Cartridge heaters are found useful in many applications,such as:

• Seal bars

• Torpedo heaters for injection molding

• Injection molding manifolds

• Mass spectrometry

• Rubber molding

• Food production

• Immersion tank heating

• HVAC compressors

• Fuel cells

• Semiconductors

• Medical devices

• Sensor measurement devices

• Extrusion

• Die casting

• Hot melt adhesives

• Heat staking / hole punch

• Plastic welding

• Fluid heating

• 3D Printers

Heating coil

• The heating coil is the actual resistance which is where the electrical load occurs. The most common type of metal alloy used for this purpose is a nickel-chromium mixture, also known as nichrome. The nichrome wire is wound around a ceramic core, and the number of spirals per inch vary according to the requested watt density. Potential from an alternating current source, which can either be 2 phase or 3 phase, flows through the coiled nichrome wire, heating up the wire, which in turn, heats the cartridge heater sheath. 

Insulation is used to prevent the nichrome coil contacting the sheath, an event that would ground the resistance and could produce a catastrophic short-circuit, resulting in a melted sheath and a major equipment failure. Damage can be mitigated by installing a ground fault interrupting circuit. To prevent the coil from touching the sheath, the coil is inserted into the sheath, and immediately filled with magnesium oxide (MgO). To ensure the MgO fills the empty space between the sheath and the coil, the cartridge heater is filled under vibration.

The sheath is the part of the cartridge heater which makes contact with the material or substance to be heated. Several metal alloys are used, depending on the type of application, such as highly acidic or corrosive environments. The most common types of sheaths are 304 stainless steel, 316 stainless steel, and incoloy 800. Incoloy has the highest temperature rating, and is considered a superalloy.

After the cartridge heater has been filled with MgO, a seal is applied to the open end of the cartridge heater (where the nichrome coil was introduced). This prevents the coil and the MgO from coming out, as well as preventing contaminants such as plastic debris, air, or moisture from entering the heater.

Since cartridge heaters are installed in a wide variety of machines, manufacturers must design the heaters to meet certain clearances. [dead link] The cartridge heaters might be terminated with the leads coming out straight, or in a right angle. Also, manufacturers must be careful that the leads are not exposed to temperatures higher than the maximum rating for the lead wire. In order to prevent lead wire damage from temperature, movement or contamination, the lead wire can be protected with a metal conduit, braided metal or silicone sleeves.

Depending on the clearance and the design of the machine where the cartridge heater will be inserted, the type of wire used will vary. Fiberglass is the commonly used for cartridge heaters and other high-temperature applications, such as automotive wiring harnesses and industrial equipment. Other variants used are silicone impregnated fiberglass and silicone rubber. It is a type of wire.

Cartridge Heaters Metric – Description

 Metric & Imperial high density cartridge heaters are round tubular heaters with electrical terminations on one side. These dependable heaters are made to withstand tough industrial usage. With a tolerance of +/-0.002" on its outside diameter to secure a tight fit inside receptacle holes, and rock hard compaction of MgO insulation through swaging, these heaters can attain 1500ºF sheath temperature. High density cartridge heaters are available with various termination styles and mounting attachments. In high-density cartridge heaters the resistance wire loops are positioned as close as possible to the outside shell. Because the MgO powder insulation around these loops is compacted by swaging and transformed into a very hard medium, heat transmission is very efficient.

Metric and Imperial cartridges can have up to 200 w/in watt densities.

Cartridge Heaters are usually supplied with lead wires. The attachment of the leads to the central pins is done internally, in a 3/8” cold section. In excessively hot applications the length of this cold section could be increased. To facilitate installation and avoid

excessive air pockets, cartridge heaters are made 0.004” less than the nominal size of the receptacle hole with a tolerance of +/- 0.002”. Metric and Imperial cartridges can be dual-voltage, three-phase, and/or be supplied with a ground terminal. With ten different

termination styles, mounting attachments and various optional features, Our high density cartridge heaters are widely used in numerous high temperature applications. 

