Annealing acrylic glass

Acrylic glass can be processed differently. Many of these processing techniques lead to tensions in the acrylic glass, which can later have negative effects. To avoid this, acrylic glass is tempered after certain machining processes. Why you should anneal acrylic glass and how you do it, you will learn in the following guide.

The diverse use of acrylic glass

Acrylic glass enjoys enormous popularity in industry, crafts as well as in private home improvement and hobbyists. Among other things, this is due to the extremely diverse processing options. You can:

  • Polish acrylic glass and sand
  • Acrylic glass lasers and welding
  • Acrylic glass shape and bend
  • Cut acrylic glass and saw
  • Glue and join acrylic glass

Mechanical processing creates heat

Many of these processing techniques produce more or less unavoidable heat. Very classic here is the drilling or milling of acrylic glass called. But even when repairing cracks that is the case. First, a scratch is milled out, then filled in several steps with liquid acrylic. When everything is hardened, the protruding bead must be ground flat. Even these temperatures are enough to trigger a certain effect.

The molecular chains of acrylic glass create tensions

The resulting heat on or in the acrylic glass unfavorably changes the molecular chains - they often freeze under tension. If you want to continue working on acrylic glass or just wait a while, you will notice that small cracks will appear at first, but they will get bigger and bigger. The stress from these marginal areas of the acrylic glass, where the heat was too strong, now propagates throughout the acrylic glass workpiece.

Annealing neutralizes this effect again

However, there are ways to "relax" the strained molecular chains. This process is called annealing. The workpiece made of acrylic glass is controlled to a certain temperature. At this temperature, the acrylic glass must then be stored for a certain period of time, ie the temperature must be maintained.

What happens when annealing acrylic glass

Then the acrylic glass is checked again and cooled relatively time consuming to the normal ambient temperature. Thus, by avoiding an abrupt temperature difference further thermal deformations of the molecular chains and thus renewed stress cracks can be avoided. It does not matter what kind of workpiece it is - annealing is done on the hood for an aircraft as well as on the acrylic glass object of a modeler.

Perform the tempering

However, corresponding industrial and craft enterprises also have tempering ovens, which are built specifically for plastic and which also have the necessary size. Tempering is more difficult for home users and DIY enthusiasts. However, you can build yourself an annealing chamber as long as the workpieces are not too big.

Annealing in the home improvement workshop

For smaller workpieces you can either use the oven or build a thermally insulated box yourself. Then there are corresponding radiant heaters, which can be set exactly. Achieving and maintaining the right temperature is as important as controlled cooling. However, these values ​​differ because they depend on different factors:

  • Thickness of acrylic glass
  • Production method of the acrylic glass: rolled (extruded) or cast acrylic glass
  • in the case of solids (cuboid, spheres, prisms, etc.) their volume is natural too

Values ​​for calculating annealing and cooling time

You can work with the following values ​​if you want to temper acrylic glass or have to:

  • Temperature to be maintained for extruded acrylic: 70 degrees Celsius
  • Temperature to be maintained for cast acrylic: 80 degrees
Time span that needs to be tempered

To calculate the time that this temperature must be maintained, take the material thickness (in millimeters) and divide by a factor of 3. Therefore, you would need a 10 mm acrylic sheet with 3 hours 20 minutes and 20 mm with at least 6 Heat for 40 minutes. For very thin Plexiglas with a result below "2", the minimum annealing time is always two hours.

Required controlled cooling time after annealing

You can also use a similar formula for cooling the acrylic glass. To do this, divide the material thickness of the acrylic glass (again in millimeters) by a factor of 4. 10 mm thick acrylic must therefore be allowed to cool for at least 2.5 hours and 20 mm thick acrylic for 5 hours. Further cooling rules state that the temperature per hour must not fall by more than 15 degrees Celsius. In addition, the acrylic glass must be well below 60 degrees before you can take it out of your tempering or heating cabinet.

Tips & Tricks

Annealing is necessary without exception for all processing techniques that produce heat in acrylic glass. So also when lasering or chemical bonding, since there is also heat.

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