System and method for cleaning liuid passage by negative pressure

Abstract

 A cleaning system and method for cleaning an interior of a liquid passage (10) formed in a metal mold (1) or other pipeline system so as to remove scales, slime or rust deposited on or generated in the interior of the passage. A cleaning liquid tank (2) is connected to an inlet (10a) of the liquid passage through a cleaning liquid supply passage (8), and outlet of the liquid passage is connected to the tank by way of a cleaning liquid discharge passage (10b) for recirculating the liquid. A diaphragm type pump (3) is provided at the cleaning liquid discharge passage so as to introduce the cleaning liquid into the liquid passage under negative pressure. The diaphragm type pump generates liquid flow pulsation to impart a physical impact on the deposited material. Compressed air can be applied into the cleaning liquid flowing at the cleaning liquid supply passage.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a system and method for cleaning a liquid passage, and more particularly, to such a system and method for cleaning an inner peripheral wall surface of a liquid passage formed in a metal mold, the passage being adapted for controlling the temperature of the metal mold.

[0002] Metal molds have formed therein internal liquid passages for controlling the temperature of the metal mold. A controlled amount of heated medium such as water or oil is passed through the internal liquid passage to control the temperature of the metal mold. Over a number of castings, scale mainly containing calcium or slime is deposited onto the inner peripheral surface of the liquid passage. The peripheral surface may also rust. The built-up scale, slime and rust may restrict the flow of the heated medium through the liquid passage. Calcium based scale deposited in the passage may greatly reduce heat conduction efficiency in the metal mold so that the temperature of the metal mold becomes difficult to control, thereby lowering casting performance. Further, rust generated in a tubular pipe connected to the liquid passage may also become a source of clogging.

[0003] The liquid passage and tubular pipe must be periodically cleaned to prevent such clogs. For example, a pressure feed pump circulates a strong acid, such as hydrochloric acid and organic acid, which serves as a cleaning liquid through a liquid circuit. Alternatively, deposits in the passage and tube can be mechanically removed by a drill.

[0004] However, cleaning by pressure feeding a cleaning liquid takes a long time to completely dissolve and remove the scale. If the cleaning liquid leaks through a minute hole in the liquid circuit, the pressure feeding may spray the strong acid liquid through the minute hole, possibly injuring the operators or damaging ambient devices. Cleaning with the drill is also time consuming. Also scale may be scattered during the drill work, thereby deteriorating the working atmosphere. Furthermore, drills are not well suited for cleaning bending or small inner diameter portions of the liquid passage. Therefore, complete cleaning cannot be accomplished.

[0005] Japanese Patent Application Kokai No. Sho 58-211405 discloses a device for controlling the temperature of the metal mold. According to the disclosed device, a pump circulates heated medium from a heated medium tank through a connection pipe and a liquid passage in the metal mold, and then back to the tank. The outlet side of the pump is connected to the heated medium tank, so that the heated medium passes through the liquid passage under negative pressure. Thus, even if leakage occurs at the connection pipe, the heated medium will not spray out of the connection pipe. However, the device is for controlling the temperature of the metal mold. Liquid circulation under negative pressure does not appear to have sufficient force for removing scale, slime and rust from the liquid passage.

[0006] Japanese Patent Application Kokai No. Sho 62-158533 discloses a method for drying the water passage in the metal mold to prevent the water passage from rusting. According to the method, heated compressed air is forced through the water passage to blow out the water in the water passage. However, compressed air pressure may be insufficient to remove scale or rust tightly deposited in the water passage.

SUMMARY OF THE INVENTION

[0007] It is therefore, an object of the present invention to provide an improved system and method for cleaning a liquid passage and pipe, the system and method being capable of efficiently and safely removing the scale, slime and rust deposited therein.

[0008] This and other objects of the present invention will be attained by providing a system for cleaning a liquid passage which may be deposited with scale, slime or rust, the liquid passage having an inlet and an outlet, and the system including a cleaning liquid tank for accumulating therein a cleaning liquid, cleaning liquid supply passage means connected between the cleaning liquid tank and the inlet of the liquid passage, cleaning liquid discharge passage means connected between the outlet of the cleaning liquid passage and the cleaning liquid tank for recirculating the cleaning liquid into the tank, and circulation means. The circulation means is disposed at the cleaning liquid discharge passage means for sucking the cleaning liquid in the cleaning liquid tank through the cleaning liquid supply passage means and through the liquid passage to introduce the cleaning liquid under negative pressure into the liquid passage. The circulation means includes pulsation means for generating pulsation of a flow of the cooling liquid.

