JPH09143754A - Method for heating liquid chemical tank in metal surface treating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of slag due to the decomposition of a processing soln. and to efficiently heat the soln. by heat exchange at the time of heating after metal surface treatment by forming the treating device with an inner tank and an outer tank and installing a heat exchanger in the inner tank contg. the soln. SOLUTION: In the device for forming a phosphate film on the surface of a metal, the device is formed with an inner tank 1 and an outer tank 2, a heat insulating material 3 is furnished on the peripheral wall, and a zinc phosphate film processing soln. is put into the inner tank 1. The hot water from a heat exchanger 13 is supplied to the outer tank 2 to heat the processing soln. in the inner tank 1. Meanwhile, the hot water from the heat exchanger 13 is passed through the coil 4 of the auxiliary heat-exchange part in the inner tank 1 to heat the processing soln. in the inner tank 1. Simultaneously, the processing soln. in the inner tank 1 is discharged by a pump 10 from the inner tank 1 through a conduit and sprayed into the inner tank 1 from a nozzle 11, hence the processing soln. in the inner tank 1 is agitated and circulated, and the heat-exchange efficiency is improved as the outer tank.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating a chemical liquid tank of a metal surface treatment apparatus, which is suitable for performing surface treatment such as degreasing, washing with water, and film formation using a fluid such as chemical liquid or water.

[0002]

2. Description of the Related Art There are processes such as degreasing, washing with water, and film formation when performing a metal surface treatment. The chemicals used in these processes store a chemical solution heated at around 50 ° C. Immerse in this tank, or pump the chemical solution stored in the tank into a separately installed spray chamber with a pump,
Surface treatment is performed by spraying with a spray nozzle, collecting the sprayed chemical solution in a tank, and circulating spraying.

The surface treatment of metals is usually performed by degreasing cleaning, water cleaning,
After undergoing the steps of forming a phosphate film and washing with water, it is drained, dried and painted.

[0004] Here, by heating the chemicals used for the phosphate film chemical conversion, especially the zinc phosphate type chemical conversion treatment agent, the film chemical component is hydrolyzed to generate a precipitate (sludge). . Hydrolysis is more likely to occur as the contact temperature of the heating means is higher.

When the coating agent reacts with the treated material, phosphate coating crystals are deposited on the iron surface, while the iron content dissolved from the treated material also reacts with the coating agent component and is deposited as sludge in the liquid.

The sludge thus produced adheres to the inner wall of the tank, the bottom surface, the heat exchanger and the like and is accumulated. In particular, since the hydrolysis due to heating is likely to occur in the heat exchanger portion, the sludge accumulated is fixed and becomes a layer to increase the thickness.

In these heat exchangers, steam is generated by a boiler as a heat source, and steam is sent to a heat exchange section in the tank, for example, a spiral tube or a panel heater to heat a chemical solution, or a heat exchanger is installed outside. A method of sending a chemical solution and steam to the heat exchanger through a pipe to heat the heat exchanger is implemented.

[0008]

As described above, sludge is gradually deposited and deposited on the heat exchanger portion in the film formation tank, and heat exchange efficiency deteriorates. When a certain amount of sludge adheres, the chemical solution is temporarily moved to the outside of the tank, and the inside temperature of the tank cannot be maintained unless the inside of the tank is cleaned and the adhered sludge is removed.

Therefore, it is necessary to perform maintenance work at regular intervals, and this work is indispensable. However, if the inside of the tank is narrow and there are heat exchangers and heating pipes, the maintenance work is extremely difficult. Hateful. .

Therefore, a method has been implemented in which the heat exchanger is placed outside the tank, the chemical liquid is sent to the heat exchanger through a pipe, and steam is sent to one heat source to heat the chemical liquid.

In this system, the sludge formed in the chemical solution is removed by sending the chemical solution to a filter or a sedimentation separation device, and heating is also performed outside the chemical solution tank, so that sludge adhesion and accumulation in the tank are reduced. The heat exchanger can also be easily removed and cleaned.

Further, it is convenient that a pickling pipe using nitric acid is installed as a bypass and the inside of the heat exchanger at the chemical liquid side can be cleaned by switching valves.

However, when steam is used as the heat source of the heat exchanger, the temperature of the heat exchange section on the chemical liquid side becomes high, so that the hydrolysis of the film forming agent is promoted and the fixed sludge accumulated in the heat exchange section is Must be washed often. Further, since sludge is firmly adhered and deposited, it cannot be easily dissolved even with acid cleaning, and a long cleaning time is required.

This problem occurs because the chemical solution and the high-temperature steam are directly heat-exchanged with each other through the heat exchanger. Therefore, in order to solve this problem, two heat exchangers are prepared and the first one is used. In the heat exchanger of, the heat source steam exchanges heat with water to make hot water,
There is a method of performing heat exchange between the hot water and the chemical solution via another heat exchanger, which is widely adopted.

By the way, since the steam boiler is used in the above-mentioned methods, a large amount of sludge is likely to adhere to it, and this problem can be solved by using the hot water boiler. The use of a hot water boiler is a good method for heating the film forming solution, but there is a problem that it takes time to raise the temperature because the temperature difference between the set temperature and the heat source is small.

If sludge is not generated even when heat exchange of the chemical solution is performed directly from the steam boiler through a flexible pipe as in the degreasing and washing process, and heating can be performed extremely efficiently, the warm water boiler is purposely used to raise the temperature. No need to warm.

If a steam boiler is installed and it has the capacity, heat exchange with the hot water can be done easily, and it can be supplied to the place where you want to use it with steam. Boiler is adopted.

In any case, when hot water is used as a heat source for heat exchange and a heat exchanger is installed outside the tank, a general heating source is a steam boiler.

Therefore, as described above, two heat exchangers are prepared, and the first unit exchanges heat with steam to obtain hot water.
In many cases, heat is exchanged between the hot water and the film forming agent on the second unit to heat them. In this heating system, since sludge adheres to the pipe of the heat exchanger for hot water and the film forming agent on the side where the film forming agent comes into contact with the liquid, a washing circuit with nitric acid is provided and the nitric acid is pumped from the nitric acid tank by switching the valve. send,
The method of circulating cleaning in the heat exchanger is often adopted.

In such a heating system, it is necessary to install a heat exchanger, piping for cleaning nitric acid, a nitric acid tank, and the like, and if a temperature control device for controlling these is added,
Considerable space and installation costs.

It is also possible to heat by installing a flexible pipe or panel type heat exchanger in the film formation tank and passing hot water through it, but since cleaning work for maintenance is difficult to perform in the tank, the flexible pipe etc. The advent of a method of heating without installing it inside was desired.

[0022]

In order to achieve the above-mentioned object, in the present invention, the tank for the film chemical conversion agent has a double structure of an inner tank and an outer tank, and hot water is circulated in the outer tank so that the chemical solution in the tank is circulated. Take the method of heating.

It is also possible to agitate the liquid in the chemical liquid tank to improve the heat exchange efficiency and to partially dispose a heat exchanger that circulates hot water in the chemical liquid tank to assist the temperature rise and heat retention of the chemical liquid. .

The heat exchange element to be arranged in the chemical liquid tank has an area as small as possible. Specifically, a flexible pipe or a panel heater is preferable, but it is better not to have it when the amount of heat required for heating is sufficiently supplied from around the tank.

Although the inner tank and the outer tank of the tank have a double structure, it is desirable to have a double structure for the bottom of the tank because of the meaning of heat insulation. If the required amount of heat can be sufficiently obtained from the outer peripheral side surface even if omitted, the tank bottom surface may be implemented without a double structure.

When the surface treatment method is crushing, the upper surface of the tank is open as in the conventional case, and when the surface treatment method is spraying, it is usually covered with a lid.

[0027]

In the method for heating a chemical solution tank of a metal surface treatment apparatus of the present invention having the above-mentioned structure, since the chemical solution tank is heated from the outer periphery of the chemical solution tank through hot water, the chemical solution tank to be heated, particularly the film formation tank, is installed. Since the temperature difference (ΔT) between the temperature and the hot water on the heating side is small, the film-forming chemical component is less likely to be hydrolyzed and sludge is less likely to adhere.

Therefore, the heat exchange efficiency is less deteriorated,
The maintenance cycle can be extended. Furthermore, since heating is performed from the outer periphery of the chemical liquid tank, there is no complicated heat exchange section in the tank, and maintenance work becomes easy.

