All materials change dimension with temperature. Plastics, in this case polycarbonate, tend to expand and contract more with temperature fluctuations than non-plastics, like metals or glass. To avoid buckling or deformation of the sheet during elevated temperatures, it is necessary to compensate by calculating the linear thermal expansion of Polycarbonate sheet. If the polycarbonate is subject to cold temperatures, it is also helpful to calculate the contraction rate of the material.
Formula for calculating expansion and contraction.
The formulation for calculating Linear Thermal Expansion is:
ΔL = α (L0 * ΔT)
Where:
ΔL = the change in length in inches of the sample due to heating or cooling at a specific temperature.
α = coefficient of linear thermal expansion (CLTE). The CLTE for polycarbonate is 3.75 x 10⁻⁵ in/in/°F
L0 = the original length of the sample at room temperature. For this example we use 75°F for room temperature. For accuracy, you should use the temperature of the room where the polycarbonate is being fabricated.
ΔT = the change in temperature in °F
Example
Example: If you wanted to calculate how much a piece of polycarbonate 48 inches in length would expand and contract when subjected to a temperature range from 0°F to 120°F, you can first calculate the expansion of the polycarbonate.
Expansion.
ΔL = 3.75 x 10⁻⁵ in/in/°F (48 inches * (120°F – 75°F)) = 0.081 inches A piece of polycarbonate 48” long when subject to 120°F would expand to 48.081 inches in length.
Contraction.
For contraction the formulation is the same.
ΔL = 3.75 x 10⁻⁵ in/in/°F (48 inches * (0°F – 75°F)) = -0.135 inches A piece of polycarbonate 48” long when subject to 0°F would contract to 47.865 inches in length.
In this scenario, to avoid buckling the channel would have to be minimum of 48.081 inches in length to account for expansion. For the polycarbonate to stay in place, the edge engagement of the channel would have to be greater or equal to 0.135 inches to account for contraction. Polycarbonate will expand and contract in all directions. Calculate for the length and the width.
For more information on the linear thermal expansion of Polycarbonate sheet, contact Liz Grimes – Technical Director HighLine Polycarbonate. Ph.: 215-872-3532 or email lgrimes@HighLinePC.com