 Cartridge Heaters -Specifications and Watt Density

Cartridge Heaters - Termination Styles

High temperature (840 deg F) fiberglass insulated wire is

connected externally to the two solid pins exiting from the

cartridge. A silicone impregnated fiberglass jacket

insulates the connection.

Internally connected Teflon leads (480 deg F) with Teflon plugs, protect the cartridge from contamination. High temperature black epoxy or silicone RTV seals are available too. A minimum cold section of 1” at the leads end is necessary to protect the Teflon leads from hightemperature.

A bracket having the same diameter as the cartridge provides a 90

degree exit to the fiberglass insulated high temperature wire. The

bracket is potted with high temperature cement (480 deg F).

For high temperature applications, screw terminals (#10-32 is standard, other sizes are available) are silver-brazed to the 1” extended solid pins of a cartridge. This type of terminals are not recommended for cartridges having less than ½" diamerter.

Internally connected Teflon leads (480 deg F) with Teflon plugs, protect the cartridge from contamination. High temperature black epoxy or silicone RTV seals are available too. A minimum cold section of 1” at the leadsend is necessary to protect the Teflon leads from high temperature.

To protect cartridge heaters against moisture and contamination, Teflon lead wires are used and the lead end is sealed using Epoxy, RTV silicone or Teflon. The temperature limitation is 480 degrees F.

Distributed wattage:

In applications such as sealing bars or rubber molds, the two ends of a cartridge heater are usually colder than the middle. To overcome this inconsistency and have a uniformly distributed heat source, cartridges could be made to have higher wattages at the ends. 35/30/35 is a common wattage distribution.

Center-less grinding:

In applications where superior heat transfer is required, the tolerance on the outside diameter could be improved to +/- 0.001” by center-less grinding.

Zones and cold sections:

We can also manufacture cartridges with cold sections and separate zones that can be controlled independently.

Moisture and contamination proofing:

Built-in thermocouples:

One optional feature on cartridges is built-in thermocouples. These could  be type “J” or “K”, grounded or ungrounded, and attached either at the disc end or middle of the cartridge.

Graphite coating:

To facilitate their installation and removal, cartridges could becoated with a graphite-like substance. This solid lubricant doesn’t increase the outsidediameter, and is suitable for temperatures up to 750 degrees F.

Cartridge heaters are designed to withstand a sheath temperature of up to 1500ºF. Therecommended maximum operating temperatures for different applications are much less than that. There are many factors that have a direct effect on the lag between the actual sheath temperature of a cartridge heater and the monitored temperature of a material

during the heat-up cycle. In some cases, this temperature lag is so significant that the cartridge will reach its elevated critical temperature even when the surrounding material is monitored to have a relatively lower temperature level. The most common factors that contribute to the degree of temperature difference are the following:

Thermal conductivity of the material being heated

The cartridge sheath watt density

The tightness of the cartridge inside the hole

The location of the monitoring sensor

The allow of the cartridge sheath material

Contamination around the cartridge heater

These factors should be taken into consideration while selecting a cartridge for a specific application. One common practice is to use stainless steel cartridge sheathes for temperatures up to 1000ºF and incoloy sheathes for temperatures up to 1400ºF. Another design consideration related to the operating temperature is the electrical termination of a cartridge. Teflon and TGGT leads have 480ºF rating while MGT wires can withstand up to 840ºF. When cartridges are used at relatively high temperatures, the terminals selected should be either different than the common high temperature lead

wires or the design should be done such that the temperature around the lead wires (whether the leads are connected internally or externally to the cartridge) is maintained at a temperature level lower than the critical temperature limit of the lead wire.

Yancheng Laiyuan Electric Equipment Co., Ltd.

HotLine : +86-15851048592

Email：jane@china-laiyuan.com

Website : www.china-laiyuan.com

Address : NO.188 Renming Road,Tinghu,Yancheng,Jiangsu Province