Even when an auxiliary coil or the like is provided, the installation area can be made very small, so that there is no obstruction of the liquid stirring due to the installation of the heat exchanger for heating or the coil in the chemical tank.
It has a clean structure. In addition, efficiency is improved even when sludge is automatically scraped.

[0030]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a plan view of a chemical liquid tank showing the basics of an embodiment of the present invention. Reference numeral 1 is an internal tank in which a chemical liquid such as a zinc phosphate coating agent is put. Reference numeral 2 denotes an outer tank of the chemical liquid tank, through which hot water for heating the chemical liquid in the inner tank is circulated. 3 is a heat insulating material for preventing heat from being dissipated from the chemical bath.

FIG. 2 is a flow chart showing the flow of the chemical bath heating method of the present invention, and a detailed explanation will be given with reference to this figure. The dimensions of the inner tank 1 are 3,000 mm (L) x 1900 mm
(W) × 850 mm (H). The outer dimensions of the tank outer tub 2 are 3,300 mm (L) x 2,100 mm (W) x 95
It is 0 mm (H). The heat insulating material 3 has a thickness of 50 mm.

The inner tank liquid volume of this tank is 70
When set to 0 mm (H), 3.000 x 1.900 x 0.
700 = 3.99 square meters, which is about 4 tons tank.
When the outer tank and the inner tank are considered as one heating target, the liquid level is 800 mm in the outer tank when the height of the inner surface is 700 mm. Therefore, the heating target that combines the inner and outer tanks is 3,300 (L) x 2,100 (W) x
It becomes 0.800 (H) = 5.544 cubic meters. When the amount of liquid in the piping and expansion tank 12 is added to this, it is a tank of about 5.6 tons.

To raise the temperature of the 5.8 ton tank to 50 ° C., 5.6 × (50 ° C.-25 ° C.) × 1,000 = 1
40,000 kcal is required. Practically, a heat quantity of 280,000 kcal / hr is required to raise the temperature in 30 minutes.

This heat is supplied from the steam boiler, steam is sent from the conduit 5 to the heat exchanger 13, and steam drain is discharged from the conduit 8. On the other hand, the water to be heated is the water in the tank outer tub, is sent from the conduit 7 to the heat exchanger 13 by the circulation pump 9, passes through the valve B1 through the conduit 6, and
It is sent to the outer tank 2 and returned to the circulation pump 9 again. The hot water that has passed through the conduit 6 can also be sent to the flexible pipe 4 of the auxiliary heat exchange section. In this case, the valve B2 is opened.

The hot water sent to the tank outer tub 2 heats the chemical solution in the tank inner tub 1 and is heat-exchanged and sent to the heat exchanger 13 again to repeatedly heat the chemical solution. On the other hand, the chemical is pump 1
0 is sent from the tank in the tank through the conduit,
1 circulates the inner tank while stirring. This improves the efficiency of heat exchange with the outer tank.

Reference numeral 12 is an expansion tank for coping with expansion of hot water in the outer tank. The theoretical amount of heat required to raise the temperature of this system in 30 minutes is 280,000 kcal / hr, and it is sufficient to secure the heat exchange amount of the heat exchanger 13 at 280,000 kcal / hr or more. In reality, there is a loss due to heat dissipation, so select with sufficient margin.

The problem is the heat transfer effect from the tank outer tank to the tank inner tank. The natural heat transfer in a system in which the tank inner tank and the tank outer tank are separated by a thin stainless steel material is an empirical value,
Approximately 400 kcal / square meter · hr · ° C., and forced stirring is 800 to 1,000 kcal / square meter · hr · ° C.

In the embodiment, the heat transfer coefficient is 8 because it is forced stirring.
It may be calculated as 00 kcel / square meter · hr · ° C. In this system, the heat transfer area at the liquid level of 700 mm in the inner tank is (0.7H x 3.0L) x 2 when only the side surface is used.
+ (0.7H × 1.9W) × 2 = 6.88 square meters. When the bottom is also used for heat transfer, 3.0L ×
1.9W = 5.7 square meters plus 12.56
Square meters.

