Method and apparatus for heat-welding lengths of profiles for sealing gaskets

A method and apparatus for heat-welding corners lengths of profiles together, for sealing gaskets, where the profiles include at least one extendible or compressible air chamber and are cut at their ends at an angle. The method includes positioning two profiles, with one of the cut ends of each profile opposite each other inside a suitable device including clamps which make the positioning possible, heating the positioned ends until the positioned ends reach a softened state, choking the profiles so as to completely occlude the air chambers along choking sections, closing the clamps in order to cause the profiles to come into mutual mating contact at the heated ends, injecting air into the air chambers by perforating the air chambers in a region between the choking sections and the heated ends so as to apply pressure to walls of the profiles in that region, pressing the walls against walls of the clamps to join the heated ends by heat-welding under pressure, and opening the occluded sections. The apparatus includes a heating element to heat one of the ends of each profiles, clamps to position the profiles with the cut ends opposite each other and for mutually mating the heated ends together, needles for injecting air inside an interior of the air chambers nearby the ends to be heat-welded, and devices to choke the profiles by completely occluding said air chambers along choking sections.

Gaskets for refrigerators made from such materials as PVC which are 
constituted by a base element designed to be fastened onto refrigerator 
door, an intermediate bellows-like chamber which secures the extension or 
compression motions and a seat designed to house magnetized material which 
realizes the tight shutting of refrigerator door by cooperating with metal 
edge of the refrigerator cabinet, are well known. 
Such gaskets are extruded as straight profiles which are then cut into 
lengths according to the size of the refrigerator cabinet to which they 
must be applied. Said extruded profiles are cut at their ends according to 
an angle of 45.degree., and at these ends the so prepared lengths of 
profile are then joined by heat-welding in order to produce ready frames 
for application to the refrigerator cabinet. 
SUMMARY 
In general, the purpose of the method proposed by the present invention is 
of providing very strong heat-welded joints at the junction zones. 
In order to achieve said purpose and to provide other advantages which will 
be clearer from the following disclosure, the present invention proposes a 
method for heat-welding, at the corners, lengths of profiles for sealing 
gaskets, for example for refrigerators of the like, of the type comprising 
at least one bellows-like extendible, or compressible, air chamber, with 
said lengths of profile being cut at their ends according to angles of 
45.degree., characterized in that said method comprises the following 
steps: 
a) positioning two lengths of profile with their ends opposite to each 
other, inside a suitable device comprising clamps which make it possible 
said positioning to be performed, 
b) heating said ends, cut according to suitable angle until said ends of 
both lengths of profile reach a softened state, 
c) choking each of said lengths of profile nearby said ends so as to 
completely occlude said air chamber along the choking section, closing 
said clamps in order to cause said pair of lengths of profile to come into 
mutual mating contact at their heated ends, while simultaneously injecting 
air into the interior of said air chamber by perforating it the region 
comprised between said choking section and the said end of each of said 
lengths of profile, so as to press the walls of the lengths of profile in 
that region against the walls of the clamps, thus heat-welding said ends 
to each other under pressure, 
d) opening said occluded sections and 
e) heat-welding a free end of the so heat-welded pair of lengths of profile 
with a third length of profile by acting in a similar way, and finally 
with the fourth, and last, length of profile, so as to form a gasket frame 
heat-welded at its corners.

