Podcast
Questions and Answers
What are some factors that can affect blender accuracy?
What are some factors that can affect blender accuracy?
- Pellet size and batch size
- Resin color and density
- Flow characteristics and throughput rate (correct)
- Material type and level of vibration
How does Mould-tek achieve superior metering accuracy in dispensing?
How does Mould-tek achieve superior metering accuracy in dispensing?
- By increasing the speed of the vibratory feeders
- Using pinch-valve dispensing and precise computer control (correct)
- Through the use of oversized load cells
- By utilizing auger feeders for dispensing
What can cause difficulty in mixing in the blender?
What can cause difficulty in mixing in the blender?
- Uniform pellet size
- Sticky resins clumping together (correct)
- High accuracy load cells
- Vibratory feeders with rapid shut-off
How does the valve in Mould-tek's system operate during dispensing?
How does the valve in Mould-tek's system operate during dispensing?
Why can color masterbatch pellets hinder uniform mixing in a blender?
Why can color masterbatch pellets hinder uniform mixing in a blender?
In what way can easy-flowing particles contribute to errors in blender accuracy?
In what way can easy-flowing particles contribute to errors in blender accuracy?
What is the primary advantage of employing gravimetric load cells in dosing devices?
What is the primary advantage of employing gravimetric load cells in dosing devices?
Why is over-dosing typically avoided in processes that use metering devices for additive amounts?
Why is over-dosing typically avoided in processes that use metering devices for additive amounts?
What is a key feature of gravimetric dosing that simplifies the calibration process?
What is a key feature of gravimetric dosing that simplifies the calibration process?
Why do processors at the machine throat seek to improve their dosing accuracy?
Why do processors at the machine throat seek to improve their dosing accuracy?
What issue arises when simple dosing devices are unable to accommodate variations in regrind supply?
What issue arises when simple dosing devices are unable to accommodate variations in regrind supply?
What does gravimetric dosing primarily rely on to adjust feed rates accurately?
What does gravimetric dosing primarily rely on to adjust feed rates accurately?
How does a volumetric blender typically meter doses?
How does a volumetric blender typically meter doses?
What common problem can significantly affect the accuracy of volumetric blenders?
What common problem can significantly affect the accuracy of volumetric blenders?
What is a key advantage of gravimetric batch blenders over volumetric blenders?
What is a key advantage of gravimetric batch blenders over volumetric blenders?
Why do volumetric blenders require consistent, free-flowing materials to work properly?
Why do volumetric blenders require consistent, free-flowing materials to work properly?
What can happen if the flow-ability of material changes in a volumetric blender?
What can happen if the flow-ability of material changes in a volumetric blender?
Which type of blender uses weight readings to verify doses without making assumptions?
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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