Equipment Materials and Suppliers
Equipment Materials and Suppliers
ACRYLITE® acrylic sheet can be formed using vacuum, pressure, or stretching equipment.
Methods of Heating
Here's summary of available heat sources:
|Heat Source||Initial Cost||Efficiency||Average Life (hrs)|
|Coiled nichrome wire||Very inexpensive||Poor||1,500|
|Metal (cal) rod||Inexpensive||Fair||3,000|
|Hot air ovens||Moderate||Poor||N/A|
Forced circulating air ovens heat uniformly at constant temperatures and are commercially available from several manufacturers.
These ovens consist of an outer and an inner shell separated by space containing fiber or rockwool insulation. Inside, the ovens have thermostatically controlled heaters. As well, baffles and electric fans can be utilized to ensure even heat distribution. Because of its relatively low molecular weight, ACRYLITE FF sheet cannot be hung from a single edge. A clamping frame should be used to support the sheet and to facilitate transfer of the sheet to the forming station.
Before heating with an air oven, be sure that:
- You can reliably control temperature thermostatically within ± 10°F (±5°C) between 140-350°F.
- Air velocities across the sheet range between 200-1000 feet per minute (1-5 m/s).
- Temperatures throughout the oven are uniform.
- The clamping frame exerts constant, uniform pressure on all sides as the sheet becomes soft.
Using horizontal infrared heaters (ceramic elements, for instance) instead of a hot air oven is faster and less labor-intensive. Horizontal units are also more flexible because either the heater or the tooling can be moved. Working clearances can often be improved by moving the heaters and systems can be designed to handle custom sized blanks.
When designing a horizontal heater system, independently controlled zones can be set up to improve control and flexibility.
Thermoforming machines are ideal when large volumes of the same shape are being produced. However, tooling costs are usually high.
Multiple shapes can be formed at the same time from a single sheet, but post machining will be needed to separate and finish the parts.
Vacuum and Pressure-Forming
Many types and sizes of forming are commercially available. Journals or trade magazines dealing with plastic (such as Modern Plastics Encyclopedia) list many of the equipment manufacturers.
How to Make a Vacuum Chamber
An air tight vacuum chamber can be fabricated from welded steel plates. However, steel should not be used for the forming plate since it may "chill" the hot sheet. A hardboard forming plate about ½ inch in thickness is recommended.
The detachable forming plate can be sealed to a flange on the top of the vacuum box using gasket. The sheet blank is clamped in place over the forming plate using a clamping or holding ring and several toggle clamps.
The shape of the formed part's base will be determined by the shape of the cut-out in the forming plate. The height (or depth) of the part will be controlled by regulating the vacuum between the vacuum chamber and a vacuum storage tank. A high speed vacuum pump (10cfm minimum), a vacuum storage tank, a 1" gate valve, a vent valve for releasing vacuum after the part is formed, and a vacuum gauge will be required.
The required equipment for free blowing includes a plywood board with an air hose attached to its underside and a forming plate for controlling the piece's contour at its base. To evenly distribute incoming air, baffle the air intake with foam, felt, cardboard, etc. Cover the plywood board with flannel or polyurethane form to prevent mark-off. The forming plate or ring should be made from approximately 1 ½" thick hardboard. Quick acting toggle clamps may be used to attach the heated sheet and the ring to the plywood base.
Plug and Ring Forming Equipment
The rings or plates can be made from hardboard, plywood or metal. The plugs are usually made from hardwood. The equipment should be coated with flocked rubber sheet to minimize mark-off.
For producing large volumes of parts, durable aluminum rings and plugs can be used.