Boom for construction machine

Abstract

In left and right web plates ( 12 ) of a boom ( 11 ), first to fifth web materials ( 12 A to 12 E) are joined at edge portions in a front-rear direction along welding lines ( 13 A to 13 D). In an upper flange plate ( 14 ), a rear upper flange material ( 14 A), a front upper flange material ( 14 B), and a middle upper flange material ( 14 C) are joined at edge portions in a front-rear direction along welding lines ( 15 A, 15 B). Ina lower flange plate ( 16 ), first to sixth lower flange materials ( 16 A to 16 F) are joined at edge portions in a front-rear direction along welding lines ( 17 A to 17 E). The welding lines ( 13 A to 13 D) of the left and right web plates ( 12 ) are disposed in positions that are different from those of the welding lines ( 15 A, 15 B) of the upper flange plate ( 14 ) and the welding lines ( 17 A to 17 E) of the lower flange plate ( 16 ) in a front-rear direction. This makes it possible to reduce the entire weight and thereby achieve reduction in weight while ensuring bending strength, torsional strength, and the like of the boom ( 11 ).

1 . A boom for a construction machine, comprising:
 left and right web plates ( 12 ,  42 );   an upper flange plate ( 14 ,  43 ) that is joined to upper end sides of said left and right web plates ( 12 ,  42 ) by welding; and   a lower flange plate ( 16 ,  44 ) that is joined to lower end sides of said left and right web plates ( 12 ,  42 ) by welding,   said boom is formed of said left and right web plates ( 12 ,  42 ) and said upper and lower flange plates ( 14 ,  43 ), ( 16 ,  44 ), and formed as the box shape structural body being a closed section structure which is quadrangular in cross section, characterized in that;   said left web plate ( 12 ,  42 ) and said right web plate ( 12 ,  42 ) are each formed by joining a total of at least five plate materials ( 12 A to  12 E,  42 A to  42 F) having different shapes at edge portions in a front-rear direction along welding lines ( 13 A to  13 D),   said upper flange plate ( 14 ,  43 ) is formed by joining a total of at least three plate materials ( 14 A to  14 C,  43 A to  43 D) having different shapes at edge portions in a front-rear direction along welding lines ( 15 A,  15 B),   said lower flange plate ( 16 ,  44 ) is formed by joining a total of at least six plate materials ( 16 A to  16 F,  44 A to  44 G) having different shapes at edge portions in a front-rear direction along welding lines ( 17 A to  17 E),   end portions ( 15 A 1 ,  15 B 1 ,  15 A 2 ,  15 B 2 ) of said welding lines ( 15 A,  15 B) between said plate materials ( 14 A to  14 C,  43 A to  43 D) forming said upper flange plate ( 14 ,  43 ) and end portions ( 13 A 1  to  13 D 1 ,  13 A 2  to  13 D 2 ) of said welding lines ( 13 A to  13 D) between said plate materials ( 12 A to  12 E,  42 A to  42 F) forming said left and right web plates ( 12 ,  42 ) are disposed in positions that are different from one another in a front-rear direction, and   end portions ( 17 A 1  to  17 E 1 ,  17 A 2  to  17 E 2 ) of said welding lines ( 17 A to  17 E) between said plate materials ( 16 A to  16 F,  44 A to  44 G) forming said lower flange plate ( 16 ,  44 ) and said end portions ( 13 A 1  to  13 D 1 ,  13 A 2  to  13 D 2 ) of said welding lines ( 13 A to  13 D) between said plate materials ( 12 A to  12 E,  42 A to  42 F) forming said left and right web plates ( 12 ,  42 ) are disposed in positions that are different from one another in a front-rear direction.   
     
     
         2 . The boom for the construction machine according to  claim 1 , wherein a boom foot-side mounting member ( 20 ) that is located on a rear end side in a front-rear direction and is welded between said upper and lower flange plates ( 14 ,  16 ), and a boom cylinder mounting member ( 21 ) that is welded to said plate material ( 12 C) located in the middle-most of said five plate materials ( 12 A to  12 E) in a front-rear direction and a boom cylinder ( 11 A) is rotatably coupled thereto, are provided between said left and right web plates ( 12 ), and
 of said five plate materials ( 12 A to  12 E) forming said left and right web plates ( 12 ), the plate thicknesses of said plate material ( 12 A) on the rear end side to which said boom foot-side mounting member ( 20 ) is welded, and said plate material ( 12 C) located in the middle are made greater than the plate thicknesses of the other three plate materials ( 12 B,  12 D,  12 E).   
     
     
         3 . The boom for the construction machine according to  claim 1 , wherein a boom foot-side mounting member ( 20 ) that is located on a rear end side in a front-rear direction and is welded between said upper and lower flange plates ( 14 ,  16 ), and a boom cylinder mounting member ( 21 ) that is welded to said plate material ( 12 C) located in the middle-most of said five plate materials ( 12 A to  12 E) in a front-rear direction and a boom cylinder ( 11 A) is rotatably coupled thereto, are provided between said left and right web plates ( 12 ),
 an arm cylinder mounting member ( 23 ) which is located in a position closer to a front side than said boom cylinder mounting member ( 21 ) and in a top face of said plate material ( 14 C) located in the middle of said three plate materials ( 14 A to  14 C), and an arm cylinder ( 9 A) is rotatably coupled thereto, is provided in said upper flange plate ( 14 ), and   in said plate material ( 12 C) located in the middle of each of said left and right web plates ( 12 ), said welding line ( 13 B) on a rear side in a front-rear direction is disposed so as to be nearly orthogonal to a first reference line (L 1 ) connecting said boom foot-side mounting member ( 20 ) and said boom cylinder mounting member ( 21 ) and said welding line ( 13 C) on a front side in a front-rear direction is disposed so as to be nearly orthogonal to a second reference line (L 2 ) connecting said boom cylinder mounting member ( 21 ) and said arm cylinder mounting member ( 23 ).   
     
     
         4 . The boom for the construction machine according to  claim 1 , wherein said left and right web plates ( 12 ) are each formed of a total of five plate materials ( 12 A to  12 E), such as, a first web material ( 12 A) located on a rear end side in a front-rear direction, a second web material ( 12 B) whose rear end portion is joined to a front end portion of said first web material ( 12 A), a third web material ( 12 C) whose rear end portion is joined to a front end portion of said second web material ( 12 B), a fourth web material ( 12 D) whose rear end portion is joined to a front end portion of said third web material ( 12 C), and a fifth web material ( 12 E) whose rear end portion is joined to a front end portion of said fourth web material ( 12 D), and
 between said second web materials ( 12 B) forming said left and right web plates ( 12 ), a first partition plate ( 18 ) is provided so as to be located between said upper and lower flange plates ( 14 ,  16 ), and, between said fourth web materials ( 12 D), a second partition plate ( 19 ) is provided so as to be located between said upper and lower flange plates ( 14 ,  16 ).   
     
     
         5 . The boom for the construction machine according to  claim 1 , wherein an arm-side mounting member ( 22 ) that is located on a front end side in a front-rear direction and is welded between said upper and lower flange plates ( 14 ,  43 ), ( 16 ,  44 ) is provided in said left and right web plates ( 12 ,  42 ).