Jan 25, 2019
During Cooling, the injection molded part shrinks onto the mold components.
For ejection of the part, draft angles are used.
If they are missing, it might lead to no ejection of the part, or visible scratches or scoring arise during ejection.
Dependent on material and surface, different draft angles are chosen:
Amorphous materials need larger draft angles on a rib than semi-crystalline materials.
On the other hand, if the part shrinks to a core, it is vice versa.
The higher shrinkage of semi-crystalline materials is the reason for this.
Quality: A cut through the
part without (left) and with (right) draft angles.
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This glossary of plastic industry is provided by PLEXPERT Canada Inc.
May 25, 2021
Contamination on mold surfaces can have various causes and must be eliminated in order to produce molded parts with high quality.
One method of cleaning is dry ice blasting. This is similar to sandblasting, but much gentler. Dry ice pellets are used as the blasting medium.
The pellets are accelerated to extremely high speed in the dry ice blasting unit with a jet of compressed air and blasted onto the object to be cleaned using a gun and nozzle.
Upon impact with the surface, mini-explosions occur which, in combination with the locally generated cold shock (-78.5°C), detach dirt particles from the substrate.
Quality assurance:
Dry ice unit with compressed air hose and
dosing gun
Quality assurance: Cleaning method
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Oct 21, 2019
A flat glass, also known as plan test glass or plane-parallel test glass, is used for testing small flatness deviations.
It is a manual test device with lapped or polished surfaces and a test method based on the interference of light.
A flat glass is a round, high-precision round glass which is fitted with a frame made of plastic or metal.
This is done to protect the glass from fingerprints.
During the test, the glass is slightly pressed onto the test specimen on one side,
whereby a wedge-shaped slit is formed in which the light forms interferences through reflections.
Visible straight stripes appear on flat surfaces, while concave and convex deviations form ring-shaped stripes,
which, however, stand in opposition to each other.
Between the interference fringes, the measuring surface to the glass pane is about 0.27 µm away in white light.
It is suggested to use monochromatic light for better results.
The prerequisite for the use of flat glass is that the surface to be measured reflects sufficient light.
There are flat and spherically curved test tubes which are specified in DIN 58161 Part 1 and Part 2 respectively.
For example, the measuring surfaces of micrometers can be checked for flatness and parallelism with plane glasses.
Quality:
Flat glass on a surface to be tested.
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Dec 9, 2021
To ensure that after manufacturing a surface has a certain distance between two parallel planes, the symbol Flatness is used.
The distance is entered after the symbol.
Flatness is a shape tolerance and describes in which range the most protruding and the most curved area of a surface may be apart.
Quality Assurance: Symbol of tolerated property with 0.06mm required
flatness
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This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Aug 12, 2019
Differences in wall thickness cause changes in the speed of the melt front.
This can lead to air traps, weld lines, e.g..
To get a well balanced, homogeneous flow behavior, decreasing local wall thickness, called flow deflector, can slow down the flow front in a specific area.
Quality: The melt advances in the thick area (Animation 1) leading to an
air trap. By adding a
flow deflector (Animation 2) the thick wall is reduced and the
air trap gone.
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This glossary of plastic industry is provided by PLEXPERT Canada Inc.
