Method of and apparatus for thermally severing glass

A method of and apparatus for cutting relatively thick glass sheets by applying surface contact, conductive heat to the glass surface along the desired line of cut. An elongated, heated conductor rod is placed on the glass surface along the desired line of cut for transmitting heat thereto to create a thermal differential line and effect a cut therealong. Pressure means bear against the conductor rod to maintain the same in continuous contact throughout with the glass surface along the length of the desired line of cut.

BACKGROUND OF THE INVENTION 
The present invention relates generally to glass cutting and, more 
particularly, to the thermal cutting of relatively thick glass plates or 
sheets. 
Various attempts have been made to thermally cut glass plates or sheets in 
an effort to overcome the arduous, time-consuming technique of scoring one 
surface of the sheet along a desired line of cut and then applying a 
bending force about the score line. This well-known procedure is 
especially tedious and costly when trimming the bulb edge of relatively 
thick glass sheets having thicknesses of 3/4 inch or greater because at 
least two, and sometimes three, successive trim cuts inwardly of such edge 
must be made in order to achieve a final satisfactory edge. Moreover, a 
finishing operation, such as belt seaming for example, is sometimes 
required for certain commercial applications. 
Thermal glass cutting involves the application of heat to a surface of the 
glass along the intended line of cut to produce a thermal differential 
line through the thickness of the sheet and along which the compressive 
stresses adjacent the surface are decreased while the tensile stresses 
within the central region or core of the glass sheet are increased until 
reaching a level at which the glass will fracture along the thermal 
differential line. The most familiar of the various proposals for 
thermally severing glass involves the application of radiant heat along 
the intended line of cut from a non-contact thermal source spaced from the 
glass sheet surface. Also, one edge of the glass sheet is nicked to 
provide an edge score in alignment with the intended line of cut. As a 
practical matter, however, it has been found that the foregoing method of 
thermally severing glass is not always reliable in producing true linear 
cuts. It has been theorized that the reason for this resides in the fact 
that the radiated heat emanating from the source converges and enters the 
glass surface along the intended line of cut and then diverges as it 
migrates inwardly through the glass thickness. The progressively widening 
heated area creates at the tension layer, a heat band of substantially 
greater lateral extent than the thermal differential line. This can cause 
the glass to fracture uncontrollably in a meandering path along such band. 
Moreover, when attempting to make straight linear cuts parallel to the 
trim side of the blank where the desired line of cut is located inwardly 
of, or offset from, the centerline of the blank sheet, the cut has a 
tendency to run in an arcuate path toward the trim side to produce an 
arcuately curved or bowed edge projecting toward the trim side. 
SUMMARY OF THE INVENTION 
Accordingly, it is a primary object of the present invention to obviate the 
above-noted disadvantages by providing a new and improved method of 
thermally cutting glass by the application of localized, conductive heat 
to a glass surface along a desired line of cut to effect a fracture 
therealong. 
It is another object of this invention to provide a new and useful thermal 
cutting apparatus having surface contact, heat conducting means in 
substantial contact throughout with the underlying glass along a desired 
line of cut. 
It is a further object of this invention to provide means for maintaining 
the foregoing heat conducting means in substantial continuous contact with 
the underlying glass sheet throughout the length of the desired line of 
cut. 
The foregoing and other objects, advantages, and characterizing features of 
the present invention will become clearly apparent from the ensuing 
detailed description thereof considered in conjunction with the 
accompanying drawings wherein like reference characters denote like parts 
throughout the various views.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now in detail to the illustrated embodiment depicted in the 
accompanying drawings for carrying out this invention, there is shown in 
FIG. 1 a glass cutting apparatus, comprehensively designated 10, mounted 
above a glass supporting table 11 suitably supported on a plurality of 
legs 12. The cutting apparatus 10 is mounted on a structural frame 13 
including a pair of spaced, upstanding columns 15 on each side of table 11 
(only one pair being shown in FIG. 1), each pair being laterally aligned 
with the other. Columns 15 extend upwardly above table 11 and are tied 
together at their upper ends by horizontally extending hollow beams 16 
secured at their opposite ends to the aligned columns 15 to form a rigid, 
box-like structure. An I-beam 17 is welded or otherwise fixedly secured to 
the bottom sides of horizontal beams 16 and extends across the table 11 in 
vertical spaced, but parallel, relation to the upper surface of table 11. 
A pair of parallel guide rails 18 (FIG. 3) are rigidly secured to the 
opposite ends of the lower flange 20 of I-beam 17 and extend lengthwise 
thereof for supporting a carriage 21 adapted to be reciprocated 
horizontally therealong. 
As best shown in FIGS. 2 and 3, the carriage 21 comprises a pair of 
laterally spaced, upright plates 22 and 23 connected together adjacent 
their lower ends by a pair of longitudinally spaced tie rods 25 located 
adjacent the opposite ends of the plates. Each tie rod 25 is provided with 
a pair of laterally spaced lower rollers 26 suitably journalled thereon 
and having generally V-shaped grooves 27 extending circumferentially 
thereabout engageable with the complementary shaped lower edges 28 of 
guide rails 18. Suitable spacers 29 are mounted on tie rod 25 on opposite 
sides of rollers 26 to maintain the same in the desired lateral position 
in registry with guide rails 18. 
A pair of upper rollers 30 are mounted on opposite ends of plates 22 and 23 
adjacent the upper edges thereof in vertical alignment with the lower 
rollers 26. The rollers 30 are connected to their respective plates by 
bolt fasteners 31 and are spaced inwardly therefrom by suitable spacers 
32. Rollers 30 also are provided with V-shaped circumferential grooves 33 
engageable with and adapted to ride on the complementary shaped upper 
edges 35 of guide rails 18. 
An inverted L-shaped bracket 36 is mounted on plate 22 and is provided with 
a horizontal leg 37 for mounting thereon an actuator 38 adapted to engage 
the actuating levers 40 and 41 of a pair of longitudinally spaced limit 
switches LS-1 and LS-2 mounted on I-beam 17 for a purpose hereinafter 
explained. 
The means for reciprocating the carriage 21 includes an electric reversible 
motor 42 connected to a suitable source of electrical power (not shown) 
and operatively connected, via gear reduction box 43, to a drive shaft 45 
having a drive pulley 46 rigidly secured thereto. The drive thus far 
described is mounted on a platform 47 rigidly secured to one end of I-beam 
17. A drive cable 48 is trained about the drive pulley 46 and about an 
idler pulley 50 (FIG. 1) mounted on a shaft 51 suitably journalled for 
rotation in spaced bearings 52 mounted on upright supports 53 of a 
box-like frame 55 secured to the other end of I-beam 17. The drive cable 
48 is anchored at its ends to carriage 21 by means of a U-shaped anchor 
block 56 (FIG. 2). Each end of the cable 48 is secured to an eye bolt 57 
adjustably threaded into a tapped bore formed in one leg of the block 56, 
in turn welded or otherwise fixedly secured to the carriage 21. 
The surface contact, conductive heating means, generally designated 58 and 
hereinafter more fully explained, is indirectly suspended from the 
carriage 21 by means of an intermediate lift assembly, generally 
designated 61. The lift 61 comprises a pair of laterally spaced, 
longitudinal members 62 connected together by means of a plurality of 
relatively short cross members 63. Lift 61 is suspended from carriage 21 
at two longitudinally spaced points for generally vertical - arcuate 
movement relative thereto by means of longitudinally spaced, pivotal 
brackets 65, each of which is formed with an upper collar 66 (FIG. 3) 
pivotably mounted about the tie rod 25 of carriage 21 and a lower collar 
67 pivotably mounted on a shaft 68 secured at its opposite ends in a pair 
of laterally spaced lugs 70 projecting upwardly from the longitudinal 
members 62 of lift 61. The means for raising and lowering the lift 61 
relative to the carriage 21 includes a fluid actuator 71 pivotably mounted 
at its head end to a lug 72 rigidly secured to carriage 21 and at its rod 
end to a lug 73 rigidly secured to lift 61. 
It has been found that in order to obtain a smooth, straight line cut 
through a sheet of glass, especially a relatively thick glass sheet of 5/8 
inch thickness of greater, it is important to localize or confine the 
applied heat to the above-mentioned thermal differential line as the heat 
migrates inwardly through the glass thickness. This is difficult to 
achieve repeatedly by non-contact thermal severing techniques involving 
thermal radiation for example, because the radiated heat diverges 
outwardly as it migrates inwardly of the glass surface and is absorbed on 
interior regions of the glass extending laterally outwardly in opposite 
directions from the thermal differential line or desired line of cut. This 
creates a band-like area of heated glass at the tension layer having a 
lateral extent greater than the desired line of cut and often causes the 
glass sheet to fracture or split apart uncontrollably in a somewhat 
meandering path. Moreover, when thermally severing a glass sheet by 
radiation along a line of cut displaced from the centerline of the sheet, 
there is a tendency for the cut to bow or arch in the direction of the 
trim side of the sheet because of the unbalanced temperature profile on 
opposite sides of the desired line of cut. 
