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Payback And Accuracy of Gravimetric Blenders

The competing accuracy between models of gravimetric blenders is often debated within the plastic processing world. This can make choosing the right gravimetric blender for your processes tricky – especially when it comes to calculating payback.

When used and maintained properly, gravimetric blenders precisely measure and blend different materials, ensuring a consistent and uniform mixture every time.

Here, we discuss the accuracy and payback of gravimetric blenders, to help you achieve optimum results with your machinery.

Definition of Gravimetric Blenders

Gravimetric blenders are used across plastic processes, such as extrusion, injection, and blow moulding operations.

They work by dispensing the assigned percentage of polymers into the weigh bin. Once the desired weight is met, the material is released into the mixing chamber, and then blended together, ensuring that the exact proportions are achieved every time. By measuring and dispensing materials based on their weight, gravimetric blenders eliminate the inconsistency associated with volumetric blending methods.

Gravimetric blenders also remove any guesswork or human error that may occur with manual blending. With the correct use of gravimetric blenders, consistent and repeatable results are achievable, leading to improved product quality and reduced waste. Additionally, these blenders offer quick payback due to their efficiency and accuracy – optimising material usage and helping to minimise production costs in the long run.

With gravimetric blenders, accuracy and payback are key factors that contribute to their effectiveness.

  • Accuracy: Gravimetric blenders ensure ingredient percentages are accurate within - 0.1% on a 1% setting.

Payback: Gravimetric blenders offer a quick payback period due to their ability to consistently deliver accurate blends, and reducing unnecessary excess material consumption which happens with other blending techniques. Even small improvements in accuracy can have a significant impact on profits.

Understanding Gravimetric Blenders

How Gravimetric Blenders Work

Gravimetric blenders ensure blend by weighing each material before mixing. The control system continuously adjusts the measurements to maintain the proper concentration of polymer.

The materials are dispensed into hoppers and then dropped into a weigh bin. Once the load cell determines that the batch is ready, it is sent to the mixing chamber. The mixer blends the batch, and the mixture is emptied from the blender.

Key Components and Functionality

The key components of a gravimetric blender include hoppers, weigh bins, mixers and dispense valves.

  • Hoppers: These hold the individual materials to be blended.
  • Dispense Valves: release material from the Hopper to the Weigh bin.
  • Weigh Bins: They accurately measure the weight of each material before blending.
  • Mixers: These thoroughly mix the materials to ensure a homogeneous blend.

By integrating these components, gravimetric blenders eliminate the need for time-consuming and costly material changes.

Advantages Over Volumetric Blenders

One of the key advantages to using gravimetric blenders over volumetric is its ability to consistently deliver precise material measurements.

Volumetric blenders rely on measuring materials by volume, which can lead to inaccuracies due to density variations. In contrast, gravimetric blenders measure materials by weight, resulting in more accurate and consistent blends.

Gravimetric blending also offers flexibility by accommodating various materials, allowing for the production of a wide range of blends. While gravimetric blenders may have a higher initial cost, they offer higher returns on investment by maintaining product quality and reducing waste.

Importance of Payback in Gravimetric Blenders

Definition of "Payback" in Industrial Equipment

Payback of industrial equipment refers to the length of time it takes to make up the cost of the machine – otherwise known as your return on investment.

Gravimetric blenders offer improved payback over volumetric blenders thanks to their blend accuracy amongst other factors.

Achieving High Accuracy in Gravimetric Blenders

Definition of "Accuracy" in Gravimetric Blending

Accuracy refers to the difference between the required weights and the actual weight being blended. The gravimetric blenders can do a +/- 0.1% on a 1% setting due to the load cells being regularly calibrated.

The accuracy is consistent whether using pellets, flakes or powders.

Factors Influencing Accuracy Levels

Several factors contribute to the accuracy of gravimetric blenders. Load cells, blender software, and dispensing mechanisms play crucial roles in ensuring accurate measurements.

Load cells provide precise readings. However, external factors such as vibration can affect the accuracy and may require additional time for accurate readings.

Additionally, the type of resin, pellet size, density, flow characteristics, regrind type and level, batch size, and throughput rate can all influence blender accuracy. Oversized, heavy, or irregular particles can hinder uniform mixing, for example. Furthermore, the flow characteristics of materials, such as poor-flowing particles rushing through slide gates, can lead to errors. Sticky resins can also pose challenges in the blending process.

Calibration and Maintenance of Gravimetric Blenders

Regular maintenance and calibration ensure the performance and accuracy of gravimetric blenders is optimised.

Regular maintenance is necessary to keep the blenders in good working condition. This includes cleaning the equipment, checking for any signs of wear or damage, and replacing any worn-out parts.

Calibration is also crucial to ensure precise measurements. By calibrating blenders, you can verify the accuracy of the weighing scales and adjust them if necessary. This helps to eliminate any errors or discrepancies in the measurements.

Additionally, calibration ensures that the blenders are operating within the specified tolerances, allowing for consistent and reliable results.

Proper maintenance and calibration of gravimetric blenders not only improve accuracy but also extend the lifespan of the equipment.

Best Practises for Optimal Payback and Accuracy

Selecting the Right Gravimetric Blender for Specific Needs

When selecting the appropriate gravimetric blender for your specific needs, it's crucial to consider the unique requirements of your operation.

  • Process type
  • Polymer type
  • Kilo per hour required
  • Percentage mix of the blend

Summit Plastics Automation supplies the Maguire Gravimetric Blender range. These intuitive, precision machines are suitable for the accurate blending of up to 12 ingredients – and can provide typical savings of 30% or more compared to manual or volumetric dosing.

Operator Training and Skill Development

Another way to improve the stability and consistency of your moulding or extrusion processes is by investing in operator training and skill development.

By ensuring that your operators have the necessary knowledge and expertise to operate blenders efficiently, as well as make adjustments, you can minimise errors and reduce variability in the process.

Regular Auditing and Performance Evaluation

Conducting regular audits and evaluating performance can lead to greater operational efficiency and consistent output quality in the gravimetric batch blending process.

Benefits of regular auditing and performance evaluation include:

  • Identify and rectify any equipment malfunctions or calibration errors.
  • Optimise the blending process by adjusting settings and parameters based on performance evaluations.
  • Ensure that the blenders are accurately measuring and dispensing the required materials.
  • Monitor and track any variations or deviations in the blending process to maintain consistency in output quality.
  • Improve overall productivity and reduce material waste by identifying and implementing process improvements based on audit findings.


Gravimetric blenders play a crucial role in ensuring accuracy and efficiency in industrial processes. With proper calibration, maintenance, and operator training, gravimetric blenders can deliver consistent and precise blending results. Regular auditing and performance evaluation are key to ensure that the blenders continue to meet the specific needs of the operation.

The payback of investing in these blenders is evident through improved product quality, reduced material waste, and increased productivity.

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