Hello, and welcome to the lab!
In most high-school chemistry or chemistry 101 courses, students learn how to cut and bend glass tubing. Glass tubing is an essential part of any chemistry lab and is necessary in many experimental apparatuses... apparati? :)
This Instructable is a tutorial on the basics of working with glass tubing, much like what you would be taught on one of your first days of chem lab: cutting, fire polishing, and bending.
So whether you are a chemistry student looking for a refresher, a homeschool parent learning at home with your student, or you missed that first day of class, this tutorial can provide you with an overview and instruction on how to begin handling some important lab equipment.
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Step 1: Supplies & Safety Points
The supplies you will need for this tutorial are:
- Multiple pieces of glass tubing*
- A glass cutting file**
- A butane burner / bunsen burner***
- A lighter
- Safety goggles
- Laboratory gloves
* Note on the glass tubing: Standard borosilicate glass tubing is pretty cheap. It is good to have extra when learning to work with glass tubing in case of breakage or other mistakes. A smaller size tubing will be easier to work with.
** Note on the glass cutting file: These are triangularly shaped files used to cut groves in glass tubing.
***Note on the butane/bunsen burner: Do not try to use an alcohol burner in place of a butane or bunsen burner. Alcohol burners and many similar devices do not produce a flame hot enough to soften glass.
Before beginning to cut, bend, or fire polish glass, first put on laboratory gloves and safety goggles.
Be cautious! This tutorial involves:
- a very hot open flame
- sharp, cut glass and breaking glass
- very hot, melting glass
- pressurized gas that is harmful to breathe if not burned
- risk of carbon monoxide in poorly ventilated area
- aerosol cans
To reduce risk:
- Wear gloves and goggles.
- Remain in well ventilated area.
- Always be burning the gas from the burner when it is turned on.
- Prevent others from handling hot pieces if glass tubing.
- Be careful with open flames and sharp glass.
- Make sure the gas is turned off on the burner after using it and check for leaks.
Step 2: Cutting Glass Tubing
To cut glass tubing:
1. Use the file to cut a groove in the glass.
Grip the file with your thumb and forefinger, and press one corner of the file firmly on the glass. While pressing downward, quickly pull the file across the glass and towards yourself. The file will cut a small groove on the surface of the glass. (If you feel it is necessary, you can repeat this step again as long as the corner of the file is exactly in the groove you cut the first time.)
2. Grip the glass tube in both hands.
Grip the glass tube with one hand on either side of the groove you cut with the file. Extend thumbs towards the center, where the groove is located. The groove should be on the opposite side of the tube as your thumbs, facing away from you. See pictures for clarification.
Break the glass by firmly bending the tube away from yourself - pushing with your thumbs against the cut glass. This should produce a nice, clean cut and you are ready for the next step!
Step 3: Fire Polishing Glass Tubing
Now you have a neat cut, but the edges of the glass will be very sharp. To remove the sharp edges, we use a technique called fire polishing.
To fire polish glass tubing:
1. Fire it up.
Turn on the butane burner and quickly ignite the gas with a lighter. Turn up the flame so that it gets large enough for you to see two 'cones'. The outer cone will be a fainter blue and the inner cone more distinct. It is important that the flame is hot enough for you to see a center cone.
2. Position glass tube in flame.
Hold the glass tube into the flame, tilted slightly downwards, so that the edge of the tube is directly on the outermost edge of the center cone. The flame burning the glass should be a bright orange. It may take a moment to position it right, but keep moving it around until you see that bright orange flame.
3. Rotate until edges are rounded.
Once the glass tubing is positioned correctly, rotate it slowly, back and forth, so that the edge is heated all the way around. Watch it closely as it starts to soften. Keep rotating the tube to maintain its shape. The edges will become smooth and rounded.
4. Let cool.
Now that the edges have been fire polished, remove the tubing from the flame. Keep rotating it slowly for a few seconds to allow it to cool without changing its shape. Then, set it down to cool completely on a clean surface. Prevent anyone else from touching the hot glass.
Step 4: Bending Glass Tubing
Often, a lab experiment requires a piece of glass tubing that is bent or shaped in a specific way. Here, you will learn to bend glass tubing by creating a simple 90 degree angle bend.
To bend glass tubing:
1. Turn on the flame.
Light the flame on the burner just like you did before, and turn it up so you can see the two cones.
2. Heat the tubing.
Begin to heat the tubing by moving it back and forth through the tip of the inner cone. The flame will be a faint orange that will intensify as the glass gets hotter. Heat the glass about an inch on either side of the point you want to bend -- two inches total. Linger slightly longer on the center of the section you are heating.
3. Carefully bend tubing.
When the glass in the center starts to melt, you will feel the tension release in the glass and you will see it start to bend. Keep moving it evenly through the flame and bend it carefully - slowly - into a 90 degree angle. If it gets too soft too fast, remove it from the fire and keep slowly bending it and then put it back in. It is ok to mess up a couple times before you get it right - practice makes perfect! That is why you should have some extra glass tubing on hand.
4. Anneal the glass.
Once the glass is bent to a 90 degree angle, promptly remove it from the flame and hold it steady in the air to cool for 30 - 60 seconds. Then, you will anneal the glass by running the bent part of the glass tube through the tip of the outer cone for a while. Annealing is a process of slowly cooling glass so that the glass can relax into shape and not be as prone to breakage. The added heat will help relax the glass in the bend to not be so fragile. The glass should not get so hot as to get soft again in this step.
5. Let cool.
Once the annealing is done, remove the glass tubing from the fire and set it on a clean surface to cool completely. Prevent others from touching the hot glass.
6. (optional step) Mold tubing to a specific shape using other objects.
If you want, during step 3 when you are bending the glass tubing, you can try more precise angles or specific shapes by forming the glass to the side of other objects. To do this, when the glass is hottest and melting, remove it from the fire and press it against the side or corner of some other object in the lab: such as the corner of a table if you want a right angle, or a cylindrical object of you want a semicircle. Then complete steps 4 and 5.
Step 5: Conclusion
Congratulations! You can now cut, fire polish, and bend glass tubing. You are now ready to cut and bend glass tubing in the lab for all of those incredible experiments and inventions you will get famous for someday.
Remember that practice makes perfect. Remember to keep learning new skills. And remember to turn off the bunsen burner. ;)
I hope that this tutorial was helpful.
“You have to learn the rules of the game. And then you have to play better than anyone else.”
- Albert Einstein
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