Weld back up assembly

An assembly for shielding the underside of a weldment joint comprising an elongated, flexible, preferably metallic mounting strip and a plurality of small, discrete back up blocks made of a refractory material suitably secured in end to end array to one face of the metallic strip centrally thereof. The blocks preferably having a groove wider than the weldment joint, the grooves being aligned to define a channel confronting the joint and of a predetermined depth to control the penetration and depth of the weld bead. The back up blocks are of a width narrower than said metallic strip to expose side edge portions of said metallic strip, the exposed side edge portions having an adhesive coating to provide a substantially air-tight sealing engagement with the weldment joint along both edges of the mounting strip. The assembly has a degree of flexibility to permit conformation of the assembly to the shape of the weldment and in use supports slag and the welding pool formed during welding.

DESCRIPTION OF THE INVENTION 
This invention relates to an improved weld back up assembly. Weld back up 
tape described in U.S. Pat. No. 3,365,566, issued to me on Jan. 23, 1968, 
has found widespread acceptance in the welding art. My earlier weld back 
up tape and a variety of other weld tape products and their application 
are discussed in an article authored by R. H. Keith, entitled "Weld 
Backings", in the June, 1975 edition of Welding Journal. My prior tape 
essentially comprises a layer of flexible metallic foil having a strip of 
woven fiberglass supported centrally thereof which confronts the weldment 
joint. 
The weld back up tape described in my earlier patent produces high quality 
weld, serves to back up the underside of the joint being welded and 
prevents the underside of the weld from being exposed to contamination 
from the atmosphere while in the molten state. In addition, my earlier 
weld back up tape has the advantages of ease of attachment to the weldment 
by pressure sensitive adhesive and ready conformability to curved surfaces 
as the result of its flexible nature. Another significant advantage is 
that welds can be made without inert gas shielding as the weld back up 
tape serves to seal the weldment from the atmosphere. 
It has been found that use of my earlier weld back up tape may have certain 
disadvantages particularly when welding heavy gauge material, i.e., 
material 0.500" thick or more, as the result of burn through the heat 
resistant fibrous material during welding. When "burn through" occurs as 
the result of the high temperatures and relatively long time required for 
heavy gauge welding, the weldment may be exposed to the atmosphere and the 
back up tape loses its ability to influence the shape and condition of the 
underbead. In some instances, it has been found necessary to use an inert 
gas to shield the underside of the weld. This of course, adds to the 
expense of the welding operation. 
It is the object of this invention therefore, to provide an improved weld 
back up assembly which eliminates the problem of "burn through", and which 
is flexible, easily conformable to the weld surface, and useful in heavy 
gauge, high-temperature welding applications. 
Another object is to provide a weld back up assembly which is flexibly 
conformable and provides support for slag and the welding pool produced 
during welding, providing an underbead which is of a controlled, 
substantially uniform depth and which is clean, smooth and free of 
defects. 
It is a further object of the present invention to eliminate the need for 
inert gas shielding on the underside of the weld.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1 of the drawing, there is illustrated a conventional 
electric welding apparatus for use in welding structural plate members 10 
and 12 of a weldment 13 to one another. The apparatus includes a tungsten 
or carbon electrode 14 which is connected to a source of electric power 
and which is mounted centrally of a cylindrical cup 16 and a lead 17 
connecting one of the members to ground. Inert gas from a suitable source 
is delivered through cup 16 to provide a shield adjacent the tip of 
electrode 14. Plate members 10 and 12 to be joined are maintained in a 
spaced apart relation in a conventional manner to define a joint 18 
therebetween. By this arrangement, filler metal 19 may be introduced in 
the arc struck by electrode 14 to form the bead 20 joining the structural 
members together at the joint 18. 
In accordance with this invention, means is provided for supporting the 
underside of the weld to protect the same from atmospheric contamination, 
to support the slag and weld pool providing an underbead which is smooth, 
clean and free of defects. The principal embodiment of weld back up 
assembly of the present invention is best illustrated in FIG. 5 and 
comprises a series of small generally square back up blocks 30 supported 
in end to end array in an elongated, flexible thin mounting strip 32, 
preferably of a metallic material such as copper or aluminum alloy. The 
blocks 30, which are aligned in a row, are of a width narrower than the 
strip 32 to expose side edge regions 32a,32a coated with a suitable heat 
resistant adhesive, such as a silicone pressure sensitive type to permit 
application of the back up assembly flush to the underside of the weldment 
in the manner shown. The end to end abutment of the short support blocks 
30 provides a tractor tread like form allowing close conformability of the 
weld back up assembly 29 even to weldments which are arcuate or curved. 
The tractor tread form of the support blocks in the back up assembly of 
this invention provides considerable improvement over other weld back up 
systems employing ceramic back up materials, such as that supplied by the 
Varios Comany in Holland in which ceramic sections of considerable length 
of 6" to 24" or more are supported by lengths of an inflexible metal back 
up bar and attached to a weldment by awkwardly applied magnetic and spring 
clamping means. To facilitate packaging and handling a removable liner 36 
overlies the side edge regions 32a, the liner 36 being a treated paper, 
coated parchment, vinyl film or other suitable commercially available type 
which peels easily. 
