JP2005030089A - Turning frame structure of construction machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a turning frame structure of construction machine capable of ensuring joint strength without requiring the grinder finishing when an upper flange of a frame member forming a tail frame is welded and connected to side plates forming the center frame. <P>SOLUTION: In the turning frame structure of a hydraulic shovel provided on a turning body 21 and constituted by welding and joining upper flanges 11c and 12c of I-beam members 11 and 12 as frame members included in the rail frame 2 to the side plates 6 and 7 included in the center frame 1, opening sections 11c1 and 12c1 are formed in the front end sections of the upper flanges 11c and 12c of the I-beams 11 and 12, the side plates 6 and 7 of the center frame are inserted in the opening sections 11c1 and 12c1, and the upper flanges 11c and 12c and the side plates 6 and 7 are respectively welded to form a welded part 17. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a swing frame structure for a construction machine, which is provided in a swing body of a construction machine such as a hydraulic excavator and welds and joins an upper flange of a frame member included in a tail frame and a side plate included in a center frame.

  FIG. 12 is a perspective view showing a hydraulic excavator exemplified as a construction machine. In this hydraulic excavator, a revolving body 21 is disposed on a traveling body 20, and the revolving body 21 is provided with a revolving frame 22 that is a subject of the present invention.

  As a conventional structure of the revolving frame 22, for example, one shown in FIGS. 13 and 14 has been proposed. 13 is a plan view and FIG. 14 is a side view.

  The conventional revolving frame structure shown in FIGS. 13 and 14 includes a center frame 23 at a front position and a tail frame 24 at a rear position. The center frame 23 includes a bottom plate 25, a pair of webs or side plates 26 and 27 that are erected on the bottom plate 25 and welded together, and plate members or partition walls 28 that are welded and joined between the side plates 26 and 27. It has. The tail frame 24 includes a pair of frame members 29 and 30, and transverse beams 31 and 32 that are disposed between the frame members 29 and 30 and are joined to the frame members 29 and 30. Each of the frame members 29 and 30 described above has side plates 29a and 30a to which the lateral beams 31 and 32 are joined, and upper flanges 29b and 30b positioned on these side plates 29a and 30a (for example, patents). Reference 1).

  FIG. 15 is a view showing a connection structure between an I beam constituting the tail frame provided in the turning frame structure shown in FIG. 13, that is, an upper flange of the frame member, and a side plate constituting the center frame. FIG. The top view and (b) are principal part side views.

  Conventionally, for example, the front end surface of the upper flange 30b of the frame member 30 constituting the tail frame 24 and the side plate 27 constituting the center frame 23 are, as shown in FIGS. 33 is joined. As shown in FIG. 15 (a), the welded portion 33 includes a butt portion between the front end portion of the upper flange 30b and the side plate 27, and a front end of the upper flange 30b as shown in FIG. 15 (b). And between the side surfaces of the side plate 27. The same applies to the joint portion between the upper flange 29b (not shown) and the side plate 26 constituting the center frame 23. In addition, L1 shown to Fig.15 (a) figure is a bead extension dimension set in order to ensure the joining strength of the frame member 30 and the side plate 27 of the center frame 23. FIG.

In particular, the welded portion 33 formed on the side surfaces of the side plates 26 and 27 of the center frame 23 is usually tapered along the shape of the upper flanges 29b and 30b after being manually welded many times. A grinder finish is applied. The reason for the grinder finishing in a tapered shape along the shapes of the upper flanges 29b and 30b is to alleviate the stress concentration in the welded portion 33, that is, the welded joint portion.
Japanese Patent No. 2719469 (paragraph 0009, FIGS. 1 and 2)

  In the above-described prior art, when the upper flanges 29b and 30b of the frame members 29 and 30 constituting the tail frame 24 and the side plates 26 and 27 constituting the center frame 23 are welded and joined, the above-described prior art is performed manually as described above. After the build-up welding, a grinder finish for removing a part of the build-up weld is required, which increases the work man-hours and increases the production cost.

  The present invention is made from the actual situation in the prior art as described above, and its purpose is to require a grinder finish when welding the upper flange of the frame member constituting the tail frame and the side plate constituting the center frame. Another object of the present invention is to provide a construction machine turning frame structure capable of ensuring a sufficient joint strength.

