Patent Application
20200239741
The present disclosure relates generally to welding. More particularly, the invention is directed to heat-resistant weld backing tape for double-sided arc welding of grooved joint preparations.
By way of background, heat resistant weld backing tape has been used for many years for single-sided arc welding of carbon steel and other metals to eliminate the need for back-purging. Existing weld backing tape products typically include a thin and flexible aluminum or copper alloy tape substrate having a layer of adhesive material covering one face of the substrate. A strip of non-metallic heat-resistant material, such as woven fiberglass, is centrally disposed on the adhesive. The exposed portions of the adhesive that lie on each side of the heat-resistant strip are used to adhere the weld backing tape to the underside of a workpiece, with the heat-resistant strip backing the root gap that separates the two workpiece structures to be welded.
Prior to adhering the weld backing tape to the workpiece, a welder will sometimes create a central longitudinal fold by bending the tape into a tent-like shape, with the heat-resistant strip on the concave side of the fold. When the weld backing tape is adhered to the workpiece, the center of the heat-resistant strip will be spaced from the back side of the root gap. This will still contain the purge gas at the torch tip but avoid consuming the heat-resistant material during welding.
The dimensions of existing weld backing tape designed for single-side arc welding applications are such as to readily permit the tape to be tented in the manner described above, while ensuring that the heat-resistant strip completely spans the root gap. This provides a proper backing for the weld site that prevents hot weld pool material from escaping the root gap area and coming into contact with the aluminum tape substrate. Allowing such contact to occur could result in burning, melting or other degradation of the tape substrate. Insofar as the tape substrate is needed to isolate the underside of the root gap from atmospheric contaminants, loss of integrity of the tape substrate could easily degrade the weld.
Applicant submits that there is presently a need for a solution that allows welding tape to be used for double-sided arc welding applications, particularly those involving double-groove joint preparations, such as double-V grooves, double-J grooves, double-U grooves, H grooves and K grooves.
In one aspect of the present disclosure, a heat-resistant weld backing tape is provided for double-sided arc welding of grooved joint preparations. The weld backing tape includes a flexible tape substrate having a longitudinal length that extends between first and second tape substrate ends, and a lateral width that extends between first and second tape substrate side edges. The tape substrate has a substantially planar first face and a substantially planar second face, each tape substrate face being bounded in a longitudinal direction by the first and second tape substrate ends and in a lateral direction by the first and second tape substrate side edges. The first and second tape substrate faces are mutually parallel and spaced from each other by a tape substrate thickness. The tape substrate length and the tape substrate width are substantially larger than the tape substrate thickness.
A heat-resistant material is supported by the first tape substrate face at a location that is substantially centered between the first and second tape substrate side edges. An adhesive material is supported by the first tape substrate face on each side of the heat-resistant material. The weld backing tape is bendable into a folded shape with the heat resistant material being on a convex side of the fold. In this configuration, the weld backing tape may be seated in a back-side groove of the joint preparation, with an apex of the heat-resistant material substantially packing an apex of the back side groove to block weld pool material introduced into a front-side groove of the double groove joint preparation during arc welding. The back-side groove is defined by a pair of side walls extending from the groove apex to a rear surface of the workpiece. The heat-resistant material has a maximum width selected to leave a portion of each side wall of the back-side groove exposed for engagement by the adhesive material to retain the heat-resistant material in position in the back side groove during welding.
In an embodiment, the width of the heat-resistant material is selected to expose at least approximately 9 mm of each back-side groove side wall for engagement by the adhesive material.
In an embodiment, the tape substrate width exceeds the width of the heat-resistant material by at least approximately 18 mm.
In an embodiment, the width of the heat-resistant material ranges between approximately 12-16 mm and the tape substrate width ranges between approximately 30-40 mm.
In an embodiment, the width of the heat-resistant material does not exceed approximately 15 mm and the tape substrate width does not exceed approximately 40 mm in order to provide approximately 12.5 mm of adhesive on each side of the heat-resistant material.
In an embodiment, the heat-resistant material comprises a woven fiberglass strip having a thickness of approximately 2 mm.
In an embodiment, the woven fiberglass strip having a thickness of approximately 2 mm is provided by a woven fiberglass strip having a thickness of approximately 1 mm that is folded lengthwise over itself to double its thickness and is stitched to maintain its folded position.
In another aspect, a double-sided arc welding assembly is provided that includes a heat-resistant weld backing tape as summarized disposed in a back-side groove of a workpiece configured as double-groove joint preparation.
In a further aspect, a double-sided arc welding method is provided that includes installing a heat-resistant weld backing tape as summarized above in a back-side groove of a workpiece configured as a double-groove joint preparation, performing welding in a front-side groove of the workpiece, and removing the weld backing tape from the back-side groove without the need for back gouging.
The foregoing and other features and advantages will be apparent from the following more particular description of example embodiments, as illustrated in the accompanying Drawings, in which:
Before describing the inventive subject matter of the present disclosure, it will be helpful to elaborate on the problems and disadvantages of using conventional weld backing tape designed for single-sided arc welding in applications involving double-sided arc welding of grooved joint preparations. As shown cross-sectionally in
The prior art weld backing tape T is exemplified by Fiback® weld backing tape from Aquasol Corporation of North Tonawanda, N.Y. Fiback® weld backing tape is sold in two standard widths. Fiback® product number AFBT-2.5 has a narrow profile wherein the width of the heat-resistant material “H” is 28.5 mm (1.125 inches) and the width of the tape substrate “S” is 64 mm (2.5 inches). Fiback® product number AFBT-4.0 has a wider profile wherein the width of the heat-resistant material “H” is 38 mm (1.5 inches) and the width of the tape substrate “S” is 102 mm (4.0 inches).
Applicant has discovered that problems can arise when the prior art weld backing tape “T” of
Testing by applicant has revealed that the weld backing tape arrangement of
Without being bound by any particular theory of operation, applicant surmises that the above-described failure of the prior art weld backing tape “T” may be due at least in part to the fact that the heat-resistant material “H” is held in place solely by way of the adhesive “A” adhering to the back-side surface of the workpiece, with no portion of the adhesive “A” engaging any portion of the sidewalls of the back-side groove. This lack of sidewall adhesion may allow the apex portion of the weld backing tape “T” to deflect downwardly in response to pressures exerted by the welding heat and gasses. Such downward deflection may force the weld backing tape “T” away from the sidewalls of the back-side groove, allowing the welding heat and gasses to flow into the newly-formed sidewall gaps and thereby produce further tape degradation.
An improvement to the prior art heat-resistant weld backing tape of
Like the prior art weld backing tape “T,” the weld backing tape 2 includes a flexible tape substrate 4 supporting a centrally-disposed heat-resistant material 6 flanked by adhesive material 8 on each side. Unlike the prior art weld backing tape “T,” the heat-resistant material 6 of the weld backing tape 2 has a maximum width selected to leave part of each side wall of the back-side groove exposed for engagement by the adhesive material 8. Testing has shown that this arrangement optimally retains the heat-resistant material in position in the back-side groove during double-sided arc welding.
The first and second workpiece structures 10A and 10B are configured and arranged to form a grooved joint preparation. The grooved joint preparation is defined by a front-side groove 18 formed in the front surface 14 of the workpiece and a back-side groove 20 formed in the rear surface 16 of the workpiece. In the illustrated embodiment, the grooves 18 and 20 are V-shaped to provide what is commonly referred to as a double-V groove joint preparation. Other types of double-groove joint preparations could also be used, including but not limited to double-sided weld preparations formed with double-J grooves, double-U grooves, H grooves, K grooves, etc.
Regardless of which type of double-groove joint preparation is used, the front-side and rear-side grooves of such preparations will usually be characterized by a common apex defined at the welding root gap, and a pair of sidewalls extending from the apex to the respective front and rear surfaces of the workpiece. In
In
As noted above, the heat-resistant material 6 has a maximum width selected to leave a portion of each side wall 20A of the back-side groove exposed for engagement by the adhesive material 8, in order to retain the heat-resistant material in position in the back side groove during welding.
