time for forming

TIME AVAILABLE FOR FORMING

Heated Chemcast® GP sheets must be completely formed before their surface and internal temperatures drop below 275°F. Unless forming is completed at or above these temperatures the parts will be cold formed with resultant inherent stresses within the material. These stresses cannot be removed by annealing unless the annealing takes Place at temperatures high enough to cause significant deformation of the part.

The time available for forming heated Chemcast® GP sheets before they cool below the minimum forming temperatures depends on Chemcast® GP thickness and temperature, air temperature in the fabricating shop and mold material and temperature. To minimize the time required to form the heated sheet, place the forming apparatus near the heating oven and use conveyors, quick acting clamps and other timesaving devices.

Another method of increasing the time available for forming is to keep the forming molds warm. This can be done by using a properly spaced bank of infrared lamps focused on the molds or by using metal molds which are cored for circulating warm water or oil. Metal molds and greased molds cool the Chemcast® GP faster than those made of wood, plaster or thermosetting resins; hence, it is more important that they be kept warm during forming. The molds should not be allowed to get too hot or the Chemcast® GP will require too long to cool. Best results are usually obtained with a mold temperature of about 170°F. for Chemcast® GP.

SLOW COOLING

After the Chemcast® GP has been formed, it should be allowed to cool slowly and uniformly. Slow, uniform cooling will help minimize internal stress and often results in true contours, particularly in thick parts. Many fabricators cover a formed part with a soft, heavy blanket for these reasons.

Chemcast® GP should be cooled below 180°F. for Chemcast® GP before removing it from the form. Otherwise, the material will tend to go back to its flat sheet shape. On the other hand, formed parts should not remain on the form till completely cooled or cracking may occur. Definite heating, forming, and cooling time cycles should be established for pro auction of uniform parts.

Forming Temperatures and Cycles