Patent Application
20140353400
The invention relates to an apparatus for thermal stabilization, that is designed for and can be coupled to atomization devices for air spray-painting systems, the thermal stabilization being obtained by heating or cooling said atomization devices used in industrial painting, for example paint-spray guns or rotary-bell atomizers.
In particular, the apparatus finds application in painting systems for production of dried and filtered compressed air, or modified air enriched in nitrogen, or binary or ternary mixtures constituted by molecular elements that make up the atmosphere, for example nitrogen, argon, and oxygen, designed for spray painting, with air spray systems, low pressure systems, or rotary-bell systems, or other systems operating at high pressure, for technical control of the paint-carrier fluid as regards the preferred temperatures for keeping the viscosity constant.
It is known that in the steps of automatic painting, in particular using air guns, low pressure guns, or rotary-bell atomizers, to obtain atomization of the paint there is frequently used as carrier fluid compressed air or modified air rich in nitrogen at room temperature or preheated. Usually, the pressures used for atomization and for the spray fan range between 10 and 0.3 bar. It is thus evident that, in the atomization step, the paint carrier tends to cool as a result of expansion; hence the guns undergo cooling, and consequently also the atomized fan cools and interferes with the viscosity, thus creating problems on the spreading, penetration, and evenness of the thicknesses of the film of paint applied on the products, jeopardizing the quality and finish.
As the ambient temperature varies, this effect is even more evident because, for example, in hot periods the expansion of air is greater and causes a colder fan with consequent difficulty of spreading of the film of paint. In fact, the paint is affected by the variables that may create problems of grip of the paint on the substrate to the painted and of evenness of the thicknesses themselves. Moreover, the relative humidity that is naturally present in air creates a further interference as regards atomization, producing a non-perfect application, for example causing the effect of microbubbles determined by microparticles of humidity that remain trapped underneath the film of paint thus subsequently leading to cracking of the film of paint as a result of the changes of ambient temperature.
It is to be emphasized that, for a perfect application of a layer of paint, whether solvent-based, water-based, or of some other type, the ideal temperature is preferably between 15° C. and 25° C. with possible variations according to the ambient operating temperatures.
In the current state of the art systems are known for heating the carrier fluid, described for example in the patents filed in the name of the present applicant under Nos. EP1819445 and EP1778406.
However, known systems are not satisfactory for keeping the viscosity of the paint constant, in particular in robotized automatic painting systems.
A first object of the present invention is thus to provide an apparatus that will be free from the aforesaid drawbacks of the known systems described above and that will be able to maintain the temperature of the gun or of the paint-atomization device constant at a pre-set optimal temperature, in order to keep the viscosity of the paint constant and eliminate the lack of uniformity of the thicknesses and the consequent production rejects.
A second object of the present invention is to provide an apparatus for heat conditioning of the paint-atomization device (gun or rotary-bell atomizer), in particular of the type mounted on automatic painting robots that usually work within paint booths in so-called “classified” environments (i.e., with a high risk of explosion where the presence of any electrical part is not allowed unless purposely certified according to the ATEX directives or in any case international directives for environments with high risk of explosion, such as NFPA, areas classified as “Hazardous (Classified) Locations, class I, II, III, divisions 1,2”).
A further object of the present invention is to propose an apparatus as described above, suitable for installation both on paint-atomization devices (spray guns or rotary-bell atomizers) just being produced and on paint-atomization devices already used on painting lines in industrial and professional plants.
The above and further purposes have been achieved with an apparatus according to one or more of the annexed claims.
A first advantage of the invention lies in the fact that the paint, passing through the atomization circuit in the body of the atomization device exchanges heat therewith, and hence with the particles of paint during atomization, in such a way as to maintain the viscosity of the paint constant in order to achieve a perfect spreading of the film of paint applied on the substrate and a faster evaporation and drying, respecting the temperatures indicated by paint manufacturers in order not to change the physico-chemical characteristics of the product.
Further advantages are the following:
A further advantage is achieved in so far as, since it is possible to use smaller nozzles and to improve the transfer efficiency by approaching the guns to the substrates to be painted, the waste of product is reduced considerably with marked reduction of overspray, with an increase of the transfer efficiency of up to 90%.
The system can be adopted both on guns already operating installed on board automatic systems or robots and during production of new guns, in which case there may be provided an enveloping chamber for heat exchange in order to obtain heating of the chamber itself, which is provided in the body of the gun.
