EP1472948A1

EP1472948A1 - Improved oven for the stabilization of shoe uppers

Info

Publication number: EP1472948A1
Application number: EP03425285A
Authority: EP
Inventors: Mario De Fulgentis
Original assignee: Officina Meccanica Bdf SpA
Current assignee: Officina Meccanica Bdf SpA
Priority date: 2003-05-02
Filing date: 2003-05-02
Publication date: 2004-11-03

Abstract

Oven for the stabilisation of shoe uppers in which the shoe upper is fixed to the insole by gluing. The shoe upper, mounted on a last, rests on a conveyor belt inside an oven chamber heated by hot air jets, and is simultaneously cooled by convection and/or conduction at a temperature lower than the temperature at which ungluing of the shoe upper from the insole may occur.

The conveyor belt is preferably made of a low thermal conductivity material, such as a fibre material.

Description

The present invention relates to an oven for the stabilisation of shoe uppers mounted on lasts, and in particular to an oven for the stabilisation of shoes of the type in which uppers are glued to insoles.
As is common knowledge in the shoe-manufacturing industry, oven stabilisation is a step in the shoe manufacturing process during which the upper, already mounted on a last and fixed to the insole, undergoes thermal treatment. Such treatment causes the release, in a relatively short time, of the internal stresses of the upper resulting from its being mounted on the last and allows therefore the permanent moulding of the upper itself, so that the inner last can be removed during subsequent manufacturing steps.
Shoe stabilisation normally takes place in hot-air ovens, through which the last-mounted shoes are conveyed on suitable conveyor belts. The hot air temperature inside the oven, which is generally between 70° and 200°C, is adjusted according to the oven length, the transit speed of shoes inside the oven, the type of leather, and the degree of humidity of the heating air. Generally speaking, the stabilisation process is the more speedy and effective, the higher the treating temperature within the oven, obviously taking into consideration the upper temperature limits imposed by the different types of leather or shoes. There is therefore an economic interest in devising high-temperature stabilisation processes that can reduce the overall shoe manufacturing time.
However, the use of higher operating temperatures within the stabilisation oven is prevented by another limiting factor, which becomes evident in the case - nowadays by far the most frequent one in shoe manufacturing - of shoe upper edges being fixed, after having been folded over on to the insole, to the insole itself exclusively by gluing and not by rivets as was the case in the traditional technique.
This technique of upper fixing effectively constitutes a limiting factor in the stabilising oven operating temperature. This is due exclusively to the fact that the shoe stabilising process is performed immediately after the upper gluing step, which causes shoes to enter the stabilisation oven when the glue has developed only an initial, partial and hence still reversible curing. This means that if during this phase the glue is subjected to excessively high temperatures, softening of the glue is likely to develop, possibly causing the upper to detach from the insole due to the fact that the internal stresses of the upper have not yet been neutralised by the stabilising process. This drawback has become more common with the recent popularity of glues based on reactive-polyurethane (PUR). While possessing other useful features, these glues have longer crosslinking times than traditional glues and are therefore more susceptible to softening, with the consequent detaching of the shoe upper if they are subjected to high temperatures for prolonged periods of time.
The ungluing of the shoe upper from the insole is of course an absolutely injurious event for the shoe manufacturing process, both when it affects the whole shoe upper and is therefore immediately visible to the operative, and when it affects only a single portion, even a limited one, of the shoe upper, and is therefore less easily detectable. In the former case, this causes a disruption to the production line, meaning that it will be necessary to manually recycle shoes that have been found defective sending them back to the gluing step, and a general slowing down of production. In the latter case, even more damaging effects can easily be caused, namely the unnoticed production of defective shoes, which will reveal the flaw in the glued upper only when the end user starts using the product, with an obviously detrimental effect to company image, as well as the costs of replacement of the faulty product, which must now be discarded.
The seriousness of the drawback that can be caused by the ungluing of the shoe upper in the stabilisation oven thus is such that manufacturers currently prefer to forfeit the increased productivity made possible by a stabilisation oven at higher temperatures, rather than running the risk of a potential ungluing of shoe uppers.
