Dec 19, 2018
The cavity contains air, which is pushed out by the arriving melt.
Therefore, venting is necessary to allow the air to escape the cavity.
Otherwise a compression of the air occurs, which leads to a rise of the temperature (burn mark).
The venting consists of small gaps, which are situated for example at the parting line, at the sliders and at the ejector pins.
Depending on the used polymer, the height of the gap needs to be adjusted.
If the gap is too small, it prevents the air from escaping.
If the gap is too big, flash formation occurs at the part.
Mar 11, 2019
Even when the mold halves are exactly centered on top of each other core shift might happen.
Especially long, thin cores are pushed away due to unbalanced filling.
The unbalanced injection of the melt leads to a one-sided pressure on the core.
The movement results in changing wall thickness in the part.
In the area of reduced wall thickness the filling is more difficult than in the are with higher wall thickness.
Weaknesses due to the changed wall thickness lead to problems during the usage of the part.
A balanced flow around the core and a hold on both sides of it helps to reduce the risk of core shift.
Feb 15, 2019
All cylindrical sorting machines, which put parts on a given track and bring them into a specific position, are called vibratory bowl feeder.
The bowl, with unsorted small parts, is brought into vibration (mechanical or electromagnetic). These vibrations transport the parts on spiral lanes equipped with order systems to ensure that the parts will leave the bowl in a given position. Single vibrator bowl feeders can sort up to 30.000 parts per hour.
Due to the noise, it is advisable to use a noise insulating hood to reduce noise pollution.
General:
Vibratory bowl feeder sorting sealing rings.
Related topics:
Sorting
This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Dec 19, 2018
In injection molding, the viscosity describes the flow resistance of the plastic in the cavity.
Higher slow-moving of the material means higher viscosity.
Flow curves show that the viscosity of a plastic varies by different shear rates and temperatures.
These curves need to be measured with the help of a viscometer or rheometer.
The viscosity is described by the formulaic character 𝜏 (Tau).
Its unit is Pascal seconds.
Examples of Viscosities:
Water: 0,001 Pas
Oil: 0,03-0,1 Pas
Glycerin: 1,5 Pas
Honey: 10 Pas
Easy flowing plastic melt: 1000-5000 Pas
Heavy flowing plastic melt: 10000 – 100000 Pas
Image 1: Plastic: The temperature curves describe the viscosity over shear rate.
Image 2: Plastic: The higher the viscosity the better the dimensional stability.
Left: A material with higher viscosity; right: lower viscosity.
Related topics:
pvT – Diagram
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This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Dec 27, 2018
In areas with thick walls and across from ribs, a “hole” in the inside might appear.
Mass accumulation leads to a higher volumetric shrinkage, which is not insufficiently adjusted by packing pressure.
The melt is pulled to the surface during cooling, that a hollow remains in the inside.
CT-Scan and cutting the part help to detect these errors.
Small wall thickness and higher packing pressure in the critical area reduce the risk of voids.