It has been found that the most efficient expedient for consistently 
producing a true linear, thermal cut is to apply surface contact, 
conductive heat therealong with continuous glass contact along the entire 
line of cut. To this end and, in accordance with the principles of this 
invention, the heat conducting means 58 is formed of an elongated, 
cylindrical hollow pipe or rod 59 adapted to engage the non-scored upper 
surface of the glass sheet along the desired line of cut and transmit heat 
thereto. The cylindrical peripheral surface of the rod 59 provides line 
contact only with the glass surface at the desired line of cut and 
confines the applied heat thereto. Rod 59 should be at least as long as 
the intended line of cut, and preferably longer. Cutting trials employing 
rods formed of thick walled, stainless steel tubing, as well as thick 
walled, galvanized steel tubing have been successful. The conductor 59 can 
be uniformly heated up to the desired temperature by an elongated, 
electrical resistance heating element 60, such as the electrical heating 
unit commercially available under the trademark "Calrod" for example, 
extending through the rod 59 and projecting outwardly from the opposite 
ends thereof for connection to a suitable electrical power source (not 
shown). 
The conductor rod 59 is suspended from lift 61 by a series of paired lift 
arms 75 depending downwardly from the lift longitudinal members 62 at 
three equally, longitudinally spaced points therealong. The arms 75 of 
each pair are provided with lift fingers 76 (FIG. 4) in the form of 
setscrews threaded through their respective arms at a downwardly directed 
angle relative to a true horizontal in a converging relation and have 
tapered end portions 77 engageable with opposite sides of the conductor 
rod 59 below the vertical midpoint thereof. The conductor rod 59 rests and 
is supported on these tapered end portions 77 in the elevated position of 
lift 61. When lowering the lift to place the conductor rod 59 on the glass 
sheet, rod 59 engages the upper surface of the sheet S before the lift 
reaches the end of its downstroke, causing the lift fingers 76 to be 
disengaged from the rod 59 so as to provide the necessary clearance for 
the reciprocating pressure applying rollers, hereinafter more fully 
described. 
Means are provided for vertically guiding the conductor rod 59 when raised 
or lowered. Such means comprise a pair of conductor rod guides 69 provided 
at the opposite ends of table 11 and depending downwardly from the I-beam 
17 for receiving the opposite ends of the conductor rod 59. The guides 69 
are provided with a plurality of vertically spaced, laterally aligned 
openings 74 through which suitable pins (not shown) can be inserted for 
supporting the opposite ends of conductor rod 59 at rest in an elevated 
position above table 11. 
In order to preclude lateral rolling movement of the rod 59 when placed on 
the glass surface, a collar 78 (FIG. 7) is secured to at least one end of 
rod 59 and is provided with a flatsided block 79 welded or otherwise 
fixedly secured to collar 78 and which fits snugly between guides 69 for 
sliding movement relative thereto. 
Placing the heated conductor rod 59 on the upper surface of the glass sheet 
S coincident with the desired line of cut transmits heat directly to the 
glass along the length of this desired line of cut to produce a thermal 
differential line inwardly through the thickness of the sheet, the 
propagating heat transfer being substantially confined to the thermal 
differential line extending perpendicularly to the opposite surfaces of 
the sheet. As a result of this applied conductive heat, the surface of the 
glass along such line expands somewhat to relieve or decrease the 
compressive stresses on and immediately below the glass surface while the 
tension layer along the thermal differential line attempts to contract in 
an effort to counteract such expansion and consequently increases the 
tensile stresses. A continued increase in tensile stresses, coupled with 
the initial damage imparted to the edge of the sheet by scoring or 
nicking, causes the intermediate tension layer to split along the entire 
length of the thermal differential line, the split being propagated 
perpendicularly through the compression layers to both opposite surfaces. 
Once started, the split or fracture is effected within a fraction of a 
second to complete the cut. It has been found that substantially 
continuous contact of the conductor rod with the glass surface along the 
full length of the desired cut is necessary to effect a true linear cut 
yielding smooth and even severed edges therealong. 
While relatively short linear cuts, say up to 48 inches for example, can be 
satisfactorily made by the heat conducting technique described above, 
problems are encountered in making longer cuts in a true linear path. This 
is due to the interruption of contact between the rod and the glass 
surface caused by the warpage or bowing of portions of the conductor rod 
away from the glass surface as a result of thermal variations therein 
caused by engagement of the heated rod with the relatively cool surface of 
the glass. Attempts to overcome this warpage by employing elongated, rod 
abutting press members and the like without imparting excessive physical 
stresses to the sheet have not been successful because of the heat 
transfer to such members causing them also to warp along with the rod. On 
the other hand, applying the necessary physical force to counteract this 
warpage induces physical stresses in the glass which can promote chipping 
or uncontrolled breakage. Nor would the application of pressure to the rod 
at fixed, spaced points solve the problem because those portions of the 
rod between the pressure points would bow sufficiently to interrupt the 
necessary surface contact with the glass. 
