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What is a molecular eraser?

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What is the principle of eraser

Prince Yuan Shao

2022-03-14 06:20:26

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The eraser is a tool used to erase pencil writing. The pencil lead is made of graphite and clay. By adjusting the ratio of graphite and clay, the shape of the pencil lead can be changed. hardness.

When you use a pencil to write on paper, the pencil lead will rub against the paper, and the pencil lead will be ground into fine powder. Some of these powders enter the gaps between the fibers of the paper that are invisible to the naked eye, and some On the surface of the paper, and due to the intermolecular force between the paper and the refill powder, it is adsorbed on the paper.

Use an eraser to remove the pencil characters on the paper. In one case, the intermolecular force of the eraser on the pen core powder is greater than the intermolecular force between the paper and the pen core powder, so it will be erased. Eraser adsorption. You can try it out by pressing the pencil characters on the paper with the eraser, and the pencil characters will stick to the eraser, as shown in the picture below.

However, some refill powder penetrates deeply into the paper, and it is difficult to absorb the refill powder solely by relying on the intermolecular force between the eraser and the refill powder. Therefore, you need to use an eraser to rub on the writing, and use friction to overcome the intermolecular force to make the pen core powder fall off. Of course, a small amount of it will fall off on the surface of the paper, and the eraser will also fall off. The three powders rolled with the eraser and bonded together, forming something like thread.

A small piece of eraser can erase pencil marks. We have known this function since childhood, so what is its principle?

Let’s first look at why pencils can write on paper. The main components of pencil lead are graphite and clay. These two raw materials are mixed in different proportions. They are mixed, pressed, roasted at high temperatures, and finally immersed in oil. The different proportions of graphite and clay determine the hardness of the pencil. Clay The higher the content, the greater the hardness. For example, a 6h refill is harder than a 3h refill. In addition, the b in the pencil mark indicates blackness, which represents the content of graphite. 6b is the blackest color, while the hb pencil commonly used in painting indicates that the graphite and clay content are equal, taking into account both texture and blackness.

Because the graphite in the pencil lead is relatively soft, the internal molecules have a layered structure, and the layers are easy to peel off. There are many fine wrinkles and fiber gaps on the surface of the paper. When writing hard, the friction between the pen core and the paper will cause the graphite on the pen tip to form powder, which will adhere to the surface of the paper or in the gaps on the fiber surface, forming a pencil-drawn pattern. trace.

Let’s look at the eraser again. The main component of rubber is rubber, with sulfur, vegetable oil, and tiny sand grains also added. During the rubbing process of the eraser, the temperature of the contact surface between the eraser and the paper increases due to friction, which exerts a strong adsorption force on the graphite and clay molecules attached to the surface of the paper, thus "sticking" to the surface of the eraser, and the pencil characters It fades from the paper until it disappears. At the same time, due to the presence of sulfur and fine sand particles in the rubber, it is easy to shed crumbs during friction, so the adsorbed pencil foam, rubber slag and paper surface fibers will be kneaded into long strips, similar to the ones that form when taking a bath. It looks like putty rubbed off the skin.

As for why it is difficult for an eraser to erase words written by fountain pens and ballpoint pens, it is mainly because the words written by them are formed by ink and ink after they have dried. The ink and ink molecules are not attached to the surface of the paper. Instead, it has penetrated into the paper fibers. Unless these impregnated paper fibers are rubbed off with great force, it cannot be wiped off at all.

To understand the principle of the eraser, first we need to understand the paper and pencil we use to write.

Although paper feels very clean and smooth to us, in fact, these papers are made of wood pulp fibers. Therefore, if you magnify the surface of the paper dozens of times, you can see the actual The surface of the paper is uneven, with some ridges and ravines left by wood pulp fibers, but it is precisely because of this structure on the surface of the paper that pencils can write traces on the paper.

Secondly, let’s look at why pencils can write on paper.

The black pencil lead inside the pencil is actually made of graphite and sticky soil, which are mixed with water and then burned to form a specific shape. This specially treated graphite lead has good softness and Adsorbent, and because it is made of graphite, the color appears black. Due to the strong adhesion of the black pencil lead and the uneven surface of the writing paper, when you write, the graphite powder on the pencil lead will be worn off when it comes into contact with the paper, and then adsorbed on the paper. So what you see is the clearly colored pencil words you wrote.

After understanding the principles of paper and pencil, the working principle of the eraser can be easily solved.

Why can the eraser erase words? Why can graphite powder with strong adhesion be easily wiped away? Erasers are made of rubber. Unlike paper, which looks smooth and flat, most erasers have a more obvious concave and convex surface. Therefore, if the two rub against each other, the eraser has stronger friction, so Compared with paper, the eraser will wipe off a thin layer of paper with its stronger friction, peel off the graphite powder from the surface of the paper, and make the graphite powder adsorb on the eraser, and then a lot of eraser ash will be formed, and then the paper will be became clean.

But if it is a water-based pen or a fountain pen, the eraser cannot erase it, because this type of pen will penetrate the ink into the fibers of the paper, and the eraser cannot erase it.

Tell me the story of pencil and eraser. Most people think pencils are made of lead, but it turns out that this is wrong. Although we call it a pencil, pencil lead is actually graphite, which is composed of carbon. When you write with a pencil, the graphite particles in the central cylinder rub and stick to the paper you are writing on. If left undisturbed, these graphite particles will remain on the paper for a long time (ten years or so).

With an ordinary pencil, you can draw a line approximately 56 kilometers long. It's also possible to write the first word with a pencil, but you're likely to make a lot of mistakes in the process. It's human to make mistakes, so if you have an eraser, you can fix them.

The function of the eraser is based on the principle we use in daily life: friction. It is only because of friction that we can walk on the ground. This is why your hands heat up when you rub them together. Eraser is the result of friction between the eraser and paper. When the eraser rubs against the paper, the resulting friction generates heat, which helps the eraser become sticky enough to "stick" to the graphite particles. Typically, erasers are composed of synthetic rubber, but more expensive erasers use vinyl and plastic. These materials are used because they are stickier than paper fibers, making it easier to stick graphite particles to them. Essentially, anything stickier than paper fibers can be used as an eraser, it’s that simple!

The earliest eraser used by humans was wet bread crust. The first rubber was invented by British engineer Edward Nairn in 1770. It is said that the invention of the eraser was actually an accident, when Nairn picked up an eraser while trying to pick up a crust of bread. Then, as he used rubber to erase pencil marks, he realized the erasing properties of rubber.

Erasers are called erasers because they are made of rubber and because the process of erasing involves "wiping" pencil marks off the paper - hence the rubber. Friends, this is a story about pencil and eraser, which shows us that we should not be afraid of making mistakes and should learn how to correct them.

Friction

The principle is very simple, one is friction and the other is adsorption.

Before the invention of rubber, people commonly used bread to wipe pencils. In 1770, British scientist Priest first discovered that rubber could erase pencil writing. This discovery brought great convenience to people. . It can also be seen that the rubber first used the viscosity and adsorption force of rubber to erase pencil writing (powder mixed with clay and graphite) through friction and adsorption.

The earliest eraser was made of natural rubber. It did not shed any scraps when erasing. It just stuck the pencil end on the eraser. The more it was rubbed, the dirtier it became.

Later, people added substances such as sulfur and oil when making rubber, which made the rubber brittle and easy to chip. The erased pencil ends left the rubber with the chips. In this way, the eraser could always be kept clean, and the eraser could be kept clean. It won't stain the paper.

With the development of products, the classification of erasers has gradually become more detailed. There are those specially designed to erase pencil writing, and later there are those that can erase pen writing. By adjusting the proportion of rubber in the eraser and changing the hardness, Erase pen marks. People also add different directional ingredients to the rubber clay to give the rubber different aromas.

In the field of painting, the classification of rubber is more detailed. According to the hardness of drawing pencils, they range from 6H, 5H, 4H, 3H, 2H, H, HB, 1B, 2B, 3B, 4B, 5B, 6B, 7B, 8B. The higher the H number, the harder the pencil. For handwriting investigation in Vietnam, the B number The higher the pencil, the softer it is, the higher the graphite content, and the easier it is for the writing to become "dirty". There are corresponding special erasers for different pencils.

In addition to pencils, there are also drawing tools such as carbon rods and carbon crystal strips in the field of painting. In order to deal with this opponent in the rubber field, there are softer "plasticine" products. (This plasticine is not plasticine for children's toys, but plasticine for art.) The viscosity and adsorption capacity of the plasticine for erasing painting traces mainly depend on it.

Principle of friction

High resistance

Consume your own body to take away dirt

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