In the cases of operation in very hot environments, when the temperatures of application exceed the values indicated in the data sheets for the paints, for example +18° C. to +25° C., the apparatus according to the invention enables reduction of the temperature, causing flow of a cold thermovector liquid or air or mixtures supplied by a cooler, for example a plate chiller, that will make it possible to work with the parameters suitable for keeping the viscosity of the paint constant. In fact, atomization temperatures higher than 25° C. create problems of running, pitting, in addition to the orange-peel effect.
The above and further advantages will be better understood by any person skilled in the branch from the ensuing description and from the annexed drawings, which are provided by way of non-limiting example and in which:
a is an exploded view of the apparatus and of the device of
a shows a further preferred embodiment of a painting plant with an apparatus according to the invention;
b shows a multiple apparatus for heating three dispensers;
a shows the apparatus of
a,b respectively show an exploded view, a rear view and a section view A-A and B-B of a further embodiment of a heating according to the invention, made by welded metal sheets or plates;
With reference to the drawings, described hereinafter is an apparatus for heat conditioning of an atomization device for air-painting systems comprising a body 1 made of a thermally conductive material and provided with at least one outlet 2 for a flow of atomized paint designed to form a spray fan V on a substrate S to be painted.
Preferably, the body 1 is a one piece body or made of welded plates, by example in stainless steel or aluminium plates.
The atomization device, which is of a type in itself known, is provided inside with an atomization circuit 4 comprising a duct 5 for delivery of a pressurized atomization fluid and a second duct 6 for supply of an amount of paint to be atomized.
By way of example, the atomization device may use as atomization fluid dried and filtered compressed air or modified air enriched in nitrogen, or binary or ternary mixtures constituted by molecular elements that make up the atmosphere, for example nitrogen, argon, and oxygen, in combination with air spray systems, airmix systems, or rotary-bell systems or other high-pressure systems, which envisage control of the carrier for atomization of the paint according to the preferred temperatures for keeping the viscosity constant.
The heat-conditioning apparatus according to the invention comprises a heat-exchanger body 9 that in use is in thermal contact with the body 1 of the atomization device, and adjustable means for heat conditioning of the heat-exchanger body 9 that are enabled or disabled by purposely provided sensors 11 for detecting the temperature of the heat-exchanger body in response to a difference between the temperature Tr detected and a desired temperature Tv. Control in temperature of the body 9 is consequently obtained via the temperature sensor 11, which sends to the heat-conditioning means an appropriate signal for the system for self-regulation of the temperature. Preferably, the heat-exchanger body 9 is made of aluminium or shaped sheet metal, or else some other material in such a way that, once positioned in contact with the atomization device, for example a gun body usually having a square shape, it transmits heat or cold thereto bringing it to the desired temperature Tv, ranging, for example, between +100° C. and −10° C.
It is to be understood that these values are purely indicative and depend upon the ambient conditions of painting and upon the characteristics of the painting products used, and may be adapted and optimized in order to obtain an atomization at the ideal temperatures for keeping the viscosity of the paint used constant.
With reference to
For example, when the atomization device is a gun having a quadrangular shape, the conductive body 9 is shaped like a U turned upside down, is preferably thermally insulated on the outside, and acts as heat exchanger on the body 1 of the gun.
In greater detail, the heat-exchanger body 9 is made up of a main portion 38 joined via a shaped gasket 34 and screws 36 to a lid 35. The body 9 may moreover be fixed to the body 1 of the gun via a pressure screw 37 passing through a corresponding hole 39 of the heat-exchanger body 9.
According to the invention, the heat-conditioning means comprise a conduit 19 for passage of a thermovector fluid that circulates between a point of inlet 40 and a point of outlet 41 in heat exchange with the heat-exchanger body 9.
With this solution, the heat-exchanger body 9 is heated or cooled via the thermovector fluid (preferably a liquid) previously heated or cooled, and sensor 11 may be in direct thermal contact with the thermo vector fluid.
For transfer of the heat to the apparatus a thermovector fluid is preferably used having a high heating load with a base of propylene glycol, water, and inhibitors, having, by way of example, the characteristics listed below.
