly in the hole. An improper fit can cause the heater to overheat and burn out. Additionally, the leads should be positioned outside the hole to dissipate heat, and the heated length should be fully enclosed within the material being heated.
The heater should be operational approximately 80% of the time. Frequent cycling between hot and cold conditions can cause internal wires to oxidize, leading to heater failure.
Ensure the bore fit is ideal for the application. A poor fit can lead to the heater seizing inside the bore, potentially blocking the hole.
The cartridge heater should not be completely enclosed within the hole. A part of the heater, typically the leads, should be outside. However, the heater must be fully inserted with no gaps at the inserted end, especially with regard to the heated length.
A cartridge heater should not be operated at its maximum watt density. Controlling the watt density to a lower level can significantly extend the heater's lifespan.
The image below shows a three-zone multi-zone cartridge heater being inserted into a nine-zone plate.
Effective power control is crucial for high watt density applications. While on-off switches can be employed, they often result in temperature fluctuations in both the heater and the part being heated. Thyristor power controls offer a more stable solution by extending the heater’s life and eliminating the issues associated with on-off cycling.
There are several types of temperature controls and sensors that can be used with cartridge heaters. Surface mounted temperature sensors are used the most. Thermocouples, RTDs, and thermistors have an adhesive backing allowing them to be mounted on the surface of a heater.
Digital temperature controllers come in multiple configurations, with different input and output options. Thermocouple and RTD inputs are popular choices, typically paired with a DC pulse output. This output type allows for the use of larger relays to switch the heater load and facilitates proportional control.
Using a cartridge heater control system can significantly enhance the longevity and effectiveness of a cartridge heater. While on-off switches offer convenience, they lack the precision and accuracy required for optimal heating processes.
Cartridge heaters vary in several aspects, including maximum temperature, watt density, application type, heated length, overall length, tube diameter, and the type of heating element. These factors influence both the selection and usage of the heater.
While the fundamental construction of cartridge heaters—including wiring, core, and casing—is generally consistent, there are differences in the metals, wires, and cores used. The quality and durability of a cartridge heater are significantly impacted by the materials and manufacturing processes involved.
Cartridge heaters equipped with a thermocouple heat the surface directly and utilize complex formulas to determine wattage, density, and fit. The internal thermocouple measures the sheath temperature, making these heaters suitable for applications with limited space. Thermocouples monitor the sheath temperature of an electric radiant element and send a 4 to 20 mA signal to the DCS when the set temperature is exceeded.
The primary function of thermocouples is to provide overtemperature protection. Both the power and sensor leads of the thermocouple are positioned outside the sheath. There are various types of thermocouple-equipped cartridge heaters designed for specific applications, with the thermocouple typically attached to the middle or inside of the heater.
Flanged cartridge heaters feature a flange permanently attached to the exterior end of the heater, allowing them to be securely mounted to the component being heated. This design ensures a more stable and reliable fit.
During the swaging process, all components of the heater—such as the core, resistance wiring, and oxide powder—are assembled before the heater undergoes swaging. Mechanical swaging involves forcing the heater into a die, which compresses and reduces its diameter while compacting the internal components. This process improves heat transfer and enhances the heater's efficiency.
Magnesium oxide is the powder used to fill the elements. It acts as an electrical insulator, allowing heat to pass through while preventing electrical shock if the energized element is touched.
Miniature cartridge heaters typically have a length of three inches or less and come in diameters of 3.175 mm, 3.97 mm, and 4.76 mm. The exterior of these heaters is usually constructed from 304 or 316 stainless steel. Most miniature heaters are swaged to provide resistance to shock and vibration, as well as to enhance dielectric strength.
In multi-zone cartridge heaters, each section is equipped with its own wound coil and power leads, with two leads per zone. Some configurations include a single common wire for one of the leads, enabling individual control of each zone. A key advantage of a multi-zone system is the ability to deactivate specific zones when they are not needed, thereby reducing overall energy consumption.
