Tips for Annealing Parts Made from Acrylic Sheet

We recently had a customer ask us for some tips on annealing cast acrylic. There are definitely some potential pitfalls when working with acrylic in both sheet and finished part form, but following the guidelines outlined below should yield excellent results.

First… What is Annealing?

Annealing is the process of relieving stresses in molded or formed plastics by heating to a predetermined temperature, maintaining this temperature for a set period, and slowly cooling the parts. Sometimes, formed parts are placed in jigs to prevent distortion as internal stresses are relieved during annealing.

Tips for Annealing Acrylic Sheet

To anneal cast acrylic sheet, heat it to 180°F (80°C), just below the deflection temperature, and cool slowly. Heat one hour per millimeter of thickness – for thin sheet, at least two hours total.

Cooling times are generally shorter than heating times – see the chart below. For sheet thickness above 8mm, cooling time in hours should equal thickness in millimeters divided by four. Cool slowly to avoid thermal stresses; the thicker the part, the slower the cooling rate.

With coronavirus cases surging in the U.S., many people are concluding they'll have to learn to live with the virus until a COVID-19 vaccine is widely available — and that's led to a huge increase in orders for plexiglass and other types of clear plastic barriers meant to keep us safe.

"Demand is ridiculously high," said Jackie Yong, a 17-year employee of J. Freeman, Inc., a plastics distributor and sign supplier in Boston whose products include plexiglass and other plastic sheets. "Everything's just been flying out the door."

That's the story of the plexiglass industry these days: As many businesses struggle to reopen safely during the pandemic, from nail salons to barbershops to restaurants to casinos, they're installing protective barriers to try to prevent employees and customers from catching the virus.

"People are afraid they're going to lose their businesses, and so they're trying to put up as much protection as possible so that when people come, they'll feel safe," said J. Freeman, Inc., owner Jacqueline Freeman.

"We've had people asking for massive amounts — 400, 500, 600 sheets," she added. "Before it even hits our building, it's gone."