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Questions and Answers
What are some factors that can affect blender accuracy?
How does Mould-tek achieve superior metering accuracy in dispensing?
What can cause difficulty in mixing in the blender?
How does the valve in Mould-tek's system operate during dispensing?
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Why can color masterbatch pellets hinder uniform mixing in a blender?
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In what way can easy-flowing particles contribute to errors in blender accuracy?
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What is the primary advantage of employing gravimetric load cells in dosing devices?
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Why is over-dosing typically avoided in processes that use metering devices for additive amounts?
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What is a key feature of gravimetric dosing that simplifies the calibration process?
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Why do processors at the machine throat seek to improve their dosing accuracy?
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What issue arises when simple dosing devices are unable to accommodate variations in regrind supply?
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What does gravimetric dosing primarily rely on to adjust feed rates accurately?
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How does a volumetric blender typically meter doses?
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What common problem can significantly affect the accuracy of volumetric blenders?
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What is a key advantage of gravimetric batch blenders over volumetric blenders?
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Why do volumetric blenders require consistent, free-flowing materials to work properly?
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What can happen if the flow-ability of material changes in a volumetric blender?
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Which type of blender uses weight readings to verify doses without making assumptions?
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Study Notes
Factors Affecting Blender Accuracy
- Load cells are accurate to 0.025 g, or one pellet, but vibration can affect accuracy, requiring more time for accurate readings
- Dispensing mechanisms, such as air-actuated slide gates, pinch valves, auger feeders, and vibratory feeders, can impact accuracy
- Factors affecting blender accuracy include resin type, pellet size, density, flow characteristics, regrind type and level, batch size, and throughput rate
Pinch-Valve Dispensing
- Mould-tek's pinch-valve dispensing system provides superior metering accuracy
- The valve is fully open until 80-90% of target weight is dispensed, then it feathers open and shut rapidly until the target is reached
- Each dose is weighed by the quick-acting load cells of Mould-tek's RLTS (real-time live scale) system
Challenges in Mixing
- Oversized, heavy, or irregular particles can cause difficulty in mixing in the blender
- Color masterbatch pellets tend to be heavy and often of a different size from virgin, which can hinder uniform mixing
- Easy-flowing particles can cause errors by rushing too fast through slide gates, while sticky resins clump and bridge
Gravimetric Load Cells
- Gravimetric load cells are employed to sense minute changes and accommodate them automatically for the highest level of accuracy
- They allow for extreme precision in the process and eliminate the need to “over-dose” to assure proper coloring
Metering Devices
- A wide range of metering devices have been developed for the smaller additive amounts to allow for extreme precision and accuracy
- These devices keep track of all material dynamics to assure an accurate blend being delivered to the process with each and every cycle
Inaccurate Dosing
- Inaccurate dosing at the machine throat due to material variations or calibration process can be time-consuming and challenging for shop level workers
- Typical results of inaccurate dosing include over-dosing and inaccuracy
Solution: Gravimetric Dosing
- Gravimetric dosing units weigh the metered material, permitting rapid start-ups with only infrequent calibration
- The user can directly input specific weight or ratio percentage settings into the control with no translation into time settings
Volumetric vs Gravimetric Blenders
- Volumetric blenders meter by timed sequences of volume doses, assuming consistent flow and material mass
- Gravimetric batch blenders use weight readings to verify every single metered dose of all materials, with no assumptions
- Volumetric blenders require consistent, free-flowing materials and can be affected by material flow problems, while gravimetric blenders are more accurate and reliable
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Description
Explore the factors that contribute to accuracy in blenders, including load cells, batching software, and dispensing mechanisms like air-actuated slide gates and pinch valves. Learn about the precision of load cells and software resolution in achieving accurate dispensing.