The back up assembly of the present invention is very easy to manufacture. 
For example, an adhesive coating is simply applied to one face of the 
strip 32, the blocks 30 are then laid on the adhesive coated surface 
centrally of the strip and then the paper liner is applied over the side 
edge regions 32a, 32a. The mounting strip 32 may be positioned over a 
fixture having a groove or channel of a width slightly greater than the 
blocks to obtain good conformity and adherence of the strip to the base 38 
and outer side walls 40 of the blocks 30. The liners are easy to remove 
prior to application of the assembly to the underside of a weldment and 
serve to preserve the bonding quality of the adhesive. 
The back up blocks 30 (FIGS. 1 and 2) as shown, are thin wafer like 
elements of square or rectangular shape and are of a comparatively short 
length to permit conformation to weldments which are contoured as 
contrasted to flat. The upper face 42 of each block has a grooved recess 
43 of a predetermined width W greater than the width W.sub.1 of weldment 
joint 18 to allow for slight misalignment of the assembly when applying it 
over the weldment joint. The outer edges of the groove are slightly 
beveled as at 44 and are spaced inwardly from the sides of the block to 
define flat, land areas 46 on either side of the groove 44 engaging flush 
against the weldment on either side of the joint. 
Describing the weld back up assembly with greater particularity, the 
flexible metallic strip comprises aluminum or an aluminum alloy of a 
thickness between 0.003 and 0.009 inches having an adhesive on one surface 
thereof. Alloys of other metals such as copper and stainless steel could 
be used to form the flexible metallic mounting strips. 
Support blocks 30 are individually rigid, inflexible objects manufactured 
from materials selected from the group consisting of ceramic, glass, 
metal, fibrous and "solid" refractory materials. The materials from which 
supporting blocks 30 are prepared share the common property of resistance 
to the temperatures encountered in the welding operation, i.e., the 
supporting blocks do not melt at welding temperatures, and therefore, in 
the case of metal supporting blocks, for example, they are incompatible 
with and do not become alloyed with the weld joint. Other common 
properties include insensitivity to humidity, that is, the supporting 
blocks will be prepared from refractory materials which absorb little, if 
any, moisture. High temperature, heat resistant metals such as copper, 
stainless steel and tungsten alloys may be used as blocks 30. Similarly 
powdered metal alloy molded together with high temperature resistant 
binders and chopped fibrous materials, such as fiberglass held together 
with high temperature resistant binders, may be used to form blocks 30. 
The supporting blocks of this invention are preferably ceramic blocks about 
1" square and about 0.250" thick. The depth D of groove 43 (FIGS. 2 and 4) 
is between about 0.055" and about 0.065" , preferably about 0.062", so 
that the thickness T of the block between the base of the groove and the 
bottom of the block is between about 0.185" and about 0.195". The 
thickness T can be varied somewhat to eliminate thermal cracking. A 
suitable ceramic refractory material is available commercially and has 
long been known in the ceramic art as steatite. 
As the result of the dimensions of groove 43 described herein, the groove 
provides means for supporting the weld puddle formed during welding and 
provides an excellent back stop against which a smooth underbead can form. 
Further, since the weld back up assembly is adhered in an air tight manner 
to the weld assembly, the weldment is protected from contamination by the 
atmosphere producing a clean weldment of good quality. 
The particular metal used to prepare refractory support blocks for use on 
the weld back up assembly of the invention will depend on the metal being 
welded, that is, if the supporting block is metal, it must be of a 
material refractory to the temperatures at which welding occurs, e.g., a 
metal having a higher melting point than the metals being welded. For 
example, support plates of copper or stainless steel could be used in weld 
back up tapes for use in welding aluminum. 
In the process of preparing weldment 13 employing the weld back up tape of 
this invention, the joint surfaces of the weldment 13 are cleaned in the 
usual manner and plate members 10 and 12 of the weldment are supported in 
a fixture or by tack welding to define joint 18. Thereafter, weld back up 
assembly 29 (FIG. 5) is applied to the underside of joint 18 as 
illustrated with ceramic blocks 30 confronting and covering joint 18 as 
illustrated, and the adhesive area 32a of back up assembly bonded to 
members 10 and 12 to support the assembly 29 in position as indicated in 
FIGS. 2 and 3. 
The weldment 13 is now ready for welding whereby, in the process 
illustrated, the arc is struck by electrode 14 and weld rod 19 placed in 
the region of the arc to provide the weld puddle. The weld puddle 
penetrates joint 18 to a depth controlled by channel defined by the 
grooves 43 of the blocks 30. 
It has been demonstrated that the weld back up assembly 29 of this 
invention effectively precludes atmospheric contamination of the underside 
of the weldment and provides good support for the weld puddle producing a 
finished weld with a good underbead which requires little, if any, post 
weld gouging or cleaning even in high temperature welding operations. In 
addition, it will be appreciated that, as the result of their refractory 
nature, blocks 30 serve as a heat sink during welding operations, and 
preclude the possibility of burn through of the back up assembly during 
welding. Prevention of burn through further ensures the integrity of the 
air tight enclosure of the weld joint and eliminates the possibility of 
contamination of the weld being formed as the result of contact with the 
atmosphere which would lead to undue oxilation and the formation of a 
weakened or "dirty" underbead requiring cleaning or additional welding. 
