CA1142419A - Process and apparatus for removing sludge from salt baths - Google Patents
Process and apparatus for removing sludge from salt bathsInfo
- Publication number
- CA1142419A CA1142419A CA000347843A CA347843A CA1142419A CA 1142419 A CA1142419 A CA 1142419A CA 000347843 A CA000347843 A CA 000347843A CA 347843 A CA347843 A CA 347843A CA 1142419 A CA1142419 A CA 1142419A
- Authority
- CA
- Canada
- Prior art keywords
- bath
- sludge
- salt
- filter
- melt
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000010802 sludge Substances 0.000 title claims abstract description 53
- 150000003839 salts Chemical class 0.000 title claims abstract description 44
- 238000000034 method Methods 0.000 title claims description 13
- 238000005121 nitriding Methods 0.000 claims description 5
- 238000000746 purification Methods 0.000 claims description 4
- 239000000155 melt Substances 0.000 abstract description 7
- 239000000463 material Substances 0.000 abstract description 3
- -1 nitride salt Chemical class 0.000 abstract description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- 239000002245 particle Substances 0.000 description 6
- 239000000470 constituent Substances 0.000 description 4
- 238000001816 cooling Methods 0.000 description 4
- 229910052742 iron Inorganic materials 0.000 description 4
- 229910000831 Steel Inorganic materials 0.000 description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 3
- 239000011491 glass wool Substances 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 239000011490 mineral wool Substances 0.000 description 3
- 239000010959 steel Substances 0.000 description 3
- 239000010936 titanium Substances 0.000 description 3
- 229910052719 titanium Inorganic materials 0.000 description 3
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 2
- 229910052783 alkali metal Inorganic materials 0.000 description 2
- 230000001174 ascending effect Effects 0.000 description 2
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 229910001149 41xx steel Inorganic materials 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- 229910001854 alkali hydroxide Inorganic materials 0.000 description 1
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 150000001913 cyanates Chemical class 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000005242 forging Methods 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910001337 iron nitride Inorganic materials 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
- 238000007514 turning Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/34—Methods of heating
- C21D1/44—Methods of heating in heat-treatment baths
- C21D1/46—Salt baths
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/0012—Settling tanks making use of filters, e.g. by floating layers of particulate material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/003—Sedimentation tanks provided with a plurality of compartments separated by a partition wall
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/24—Feed or discharge mechanisms for settling tanks
- B01D21/245—Discharge mechanisms for the sediments
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
- B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
- B01D29/13—Supported filter elements
- B01D29/23—Supported filter elements arranged for outward flow filtration
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
- B01D29/60—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor integrally combined with devices for controlling the filtration
- B01D29/605—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor integrally combined with devices for controlling the filtration by level measuring
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D35/00—Filtering devices having features not specifically covered by groups B01D24/00 - B01D33/00, or for applications not specifically covered by groups B01D24/00 - B01D33/00; Auxiliary devices for filtration; Filter housing constructions
- B01D35/26—Filters with built-in pumps filters provided with a pump mounted in or on the casing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D35/00—Filtering devices having features not specifically covered by groups B01D24/00 - B01D33/00, or for applications not specifically covered by groups B01D24/00 - B01D33/00; Auxiliary devices for filtration; Filter housing constructions
- B01D35/30—Filter housing constructions
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Crystallography & Structural Chemistry (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Thermal Sciences (AREA)
- Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
- Filtering Materials (AREA)
- Treatment Of Sludge (AREA)
- Chemical Treatment Of Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The removal of sludge from polluted salt baths, parti-cularly nitride salt baths, has been very time-consuming hereto-fore and resulted in interruptions of the operation and in varying qualities of the treat material. These disadvantages are removed by continuously purifying the salt melt during the operation of the baths in that the melt is continuously passed over a filter. The apparatus preferably comprises an air compressor immersed in the melt and a filter disposed above and outside the bath.
The removal of sludge from polluted salt baths, parti-cularly nitride salt baths, has been very time-consuming hereto-fore and resulted in interruptions of the operation and in varying qualities of the treat material. These disadvantages are removed by continuously purifying the salt melt during the operation of the baths in that the melt is continuously passed over a filter. The apparatus preferably comprises an air compressor immersed in the melt and a filter disposed above and outside the bath.