In order to preclude such warpage, means in accord with this invention are 
provided for maintaining the conductor rod 59 in substantially continuous 
contact throughout with the glass sheet surface without inducing physical 
stresses in the glass. To this end, such means comprise a plurality of 
equally spaced, longitudinally aligned rollers 80 adapted to bear against 
the conductor rod 59 and rollable thereon to apply a moderate, uniform 
pressure therealong. Since all of the rollers 80 and their mountings are 
identical in construction and operable in the same manner, it is believed 
that a detailed description of only one will suffice, it being appreciated 
that the same reference characters will be applied to identical parts. 
With reference to FIGS. 3, 5 and 6, each roller 80 comprises a body portion 
provided with enlarged diameter flanges 81 at the opposite ends thereof 
and having a peripheral V-shaped groove 82 for receiving the conductor rod 
59. The V-shaped configuration of groove 82 permits the use of a wide 
variety of differently sized conductor rods without the necessity of 
changing rollers. Each roller 80 is journalled on a shaft 83 mounted at 
its opposite ends in the bifurcations 85 of a yoke member 86, in turn 
pivotably mounted on a shaft 87 secured at its opposite ends in the 
depending legs 88 of an inverted U-shaped bracket 90 secured, as by 
fasteners 91, to the longitudinal members 62 of lift 61. 
Means are provided for swinging each roller 80 between an operative 
position bearing against conductor rod 59 and an elevated, inoperative 
position shown in phantom at the right in FIG. 2. Such means comprise a 
fluid cylinder 92 connected, as shown at 93 in FIG. 5, to a cross member 
63 provided with the usual piston rod 95 pivotably connected, as shown at 
96 in FIG. 6, to a shaft 97 mounted in yoke member 86. Cylinders 92 are 
designed to apply only a moderate amount of pressure, on the order of 
approximately 10 to 30 psi, and preferably 15 psi for example, to 
counteract the tendency for the rod to warp or bow away from the glass 
surface. 
The mode of operation of the apparatus of this invention in severing from a 
blank plate or sheet S of glass an elongated, relatively narrow strip, 
such as can be employed as a stabilizer in architectural constructions for 
example, is as follows: 
With the heating element 60 energized to maintain the conductor rod 59 at 
the desired elevated temperature and the latter in an elevated position 
above the surface of table 11, an enlarged sheet S is placed on the upper 
flat surface of table 11 with the desired line of cut vertically aligned 
with the conductor rod 59. The sheet S may be moved relative to the 
cutting apparatus for proper positioning or alternatively, the I-beam 17 
can be mounted on horizontal beams 16 by means of a trolley-track 
arrangement (not shown) for horizontal movement relative to beams 16 to 
position conductor rod 59 in vertical registry with the desired line of 
cut. In either event, once the rod 59 is aligned with the desired line of 
cut, lift 61 is lowered by extending the piston rod of cylinder 71 to 
bring conductor rod 59 into engagement with the glass sheet surface 
coincident with the desired line of cut. The lift 61 continues to descend 
until the lift fingers 76 are lowered out of engagement with the rod 59, 
as shown in FIG. 4, to provide clearance for the reciprocating rollers 80 
when lowered. The series of cylinders 92 are then actuated to extend their 
respective piston rods 95 to bring the rollers 80 into bearing contact 
with the upper portion of conductor rod 59. It should be appreciated that 
only a moderate pressure, on the order of about 15 psi for example, is 
applied to the rollers to prevent undesirable physical stress build-up in 
the glass. An edge score is applied to the edge of the large sheet in 
alignment with the desired line of cut to initially damage or weaken 
slightly the tension layer of the sheet S. 
When placed on the glass surface, the heated conductor rod 59 heats, via 
conduction, the glass sheet immediately adjacent or underlying the 
conductor rod along the desired line of cut to produce a thermal 
differential line through the sheet. The conductive heat applied along 
this thermal differential line relieves some of the compressive stresses 
in the compression layer as it migrates inwardly through the sheet 
thickness while proportionately increasing the tensile stresses in the 
intermediate tension layer. The tensile stresses increase until they reach 
a level which, when assisted by the initially weakened scored edge, create 
a split or fracture in the tension layer along the thermal differential 
line. This split or cut is propagated outwardly through the compression 
layers to the opposite surfaces of the glass sheet along the entire 
desired line of cut, leaving smooth and even severed edges throughout. 
