Glass Bending Temperatures

Glass bending is the process by which glass is shaped without obtaining mould marks on the glass.  It also attempts to shape the glass without changing the thickness of the glass across its length and width. Glass bending can be done as a free drop curve or into a mould. This bending is usually done at much lower temperature than slumping.

Determining the temperature at which glass should be bent is a matter of experimentation with each new shape and thickness of glass.

If the temperature is too high you find distortions are created in the glass.  Sometimes wrinkles develop.  In general, a high temperature leaves a lack of time to compress and stretch evenly into irregular shapes.

If the temperature is too low the whole process takes an impractically long time to complete.

The just right temperature is in the region of 50C above the annealing point of the glass being used.  Experimentation with the shape and thickness of the glass is needed to establish a reasonable time for the bending; and for it to be achieved at a low enough temperature to get the shape required.

An example is this tapered cylinder.

 

Lantern frame for the glass

Mould shaped from the lantern into which the glass is to be bent

Flat template for cutting the glass

The bent glass

The curve was achieved at 590C in 20mins

A 1/8 sphere requiring bending in two directions was achieved at 570 in 45 mins to avoid ripples at edges.

The span as well as the shape affects the temperatures and times.  More information on bending glass is given in this blog entry.