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How to choose high quality EM strips

 

There are two kinds of EM strips in the present market and they are cobalt strips and iron strips. They are made of metal cobalt and pure iron. In terms of whether they could be magnetized or be degaussed, there are composite strips and permanent strips. Generally the composite strips are used for open-shelf books and the permanent strips are always used in reading room because the books cannot be lent outside. Each iron strip is half the price of cobalt one but the cheaper ones have brought many trouble to libraries, such as:
● The system doesn’t alarm when the books with strips are passing by the detecting channels.
● Sometimes it alarms and sometimes it doesn’t alarms.
● It alarms when the new strips are passing by the detecting channels but it doesn’t alarm after setting them inside the books.
● The EM strips alarmed in a short while after being set inside the books but they stop alarm later.
Why do these problems happen?
The bad quality EM strips probably result in these problems, especially the iron strips. Better cobalt strips will be a wise choice for libraries to avoid the problems.


How to choose cobalt EM strips?
The following questions should be clear first:
1. What kind of strip feature is used for the burglarproof system?
This strip is made from non-crystal material which is composed by some high temperature molten metal that was spouted out from the quartz nozzle in a very short time with a high speed to form solid strip. Short-time makes it non-crystal. This kind of non-crystal has a high permeability with rational components and scientific process. So its high permeability is used for alarming. Present cobalt and iron strips are made from non-crystal material.
2. Since iron strip and cobalt strip are both made from non-crystal material, should both of them have high permeability for burglarproof strips for books?
The answer is YES theoretically. But the magnetization is different in cobalt strips and iron strips actually because of many factors. Their permeability stress is different from each other. Iron strips will be influenced more than cobalt strips. Some users might find that the new strips worked normally, but after being set inside the books and the gumwater was dry, they could not alarm in the detecting channels or there was a large blind area. That was because of the stress. When the gumwater is dry, the paper will have a shrinking stress which will reduce the permeability, so the detectors could only find weak signal or no signal at all, that reduces the sensibility. Some iron strips will lose their sensibility at all. But this kind of stress has less influence on cobalt strips.
3. Could cobalt strips make it perfectly safe?
Not always. But cobalt ones are much better than iron ones. Cobalt strips will never lose their sensibility. (Generally, the sensitivity of normal stress cobalt strips becomes 40%~70% of its original sensitivity after being set inside the books and the sensitivity of negative cobalt strips won’t change.) But why the systems in some libraries still have low sensitivity with cobalt strips? The high quality cobalt strip has certain proportion of cobalt (60%~70%) with rational producing processes. There are many manufactories producing EM strips presently with different material proportion and cobalt proportion. The producing processes are relative to the operators’ working experience closely. So cobalt strips are not always the high qualified EM strips.

 

Introduction of capability parameters of EM strips
1. Sensitivity
The special EM strips should alarm everywhere inside the detecting area even in the weakest field, which means the EM strips have enough sensitivity.
The sensitivity of strips is decided by the material. The sensitivity is decided by original permeability μ0 and maximum permeability μm in magnetics. Higher μ0 and μm mean the higher sensitivity. Higher sensitivity EM strip has 60%~70% corporation of cobalt. When the cobalt corporation is higher than 70%, μ0 and μm will go smaller and the magnetization will reduce and the sensitivity of burglarproof strips will reduce contrarily.
2. Reliability
EM strips used in libraries need to be high reliable. However the strips are set inside the books, it will never influence the burglarproof capability. They are fixed by gumwater or latex generally, which result in strong stress on strips.
When EM strips are being magnetized when entering detecting areas, magnetostriction phenomenon happens on strips in magnetics. (The phenomenon that, when EM strips being magnetized, the length of the object will be elongated or shortened with the magnetized direction, is called magnetostriction. ) One magnetizing capability of the magnetizing material is magnetostrictive saturation factor λs, which is used to show the magnetostrictive extent of object length along with magnetizing direction in magnetization, higher λs means higher elongation or shortening.
Ø Set the iron EM strips inside the books and fix them with gumwater or latex or stickers. Magnetostriction phenomenon results in a big stress on strips in magnetostriction which will reduce the capability of strips even invalidate them totally.
Ø The λs of iron strips is about 10~35 (x10~6), outside stress has a huge influence on them. Their reliability is bad.
Ø The λs of cobalt EM strips is always lower than 5 (x10~6), outside stress has a smaller influence on them. Their reliability is better.

 

 

The contrast table of presenting market EM strips


Manufactory

μ0.005

μm

λs(x10-6)

Content of cobalt

We

Higher cobalt content strips

140000

280000

<1

60%~70%

Some others

Normal cobalt content strips

10000

210000

<5

40~50%

Some others

Lower cobalt content strips

<40%

Some others

Iron EM strips

μ0.01
1500

65500

10~35

0

 

3. Life duration
The life duration of the burglarproof strips is considered by users most.
Ø Water or humid environment rust Iron EM strips easy and rusted iron strips will lose their capability even forever. The actual life duration of iron strips is about 3 years.
Ø Cobalt strips have excellent corrosion resistance with limitless actual life duration, especially high cobalt content strips (60%~70%).


Composite EM strips
Composite magnetized/degaussed strip is an extension product of permanent strips. It is composed by permanent strips and semi-hard strips and stickers. There are two kinds of stickers in China, and they are water-based stickers and oil-based stickers. At the beginning, the capability is same, but the permanent paste capability of oil-based stickers is stronger.
Ø  Water-based stickers are easy to aging, compaction and hardening.
Ø  Oil-based stickers are not easy to aging and compaction.
Iron composite magnetizing/degaussing EM strips (iron permanent strips and water-based stickers) are easy to aging and compaction because of the water-based stickers, hardening makes the strips lose magnetization. The life duration is about 3 years.
Cobalt composite magnetizing/degaussing EM strips (permanent strips and oil-based stickers) has permanent life duration.
The contrast table of composite magnetizing/degaussing EM strips

 

 

Advantages

Disadvantages

Iron composite magnetizing/degaussing EM strips

Low price

Low paste capability, easy aging, harden, lose magnetization and short life duration

Cobalt composite magnetizing/degaussing EM strips

Permanent, strong paste, not easy to aging, long life duration

High price

 

Disadvantages of handmade EM strips
1. It is hard to keep consistent with light belt for degaussing piece.
2. The spaces between every degaussing piece are not the same.
These disadvantages result in lack of magnetization and not degaussed enough and bad sensitivity. The books with this kind of strips always cause misreport or no report.
Picture 1: handmade EM strips

Advantages of machine –made EM strips

  1. The degaussing piece keeps consistent with light belt.
  2. The spaces between every degaussing piece are same.

Machine-made EM strips are magnetized enough and they are degaussed completely with high sensitivity. The books with machine-made strips could be protected well.
Picture 2: machine-made EM strips
We have developed some equipments to product magnetized/degaussed EM strips independently, all the strips are produced by the equipments which make sure the excellent capability of strips.
We are the only manufactory producing strips with equipments in China and we promise to offer the best quality EM strips.

 

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