In fact, caused all of these are caused by temperature changes, the temperature difference between day and night in the North is relatively large, and in some places even reach 30 degrees Celsius, not to mention the four seasons temperature difference, the temperature difference can reach the sum of four seasons in the south.
In physics, metals exhibit different properties at different temperatures. For example, pig iron becomes very brittle at low temperatures and tends to crack. A slight impact causes the iron buttons in metal buttons to become halved . Therefore, a large temperature difference in the choice of iron buttons to be careful. Zinc buttons and iron buttons similar nature, in the case of sudden changes in temperature easily broken, the same careful choice.
The cadmium button in the high temperature easily vaporized, vaporized on the human body will cause some harm, high temperature, it is best not to choose cadmium button.