In this lesson we will learn what extrusion is, how it works, and what products can be created using the extrusion process. We will also review pressure and the ideal gas law in order to better understand extrusion.
Look at a macaroni noodle or a cheese puff. How did they ever get these foods into these shapes? Somehow the macaroni ended up with a tube and a curve. And how did that cheese puff get puffy? These foods are made with the same processing that makes a pipe called extrusion.Extrusion is a process that uses a die in order to get a material with a constant cross-sectional cut.
The die is what the material is pushed through in order to get the desired shape. Each product has a specific die that will create that shape and characteristics. Extrusion is used with materials such as plastic, aluminum, and dough. These products are either too brittle or too soft to be formed using bending or hammering. So in order to form the desired shapes extrusion is necessary.
Extrusion works by forcing the dough or semi-liquid material through a shaft.
At the end of the shaft is the die with the particular shape to form the desired cut. For a tube, the die will simply be a circle that the material gets pushed through. To make a curve the die will have a more narrow circle at first, that then gets wider. These designs often use different pressures in order to create the desired shape. Having a more narrow circle at first creates a higher pressure, forcing it to curve.
Think about playing with play dough as a child. You could push the play dough through different shapes in order to create the desired shape. There was a handle that would push the dough through the mold and out would come the desired shape. The use of these play dough molds were simple examples of extrusion. They weren’t very intricate designs and so are easier to understand how the shape is formed, but the same idea is used for extruding other products.
Extrusion and the Ideal Gas Law
There are some other key variables that affect the extrusion process. Let’s look at a balloon. When you initially blow up a balloon it’s fairly large. But as time passes the balloon slowly gets smaller because it is losing air.
The air acts as pressure on the balloon giving more volume the more air the balloon has. Also if you were to put that balloon outside on a cold day it would become smaller. This is because temperature also affects pressure and volume.When thinking about pressure and volume always remember the ideal gas law which is shown asPV=nRTwhere P is pressure, V is volume, n is moles of gas, R is a constant, and T is temperature. This equation always needs to remain in equilibrium.
So if you increase temperature but pressure remains the same then the volume needs to increase. If you increase the number of moles of gas (the amount of air you are putting into the balloon) then the pressure and volume needs to increase. If the volume can not increase any further then just the pressure will increase. When the pressure gets too high it could break the material, which is what happens when you blow up a balloon too much and it explodes.
Understanding pressure is important in extrusion because extrusion often uses pressure to create the desired product. Particularly for puffed products the pressure is manipulated to create a puffed product, like cheese puffs. The dough is put into the shaft, and the shaft is then heated. The heat increases the temperature which also increases the pressure (remember PV=nRT). But since the shaft and die are so solid the dough can’t expand anywhere, so the volume stays the same, but the pressure just increases. As soon as the dough exits the die there is nothing to keep the dough from increasing in volume, so it does. So why does the cheese puff stay puffed? Once it has exited the die, it is no longer hot, and since the temperature has decreased, the pressure and volume should decrease too.
This is because the added heat also cooked the dough by the time it exited the die, and the dough has solidified. It now has enough structure to hold the new shape instead of falling in on itself like it would if it was still a dough.The extrusion process can make many different shapes. These different shapes can be created by cutting a die into a specific form and manipulating the pressure.
Extrusion is a process used in many different industries to create a product with a specific shape.
Extrusion can only create a constant shape. The different shapes can be created by changing the shape of the die and manipulating the pressure. Products such as plastic containers, pipes, and pasta noodles are all created using the extrusion process.