JPH0333386B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a hot air circulation type coating drying furnace for heating and drying an object to be coated by circulating and convecting hot air in the furnace, and a heating method thereof.

[Prior art and its problems]

This type of paint drying oven is a direct heating type (direct-fire type) drying oven that circulates and convects the combustion gas generated by burning fuel such as heavy oil, kerosene, city gas, or LP gas in a burner. and indirect heating type (heat exchange type) drying furnaces, in which the combustion gas from the burner is sent to a combustion gas-air heat exchanger to heat the air, and the heated hot air is circulated and convected within the furnace. Can be done.

Here, a direct heating type drying oven has the advantage that it has very good thermal efficiency and can quickly raise the temperature inside the oven because there is no heat loss due to heat exchange and combustion gas is directly introduced into the oven. On the other hand, there is a drawback that dust, impurities, etc. contained in the combustion gas adversely affect the product quality of the object to be coated. In particular, it is known that when petroleum-based fuel is used, sulfur content is generated, which significantly impairs the quality of the coating film.

Therefore, in the case of direct-heating drying ovens for drying top coats of automobile paint, which require strict product quality, relatively clean fuels such as city gas and LP gas, which have low impurities such as sulfur content, have traditionally been used. I plan to use it.

However, according to the experiments and research conducted by the present inventors, when baking and drying an automobile body using a direct heating type drying oven that directly supplies combustion gas into the oven, the automobile body Because it is heated at a high temperature of around 200℃ (usually 150-160℃),
Organic solvents such as thinner and toluene contained in the paint, and amine compounds such as hardeners for paint resins, etc., evaporate from the paint film, and these are thermally decomposed by direct contact with the burner flame, resulting in combustion products such as water and By reacting with radical nitrogen oxides (NOx components), a greasy substance whose main component is precipitates of low molecular weight resin is produced, which adheres to the surface of the car body and causes yellowing of the paint film. It has been found that this causes problems such as delamination and delamination.

Therefore, in order to prevent these disadvantages specific to direct heating, it is necessary to use a burner with as large an air ratio as possible, or to reduce the amount of fresh air supplied to the furnace and the amount of contaminated air exhausted from the furnace. It is necessary to reduce the concentration in the furnace of evaporated organic solvents, etc., which are the causative substances for the production of greasy substances, and this has a serious disadvantage in that the running cost for this purpose increases significantly.

On the other hand, indirect heating type drying ovens have the advantage of being able to completely block out dust, impurities, etc. generated by the combustion of fuel, and not causing the harmful effects of producing greasy substances as described above. In this respect, it is suitable for finishing drying automobile bodies, etc., but it has the disadvantage that the rate of temperature rise is extremely slow compared to direct heating type drying ovens, and it takes a long time to preheat the inside of the oven. It is especially important for paint drying ovens to raise the temperature to a specified temperature in as short a time as possible.
This was an extremely serious drawback.

[Purpose of the invention]

Therefore, the present invention makes it possible to heat the inside of the furnace to a predetermined temperature in a short time by directly circulating and convecting the combustion gas inside the furnace like in a direct heating drying furnace when the temperature is raised to preheat the inside of the furnace. When the object to be coated reaches a predetermined temperature and is brought in, hot air heated by heat exchange with combustion gas is circulated and convected in an indirect heating drying oven to prevent yellowing of the coating film and delamination. It is an object of the present invention to provide a coating drying oven and a heating method thereof that can heat the interior of the oven without producing greasy substances that cause the occurrence of oily substances.

[Structure of the invention]

In order to achieve this objective, the present invention has a structure in which a return duct that sucks air in the furnace and a supply duct that introduces combustion gas generated from a heat source into the furnace communicate with each other to form a direct heating type hot air circulation path. In the drying oven for painting, the return duct and the supply duct are provided with a passage opening/closing means that can block each passage in the middle and divide each passage into a front stage side and a rear stage side, and the passage opening/closing means can open and close both passages. Two branch ducts are connected in parallel between the return duct and the supply duct so as to sandwich them from the front and back, and a combustion gas-air heat exchanger is interposed between the branch ducts to provide a direct heating type hot air circulation path. By blocking both passages of the return duct and supply duct to be formed by the passage opening/closing means and opening both passages of each branch duct, the combustion gas generated from the heat source is passed through the heat exchanger. A closed circuit for circulation and an indirect heating type hot air circulation path are formed in which air sucked from inside the furnace is sent to the heat exchanger, receives heat from the combustion gas circulating in the closed circuit, and is introduced into the furnace again. It is characterized by being configured so that

[Action of the invention]

The paint drying oven according to the present invention connects the return duct and the supply duct to form a direct heating type hot air circulation path when the temperature rises to preheat the interior of the oven, and directs the combustion gas generated from the heat source into the oven. It is possible to quickly heat up to a predetermined temperature by circulating convection, and when carrying the workpiece into the furnace, the passage of the return duct and supply duct is divided into two in the middle, allowing indirect heating type hot air circulation. By forming a path, hot air heated by heat exchange with the combustion gas can be circulated and convected in the furnace.

In addition, the heating method for the coating drying oven according to the present invention is such that when the temperature inside the oven is preheated, the combustion gas generated from the heat source is circulated and convected inside the oven for direct heating. It is heated to a predetermined temperature within a certain period of time. Further, when the inside of the furnace reaches a predetermined temperature and the object to be coated is carried in, the passage through which the combustion gas was introduced into the furnace is cut off, and the combustion gas is circulated via a heat exchanger, Since hot air that has received heat from the combustion gas in the heat exchanger is circulated and convected in the furnace for indirect heating, it is possible to eliminate greasy substances that cause yellowing and delamination of the paint film. Generation is prevented.

〔Example〕

Hereinafter, the present invention will be described based on specific embodiments shown in the drawings.

The figure is a flow sheet diagram shown to explain an example of a coating drying oven and a heating method thereof according to the present invention.

In the figure, reference numeral 1 denotes a paint drying furnace for baking and drying automobile paint, etc., and the furnace body 2 is open at both ends and formed in a tunnel shape, such as a flat furnace or a mountain-shaped furnace. The object to be coated 3 is continuously transported at a predetermined speed.

Reference numeral 4 indicates a return duct that sucks air in the furnace, and reference numeral 5 indicates a supply duct that introduces hot air into the furnace. A heated hot air circulation path N1 is formed.

The return duct 4 and supply duct 5 include
Dampers 7 and 8 as passage opening/closing means for adjusting the air volume or blocking the passage are interposed in the middle of each passage, and two branches are provided between the return duct 4 and the supply duct 5 with the dampers 7 and 8 sandwiched between them. Ducts 9 and 10 are connected in parallel, and a combustion gas-air heat exchanger 11 is interposed between these branch ducts 9 and 10, closing the dampers 7 and 8 to open the passages of the return duct 4 and supply duct 5. By dividing each burner into two, the combustion gas generated from the burner 6 is transferred from the branch duct 9 to the heat exchanger 11.
indirect heating in which the furnace air sucked from the return duct 4 is sent into the heat exchanger 11 from the branch duct 10 to receive heat from the combustion gas, and then introduced into the furnace. A hot air circulation path N2 of the formula is formed.

In addition to the burner 6 to which combustion air is supplied from the blower 12, a circulation fan 13 is installed in the closed circuit G, and the combustion gas generated from the burner 6 is heat exchanged by the circulation fan 13 through the branch duct 9. After being sent into the erofinche tube of the container 11 and effectively dissipating heat from the fins of the fins, etc., it is heated again by the burner 6 and circulated. Further, two dampers 14 and 15 are interposed in the branch duct 9 with a heat exchanger 11 in between, so as to open and close the passage of the branch duct 9.

In the hot air circulation path N2, a filter 16 is installed on the return duct 4 side, and a circulation fan 17 is installed on the supply duct 5 side, and the furnace air is sucked from the return duct 4 by the circulation fan 17. , is sent to the heat exchanger 11 installed in the branch duct 10, is heated through the air-finches in the heat exchanger 11, and is then circulated and convected into the furnace through the supply duct 5. has been made. In addition, a heat exchanger 11 is provided in the branch duct 10.
Two dampers 18 and 19 are interposed between them,
The flow rate of air passing between the air-finches is adjusted to an optimum value (for example, about 4 m/sec), and the passage of the branch duct 10 is opened and closed.

Although not shown, each damper is automatically opened and closed by a cylinder or module motor, etc., which operates in accordance with an operation signal issued from a temperature safety limit switch, temperature control potentiometer, etc. installed in the furnace. It is made to be controlled.

The above is an example of the structure of the coating drying oven according to the present invention, and next, its operation and a specific heating method of the coating drying oven according to the present invention will be explained.

First, when the drying oven starts operating and the temperature rises to preheat the inside of the oven, the dampers 14 and 15 installed in the branch duct 9 are completely closed, and the branch duct 10
The dampers 18 and 19 installed in the return duct 4 and the supply duct 5 are opened, and the burner 6 and circulation fans 13 and 17 are operated. ,
A direct heating type hot air circulation path in which the air in the furnace sucked through the return duct 4 is heated to a high temperature of, for example, about 300°C with the combustion gas generated from the burner 6, and is circulated and convected into the furnace together with the combustion gas through the supply duct 5. N1 is formed, and the inside of the furnace is quickly heated to a predetermined temperature.

