Seam welder for thermoplastic coated fabric

A seam welding machine for thermally seaming edges of coated fabric panels (P and P') in the field, said machine having a guiding head (16) with opposed laterally open overlapping slots (19 and 20) for guiding overlapping panel edge portions into a nip area behind the head (16) wherein the tip (25) of a hot air welding gun is directed, upper and lower pressure rolls (30 and 31) and upper and lower drive belts (34 and 41) following said nip area to press said overlapping edge portions into a seam (S).

TECHNICAL FIELD 
The invention relates to machines for heat welding seams of flexible 
thermoplastic membrane by hot air jets, and more particularly to a seam 
welding machine adapted to join large sheets of flexible thermoplastic 
membrane in the field over irregular terrain and in adverse weather 
conditions. 
BACKGROUND ART 
Flexible membrane linings have been used for many years to provide 
impermeable ground protection and retain liquids in excavated pits and 
reservoirs, and to transport water in irrigation ditches. 
More recently, such lining systems have been used in the containment of 
hazardous waste materials and municipal landfills to prevent the leaching 
of chemicals or waste materials into the ground surfaces, whence they 
ultimately contaminate public or private water supplies. 
Where the linings required are small enough in area to be handled and 
installed in one piece, they can be prefabricated of sections seam welded 
at the factory and transported to the field site. A prior welding machine 
suitable for factory welding is disclosed in U.S. Pat. No. 3,402,089. 
However, such machine requires a solid, smooth foundation such as a 
factory floor and is not suitable for seam welding large panels of lining 
over irregular terrain in the field. 
A great many of the outdoor installations are quite extensive, covering 
areas of several acres, so that it is literally impossible to fabricate a 
flexible membrane liner as a one-piece liner at the factory and then 
transport and install it in the field. Most such applications require 
panels of not over 70 feet wide by 200 feet long and weighing less than 
4000 pounds to be prefabricated in a factory environment, and the 
individual panels are then unrolled and installed in the field by 
overlapping and seaming their edges together. 
In the past, sustantially all such field seaming has been accomplished by 
the use of solvents or adhesives to join the overlapping marginal portions 
together, as hot air or thermal seaming has been impractical, if not 
impossible, due to adverse field conditions such as wet, muddy, sandy or 
rocky soil conditions precluding the required smooth, solid backup 
pressure required for prior thermal seam-welding machines. 
However, while solvent or adhesive systems have been, to some extent, 
satisfactory for the containment of water, they are not satisfactory or 
desirable for the containment of chemicals and hazardous waste materials. 
Solvent and adhesive seams are susceptible to defects in applicator 
techniques, and to environmental conditions at the time of application, 
such as moisture or cold temperatures. Whereas, a slight seam failure in a 
water containment system causing a small leak might not be critical, such 
a leak in a hazardous waste system is extremely critical, and consequently 
governmental regulatory agencies such as EPA require almost failsafe seam 
conditions. 
Moreover, solvent and adhesive seams are subject to attack not only by the 
chemicals in the liner itself, but also to microbiological organisms which 
actually feed on the adhesive material. Hence, even if the seam is 
substantially perfect when installed, over a period of time it can lose 
its bonding strength and result in a seam failure. 
There is a strong need and a strong desire by private contractors and by 
government agencies for the production of a thermal seam in the field 
comparable to a factory thermal seam, as it is well recognized that such a 
seam is far superior for all purposes to a solvent or adhesive seam. 
DISCLOSURE OF INVENTION 
The novel and improved seam-welding machine comprising the present 
invention is adapted to produce thermally welded seams of highest quality 
in the field comparable to factory thermally welded seams regardless of 
adverse weather and terrain conditions, by lifting adjoining panels of the 
lining material off the ground and providing its own necessary hot air and 
pressure conditions for seam welding independently of the underlying 
ground surface. 
It is an object of the present invention to provide an improved thermal 
seam welding machine for joining large panels of thermoplastic coated 
fabric in the field over uneven or adverse terrain surfaces. 
Another object is to provide an improved thermal seam welding machine 
capable of producing high quality seam welds in the field which are 
resistant to chemicals and microbiological organisms. 
A further object is to provide an improved seam welding machine capable of 
producing high quality seam welds in the field under adverse weather 
conditions and without the use of solvents or adhesives. 
These and other objects are accomplished by the improvements comprising the 
present invention, a preferred embodiment of which is shown by way of 
example in the accompanying drawings as embodying the best known mode of 
carrying out the invention. Various modifications and changes in details 
of construction are comprehended within the scope of the appended claims.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION 
As shown in FIG. 1, the improved seam welder is rollably supported on two 
laterally opposite wheels 10, journaled in the ends of a transverse upper 
frame 11, preferably having upstanding side flanges 12 and end flanges 13. 
The upper frame 11 is supported on a lower frame assembly which comprises 
two laterally spaced upper longitudinal tubular frame members 14 and two 
laterally spaced lower longitudinal tubular frame members 15, the members 
14 being secured to the underside of the upper frame 11. 
At the head or front end of the lower frame assembly is a block or guiding 
head 16 between the inner surfaces of the tubular frame members 14 and 15, 
and it is secured thereto by transverse bolts 17, as best seen in FIG. 5. 
Viewed from the front end as in FIGS. 3 and 5, the block 16 has a 
horizontal upper slot 19 extending laterally inward from the right 
substantially parallel to the bottoms of upper tubes 14 and a horizontal 
lower slot 20 extending laterally inward from the left substantially 
parallel to the tops of the lower tubes 15. 
The slots 19 and 20 extend past the longitudinal centerline of the block 16 
and overlap each other a predetermined amount. The horizontal center plane 
of the block is midway between the slots 19 and 20. Viewed from the front 
end the positions of the slots 19 and 20 give the block substantially an 
S-shape in appearance. Preferably, the block is hollow above the slot 19 
and below the slot 20 to save weight and material. A U-shaped handle 21 is 
preferably secured to the transverse upper frame 11 and extends rearwardly 
and inclines upwardly therefrom. 
The slots 19 and 20 provide guides for the marginal edges of two 
side-by-side thermoplastic-coated fabric panels P and P' to guide them in 
overlapping relation to a nip area at the rear side of the block 16, where 
hot air is directed through a welding nozzle 24 and tip 25 between the 
overlapping marginal edges, thereby rendering the thermoplastic coatings 
substantially molten so that when pressed together they become welded. Hot 
air is delivered from the hot air gun 26 supplied with incoming air 
through conduit 27. The panels P and P' are preferably fabric coated with 
a special vinyl composition in which the plasticizer is substantially 
inhibited against migration under adverse weather conditions and over long 
periods of time. 
Immediately following the nip area the overlapping edge portions of panels 
P and P' are pressed together between upper pressure roll 30 and lower 
pressure roll 31. Roll 30 is driven through a sprocket chain 32 by a front 
drive roll 33 which is connected by a driven timing belt 34 to a rear 
drive roll 35. The timing belt 34 and roll 35 are driven by a governed 
speed electric motor 36 through a sprocket chain 37. The motor 36 is 
mounted on rear extensions of the upper tubular frame members 14 and has a 
speed control knob 38. 
The lower pressure roll 31 is driven through a sprocket chain 39 by a front 
drive roll 40 which is connected by a driven timing belt 41 to a rear 
drive roll 42. Idler sprockets (not shown) may be provided to engage and 
tension the sprocket drive chains 32 and 39 in a wellknown manner. The 
timing belt 41 and roll 42 are driven by an air powered gear motor 43 
through sprocket chains 44 and 45 and reduction gear 46 which increases 
the effective speed of the gear motor causing it to develop increased 
torque on the timing belt 41. The motor 43 is mounted on a wall of one of 
the lower tubular frame members 15. 
