1. The development history of paper clips
A paper clip is a tool made by simply bending a metal wire. However, this seemingly simple invention has, in fact, undergone repeated designs: In the past,it was easy for people to stack documents together and tie these documents into a roll with a tape or string them together with strings, but it was troublesome for people to find one of the already tied or stringed ducuments. Later, people started to pin the paper sheets together. But the needles are found to be damaging the paper and it is easy for the users to get stabbed.
So, how to solve these problems? Eventually, people designed and invented paper clips. It is generally believed that the paper clip was designed in 1899 by the Norwegian mathematician John Waller. In February 1990, a paperclip-shaped stainless steel monument was erected in the center of Oslo, the capital of Norway.
2. Paper clip manufacturing process
If you are a person who majors in the study of materials, I bet you cannot help asking, what materials are used in the paperclip manufacturing process, and how are they made?
Generally speaking, making a paper clip will require the wire of nickel-plated, zinc-plated or color-plated iron. Zinc-plated iron wire, or galvanized wire, has good toughness and elasticity, and it also has strong corrosion resistance. And galvanized wire can also be further divided into hot-dip galvanized wire and cold-dip galvanized wire (electro-galvanized wire). The differences between these two galvanized wires are shown as follows:
(1) Hot-dip galvanizing refers to the process of immersing plating in the molten zinc solution. The production speed of hot-dip galvanizing is fast, and the coating is thick, but normally the coating is tend to be uneven. The thickness of the galvanized iron wire is usually above 45 microns. And the galvanized iron wire is darker in color and has good corrosion resistance. It can be maintained for decades in outdoor environments.
(2) Different from hot-dip galvanizing, cold galvanizing (electro-galvanizing) is a process of making the zinc gradually coat the metal surface through the unidirectional current in the electroplating tank. And unlike the hot-dip manufacturing process, the production speed of the cold-dip galvanizing is slow, but the coating layer is uniform. Moreover, the cold-dip galvanized wire is usually very thin. The thickness of it is only 3-15 microns. And the appearance of cold-dip galvanized wire is bright and resistant. However, this shining appearance of cold-dip galvanized wire is easy to get corroded and will get rusty in a few months.
Besides the two wires mentioned above, there also exists plastic coated wire (PET). PET is the abbreviation of English Polyethylene terephthalate. Polyethylene terephthalate is a high polymer, derived from the dehydration condensation reaction of ethylene terephthalate. Ethylene terephthalate is obtained by the esterification reaction of terephthalic acid and ethylene glycol.
PET is a milky white or light yellow, highly crystalline polymer with a smooth and shiny surface.
It has excellent physical and mechanical properties in a wide temperature range. It also holds the characteristics of excellent electrical insulation, creep resistance, fatigue resistance, friction resistance, and dimensional stability. At present, PET and PBT together are used as thermoplastic polyesters and polyester has become one of the five major engineering plastics.