DESCRIPTION

The scope of the invention relates to the field of heat treatment of pieces, and in particular but not limitedly to industrial furnaces for polymerizing liquid or dust paints, applied to extruded pieces or metal profiles, and with a pre-treatment tunnel in order to prepare the extruded pieces or metal profile to a painting process with dusts or liquids.

At the present state of the technical and technological knowledge, the liquid and dust paints applied on metal surfaces just after their application must be submitted to a cooking or polymerizing phase, which can be actuated by keeping the painted artefacts in a suitable furnace, maintained for a certain time at a given temperature. The time and temperature are depending on the characteristics of the applied paints.

For example only, in order to polymerize the dust paints applied on certain extruded bars of aluminium alloy, a constant and uniform temperature in a furnace at 195°-200° C for a time of 25-30 minutes is needed.

The used furnaces can be either "static" or "continuous". In the static furnace, the painted pieces are introduced and closed by means of simple sliding doors or shutter doors. Such types of furnaces are suitable for batch artefacts, are simple and do not have functional problems.

The "continuous" furnaces are on the other hand characterized in that the pieces are continuously moving, as they enter in the furnace proceeding inside it and exit without interruptions. They are suitable for a continuous production of industrial kind, with high productivity results but with power energy consumption and serious defects that negatively affect the quality of the finished products.

Therefore the need exists of eliminating the serious defects until now unsolved of the "continuous" industrial furnaces, in particular of the furnaces suitable for the polymerization of the dust paints applied on the extruded bars of aluminium alloy. In painting plants of the bars painted in vertical, in order to reach maximum results in productivity a continuous movement is required, by means of an air conveyor on which the pieces are hanged in vertical, in a consecutive way and with the least affordable pitch, according to the sizes of the produced pieces.

Once having ended the painting, the conveyor loaded with hanged pieces enters in the polymerization furnace and follows a longitudinal path corresponding with the time needed by the polymerization, and then exits and proceeds towards the discharge at the end of the process.

Internally, the continuous furnaces must have a free height able to contain the air conveyor, the hanging hooks, the hangers, the pieces in vertical with a suitable lower safety margin. Normally, their internal height is equal approximately to 9-10 m or more.

The continuous proceeding of the air conveyor, and also the minimum hanging pitch of the pieces which do not permit any kind of static closure of the inlet and outlet ports, and this physical limitation cause two serious not yet solved defects, i.e. the continuous heat losses and the harmful oscillations of the pieces entering and exiting the furnace.

Concerning the continuous heat losses, they are caused by the relevant but necessary difference of the air temperature between the inside of the furnace (195°- 200°C) and the outside (ambient). This difference inevitably generates the known "chimney effect" consisting in the natural entry of a great quantity of ambient air (therefore at a low temperature) from the lower part of the port and the contemporary natural exit of the same quantity of hot air from the upper part of the port.

Fig. 1 represents the phenomenon with an empiric graph in which 1 indicates the entry threshold, and 2 indicates the inner room of the furnace. It is known that the air speed and therefore its entry flow rate is maximum in the lower portion 3, and they practically go to zero at a half height of the port 4, whereas at the same time the exit air speed is maximum in the upper portion 5. It is also known that the thermal energy losses from the open ports represent the highest percentage of the global power balance of the lost energy in the continuous furnaces.

At the present state of the art, a more efficient system as other possible is applied, the so called "air curtain", in any case able to limit very partially the output of hot air. Such system requires the expensive creation of one or more forced aeration tunnels, realized through the further application of one or more fans, capable to generate a continuous vertical movement of air, with a rather rapid speed, with the scope of blocking the output of hot air as in the case of the entrances of some supermarkets, airports, etc. On the other hand, such system requires the occupation of a certain layout area, a greater investment and also a further request for electric energy for the actuation of the fans.

For a better clarity and as an example, Fig. 2 represents in section the actuation layout of the known system.

The fans 6 suck air in the upper portion from suitable tunnels 7 and 8, open in the inlet and outlet ports and which force the same air for being vertically conveyed upwards (arrows 9). Today neither less expensive, nor more efficient systems exist of the "air curtain" for limiting the losses from the open ports for which they are greatly used.

Concerning the resulting harmful oscillations of the inlet and outlet pieces from the furnace, they are directly due to the directions and ways (5 and 3 in fig. 1 ) of the air moving in the inlet and outlet tunnels. Such directions with mutually opposed ways are useful to trigger longitudinal oscillations, in many cases disturbed by the vertical movement of the forced air of the "air curtain". Finally, the various natural or forced air flows are absolutely not controllable, are varying in time and also depend from the weight and the geometric form of the pieces.

These fluctuating oscillations create a first quality damage as the pieces just painted often hit other contiguous pieces, until sometimes being mutually glued because of the fresh and not yet polymerized paint. It is clear that a relevant damage derives from the needs of the final selection and the consequent disposal of the waste. Furthermore the air movement of the forced ventilation, before the polymerization occurs, sometimes is able to detach surface particles of paint in the fresh dust, these particles being directed from the air itself and inevitably falling on the surface of other batches, painted with a different colour, so contaminating the same and subjecting them to a final quality waste.

