Manya-manyan injuna suna da mahimmanci a cikin ƙarfe don ƙarfafa kayan aiki masu nauyi kamar masu hura wuta, injinan birgima, da tsarin jigilar kaya. An ƙera shi don yin aiki a cikin matsanancin zafi (har zuwa 60 ° C) da yanayin ƙura mai ƙura, waɗannan injiniyoyi suna tabbatar da ci gaba da samarwa a cikin tsire-tsire na ƙarfe da kuma sarrafa ƙarfe maras ƙarfe. Maɓallin aikace-aikacen sun haɗa da narkakkar famfo famfo, jujjuyawa daidai, da tsarin sarrafa kayan sarrafa kansa.