Glass spacer bar for use in multipane window construction and method of making the same

A multipane window assembly has first and second panes of glass separated by a spacer frame that is constructed of joined tubular members. The tubular members are glass tubes, each of which has a first and second side adjacent the glass panes and a third side that bridges the first and second sides and is adjacent the airspace between the glass panes of the multipane window assembly. A plurality of holes is formed in the third side of the glass tube to allow airflow between the interior of the spacer tube and the airspace defined by the glass panes. The third side of the glass tube includes a reduced-thickness portion in which the holes are formed. The holes are preferably formed by exposing the reduced-thickness portion to a focused laser beam with sufficient energy to melt the holes in the glass. Capture of energy from the laser beam is enhanced by treating the surface of the reduced-thickness portion to make it opaque to the laser beam, either by etching or by coating with paint or ink. Alternatively, the laser beam could be matched to the composition of the glass such that the laser beam is of a frequency that the glass is opaque to the particular frequency of light used. An apparatus to form the glass tube includes a laser beam source, a focusing means to focus the laser beam on the glass tube, and a conveyor means to move the glass tube through the path of the laser beam in a controlled fashion to allow the surface to be exposed to the laser beam sufficiently to melt the hole in the tube and then move on so that a succession of spaced holes are formed in the glass tube. The apparatus can also include a means for moding the surface of the glass tube that is exposed to the laser beam, either by coating or frosting the surface.

NATURE OF THE INVENTION 
This invention relates to multipane windows and, more particularly, to a 
glass spacer bar used in separating the panes of the multipane window. The 
invention also relates to a method of making the glass spacer bars. 
BACKGROUND OF THE INVENTION 
It is well known in the art to provide a window having more than one pane 
of glass, the panes being separated by an airspace. Typically, such 
insulating windows have their glass panes separated by a frame interposed 
between the panes at their edges. The interior space between the panes 
then serves as an insulator to reduce heat flow through the glass. In the 
prior art it is known to manufacture the spacer frame of individual tubes 
made of aluminum joined at their ends to form a continuous frame. A 
sealant is injected around the perimeter of the glass panes to seal the 
glass panes and spacer frame into a single unit. 
One disadvantage to the use of aluminum in the spacer frame separating the 
glass window panes is that the aluminum typically has a higher heat 
conductivity rating than the glass that it separates. Therefore, while the 
central portion of the window is an effective insulator by virtue of its 
glass-and-air construction, the edges of the window conduct heat at a more 
rapid rate because of the higher conductivity factor of the aluminum. 
Also, in situations where there are extremes of temperature encountered by 
the window, the coefficient of expansion of the aluminum and the glass 
will be different and internal stresses will build up along the edges of 
the glass panes due to the unequal rates of expansion of the glass and 
aluminum members. It would be advantageous to have a glass panel comprised 
of separated glass panes in which the separation was accomplished by a 
medium having a similar heat conductivity rating to the glass panes and a 
coefficient of thermal expansion equivalent to that of the glass panes. 
SUMMARY OF THE INVENTION 
In order to achieve the desired result discussed above, a multipane window 
assembly is provided that includes first and second panes of glass 
separated by a spacer frame constructed of joined tubular members. The 
tubular members are constructed of glass tubes, each tube having a first 
and second side adjacent the glass panes and a third side bridging the 
first and second sides and facing the space between the panes. The third 
side has a plurality of openings formed in it to provide airflow between 
the inner airspace and the interior of the glass tube. The airflow allows 
any moisture trapped within the panes of glass to be absorbed by a 
desiccant placed within the spacer frame tubing. In a preferred embodiment 
the third side of the tube has a reduced-thickness portion in which the 
holes are formed. 
A method of constructing the glass tubes for use in the spacer frame 
includes the steps of extruding the tube from a batch of molten glass and 
forming a plurality of holes in the side of the glass tube that is in 
communication with the interior space between the glass panes. In a 
preferred embodiment the method also includes the step of forming the 
glass tubes with a reduced-thickness portion running the length of the 
tube along the side of the tube in which the holes are formed. The holes 
are then formed in the reduced-thickness portion. One of several methods 
can be used to form the holes in the glass tubing the preferred method 
being a use of a laser beam that is focused by a system of lenses onto the 
reduced-thickness portion of the tube. The beam is focused to a point to 
sufficiently concentrate the laser to melt a hole into the glass tube. In 
order to better concentrate the energy of the laser in order to provide 
enough energy to melt the hole into the glass, a surface of the 
reduced-thickness portion is treated to enhance its energy absorption from 
the laser beam. One method of treatment is to frost the surface of the 
reduced-thickness portion using either an acid etching or sandblasting 
technique or, alternatively, to coat the surface of the reduced-thickness 
portion with an energy-absorbent substance such as paint or ink, which 
makes the surface opaque to the laser beam and, therefore, absorbs energy 
from the laser beam rather than allowing it to pass through the 
reduced-thickness portion of the tube. 
Another method of making the holes contemplates striking the 
reduced-thickness portion of the robe with an impact tool with such force 
that a hole is punched into the reduced-thickness portion. Preferably, the 
tool is formed to a point so that the energy of impact is concentrated in 
a point on the reduced-thickness portion so that the hole is formed 
cleanly without fracturing of the glass surrounding it.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates one embodiment of a spacer robe made in accordance with 
the principles of the present invention. The spacer robe 10 has an 
essentially rectangular cross section and is a hollow glass robe having 
opposing sidewalls 12 and 14, which are adjacent the glass panes that the 
spacer bar is separating in the insulated window assembly. An outer wall 
16 connects the sidewalls 12 and 14 and when the tube is in place in the 
window frame assembly the wall 16 is the wall that faces the exterior edge 
of the insulated glass panel. An interior wall 18, which is spaced from 
and opposite the exterior wall 16, is the wall that faces the interior 
airspace formed between the two glass panes of the insulating glass 
window. 
The interior wall 18 has first and second portions 18a and 18b that are of 
a thickness approximately equal to the thickness of the sidewalls 12 and 
14 and exterior walls 16. A central portion 18c has a reduced thickness 
and is, preferably, connected to the portions 18a and 18b by a sloped 
shoulder. The precise shape of the shoulder portions 20 is in part 
determined by the method used to construct the glass tube. 
As is known in the art, the air trapped within the space between the two 
glass panes of an insulating window will have some residual moisture also 
trapped therein. In order to prevent this moisture from causing fogging on 
the inside of the glass window panes, a desiccant is typically inserted 
within the hollow of the spacer robe and openings are provided in the 
interior wall of the spacer robe to allow airflow between the interior of 
the tube and the interior space between the glass panes to allow the 
desiccant to absorb moisture from the air within the space between the 
glass panes. In the glass spacer tube of the present invention such 
pathways are provided by holes 22 formed in the reduced-thickness portion 
18c of the interior wall 18. 
While the holes 22 can be formed in several different ways, specific 
methods of making the holes will be discussed below as part of the 
invention. In order to add to the strength of the glass tube, it is 
possible to provide ribs 24 and 26 in the exterior wall 16. The exact 
shape and size and number of ribs are determined by the strength 
requirements for any particular glass insulating panel construction. 
FIG. 2 illustrates in somewhat schematic fashion a method and apparatus for 
making the spacer tubes of the type shown in FIG. 1 and more particularly 
shows a method and apparatus for producing the holes 22 in the interior 
wall 18. Referring now to FIG. 2, the glass tube 10, after it has left the 
point of extrusion and has cooled enough to provide some rigidity to the 
tube, passes below a laser light source 30. A laser light beam 32 emitted 
from the laser passes through a lens means 34, which focuses the laser 
beam onto the surface of interior sidewall 18. More particularly, the lens 
means 34 focuses the beam so that it is incident upon the surface of the 
reduced-thickness portion 18c. The reduced thickness of portion 18c means 
that there is less glass material that must be penetrated in order to make 
the holes 22. A controller 36 is used to control the emission of light 
from the laser source to coincide with the positioning of the tube 10 so 
that the laser emits sufficient energy to melt a hole in the wall portion 
18c. The controller then preferably shuts down the laser until the tube 10 
is moved a predetermined distance until the next location, where a hole 22 
is to be formed in the wall portion 18, is positioned beneath the laser 
source. The laser is then reenergized to melt the hole into the wall 
portion 18c. The process is repeated until a predetermined number of holes 
have been formed in the length of the tube 10, at which time the tube is 
then moved to a storage location to await the next step in the formation 
of a spacer frame. 
It is necessary for the laser 30 to be of sufficient power output to 
provide enough energy to melt a hole in the glass tube. At the same time, 
it is preferable to utilize as low-powered a laser as possible, primarily 
for cost and installation purposes but also for enhanced safety. 
