JPH0335433Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention is an open precision cleaning method that performs precision cleaning with steam using a chlorinated hydrocarbon-based or fluorinated chlorinated hydrocarbon-based solvent with a mainly low boiling point. The present invention relates to a solvent heating control device that controls the heating of a solvent in a tank to keep the amount of vaporized solvent gas generated constant.

(Prior Art) In an open type precision cleaning tank, a solvent contained in the open tank is heated and vaporized, and then used for precision cleaning. The vaporized solvent gas is heavier than air and tends to stay in the precision cleaning tank. However, since this solvent gas is continuously generated in order to constantly supply new solvent gas, it will overflow if left as is. Conventionally, a condenser pipe is installed inside the peripheral wall of the precision cleaning tank, which attracts and condenses the stagnant solvent gas, and continuously collects it through natural flow due to liquefaction.

However, if the precision cleaning tank is large and the distance from the center of the tank to the surrounding condenser pipes becomes large, the condenser pipe's effect of attracting and condensing the solvent gas will reach the solvent gas around the periphery of the tank, but the distance from the center of the tank will increase. It is hard to reach the solvent gas of the part.

For this reason, the solvent gas in the center of the tank gradually rises, and eventually dissipates into the atmosphere from the tank opening.

This release of solvent gas into the atmosphere leads to the premature loss of expensive solvents, which increases usage costs, and also poses the danger of ozone layer depletion, which has been recently warned by the WHO and other organizations.

In order to suppress this, it is possible to increase the size of the capacitor, but there are physical and economical limits to this.

Conventionally, in order to ensure that the vaporization of the solvent is sufficient for precision cleaning, but not excessively, the heat of evaporation is simply applied by heating in accordance with the amount of required solvent gas calculated from the amount of solvent that can be liquefied and recovered.

(Problem that the invention aims to solve) However, simply heating as in the past cannot fully control the boiling state of the solvent that generates solvent gas.
This tends to lead to an excess or deficiency of solvent gas. A lack of solvent gas will only extend the time required for precision cleaning, but an excess of solvent gas is an environmental safety issue as mentioned above, and the actual amount of solvent gas generated is being controlled by the US Environmental Agency and others. It is desirable to do so.

For this purpose, it is necessary to detect the temperature of the solvent and the gas pressure corresponding to the generation of solvent gas. However, the former does not change when the solvent starts boiling because it is at the boiling point temperature and is saturated. The latter does not change because the cleaning tank is an open type.

Therefore, it is an object of the present invention to provide a solvent heating control device for an open type precision cleaning tank that can meet the above requirements by capturing pressure changes according to the amount of solvent gas generated without impairing the function of the open type cleaning tank in the slightest. The purpose is to

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention aims to reduce the amount of solvent contained in an open type precision cleaning tank in which the contained liquefied solvent is heated by a heater and gasified for precision cleaning. A cap that covers the liquid level is installed at a certain height, an orifice is formed on the ceiling wall of the cap to restrict the outflow of solvent gas, and a means for detecting the liquid level in the range covered by the cap is provided. The present invention is characterized by comprising a control means for controlling energization to the heater in accordance with the above.

(Function) As before, solvent is circulated and supplied to the open precision cleaning tank to maintain a constant liquid level.
One portion of this constant level liquid surface is separated from the other by a cap that covers each portion. This separated liquid surface also generates vaporized solvent gas at the same rate as the surrounding liquid surface. This solvent gas fills the cap and flows out from the orifice installed in the cap ceiling wall into the open cleaning tank due to the differential pressure between the cap internal pressure and atmospheric pressure, and mixes with the solvent gas generated from other liquid levels. They can join together and take part in precision cleaning.

As the amount of solvent gas generated increases, the flow rate of the solvent gas passing through the orifice also increases, and the passage resistance due to the orifice increases. Correspondingly, the pressure inside the cap increases, pushing down the liquid level covered by the cap.

Fluctuations in the liquid level are detected by the liquid level detection means, and are caused by changes in the amount of solvent gas generated.The control means controls the energization of the heater according to the detected liquid level, thereby increasing the amount of solvent gas generated. The constant quantity can be precisely controlled by direct information from the solvent gas generation state without any other influence.

(Example) An example of the present invention shown in the drawings will be described.
The precision cleaning tank 1 is of an open type, and is connected to a solvent circulation system that repeatedly supplies a solvent 2 (not shown) while distilling and recovering it, so that the clean solvent 2 is always maintained at a constant level. This solvent 2
is vaporized by heating with the heater 3, and the vaporized solvent gas 2a is used for precision cleaning.

A condenser pipe 4 is installed inside the cleaning area of the tank wall 1a of the precision cleaning tank 1, and is designed to attract and condense the solvent gas 2a staying in the cleaning area. The solvent 2, which is liquefied by this condensation and flows down by gravity, is received in a receiving groove 5 formed on the inner surface of the tank wall 1a, passed through a pipe 6, and collected.