Further details of the weld backing tape 2 will now be described with reference to
With further reference to
In an embodiment, the tape substrate length L and the tape substrate width Ws are substantially larger than the tape substrate thickness Ts. For example, the tape substrate thickness Ts may be approximately 0.075-0.25 mm (e.g., 3-9 mils) for many double-sided welding applications, whereas the tape substrate length L may be approximately 12.5 meters (e.g., 41 feet) for a long backing tape roll or 25 meters (e.g., 82 feet) for a short backing tape roll, and the tape substrate width Ws may be approximately 30 mm (1.2 inches) for a narrow profile backing tape roll or 40 mm (1.6 inches) for a wide profile backing tape roll. It will be appreciated that other length, width and thickness dimensions could also be used for the tape substrate 4.
In the illustrated embodiment, the adhesive material 8 may be disposed on the tape substrate face 32 as a layer of heat-resistant adhesive, such as halogen-free acrylic base adhesive of the type used in existing welding tape products. As shown in
As shown in
Conventional roll coating, spray coating or other techniques may be used to apply the adhesive adhesive material 8 to the first tape substrate face 32. An alternative would be to apply the adhesive material 8 as one or more pre-formed adhesive strips (e.g., with double-sided adhesive) to the first tape substrate face 24. As shown in
In the illustrated embodiment, the heat-resistant material 6 is centrally disposed on the first adhesive face 36. As previously noted, the purpose of the heat-resistant material 6 is to provide a heat-resistant backing for the root gap 12 (see
As shown in
In a widthwise direction, the heat-resistant material 6 may have a substantially uniform heat-resistant material width Whrm that spans as little of the tape substrate width Ws as may be required to adequately back the welding root gap 12. This will ensure that the weld backing tape 2 is useable with even relatively thin workpiece structures without heat-resistant material 6 substantially covering the sidewalls of the back-side groove, so that there adequate room on the sidewalls for the adhesive material 8 to adhere thereto. In an embodiment, the width Whrm of the heat-resistant material 6 may be selected to expose at least approximately 9 mm (0.35 inches) of each back-side groove side wall for engagement by the adhesive material. In that case, the tape substrate width Ws may exceed the width Whrm of the heat-resistant material 6 by at least approximately 18 mm (0.7 inches).
For many welding applications, a heat-resistant material width Whrm of not more than approximately 12-16 mm (0.47-0.63 inches) will be sufficient to achieve the foregoing ends. This will allow the weld backing tape 2 to be used with workpiece structures as thin as approximately 28 mm (1.1 inches) or less. To see why this is so, consider an embodiment of the workpiece 10 shown in
It was previously stated that the width Whrm of the heat-resistant material 6 may be selected to expose at least approximately 9 mm (0.35 inches) of each back-side groove side wall 20A for engagement by the adhesive material. If the width Whrm of the heat-resistant material 6 is not more than approximately 12-16 mm (0.47-0.63 inches), the amount of heat-resistant material that overlies each sidewall 20A will be approximately 6-8 mm (0.24-0.32 inches). If it is desired to provide approximately 9 mm (0.35 inches) of exposed surface on each sidewall 20A for adhesive bonding, the total sidewall length Lsw would then need to be approximately 6-9 mm+9 mm (0.24-0.32 inches+0.35 inches), which is approximately 15-18 mm (0.6-0.7 inches). Because it was determined above that Lsw=0.54Twp for a 45° back-side notch, it may will be seen that the workpiece thickness Twp needed to provide a specific sidewall length Lsw is Twp=Lsw/0.54. Therefore, if the required sidewall length Lsw is approximately 15-18 mm (0.6-0.7 inches), the required workpiece thickness Twp will range between approximately Twp=15/0.54 mm≈28 mm (1.1 inches) and Twp=18/0.54 mm≈33 mm (1.3 inches). For many double-groove joint preparations, the workpiece thickness will be above this minimum thickness range. However, if it desired to use the weld backing tape 2 with smaller gauge workpieces, the width Whrm of the heat-resistant material 6 may be reduced accordingly. Alternately, the back-side groove angle could be increased, which has the effect of increasing the available sidewall length Lsw per the above equation: Lsw=0.5Twp/(cos α).