The object of the present invention is therefore to offer an improved oven for the stabilisation of shoe uppers which is free from the drawbacks described above. Such an oven would allow the treatment of shoes at temperatures higher than those so far thought possible in traditional ovens, because of the ungluing of shoe uppers, and would prevent such a phenomenon from occurring.
This object is achieved, according to the present invention, by an oven for the stabilisation of shoe uppers of the type in which the shoe upper, fixed to the insole by gluing and mounted on a last, is transported by means of a conveyor belt into an oven chamber heated by hot air jets, characterised in that it further comprises a cooling system, which maintains the bottom area of the uppers mounted on lasts and resting on said conveyor belt, at a temperature lower than the temperature at which ungluing of the upper from the insole may occur.
According to a feature of the invention, said cooling system comprises a chamber in which a cooling liquid is circulated, said chamber being the supporting surface of the conveyor belt. The above said cooling liquid is preferably air.
According to another feature of the invention, the conveyor belt is manufactured with a low thermal conductivity material, such as a fibre material.
According to a further feature of the invention, the belt is of a mesh-type or made of an open-weave fabric and the chamber which makes up its supporting surface is drilled so that cooling air can circulate through said belt and cool the bottom part of the shoe uppers mounted on lasts and resting on the belt.
Further features and advantages of the oven for the stabilisation of shoe uppers according to the present invention will be evident from the following detailed description of a preferred embodiment of the oven itself, taken in conjunction with the accompanying drawings wherein:
fig. 1 is a schematic side view of an improved oven for the stabilisation of shoes according to the present invention, and
fig. 2 is a schematic front view of the fig. 1 oven.
The general design of the shoe stabilisation oven according to the present invention can be seen clearly in fig. 1 and comprises mainly the following elements, which are already present in stabilisation ovens of known design: a centrifugal fan V which blows into the oven the hot air produced in a heat exchanger (not shown); a hot air plenum box P connected to the outlet of fan V by a main pipe A; a member of secondary pipes C which connect the plenum box P to hot air flow distributors D, which are positioned all along the oven chamber F; two conveyor belts for the last-mounted uppers (located in the space between pipes C in fig. 2, and which are not shown in the drawings for clarity) whose backward branch is situated within oven chamber F, in the area underneath distributors D, and whose forward branch is situated in an area outside oven chamber F and underneath it, in the space between said oven chamber F and the plenum box P.
As well as the elements described above, and in order to achieve the desired object, the oven for the stabilisation of shoe uppers according to the present invention comprises a cooling system for the bottom part of the last-mounted uppers to be stabilised. Thanks to this, during their crossing of the oven, said bottom part, which is precisely the one where the gluing between upper and insole has taken place, is maintained within a temperature range distinctively lower than the operating temperature of the oven, which temperature will reach instead the rest of the shoe upper, as desired.
In this way it is therefore possible to perform a stabilisation process of shoe uppers at two different temperatures: a higher temperature which affects the whole visible part of the shoe upper and allows its stabilisation in shorter times, and a lower temperature which affects the part of the shoe upper that is folded and glued onto the insole, where the need for stabilisation is distinctively smaller anyway. Such temperature can be adjusted so as to avoid any ungluing problem of the upper edge from the insole.
A special cooling system for the bottom part of last-mounted shoe uppers is shown in the drawings as an example. Such system should obviously not be interpreted as limiting the scope of the invention, as the desired cooling can be obtained with equivalent systems, too, regardless of the fact that the cooling liquid is a liquid or a gas. The cooling system described here runs along the whole forward branch of the two conveyor belts and can employ either conductive-type, or mixed-type (conductive and convective) cooling.
