Professional manufacturer of thermoforming machines.
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Professional manufacturer of thermoforming machines.
What Is a Thermoforming Mold?
Types of Thermoforming Molds
Thermoforming molds can be broadly divided into two categories: male molds (positive molds) and female molds (negative molds).
Male Mold
A male mold, also known as a plug-assist mold, has a raised shape over which the thermoplastic sheet is draped. This type of mold is advantageous when internal details or surface textures are required in the product. Male molds are typically used in applications where wall thickness uniformity is crucial.
Female Mold
A female mold, also known as a cavity mold, has a recessed shape into which the thermoplastic sheet is pressed. This type of mold is suitable for applications where detailed surface texture is needed on the exterior of the product. Female molds are commonly used to produce items such as trays, lids, and packaging containers.
Thermoforming Mold Materials
Because thermoforming does not involve high pressure and the part shapes are relatively simple, the pressure exerted on the mold is low, and the mold does not require very high rigidity. Thermoforming molds can be made from various materials such as wood (hardwood and compressed wood), plaster, plastics (phenolic resin, epoxy resin, etc.), steel, and aluminum alloys.
What Anti-Corrosion Protection Methods Are Used for Cooling Channels in Thermoforming Molds?
The purpose of anti-corrosion protection in thermoforming molds is to maintain the mold’s heat transfer capability. In thermoforming molds, the water temperature ranges from 5–150°C. Under normal conditions, water can cause varying degrees of corrosion damage to the mold. The following anti-corrosion protection methods are used for cooling channels in thermoforming molds:
Pay attention during mold design and manufacturing to prevent aluminum and copper from coming into direct contact in the water channels. Direct aluminum–copper contact can easily cause corrosion of the aluminum. A stainless steel or plastic separator of at least 30 cm in length must be inserted between the aluminum and copper.
When the mold walls are thin (separating the baffle into individual sections), as is common in typical forming situations and in the cutting molds of automatic roll-feeding thermoforming machines, it is recommended to install sacrificial magnesium anodes in the water channels.
When establishing the cooling system, if possible, the cross-section should be made as large as possible so that the water velocity does not exceed 1.5 m/s. High water velocity can lead to erosive corrosion.
Before the mold is used, the water channels must be carefully cleaned. If possible, first blow thoroughly with air in both directions, then use water to check for leaks and rinse afterward. It is very important to use a filter to ensure cleanliness in the mold circuit or pump, and finally blow dry with air.
It is recommended to use a cooling medium with a higher concentration of corrosion inhibitors. The required concentration depends on the type of inhibitor used.
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