Understanding Plastic Melt Temperature

for Packaging and Processing

Reaching the plastic melt temperature is a crucial step in the plastic packaging and processing industries, as it allows manufacturers to mold, shape, or extrude plastic materials effectively. The process requires precise control over temperature and heating methods to ensure that the polymer reaches its designated melting point without degrading. In this blog, we explore how to reach plastic melt temperatures, the types of heaters used in the manufacturing processes, and how these heaters play a vital role in the production cycle.

Understanding Plastic Melt Temperature 

Different types of plastics have varying melt temperatures, typically dependent on their chemical composition. For example:

• • • Polyethylene (PE): Melt temperature around 120-180°C (248-356°F)
    • Polypropylene (PP): Melt temperature around 160-230°C (320-446°F)
    • Polyvinyl Chloride (PVC): Melt temperature around 75-105°C (167-221°F)
    • Polystyrene (PS): Melt temperature around 90-240°C (194-464°F)

How Heaters Achieve Melt Temperatures 

To reach the desired melt temperature, manufacturers must ensure effective and uniform heating. 

1. Temperature Control: Most manufacturing systems are equipped with advanced temperature control systems that monitor and control the heating elements. Thermocouples and thermistors measure the temperature, allowing for real-time adjustments to maintain the desired melt temperature.

• • • General Purpose Thermocouples measure the temperature of the barrel, die or tool and relay that temperature back to the controller. They do not have contact with the melt itself.
    • In Melt Thermocouples measure the temperature of the melt itself. These are inserted often into a die head or barrel and provide feedback directly to the changes of the melt.  
      • Fixed Melt Bolt Thermocouple—the tip is flush with the interior tool or barrel or pre-set to a ¼ to 1 inch depth.  
      • Retractable Melt Bolt Thermocouple—this device allows the user to adjust the probe length into the melt to measure a variety of temperature points. These are often seen in film type applications where melt temperature precision is critical.   They can also be used in food production.

2. Uniform Heating: Properly designed heating systems ensure even heat distribution throughout the heating elements. For example, barrel heaters wrap around the barrel of an injection molding machine, providing continuous heat to prevent cold spots that could lead to incomplete melting.

• • • Feedback Systems: Many systems use closed-loop feedback to regulate temperature. This means that as the plastic approaches its melt temp, the heating element adjusts its output accordingly to maintain the desired temperature.
    • Material Handling: Properly managing the way plastic is introduced to the heating elements, such as by controlling feed rates in extruders or ensuring quick cycling in injection molding, helps prevent degradation and achieves optimal melting conditions.
      
      

Heaters Used in Plastic Processing

Reaching the plastic melt temperature in the plastic packaging and processing industries is essential for successful manufacturing. By employing various heater types, manufacturers can achieve precise temperature control and ensure efficient processes. A combination of advanced temperature regulation, uniform heating, and effective material handling techniques ensures that plastics are melted adequately and consistently, driving productivity and quality in the production cycle. Here’s a detailed explanation of the types of heating elements involved.

• • • Description: These heaters convert electrical energy into heat through resistance in heating elements. They are commonly found in injection molding, extrusion, and blow molding machines. Electrical resistance heaters are often used in barrel heaters and nozzle heaters for consistent heat distribution, ensuring the plastic reaches its melt temperature uniformly.
    • Application: Commonly used in barrel heaters and nozzle heaters in injection molding, extrusion, and blow molding machines, electrical resistance heaters ensure uniform heat distribution around the processing equipment. This uniformity is crucial for maintaining a consistent melt temperature throughout the plastic material, avoiding cold spots that could lead to defects in the final product.
    • Common heating elements used:
      • • Cartridge Heaters: These are commonly used in barrel heaters and nozzle heaters. They consist of a metal sheath enclosing a heating element made of resistance wire. Cartridge heaters provide precise, localized heat and are often used for heating the barrels of extrusion and injection molding machines.
        • Band Heaters: These are often used around the barrels of extrusion machines. They consist of a metal band wrapped around the barrel with embedded heating elements. Band heaters are designed to provide uniform heat distribution over a larger surface area.
        • Strip Heaters: Used in applications where heating over a flat surface is required, such as in some types of molds or equipment. They consist of a flat metal strip with a heating element inside and are used in applications needing consistent, broad-area heating.