  In order to achieve the above object, the present invention provides a swivel frame for a construction machine, which is provided in a swivel body of a construction machine and welds and joins an upper flange of a frame member included in a tail frame and a side plate included in a center frame. In the structure, an opening is formed at a front end portion of the upper flange of the frame member, and the side plate of the center frame is inserted into the opening.

  In the present invention configured as described above, when welding the upper flange of the frame member included in the tail frame and the side plate included in the center frame, the opening formed in the front end portion of the upper flange of the frame member, The side plate of the center frame is inserted, and in this state, the front end portion of the upper flange and the side plate of the center frame are welded. Therefore, the movement between the upper flange of the frame member and the side plate of the center frame is restricted through the opening, and welding in this state can ensure a desired joint strength without requiring a grinder finish.

  Further, since welding is not required when welding the front end portion of the upper flange and the side plate of the center frame, automatic welding is possible.

  Further, the present invention is the above invention, wherein a step portion is provided in the side plate portion of the center frame facing the opening portion of the upper flange, and the height dimension of the upper step surface and the lower step surface forming the step portion is set. The upper flange is set to be larger than the thickness dimension thereof.

  According to the present invention configured as described above, when the side plate of the center frame is inserted into the opening formed at the front end portion of the upper flange, the upper step surface of the step portion formed on the side plate of the center frame is It can be made to protrude from the upper surface. Therefore, the upper flange and the side plate of the center frame can be welded using the protruding portion.

  Further, the present invention is the above invention, wherein between the step portion of the side plate of the center frame and the wall surface of the opening of the upper flange, between the upper surface of the upper flange and the side surface of the side plate of the center frame. Further, a welded portion is formed between the front end surface of the upper flange and the side surface of the side plate of the center frame, and between the lower surface of the upper flange and the side surface of the side plate of the center frame. .

  In the present invention configured as described above, in the state where the side plate of the center frame is inserted into the opening of the front end portion of the upper flange, for example, welding work between the step portion of the side plate and the wall surface of the opening, the upper surface of the upper flange, Welding work between the side surface of the side plate, welding work between the front end surface of the upper flange and the side surface of the side plate, and welding work between the lower surface of the upper flange and the side surface of the side plate can be performed continuously. At the same time, it is possible to ensure a strong joint strength by performing these welding operations.

  The present invention is characterized in that, in the above invention, the shape of the opening in plan view is formed in a U-shape.

  In the present invention configured as described above, when the side plate of the center frame is inserted into the opening of the front end portion of the upper flange, the side plate can be brought into close contact with the inner wall of the opening, and the upper flange and the side plate of the center frame can be brought into close contact with each other. Positioning accuracy can be increased.

  Further, the present invention is characterized in that, in the above invention, the shape of the front end portion where the opening of the upper flange is formed is tapered.

  In the present invention configured as described above, the front end portion of the upper flange is formed in a tapered shape in plan view, so that stress concentration at the welded joint between the front end portion of the upper flange and the side plate of the center frame can be reduced. .

  In the present invention, an opening is formed at the front end of the upper flange of the frame member, and the side plate of the center frame is inserted into the opening. Therefore, when the upper flange and the side plate are welded, the opening is formed. Thus, the movement between the upper flange and the side plate is restricted, and welding in this state can ensure a predetermined joint strength without requiring a grinder finish. As a result, the number of work steps can be reduced as compared with the conventional case, and the production cost of the swivel frame can be reduced as compared with the conventional case.

  In addition, as described above, when welding the upper flange and the side plate, build-up welding is not required, and grinder finishing after welding is not required, so that automatic welding is possible. Therefore, if the upper flange and the side plate are welded by this automatic welding, the number of work steps can be further reduced.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a turning frame structure for a construction machine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view showing the overall configuration of an embodiment of the present invention.

  This embodiment is provided in a construction machine such as a hydraulic excavator. As shown in FIG. 1, a center frame 1 is provided at a front position, a tail frame 2 is provided at a rear position, and side frames 3 are provided at both side positions. , 4 are provided.

[Joint structure of center frame side plate and bulkhead]
2 is an enlarged perspective view showing the center frame provided in the present embodiment shown in FIG. 1, FIG. 3 is a plan view of the center frame shown in FIG. 2, and FIG. 4 is a side view of the center frame shown in FIG. 5 is a cross-sectional enlarged view taken along the line AA in FIG. 4, and FIG. 6 is an enlarged view of a portion E in FIG.

  In the present embodiment, the pair of side plates 6, 7 included in the center frame 1 and the partition wall 8 disposed between the side plates 6, 7 are engaged with each other and provided with an engaging portion. This engaging part consists of the insertion structure part, for example.

  For example, as shown in FIGS. 3, 4, and 5, the insertion structure portion that constitutes the engaging portion is formed in the holes 6 a and 7 a formed in each of the pair of side plates 6 and 7, and on both side edges of the partition wall 8. The projections 8a and 8b are inserted into the holes 6a and 7a.

  As shown in FIG. 4, each of the side plates 6 and 7 has a suspension hole 9 that allows the hydraulic excavator to be lifted, and a boom foot pin hole 9a into which a pin that connects the root portion of the boom (not shown) is inserted. A boom cylinder pin hole 9b into which a pin for connecting a boom cylinder (not shown) for driving the boom is inserted is formed.

  The holes 6a and 7a formed in the side plates 6 and 7 described above are positioned below the line connecting the center of the boom foot pin hole 9a and the center of the suspension hole 9 as illustrated in FIG. The boom cylinder pin hole 9b is formed above the line connecting the center of the suspension hole 9 and the center of the suspension hole 9.

[Joint structure between side plate and bottom plate of center frame]
In the present embodiment, the pair of side plates 6, 7 included in the center frame 1 and the bottom plate 5 are engaged with each other and provided with engaging portions. This engaging part also consists of an insertion structure part, for example.

  For example, as illustrated in FIGS. 4, 6, etc., the insertion structure portion constituting the engaging portion corresponds to the side plate 7 and a pair of holes 5 a and 5 b formed in the bottom plate 5, and the bottom plate 5 corresponding to the side plate 6. A pair of holes formed on the bottom plate 5, that is, a total of four holes, corresponding to the projections 7c and 7d of the side plate 7 inserted into the corresponding ones of the holes 5a and 5b of the bottom plate 5, and the corresponding ones of the other holes of the bottom plate 5 It consists of two protrusions of the side plate 6 to be inserted.

  The protrusions 7c, 7d and the like formed on the side plates 7, 6 described above are set to have the same shape and size as illustrated by the E part and the F part in FIG. Accordingly, a total of four holes such as holes 5a and 5b formed in the bottom plate 5 are also set to have the same shape and size.

  Moreover, the insertion structure part mentioned above is located in the outer side of the turning wheel attachment surface 5c, as shown in FIG.

[Joint structure between engine bracket and side plate of frame member]
7 is a perspective view showing a tail frame provided in the present embodiment shown in FIG. 1, FIG. 8 is an enlarged side view of the tail frame shown in FIG. 7, and FIG. 9 is a sectional view taken along line BB in FIG.

  In addition, the present embodiment includes an engaging portion for engaging and positioning the engine brackets 13 and 14 included in the tail frame 2 and the pair of frame members, that is, the side plates 11b and 12b of the I beams 11 and 12 with each other. . This engaging part also consists of an insertion structure part, for example.

  For example, as illustrated in FIGS. 8 and 9, the insertion structure portion constituting the engaging portion includes a hole 12 b 3 formed in the front portion 12 b 1 of the side plate 12 b of the I beam 12, a hole 12 b 4 formed in the rear portion 12 b 2, A hole formed in the front part of the side plate 11b of the I beam 11 and a hole formed in the rear part, that is, a total of four holes, and a protrusion 13a formed at both ends of the engine bracket 13 and inserted into the hole 12b3 of the side plate 12b. , A protrusion inserted into a hole formed in the front portion of the side plate 11b, a protrusion 14a formed at both ends of the engine bracket 14 and inserted into a hole 12b4 of the side plate 12b, and a hole formed in the rear portion of the side plate 11b. It consists of a total of four protrusions.

  The hole 12b3 formed in the side plate 12b of the I beam 12 is positioned on the neutral shaft 15 of the front portion 12b1 of the side plate 12b, and the hole 12b4 formed in the side plate 12b is located in the rear portion 12b2 of the side plate 12b. It is located on the vertical axis 14. Similarly, the hole formed in the front side portion of the side plate 11b of the I beam 11 is located on the neutral axis of the front side portion of the side plate 11b, and the hole formed in the rear side portion of the side plate 11b is located behind the side plate 11b. Located on the neutral axis of the side part.

  As shown in FIG. 7, the I beam 11 is integrally provided with a lower flange 11a at the lower part of the side plate 11b and an upper flange 11c at the upper part. Similarly, the I beam 12 is integrally provided with a lower flange 12a at the lower part of the side plate 12b and an upper flange 12c at the upper part.

[Joint structure of I-beam upper flange and center frame side plate]
FIG. 10 is a view showing a joint structure of the upper flange of the I beam constituting the tail frame shown in FIG. 7 and the side plate constituting the center frame. FIG. 10 (a) is a plan view of the main part, and FIG. FIG. 11 is a view showing a state when the upper flange and the side plate of the I beam shown in FIG. 10 are assembled, (a) is a plan view of the main part, and (b) is a side view of the main part. .

  As shown in FIG. 11 (a), for example, an opening 12c1 is formed at the front end of the upper flange 12c of the I-beam 12 in a plan view, and the side plate 7 of the center frame 1 is formed in the opening 12c1. It is structured to insert. As shown in FIG. 11B, a step 7 b is formed on the side plate 7 of the center frame 1, and the height dimension of the upper step surface and the lower step surface forming the step 7 b is determined by the height of the I beam 12. The dimension is set to be larger by L3 than the thickness dimension of the upper flange 12c.

  Similarly, as shown in FIG. 7, an opening 11c1 having a U-shape in plan view is formed at the front end of the upper flange 11c of the I beam 11, and the side plate 6 of the center frame 1 is inserted into the opening 11c1. It is. As shown in FIG. 2, a step 6 b is formed on the side plate 6 of the center frame 1, and the height dimension of the upper and lower steps forming the step 6 b is determined by the thickness of the upper flange 11 c of the I beam 11. The dimension is set to be larger by L3 than shown in FIG. 11B.

  Further, as shown in FIG. 11A, the shape of the front end portion where the opening 12c1 of the upper flange 12c of the I beam 12 is formed is tapered. When the dimension of the opening 12c1 is L, for example, the range of the dimension L2 from the front end of the upper flange 12 is set to the same width dimension, and the range of the dimension L1 following this dimension L2 gradually increases as the distance from the front end increases. The width dimension is set to be larger. The upper flange 11c side of the I beam 11 is set similarly.

  After the side plate 7 of the center frame 1 is inserted into the opening 12c1 of the upper flange 12c of the I beam 12 from the state shown in FIGS. 11 (a) and 11 (b), it is shown in FIGS. 10 (a) and 10 (b). Thus, the upper flange 12c and the side plate 7 are welded together. That is, between the stepped portion 7b of the side plate 7 and the wall surface of the opening 12c1 of the upper flange 12c, between the upper surface of the upper flange 12c and the side surface of the side plate 7, and between the front end surface of the upper flange 12c and the side surface of the side plate 7. The welded portion 17 is formed between the lower surface of the upper flange 12 c and the side surface of the side plate 7. This welding part 17 is continuously formed, for example by automatic welding.

  The I-beam 11 shown in FIG. 7 and the side plate 6 of the center frame 1 shown in FIG. 2 are also welded in the same manner as described above.

  The operation and effect of each joint structure configured as described above will be described below.

[Effects of joint structure between side plate of center frame and partition wall]
In the present embodiment, when the center frame 1 is manufactured, the corresponding ones of the protrusions 8a and 8b formed in the partition wall 8 are inserted into the holes 6a and 7a formed in the pair of side plates 6 and 7, respectively. The pair of side plates 6 and 7 and the partition wall 8 disposed between the side plates 6 and 7 can be brought into close contact with each other and positioned. For example, in this state, the side plates 6 and 7 and the partition wall 8 are held in a predetermined state. By holding it with a jig, a strong integral object can be formed. Therefore, if the side plates 6 and 7 and the partition wall 8 which are made as such a strong unit are arranged on the bottom plate 5, the one unit including these side plates 6 and 7 and the partition wall 8 is stably arranged on the bottom plate 5. And can be positioned.

  That is, there is no need for a large holding jig for holding the side plates 6 and 7 and the bottom plate 5 before starting welding when the center frame 1 is manufactured. Therefore, the cost for the holding jig can be reduced. Further, it is not necessary to consider the handling of the holding jig for holding the side plates 6 and 7 and the bottom plate 5 and the storage location, and the maintenance cost of the holding jig required for the entire manufacture of the center frame 1 can be reduced.

