Barrel In Injection Moulding: What You Need To Know

Barrel In Injection Moulding: What You Need To Know

Barrel in injection moulding is one of the most important components of an injection moulding machine. It is where the plastic material is heated, melted, and injected into the mould cavity. In this blog post, we will explain what barrel in injection moulding is, how it works, what are its functions and features, and how to maintain it properly.

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What is Barrel in Injection Moulding?

Barrel in injection moulding, also known as material tube and barrel, is a metallic cylinder that houses the screw or plunger in the injection moulding machine. The barrel is connected to the hopper, where the plastic material is fed into the machine, and to the nozzle, where the molten plastic is injected into the mould cavity.

The barrel has a heating system that consists of several heaters and thermocouples that regulate the temperature of the barrel according to the type and grade of plastic material being processed. The barrel also has cooling channels that circulate water or oil to remove excess heat from the barrel and prevent overheating.

The barrel is usually made of steel or aluminium alloy, and it has a hard chrome plating or nitriding treatment on its inner surface to increase its wear resistance and corrosion resistance. The barrel also has a smooth and polished surface to reduce friction and improve material flow.

How Does Barrel in Injection Moulding Work?

Barrel in injection moulding works together with the screw or plunger to melt and inject the plastic material into the mould cavity. The screw or plunger is a helical device that rotates inside the barrel and pushes the plastic material forward.

The screw or plunger has three zones: feed zone, compression zone, and metering zone. The feed zone is where the plastic material enters from the hopper and fills up the spaces between the flights of the screw or plunger. The compression zone is where the plastic material is compressed and heated by the friction and shear forces generated by the rotation of the screw or plunger. The metering zone is where the plastic material reaches its melting point and becomes a homogeneous molten mass.

The screw or plunger also has a check valve at its tip that prevents the molten plastic from flowing back into the barrel during injection. When enough molten plastic accumulates at the tip of the screw or plunger, a hydraulic system pushes it forward through the nozzle into the mould cavity. This process is called injection.

What are the Functions and Features of Barrel in Injection Moulding?

Injection moulding is a process of producing plastic parts by injecting molten plastic into a mould cavity. The barrel is an essential component of the injection moulding machine, which consists of a cylindrical metal tube with a screw inside. The barrel has several functions and features that affect the quality and efficiency of the injection moulding process.

The main functions of the barrel are:

  • To heat and melt the plastic granules that are fed into the hopper.
  • To convey and compress the molten plastic along the screw towards the nozzle.
  • To mix and homogenize the molten plastic to ensure uniform temperature, viscosity and color.
  • To inject the molten plastic into the mould cavity under high pressure and speed.

The main features of the barrel are:

  • The length-to-diameter ratio (L/D), which determines the residence time and shear rate of the plastic in the barrel. A higher L/D ratio means more heating, melting, mixing and pressure generation, but also more material degradation and energy consumption.
  • The heating zones, which are controlled by electric heaters or oil circulation systems. The heating zones regulate the temperature profile of the barrel, which affects the melting, flow and cooling of the plastic. The temperature profile should be gradually increased from the feed zone to the metering zone, and then decreased at the nozzle.
  • The cooling system, which consists of water or air channels around the barrel. The cooling system prevents overheating and thermal expansion of the barrel, which can cause wear and leakage. The cooling system also helps to control the temperature profile of the barrel and maintain a consistent melt quality.
  • The lining material, which is usually made of hardened steel or bimetallic alloys. The lining material protects the barrel from abrasion and corrosion caused by friction and chemical reactions with the plastic. The lining material also influences the heat transfer and friction coefficient of the barrel, which affect the melting and flow characteristics of the plastic.

How to Maintain Barrel in Injection Moulding?

Injection moulding is a process that involves melting plastic pellets and injecting them into a mould cavity under high pressure and temperature. The barrel is the part of the injection moulding machine that contains the screw and the heater bands that melt and convey the plastic material. The barrel is subject to wear and tear due to the friction, corrosion and heat generated by the plastic material and the screw movement. Therefore, it is important to maintain the barrel properly to ensure the quality of the moulded products and the efficiency of the machine.

The following are some tips on how to maintain the barrel in injection moulding:

  • Clean the barrel regularly. The barrel should be cleaned at least once a week or whenever there is a change of material or colour. Cleaning the barrel can prevent the accumulation of degraded material, which can cause black specks, streaks, bubbles or burn marks on the moulded products. Cleaning can also prevent cross-contamination of different materials or colours. To clean the barrel, use a purging compound that is compatible with the plastic material and follow the manufacturer’s instructions.
  • Check the temperature settings. The temperature settings of the barrel should be adjusted according to the type and grade of the plastic material used. The temperature settings should also be consistent along the length of the barrel, from the feed zone to the nozzle. The temperature settings can affect the viscosity, flowability and stability of the plastic material, which can influence the quality and appearance of the moulded products. To check the temperature settings, use a thermocouple or an infrared thermometer and compare them with the controller readings.
  • Inspect the heater bands. The heater bands are responsible for heating up the barrel and maintaining a uniform temperature distribution. The heater bands should be inspected regularly for any signs of damage, such as cracks, breaks, loose wires or corrosion. Damaged heater bands can cause uneven heating, hot spots or cold spots in the barrel, which can affect the melting and flow of the plastic material. Damaged heater bands should be replaced as soon as possible to avoid further damage to the barrel or other components of the machine.
  • Lubricate the screw. The screw is the part of the barrel that rotates and pushes the plastic material forward. The screw should be lubricated periodically with a suitable lubricant to reduce friction and wear between the screw and the barrel. Lubricating the screw can also prevent seizing, galling or jamming of the screw, which can cause damage to both parts. To lubricate the screw, follow the manufacturer’s recommendations on how often and how much lubricant to apply.
  • Monitor the wear of the barrel and screw. The wear of the barrel and screw can affect their performance and efficiency over time. The wear can be caused by various factors, such as abrasion, corrosion, erosion or thermal expansion. The wear can result in reduced diameter, increased clearance or reduced compression ratio of both parts, which can affect their ability to melt and convey the plastic material properly. To monitor the wear of the barrel and screw, use a caliper or a micrometer to measure their dimensions and compare them with the original specifications. If the wear exceeds the acceptable limits, the barrel and screw should be repaired or replaced.