Metal fusion bonding – Process – With shaping
Reexamination Certificate
2001-01-08
2002-05-14
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
With shaping
C228S137000, C228S161000, C403S272000, C219S061000
Reexamination Certificate
active
06386427
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention belongs to the technical field in which a one-side welding is performed in a building structure, a bridge structure, a general structure, and like.
The present invention relates to a method for obtaining a throat depth exceeding a thickness and a width of an end face of the member for a welding joint. This method can be attained by joint welding using a one-side welding process in which the member is easily welded from the one side without using a consumable backing metal and backing material after performing a welding process for increasing a height and a width of a front bead or a process in which a back face of the end of the member to be welded is subjected to overlay welding and then the groove of the welding member including the overlay weld is made and welded, or a process in which the end of the member is bent to prepare the edge of the member and the prepared edge is subjected to joint welding.
2. Description of the Related Art
FIGS. 39 and 40
illustrate cross-sectional views showing one example of a conventional steel structure welding method. In this example, a member
1
and a member
2
with an edge prepared to have an inclination of about 35° are butted and welded by a T-joint. A backing metal
3
is abutted on a back face so as to perform tack welding
4
such that they are stably welded from one side to be fully penetrated as shown in FIG.
39
. After that, joint welding
6
is carried out as shown in FIG.
40
. Namely, according to the prior art, the joint with backing metal in which welding is performed from one side is being the standard for the steel structure welding for building as shown in
FIGS. 39 and 40
.
In the above conventional method, as shown in
FIG. 39
, two recesses
1
R and
2
R are formed at a root of a groove
5
where the members
1
and
2
are brought in contact with the backing metal
3
, and these portions are not easily to be melted, making it prone to cause incomplete penetration.
Moreover, this requires the production of the backing metal
3
and the tack welding
4
for attaching the backing metal after preparing a groove
5
, and this results in an increase in the number of man-hours needed to produce the steel structure in view of efficiency of joint welding.
Additionally, in the following joint welding
6
, since the backing metal
3
is left, there remain a harmful notch, which generates stress concentration due to the residual of the tack welding
4
, and harmful notches
7
and
7
A, which apply stress concentration to the portion among the backing metal
3
and the base metals
1
and
2
. This causes the joint properties such as bending ductility, fatigue strength, earthquake resisting strength, etc., to be damaged. In the experiment, when the member
2
received a upward bending load
2
B in the joint form shown in
FIG. 40
, cracks occurred mainly at harmful notches
7
and
7
A and the joint was broken.
In the conventional method, the production of the backing metal
3
and the tack welding
4
for attaching the backing metal
3
are needed after performing the edge preparation of the end face to be welded of the member, so that welding
6
of the actual joint cannot be immediately started. This results in a disadvantage in which the number of man-hours needed to produce the steel structure is increased in view of the production processes and steps.
Moreover, in this conventional art, if the backing metal
3
is omitted, there must be carried out uranami welding that forms a good shaped uranami bead with no defect from the front side of the groove to the back face of the first layer. In the steel structure production, however, there are difficulties in maintaining the groove accuracy resulting from the size accuracy of material, ensuring an amount of uranami welding, and using high current from the first layer, and these makes it difficult to implement such good uranami welding.
Though the use of consumable backing material is possible to form an excellent uranami bead, this method causes problems in which the consumable backing material is expensive and much time is required to attach and detach the backing material. In a case in which a space whose interior is closed as in a connection of a building steel structure using square pipes or circular pipes as columns as shown in
FIG. 47
, there is problem in which the consumable backing material cannot be detached after welding.
There is another method in which an overlay welding bead
13
is preset on the member
1
, which is not the end face of T-joint, the member
2
is placed thereto, and welding
14
of the first layer is performed from the front side of the groove, thereafter joint welding
6
is carried out as shown in FIG.
41
.
Though this method is a simple and easy way in which the backing metal can be omitted, projections and depressions are generated by the waves of the overlay welding bead and the position of the overlay welding bead
13
is preset, whereby making it difficult to adjust and change the setting position of members each having a different size accuracy. Further, this welding is difficult to be carried out unless the welding position is horizontal welding. The member
1
needs a constant inclination to form the good uranami bead. Some experience is required to perform welding
14
of the first layer from the surface and high current cannot be used. Moreover, the above method does not lead to an increase in a throat depth
2
A.
There is another method in which an overlay welding bead
13
A is preset on the back face of the member
2
whose end face is subjected to edge preparation in addition to the overlay welding bead
13
preset on the surface of the member
1
of the T-joint, the member
2
is placed thereto, the welding
14
of the first layer is performed from the front side of the groove, thereafter the joint welding
6
is carried out. Though this method is a simple and easy way in which the backing metal can be omitted, the same problem as explained in
FIG. 41
exists therein. When the overlay welding bead
13
A is placed to the top end of the member
2
, welding is not easily carried out. In addition, the overlay welding bead must be present with respect to two portions of both members of the T-joint, resulting in difficulty of welding and an increase in the number of man-hours needed to produce the steel structure.
Unlike the peripheral welding of the square pipe and the circular pipe in which a welding start point and a welding end point are overlapped with other, a width of an H shape steel flange has a finite width in welding the end portion of the flange. In order to obtain satisfactory welding with no defect at a start point of weld bead and an end point of weld bead, steel end tabs are needed as shown in FIG.
43
. As a result, much production cost of end tabs and numerous attaching steps are required. The use of ceramics end tab has been recently increased in place of the steel end tab. In this case, high production cost and the attaching work are also required. Moreover, the steel end tab has a notch, which generates stress concentration between the tab and the flange, and the ceramics end tab has a disadvantage in which weld detects are easily generated.
“Japan Architectural Standard Specification JASS6” dated Feb. 20, 1997 and “Recommendation for Quality Criteria and Inspection of Steel Structures” dated Jul. 1, 1998 of The Architectural Institute of Japan define as follows:
The reinforcement height of the member
2
at the surface position of the opponent member
1
must not only satisfy the size ranging from 25% of a plate thickness t to addition of 10 mm to the value of 25% but also be smoothly changed from the base metal surface, in the T-joint with the plate thickness of, for example, 40 mm or less, as shown FIGS.
44
and
45
.
The above requirement is useful to relax the stress concentration of a face bead, but the above reinforcement height is allowable even if the height at the center of bead is zero and this requirement does not refer to t
Iwago Shunji
Uchida Masayoshi
Dunn Tom
Johnson Jonathan
Machida Steel Structure Corporation
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