[0009] In another aspect of the present invention, there is provided a method for cleaning a liquid passage including the steps of supplying a cleaning liquid accumulated in a cleaning liquid tank into the liquid passage to be cleaned by way of a cleaning liquid supply passage, and discharging the cleaning liquid from the liquid passage into the cleaning liquid tank by way of a cleaning liquid discharge passage; and the improvement comprising the steps of sucking, at the cleaning liquid discharge passage. the cleaning liquid in the cleaning liquid tank by way of the cleaning liquid supply passage and the liquid passage during the supplying step for allowing the cleaning liquid to pass through the liquid passage under negative pressure, and pulsating the cleaning liquid during the sucking step.

[0010] Preferably, a change-over cock is provided at the cleaning liquid supply passage means, and an air source is connected to the change-over cock for selectively supplying a predetermined amount of air into the cooling liquid supply passage means in accordance with opening degree and period of the cock.

[0011] In still another aspect of the invention, there is provided a method for cleaning a liquid passage including the steps of supplying a cleaning liquid accumulated in a cleaning liquid tank into the liquid passage to be cleaned by way of a cleaning liquid supply passage, and discharging the cleaning liquid from the liquid passage into the cleaning liquid tank by way of a cleaning liquid discharge passage; and the improvement comprising the steps of a first cleaning step, air supplying step second cleaning step, and air introducing step. The first cleaning step comprises the steps of accumulating water as a first cleaning liquid in the cleaning liquid tank, sucking, at the cleaning liquid discharge passage, the water in the cleaning liquid tank by way of the cleaning liquid supply passage and the liquid passage during the supplying step for allowing the water to pass through the liquid passage under negative pressure, and pulsating the water during the sucking step. In the air supplying step, air is supplied into the cleaning liquid supply passage for removing a residual water in the liquid passage. The second cleaning step comprises the steps of replacing the water from a acidic liquid as a second cleaning liquid in the cleaning liquid tank, sucking, at the cleaning liquid discharge passage, the acidic liquid in the cleaning liquid tank by way of the cleaning liquid supply passage and the liquid passage for allowing the acidic liquid to pass through the liquid passage under negative pressure, and pulsating the acidic liquid during the sucking step. In the air introducing step, the air is introduced into the liquid passage for removing a residual acidic liquid from the liquid passage.

[0012] The cleaning liquid preferably comprises at least one kind selected from the group consisting of water, acidic liquid, a mixture of acidic liquid and from 0.1 to 10 % by weight of abrasives having grain size not less than 0.2 mm, a mixture of acidic liquid and an acid soluble abrasives, and a mixture of water and aqueous abrasives.

[0013] In still another aspect of the present invention, there is provided a method for cleaning a liquid passage including the steps of supplying a cleaning liquid accumulated in a cleaning liquid tank into the liquid passage to be cleaned by way of a cleaning liquid supply passage, and discharging the cleaning liquid from the liquid passage into the cleaning liquid tank by way of a cleaning liquid discharge passage; and the improvement comprising the steps of accumulating a mixture of water and aqueous abrasives as the cleaning liquid in the cleaning liquid tank, sucking, at the cleaning liquid discharge passage, the mixture in the cleaning liquid tank by way of the cleaning liquid supply passage and the liquid passage during the supplying step for allowing the mixture to pass through the liquid passage under negative pressure, pulsating the mixture flowing through the liquid passage during the sucking step; and supplying air from the cleaning liquid supply passage to remove a residual mixture from the liquid passage.

[0014] According to the system and method for cleaning the liquid passage, pulsating cleaning liquid flows through the liquid passage. Therefore, scale, slimes and/or rust deposited on or generated in the liquid passage can be physically removed. Further, since negative pressure is provided in the cleaning liquid up to the circulation means, leakage of the cleaning liquid from the liquid circuit up to the circulation means can be avoided even if minute cracks or holes are formed in a pipe or a metal mold which constitute the liquid circuit. Thus, work can be safely performed even if a dangerous cleaning liquid such as an acidic liquid is used, and any work or countermeasures for avoiding leakage can be dispensed with.

[0015] By introducing air into the cleaning liquid supply passage means while the cleaning liquid is being circulated, aggregation of minute air bubbles occurs, and shock waves are generated because of mixing of two different phase materials, i.e., air (gas) and liquid (cleaning liquid). Further, a pressure difference is generated between the sucked air and the cleaning liquid. By these phenomena, materials deposited on the liquid passage are quickly peeled off. By exclusively introducing air into the cleaning liquid supply passage after stopping supply of the cleaning liquid, any residual cleaning liquid can be sufficiently removed.

[0016] Cleaning can be less expensively performed by using water as the first cleaning liquid before using the acidic liquid as the second cleaning liquid, because almost all the deposited material can be removed from the liquid passage by the water and the air in the first cleaning step. before using expensive chemicals. If chemicals such as acidic liquid are used from the start, the deposited material successfully separated from the liquid passage may be dissolved in the cleaning liquid. However, the deposited material need only be separated and removed from the liquid passage. Dissolution may shorten the service life of the chemicals. Deposited materials which were not removed during the first cleaning step can then be removed by dissolution in the acidic liquid of the second cleaning step. Thus, only a small amount of deposited material is dissolved in the acidic liquid, thereby prolonging the service life of the cleaning liquid. Further, according to this method, the entire cleaning period can be reduced. Furthermore, because the second cleaning step is shorter, the metal mold is less likely to break down from hydrogen brittleness.

[0017] If the mixture of acidic liquid and rigid abrasives is used as the cleaning liquid, the rigid abrasives mechanically impacting against the deposited material will enhance the ability of cleaning liquid to remove deposited material. If the mixture of acidic liquid and an acid soluble abrasive is used as the cleaning liquid, mechanical force can be applied to the deposited material because of the mass of the abrasives as described above. Further, since the abrasives are finally dissolved into the liquid, the abrasives do not clog the liquid passage. If the mixture of water and aqueous abrasives is used as the cleaning liquid, the abrasives dissolve into the water, and therefore do not remain in the liquid passage.

[0018] If the mixture of water and aqueous abrasives is exclusively used as the cleaning liquid, the cleaning liquid need not be completely removed from the liquid passage because residual cleaning liquid will not harm the liquid passage. Therefore, the overall cleaning process can be simplified. Further, the mixture can provide greater cleaning ability than employment of mere water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the drawings;

Fig. 1 is a schematic illustration showing a system for cleaning a liquid passage according to a first embodiment of the present invention;

Fig. 2 is a schematic illustration showing a system for cleaning a liquid passage according to a second embodiment of the present invention; and

Fig. 3 is a schematic illustration showing a system for cleaning a liquid passage according to a comparative example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A system for cleaning a liquid passage according to one embodiment of the present invention will be described with reference to Fig. 1.

[0021] A metal mold 1 is internally formed with a liquid passage 10 having an inlet 10a and an outlet 10b. A cleaning liquid supply passage 20 connects the inlet 10a to a cleaning liquid tank 2 which accumulates therein a cleaning liquid 13. A cleaning liquid discharge passage 30 connects the outlet 10b to the tank 2.

[0022] The cleaning liquid supplying passage 20 includes a supply pipe 14a, 14b, a change-over cock 4, an intake manifold 5 having a connection port 5a, and an inlet side hose 8. The supply pipe 14a connects the cleaning liquid tank 4 to the change-over cock 4, the supply pipe 14b connects the change-over cock 4 to the intake manifold 5, and the inlet side hose 8 connects the connection port 5a of the intake manifold 5 to the inlet 10a.

[0023] The cleaning liquid discharge passage 30 includes a discharge side hose 9, an exhaust manifold 6 having a connection port 6a, recirculation passages 15b, 15a, and a circulator 3. The outlet side hose 9 connects the outlet 10b of the liquid passage 10 to the connection port 6a of the exhaust manifold 6, the circulation passage 15b connects the exhaust manifold 6 to the circulator 3, and the circulation passage 15a connects the circulator 3 to the tank 2.

[0024] The cleaning liquid tank 2 is adapted for accumulating various kind of cleaning liquid such as water, commercially available inorganic acids (hydrochloric acid), organic acids (formic acid), strong acids, and neutral chemicals using chelate, those having dissolution power against scale, slime and rust. Rigid abrasives having particle size of not less than 0.2 mm can be added to the above-described cleaning liquid by 10 % by weight. High hardness particles such as alumina particles and silicon carbide particles are available as abrasives. Alternatively, aqueous particles or acid soluble particles can be added into the above-described cleaning liquid. A crystal of nickel sulfate is available as the aqueous abrasive, and aluminum or zinc particles are available as acid soluble abrasives.

[0025] The cleaning liquid is selected dependent on the material, such as carbonate scale and ferrous rust, deposited onto the liquid passage and the pipe or on the amount of the deposited material. Water is the least expensive cleaning liquid, and can be forced through the liquid passage under high pressure to remove the scale and slime deposited onto the surface of the liquid passage. Another cleaning liquid having greater dissolving power can be used for dissolving the scale and slime deposited onto the passage wall into the liquid. However, upper dissolving power limit may exist and the cleaning liquid may have its own service life. Generally, dissolving power may be improved by heating the liquid thereby increasing its saturation point. However, water alone may be sufficient for removing some types of scale. In this connection, deposits can be removed using a single cleaning liquid or two or more kinds of cleaning liquids in sequence.

[0026] One of the ports of the change-over cock 4 is connectable to an air source 7 for introducing a predetermined amount of air into the liquid passage. If the air source 7 is selectively connected to the liquid passage, air bubbles could be mixed with the cleaning liquid to promote removal of the deposited material from the passage. Further, the change-over cock 4 could be configured as an air supply cock for introducing only air into the liquid passage 10. Examples of the air source 7 include a compressor which can supply highly pressurized air or a blower which can supply low pressure air.

[0027] By controlling opening degree of the air introduction port of the change-over cock 4, a desired amount of air can be introduced into the liquid passage. Continuous or discontinuous opening of the cock may be performed. In the latter case, air flow speed differential may be provided for efficiently removing the deposits.

[0028] It should be noted that, although not shown in the drawings, a plurality of the liquid passages 10 are formed in the metal mold 1. The intake manifold 5 and the exhaust manifold 6 are provided for facilitating fluid connection with a plurality of inlet side hoses 8 and outlet side hoses 9, respectively.

[0029] An example of the circulator 3 would be a conventional diaphragm type pump used for sucking the cleaning liquid in the tank 2 through the liquid supply passage 20, the liquid passage 10, the outlet side hose 9, and the circulation passage 15b in that order. Thus, the cleaning liquid passing through the liquid passage 10 has a negative pressure. Accordingly, even if a minute crack or hole is formed in the pipes 14, 15 and hoses 8, 9, the cleaning liquid is not ejected nor sprayed from the minute crack. Further, reciprocal motion of the diaphragm pulsates the sucked cleaning liquid so that the flow velocity of the cleaning liquid cyclically changes. Consequently, the cleaning liquid mechanically impacts deposits in the liquid passage 10. In view of this, the diaphragm type pump 3 serves as a pulse flow generator as well as the forcible liquid circulator.

[0030] Cleaning processes will next be described.

(1) First cleaning method

[0031] An acidic liquid is used as the cleaning liquid in this first method. The liquid is accumulated in the cleaning liquid tank 2, and the change-over cock is opened, when desired to introduce air into the supply pipe 14b. Then, the circulator 3 is actuated to suck the cleaning liquid from the tank 2, so that the liquid is introduced into the liquid passage 10. With this arrangement, the deposits such as scale and rust are dissolved into the acid liquid and are removed from the liquid passage 10. Further, the circulator 3 generates pulsation in the acid liquid that physically shocks the deposits and promotes separation of the deposits from the passage wall. If the change-over cock 4 is opened, the air source 7 is brought into communication with the liquid supply passage 20, so that air bubbles mix with the cleaning liquid. By mixing the air bubbles with the cleaning liquid, minute air bubbles aggregate together, and shock waves are generated because of mixing of two different materials, air (gas) and cleaning liquid. Also, a pressure difference is generated between the sucked air and cleaning liquid. Accordingly, deposit removing ability is further enhanced. Incidentally, the smaller the bubbles in the bubble aggregations, the better. The cleaning liquid is then recirculated into the cleaning liquid tank 2 through the circulator 3.

(2) Second cleaning method

[0032] In the second cleaning method, water and acidic liquid are used as the cleaning liquid. The liquid passage 10 is cleaned in a manner similar to the first cleaning process but with water instead of an acidic liquid. That is, hydraulic pressure alone can remove scale that is loosely deposed on the liquid passage 10 and the hoses 8, 9. Therefore, initially, most of the deposited materials are removed using water. In this case, similar to the first process, the change-over cock 4 is selectively opened for introducing air into the supply pipe 14b.

[0033] Then, the liquid supply pipe 14 is drawn out of the water in the tank 2, and the circulator 3 is deenergized. Thereafter, air from the air source 7 is introduced into the pipe 14b, the hoses 8, 9 and the liquid passage 10 through the change-over cock 7 so as to remove water affixed to the walls of the pipe, the hoses and the liquid passage.

[0034] Then, the water in the tank 2 is replaced by the acidic liquid which is introduced into the liquid circuit in a manner similar to the first cleaning process. The dissolving power of the acidic liquid, the pulsation provided to the acidic liquid, and the air bubbles introduced into the acidic liquid synergetically combine to remove deposited material which could not be removed by water alone.

[0035] Next, fluid communication between the supply pipe 14 and the cleaning liquid is blocked for exclusively introducing air from the air source 7 into the liquid passage 10 by way of the supply passage 20. Consequently, acidic liquid remaining in the liquid passage 10 can be removed to prevent the passage wall from being corroded by the acidic liquid.

[0036] In accordance with the second cleaning method, water removes a great deal of the deposited scale in the initial cleaning step. Therefore, it is possible to reduce the amount of the chemicals, which are more expensive than water used, in the subsequent cleaning step, and the service life of the chemicals can be prolonged. In other words, if the acidic liquid is used even at the initial cleaning step, the scale which has been successfully separated from the wall of the liquid passage 10 may be dissolved into the acidic liquid. It should be noted that the scale need not be dissolved by the acidic liquid if the scale is peeled off from the wall of the liquid passage. Accordingly, the acidic liquid may be saturated unnecessarily, so that its service life is shortened. Therefore, the second cleaning method is economically advantageous.

(3) Third cleaning method

[0037] The third cleaning method is similar to the second cleaning method, but the acidic liquid of the second cleaning method is replaced with a mixture of the acidic liquid and 0.1 to 10 % by weight of rigid abrasives having grain size of not less than 0.2mm. This mixture further enhances scale removing ability because of the mechanical impact imparted by the rigid abrasives. Incidentally, if the grain size is less than 0.2 mm, kinetic energy of the particles is too small to enhance the scale removing ability.

(4) Fourth cleaning method

[0038] In the fourth cleaning method, the acidic liquid used in the second cleaning method is replaced with a mixture of the acidic liquid and acid soluble abrasives, or a mixture of water and aqueous abrasives. Rigid abrasives added to the cleaning liquid in the third cleaning method may cling to or settle in narrow portions of the liquid passage 10. On the other hand, acid soluble abrasives or aqueous abrasives will dissolve in the cleaning liquid, so that the problem of the remnants does not occur.

(5) Fifth cleaning method

[0039] In the fifth cleaning method, acidic liquid used in the first cleaning method is replaced with a mixture of the acidic liquid and 0.1 to 10 wt% of rigid abrasives having grain size not less than 0.2 mm, or an acidic liquid added with the acid soluble abrasives, or a mixture of water and the aqueous abrasives. The same advantages as obtained in the third and fourth cleaning methods can be obtained.

(6) Sixth cleaning method

[0040] In the sixth cleaning method, the acidic cleaning liquid of the first cleaning method is replaced with water added with aqueous abrasives. After cleaning the liquid passage 10 in accordance with the first cleaning method, fluid communication between the supply pipe 14 and the cleaning liquid is blocked. Then, air from the air source 7 is introduced into the liquid passage 10 through the supply passage 20 so as to remove residual water in the liquid passage 10. In the cleaning step employing the aqueous abrasives, the abrasives are dissolved into the water. Any residual abrasive remaining in the liquid passage 10 will finally be dissolved and removed because of the water flowing through the liquid passage.

[0041] Incidentally, in the first to fifth cleaning methods, chemicals containing a chelate can also be used as the cleaning liquid.

[0042] A system for cleaning a liquid passage according to a second embodiment of the present invention will be described with reference to Fig. 2. Components and their configuration according to the second embodiment are substantially the same as in the first embodiment except for the circulator. That is, in the second embodiment, the diaphragm type pump 3 of the first embodiment is replaced with an ordinary pump 3A and a pulse flow generator 3B provided immediately upstream of the pump 3A. The ordinary pump 3A may be a vane pump or a rotary type pump, and the pulse flow generator 3B may be an electromagnetic valve. By repeatedly turning the electromagnetic valve 3B on and off while continuously operating the pump 3A, the circulation passage 15c is cyclically opened and closed thereby pulsating the cleaning liquid. The above described first to sixth cleaning method can be performed in the cleaning system of the second embodiment.

Example 1

[0043] The cleaning system shown in Fig. 1 was connected to an 800 ton metal mold. A diaphragm type pump was used as the circulator, and the change-over cock was maintained closed. The above described first cleaning method was performed with using Zoron V5 which is a trade name of an acidic cleaning liquid and produced by Lux Co., Ltd.

Example 2

[0044] Cleaning in a manner similar to the Example 2 was performed except that the change-over cock was opened by 1/3 so as to continuously mix air with the cleaning liquid.

Example 3

[0045] The cleaning system shown in Fig. 2 was connected to an 800 ton metal mold. The above described first cleaning method was performed using the vane pump 3A and the electromagnetic valve 3B as a pulse flow generator. The electromagnetic valve was closed 1 second every 4 seconds to generate a pulsating flow. The same cleaning liquid was used as was used in the Example 1.

Comparative Example

[0046] This comparative example concerns a conventional method as shown in Fig. 3 wherein like parts and components are designated by the same reference numerals and characters as those shown in Figs. 1 and 2. An extrusion type pump 3X was connected immediately downstream of the cleaning liquid tank 2. The cleaning liquid was supplied to the liquid passage 10 under liquid feeding force provided by the pump. The cleaning liquid and the metal mold were the same as those of the Example 1.

[0047] In the above Examples, the interior of the liquid passage 10 was observed using a bore scope. In the Example 1 through 3, the internal surface of the liquid passage 10 was cleaned within 2 - 3 hours. On the other hand, in the comparative example, from 8 to 9 hours was required for complete removal of the deposited material from the liquid passage 10. Further in the comparative example, the high pressure applied to the cleaning liquid caused the hose 8 to disengage from its connection portion, thereby scattering the chemicals. However, in the Examples 1 through 3, the hose and the pipe did not disengage.

Example 4

[0048] The second cleaning method was performed using the cleaning system shown in Fig. 1. The metal mold and the cleaning liquid were the same as those of Example 1. Cleaning in Example 4 was more efficient than in Examples 1 through 3. That is, from 1 to 3 hours was required for complete cleaning in Example 4. Most of the scales, such as calcium carbonate and ferrous rust, were removed from the liquid passage 10 by cleaning with water in the first cleaning step. All residual deposits were dissolved by then cleaning with acidic liquid in the second cleaning step for complete removal of the deposited material. With these steps, service life of the acidic liquid was prolonged by 30 times longer than the service life of the acidic liquid in the first cleaning method. Further, generation of hydrogen which occurs when employing acid was reduced, thereby restraining the danger of damaging the metal mold from hydrogen brittleness.

Example 5

[0049] The cleaning system shown in Fig. 1 was used where the above described third cleaning method was performed. The same metal mold and the cleaning liquid was used as was used in Example 1. The cleaning liquid was prepared by adding 1 % by weight of alumina abrasives having grain size of 1 mm to an acidic cleaning liquid. After cleaning for 1 hour, the cleaning liquid was passed through a filter of 0.5 mm mesh to collect the abrasives. Bore scope observation of the interior of the liquid passage 10 revealed that scale and rust were sufficiently removed from the liquid passage 10.

Example 6

[0050] The fourth cleaning method was used in the cleaning system shown in Fig. 1. The metal mold was the same as that used in Example 1. A mixture of a water and 5% by weight of nickel sulfate was used as the cleaning liquid. Observation performed after removing the residual water from the liquid passage revealed that scale and rust were sufficiently removed and that no abrasives remained in the liquid passage.

[0051] While the invention has been described in detail with reference to the specific embodiments and Examples, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. For example, in the depicted embodiment, the cleaning system is applied to a metal mold for casting purposes. However, the invention can be applied to a liquid passage for cooling a heat treatment apparatus. Further, the present invention can be applied to any type of apparatus with a liquid passage in which passage of water may deposit scale.

Claims

1. A system for cleaning a passage for liquid which passage may be deposited with scale, slime or rust, the liquid passage having an inlet and an outlet, the system including:

a cleaning liquid tank for accumulating therein a cleaning liquid;

cleaning liquid supply passage means to be connected between the cleaning liquid tank and the inlet of the liquid passage;

cleaning liquid discharge passage means to be connected between the outlet of the cleaning liquid passage and the cleaning liquid tank for recirculating the cleaning liquid into the tank; and

circulation means disposed at the cleaning liquid discharge passage means for sucking the cleaning liquid in the cleaning liquid tank through the cleaning liquid supply passage means and through the liquid passage to introduce the cleaning liquid under negative pressure into the liquid passage, the circulation means including pulsation means for generating pulsation of a flow of the cooling liquid.

2. The system as claimed in claim 1, wherein the circulation means comprises a diaphragm type pump.

3. The system as claimed in claim 1, wherein the circulation means comprises one of a vane pump and a rotary pump, and an electromagnetic valve positioned immediately upstream of one of the vane pump and the rotary pump.

4. The system as claimed in claim 1, 2 or 3, further comprising:

a change-over cock provided at the cleaning liquid supply passage means; and

an air source connected to the change-over cock for selectively supplying a selected amount of air into the cleaning liquid supply passage means in accordance with opening degree and period of the cock.

5. The system as claimed in any preceding claim, including a cleaning liquid which comprises at least one kind selected from the group consisting of water, acidic liquid, a mixture of acidic liquid and from 0.1 to 10% by weight of abrasives having grain size not less than 0.2 mm, a mixture of acidic liquid and an acid soluble abrasive, and a mixture of water and aqueous abrasives.

6. A method for cleaning a passage for liquid including the steps of;

supplying a cleaning liquid accumulated in a cleaning liquid tank into the liquid passage to be cleaned by way of a cleaning liquid supply passage, and discharging the cleaning liquid from the liquid passage into the cleaning liquid tank by way of a cleaning liquid discharge passage;

sucking, at the cleaning liquid discharge passage, the cleaning liquid in the cleaning liquid tank by way of the cleaning liquid supply passage and the liquid passage during the supplying step for allowing the cleaning liquid to pass through the liquid passage under negative pressure; and

pulsating the cleaning liquid during the sucking step.

7. The method as claimed in claim 6, wherein the cleaning liquid comprises at least one kind selected from the group consisting of water, acidic liquid, a mixture of acidic liquid and from 0.1 to 10 % by weight of abrasives having grain size not less than 0.2 mm, a mixture of acidic liquid and an acid soluble abrasives, and a mixture of water and aqueous abrasives.

8. A method according to claim 6 or 7 including a first cleaning step comprising the steps of accumulating water as a first cleaning liquid in the cleaning liquid tank; sucking, at the cleaning liquid discharge passage, the water in the cleaning liquid tank by way of the cleaning liquid supply passage and the liquid passage during the supplying step for allowing the water to pass through the liquid passage under negative pressure; and pulsating the water during the sucking step;

supplying air into the cleaning liquid supply passage for removing a residual water in the liquid passage;

a second cleaning step comprising the steps of replacing the water from an acidic liquid as a second cleaning liquid in the cleaning liquid tank; sucking, at the cleaning liquid discharge passage, the acidic liquid in the cleaning liquid tank by way of the cleaning liquid supply passage and the liquid passage for allowing the acidic liquid to pass through the liquid passage under negative pressure; and, pulsating the acidic liquid during the sucking step; and

introducing air into the liquid passage for removing a residual acidic liquid from the liquid passage.

9. The method as claimed in claim 8, wherein the first cleaning step further comprises the step of supplying air to the cleaning liquid supply passage.

10. The method as claimed in claim 8 or 9, wherein the second cleaning step further comprises the step of supplying air to the cleaning liquid supply passage while the acidic liquid flows through the liquid passage.

11. A method according to claim 6 or 7 including the steps of:

accumulating a mixture of water and aqueous abrasives as the cleaning liquid in the cleaning liquid tank;

sucking, at the cleaning liquid discharge passage, the mixture in the cleaning liquid tank by way of the cleaning liquid supply passage and the liquid passage during the supplying step for allowing the mixture to pass through the liquid passage under negative pressure;

pulsating the mixture flowing through the liquid passage during the sucking step; and

supplying air from the cleaning liquid supply passage to remove a residual mixture from the liquid passage.

Drawing