Resistance weld pin and method of welding

A resistance welding pin for connecting insulation batts to ducts comprises a head having a shank and a sharpened tip remote from the head. The shank, adjacent the tip, includes an abutment against which a welding electrode may bear, the electrode being passed through an aperture or passage in the head.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to a resistance weld pin, and more 
particularly relates to a welding pin adapted to attach batts of thermal 
insulation to the interior surface of ducts. 
2. The Prior Art 
In order to improve the energy efficiency of air conditioning and heating 
installations employing metal duct work, batts or sheets of insulation 
ranging from one to two inches are typically secured to the interior 
surfaces thereof. Attachment is conventionally effected by adhesive alone 
or in conjunction with headed metallic pins extending through the 
insulation and bonded to the metal as by impact fastening or welding. 
Suitable welding pins are disclosed in U.S. Pat. Nos. 3,624,340 of Nov. 30, 
1971; 3,835,285 of Sept. 10, 1974; 3,858,024 of Dec. 31, 1974; 4,429,209 
of Jan. 31, 1984; 4,482,795 of Nov. 13, 1984; and 4,614,855 of Sept. 30, 
1986. 
In each of the noted patents (all of which are owned and/or licensed to the 
holder of rights under the instant application), the welding pins are 
attached by passing an electrical current along the shank of the weld pin 
while the sharpened tip of the pin is pressed against the duct, which is 
connected to a ground electrode. 
While the noted structures are effective to secure the insulation material 
in position, they are all subject to certain disadvantages in terms of 
function and economy. 
Specifically, since the pin must function as a conductor, the current 
carrying capacity and, hence, the diameter of the pins must be 
sufficiently great to carry the high current needed to effect a weld. The 
necessity for providing thickened shanks to carry welding current, in 
addition to increasing the cost of the pins, also provides a significant 
thermal bridge between the interior and the exterior of the ducts, 
reducing the thermal efficiency of the insulation. 
Also, since the welding current passes through the entire length of the 
pin, the external surfaces of the shank are raised to high temperatures 
during the welding procedure, with resultant possible damage to the 
insulating material surrounding the pin. 
SUMMARY OF THE INVENTION 
The present invention is directed to an improved welding pin and method of 
applying the same. More particularly, the invention is directed to a 
welding pin having an enlarged head portion preferably defined by a washer 
subjacent a smaller sized head, and is characterized by the provision of a 
thinned shank portion in the area between the head and the sharpened tip. 
The pin is provided adjacent the tip with an abutment facing the head, at 
least a portion of which abutment registers with an aperture formed in the 
washer. 
A welding electrode may thus be inserted through the aperture and pressed 
against the abutment, whereby current flow is limited to the area of the 
shank immediately adjacent the tip. 
Since the current flow need not include the major length of the shank 
portion, it is possible to provide a weld pin having a very thin shank, 
thereby reducing the amount of metal necessarily embodied in the pin, and 
at the same time decreasing thermal conductivity of the attached pin. 
Since the major length of the shank is not significantly heated during the 
welding process, damage to surrounding insulation is minimized. 
It is accordingly an object of the invention to provide an improved weld 
pin and method of attaching the same.

DETAILED DESCRIPTION OF THE VIEWS 
Referring now to the drawings, there is shown in FIG. 1 a weld pin 10 in 
accordance with the invention, the pin being comprised of a head member 
11, an elongate shank portion 12 and a tip portion 13. 
The tip portion 13 includes a sharpened point 14 and an abutment portion 15 
directed upwardly toward the head. 
The abutment portion 15 may take the form of an annular shoulder projecting 
radially beyond the shank. 
The washer 16 may be sleeved over the shank such that the upper surface 17 
of the washer underlies the head 11, it being understood that the washer 
and head may be integrally formed but that, for economy of manufacture, 
separate elements are preferred. The washer 16 includes arcuate slot 18 
for purposes which will appear hereafter. 
As shown in FIG. 2, the pin 10 is to be attached to a metallic substrate 19 
comprising a duct surface through an insulating batt 20 having a smooth 
polymeric surface 21. Attachment is effected by forcing the tip 13 through 
the body of insulation and into contact with the substrate 19 either 
manually or through the use of a welding electrode 22 comprising the 
"live" electrode of a resistance welding gun or apparatus known per se. 
Preferably the electrode 22 includes an arcuate lower portion 23 
terminating in end 24 adapted to engage abutment 15 of the weld pin. 
Desirably the weld pin is mounted on electrode 22 prior to forcing the pin 
through the insulation batt so as to assure contact between the base 24 of 
the electrode and the abutment 15, and prevent the ingress of insulation 
between the base and abutment, which ingress would interfere with proper 
current flow. 
With the parts disposed as depicted in FIG. 2, welding current is caused to 
flow through the electrode 22, resulting in melting of the tip portion 13, 
which is pressed downwardly against substrate 19 by the electrode. 
The attached pin is disclosed in FIG. 4. 
As will be apparent, the pin will be securely welded to the substrate 19. 
Importantly, since the welding current is not required to flow through the 
shank 12 it is possible to use a thin diameter shank material which would 
otherwise melt in the course of welding. 
The shank portion is amply strong to retain the weld pin in position but 
provides substantially reduced thermal conductivity between the duct 
substrate 19 and washer 17 when compared to a shank sufficiently large to 
carry the necessary welding current. Since welding current does not pass 
along the shank, welding heat is contained primarily in the area of the 
tip portion and, thus, overheating of the shank, with consequent possible 
damage to surrounding insulation is minimized. 
As will be apparent to those skilled in the art, numerous variations of 
construction may occur to those familiarized with the instant disclosure 
without departing from the spirit of the disclosure. 
For instance, the weld pin may be made of sheet metal and the abutment 
portion may be comprised of a boundary of a hole punched in the sheet 
metal or a projection extending from the sheet metal. 
Such a structure is shown, by way of example, 
in FIG. 5 wherein the weld pin is an integral sheet metal blank having a 
head 30, a passage 31 formed in the PG,7 head, from which shank 32 is 
defined, the shank having an aperture 33 formed therein, the lower surface 
34 of which defines an abutment. 
In the weld pin of FIG. 5, the weld electrode would extend downwardly 
through passage 31 and include a hook-like projection at its lower end for 
engaging abutment 34 and pressing tip 35 against the substrate 19. 
Accordingly, the invention is to be broadly construed within the scope of 
the appended claims.