This allows the inside of the furnace to reach a predetermined temperature (for example, 150~
When the temperature reaches approximately 160°C), the dampers 7 and 8 are automatically fully closed and the passages of the return duct 4 and supply duct 5 are divided into two, and each damper installed in the branch ducts 9 and 10 is closed. 14,15
, 18 and 19 are opened at the required opening degree, and a closed path G and an indirect heating type hot air circulation path N2 are formed in place of the hot air circulation path N1.
That is, the drying oven 1 is automatically switched from the direct heating type to the indirect heating type, and in the closed circuit G, the combustion gas of the burner 6 is circulated by the circulation fan 13 via the heat exchanger 11, and a part of it is Exhausted to the outside through an exhaust duct 20 connected to the closed circuit G,
Further, in the hot air circulation path N2, the furnace air at a temperature of around 150°C is sucked from the return duct 4 by the circulation fan 17 and is sent to the heat exchanger 11, where it receives heat from the combustion gas and is heated to, for example, about 170°C. After that, it is circulated and convected from the supply duct 5 into the furnace. In addition, when forming the hot air circulation path N1 and performing direct heating as described above, the dampers 18 and 19 installed in the branch duct 10 are not completely closed but are slightly opened to allow a small amount of hot air to flow. If this is done, there is an advantage that the low-temperature air stagnant in the branch duct 10 at the initial stage of switching to the hot air circulation path N2 will not be introduced into the furnace and the temperature in the furnace will not temporarily drop.

After the drying oven 1 is switched to the indirect heating type in this way, the article 3 to be coated, such as an automobile body, which has been topcoated, is brought into the oven body 2 and transported. As a result, the object to be coated 3 is heated to a high temperature, and the organic solvent and the amine compound of the hardening agent evaporate from the coating film, but since these are not brought into contact with the flame of the burner 6, the coating film yellows. This prevents the production of greasy substances that cause delamination and delamination, and maintains good product quality.

〔Effect of the invention〕

As described above, according to the present invention, when raising the temperature to preheat the inside of the furnace, combustion gas generated from a heat source such as a burner is circulated directly into the furnace to raise the temperature inside the furnace in a short time. At the same time, when the inside of the furnace reaches a predetermined temperature and the object to be coated is brought in, hot air heated by heat exchange with the combustion gas is circulated and convected inside the furnace to prevent yellowing of the coating film. It has the excellent effect of preventing the formation of greasy substances that cause delamination and delamination.

Also, compared to conventional direct heating drying ovens,
It is necessary to use a burner with a large air ratio to reduce the concentration of organic solvents, etc. that cause the production of greasy substances, or to use large-scale equipment that supplies fresh air and exhausts contaminated air. This also has the effect of significantly reducing running costs.

[Brief explanation of drawings]

The figure is a flow sheet diagram shown to explain an example of a coating drying oven and a heating method thereof according to the present invention. Explanation of symbols, 1... Painting drying oven, 2... Furnace body, 3... Subject to be coated, 4... Return duct, 5...
...Supply duct, 6...Burner (heat source), 7,
8... Damper, 9, 10... Branch duct, 11...
... Combustion gas-air heat exchanger, 13 ... Circulation fan, 14, 15 ... Damper, 17 ... Circulation fan, 18, 19 ... Damper, N1 ... Direct heating type hot air circulation path, N2 ... Indirect Heated hot air circulation path, G...closed circuit.

Claims (1)

[Claims] 1. A return duct 4 that sucks air in the furnace and a supply duct 5 that introduces combustion gas generated from a heat source 6 into the furnace communicate with each other to form a direct heating type hot air circulation path _N1 . In the drying oven for painting, the return duct 4 and the supply duct 5 are provided with passage opening/closing means 7 and 8 that can block each passage in the middle and divide each passage into a front stage side and a rear stage side. Two branch ducts 9 and 10 are connected in parallel between the return duct 4 and the supply duct 5 so as to sandwich the passage opening/closing means 7 and 8 from the front and back, and between the branch ducts 9 and 10, combustion gas and air are A heat exchanger 11 is interposed between the return duct 4 and the supply duct ₅ , which form a direct heating type hot air circulation path N1, and the passage opening/closing means 7 and 8 block off both passages, and each of the branch ducts 9,
By opening both passages of 10, the heat source 6
A closed circuit G circulates combustion gas generated from the furnace via the heat exchanger 11, and air sucked from inside the furnace is sent to the heat exchanger 11 to receive heat from the combustion gas circulating in the closed circuit G. A painting drying oven characterized in that it is configured to form an indirect heating type hot air circulation path _N2 for receiving the hot air and introducing it into the oven again. 2. When raising the temperature to preheat the inside of the furnace, the return duct 4 that sucks the air inside the furnace and the supply duct 5 that introduces the combustion gas generated from the heat source 6 into the furnace are connected to directly heat hot air. circulation path
The combustion gas is directly circulated and convected into _the furnace through the hot air circulation path _N1 , and when the inside of the furnace reaches a predetermined temperature due to the circulation convection of the combustion gas, the return duct 4 and Each passage of the supply duct 5 is blocked in the middle to divide each passage into a front stage side and a rear stage side, and is connected in parallel between the return duct 4 and the supply duct 5 so as to sandwich the divided part. A closed circuit G in which both passages of the two branch ducts 9 and 10 are opened and the combustion gas is circulated via the combustion gas-air heat exchanger 11 interposed between the two branch ducts 9 and 10.
Then, an indirect heating type hot air circulation path _N2 is formed in which the air sucked from inside the furnace is sent to the heat exchanger 11 and introduced into the furnace again, and the air is circulated in the closed circuit G through the hot air circulation path _N2 . A method for heating a paint drying furnace, characterized in that hot air heated by heat exchange with combustion gas is circulated and convected within the furnace.