As previously noted, the width Ts of the tape substrate 4 may be selected so that the first and second tape substrate side edges 28 and 30, and consequently the corresponding side edges of the adhesive side material 8, terminate approximately 9 mm (0.35 inches) beyond each of the first and second side edges 46 and 48 of the heat-resistant material. This will ensure there is sufficient adhesive to take advantage of the approximately 9 mm (0.35 inches) of exposed sidewall 20A. In such an embodiment, if the width Whrm of the heat-resistant material 6 ranges between approximately 12-16 mm (0.47-0.63 inches), the width Ts of the tape substrate 4 could range between approximately 30-34 mm (1.18-1.34 inches). In a further embodiment, the width Whrm of the heat-resistant material 6 ranges between approximately 12-16 mm (0.47-0.63 inches) and the tape substrate width Ts ranges between approximately 25-65 mm (1-2.5 inches), and preferably approximately 30-40 mm (1.2-1.6 inches). The low end of the preferred range (i.e., 30 mm (1.2 inches) ensures there will be sufficient adhesive material 8 to provide a strong adhesive bond onto the sidewall 20A. The high end of the preferred range (i.e., 40 mm (1.6 inches) ensures there will be minimal excess tape substrate material 4 (and adhesive material 8). In a still further embodiment, the width Whrm of the heat-resistant material 6 does not exceed approximately 15 mm (0.6 inches) and the tape substrate width Ts does not exceed approximately 40 mm (1.6 inches) in order to provide approximately 12.5 mm (0.5 inches) of adhesive on each side of the heat-resistant material.
In the illustrated embodiment, the heat-resistant material 6 may have a substantially rectangular cross section defined by the substantially uniform heat-resistant material width Whrm and a substantially uniform heat-resistant material thickness Thrm (see
One way that the heat-resistant material thickness Thrm may be increased to 2 mm (approximately 80 mils) is by folding in half a 1 mm (approximately 40 mils) thick heat-resistant material strip along its length, and machine-stitching the folded strip at one or more locations. Such an embodiment is illustrated cross-sectionally in
The double-sided arc welding assembly of
Initially, the weld backing tape 2 is folded lengthwise with the heat-resistant material 6 on the convex side (outside) of the fold. The shape of the fold may be fashioned to substantially correspond (as much as possible) to the shape of the back-side groove 20. Thus, if the weld preparation is a double-V groove or K-joint preparation, the folded weld backing tape may have a generally V-shaped cross-sectional configuration. Likewise, if the weld preparation is a double-U groove, double-J groove or H-groove preparation, the folded weld backing tape may have a generally U-shaped cross-sectional configuration.
After the weld backing tape 2 has been folded, any removable backing sheet 40 covering the adhesive material 8 may be removed. The folded weld backing tape 2 may then be attached to the workpiece 10 by seating it in the back-side groove 20, with the apex 6A of the heat-resistant material 6 substantially packing the apex of the back-side groove (i.e., the root gap 12) as much as possible. This positioning will maximize the ability of the heat-resistant material 6 to block weld pool material introduced into a front-side groove 18 of the joint preparation during arc welding.
With the welding assembly 2 securely formed in this manner, welding may be commenced to apply weld material into the front-side groove 18 in order to form a weld seam between the first and second workpiece structures 10A and 10B. Once the welding operation has been completed, the weld backing tape 2 should still be intact in the back-side groove 20 without significant degradation, as shown in
Accordingly, a heat-resistant weld backing tape for double-sided arc welding of grooved joint preparations, together with a related weld assembly and welding method, have been disclosed. While various embodiments have been described, it should be apparent that many variations and alternative embodiments could be implemented in accordance with the invention. It is understood, therefore, that an invention as disclosed herein is not to be in any way limited except in accordance with the spirit of the appended claims and their equivalents.
