DESCRIPTION OF THE PRIOR ART After different parts forming the shoe upper have been stitched, the shoe upper presents wrinkles, which are eliminated, or reduced, usually by stretching, so as to improve the aesthetic aspect.

A shoe upper is fitted on a last made of plastic or another material, which is heated (electrically or by a fluid circulating thereinside), in order to soften the leather, and then the wrinkles are acted upon from outside in order to be flattened, that is they are stretched.

The wrinkles are stretched by suitable hammers operated either directly by an operator (manual stretching) or by mechanical motorized means (mechanical stretching).

The manual stretching depends entirely on the operator's skill (also on his experience), from the quality point of view, as well as from the stretching operation speed: obviously, this way influences considerably the cost of the shoe.

The quality of the mechanical stretching is at least insufficient; actually, many wrinkles are more squashed than stretched.

Another disadvantage of the mechanical stretching results from the fact that sometimes the hammer damages the leather in the stretching area.

According to a known upper stretching procedure, a plurality of identical basic steps is repeated cyclically, each step including a gradual wrapping, with adjustable speed, of a portion of leather to be stretched on a contrast surface, continuous or discrete, which presses the portion of leather with a prefixed, adjustable force.

Therefore, an elastically deformable membrane is carried by a support, which defines, together with the membrane, a chamber, to which a suitable fluid is sent under pressure, possibly heated to a prefixed temperature.

During the stretching, the shoe upper is wrapped gradually, with strict adherence thereto, by the membrane, which is subjected to the pressure of the fluid contained thereinside and performing a kind of massage, thus stretching the upper together with the action of heat supplied to the upper by the last and, possibly, also by the fluid.

Moreover, industrial processes are used to stretch an upper fitted on a last. According to one of them, the upper, fitted on the last, is hit by a flow of hot air (of suitable temperature) and steam, in order to soften the upper leather to facilitate its spreading, while the flow of air eliminates the humidity of the steam, thus stretching the upper.

The leather, of which the upper is made, is naturally humid ; the above mentioned stretching operation has a drawback deriving from the fact that the hot air and steam hit only the surface of the leather.

The steam hitting the upper is not absorbed, but in small part only, by the leather, and therefore, the humidity of the leather, which should not change due to drying and subsequent stretching, on the contrary is changed.

The leather humidity is brought to very low level, equal to 2-3%, making the leather dry and burning the surface full grain. This disadvantage is caused by the high temperature of the air hitting the leather during its stretching.

Due to the stretching, the quality of the shoe is poor.

Actually, after the shoe has been worn for few times, the outer surface (full grain) have small cracks and folds, which cannot be removed, because the leather is no longer in its natural state, since its physical-chemical components have been entirely changed.

SUMMARY OF THE INVENTION The object of the present invention is to propose a method, which avoids the above mentioned disadvantages, more precisely, a method, which allows stretching the shoe upper, fitted on a last, in a uniform way on the whole surface of the leather, restoring its natural qualities.

Another object of the present invention is to propose a method, which allows to stretch a shoe upper maintaining the natural characteristics of the leather, that is maintaining its humidity and fibrous composition.

A further object of the present invention is to propose a method, whose carrying out does not require highly specialized staff.

A still further object of the present invention is to propose an apparatus, which carries out the above mentioned method.

The above mentioned objects are obtained, in accordance with the contents of the claims, by a method for stretching a shoe upper fitted on a last, the method including: forming an upper-last assembly by fitting a shoe upper on a corresponding last; positioning the upper-last assembly in a first station, and keeping the upper-last assembly at said first station and inside a first chamber for a prefixed time; activating heating means situated in the first chamber, so as to"hit"the upper-last assembly with a flow of hot air, so as to soften the leather, thus facilitating the spreading thereof on the last; activating means for creation of a vacuum condition in the first chamber, in order to increase the leather porosity, that is to determine the dilation of the leather pores, to facilitate elimination of air from the leather pores; activating, after a prefixed time from the generation of the vacuum condition, of means for introduction of steam, situated in said first chamber, so as to increase the percentage of humidity inside said first chamber, and consequently to increase the percentage of humidity present in the shoe upper leather; deactivating said means for heating, steam introduction, and removal of vacuum condition ;

positioning of the upper-last assembly in a second station, and keeping the upper-last assembly at said second station and inside a second drying chamber for a prefixed time; activating heating and ventilation means, situated in the second drying chamber, in order to create a movement of hot air, which hits the upper-last assembly, to eliminate at least partially, the humidity present in the leather, with consequent stretching of the upper; deactivating said heating and ventilation means; leaving of the second station by the upper-last assembly.

The above mentioned method is carried out be an apparatus for stretching a shoe upper fitted on a last, the apparatus including: a belt feeder, conveying stepwise a upper-last assembly, formed by a shoe upper fitted on a last; a control unit, which has stored instructions concerning the step movements of the assembly; a first station, situated above the feeder and including a first bell-shaped covering, featuring connected thereto: heating means, situated inside the first bell-shaped covering, so that a flow of hot air hits the upper-last assembly, in order to soften the leather, thus facilitating its stretching on the last, means for creating a vacuum condition inside the first bell-shaped covering, in order to increase the leather porosity, that is to dilate the leather pores to facilitate elimination of air from the leather pores, and

means for introduction of steam, situated in said bell- shaped covering, which, after a prefixed time from the generation of the vacuum condition, increase the percentage of humidity inside said bell-shaped covering, and consequently, increase the percentage of humidity present in the upper leather, with said heating means, vacuum creation means and steam introduction means being controlled by the control unit; a second station, situated above the feeder downstream of the first station, formed by a second drying chamber, which is equipped with heating and ventilation means, controlled by the control unit, to eliminate at least a part of steam from the shoe upper leather.

The characteristic features of the present invention will be pointed out in the following description of a preferred, but not unique embodiment, with reference to the enclosed stretching, which shows a schematic lateral view of an apparatus for stretching an upper fitted on a last.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the enclosed figure, the reference letter K indicates the apparatus for stretching a shoe upper of a shoe fitted on a last, and the reference letter M indicates the last-upper assembly.

The last-upper assembly M is situated on a belt feeder 1, driven by a control unit C, which stores information concerning the step movement of the group M toward a machine structure T, where a first station Sl, a second station S2, a third station S3 and a fourth station S4 are set up for performing the stretching operation.

Upstream of the first station Sl, a detection element R, for example a sensor, is connected to the machine structure T and to the control unit C, to detect the height of the last-upper assembly.

The function of the detection element R will be explained later.

The first station Sl, situated above the feeder 1, is formed by a first bell-shaped covering 2, operated to move vertically by, for example, known pneumatic systems 3 fastened to the upper portion of the machine structure T.

The first bell-shaped covering 2 moves between two positions: a rest position I (indicated with broken line in Figure 1), in which the bell-shaped covering is raised, and a working position O, in which the bell- shaped covering 2 is lowered above the upper-last assembly M to touch the upper run la of the feeder 1, so create an airtight contact with the feeder 1 : in this way a first chamber 2a is defined.

The bell-shaped covering 2 is equipped with suitable heating means, for example electrical heating elements (not shown) situated inside the bell-shaped covering, and with means 4 for steam inlet, connected to a steam generator Cv, suitably controlled by the control unit C.

Moreover, the bell-shaped covering 2 can be connected, by a pipe 70, to a vacuum source Pv, which is likewise controlled by the control unit C, and whose function will be explained later.

An on/off device 170 (for example an electric valve), controlled by the control unit C, is fitted along the pipe 70.

The second station S2, situated above the feeder 1, after the first station Sl, is composed of a second drying chamber 5, equipped with heating means (for example electrical heating elements, not shown) and ventilation means, for example a centrifuge fan, suitably controlled by the control unit C.

The heating and ventilation means are connected to a roof 50, which moves vertically in relation to the detection of the upper-last assembly M, performed by the detecting means R, in order to take prefixed positions, for example three, depending on the type of upper (of a shoe or a boot) fitted on the corresponding last.

The roof 50 is operated to move vertically by a known pneumatic actuator 6, fastened to the upper portion of the machine structure T and connected to the control unit C.

The third station S3, situated above the feeder 1 and after the second station S2, is composed of a second bell-shaped covering 7, which is moved vertically, for example by known pneumatic means 30 fastened to the upper portion of a machine structure T, to assume two positions: a rest position N, in which the bell-shaped covering 7 is raised, and a working position P (indicated with broken line in Figure 1), in which the bell-shaped covering 7 is lowered above the upper-last assembly M, to touch the upper run la of the feeder 1, so as to form an airtight contact with the feeder 1 : in this way a third chamber 7a is defined.

The bell-shaped covering 7 is also connected to the vacuum source Pv, likewise controlled by the control unit C, whose function will be explained later.

Suction means Z, connected to the upper portion of the machine structure T, are aimed at sucking air and fumes deriving from the upper drying and stretching treatment in the second station S2.

The fourth station S4, situated after the third station S3, is formed by a cooling device F of known type, connected to the machine structure T, above the upper run la of the feeder 1.

According to the method for stretching a shoe upper, the upper is fitted on a corresponding last, usually made of plastic material, in order to define the upper-last assembly M, which is placed on the feeder 1.

The control unit C operates the feeder 1, so as to convey the upper-last assembly M forward and the sensor R detects the height of the upper-last assembly M.

As a consequence of the detection, the actuator 6 is activated by the control unit to bring the roof 50 of the second station S2 to the position corresponding to the detected height of the group M.

Afterwards, the upper-last assembly M is conveyed into the first station SI, where it is kept motionless for a prefixed time; in step relation the first bell-shaped covering 2 lowers (working position 0).

Then, the means for heating the first bell-shaped covering 2 are activated, so as to"hit"the upper-last assembly M (in particular the leather outer surface) with a flow of hot air in order to soften the leather, thus facilitating the spreading of the leather on the last.

Afterwards, due to the activation of the electric valve 170, the source of vacuum Pv creates a vacuum inside the first chamber 2a (with high vacuum), so as to increase

the leather porosity, that determines the pores dilatation, in order to facilitate elimination of air from the leather pores.

Then, in suitable step relation, the electric valve 170 is deactivated and the means for introduction of steam are activated, so as to increase the humidity percentage inside the first chamber 2a, and consequently to increase the percentage of humidity of the upper leather; in this way vacuoles created in the leather, due to the vacuum in the chamber 2a, are filled with the steam.

It is to be pointed out that a minimum prefixed vacuum value must be maintained inside the first chamber 2a; if this value is not respected, the control unit C activates again the electric valve 170, until the minimum prefixed value is resumed.

After the steam has been introduced, the heating means and the steam introducing means are deactivated, the initial conditions are restored inside the chamber 2a (vacuum condition removal) and the first bell-shaped covering 2 is raised to return to its rest position I.

Afterwards, the feeder 1 is operated, so as to convey the upper-last assembly M to the second station S2, into the second drying chamber 5, where the upper-last assembly M is kept motionless for a prefixed time.

In step relation, the heating and ventilation means are activated to create, inside the second chamber 5, a movement of hot air, which hits the upper-last assembly M, in order to dry, at least partially, the upper leather (partial elimination of the excessive humidity from the leather), which is then stretched following the shape of the last (upper stretching).

The assembly M remains in this situation for a prefixed time, corresponding to a number of the feeder steps.

Then, the heating and ventilating means are deactivated, and the feeder 1 is activated, so as to convey the upper- last assembly M, with the upper already stretched, to the third station S3.

Afterwards, the second bell-shaped covering 7 lowers to touch the upper run la of the feeder and a vacuum is created inside the third chamber 7a, so as to dilate the leather pores and to eliminate a prefixed quantity of humidity present in the leather, so as to bring the latter substantially back to the natural state, that is to the initial humidity, before stretching, thus making the leather stable in the acquired configuration.

After the stretching has been finished and the excessive humidity has been eliminated, the initial conditions of the third chamber 7a are restored (the vacuum condition is eliminated, the second bell-shaped covering 7 is raised to return to the rest configuration P), and the feeder 1 is activated.

In this way, the upper-last assembly M leaves the third station S3 and passes to the fourth station S4.

The cooling device F sucks air of room temperature from outside of the structure T and conveys it onto the upper- last assembly M, so as to cool the latter to the temperature acceptable for continuing the working cycle.

It is pointed out that: the control unit C controls and handles the duration of stays of the upper-last assembly M in different stations, which have been studied by the experts so as not to change the leather characteristics; during the upper stretching, in different working steps, the suction means Z are activated in order to convey and

expel air and fumes toward suitable hoods (not shown), associated thereto.

The above described method and apparatus for stretching an upper fitted on a last are particularly advantageous.

One of the advantages results from the fact that first the vacuum in the first station S1 is created and then the steam is introduced therein, i. e. only after the vacuum has been generated and maintained for a prefixed time, and thus the leather is softened due to the action of the vacuum on its pores, which open to absorb steam and increase the leather humidity.

The excessive humidity makes the leather soft (the leather is wet and its fibers modify), so that the upper adapts perfectly to the shape of the last.

The stay in the second station S2 allows the shoe upper to dry and consequently to stretch on the last. This stay is necessary to eliminate a part of humidity supplied to the leather in the first station.

The detecting means R, situated upstream of the first station S1 allows to detect the height of the upper-last assembly M, which results in the adjustment of the height of the roof 50 in the second station S2, so that the distance between the height of the assembly and the roof 50 of the second station S2 remains unchanged for each shoe shape and type.

This distance is adjusted in order to avoid burnings and/or changes of the upper characteristics caused by the flow of hot air hitting the upper-last assembly M.

The presence of the third station S3, in which vacuum is created again, allows to accelerate the drying step and consequently, to eliminate a further quantity of humidity

present in the leather, so as to bring the latter to its natural state, that is with a humidity percentage equal to the initial one, before the stretching.

Consequently, the method can be carried out by the working steps performed in the first two working stations S1, S2; the third station S3, used when needed, allows to reduce the drying step duration, and consequently, the upper stretching process.

The described method allows to obtain a stretching of best quality, since the leather is not wrinkled and dry, due to the fact that the natural state of its fibers and humidity quantity are maintained. Consequently, the apparatus does not have to work at high temperatures and does not burn the leather surface grain.

The so conceived method for stretching the shoe upper allows to obtain a soft, flexible and natural shoe.

It is understood that what above, has been described as a pure, not limitative example, therefore, possible variants of the invention remain within the protective scope of the present technical solution, as described above and claimed hereinafter.