  Further, the hole 7a of the side plate 7 constituting the engaging portion is an area below the line connecting the center of the boom foot pin hole 9a and the center of the suspension hole 9 and is suspended from the center of the boom cylinder pin hole 9b. Since it is located in the region above the line connecting the center of the hole 9, a decrease in strength of the side plate 7 can be suppressed. Similarly, a reduction in strength can be suppressed for the side plate 6. As a result, a stable structural strength of the center frame 1 can be ensured.

  After the side plates 6, 7 and the partition wall 8 are positioned on the bottom plate 5 while being held by a predetermined holding jig as described above, the side plates 6, 7 and the partition wall 8 are also replaced with the side plate. 6, 7 and the bottom plate 5 are tack welded respectively. Thereafter, final positioning adjustment between the side plates 6 and 7, the partition wall 8, and the bottom plate 5 is performed, and the main frame is completed by performing the main welding.

[Effects of joint structure between side plate and bottom plate of center frame]
In the present embodiment, when the center frame 1 is manufactured, the side plates 7, 6 are respectively formed in the holes 5 a, 5 b formed integrally with the bottom plate 5 corresponding to the side plate 7 and the holes formed integrally with the bottom plate 5 corresponding to the side plate 6. By inserting corresponding ones such as the protrusions 7c and 7d formed in the above, the pair of side plates 6 and 7 and the bottom plate 5 can be brought into close contact with each other and positioned. Thereby, these side plates 6 and 7 and the bottom plate 5 can be welded without requiring a holding jig for fixing the side plates 6 and 7 and the bottom plate 5 to each other. Therefore, as described above, the cost required for the holding jig can be reduced, and the handling and storage location of the holding jig for holding the side plates 6 and 7 and the bottom plate 5 need not be considered. It is possible to reduce the maintenance cost of the holding jig required.

  In addition, since the insertion structure portion between the side plates 6 and 7 and the bottom plate 5 is positioned outside the turning wheel mounting surface 5c, rainwater and the like can be prevented from entering the grease bath inside the turning wheel via this insertion structure portion. Can contribute to the realization of a stable hydraulic excavator structure.

[Effects of joint structure between engine bracket and side plate of frame member]
In the present embodiment, when the tail frame 2 is manufactured, the projections 13a formed on the engine brackets 13 and 14 are formed in the holes 12b3 and 12b4 formed in the frame members, that is, the side plates 12b and 11b of the I beams 12 and 11, respectively. By inserting corresponding ones such as 14a, the engine brackets 13 and 14 and the I beams 11 and 12 can be positioned in close contact with each other and arranged so as not to move on the bottom plate 10 of the tail frame 2. Accordingly, there is no need for a holding jig for holding the engine brackets 13 and 14 and the I beams 11 and 12, and the cost related to the holding jig can be reduced, and the engine brackets 13 and 14 and the I beams 11 and 12 can be connected. The handling of the holding jig for positioning and holding and the storage location need not be considered, and the manufacturing cost of the tail frame 2 can be reduced.

[Effects of joint structure between upper flange of I-beam and side plate of center frame]
When welding the upper flanges 11c and 12c of the I beams 11 and 12 included in the tail frame 2 and the side plates 6 and 7 included in the center frame 2, they are formed at the front end portions of the upper flanges 11c and 12c. In a state where the side plates 6 and 7 are inserted into the openings 11c1 and 12c1, the front end portions of the upper flanges 11c and 12c and the side plates 6 and 7 are welded. Therefore, the movement between the upper flanges 11c and 12c and the side plates 6 and 7 is restricted through the openings 11c1 and 12c1, and welding in this state does not require build-up welding and requires grinder finishing. Therefore, a predetermined bonding strength can be ensured. Thereby, work man-hours can be reduced and the production cost of this turning frame can be suppressed.

  Further, as described above, when welding the upper flanges 11c, 12c and the side plates 6, 7, no build-up welding is required, and no grinder finishing after welding is required. It becomes possible. If this automatic welding is carried out, the number of work steps can be further reduced.

  Further, when the side plates 6 and 7 are inserted into the openings 11c1 and 12c1 of the upper flanges 11c and 12c, the upper step surfaces of the step portions 6b and 7b formed on the side plates 6 and 7 are the upper surfaces of the upper flanges 11c and 12c. Can protrude more. Therefore, the upper flanges 11c and 12c and the side plates 6 and 7 can be welded using the protruding portion, and a stable welding structure can be secured.

