Tube-making

Just over a hundred years ago,steel tubes began to be used in making bicycles. They possess the correct combination of strength,flexibility and lightness,so that nowadays tubes are used widely at home ,in traffic,industries etc.

One of the world’s largest manufacturers has modestly described the two basic ways of making tubes as either wrapping an accurate hole in strip steel or pushing a very strong hole through a steel bar.

The first method begins with coils of steel strip which are fed automatically through a series of forming rolls which gradually curl the flat strip into a tube shape. The edges of the tubes are heated by electric induction and pressed together so that they join by welding. Then the tube travels through a series of rolls which size and straighten it. Although many such tubes are supplied in straight lengths,a great number of tubes are manipulated bent,tapped and slotted,into the shapes required by manufacturers.

The second type of process,where the strong hole is pushed through a steel bar, has many variations but the products are generally described as seamless tubes. The Mannesmann process for making seamless steel tubes is a piece of rolled steel bars which is cut to billet length by torch cutter. Secondly,each piece,called a billet,is passed to a heat furnace by a conveyor. Next,the hot billets are passed to a hydraulic press which makes a coneshaped indentation in the center of the billet’s end,making it ready for the piercing operation which will follows.Then a solid rod of hot steel is spun between tow mutually inclined rolls which rotate in the same direction,so that the rod is pulled. Forward between them,and passes over the mandrel.After that the tube-shape can be fabricated into a thin walled tube by further processes.If a tube of optimum surface appearance and strength is required for,say,aircraft structures or hypodemic needlesa further process of cold drawing is applied.