Referring to FIG. 1 of the accompanying drawings, the reference numerals 
(10) and (11) show two lengths of profiles foe sealing gaskets of the type 
shown in particular in FIG. 7. 
Such a gasket of FIG. 7 comprises a base element (12) designed for being 
used in order to fasten the gasket, for example to the counter-door piece 
of the refrigerator cabinet, a bellows-like extendible, or compressible, 
intermediate air chamber, and finally a front seat (14) designed to 
receive and house a magnetized material. 
Going back to FIG. 1, both lengths of profile (10) and (11) are cut, at 
their respective ends (15) and (16), with an angle of 45.degree.. 
Both lengths of profile (10) and (11) are positioned, with said ends (15) 
and (16) being mutually opposite, inside the interior of a suitable 
heat-welding device constituted by a pair of fixed clamp jaws (17) and 
(18), designed to cooperate with a complementary pair of mobile clamp jaws 
(19) and (20). 
Once that both lengths of profile (10) and (11) are positioned as shown in 
FIG. 1, the mobile clamp jaws (19) and (20) are moved towards the fastened 
clamp jaws, until they come to their operating position as shown in FIG. 
2. 
The ends (15) and (16) of both lengths of profile are then heated by 
placing, between them, a heating element (21) until said ends of both 
lengths of profile reach a softened state. 
The heating element (21) is then removed as displayed in FIG. 4. 
Finally, the heat-welding clamps are definitively clamped, as shown in FIG. 
5, i.e., by closing said pairs of clamp jaws (17), (18) and (19), (20) so 
as to firmly lock both lengths of profile (10) and (11) inside the mould 
interior, as shown in FIG. 5. 
In FIG. 5 there is displayed an air injecting device with which the fixed 
clamp jaws (17) and (18) are equipped. 
In fact, longitudinally inside said clamp jaws and parallel to each other, 
two hollow cylinders (21) and (22) are provided inside each of which a 
respective piston (23) can slide which is equipped with a hollow needle 
(24) opened at its end (25) (see the detail of FIG. 7). 
Each of said air injecting devices is controlled by a solenoid valve (26) 
which controls the compressed air injection into the interior of each of 
said cylinders (21) and (22). Air fed into the interior of the cylinders 
causes the piston (23) to istantaneously move forward and is discharged 
through the perforated tip (25) throughout the time during which the 
solenoid valve remains energized. 
When the solenoid valve is de-energized, the piston with its needle returns 
back to its resting position, by being urged to return by a spring (29) 
provided inside the interior of the cylinder. 
In such a way, the needle (24) borne by the piston (23), under the effect 
of pressure of injected air can extend outwards from the head of the 
cylinder (21) and (22), until it comes into contact with the side wall of 
the air chamber (13) of the gasket facing it in that position in which 
said profile for sealing gaskets is kept by the heat-welding mould. 
Going back to the position shown in FIG. 5, when the heat-welding mould is 
totally closed in order to cause both ends (15) and (16) of both lengths 
of profile to come into mutual mating contact, simultaneously with such 
position reaching, the solenoid valve (26) commands air to be injected 
through both cylinders (21) and (22) and the respective needles (24) to 
move forward, which are consequently pushed to extend outside from their 
seat until they come into contact with the side wall, and perforate the 
air chamber (13), of the profile for sealing gaskets, as schematically 
shown in FIG. 7. Compressed air is then injected through the bore of the 
hollow needle (24), through the opening (25), into the interior of said 
air chamber (13). Simultaneously, each of both lengths of profile (10) and 
(11) is choked at a cross-section thereof by means of the devices (27) and 
(28), as shown in particular in FIG. 6. 
Such devices (27) and (28) can be constituted, for example, by cylindrical 
compressive means integral with pneumatic pistons which drive them 
automatically. 
Compressed air injected into the interior of the air chamber (13) cannot 
therefore escape from said air chamber from the heat-welding area, because 
the internal bores of said profile for sealing gaskets are totally 
occluded at (27) and (28), and, as a consequence thereof, compressed air 
injected into the interior of the air chamber (13) by the needle (24) 
remains under pressure inside the region bounded by said choking section 
and said end of said length of profile, consequently applying a pressure 
to the walls of said lengths of profile in that region, pressing them 
against the walls of the clamping jaws. 
In that way, while the heat-welding of both heated ends (15) and (16) of 
the lengths of profile is taking place, a pressure is simultaneously 
exerted from the interior of the air chamber of the profile for sealing 
gaskets, the effect of which will be of pushing both ends (15) and (16) 
against each other, as well as of exerting an expansion and consequently a 
compression of the walls of the profile for sealing gaskets against the 
walls of the heat-welding mould. 
Pressurized air so fed to the air chamber performs the task of causing the 
walls of the profile for sealing gaskets to perfectly adhere to the wall 
of the clamps, thus considerably improving the mutual contact of the parts 
which must be heat-welded to each other during the heat-welding time. 
We wish to remind that a further advantage is obtained thanks to the 
improved mutual adherence of those parts of both lengths of profile which 
must be heat-welded, associated with the normal formation of burr of 
material in the heat-welding area, which generally produces fins which 
must be removed. 
The presence of compressed air injected from the outside according to the 
method of the present invention makes it possible such an excess of 
material, which otherwise would form such burrs, to be advantageously 
conveyed into the interior of a suitable groove provided along the inner 
angle of both lengths of profile of FIG. 5, between both fixed clamp jaws 
(17) and (18) which therefore acts as a suitable seat for receiving said 
material excess, so that at the inner angle of both so heat-welded lengths 
of profile a rib (30) of plastic material is formed which will act as a 
stiffening means of the profile frame in the angle in question, with a 
further reinforcement of the end effect of joining both said lengths of 
profile. 
Air injection according to the method of the present invention offers a 
further advantage deriving from that it causes a fast cooling to take 
place of the parts heat-welded to each other, consequently allowing the 
heat-welding operation to be speeded up and offering the possibility of 
de-moulding more rapidly the heat-welded frame, with said frame being 
immediately handeable. 
A further object of the present invention is a suitable apparatus for 
implementing the method disclosed hereinabove. 
Such an apparatus comprises both the heat-welding mould with the relevant 
clamps as disclosed above, and the air injection device and the choking 
devices and, relatively to as disclosed in the preceding examples, it may 
comprise several variants capable of producing the same effect of 
pressurized air injection into the interior of the air chamber of the 
profile for sealing gaskets. 
The method according to the present invention can then be further improved 
by applying a vacuum from outside of the heat-welding device, thus making 
it possible the lengths of profile to be positioned in an ideal way inside 
the interior of the same mould, because the effect of said vacuum is of 
causing said lengths of profile to adhere even better to the clamps, thus 
improving the static conditions of the system during the heat-welding 
operations and consequently the working precision. 
The heat-welding method of the present invention is suitable for 
application to any suitable materials used for manufacturing gaskets for 
refrigerators and gaskets for other applications different from 
refrigeration industry, for example for motor vehicles, which may use, or 
less, magnetic effects, for example for such polymeric materials as PVC, 
or different from PVC.