An empirical device, oriented to avoid the hitting of the pieces hanging in vertical, is known and normally applied. It concerns the manual application of rigid, semirigid or flexible connections among contiguous pieces, so avoiding that each piece freely and disorderly oscillates until hitting against other ones near to it.

Fig.3 represents one among different and similar systems, nowadays adopted.

The pressing pinches 10, before the entry of the pieces in the furnace, are applied in the lower part of each piece in movement and being integral with a small chain 1 1 , which connects the pieces in chain one with the other and does not permit great oscillations, in any case such to reach a mutual hitting.

The defect is therefore only partially avoided, as the lower end parts of the painted pieces are all inevitably damaged by the pinches so that such parts must be cut and disposed of in the final operation in 12 parts.

The application of any connection system generates a second negative drawback, referred to the need of a stable use of the pinches 10, by one or two persons in the applicative operations at the entry, and of the removal operations at the exit from the furnace. The pinches in turn must be frequently disposed of, as they smear with paint or break when they are detached from the piece with which they are frequently connected by gluing with the polymerized paint.

Problems similar to those mentioned for a traditional polymerization furnace occur in a traditional pre-treatment tunnel, placed upwards of the polymerization furnace, and able to prepare the extruded or metal profiles in the painting process with dusts or liquid.

In particular the pre-treatment is realized with a liquid detergent generally heated at a temperature of 50/55°C, at which it partially evaporates.

The hot steam creates with a chimney effect a movement of hot, wet and ascending air exiting from the tunnel, through the upper portion of its inlet and outlet ports and at the same time it determines a return of cold air inside the tunnel through the lower portion of its inlet and outlet ports.

This results in a greater energy consumption for heating the pre-treatment liquid which must be kept at the desired temperature.

The technical scope of the present invention is to realize an industrial plant for hot treatment of pieces, able to avoid the drawbacks lamented in the known art.

Within this technical scope, an aim of the invention is to provide an industrial plant for hot treatment of pieces, able to permit a strong reduction of the heat losses and consequently a relevant energy saving.

Another aim of the invention is to provide an industrial plant for hot treatment of pieces, able to avoid the harmful oscillations of the pieces at the entry and exit from the plant.

These and other aims are obtained, according to the invention, with an industrial plant of hot treatment of pieces, having a main line of overhead transport of pieces, at least one inlet port for the pieces and at least one outlet port for the pieces, characterized in that it comprises a secondary line of transport of pieces, distribution means for the pieces entering and exiting between the main transport line and the secondary transport line, so that it automatically creates alternate hollow lengths of the first and second transport line, dynamic and permanent closing means of said at least one inlet port and of said at least one outlet port, and synchronizing means for the movement of the dynamic closing means with the movement of said main and said secondary transport lines, said alternate hollow spaces being functional to the passage of pieces through said at least one inlet port and said at least one outlet port, without interference with said dynamic permanent closing means.

Preferably, the dynamic permanent closing means comprise, for each port, at least one rotary turnstile positioned at the inside of two lateral walls, with a cylindrical shape of the port. Preferably the synchronization means comprise, for each turnstile, a direct mechanic transmission with the transport line to which it is associated.

The scope of the finding consists in the invention of a new, double separation system of the pieces hanged on two different conveyor lines with the same direction, with the main scope to realize, when the ports are dynamically closed, the passage from the inlet and outlet ports to small alternate groups of the same size, in any case able to be suitably housed in the hollow spaces of a suitable rotary turnstile, with an automatic synchronism with the speed of the air conveyors. These new features of the system permit to obtain the same results of containing the losses and eliminating the harmful oscillations, also in any plant which functions with a snap system (i.e. step by step) and not due to the fact that the turnstile closure of the plant is always guaranteed for any stopping position of the air conveyor.

The present invention is shown with reference to its preferred and exemplary but not limitative embodiment of the more general concept, with reference to the annexed figures in which:

Figures 1, 2 and 3 above described refer as already said, to solutions concerning the known state of the art.

Figure 4 shows a top view of the furnace, according to a preferred way of realization of invention, with the length of the primary and secondary transport lines highlighted;

Figure 5 shows an enlarged detail in Figure 4;

Figure 6 shows the structure of a turnstile of the furnace in Figure 4;

Figure 7 shows a port, provided with the turnstile in Figure 6, and Figure 8 shows a detail of Figure 7.

With reference to the shown Figures, an exemplary path or double separation of the pieces 41 is shown, with a relative passage through the rotary turnstile with a continuous water tightness. The main air conveyor 13 coming from the painting (arrow 14) moves loaded with painted pieces, hanged one after the other. The minimum hanging pitch is useful for the productivity effects as already said, and in any case it would not permit to introduce suitable hollow spaces of the turnstile without interfering with its blades.

