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2.5

Minor Versionm

by Madhushree HS

Introduction

A bimetallic strip is used to convert a temperature change into mechanical displacement. It consists of two different metal strips stuck together along their length. The direction of the bending of the strip changes accordingly on heating and cooling.

Video Overview

    • Handle scissors with care.

    • Beware of the edges of the metal tape strips as they can cut the skin if handled improperly.

    • Do not heat the strip too much; the adhesive on the tape will start to burn.

    • Use match stick under adult supervision.

  1. The DIY Battery Holder is designed to provide 3V, using two AA cells along with a foam piece, aluminium tape, connecting wire and a cardboard base. For more details on making a DIY Battery Holder, please go to DIY Battery Holder.
    • The DIY Battery Holder is designed to provide 3V, using two AA cells along with a foam piece, aluminium tape, connecting wire and a cardboard base. For more details on making a DIY Battery Holder, please go to DIY Battery Holder.

  2. Take a copper strip and an aluminium tape. For easier electrical connection, it is better if the copper strip is  1 cm shorter than the aluminium tape. Peel away the paper at the back of the aluminium tape to reveal its sticky side.
    • Take a copper strip and an aluminium tape.

    • For easier electrical connection, it is better if the copper strip is 1 cm shorter than the aluminium tape.

    • Peel away the paper at the back of the aluminium tape to reveal its sticky side.

    • Now, carefully stick the copper strip along the length of the aluminium tape.

    • If the widths of the aluminium tape and the copper strip are unequal, then trim them with the help of scissors. Ensure that both the metal strips are of equal width after trimming.

  3. Now, peel back the aluminium tape slightly (about 0.5 - 1 cm) from the shorter end of the copper strip. Make a mark on the thick binding wire taking the safety pin's height as the reference. Insert the thick binding wire between the bimetallic strips such that the upper edges of the strip are placed exactly at the reference mark. Press and stick the two metal strips such that the thick binding wire is in between them. Your bimetallic flag post is now ready.
    • Now, peel back the aluminium tape slightly (about 0.5 - 1 cm) from the shorter end of the copper strip.

    • Make a mark on the thick binding wire taking the safety pin's height as the reference. Insert the thick binding wire between the bimetallic strips such that the upper edges of the strip are placed exactly at the reference mark.

    • Press and stick the two metal strips such that the thick binding wire is in between them. Your bimetallic flag post is now ready.

  4. Take a rubber foam piece of size 12 cm x 2 cm and pierce the bimetallic flag post at a distance of 1 cm from one of its shorter edges. The rubber foam piece is 1 cm thick and it will act as a base. Ensure to pierce the bimetallic flag post 1 cm deep into the rubber foam piece. The bimetallic strip should be 4-5 cm above the foam base.
    • Take a rubber foam piece of size 12 cm x 2 cm and pierce the bimetallic flag post at a distance of 1 cm from one of its shorter edges.

    • The rubber foam piece is 1 cm thick and it will act as a base. Ensure to pierce the bimetallic flag post 1 cm deep into the rubber foam piece.

    • The bimetallic strip should be 4-5 cm above the foam base.

    • Use a drop of glue to secure the bimetallic flag to the foam base. Allow it to dry for 5 minutes.

  5. Once the glue is dry, straighten the strip and make sure it runs parallel to the base. Take a connecting wire of length 15 cm. Strip around 2 cm of insulation from both ends of the wire. Make a small hole with a safety pin on the aluminium tape and tie one end of the connecting wire to it.
    • Once the glue is dry, straighten the strip and make sure it runs parallel to the base.

    • Take a connecting wire of length 15 cm. Strip around 2 cm of insulation from both ends of the wire.

    • Make a small hole with a safety pin on the aluminium tape and tie one end of the connecting wire to it.

  6. Make a small fold on the strip, around the connecting wire to make sure the exposed wire is connected to both sides of the strip. Make two holes with scissors on the foam base, at a distance of 1 cm from the side opposite to the bimetallic flag post. These holes should be spaced  0.5 cm apart. Alternatively, you can measure 10 cm   from the bimetallic flag post and make  the holes. The holes made are at a distance of 0.75 cm from the longer edges.
    • Make a small fold on the strip, around the connecting wire to make sure the exposed wire is connected to both sides of the strip.

    • Make two holes with scissors on the foam base, at a distance of 1 cm from the side opposite to the bimetallic flag post. These holes should be spaced 0.5 cm apart.

