Do not connect the power cord of the vacuum pump!
The potential of copper and aluminum is different. The contact between copper and aluminum will accelerate the oxidation of the aluminum wire due to the reaction of the primary battery. For a long time, the copper-aluminum joint will be in poor contact. In order to be connected together, it is necessary to use copper and aluminum over-clamps or over-line tubes.
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This is a chemical problem. The chemical properties of metals are relatively lively and inactive. For example, gold is never rusted. This means that gold is chemically inert, iron is easy to rust, and iron is more active than gold. If two metals are placed Together, it accelerates the oxidation of active metals. Compared with copper, aluminum is more active. The connection of two cables will accelerate the oxidation of aluminum (that is, rust) and affect the use.
When the copper and aluminum conductors are directly connected, the contact surfaces of the two metals are easily formed into an electrolyte under the action of moisture, carbon dioxide and other impurities in the air, thereby forming a primary battery using aluminum as a negative electrode and copper as a positive electrode. The galvanic corrosion of aluminum causes an increase in the contact resistance at the junction of copper and aluminum.
Do not connect the power cord of the vacuum pump!
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In addition, since the elastic modulus and thermal expansion coefficient of copper and aluminum differ greatly, after a plurality of thermal cycles (energization and power-off) during operation, a large gap is generated at the contact point to affect the contact, and the contact is also increased. Large contact resistance. An increase in contact resistance causes an increase in temperature during operation. Corrosion oxidation will be intensified at high temperatures, causing a vicious cycle, which will further deteriorate the quality of the connection, and finally lead to excessive temperature of the contact point and even accidents such as smoking and burning.
Why use copper and aluminum transition clamps when connecting copper wire and aluminum wire?
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The gray-white substance formed at the junction of the copper wire and the aluminum wire is slightly longer in the time of the aluminum oxide, and the contact resistance at the joint increases and heats up, which causes the building to be broken when the circuit is broken. So use a special copper-aluminum transition clamp. Avoid unnecessary trouble!
Copper and aluminum wire connecting device (commonly known as "copper aluminum nose")
If the copper wire and the aluminum wire are directly hinged together, the joint is easily oxidized, resulting in an increase in electrical resistance and thus more likely to burn out. The real reason for this damage is that the aluminum element is more active than the copper element, and a much micro-potential (i.e., micro-battery) is generated on the copper-aluminum bonding surface, thereby causing micro-electro-erosion, and the contact resistance becomes large over time. In ordinary homework, it is more reliable to connect the copper to the tin.
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In the power system, copper and aluminum are directly connected, and galvanic corrosion occurs when current flows. Therefore, a copper-aluminum transition is required, or a tin sheet is placed in the middle of the contact surface, and a layer of conductive paste is optionally applied. When the ordinary household is connected, the copper wire can be connected to the aluminum wire and connected to the aluminum wire to avoid galvanic corrosion.