Therefore, any steps that can be taken to enhance the energy absorption of 
the wall portion 18c, so that the power output of the laser can be 
minimized, will help to produce a more efficient system for forming holes 
in the glass tube. One such method of enhancing the energy absorption 
facility of the wall portion 18c contemplated by the invention is to 
render the wall portion 18c opaque to the laser beam so that more energy 
is absorbed rather than being transmitted through the glass. Again 
referring to FIG. 2, a spray means 38 is positioned above the path of 
travel of the tube 10 and upstream of the laser source 30. The tube 10, 
therefore, passes underneath the spray means prior to its exposure to the 
laser beam. The spray means can be used to spray an opaque coating onto 
the surface of the wall portion 18c to increase its opacity with regard to 
the laser beam. Such a spray could be comprised of a paint or an ink 
selected particularly for its quality of being opaque to the laser beam. 
At the same time, the spray should only thinly coat wall portion 18c so 
that the energy is not absorbed within the coating layer but, rather, is 
sufficient to supply heat to melt a hole in the wall portion 18c. 
Alternatively, the spray means could provide an etching solution such as an 
acid to etch or "frost" the surface of the wall portion 18c, thereby also 
increasing its energy absorption of the laser beam. The etching could also 
be accomplished by a small sandblasting device positioned in the same 
location as the spray means 36. 
As an alternative to physically altering the surface of reduced-thickness 
portion 18c, it would also be possible to analyze the makeup of the glass 
spacer tube and match it to a laser beam of the desired frequency that 
would cause the particular glass making up the spacer tube to be opaque to 
that frequency of light. This would allow the maximum energy absorption to 
occur without any physical alteration of the glass tube, thereby 
eliminating some of the apparatus otherwise required. 
FIG. 3 shows an alternate method and apparatus for producing the holes 22 
in the reduced-thickness portion 18c of the glass tube 10. In the system 
of FIG. 3, the glass tube is passed beneath a hammer-drive module 40, 
which contains a punch 41 with a sharp point thereon. A controller 42 
senses the position of the tube 10 in a conventional manner, such as with 
LED position sensors, and at the proper time sends a drive signal to the 
hammer drive, which causes the hammer drive to move the punch to impact 
the reduced-thickness portion 18c of the glass tube. The punch and the 
hammer drive are designed so that a short-term high-velocity impact is 
made on the glass tube sufficient to punch a small hole in the glass tube 
without inducing cracks in the area of the tube wall surrounding the hole. 
The tube is then moved along its length beneath the hammer drive and the 
hammer drive is, again, driven by the controller to impact the glass tube 
at the next desired location to punch another hole. When a sufficient 
number of holes have been punched in the glass tube the tube is then moved 
to a storage area to await further assembly of the spacer frame. 
It can be seen by those of ordinary skill in the art that the provision of 
a reduced-thickness section in one wall of the glass tube is important in 
that it lessens the amount of material through which a hole has to be 
formed in order to provide air passages between the interior of the spacer 
tube and the interior space between the glass panes of the glass insulated 
window assembly. The reduced-thickness portion allows the use of different 
methods of providing holes in the glass spacer tube, including the melting 
of the hole with a laser beam or punching the hole with a highspeed impact 
punch. The reduced-thickness section also provides less of an opportunity 
for cracks to form in the area surrounding the hole after formation. It is 
also important that whatever means is used to provide the hole in the 
interior wall of the glass tube, which is adjacent the airspace, the hole 
not be created in the exterior wall of the glass tube, which faces the 
outside of the glass window assembly. By reducing the thickness of the 
central portion of the interior wall, energy can be directed to that 
portion sufficient to form a hole in the reduced-thickness portion and, 
yet, the energy would not be sufficient even if it accidentally was 
partially absorbed by the exterior wall to form a hole in the exterior 
wall, because of its greater wall thickness, compared to the thickness of 
the central portion of the interior wall. This means that one other 
problem in the manufacture of the glass tube is eliminated. It should be 
understood by those of ordinary skill in the art and others that the glass 
tube and manufacturing system illustrated and described are merely 
exemplary and that changes can be made to the illustrated embodiments of 
the invention while remaining within the scope of the invention. The shape 
of the glass tube illustrated herein is not intended to be limiting in 
that the tube could have a square or other shape as the particular 
instance required. Also, the number and size of the holes formed within 
the glass tube are matters of choice matched to the particular 
installation requirements for the glass window being formed. Since changes 
can be made to the illustrated embodiments, the invention should be 
defined solely with reference to the claims that follow.