Acrylic sheet can be thermoformed using several types of equipment employing a variety of heating methods. The following technical information is offered as a resource for thermoforming equipment and procedures. Users should undertake sufficient verification and testing to determine the suitability for their own particular purpose.

Heating Methods:
Vertical Ovens
Forced circulating-air ovens heat uniformly at consistent temperatures. These ovens consist of an outer and inner shell separated by a space containing fiber or rockwool insulation. Inside, the ovens have thermostatically controlled heaters. Ovens capable of operating at temperatures ranging from 140-380 degrees F (60-193C) and to within 10 degrees F (5C) are required; air velocities across the sheet should range between 200-100 feet per minute (1-5 m/s). Baffles and electric fans can also be used to ensure even heat distribution.

Because of its relatively low molecular weight, continuously manufactured or extruded acrylic sheet cannot be hung from a single edge. A clamping frame should be used for support and to facilitate sheet transfer to the forming station. Do not leave continuously manufactured sheet hanging in the oven after it has reached its forming temperature. The material can soften, deform and fall out of the clamping frame if heated too long. Cell cast sheet, on the other hand, can be hung from a single edge, and is unlikely to fall out of the clamps if heated longer than required. Be sure that temperatures throughtout the oven are uniform, and the clamping frame exerts constant uniform pressure on all sides of the sheet as it becomes soft.

Horizontal heaters
Using horizontal infrared heaters (ceramic elements for instance) instead of hot air ovens is faster and less labor intensive. Horizontal units are also more flexible because either the heaters or the sheet and clamping frame can be moved. Working clearances can often be improved by moving the heaters, and systems can be designed to handle custom made blanks.

When designing a horizontal heating system, independently controlled heating zones should be set up to improve control and flexibility.

Thermoforming mahines
Many types and sizes of forming equipment are commercially available. Thermoforming machines are ideal when small to medium volumes of the same shape are being produced. This is because the tooling required for thermoforming is much less expensive than the tooling required for injection molding.

For more information contact Mike at Ultra Acrylics, Inc.