Mold scale occurs in almost all thermoplastics during injection molding. When the functional requirements of the final product must be mixed with related additives (such as modifiers, fire retardants, etc.), these additives are likely to remain on the surface of the cavity during the molding process, resulting in the formation of mold scale.

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How To Quickly Clean The Injection Mold?
1. Formation of mold scale
Mold scale occurs in almost all thermoplastics during injection molding. When the functional
requirements of the final product must be mixed with related additives (such as modifiers, fire
retardants, etc.), these additives are likely to remain on the surface of the cavity during the
molding process, resulting in the formation of mold scale.
There are other reasons for the formation of mold scale, the most common reasons are as
follows:
Thermal decomposition products of raw materials
During injection molding, melt flow extreme shear force
Inappropriate exhaust
The mold scale caused by the above is often a combination of different factors, and it is very
troublesome to find out what causes these mold scales and how to prevent them, and mold
scales will not form until a few days later.
2. Types of mold scale
Various additives produce a specific type of mold scale. Fire retardants react at high
temperatures, forming products that decompose and may produce mold deposits. Under the
influence of excessive-high temperature or extreme shear force, the impact resistance agent will
separate from the polymer and remain on the cavity surface to form a mold scale.
The pigments in thermoplastic engineering plastics melt at high temperature, which will reduce
the thermal stability of the molding materials, resulting in a combination of degraded polymers
and decomposed pigments to form a mold scale.

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Particularly hot parts on the mold (such as mold cores), modifiers/stabilizers and other additives
may adhere to their surfaces and cause mold fouling. In this case, measures must be taken to
achieve better mold temperature control or the use of special stabilizers.
3. Countermeasure for sudden mold fouling
If mold fouling occurs suddenly, it may be due to changes in molding conditions, or because of
different batches of molding materials. The following suggestions can help improve mold fouling.
First, measure the temperature of the melt and visually check whether the melt has
decomposition phenomena (such as burnt particles). At the same time, check whether the
molding materials are contaminated by foreign substances and whether the same cleaning
materials are used. Check the exhaust condition of the mold.
Again, check the operating machine: use dye-colored molding raw materials (except black), turn
off the injection molding machine after about 20 minutes, remove the nozzle and the connecting
seat, and if possible remove it together with the screw, check the raw material for burnt particles
Color comparison, quickly find the source of mold scale.
In many cases, surprising causes of mold defects were found. This technology is most suitable for
smaller injection molding machines with a maximum screw diameter of 40mm. The elimination
of mold scale also allows the quality of the parts to be clearly improved when molding other raw
materials. The above countermeasures are also applicable to the molding of hot runner systems.
Mold fouling leads to defects in the appearance of injection molded parts, especially those with
surface etched lines, which can be repaired by sandblasting machine.
4. Maintenance of the mold
When all the above measures can not eliminate the mold scale, the mold maintenance and
maintenance must be strengthened.
The mold scale on the surface of the mold is relatively easy to remove at the initial stage, so the
mold cavity and the exhaust channel must be cleaned and maintained regularly (for example,
after each batch of molding production). If the mold is not maintained and maintained for a long
time, it is very difficult and time-consuming to remove the mold after forming a thick layer of
mold scale.
The main sprays used for the maintenance and maintenance of injection molds are mold release
agent, rust inhibitor, thimble oil, glue stain remover, mold cleaning agent and so on.
The chemical composition of the mold scale is very complex and must be removed using new
methods, such as general solvents and various special solvents, oven sprays, caffeinated
lemonade, etc. Another peculiar way is to use a clean model rail rubber.
5. Suggestions for preventing mold fouling
When hot runner molding and heat-sensitive raw materials are used, the residence time of the
melt will become longer, thereby increasing the risk of decomposition of the raw materials to
form a mold scale. Clean the screw of the injection molding machine.
When forming shear-sensitive materials, large-sized runners and gates are used. Multi-point
gates can reduce the flow distance, low injection speed, and reduce the risk of mold fouling.
Efficient mold venting can reduce the possibility of mold fouling, and proper mold venting should

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be set during the mold design stage. Automatically removing the exhaust system, or an exhaust
method that can easily remove mold scale is the best choice. The improvement of the exhaust
system often leads to the reduction of mold scale on the mold.
The surface of the mold cavity is covered with a special non-stick coating to prevent the
formation of mold scale, and a test should be conducted to evaluate the effect of the coating.
Titanium nitride treatment on the inner surface of the mold can avoid the formation of mold
scale on the mold.