Precision Heating for Small Diameter Industrial Applications

Split sheath miniature cartridge heaters with hot tip are designed for high-precision heating in small bore applications where conventional heaters cannot fit. These heaters are typically manufactured in 1/8 inch (3 mm) and 4 mm diameters and provide uniform heat distribution, rapid heat transfer, and long service life.

The split sheath design expands during operation, ensuring tight contact with the bore wall. This improved contact dramatically enhances heat transfer efficiency while reducing internal element temperature, helping extend heater life.

Combined with a true hot tip configuration, split sheath miniature cartridge heaters deliver heat precisely where it is required-making them ideal for plastic processing equipment, hot runner systems, instrumentation, and precision tooling.

Split Sheath Construction and Operating Principle

Split sheath miniature cartridge heaters use a continuous resistance wire embedded in high-purity magnesium oxide (MgO) insulation. The MgO provides excellent electrical insulation while transferring heat efficiently to the outer sheath.

The outer sheath includes a longitudinal split, allowing the heater to expand slightly when energized.

This expansion provides several advantages:

• Improved heat transfer to the surrounding bore
• Lower internal element temperature
• Reduced heater stress and longer service life
• Easier removal after operation

When the heater cools, the sheath contracts slightly, allowing the heater to be removed without seizing.

True Hot Tip Cartridge Heater Design

Many conventional cartridge heaters contain a small unheated tip section due to internal construction limitations.

Split sheath miniature cartridge heaters can be manufactured with a fully heated tip, allowing heat to be delivered directly to the bottom of the bore.

Benefits of hot tip designs include:

• Faster heat transfer to tooling
• Improved temperature uniformity
• Better performance in deep bore applications
• Reduced thermal losses

This design is particularly important in hot runner nozzles, plastic molds, and precision thermal systems.

Available Styles and Heater Configurations

Split sheath miniature cartridge heaters can be manufactured in several configurations depending on the application.

Common options include:

• Straight miniature cartridge heaters
• Fully heated hot tip heaters
• Custom heated lengths
• Variable watt density designs
• Precision ground diameters for tight tolerance bores

Typical Size Range

• Diameters: 1/8 inch (3 mm) and 4 mm
• Lengths: 1/2 inch to 6 inches

Custom lengths and watt densities are available for specialized industrial heating applications.

Lead Exit Options and Electrical Terminations

To accommodate different installation environments, miniature cartridge heaters can be supplied with multiple lead exit styles.

Common lead configurations include:

• Straight axial leads
• Right-angle lead exits
• Internal lead exits through tooling
• Flexible swaged-in lead wires

Lead insulation options include:

• PTFE (Teflon) insulated leads
• Fiberglass insulated leads
• High-temperature mica-glass insulation

Optional protective features such as stainless steel braid or metal armor are also available for demanding industrial environments.

Temperature Sensing Options

Accurate temperature control is critical for many heating applications.

Split sheath miniature cartridge heaters can be supplied with integrated temperature sensors including:

• Type J thermocouples
• Type K thermocouples
• Pt100 RTD sensors

External thermocouples can also be positioned near the heater tip for more precise process temperature measurement.

• PTFE (Teflon) insulated leads
• Fiberglass insulated leads
• High-temperature mica-glass insulation

Optional protective features such as stainless steel braid or metal armor are also available for demanding industrial environments.

Optional Custom Features

Split sheath miniature cartridge heaters can be customized with a variety of optional features, including:

• Moisture resistant end seals
• Custom voltage ratings
• Custom watt densities
• Stainless steel or Incoloy sheath materials
• Corrosion resistant coatings
• Precision tolerance diameters

These customization options allow heaters to be optimized for high temperature and demanding industrial environments.

Common Applications for Split Sheath Miniature Cartridge Heaters

Split sheath miniature cartridge heaters are widely used in industries requiring precise localized heating.

Plastic Processing Equipment

• Injection molding hot runner systems
• Nozzle heating
• Gate and sprue heating

Packaging and Converting

• Heat sealing equipment
• Laminating systems
• Packaging machinery

Medical and Laboratory Equipment

• Diagnostic instruments
• Medical probes
• Laboratory heating equipment

Electronics and Semiconductor Manufacturing

• Thermal test fixtures
• Sensor calibration systems
• Semiconductor process equipment

Industrial Tooling

• Small molds and dies
• Heated platens
• Precision fixtures

Split sheath miniature cartridge heaters can typically operate at temperatures up to 1200°F (650°C) depending on watt density and sheath material.

Why Choose NPH Split Sheath Miniature Cartridge Heaters

National Plastic Heater split sheath miniature cartridge heaters are engineered for precision, durability, and consistent performance in demanding industrial applications.

Key benefits include:

• Superior bore contact through split sheath expansion
• True hot tip heating capability
• High watt density designs
• Compact diameters for tight spaces
• Custom engineering support

These heaters provide a reliable solution for small diameter heating applications requiring precise temperature control.