Chapter 29 – Springs

Publisher Summary Mechanical springs can be defined as elastic bodies whose primary function is to deform under a load and return to their original shape when the load is removed. In practice, the vast majority of springs are made of metal, and of these the greatest proportion are of plain-carbon steel. Flat springs are usually made from high-carbon steel in the annealed condition, which are subsequently heat-treated. A helical extension spring offers resistance to extension and it is invariably made from circular section wire. Leaf springs are essentially strips of flat metal formed in an elliptical arc and suitably tempered, which absorb and release energy, and are commonly applied to suspension systems. A frequent cause of confusion between the spring supplier and the spring user is the lack of precision in specifying the spring. This often results in high costs due to the manufacturer taking considerable trouble to meet dimensions, which are not necessary for the correct functioning of the spring. It is therefore recommended that, while all relevant data regarding the design should be entered on the spring detail drawing, some indication should be given as to which of the particular design points must be adhered to for the satisfactory operation of the component. A method of spring specification that has worked well in practice is to insert a table of design data where all design data are entered, and the items needed for the correct functioning of the spring are marked with an asterisk. With this method, the manufacturer is permitted to vary any unmarked items, as only the asterisked data are checked by the spring user's inspector.