In the production of plastic pallets, injection molding is a primary method. The cooling time in plastic pallet injection molding accounts for about 80% of the entire injection production cycle. Poor cooling often leads to warping, deformation, or surface defects in the finished products, affecting their dimensional stability. Fairly controlling the injection, holding pressure, and cooling time can enhance product quality and production efficiency.

The cooling time of molded parts typically refers to the duration from when the plastic molding material fills the mold cavity to the point where it can be opened and the part removed. The standard time for opening the mold and removing the part is often based on the part having sufficiently cured and gained adequate strength and rigidity, ensuring it does not deform or crack upon ejection. Even with the same plastic molding material, the cooling time can vary due to wall thickness, the temperature of the molten plastic, the demolding temperature of the molded part, and the mold temperature. A formula that can accurately calculate the cooling time in all scenarios has not yet been published; instead, calculations are only made based on appropriate assumptions of the basic length. The calculation formula also differs depending on the definition of cooling time.

Analysis: Cooling Time for Plastic Pallet Injection Molding Parts

Currently, cooling time is typically referenced based on the following three standards:

The time required to cool the central layer of the wall thickness of the plastic pallet injection-molded component to below the thermal deformation temperature of the plastic pallet.

② The uniform temperature within the cross-section of the plastic pallet injection-molded part, and the time required to cool down to the specified mold temperature for the finished product.

③ The time required for the central layer of the thick wall of the crystalline plastic pallet molding piece to cool below its melting point, or to reach the designated crystallization percentage.

When solving formulas, the following assumptions are generally made:

Plastic pallets are injection-molded into the mold and cooled by transferring heat to the mold.

The plastic mold board inside the mold cavity is in tight contact with the mold cavity, not separated due to cooling and compression. There is no resistance to heat transfer and flow between the melt and the mold wall, and the temperature of the melt contacting the mold wall is immediately the same. In other words, once the plastic mold board is filled into the mold cavity, the surface temperature of the component is equal to the temperature of the mold wall.

During the cooling process of plastic pallet injection-molded parts, the temperature of the mold cavity surface consistently remains uniform.

④ The thermal conductivity level of the injection mold surface is consistent (regarding the melt filling process as an isothermal process, with uniform material temperature).

The orientation of plastic pallets and thermal stress have a negligible effect on the deformation of the product, and the product dimensions do not influence the solidification temperature.