Wikijunior:How Things Are Made/Metal/Scissors
Scissors are cutting instruments consisting of a pair of metal blades connected in such a way that the blades meet and cut materials placed between them when the handles are brought together.
What do we need to make this thing?
Scissors are usually made of 2 types of metal: carbon steel and stainless steel .
Carbon steel is used to make scissors in which the blade and the handle form one continuous piece. Carbon steel is manufactured from iron and about 1% carbon. It has the advantages of being strong and staying sharp. It is usually plated with nickel or chromium to prevent them from rusting.
Stainless steel is used to make scissors in which a plastic handle is fitted to the metal blade. Stainless steel is manufactured from iron, about 1% carbon, and at least 10% chromium. It has the advantages of being light and rustproof. The handles of stainless steel scissors are made from a strong, light substance such as ABS (acrylonitrile-buta-diene-styrene) plastic.
What is the step by step process?
For first step, there are 3 ways to produce a blank. A blank may consist of a blade and a handle in one piece or it may consist of only the blade.
- Step 1a: Cold stamping: A sharp die in the shape of the blank is stamped into a sheet of unheated steel. The die cuts through the steel to form the blank.
- Step 1b: Molding: Molten steel is poured into a mold in the shape of the blank. The steel cools back into a solid and the blank is removed from the mold.
- Step 1c: Drop forging: Like cold stamping, this process involves shaping the blanks with a die. This die, known as a drop hammer, pounds into a bar of redhot steel to form the blank. The pressure of the drop hammer also strengthens the steel.
- Step 2: The blanks are trimmed to the proper shape by grinding away excess metal. A hole is drilled through the blank. This hole will later allow two completed blades to be attached to each other.
- Step 3: The trimmed blanks are hardened by 6heating them, then cooling them quickly in cold air, water, or quenching oil. The temperature to which they are heated and the medium in which they are cooled varies depending on the type of steel from which they are made and the desired characteristics of the blade.
- Step 4: The hardened blanks are heated again and allowed to cool slowly in air. This second heating, known as tempering, gives the blank a uniform hardness on all places of blanks.
- Step 5: The repeated heating and cooling causes the blanks to warp. They are straightened by being placed on an anvil and lightly tapped with a hammer. This process is known as peening.
- Step 6: The blank is ground into a blade by applying the edge to a rapidly moving sanding belt or abrasive wheel. The surface of the belt or wheel is covered with small particles of an abrasive substance and works in the same way as sandpaper. The hard abrasive grinds away enough steel to form a sharp edge. The sharpened
blade is then polished in a similar manner using belts or wheels, containing much smaller particles of abrasive.
- Step 7: For many scissors, the handles are formed from the start as part of the blank. If not, they may be made of a metal alloy or from plastic. If they are metal, they are made in the same way as the blanks and then welded to them. If they are plastic, they are made by injection molding. In this process, molten plastic is forced under pressure into a mold in the shape of the handles. It is allowed to cool and the mold is opened to remove the handles. The handles contain
hollow slots into which the end of the blanks can be inserted. A strong adhesive is used to keep the handle firmly attached.
- Step 8: Two polished blades are attached to each other by a rivet or screw through the previously drilled holes. Rivets, which cannot be adjusted by the consumer, are used to make less expensive scissors. Adjustable screws are used in more costly scissors.