A modification of the back up assembly described above is illustrated in 
FIGS. 6 and 7. The arrangement of the refractory blocks in the flexible 
layer is the same as that previously described, the assembly 29' including 
additionally at least one layer or ribbon 50 of flexible heat resistant 
material overlying the channel formed by the back up blocks. The ribbon 50 
is supported at its outer side edges by a suitable adhesive applied to the 
flat land areas 46' of the blocks. The ribbon 50 is preferably a heat 
resistant material such as woven fiberglass fabric; i.e., a fabric 
comprising glass fibers which are non-flammable, moisture resistant and 
unaffected by most acids. A plurality of layers or ribbons of the woven 
fiberglass fabric 36, numbering from 2 to 5, more especially about 3 
layers of fabric, may be used. The woven fiberglass provides fluxing 
action as it becomes molten during the welding operation, and since 
support plates 30' provide a back up for the weld puddle, the fluxing 
action serves to provide the underbead with a smooth, polished surface. 
Additional embodiments of weld back up assemblies in accordance with the 
present invention are illustrated in FIGS. 8-14 inclusive. The back up 
assemblies are designed specifically to weld corner joints from the 
outside or inside seam of a corner joint. The back up assembly 59 
illustrated in FIG. 10, which is used on welding corner joints from the 
inside comprises a plurality of short back up blocks 60 made of a 
refractory material of the type set forth above. For example, the blocks 
60 are made of a high temperature ceramic, preferably unglazed and 
insensitive to humidity, which blocks 60 are supported in end to end array 
in a flexible layer 62 of thin gauge copper or aluminum. The blocks 60 as 
illustrated, have two right angularly disposed side wall portions 64, the 
inner faces 66 of which are designed to lie flush against the right 
angularly disposed faces of the plates 68 and 69 of the corner joint in 
the manner shown in FIG. 8. The inner faces 66 of the side walls are flat 
to provide a flat bead when the weld material is introduced into the seam 
56 of the joint. The blocks 60 as shown in FIG. 10, are mounted in 
abutting end to end relation and supported in the elongated mounting layer 
62 by a suitable adhesive. If desired, the flexible mounting layer 62 may 
be a fiberglass tape. The layer 62 is preferably of a width to extend 
beyond the outer edges of the side walls of the blocks to provide extended 
side edge regions 70 for securing the tape to the weldment at these 
extended side edge regions in the manner illustrated. The outside edges of 
the blocks are preferably beveled as at 72 so that the assembly may be 
secured flush against the corner joint in an air tight manner, and to 
ensure a stronger adhesion. 
A somewhat modified version of the back up assembly is illustrated in FIG. 
9. The general configuration of the blocks and metallic mounting layer in 
which they are supported is the same as FIG. 8, except that in the present 
instance a groove 74 is provided on the inner face of the blocks which 
defines a pocket 76 adjacent the seam for the weld material when a weld 
bead is specified for the outside surface of the corner joint. 
FIGS. 12 and 14 illustrate additional embodiments for use on corner joints 
wherein the joint is welded from the exterior. Thus, the back up assembly 
79 in FIG. 12 comprises a series of blocks 80 of triangular cross section 
mounted in an abutting end to end relation on a thin metallic flexible 
mounting layer 82, the layer 82 being of a greater width than the base 84 
of the blocks to define side edge regions 86 for securing the back up 
assembly to the corner joint in the manner shown. 
The back up assembly shown in FIG. 14 is also for the inside of a corner 
joint, except that in this instance, the blocks 90 are of a trapezoidal 
cross section thereby leaving a small triangular gap 92 for the weld 
material on the inside of the corner joint, as illustrated in FIG. 13. 
The joints illustrated are right angular joints. However, it is to be 
understood that the back up assembly has useful application to a full 
range of joint angles by simply conforming the shape of the blocks to the 
desired joint angle. Further, the back up assembly may be used on the 
underside of a double beveled butt joint. 
In sum, the weld back up assembly of this invention provides means for one 
side welding of particularly heavy gauge material. The weld back up tape 
of this invention is flexible and conformable, and easily applied to 
weldments of a variety of shapes and configurations. Importantly, the weld 
back up assembly of this invention is self-supporting and does not require 
back up bars or any of the variety of clamping and attachments means 
prevalent in weld back up systems currently in use. Of paramount 
importance, is the fact that the weld back up assembly of this invention 
provides means for the development of a well supported weld puddle thereby 
permitting the formation of a clear, smooth underbead and eliminating the 
necessity of time consuming and expensive grinding, back-gouging and 
re-welding of the bottom side of the weld after the first weld is made. 
The weld back up assemblies of this invention provides for substantial 
savings in labor and energy costs as they permit higher temperature and 
higher speed welding operations. Also, with higher temperature welding 
procedures, greater weld penetration is achieved and weld quality is 
enhanced as the result of one sided welding.