When heating only on the side surface, if hot water is sent at 80 ° C. and heat exchange is carried out, a simple calculation is 6.86 square meters ×
800 kcal x (80 ° C-25 ° C) = 301,840
kcal / hr, heating capacity is 280,000 kcel / h
exceeds r. If the bottom is also used for heat transfer, calculate in the same manner as 12.56 square meters × 800 kcel × (80
(° C.-25 ° C.) = 552,640 kcal, and the temperature rise for 30 minutes is sufficient.

Next, when the chemical solution is used in spray processing, the work weight is 30 kg / piece, the number of hanger treatments per hour is 60, the surface area of the treated material is 5.0 square meters / piece, and one hanger. If the weight per unit is 3 kg, the heat loss due to the work is 30 kg x 60 pieces x 0.
115kcal / deg · kg × (50 ℃ -25 ℃) =
5,175 kcel, heat loss by hanger is 3 kg
X 60 pieces x 0.115 x (50 ° C-25 ° C) = 518k
It is cal. The total of processed materials and hangers is 5,693k
It becomes cel / hr.

When the amount of water vaporized and exhausted by spraying the treated material is 130 l / hr, the heat radiation amount is 130
l / hr × 650 kcal / l = 84,500 kcel
/ Hr. (Evaporation latent heat is 539 kcel / l, but experience value is about 650 kcel / 1.)
The amount of heat radiated from the inner wall of the spray chamber is 0.3 kcal / square meter · hr · ° C, which is small when the temperature is kept warm.

Next, the heat loss due to the amount of exhausted air is set to 100 cubic meters / minute × 60 minutes × (50 ° C.-25 ° C.) × 1.3 (specific gravity of air) × 0.24 when the exhaust air amount is set to 100 cubic meters / min. (Air specific heat) = 46,800 kcal /
It becomes hr. Approximately 137.0 when adding all the above heat radiation
It becomes 00 kcel / hr. This amount of heat radiation is less than half of the amount of heat of 280,000 kcelhr required for heating for 30 minutes, and it is possible to sufficiently cope with running in spray-type processing by heating with warm water from the side.

The temperature difference ΔT between the circulating hot water temperature and the chemical liquid layer
Should be as small as possible. The reason is that the hydrolysis of the film components on the heat transfer surface is less likely to occur as ΔT is smaller, and the adhered sludge can be reduced. If adhered sludge accumulates on the heat transfer surface, the thermal efficiency will deteriorate, so it is better to secure a sufficient heat source for the design. In addition, it is better to perform maintenance inside the tank regularly to remove the sludge adhering to the heat transfer surface as soon as possible.

[0044]

As can be understood from the above description, according to the method for heating a chemical liquid tank of a metal surface treatment apparatus according to the present invention,
Since the zinc phosphate coating chemical solution tank is heated from the side and bottom by hot water, the temperature difference between the heat exchange part in the chemical solution tank and the chemical solution is smaller than when heated by steam, and the hydrolysis of the chemical solution is suppressed. Therefore, it becomes difficult to generate sludge.

Therefore, the amount of sludge deposited and deposited on the heat exchange portion in the chemical solution is reduced, and the heat exchange efficiency is less deteriorated. Further, since the heat exchanging portion is the wall surface and the bottom surface of the chemical liquid tank, the work becomes very easy even when cleaning. Further, the apparatus for heating the outside of the tank becomes unnecessary, and the auxiliary equipment therefor is also unnecessary, so that the economic effect is great.

[0046]

[Brief description of the drawings]

FIG. 1 is a plan view of a chemical liquid tank showing the basics of an embodiment of the present invention.

FIG. 2 is a flow chart showing the flow of a chemical bath heating method of the present invention.

[Explanation of symbols]

1 ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 8 ‥‥‥‥‥‥‥‥ Steam drain 9 ‥‥‥‥‥ Circulation pump 10 ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ valve

Claims (2)

[Claims] 1. A method for heating a chemical liquid tank in which a chemical liquid tank in a metal surface treatment apparatus has a dual structure of an inner tank and an outer tank, and hot water is sent to the outer tank for circulation. 2. A method for heating a chemical liquid tank, which comprises a heat exchanger for circulating hot water in the chemical liquid tank, in addition to the method for heating a chemical liquid tank according to claims 1 and 2.