Don't tear off the sticker on the bottom of the thermos cup!!! Otherwise...

Today I will tell you a cold but warm knowledge:

If there is a sticker on the bottom of the thermos, it is recommended that you do not tear it off, otherwise the thermos will become a stick of chicken.

Recently, a Japanese thermos manufacturing industry insider tweeted:

If you tear off the sticker on the bottom of the thermos, the insulation effect may disappear.

The thermos cup with a sticker on the bottom has a hidden secret. This sticker actually has a protective function. Image source: twitter/waheifreiz

He said that this sticker is actually called a protective sheet in the industry. If this protective sheet is torn off, the thermos will lose its heat-insulating effect.

The sticker on the bottom of the thermos is actually a protective patch that protects the exhaust hole left by the tailless thermos (see below). Image source: CN112894109A

Is this sticker or vacuum sealed? Is this true?

It's true, the sticker does protect the ".

Not only that, I advise you not to drop the thermos with a sticker on the bottom, as it may leak if dropped.

It all starts with the principle of the thermos cup.

Image source: thermos

Insulation is usually achieved by two metal barrels separated by a vacuum. The vacuum has a very poor thermal conductivity, so the liquid in the liner can keep warm.

So the question is, how to achieve a vacuum between two layers of metal?

If two layers of metal are directly put together during manufacturing, the air in between cannot be pumped out. Therefore, there must be a hole in the vacuum!

So after the vacuum is drawn, how should this hole be treated to achieve sealing?

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Two schools of thought emerged here.

The old-fashioned vacuum method is called with tail vacuum . Its principle is to leave a copper tail at the bottom of the shell to draw the vacuum.

How to seal the tail seal after vacuuming?

In fact, it is to bend the copper tail and then seal it, which is similar to tying a knot with metal. Obviously, the sealing performance of this method is not very good.

In a 2015 patent, thermos manufacturer Thermos introduced that after long-term use of a thermos with a tail seal, the space between the inner and outer layers of the thermos will gradually be filled with gas, no longer a vacuum, and the insulation effect will be lost.

Image source: See watermark

In order to protect this "tail", there is a "tail hiding room" at the bottom of the tail sealed thermos cup.

However, in this way, the available volume of the thermos cup with a sealed tail will become smaller.

So if the thermos you buy is large in size but small in capacity, it is most likely made with a tail seal and will not keep heat after a short time.

So what is the new vacuuming method?

The current method of evacuating a thermos cup is called tailless vacuum , in short, it means - making glass.

Specifically, the air extraction hole of the tailless vacuum is also on the outer layer, and there is a very small glass bead next to the air extraction hole.

Before vacuuming, the glass bead can move on the vacuum hole and does not affect the vacuuming, a bit like the valve core of a bicycle.

The exhaust holes and glass beads at the bottom of the tailless thermos before vacuuming. Image source: youtube/high caliber line

After the inner liner is put into the outer shell, the thermos cup will be placed in a vacuum furnace to evacuate the vacuum. After the vacuum is evacuated, the glass beads cannot be moved, otherwise it will leak.

To prevent the glass beads from moving, the furnace is heated to 500-700 degrees Celsius to melt the glass and seal the exhaust hole.

In this way, the thermos cup will not have a metal tail, so it is called "tailless vacuum", and the technology of sealing by melting glass is also called "melting sealing" technology.

The process of testing the tailless vacuum flask is also very interesting.

After being taken out of the vacuum oven, the outside of the cup will be heated for another 20 seconds, and then the inspector will touch the inside manually.

If it is hot, it means that the thermal conductivity is very good, which means that there is no heat preservation (insulation) effect. Such cups are unqualified products.

The tailless thermos cup after sealing. Image source: youtube/high caliber line

The current high-end metal vacuum flasks, including stainless steel and titanium vacuum flasks, are manufactured using tailless vacuum technology in the final vacuuming and sealing steps.

Although the heat preservation effect of tailless vacuum is better than that of tail sealed, and the inner liner capacity is larger, it also has many disadvantages.

First of all, the professional term for this kind of glass beads is called "glass-based flux". This kind of glass-based flux is more expensive, so the tailless vacuum flask is more expensive than the one with a tail.

Secondly, the conductivity of glass-based solder is poor, so when "beautifying" the thermos cup, that is, doing the electrostatic spraying process, the place where the glass bead is located cannot be colored and is out of tune with the surroundings.

For this reason, the tailless vacuum flask must add a butt plug above the glass beads to fill this "hole".

After removing the protective sticker, the exhaust hole at the bottom of the tailless thermos is exposed. Image source: twitter/waheifreiz

Last but not least, glass is breakable.

Therefore, if the tailless vacuum flask accidentally falls to the ground or gets bumped, the glass bead may break, and the vacuum will leak, and the insulation effect will be lost.

Manufacturers have also taken the above factors into consideration, so they will use steel sheets or silicone pads in this place.

In order to avoid being obtrusive, this protective layer is integrated into the label. This is an important reason why the label at the bottom of the thermos bottle cannot be torn off.

As soon as I let go, the thermos took a breath of cold air.

Written by: Qijun

Source: Bringing Science Home

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