Steel bobby pins are heated and cooled in different ways to demonstrate how thermal processing changes the strength and flexibility of metals. Students compare untreated, annealed, and quenched bobby pins by observing how each responds to applied loads.

1. Set aside one steel bobby pin as the control sample and do not heat it.
2. Hold a second bobby pin with pliers or tongs and heat it evenly in a Bunsen burner flame until it glows red-hot.
3. Keep the pin in the flame for about 20 to 25 seconds after it begins glowing.
4. Remove the pin from the flame and allow it to cool slowly in air on a paper towel. Label this pin as annealed.
5. Heat a third bobby pin in the Bunsen burner until part of it glows red-hot.
6. After heating for 20 to 25 seconds, immediately place the hot pin into a cup of cold water.
7. Remove the pin from the water, dry it completely, and label it as quenched.
8. Measure and record the width and height of the smooth side of the control bobby pin.
9. Set up each bobby pin so a cup can hang from the end using twine.
10. Gradually add pennies to the cup and observe how each bobby pin bends or fails.
11. Compare the behavior of the control, annealed, and quenched pins.

Thermal Processing of Bobby Pins: Interactive Science Lesson 8 - Ceramic and Glass Industry Foundation:

Heat treatment of metal Bobby pins - Grant Paul:

📄 Thermal Processing of Bobby Pins Lesson - Ceramic and Glass Industry Foundation: https://foundation.ceramics.org/teacher-resources/free-lesson-plans/thermal-processing/

📄 Heat Treatment of a Metal Bobby Pin - Chemistry Comes Alive: https://www.chemedx.org/JCESoft/jcesoftSubscriber/CCA/CCA2/MAIN/BOBBY/CD2R1.HTM

• Use different steel objects, such as paper clips, to compare results.
• Heat the pins for different lengths of time to see how heating duration affects properties.
• Test flexibility by manually bending the pins instead of using weights.

• Safety glasses must be worn at all times.
• Use pliers or tongs when heating metal to prevent burns.
• Keep flammable materials away from the Bunsen burner.
• Allow metal to cool fully before handling.
• Use caution when working with open flames and hot water.

• Which bobby pin bent the most under the same load? (The annealed bobby pin)
• Which bobby pin was the most brittle? (The quenched bobby pin)
• Why does slow cooling make the metal easier to bend? (Atoms have time to arrange into a softer structure)
• Why does rapid cooling make the metal harder but more brittle? (The atomic structure is locked into a stressed arrangement)