In both cases the system comprises a fan 1 which draws room temperature air, or air which has previously been cooled by a suitable cooling device, and blows it, by means of a main pipe 2 and secondary pipes 3, into two fairly low-hight cooling chambers 4, each of which runs along the whole area occupied by a relative conveyor belt, within oven chamber F, and whose top wall acts as supporting surface of said conveyor belt.
In a first embodiment of the cooling chambers 4 - which foresees the use of net-type or open-weave fabric belts, either made of mesh or fibre, the upper surface of chambers 4 is provided with a series of holes (not shown in the drawings) which are evenly distributed over the whole surface thereof. This allows the air blown from pipes 3 into chambers 4 to come out of said holes and cool directly the bottom part of the last-mounted shoe uppers resting on said belt where it mixes with the hot air in the oven. The cooling air of course cools down the conveyor belt in the areas where it is not covered by the lasts, too, so preventing it from overheating due to the hot air jets coming from the distributors. Indirect heating of the shoe uppers by heat conduction through the belt (which is a particularly pressing problem when the belt is made of mesh) is also avoided.
According to the invention, using conveyor belts made of low thermal conductivity materials, as are the above described fibre materials, allows to highly reduce heat absorption by the belt and simplifies ensuring that temperature is evenly distributed across the whole surface of the belt (i.e., both in the free areas, directly exposed to the hot air jets coming from distributors D, and in the areas where the lasts are located).
In a second embodiment of cooling chambers 4, which is instead suitable for use with conveyor belts made of continuous materials, the upper surface of chambers 4 is closed and the cooling air let into them from pipes 3 comes out from the opposite ends of chambers 4 through vents 5 located in their side walls, directly outside the oven chamber F. In this case, cooling of the bottom part of last-mounted shoe uppers occurs exclusively by conduction, through the conveyor belt. The conveyor belt is, in fact, generally cooled thanks to its continuous contact with the cooled surface of chamber 4 and this in turn prevents the temperature of the bottom part of the last-mounted shoe uppers resting on the belt from rising over the desired level.
The preceding description should make clear how the present invention allows to achieve the desired object by means of an extremely simple oven structure, which can be easily manufactured as a modification of existing ovens too, as its main structure would not be altered in any way. By adjusting the cooling power of chambers 4, through easy changes to temperature and/or to the cooling air flow, it is in fact possible to adjust at will the maximum temperature achieved in the bottom area of the last-mounted shoe uppers passing through the oven. This can be done without interfering at all or interfering to a negligible degree with the temperature of oven chamber F, which can therefore be raised at will, according to the stabilisation requirements of the shoe upper, avoiding in the same time the negative consequences on the gluing stability between shoe upper and insole described above.
The present invention was described with special reference to some preferred embodiments of the invention itself, but it is evident that a number of alterations and variations may be made to the cooling system described above, all of which are within the reach of an engineer with expertise in this field and all of which fall then within the scope of the invention, as defined in the enclosed claims.

Claims

Oven for the stabilisation of shoe uppers, of the type in which the shoe upper, fixed to the insole by gluing and mounted on a last, is conveyed by means of a conveyor belt into an oven chamber heated by hot air jets, characterised in that it further comprises a cooling system which maintains the bottom area of the uppers mounted on last and resting on said conveyor belt, at a temperature lower than the temperature at which ungluing of the shoe upper from the insole may occur.
Oven as claimed in claim 1), in which said conveyor belt runs, inside the oven chamber, over a supporting surface cooled by said cooling system.
Oven as claimed in claim 2), in which said supporting surface makes up the wall of a chamber in which a cooling liquid is circulated.
Oven as claimed in claim 1), in which said conveyor belt is of a net-shaped or open-weave fabric type and said cooling system causes a forced circulation of cooling air through the belt.
Oven as claimed in claim 4), in which said conveyor belt runs, inside the oven chamber, over a drilled supporting surface which makes up the wall of a chamber into which a cooling liquid is circulated.
Oven as claimed in claims 3) or 5), in which said cooling liquid is room-temperature or previously-cooled air.
Oven as claimed in any of the aforementioned claims, in which said conveyor belt is made of a low thermal conductivity material, such as a fibre material.