What is the Mold temperature of Plastics?
Mold temperature means the temperature of the actual mold after it’s been stabilized inside the molding machine.
Mold temperature is one of the most important aspects of plastic processing. It defines the amount of stress locked within a product and also affects its cooling rates. The selection of the right mold temperatures is a challenge itself. Many things need to consider for effective moldings, such as surface finish, ejecting capabilities, the part’s geometry, shrinkage, and residual stresses.
An accurate mold temperature is a must for a given plastic to form a basic wetting of mold surface. A hot mold surface must spread enough liquid on the plastic surface to create pressure in the cavity.
If the cavity fills up and cavity pressure cushions soft plastic against metal before the frozen surface hardens, it makes the cavity surface impression higher.
However, the plastic entering the lower cavity is somehow stopped; its slightest contact with the metal will create unavoidable stains; yes, you heard it right. They’re UNAVOIDABLE doesn’t matter how short the time is; the phenomena are also known as gate stains.
Below I have shared a table depicting the mold temperature for all the mainstream plastic materials.
Mold Temperature °C
|PET – Semi-crystalline||20-30|
|PET – Amorphous||20-30|
|PP – Homopolymer||30-80|
|PP – Copolymer||30-80|
There is a set surface limit for mold parts; if the limit exceeds, single or, multiple adverse effects can be witnessed. Often it is seen that higher mold temperatures result in less flow resistance.
Many molding machines are built with a mechanism for faster flow-through gates and cavities because injection flow control value doesn’t rectify the problem, and excess filling will lead to higher pressure in runners and cavities.
Generally speaking, an increase in mold temperature will reduce the condensation of plastic’s cavity, making the material flow in the cavity faster and smoother.
The better material flow will help in making the product aesthetically profound with better surface quality and finish. Another advantage of increasing mold temperature is a substantial increase in the component’s tensile strength.
The Importance of Mold Temperature –
The effects of mold temperature on the final product are less obvious but more profound than we can ever imagine. Talking about amorphous polymers, polycarbonate and ABS have higher mold temperatures and produce lower levels of molded in-stress and consequently better impact resistance, stress-crack resistance, and fatigue performance.
On the other side, in semi-crystalline materials, the mold temperature is crucial in figuring out the degree of crystallinity in the polymer. The crystallinity parameters can affect any performance factors such as fatigue resistance, creep resistance, wear resistance, and dimensional and firmness at elevated temperatures.
The mold temperature must be below the melting point but above the material’s glass transition temperature to form crystals.
A fact which has been proved that to get optimal results, higher mold temperatures must be combined with lower melt temperatures. However, visiting shop floors, I see opposite things happening; typically, melt temperatures are running higher as it is conceived to the only available method to control melt viscosity.
Higher melt temperatures will cause more harm than good. It will consume more energy, degrade the polymer, extend the cooling time needed to create an unwaveringly stable component.
To compensate for extended cycle time, manufacturers count on reduced mold temperatures to obtain lost productivity. However, the damage is done, and reversing it might make things worse. When manufacturers understand the crucial role of mold temperature and its suited attributes, they approach production with a very different mindset which blossoms productivity by reducing cost and improving quality.
The Takeaway –
That was my take on mold temperature in plastic and its importance. Using mold temperature the right way can boost your productivity and reduce time and expenditure on production.
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Have a lovely day ahead 🙂