• • • • Description: Infrared heaters emit radiant heat in the form of infrared radiation, which directly heats the plastic surface without the need to heat the surrounding air. These heaters typically use ceramic or quartz heating elements to generate infrared energy. In manufacturing processes such as film stretching and plastic welding, infrared heaters can heat specific areas quickly, promoting effective melting and forming.
      • Application: Infrared heaters are ideal for processes that require quick, localized heating, such as film stretching, thermoforming, and plastic welding. They enable precise control over which areas of the plastic receive heat, making them useful for applications that need targeted heating to melt plastic efficiently while minimizing energy waste.
      • Common heating elements used:
        • • Quartz Infrared Heaters: These heaters use quartz tubes or lamps that emit infrared radiation. They are used for rapid, direct heating in processes like film stretching and plastic welding. The infrared energy penetrates the plastic directly, heating the surface efficiently.
          • Ceramic Infrared Heaters: These heaters use ceramic elements to produce infrared radiation. They are durable and provide a high intensity of infrared heat. They are used in applications requiring consistent and intense infrared heating.

3. Hot Air Heaters

• • • Description: Hot air heaters work by circulating heated air around the plastic or the processing environment. They use electric elements or gas burners to heat the air, which is then blown over the plastic materials to raise their temperature.
    • Application: These heaters are commonly used for drying resin pellets or reducing moisture content in plastic materials before they are melted. Moisture control is critical in plastic processing, as excess moisture can cause defects such as bubbles or inconsistent melt flow. Hot air heaters are also used for surface treatment processes and preheating materials in plastic forming applications.
    • Common heating elements used:
      • • Forced-Air Heaters: These heaters use electric or gas heating elements to warm air, which is then blown over the plastic. They typically involve a fan to circulate the hot air around the processing area. Examples include convective heaters and hot air blowers.
        • Air Knives: While not a traditional heater, air knives use high-velocity hot air to treat surfaces. They are used for drying and surface heating in processes where precise air flow is critical.

• • • • Description: Utilizing steam as a heating medium, these systems can provide consistent and gentle heat into plastic surfaces through conduction. The steam is generated in a boiler and then routed through pipes or coils that surround or contact the plastic materials. Steam heating is sometimes used in certain thermoforming processes, such as bending or shaping plastic materials, where gentle heat prevents warping.
      • Application: Steam heaters are employed in thermoforming processes where gentle, even heating is required to soften plastic sheets or shapes without warping. They are used in bending and shaping applications, where plastic needs to be heated gradually to maintain its integrity during processing.
      • Common heating elements used:
        • Forced-Air Heaters: These heaters use electric or gas heating elements to warm air, which is then blown over the plastic. They typically involve a fan to circulate the hot air around the processing area. Examples include convective heaters and hot air blowers.
        • Air Knives: While not a traditional heater, air knives use high-velocity hot air to treat surfaces. They are used for drying and surface heating in processes where precise air flow is critical.

Each type of heating element is chosen based on its ability to deliver the appropriate type and amount of heat in an efficient, controlled manner, ensuring the plastic materials reach their melt temperature without compromising quality or energy consumption. The selection of heating elements depends on factors such as the heating method, the type of plastic being processed, and the requirements of the specific manufacturing process.

Why Backer Marathon

Backer Marathon is the industry leader in production speed, and reliable, quality heaters for plastics and packaging, serving OEMs with durable, customized solutions for unique heating needs since 1996. We design, manufacture, and stock industrial-grade heating elements and temperature sensors. Engineers have live, on-demand access via phone to our trained technical experts who have been pioneers in this sector for decades. 

How can Backer Marathon’s experts help you today? Nosotros hablamos español. Contact us today or oemsales@backermarathon.com to discuss your next project.