Square cartridge heaters feature a square or rectangular shape, as opposed to the traditional round diameter. They offer the same performance capabilities as round tubular cartridge heaters and can be swaged and compacted. These heaters can be clamped into milled slots on a tool surface, providing a cost-effective heating solution. Their unique design also facilitates easy removal for cleaning and maintenance.
Similar to flanged cartridge heaters, threaded fittings ensure a secure and tight fit of the cartridge heater in its application. They facilitate quick and easy removal and installation. Additionally, moisture seals are often included to provide extra protection.
The split sheath design of cartridge heaters allows for expansion, which maximizes heat transfer by increasing contact with the bore walls. In this design, the ceramic core is replaced with tightly packed magnesium oxide (MgO) surrounding the heater coil. This configuration enhances dielectric strength and heat transfer. The increased stability and strength of split sheath cartridge heaters improve their longevity and help prevent bore seizure.
High-density cartridge heaters provide exceptional power relative to their size and distribute heat evenly across the heater's casing. They are designed to endure harsh conditions, including high temperatures, vibrations, shocks, and thermal expansion and contraction. Standard high-density cartridge heaters feature a cylindrical ceramic core with tightly wound resistance wire. This arrangement allows the heater to accommodate multiple power zones.
High temperature cartridge heaters are made for high temperature applications with temperatures that range between 1400°F or 760°C up to 1600°F or 870°C. Most high temperature cartridge heaters are swagged to maximize heat transfer and vibration resistance. Typical applications that use high temperature cartridge heaters are hot stamping, heat staking, sealing bars, forming, and heating platens.
The primary function of a cartridge heater is to provide localized heat for various manufacturing processes. They are engineered for optimal performance, delivering heat precisely and efficiently.
The effectiveness of a cartridge heater hinges on its dielectric strength, heat transfer to the sheath, and heat transfer from the sheath to the metal being heated. Dielectric strength is measured by the heater's ability to maintain electrical insulation and prevent current leakage within the coil.
The die casting process involves injecting molten metal into an open or closed die to create various shapes and forms. A critical aspect of this process is monitoring and controlling the metal’s temperature. Cartridge heaters are installed in holes within the die to precisely regulate the temperature of the molten metal. This careful control ensures the quality and consistency of the final casting.
The molding process shares similarities with the die casting process but differs in materials and techniques. As with dies, it is crucial to monitor the solidification temperature of the heated metal closely. Cartridge heaters are inserted into the mold to help regulate this temperature. During solidification, the cartridge heater maintains a consistent heat, preventing weaknesses and unevenness in the molded part.
In injection molding, cartridge heaters provide precise temperature control, enhancing the process's efficiency. Their effective heat transfer capabilities ensure that the desired temperature is reached quickly, minimizing time and energy waste.
Food production requires the same level of accuracy and control as die casting and molding, with the primary focus on ensuring precise food preparation. This is particularly critical in high-volume food production, where maintaining a constant cooking temperature throughout the production run is essential. Cartridge heaters play a crucial role in achieving consistent heat control across all stages of food preparation.
Precise heat control is crucial in medical treatments to ensure patient safety and the effectiveness of various procedures. Cartridge heaters are used in applications such as regulating the temperature in baby incubators, kidney dialysis machines, and injector ports. They are instrumental in heating aluminum or stainless steel subassemblies, providing exceptional heat transfer and uniform temperature across a range of medical applications.
Engine block heaters are essential for preventing coolant and lubricants from freezing, which can cause severe damage to the engine. At extremely low temperatures, ice formation in the cooling galleries can force core plugs out of the engine block. Expansion plugs, sealing discs, Welch plugs, or core plugs are used during engine casting to seal the holes left in the engine block.
Among the various types of block heaters, cartridge heaters are the most effective and easiest to install. They utilize thermal induction to quickly and efficiently heat the fluids in an engine, preventing freezing and ensuring reliable operation.
During the extrusion process, it is crucial that molten plastic is evenly heated as it is pushed through the mold by the screw. Cartridge heaters are installed to ensure consistent heat, which is vital for the stability and quality of the extruded products.
Cartridge heaters offer several advantages for extrusion, including rapid heating and a long service life. Like all cartridge heaters, those used in extrusion processes must be customized to fit specific applications and are typically inserted into the die to maintain a constant temperature.
Although cartridge heaters vary in use and type, their main components remain consistent, though they are adjusted to meet specific heat and size requirements. One key factor that engineers focus on is watt density, which measures the rate of heat transfer through the heater's surface.
Watt density significantly impacts the lifespan of a cartridge heater. Higher watt density results in higher internal temperatures, pushing the heater's components to operate at their maximum allowable limits. Excessive temperatures can reduce the heater’s longevity.
The basic structure of a cartridge heater includes a ceramic core, resistance wire, insulation, a sheath, and lead wires. Manufacturers may arrange these components differently to enhance the heater’s quality and heating performance.
The split sheath type of cartridge heater eliminates the core and features a continuously running wire immersed in insulating material. This design is a recent innovation aimed at addressing specific limitations of traditional cartridge heaters.
Ceramic is a commonly used material for the core, but magnesium is also employed in some cartridge heaters. For heaters that include a core, the resistance wire, typically made of nickel-chromium, is wound around it.
The heating coil, or resistance wire, is responsible for the electrical load. Various types of resistance wire are available, with nichrome (NiCr), a nickel-chromium alloy, being the most prevalent. Nichrome is widely used in heating elements such as toasters and space heaters. The watt density is determined by the number of wire turns per inch around the core. As current flows through the wire, it heats up and subsequently heats the sheath of the cartridge heater.
Insulation, usually magnesium oxide (MgO), is used to prevent the resistance wire from coming into contact with the sheath. If the wire touches the sheath, it can cause grounding, short circuits, and melting of the sheath, leading to heater failure.
During the filling process, the sheath is vibrated to ensure the MgO insulation is tightly packed. Further packing and tightening occur when the cartridge heater is swaged.
The sheath serves two main functions: it houses the cartridge heater's internal elements and transfers heat to the material being heated. It remains in constant contact with the material to ensure efficient heat transfer.
Sheaths are typically made from alloyed metals, including stainless steels 304 and 316, and Incoloy 800. For specific applications, the sheath can be designed to resist acid and corrosion.
The chart below lists some common metals used for sheaths, with nichrome and Incoloy being among the most frequently used.
| Sheath | |
|---|---|
| Metal | Sheath Characteristics and Color |
| Aluminum | Silver White, Malleable, Duct, Light Weight With Good Electrical, Thermal Conductivity, and Oxidation Resistant. |
| Brass | Excellent Strength, High Temperature Resistance, Electrical Conductivity, Corrosion Resistance, and Low Magnetic Permeability. |
| Copper | Reddish, Ductile, Malleable, Heat Conductivity, and Electricity Conductivity. |
| Iron | Heat and Electricity Conductivity and Strongly Magnetic. Usually Combined with Other Metals. |
| Nickel Alloys | Most Common of the Sheath Materials. Corrosion Resistant and has Exceptional Strength. |
| Nichrome | High Thermal Conductivity, High Operating Temperature, Corrosion Resistant, Oxidation Resistant. |
| Stainless Steel | Chemical and Corrosion Resistant With A High Pressure Rating. |
| Steel | Malleable, Ductile, Exceptional Tensile Strength, Conductive, and Durable. |
The sealing process is essential for containing and securing the contents of the cartridge heater. It is completed once the MgO insulation has been tightly packed around the coil and core. Epoxy is a commonly used sealing material, as it ensures the heater can pass various electrical tests, maintains dielectric strength, and prevents electrical shorts.
