In traditional vacuum forming, the pressure that shapes the plastic sheet is primarily determined by the difference between the ambient atmospheric pressure and the reduced pressure (vacuum) created beneath the sheet and mold. The maximum theoretical pressure that can push the sheet into the mold in standard vacuum forming is limited by atmospheric pressure.
Based on the provided reference:
In theory the maximum atmospheric pressure in traditional vacuum forming is 14.7 Pounds Per Square Inch.
This 14.7 PSI represents the maximum pressure difference achievable when a perfect vacuum is pulled on one side of the heated plastic sheet, allowing the full force of the surrounding atmospheric pressure to push the material into the mold cavities.
Understanding Vacuum Forming Pressure
Vacuum forming utilizes atmospheric pressure to press a heated plastic sheet against a mold. A vacuum is created between the sheet and the mold, removing the air. This creates a pressure differential, with the higher atmospheric pressure on the outside of the sheet pushing it into the lower-pressure area of the mold.
- Maximum Pressure Source: Atmospheric Pressure
- Theoretical Limit (Traditional): 14.7 PSI (as stated in the reference)
Enhancing Forming Pressure: Beyond Traditional Vacuum
While traditional vacuum forming relies solely on atmospheric pressure, the reference notes a method to increase the total forming pressure:
- Adding air pressure (up to 60 PSI) to the non-mold side of the sheet.
- This technique (often called pressure forming) can significantly increase the overall thermoforming pressure.
- According to the reference, this can increase the pressure by as much as 4 times that of conventional vacuum forming.
Therefore, while the vacuum itself facilitates the use of atmospheric pressure, the maximum pressure applied to the material in traditional vacuum forming is capped by atmospheric pressure (around 14.7 PSI). Techniques like pressure forming add to this, enabling much higher forming pressures.
| Forming Method | Primary Driving Force | Maximum Theoretical Pressure Source (based on reference) |
|---|---|---|
| Traditional Vacuum Form | Atmospheric Pressure | 14.7 PSI |
| Pressure Forming | Atmospheric + Added Air | Up to 14.7 PSI (Atmospheric) + Up to 60 PSI (Added Air) |
This table illustrates how the reference differentiates between the atmospheric pressure limit in traditional vacuum forming and the higher pressures achievable with added air pressure.