    • Alternatively, you can measure 10 cm from the bimetallic flag post and make the holes. The holes made are at a distance of 0.75 cm from the longer edges.

  7. Insert safety pins (tail first) into each of the holes, made on the foam base earlier. Slightly tilt the bimetallic strip so that the aluminium tape touches one of the safety pin's head. The safety pins should be  5 mm apart, with the bimetallic strip in between them.
    • Insert safety pins (tail first) into each of the holes, made on the foam base earlier.

    • Slightly tilt the bimetallic strip so that the aluminium tape touches one of the safety pin's head.

    • The safety pins should be 5 mm apart, with the bimetallic strip in between them.

    • Take two connecting wires of length 15 cm. Strip around 2 cm of insulation from both ends of each of the wires.

  8. Attach connecting wires to each of the safety pin bodies. You can additionally push the wires into the holes made by the safety pins on the foam base to secure them firmly. The wiring is now complete. You will be left with three free wire ends.
    • Attach connecting wires to each of the safety pin bodies.

    • You can additionally push the wires into the holes made by the safety pins on the foam base to secure them firmly.

    • The wiring is now complete. You will be left with three free wire ends.

  9. Identify the polarity of the  LEDs. The longer leg is positive, whereas the shorter leg is negative. Join the negative legs of both the LEDs together, by twisting them.
    • Identify the polarity of the LEDs. The longer leg is positive, whereas the shorter leg is negative.

    • Join the negative legs of both the LEDs together, by twisting them.

    • This "common" negative terminal will be connected to the negative terminal of the battery.

  10. Connect the negative terminal of the battery holder to the common negative of the LEDs. Connect the free end of the wire from the bimetallic flag post to the positive terminal of the battery holder. Connect the wires from the safety pins to the positive pins of the LEDs.
    • Connect the negative terminal of the battery holder to the common negative of the LEDs.

    • Connect the free end of the wire from the bimetallic flag post to the positive terminal of the battery holder.

    • Connect the wires from the safety pins to the positive pins of the LEDs.

  11. If the connection is correct, then the green LED glows when the strip is in its default position. Make sure the bimetallic strip is almost straight,  without any creases on the aluminium tape.
    • If the connection is correct, then the green LED glows when the strip is in its default position.

    • Make sure the bimetallic strip is almost straight, without any creases on the aluminium tape.

    • Now carefully hold a lighted match stick under the bimetallic strip and watch it bend until it touches the other pin. The green LED turns off and the red LED turns on, indicating that the strip is in its 'heated' position.

    • Lighted match stick should be held under the bimetallic strip at the centre and observe the time taken by the bimetallic strip to bend. When you notice the bend, take the lighted match stick away.

    • If the bimetallic strip is heated for too long, the adhesive may catch fire or the strip may get damaged / deformed permanently.

    • If you do not see the bimetallic strip changing shape even after 30 seconds, please stop heating and refer the troubleshooting guide for possible issues.

  12. Here is a circuit diagram of this experiment. You can see that the bimetallic strip acts like a two-pole switch, routing the connection through one LED or another; depending on its temperature.
    • Here is a circuit diagram of this experiment. You can see that the bimetallic strip acts like a two-pole switch, routing the connection through one LED or another; depending on its temperature.

    • Make sure that the bimetallic strip is as straight as possible and doesn't have creases. This will help it bend in the right direction when heated.

    • The bimetallic strip bends toward the copper side when heated, so make sure that the red LED is attached to the pin on the copper side.

    • If the LEDs don't glow at all, check the polarity of the LEDs, they will not work if reversed. Longer legs of the LEDs should be connected to the positive terminal of the battery, whereas the common negative should be connected to the negative terminal of the battery.

    • If the bimetallic strip does not illuminate the red LED when heated, try reducing the distance between the two safety pins.

  13. Increase the thickness of bimetallic strip. Increase the distance between the safety pins to 1 cm and record your observations.
    • Increase the thickness of bimetallic strip.

    • Increase the distance between the safety pins to 1 cm and record your observations.

  14. Replace the copper strip with steel strip and aluminium tape with brass strip. Replace the copper strip with the brass strip. Replace the copper strip with the steel strip.
    • Replace the copper strip with steel strip and aluminium tape with brass strip.

    • Replace the copper strip with the brass strip.

    • Replace the copper strip with the steel strip.

    • Learn these variations, by going to DIY Bimetallic Strip (Variations)

Finish Line

Madhushree HS

Member since: 05/02/2017

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