3B Scientific Tyndall's Bar Breaker User Manual
3B SCIENTIFIC
Tyndall’s bar breaker U8442150
Instruction Sheet
06/09 ALF
®
PHYSICS
1 Tensioning screw
2 Abutment
3 Metal bridge
4 Stand rod
5 Bolts
6 Spare bolts
1. Safety instructions
• Set up the experiment so that any pieces of bars
that break and fly off are not able to hit any
nearby people or breakable objects.
• Do not tighten the tensioning screw too much.
• Do not touch the equipment while heating the
metal bridge.
• Allow the equipment to cool before putting it
away.
Caution! Broken bolts will be hot.
• Only pick up broken pieces with the aid of heat-
resistant gloves or a suitable cloth.
2. Description
The bar breaker demonstrates the huge forces that
are involved in a change of volume of solid materials
due to temperature.
The bar breaker consists of a U-shaped abutment
with a metal bridge and a tensioning screw. At the
open end of the fork are two drilled holes through
which cast-iron bolts may be inserted, also passing
through the metal bridge to hold it in place. A rod
attached to the side of the abutment allows the bar
breaker to be attached to a retort stand.
3. Equipment supplied
1 Bar breaker apparatus
10 Cast-iron bolts
1
4. Technical data
7. Operation
Bolt holes: 10 mm dia.
Length of abutment: 290 mm
Stand rod: 65 mm x 12 mm dia.
Weight: approx. 1.3 kg
5. Accessories
Set of 10 cast-iron bolts U8442110
6. Operating principle
As the metal bridge is heated, it expands to such a
degree that its tensioning screw needs to be tightened up. When it cools it contracts back to its original length. However, it no longer has the play to do
this, since the tensioning screw has been tightened
at one end and the bolt prevents contraction at the
other. Eventually, the resulting tension in the metal
bridge becomes so great that it snaps the bolt in two
with a loud bang.
The following equipment is also required to perform
the experiment:
1 Stand base, A-shaped U8611160
1 Stainless steel rod, 470 mm U15002
1 Universal clamp U13255
1 Cartridge burner
1 Gas cartridge
• Set up the experiment as in Fig.1. Check that the
bolt is not aligned towards any viewing persons.
• Secure the bolt with its fastening screw before
heating it.
• Heat the bridge for about 5 minutes in a naked
gas flame. As the bridge heats up, keep tightening the tensioning screw to match the expansion.
• Take away the burner and allow the bridge to
cool.
Some time later, the bolt will break apart.
Fig. 1 Bar breaker experiment set-up
Elwe Didactic GmbH ▪ Steinfelsstr. 6 ▪ 08248 Klingenthal ▪ Germany ▪ www.elwedidactic.com
3B Scientific GmbH ▪ Rudorffweg 8 ▪ 21031 Hamburg ▪ Germany ▪ www.3bscientific.com
Subject to technical amendments
© Copyright 2009 3B Scientific GmbH
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