Termination types vary widely depending on the cartridge heater type and manufacturer. As shown in the diagram below, leads can exit the cartridge heater in several configurations, with straight leads being the standard method. In applications where leads might be exposed to harsh chemicals or extreme temperatures, they are often shielded with metal or silicone for added protection.
The types and specifications of lead wires vary based on the conditions in which the cartridge heater will be used. The lead wire provides the crucial electrical connection for the heater. Since it is vital for the heater's efficient operation, it is carefully chosen to suit the specific application and conditions. For high-temperature applications, fiberglass-insulated wire is commonly used. The chart below offers an overview of different cartridge lead wires, including their temperature ratings and characteristics.
| Cartridge Heater Lead Wires | ||
|---|---|---|
| Type Wire | Rating | Qualities |
| Durable | 1022°F / 550°C | Flexible Not Waterproof |
| TGGT | 482°F / 250°C | Durable Not Waterproof |
| Teflon | 482°F / 250°C | Abrasion Resistance, Waterproof Small OD |
| Silicon Rubber | 302°F / 150°C | Flexible, Waterproof Easily Marked |
| Braided Silicon Rubber | 392°F / 200°C | Flexible, Waterproof Abrasion |
Cartridge heater seizing can significantly disrupt production and efficiency. When a heater seizes, it becomes stuck in the application and must be removed by drilling, leading to substantial delays.
To address this issue, split sheath cartridge heaters were developed. These heaters expand within the hole to ensure proper contact with the material being heated. As the heater cools, it contracts and can be easily removed.
Another method to prevent seizing involves using an anti-seize coating applied during the insertion of the cartridge heater. This coating, which is high-temperature, insulating, and thermally conductive, reduces oxidation and enhances heat transfer. It can be brushed or sprayed on to form a thin layer, facilitating easier insertion of the heater into the hole.
The diagram below illustrates the various components and parts of a completed cartridge heater.
Cartridge heaters are crucial for industrial processes that demand localized heating. Their popularity stems from their efficiency, precision, responsiveness, and reliability in providing heat.
These heaters are remarkably durable and can operate effectively under the harshest conditions. They can be customized and designed to suit a wide range of industrial heating applications, from warming molten plastic to maintaining the temperature of metal molds.
The diverse sizes, types, configurations, and adaptations of cartridge heaters make them an ideal solution for delivering directed heat. They are versatile enough to fit any application that requires a concentrated heat source, ensuring precise heat transfer to the desired focal point.
Cartridge heaters also play a crucial role in regulating the temperature of devices and components that are sensitive to condensation, such as control panels and closed circuits. In the packaging process, they ensure the consistent flow of glue, contributing to a smooth and efficient operation.
Manufacturing processes often require equipment that can withstand harsh conditions. Cartridge heaters are designed to meet these demands, being durable and robust enough to handle heavy impacts and high pressures. They are built to perform reliably in tough environments, making them a top choice for effective heat transfer.
Many industrial applications demand precise and controlled heat to meet specific requirements. Cartridge heaters excel in this area, providing highly focused and controllable heat to ensure the quality and performance of produced parts and components. Their advanced engineering enables them to deliver accurate temperature control in production settings.
Cartridge heaters offer a cost-effective solution for heat transfer in manufacturing. They are energy-efficient, require minimal maintenance, and deliver excellent performance. Additionally, they have a minimal environmental impact, making them a sustainable choice for modern manufacturing processes.
Overheating is a critical concern in heating processes, as it can damage both the final products and the heating equipment. Cartridge heaters are equipped with temperature sensing capabilities to prevent overheating, reducing the need for constant monitoring. They provide focused, controlled, and localized heat efficiently and automatically.
The built-in temperature sensing features enhance the efficiency of the heat transfer process and extend the heater's lifespan.
Cartridge heaters are notable for delivering significant heat from a compact design. This efficiency has made them widely used across various industries. With a minimal investment, manufacturers can achieve concentrated heating and improved process performance, making cartridge heaters a valuable addition to production operations.
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