Once the fracture begins, the cut is completed in a fraction of a second. 
When the conductor rod 59 is placed on the glass surface coincident with 
the desired line of cut, the reversible motor 42 is energized to rotate 
the pulley 46 and move carriage 21 axially and thereby the rollers 80 
longitudinally relative to conductor rod 59. As the carriage moves in this 
first direction, toward the right as viewed in FIG. 1, and approaches the 
end of its stroke, the actuator 38 engages the lever 41 of limit switch 
LS-2 to complete a circuit, reversing the polarity and thereby the 
rotation of motor 42 and returning carriage 21 in the opposite or second 
direction leftwardly along guide rails 18. As the carriage 21 advances in 
this second direction and reaches the opposite end of its stroke, actuator 
38 engages the lever 40 of LS-1 to complete another circuit, again 
reversing the polarity and rotation of motor 42 to change the movement of 
carriage 21 in the opposite or first direction. The continued 
reciprocating rolling action of rollers 80 against conductor rod 59 
imparts a uniform moderate pressure thereto throughout its effective 
length to counteract and overcome the tendency of the rod 59 to bow or 
warp upwardly away from the glass and thereby maintain the rod in 
substantially continuous contact with the underlying glass sheet. This 
rolling action tends to iron or flatten out any irregularities in the rod 
and resists the tendency of portions thereof to buckle upwardly out of 
contact with the glass surface. 
The carriage travel in either direction and the spacing between adjacent 
rollers 80 is such that each roller 80 has a stroke overlapping the end 
stroke of the preceding roller 80 to assure positive engagement with at 
least that length of rod 59 contacting the glass surface. As shown in FIG. 
2, the outermost roller at each end has an end stroke extending past the 
edge of the glass sheet. Satisfactory rod-glass contact was achieved by 
spacing the rollers at 12 inch centers with a carriage stroke range of 
from about 20 inches to 30 inches. 
Excellent results have been obtained in cutting strips from 3/4 inch thick, 
annealed glass having a length of 162 inches using a 3/4 inch OD conductor 
rod heated to a temperature of about 700.degree. F. The heated rod was 
left in contact with the sheet until the cuts were completed, the total 
time of rod-glass contact ranging from about 15 seconds to 40 seconds, the 
time varying in accordance with the quality of the anneal imparted to the 
glass. It was found that as the quality of the anneal increased, the 
shorter the duration of rod contact time required to complete the cut. The 
severed strips exhibited straight, smooth and even edges without the 
necessity of further finishing. While preferably the rod was formed of 
stainless steel piping, it should be appreciated that the conductor rod 
can be formed of any material having high heat conductivity properties 
with an OD from about 1/2 inch to 11/2 inches. Also, the rod can be heated 
up to a temperature varying between 300.degree. F. to 1100.degree. F. as 
determined by the thickness of the glass. Generally, an increase in glass 
thickness requires a decrease in applied heat. For example, it was found 
that excellent results were obtained on 3/4 inch glass by heating the 
conductor rod to 700.degree. F., whereas a temperature of only 600.degree. 
F. yields good results with 1 inch thick glass. It should be appreciated 
that any number of rollers can be employed as dictated by the length of 
cut desired. Also, the spacing between rollers, as well as their length of 
stroke as determined by the carriage, may vary widely within the purview 
of this invention. 
From the foregoing, it is apparent that the objects of the present 
invention have been fully accomplished. As a result of this invention, a 
new and useful cutting apparatus is provided for effecting successful 
elongated thermal cuts in relatively thick glass sheets yielding edges 
that are smooth and even and that minimizes, if not completely eliminates, 
further finishing operations. By the provision of an elongated heat 
conducting rod, the applied conductive heat is localized or concentrated 
at the desired line of cut in the underlying glass to better control 
cutting and inhibit the formation of ragged and irregular edges. The 
provision of a series of equally spaced pressure members or rollers 
reciprocable back and forth along the rod under moderate pressure assures 
substantially continuous glass contact and overcomes the tendency of the 
elongated rod to warp or bow away from the glass surface when making long 
linear cuts, on the order of 48 inches to 200 inches for example. 
It is to be understood that the form of the invention herewith shown and 
described is to be taken as an illustrative embodiment of the same, and 
that various changes in the shape, size and arrangement of parts, as well 
as various procedural changes, may be resorted to without departing from 
the spirit of the invention.