  Also, welding work between the step portions 6b and 7b of the side plates 6 and 7 and the respective wall surfaces of the openings 11c1 and 12c1 of the upper flanges 11c and 12c, between the upper surfaces of the upper flanges 11c and 12c and the side plates 6 and 7 Welding operations between the front end surfaces of the upper flanges 11c and 12c and the side surfaces of the side plates 6 and 7, and welding operations between the lower surfaces of the upper flanges 11c and 12c and the side surfaces of the side plates 6 and 7 are continuously performed. In addition to being feasible, a strong joint strength can be secured by carrying out these welding operations, and a stable turning frame can be secured.

  Further, when the side plates 6 and 7 are inserted into the openings 11c1 and 12c1 at the front ends of the upper flanges 11c and 12c, the openings 11c1 and 12c1 are formed in a U-shape in plan view. , 12c1 can be brought into intimate contact with the wall surfaces of the upper and lower flanges 11c, 12c and the side plates 6, 7, respectively, and a revolving frame with high manufacturing accuracy can be secured.

  Further, since the front end portions of the upper flanges 11c and 12c are tapered in plan view, stress concentration in the welded portion 17 between the front end portions of the upper flanges 11c and 12c and the side plates 6 and 7 can be reduced. A stable welding structure can be obtained.

It is a perspective view showing the whole composition of one embodiment of the turning frame structure of the construction machine of the present invention. It is an expansion perspective view which shows the center frame with which this embodiment shown in FIG. 1 is equipped. FIG. 3 is a plan view of the center frame shown in FIG. 2. It is the side view which fractured | ruptured the principal part of the center frame shown in FIG. It is an AA cross-sectional enlarged view of FIG. It is the C section enlarged view of FIG. It is a perspective view which shows the tail frame with which this embodiment shown in FIG. 1 is equipped. FIG. 8 is an enlarged side view of the tail frame shown in FIG. 7. It is a BB cross-sectional enlarged view of FIG. FIGS. 8A and 8B are views showing a joint structure of the upper flange of the I beam constituting the tail frame shown in FIG. 7 and the side plate constituting the center frame, wherein FIG. It is. It is a figure which shows the state at the time of the assembly | attachment of the upper flange and side plate of I beam shown in FIG. 10, (a) A figure is a principal part top view, (b) A figure is a principal part side view. It is a perspective view which shows the hydraulic shovel mentioned as an example of a construction machine. It is a top view which shows an example of the conventional turning frame structure. It is a side view of the turning frame structure shown in FIG. FIG. 14 is a view showing a joining structure of an I beam constituting the tail frame included in the swivel frame structure shown in FIG. 13, that is, an upper flange of the frame member, and a side plate constituting the center frame, and FIG. (B) The figure is a principal part side view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Center frame 2 Tail frame 6 Side plate 6b Step part 7 Side plate 7b Step part 11 I beam (frame member)
11c upper flange 11c1 opening 12 I beam (frame member)
12c Upper flange 12c1 Opening 17 Welded part 21 Rotating body

Claims (5)

In a swing frame structure of a construction machine, which is provided in a swing body of a construction machine and welds and joins an upper flange of a frame member included in a tail frame and a side plate included in a center frame,
A swing frame structure for a construction machine, wherein an opening is formed at a front end portion of the upper flange of the frame member, and the side plate of the center frame is inserted into the opening. In the invention of claim 1,
A step portion is provided in the side plate portion of the center frame facing the opening of the upper flange, and the height dimension of the upper step surface and the lower step surface forming the step portion is determined from the thickness dimension of the upper flange. The swing frame structure of the construction machine is characterized by the fact that it is also set larger. In the invention of claim 2,
Between the step portion of the side plate of the center frame and the wall surface of the opening of the upper flange, between the upper surface of the upper flange and the side surface of the side plate of the center frame, the front end surface of the upper flange, and the A swivel frame structure for a construction machine, wherein welded portions are formed between a side surface of the side plate of the center frame and between a lower surface of the upper flange and a side surface of the side plate of the center frame. In the invention of claim 1,
A turning frame structure for a construction machine, wherein the shape of the opening in plan view is formed in a U-shape. In the invention of claim 1,
A turning frame structure for a construction machine, wherein the shape of the front end portion of the upper flange where the opening is formed is tapered.

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