Description
1~2~9 The present invention relates to a process and an apparatus for removing sludge from polluted salt melts such as those used, for example, for nitriding metals, preferably iron containing metals. These salt baths are used on a large scale and consist primarily of carbonates and cyanates of alkali metals. Some of these baths also contain alkali metal cyanides.
These salt melts are normally operated at an operating temperature of 560 to 600C.
During the treatment of structural members of an iron material these baths become clogged with sludge to a varying degree, i.e., in that adhering steel particles, as for example, turnings or grindings, accumulate on the bottom of the treatment vessel or remain in a finely dlvided form in a state of suspension.
Likewise the treatment of scaled or unmachined surfaces (casting or forging skin) result in the pollution of the bath. Further-more the slude component is also formed in that nitride particles scale off from the charaing aids, such as baskets or racks, after repeated treatment and remain in the bath. The "sludge" thus formed consists chiefly of iron nitride and iron oxide.
Other salt baths, as for example, cooling baths based on hydroxide, become increasingly thick liquids due to the formation of insoluble carbonates so that the melting point of the baths increases and the cooling effect decreases. Therefore, this kind of salt bath must be purified.
Since the sludge content of the nitride bath greatly influences the reproducibility of the expected nitriding result a continuous purification of the bath is very important. There-fore, various devices for removing the sludge are used in practice. However, the fact that the operation must be interrupted in order to remove the sludge, i.e., the removal of the sludge must be carried out on the non-charged bath, has ! ~
These salt melts are normally operated at an operating temperature of 560 to 600C.
During the treatment of structural members of an iron material these baths become clogged with sludge to a varying degree, i.e., in that adhering steel particles, as for example, turnings or grindings, accumulate on the bottom of the treatment vessel or remain in a finely dlvided form in a state of suspension.
Likewise the treatment of scaled or unmachined surfaces (casting or forging skin) result in the pollution of the bath. Further-more the slude component is also formed in that nitride particles scale off from the charaing aids, such as baskets or racks, after repeated treatment and remain in the bath. The "sludge" thus formed consists chiefly of iron nitride and iron oxide.
Other salt baths, as for example, cooling baths based on hydroxide, become increasingly thick liquids due to the formation of insoluble carbonates so that the melting point of the baths increases and the cooling effect decreases. Therefore, this kind of salt bath must be purified.
Since the sludge content of the nitride bath greatly influences the reproducibility of the expected nitriding result a continuous purification of the bath is very important. There-fore, various devices for removing the sludge are used in practice. However, the fact that the operation must be interrupted in order to remove the sludge, i.e., the removal of the sludge must be carried out on the non-charged bath, has ! ~
2~
been a common factor in all the systems used heretofore.
Furthermore in all the systems used heretofore the removal of the sludge is carried out with perforated plates, wire mesh screens or even with mineral wool, or glass wool which are housed in a suitable device. In many cases said device consists of one or several superposed basket-like structures of perforated plate, which are adapted to the shape of the crucible and, when required, thev are covered with a wire mesh screen. Even simple, disc-shaped devices with an added rim of perforated plate are used. For the xemoval of the sludge the device is placed into the non-charged salt bath and after a settling andquiescent phase it is withdrawn. The major portion of the sludge particles present in the bath settle on the wire mesh screen or on the glass wool. A cylindrical vessel having a hinged bottom of perforated plate is also disclosed in German Offenlegungsschrift No~ 2,645,669. Said vessel is placed with its opened bottom into the bath, whereupon the bottom is closed and the entire device is again withdrawn. Filtration of the bath is thus attained. In order to attain a complete removal of the sludge from the salt melts, the procedure must be repeated several times in all the conventional sludge removing processes and devices~
In all the conventional procedures the continuous interruptions of the operation, which is required for the purification of salt baths and can be substantial when re~uire-ments of purity of the bath are high, is a disadvantage. In many cases the removal of the fine suspended particles is insufficient.
Moreover in the case of sensitive structural membexs the results of the treatment vary since the sludge content of the bath increases between two removals of sludge and the results of the treatment thus deteriorate. However, in the case of sensitive structural members the way out, namely to remove the sludge z~
after each charge, is very cumbersone and time-consuming.
Therefore, the present invention provides a process and apparatus for removing sludge from polluted salt baths, particularly nitride salt baths, which operate with as little as possible an interruption of the operation and also assure complete removal of the sludge. They also are suitable for any bath size and are simple and uncomplicated to handle.
According to the present invention there is provided a process for removing sludge from a polluted salt bath in which during the operation of the bath a por~ion of the salt melt is continuously purified.
Thus in accordance with the present invention during the operation some of the salt melt is continuously purified.
This purification is carried out in that a portion of the salt melt is continuously passed over a filter to remove the sludge and that the purified melt is returned to the bath. The portion of the melt which is passed over the filter is preferably such that the total volume of the salt bath is purified once within a period of one to five hours.
The present invention also provides an apparatus for removing sludge from polluted salt bath including a filter for removing the sludge and a pump immersed in the salt adapted to continuously recirculate a portion of the salt melt from the bath through said filter.
The apparatus according to the invention thus includes a pump immersed into the salt bath and a filter into which a portion of the melt is continuously fed.
The filter is disposed above and outside the bath.
Continuous removal of sludge from the bath is thus possible.
This has the advantage of a higher productivity of the bath since it is no longer necessary to interrupt the operation.
~ 2~1~
A further advantage lies in that the state of the bath is continuously the same with respect to the sludge content i.e., the minimal sludge content of the bath does not vary over a lengthy period of time. Complete uniformity of the treatment results is thus attained.
The present invention will be further illustrated by way of the accompanying drawings in which:
Fig. 1 is a schematic of an apparatus for effecting the process according to the embodiment of the present invention;
Fig. 2 is a detail of the filter system of Fig. 1 and;
Fig. 3 is a detail of an alternate filter system of Fig. 1.
Referring to Figs. 1 and 2, the salt melt (1) is in a titanium crucible (2). An air compressor (3), for example, an air lift pump with the compressed air contact (4) and the ascending pipe (5) is dipped into the salt melt (1). The salt flow conveyed by the air lift pump (3) passes into the filter system (6) and leaves this system through the discharge pipe (7).
The filter system (6) comprises, for example, a double-walled sheet-iron jacket (8 and 9). The intermediate space is insulated with glass, slag or mineral wool (10) to avoid heat losses and the recrystallization of bath components associated therewith.
A pot of perforated plate (11), into which a sheeth of fine-meshed wire net is inserted (12), is disposed within said insulating jacket.
The liquid salt is pumped into the filter sheeth, which is open at the top. The sludge particles are retained on passing this filter. The purified salt melt leaves the filter system through the discharge system (7). In order to assure that in the case of an obstructed filter, complications due to overflowing of the pot are avoided, an overflow (13) is provided. Filter _~
sheeths filled or obstructed with sludge can be very easily exchanged without having to ~urn off the air lift pump or having to remove it from the bath since the ascending pipe (5) can be rotated about its longitudinal axis towards the bath.
Another feasible embodiment of the sludge removing unit (6) is shown in Figure 3. In this case it consists of a simple box (14), which may also be insùlated to avoid heat losses. Sheet iron barriers (15) of varying heights are disposed in the box (l4). The liquid salt melt conveyed by the air lift pump (3) passes into the first chamber (16) of the sludge-removing unit (6~. When the first chamber (1) is filled the salt melt overflows into the further chambers until it reaches the discharge pipe (7). Since the salt melt must slowly pass through several chambers, it is very quiescent whereby the sludge particles can settle on the bottom. When the chamber is filled with sludge, the viscous sludge can be removed therefrom simply by dumping it out.
The advantages of the process according to the invention are explained in greater detail by means of the Examples hereafter.
Example 1 A crucible furnace with a salt bath crucible of titanium having a diameter of 800 mm and a depth of 1500 mm contains 1100 kg of nitriding salt. At an operating temperature of 580C synchronized bodies of steel C45 having a charge weight of 400 kg are dipped in a rack of 60 kg into the bath as the members to be treated. The time of treatment (residence time in the bath) is one hour, the treatment being performed as a three-shift operation.
In conventional sludge removal the sludge had to be removed four times within the three shifts, i.e., every six hours. Between two sludge removals the content of water-insolu-- ~14~419 ble constituents in the bath varied between 0.017% (immediately after the removal of the sludge) and 0.19% (immediately prior to the next removal of the sludge).
The operation of removing the sludge took 30 minutes in each case, so that within three shifts - taking into account the time required for charging the bath and removing the members - a maximum of 18 charges with 7200 kg could be treated.
When using the process for removing sludge according to the invention and an apparatus according to Figure l and 2, the content of water-insoluble constituents was constant at 0.015%. The filter sheeths could be exchanged during the operation so that a maximum of 20 charges with a total of 8000 kg could be treated.
However, the fact that apart from the increased productivity a distinct improvement of both the quality and the uniformity of the treated material was noticed as a result of the constantly low sludge content is even more important. 540 kg of the bath are passed over the sludge removing unit per hour.
Example 2 A crucible furnace with a salt bath crucible of titanium having a diameter of 600 mm and a depth of 1300 mm contained 550 kg of nitriding salt. The operating temperature was 550C. The members to be treated were crankshafts of steel 42 CrMo 4. The weight of the charge was 240 kg and the weight of the rack 30 kg. The time of treatment (residence time in the bath) was two hours in a two-shift operation.
In this example the sludge was removed after every two charges, requiring 25 minutes. The content of water-insoluble constituents was 0.013% immediately after the removal of the sludge and 0.12~ immediately prior to the next removal of the sludge. When using an apparatus for removing sludge according to the invention corresponding to the Figures 1 and 2, the ~142~19 content of insoluble constituents in the bath could be reduced to a constant value of 0.014% at a throughput of 200 kg of salt melt per hour~ While previously six charges with a total of 1440 kg could be treated within two shifts, seven charges with 1680 kg were treated when applying the continuous sludge removal.
Example 3 A tank furnace having the size of 800 x 600 x 1300 mm was filled with an alkali hydroxide melt as the cooling bath.
The temperature of the bath was 350C.
Members according to Example 2 were dipped into this bath during a treatment time of 10 minutes. By entraining foreign salts and converting the hydroxide the content of insoluble carbonate in`the bath increased, whereby the melting point increased and the cooling effect decreased, resulting in an increase in treatment time.
In conventional sludge removal the bath had to be cooled after some time in two stages and the sludge was removed by means of a screen.
With the apparatus according to the invention, the bath could be kept free from sludge during the entire running time while the entire bath was passed over the sludge removing apparatus once in five hours.
been a common factor in all the systems used heretofore.
Furthermore in all the systems used heretofore the removal of the sludge is carried out with perforated plates, wire mesh screens or even with mineral wool, or glass wool which are housed in a suitable device. In many cases said device consists of one or several superposed basket-like structures of perforated plate, which are adapted to the shape of the crucible and, when required, thev are covered with a wire mesh screen. Even simple, disc-shaped devices with an added rim of perforated plate are used. For the xemoval of the sludge the device is placed into the non-charged salt bath and after a settling andquiescent phase it is withdrawn. The major portion of the sludge particles present in the bath settle on the wire mesh screen or on the glass wool. A cylindrical vessel having a hinged bottom of perforated plate is also disclosed in German Offenlegungsschrift No~ 2,645,669. Said vessel is placed with its opened bottom into the bath, whereupon the bottom is closed and the entire device is again withdrawn. Filtration of the bath is thus attained. In order to attain a complete removal of the sludge from the salt melts, the procedure must be repeated several times in all the conventional sludge removing processes and devices~
In all the conventional procedures the continuous interruptions of the operation, which is required for the purification of salt baths and can be substantial when re~uire-ments of purity of the bath are high, is a disadvantage. In many cases the removal of the fine suspended particles is insufficient.
Moreover in the case of sensitive structural membexs the results of the treatment vary since the sludge content of the bath increases between two removals of sludge and the results of the treatment thus deteriorate. However, in the case of sensitive structural members the way out, namely to remove the sludge z~
after each charge, is very cumbersone and time-consuming.
Therefore, the present invention provides a process and apparatus for removing sludge from polluted salt baths, particularly nitride salt baths, which operate with as little as possible an interruption of the operation and also assure complete removal of the sludge. They also are suitable for any bath size and are simple and uncomplicated to handle.
According to the present invention there is provided a process for removing sludge from a polluted salt bath in which during the operation of the bath a por~ion of the salt melt is continuously purified.
Thus in accordance with the present invention during the operation some of the salt melt is continuously purified.
This purification is carried out in that a portion of the salt melt is continuously passed over a filter to remove the sludge and that the purified melt is returned to the bath. The portion of the melt which is passed over the filter is preferably such that the total volume of the salt bath is purified once within a period of one to five hours.
The present invention also provides an apparatus for removing sludge from polluted salt bath including a filter for removing the sludge and a pump immersed in the salt adapted to continuously recirculate a portion of the salt melt from the bath through said filter.
The apparatus according to the invention thus includes a pump immersed into the salt bath and a filter into which a portion of the melt is continuously fed.
The filter is disposed above and outside the bath.
Continuous removal of sludge from the bath is thus possible.
This has the advantage of a higher productivity of the bath since it is no longer necessary to interrupt the operation.
~ 2~1~
A further advantage lies in that the state of the bath is continuously the same with respect to the sludge content i.e., the minimal sludge content of the bath does not vary over a lengthy period of time. Complete uniformity of the treatment results is thus attained.
The present invention will be further illustrated by way of the accompanying drawings in which:
Fig. 1 is a schematic of an apparatus for effecting the process according to the embodiment of the present invention;
Fig. 2 is a detail of the filter system of Fig. 1 and;
Fig. 3 is a detail of an alternate filter system of Fig. 1.
Referring to Figs. 1 and 2, the salt melt (1) is in a titanium crucible (2). An air compressor (3), for example, an air lift pump with the compressed air contact (4) and the ascending pipe (5) is dipped into the salt melt (1). The salt flow conveyed by the air lift pump (3) passes into the filter system (6) and leaves this system through the discharge pipe (7).
The filter system (6) comprises, for example, a double-walled sheet-iron jacket (8 and 9). The intermediate space is insulated with glass, slag or mineral wool (10) to avoid heat losses and the recrystallization of bath components associated therewith.
A pot of perforated plate (11), into which a sheeth of fine-meshed wire net is inserted (12), is disposed within said insulating jacket.
The liquid salt is pumped into the filter sheeth, which is open at the top. The sludge particles are retained on passing this filter. The purified salt melt leaves the filter system through the discharge system (7). In order to assure that in the case of an obstructed filter, complications due to overflowing of the pot are avoided, an overflow (13) is provided. Filter _~
sheeths filled or obstructed with sludge can be very easily exchanged without having to ~urn off the air lift pump or having to remove it from the bath since the ascending pipe (5) can be rotated about its longitudinal axis towards the bath.
Another feasible embodiment of the sludge removing unit (6) is shown in Figure 3. In this case it consists of a simple box (14), which may also be insùlated to avoid heat losses. Sheet iron barriers (15) of varying heights are disposed in the box (l4). The liquid salt melt conveyed by the air lift pump (3) passes into the first chamber (16) of the sludge-removing unit (6~. When the first chamber (1) is filled the salt melt overflows into the further chambers until it reaches the discharge pipe (7). Since the salt melt must slowly pass through several chambers, it is very quiescent whereby the sludge particles can settle on the bottom. When the chamber is filled with sludge, the viscous sludge can be removed therefrom simply by dumping it out.
The advantages of the process according to the invention are explained in greater detail by means of the Examples hereafter.
Example 1 A crucible furnace with a salt bath crucible of titanium having a diameter of 800 mm and a depth of 1500 mm contains 1100 kg of nitriding salt. At an operating temperature of 580C synchronized bodies of steel C45 having a charge weight of 400 kg are dipped in a rack of 60 kg into the bath as the members to be treated. The time of treatment (residence time in the bath) is one hour, the treatment being performed as a three-shift operation.
In conventional sludge removal the sludge had to be removed four times within the three shifts, i.e., every six hours. Between two sludge removals the content of water-insolu-- ~14~419 ble constituents in the bath varied between 0.017% (immediately after the removal of the sludge) and 0.19% (immediately prior to the next removal of the sludge).
The operation of removing the sludge took 30 minutes in each case, so that within three shifts - taking into account the time required for charging the bath and removing the members - a maximum of 18 charges with 7200 kg could be treated.
When using the process for removing sludge according to the invention and an apparatus according to Figure l and 2, the content of water-insoluble constituents was constant at 0.015%. The filter sheeths could be exchanged during the operation so that a maximum of 20 charges with a total of 8000 kg could be treated.
However, the fact that apart from the increased productivity a distinct improvement of both the quality and the uniformity of the treated material was noticed as a result of the constantly low sludge content is even more important. 540 kg of the bath are passed over the sludge removing unit per hour.
Example 2 A crucible furnace with a salt bath crucible of titanium having a diameter of 600 mm and a depth of 1300 mm contained 550 kg of nitriding salt. The operating temperature was 550C. The members to be treated were crankshafts of steel 42 CrMo 4. The weight of the charge was 240 kg and the weight of the rack 30 kg. The time of treatment (residence time in the bath) was two hours in a two-shift operation.
In this example the sludge was removed after every two charges, requiring 25 minutes. The content of water-insoluble constituents was 0.013% immediately after the removal of the sludge and 0.12~ immediately prior to the next removal of the sludge. When using an apparatus for removing sludge according to the invention corresponding to the Figures 1 and 2, the ~142~19 content of insoluble constituents in the bath could be reduced to a constant value of 0.014% at a throughput of 200 kg of salt melt per hour~ While previously six charges with a total of 1440 kg could be treated within two shifts, seven charges with 1680 kg were treated when applying the continuous sludge removal.
Example 3 A tank furnace having the size of 800 x 600 x 1300 mm was filled with an alkali hydroxide melt as the cooling bath.
The temperature of the bath was 350C.
Members according to Example 2 were dipped into this bath during a treatment time of 10 minutes. By entraining foreign salts and converting the hydroxide the content of insoluble carbonate in`the bath increased, whereby the melting point increased and the cooling effect decreased, resulting in an increase in treatment time.
In conventional sludge removal the bath had to be cooled after some time in two stages and the sludge was removed by means of a screen.
With the apparatus according to the invention, the bath could be kept free from sludge during the entire running time while the entire bath was passed over the sludge removing apparatus once in five hours.
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for removing sludge from a polluted salt bath, in which during the operation of the bath a portion of the salt melt is continuously passed over a filter for purification.
2. A process according to claim 1, in which the total volume of the salt melt is passed over the sludge removing unit during a time period of 1 to 5 hours.
3. A process according to claim 1 or 2, in which the salt bath is a nitriding salt bath.
4. An apparatus for removing sludge from polluted salt bath, including a filter and pump means immersed into the salt adapted to continuously recirculate a portion of salt melt from the bath through said filter, said filter being disposed above and outside the salt bath.
5. An apparatus according to claim 4, in which the pump means includes an air compressor.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19792911222 DE2911222A1 (en) | 1979-03-22 | 1979-03-22 | METHOD AND DEVICE FOR DISCHARGING SALBADES |
| DEP2911222.9 | 1979-03-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1142419A true CA1142419A (en) | 1983-03-08 |
Family
ID=6066098
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000347843A Expired CA1142419A (en) | 1979-03-22 | 1980-03-18 | Process and apparatus for removing sludge from salt baths |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS55161064A (en) |
| AR (1) | AR226055A1 (en) |
| AT (1) | AT367463B (en) |
| BR (1) | BR8001634A (en) |
| CA (1) | CA1142419A (en) |
| DE (1) | DE2911222A1 (en) |
| FR (1) | FR2461018A1 (en) |
| GB (1) | GB2046611A (en) |
| IT (1) | IT7969374A0 (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DD157966A3 (en) * | 1977-08-08 | 1982-12-22 | Siegfried Schelinski | METHOD AND DEVICES FOR FASTENING GLASS PRODUCTS BY ION EXTRACTION |
| EP0089219A3 (en) * | 1982-03-15 | 1984-07-04 | Protectaire Systems Company | Sludge filtration apparatus |
| FR2525491B1 (en) * | 1982-04-23 | 1988-04-29 | Stephanois Rech Mec | FILTER GROUP FOR SALT BATHS |
| DE3733721C1 (en) * | 1987-10-06 | 1988-04-21 | Degussa | Device for the continuous desludging of salt baths |
| DE3836939C1 (en) * | 1988-10-29 | 1989-06-15 | Degussa Ag, 6000 Frankfurt, De | |
| JP3280691B2 (en) * | 1992-02-18 | 2002-05-13 | パーカー熱処理工業株式会社 | Molten salt tank with integrated sludge removal device |
| ATE149223T1 (en) * | 1992-12-30 | 1997-03-15 | Merpro Tortek Ltd | WATER HANDLING SYSTEM |
| ES2138638T3 (en) * | 1994-01-13 | 2000-01-16 | Houghton Durferrit Gmbh | FILTER UNIT AND DEVICE TO UNSOLLATE SALT BATHS. |
| JP3187249B2 (en) | 1994-05-17 | 2001-07-11 | 本田技研工業株式会社 | Sludge removal device |
| CN107875870A (en) * | 2016-09-29 | 2018-04-06 | 内蒙古乌海化工有限公司 | A kind of salt dissolving pond |
| CN106861582B (en) * | 2017-03-07 | 2019-04-19 | 上海煜志机电设备有限公司 | The purification and hydrodynamics fused salt tank of high-temperature liquid state nitrate |
| JP2018187555A (en) * | 2017-05-01 | 2018-11-29 | パーカー熱処理工業株式会社 | Sludge separation apparatus |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE564595C (en) * | 1930-11-21 | 1932-11-21 | Frey & Co W | Method and device for annealing metal objects in a salt bath |
| FR938432A (en) * | 1945-10-01 | 1948-09-15 | Ajax Electric Company | Process and device for the purification of salt baths for heat treatment |
| GB606734A (en) * | 1946-01-17 | 1948-08-19 | Thomas Augustus Goskar | Improvements in or relating to the heat treatment of steel |
| DE866004C (en) * | 1950-08-14 | 1953-02-05 | Ernst Matter | Apparatus for demonstrating objects, in particular for advertising purposes |
| DE1198842B (en) * | 1958-06-03 | 1965-08-19 | Degussa | Method and device for desludging of hot baths in the hardening technique |
| DE1247361B (en) * | 1963-10-02 | 1967-08-17 | Degussa | Device for desludging of molten salts, in particular nitriding balls |
| PL84385B1 (en) * | 1973-01-11 | 1976-03-31 | Polotechnika Wroclawska Breslau (Polen) | |
| NO129964B (en) * | 1973-03-01 | 1974-06-17 | Hydro N | |
| DE2435830C3 (en) * | 1974-07-25 | 1981-11-05 | ARBED-F & G Drahtwerke Köln GmbH, 5000 Köln | Method and device for the production of steel wire |
-
1979
- 1979-03-22 DE DE19792911222 patent/DE2911222A1/en not_active Withdrawn
- 1979-12-11 IT IT7969374A patent/IT7969374A0/en unknown
- 1979-12-26 FR FR7931695A patent/FR2461018A1/en not_active Withdrawn
-
1980
- 1980-03-18 CA CA000347843A patent/CA1142419A/en not_active Expired
- 1980-03-19 BR BR8001634A patent/BR8001634A/en unknown
- 1980-03-20 GB GB8009418A patent/GB2046611A/en not_active Withdrawn
- 1980-03-20 AR AR280375A patent/AR226055A1/en active
- 1980-03-21 JP JP3480780A patent/JPS55161064A/en active Pending
- 1980-03-21 AT AT0153880A patent/AT367463B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| JPS55161064A (en) | 1980-12-15 |
| GB2046611A (en) | 1980-11-19 |
| AR226055A1 (en) | 1982-05-31 |
| BR8001634A (en) | 1980-11-18 |
| DE2911222A1 (en) | 1980-11-06 |
| ATA153880A (en) | 1981-11-15 |
| IT7969374A0 (en) | 1979-12-11 |
| FR2461018A1 (en) | 1981-01-30 |
| AT367463B (en) | 1982-07-12 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |