Patent ID: 9187875
Filing Date: 2015-11-17
Classification: E02F

Abstract:
1. An arm for a construction machine formed as a box-shaped structural body having a square cross section by a left side plate, a right side plate, an upper plate joined to upper end sides of said left and right side plates by welding, a lower plate joined to lower end sides of said left and right side plates by welding, and a rear plate joined to rear end sides of said left and right side plates and a rear end side of said upper plate by welding, in which a boom connecting boss located on rear part lower sides of said left and right side plates and joined to rear ends of said left and right side plates and said lower plate and a front end of said rear plate by welding is provided, and a pair of left and right arm cylinder brackets joined to an outer surface of said rear plate by welding are provided, characterized in that: said left side plate is formed by joining two members, that is, a left rear thick side plate located on a rear side where said boom connecting boss is joined and made of a soft steel material with a large plate thickness and a left front thin side plate located on a front side of said left rear thick side plate and made of a high tensile steel material with a small plate thickness; said right side plate is formed by joining two members, that is, a right rear thick side plate located on the rear side where said boom connecting boss is joined and made of a soft steel material with a large plate thickness and a right front thin side plate located on the front side of said right rear thick side plate and made of a high tensile steel material with a small plate thickness; said upper plate is formed by joining two members, that is, a rear thick upper plate located on the rear side where said rear plate is joined and made of a soft steel material having a large plate thickness and a front thin upper plate located on the front side of said rear thick upper plate and made of a high tensile steel material having a small plate thickness; said lower plate is formed by joining two members, that is, a rear thick lower plate located on the rear side where said boom connecting boss is joined and made of a soft steel material having a large plate thickness and a front thin lower plate located on the front side of said rear thick lower plate and made of a high tensile steel material having a small plate thickness; and said rear plate is formed by using a soft steel material having a large plate thickness.