Appearing in
density of the thermovector liquid (g/cm3),
kinematic viscosity of the thermovector liquid (mm2/s),
specific thermal capacity of the thermovector liquid (kJ/(kg·K)),
thermal conductivity of the thermovector liquid (W/(m·K))
With reference to
Advantageously, this solution makes it possible to have only passive heating elements in the proximity of the atomization device and to install the heat-conditioning elements, which are normally supplied at the grid voltage, outside the painting area in non-classified areas with risk of explosion or fire.
When the apparatus is used in an environment without any risk of explosion or fire, the conduit 19, instead of being used for passage of a thermovector fluid, may be used for housing an electrical resistance 28, represented schematically in
The heat-conditioning means of the unit 14 may be of different types and comprise, for example, an insulated electrical resistance 26 (represented schematically in
With this solution, even if the ducts 15, 16 were to be very long, for example beyond 10 m, the heat is prevented from dissipating along the path.
In addition or as an alternative, heating of the thermovector fluid may be obtained by means of an electrical resistance 27 immersed in a reservoir 18 of thermovector fluid and operatively connected to a thermoregulator 30.
In the case where it is desired to cool the thermovector fluid, the heat-conditioning means may comprise an adjustable cooling device 24, for example a plate chiller, operatively connected to a thermoregulator 30.
Once again with reference to
Advantageously, with this solution, there is obtained a perfect atomization at constant viscosity as a result of transmission of heat, or of cold, via thermal coupling of the thermovector tubes with that for the paint carrier, with the possible thermal insulation thereof. This is particularly important in the steps of start and stop of the production cycle, in particular in cycles managed by robots. The problem of maintaining and controlling constancy of the temperature in any moment of the operating cycle in order to guarantee that the viscosity of the paint is kept constant is thus solved.
Advantageously, the apparatus further comprises a sensor 25 for detecting the pressure of the atomization carrier fluid in the ducts 21 in such a way as to enable heat conditioning of the thermovector fluid only in the presence of a predetermined operating thrust pressure and disable it in the absence of said operating pressure.
With this solution it is possible to reduce rapidly the temperature of the recycling liquid in the apparatus in order to prevent triggering of cross-linking of the paint within the gun, thus preventing any waste of time and production stoppages for cleaning and refurbishing the guns themselves.
a illustrates a preferred embodiment of the invention, where the paint-carrier fluid (for example nitrogen) is a heated fluid and is sent first into the conduit 19 of the apparatus via the inlet 40, whilst the outlet of the conduit 41 is connected by means of a duct 42 to the inlet 5 for the carrier fluid into the atomization device, thus determining perfect equilibrium of the temperatures of the carrier atomization fluid and of the gun.
In order to obtain thermal equilibrium between the thermovector fluid and the carrier or atomization fluid, it may moreover be envisaged to couple thermally the ducts 21 for conveying the atomization fluid to the ducts 15, 16 for the thermovector fluid.
For example, the thermal coupling may be obtained by setting the ducts 21 and 15/16 alongside and enclosing them together in a thermally insulating sheath 34 (represented schematically in
b illustrates the case of a plant that envisages a number of atomization devices, for example three, set in series for carrying out different steps of painting of the substrate, such as application of a basecoat, of a resin, and of a transparent paint.
In this case, a further advantage of the invention is that the apparatus may be installed alone or else more than one may be installed to implement steps of heating or cooling.
Finally,
With reference to
With reference to
In this embodiment, the heating body 9 is made of two detachable sections 9a, 9b connected through screws 51 and seals 50 and preferably superimposed on a conductive plate 54.
Sections 19a, 19b further comprise respective conduits 19a, 19b which in combination form the conduit 9 for passage of the thermo vector fluid.
An insulating sheath 52 and a cover 53 are also provided to insulate the heating body 9.
With reference to
In more details, the heating body 9 of FIG. 12—is preferably made by welding an inner Ω shaped plate 45 to an outer U shaped sheet 46 to form a channel 19 which is closed by front and rear plates 47, 48. Rear plate 48 is further provided with holes 55 having connections 56 intended to allow a fluid communication of channel 19 with inlet 40 and outlet 41 and the insertion of the thermal sensor 11.
In a preferred example:
Preferably, plates 45-48 are metal plates made of stainless steel or aluminium. Advantageously, in this embodiment the heating body has a low weight and a reduced mechanical inertia, which is specifically helpful when the apparatus has to be applied to quickly moving painting head of robotised system or arms.
The present invention has been described according to preferred embodiments, but equivalent variants may be devised, without departing from the sphere of protection of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| FI2013A000134 | Jun 2013 | IT | national |