The shaft of the upper pressure roll 30 is journaled in blocks 48 which are 
movable in vertical channels 49 secured to upper tubular frame members 14 
(FIG. 7), and the blocks are mounted on piston rods 50 yieldingly urged 
downwardly by pneumatic cylinders 51 to load the roll 30 downwardly 
against the fabric. Similarly, the upper drive rolls 33 and 34 are 
journaled in blocks 52 movable in vertical channels 53 secured to upper 
frame members 14 (FIG. 8), and the blocks are mounted on piston rods 54 
yieldingly urged downwardly by smaller pneumatic cylinders 55 to load the 
rolls 33 and 35 downwardly against the fabric. The shafts of the lower 
rolls 31, 40 and 42 are journaled in bearings 46 which are fixedly mounted 
in tubular frame members 15. 
Referring to FIGS. 1 and 2, a cable 58 conducts electric current from a 
power source to a junction box 59 from which current is supplied to 
electric motor 36 and to the heating elements in hot air gun 26 by 
conventional wiring (not shown). Air is conducted from a compressor (not 
shown) by a conduit 60 through an air regulator 61 and oiler 62 to a 
junction with three branch conduits 63, 64 and 65, each having air 
regulators 66 therein. The conduit 63 supplies air to the cylinders 51 and 
conduit 64 supplies air to the cylinders 55. The conduit 65 supplies air 
to the gear motor 43 through devious interconnected conduits 67, 68 and 69 
(FIGS. 3-5) extending forwardly through one upper tubular frame member 14, 
across through block 16 and then rearwardly through a laterally opposite 
lower tubular frame member 15. 
In the operation of the machine the edge portions of two panels P and P' 
are passed into the slots 19 and 20 in the block 16 from which their 
marginal edges emerge in overlapping relation into the nip area where the 
tip 25 applies hot air between the overlapping marginal edges to render 
the coatings on their inner surfaces substantially molten. Immediately 
following the nip area the overlapping portions are pressed and welded 
together between pressure rolls 30 and 31, and then passed between the 
timing belts 34 and 41 connecting the rolls 33 and 35 and 40 and 42, 
respectively. The passage of the welded seam S through the belts assists 
in cooling the seam and also pulls the membrane through the pressure rolls 
30 and 31 to produce a wrinkle-free seam because the outer diameter of the 
drive rolls is slightly greater than that of the pressure rolls 30 and 31. 
If the panels P and P' are stationary relative to the ground, the passage 
of the welded seam through the pressure rolls and timing belts causes the 
machine to be driven over the panels in the direction of the arrow A in 
FIG. 4. 
The air-powered gear motor 43 is not rotated at a given speed as is the 
electric motor 36, but applies torque to the lower pressure roll 31 and 
the lower timing belt 41 so as to follow the speed of the upper pressure 
roll 30 and upper timing belt 34 as driven by the electric motor 36. Thus, 
regardless of the speed of the motor 36, the air motor causes the lower 
pressure roll and belt assembly to match the speed of the upper pressure 
roll and belt assembly, thereby insuring a smooth and wrinkle-free seam. 
An important feature of the improved machine is that behind the head 16 the 
machine is completely open laterally or "throatless" in the plane of the 
seam, so that there are no guides or restrictions to restrain passage of 
the panels through the upper and lower pressure rolls and belt assemblies 
regardless of the panel widths, which would cause difficulties in passage 
or wrinkling at the seam. Also, the plane of the overlapping edges of the 
panels P and P' and the welded seam S in passing through the machine is 
close to the ground at all times so that the overlappings are lifted only 
a short distance. 
The improved seam welder provides a lightweight machine adapted to produce 
high quality thermally welded weather and chemical-resistant seams over 
uneven ground in the field by lifting the marginal edge portions of 
adjoining membrane panels off the ground as it passes thereover, and 
providing its own pressure and hot air welding conditions independently of 
the underlying ground surface.