The exchange station 15, already known due to the fact that it is today used also for other actuation needs of the painting plants, provides for an "air" transfer alternatively of one piece or one group of two or more pieces at the same time, coming from the main line 13 to the secondary line 16. When the exchange has already occurred, downwards of the station 15, the main line 13 and the secondary line 16 are loaded in the same way with alternate groups 40 of pieces 41 , with the main result that therefore in both lines the groups 40 of pieces 41 are spaced, leaving both the same hollow length 17 absolutely necessary for the correct housing of the same groups 40 in the spaces 19 of successive turnstiles 18.

The hollow spaces 19 among the blades 20 of the turnstiles are placed in such a way, that in any of their angular positions, the blades keep the port always closed, avoiding the continuous entry of cold air and the contemporary exit of hot air.

The exchange station 21 permits to reconstruct in the main line 13 the pieces 41 or the groups 40 of pieces 41 which continue their movement, consecutively aligned again inside the furnace (arrow 24).

The actuation of the outlet system of the furnace (arrow 25) can be easily understood between the exchange stations 22 and 23, as it is completely similar to the inlet one which was described above.

This new system eliminates the "chimney effect" phenomenon, even if a small loss of heat remains as, each time a group of pieces passes, a hollow space of the turnstile slowly draws towards the outlet an equal volume of hot air, whereas its opposed hollow space draws in the inside an equal volume of ambient air.

For this reason it is necessary to precise that in any case a certain volume of hot air, impregnated with binders of with moving particles of paint must be expelled from the inside of the furnace, so that the hot air losses from the hollow spaces of the rotary turnstiles can be advantageously partly or completely substituted, the losses derived from chimneys with natural or forced suction being normally provided in the polymerization furnaces.

The wall 26 in Fig. 7 acts as separation between the inside of the hot furnace and the outer space. This wall is provided with an inlet (or outlet) port formed by two lateral cylinder-shaped walls 27 realized for the dynamic, permanent closure of the port.

At the inside of such walls the turnstile 18 is placed, which is shown in detail in Fig. 6. It is formed, in its entirety, by an internal cylinder 28 with three or more blades 20, provided with gaskets 30 apt to be airtight in the dynamic sliding direction on the walls 27.

The turnstile has its own axis 31 housed at the top and bottom in suitable supports which permit to the same a correct rotation.

In the upper part, the turnstile is integral with a toothed wheel 32. The air conveyor, here shown for clarity reasons without hanged pieces, is provided with appendices or hooks 34 placed with a constant pitch and necessarily provided on the hanging chain for the translation of pieces.

Such appendices or hooks 34 engage with suitable means in the hollow spaces of the toothed wheel 32, and pull the same in a slow rotation. The toothed wheel directly engaged in the appendices or hooks 34 of the air conveyor is the simple and known working use of the "rack drive". This simple solution of direct drive permits to obtain the automatic rotation of the turnstiles with an absolute mechanic synchronism at the conveyor speed. If the speed of the overhead conveyor varies for any need, the one of the turnstiles engaged with the same varies in synchronism. All without neither the use of particular extra transmissions nor of mechanical pneumatic, hydraulic, electrical, electronic and computer equipments, in any case of a relatively simple realization, which would however represent possible variables, which are non-substitute or alternative to the main inventive concept of the above described and illustrated method.

The description and the drawings have the value of purely indicative examples with the aim to make the original and novel concepts of the finding understood, which finally consist in the invention of a system able to create loaded lengths alternated with empty lengths of pieces on the overhead conveyor, in order to make physically possible the passage of the same from the outside to the inside of a furnace and vice versa through turnstiles put in synchronic rotation with the characteristics of the movement of the overhead conveyor, whereas the portal of the furnace remains closed for any angular position assumed by the turnstiles.

The forming of the groups of pieces, the quantity and position of the turnstiles, the number of blades, the paths of the conveyor, the shape and position of the exchange stations, etc. lend themselves to endless constructive variations in relation to the various placing needs in the layout of the plants and in relation to the various solutions chosen for the realization of the continuous or stepped furnaces, without prejudice to the original and novel inventive concept of the present finding , as it was described and illustrated before.

The overall finding realizes following important industrial results:

dramatic reduction of the heat losses from the furnace with consequent lesser energy consumptions.

reduction of the post-combustion emissions.

elimination of the harmful oscillations of the painted pieces.

constancy of the quality of production,

reduction of the passive energy costs in relation to the elimination of the today adopted systems for containing the losses based on the application of fans used for producing the "air curtain."

elimination of the further manpower costs dedicated to the application of the means impeding the hitting of the pieces.

elimination of the costs inherent to the selection and disposal of the working scraps.

What was said and illustrated with reference to a polymerization furnace can also be applied in the case in which the plant is made by a pre-treating tunnel for preparing metal extruded or profiled parts for a dust or liquid painting process.

So in particular the production line continues providing both a pre-treatment tunnel according to the invention and a polymerization furnace according to the invention, the advantages obtained with them being still more evident.

All this as it was substantially described and illustrated and for the specified purposes.