However, if the precision cleaning tank 1 is large and the distance from the tank center to the condenser pipe 4 is long, the action of condensing and recovering the solvent gas 2a by the condenser pipe 4 will not reach the center of the tank, making it difficult to recover the solvent gas. It is.

Therefore, the amount of solvent gas 2a generated in the precision cleaning tank 1 is kept constant so as to be sufficient for precision cleaning but not excessive.

In the present invention, the energization of the heater 3 is controlled based on the information on the amount of solvent gas 2a generated.
A part of the liquid surface 2b of the solvent 2 is covered with a cap 7, and the cap 7 is attached to the tank wall 1a with a fixture 8. The cap 7 has an orifice 9 on its ceiling wall to restrict the outflow of the solvent gas 2a generated from the solvent liquid level 2c that the cap 7 covers.

The cap 7 is also provided with a liquid level sensor 10 for detecting the level of the liquid surface 2c. This liquid level sensor 10 is of a current-carrying type in which a reference electrode and electrodes at different heights are energized or de-energized depending on the liquid level, or they are insulated from each other and from the solvent 2. A known method such as a capacitance method that obtains a capacitance depending on the liquid level between the two electrodes can be used.

A detection signal from the liquid level sensor 10 is applied to a control circuit 11 that controls energization of the heater 3 .

The operation will be explained in detail below. The solvent 2 is heated by the heater 3 and vaporized, but the solvent gas 2a generated from the liquid level 2c flows out from the orifice 9 into the precision cleaning tank 1 while filling the cap 7, and the liquid level 2c flows out into the precision cleaning tank 1.
It joins with the solvent gas 2a generated from other parts of b and participates in precision cleaning. Therefore, by covering the cap 7, the effective area of the liquid surface 2b is not reduced.

The solvent gas generated from the liquid level 2c flows through the orifice 9.
When it flows out, it is restricted by resistance depending on the amount generated.

This is given as the relationship between the flow rate Q and the flow coefficient (resistance) C in the equation Q=CA√2, and as the flow rate Q increases, the flow coefficient C increases.

Therefore, for example, if the opening area A of the orifice 9 is set so that the outflow is greatly restricted when the solvent gas 2a exceeds the set generation amount, the solvent gas 2a
When the amount a reaches the set generation amount, the outflow is hardly restricted by the orifice 9, and the solvent gas 2a generated at the liquid level 2c can be efficiently used for precision cleaning.

When the amount of solvent gas 2a exceeds the set generation amount, the flow is greatly restricted by the orifice 9, and the pressure inside the cap 7 is increased to raise the liquid level 2c to a corresponding position.
lower.

This change in the liquid level is detected by the liquid level sensor 10, and the control circuit 11 suppresses the heat generation of the heater 3 or temporarily stops it by detecting the liquid level when the amount of solvent gas exceeds the set generation amount. Controls energization.
As a result, the amount of temporary evaporation of the solvent is reduced, and the amount of generated solvent gas 2a is reduced.

As the amount of solvent gas 2a generated decreases, the pressure within the cap 7 decreases accordingly, and the liquid level 2c returns to its original level. When the level of the liquid surface 2c returns, it means that the amount of generated solvent gas 2a has returned to the set value, and based on the detection of the liquid level at that time, the control circuit 11 returns the heater 3 to the normal energized state.

By repeating the above energization control, the amount of solvent gas 2a generated can be kept constant.

Note that the control circuit 11 can energize the heater 3 stepwise or steplessly. To carry out the process in stages, a plurality of heaters with different capacities or the same capacity can be used in combination, and the energization control can be performed simply by a switching circuit that determines which heater is energized.

(Effect of the invention) Since the invention has the above-mentioned structure and operation, it is possible to accurately control the amount of solvent gas generation using the amount itself as information, so that the amount of generation is constant. There is no reduction in the effective surface area.

[Brief explanation of the drawing]

The figure is a sectional view showing an embodiment of the present invention. 1... Precision cleaning tank, 2... Solvent, 2a... Solvent gas, 2c, 2c... Liquid level, 3... Heater, 7...
... Cap, 9 ... Orifice, 10 ... Liquid level sensor, 11 ... Control circuit.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) In an open type precision cleaning tank in which the contained liquefied solvent is heated by a heater and gasified for precision cleaning, a cap is provided at a certain height to cover the liquid level of the contained solvent. , means for forming an orifice in the ceiling wall of this cap to restrict the outflow of solvent gas, detecting the liquid level in the range covered by the cap, and controlling means for controlling energization to the heater according to the detected liquid level. A solvent heating control device for an open type precision cleaning tank, characterized by comprising: