Claims:We Claim:

1. Spray coating system for steel melting shop such as for slag pot coating comprising:
a main vessel;

a charging port positioned on top of said main vessel for charging coating material comprising sodium silicate, graphite and water in a predetermined ratio in the machine to obtain a spray of the mixture;

a substantially vertically upright discharge pipe located spaced from the base of the main vessel which cooperates with a outlet discharge pipe line for spraying purposes

a compressed air source operatively connected to said main vessel via cooperative compressed air pipelines enabling (i) compressed air supply at the bottom of the vessel such as to generate a circular movement of the spray mix liquid avoiding sedimentation and force the spray mix liquid through said substantially vertically upright discharge pipe towards the top and (ii) forcing the spray liquid mix form said substantially vertically upright discharge pipe via said outlet discharge pipe line for spraying purposes;

said compressed air pipe line and outlet discharge pipe line provided with stop valves to close or open the flow through said lines for desired operating requirements;

a vent valve to release pressure when spraying is over.

2. Spray coating system as claimed in claim 1 comprising

a substantially cylindrical shaped main vessel having a detachable cover;

a charging port with a closable lid positioned on top cover of said main vessel for charging coating material comprising sodium silicate, graphite and water in a predetermined ratio in the machine to obtain a spray of the mixture;

an compressed air inlet pipe disposed from top of the main vessel through cover;

a discharging pipe line with a low pressure supporting compressed air line connected thereto at one end, disposed from top of the main vessel through cover, and a flexible hose connected to the other end for spraying;

said compressed air line and discharge line provided with stop valves to close or open the flow through said lines for desired operating requirements;

a vent valve to release pressure when spraying is over.

3. Spray coating system as claimed in anyone of claims 1 or 2 comprising said compressed air inlet pipe cooperatively connected to a substantially circular shaped pipe at the inside bottom of said main vessel to favour thorough mixing and homogenization of the spray mix by developing a circular motion of the mix under the action of compressed air.

4. Spray coating system as claimed in anyone of claims 1 to 3 wherein the open bottom end of discharge pipe line is disposed inside the main vessel through top cover positioned 70mm above the bottom of the vessel so that the spray mixture rises through the discharge pipe because of the air pressure inside the vessel.

5. Spray coating system as claimed in anyone of claims 1 to 4 wherein said low pressure supporting compressed air line is connected to discharge pipe line through stop valve to provide sufficient pressure required for spraying of coating mixture in a uniform manner.

6. A method of spray coating such as for slag pot coating comprising the steps of

(i) Providing the desired spray mix into said main vessel;
(ii) Operating the said compressed air pipelines connected to said compressed air source and cooperative valves such as to enable (i) compressed air supply at the bottom of the vessel to generate a circular movement of the spray mix liquid avoiding sedimentation and force the spray mix liquid through said substantially vertically upright discharge pipe towards the top and (ii) forcing the spray liquid mix form said substantially vertically upright discharge pipe via said outlet discharge pipe line for spraying purposes.

7. A method of spray coating as claimed in claim 6 comprising,
(i) providing sodium silicate, graphite and water in a predetermined ratio in side main vessel of the machine through the charging port and closing the lid;
(ii) closing the stop valve on discharge line and closing the
pressure release vent valve;
(iii) opening the stop valve on the compressed air inlet line to allow entry of compressed air inside the main vessel to enable thorough mixing of coating materials;
(iv) opening the stop valve on supporting compressed air line followed by opening the stop valve on the discharge pipe line after allowing some time for desired mixing of the spray mix inside the main vessel, thus obtaining desired spray of homogenized coating mix for coating of slag pot.

8. A method of spray coating as claimed in anyone of claims 6 or 7 wherein the compressed air is supplied at pressure range of 4 to 6 kg/cm2, preferably 5kg/cm2.

9. A method of spray coating as claimed in anyone of claims 6 to 8 wherein after spraying is over the spraying valve is put off and pressure release valve is opened and the inlet valve is throttled to a lower pressure, to ensure that the remaining mixture inside the vessel keeps on moving and therefore no sedimentation takes place in bottom.

Dated this the 20th day of August, 2016
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

, Description:FIELD OF THE INVENTION

The invention relates to a spray coating system for spray coating of slag pots used as an integral part of any Steel Melting Shop. More particularly, the present invention is directed to provide a slag pot coating machine which can be used for spray coating of mixed coating material at room temperature in a user friendly manner involving single flexible hose for delivery of coating material comprising sodium silicate, graphite and water charged in the machine to prepare a spray of the mixture aided by compressed air to favour easy removal of slag from slag pot. The machine can be operated and used without any interruption or jamming and free of bottom sedimentation of spray mixture.

BACKGROUND OF THE INVENTION

Basic oxygen furnace is being used for converting Hot Metal into liquid Steel. Hot metal produced in blast furnace contains impurities like Carbon, Silicon, Phosphorous and Sulphur. The typical composition of hot metal is(C=3.8%,Si=0.58 %, Mn = 0.07 %, S=0.055%, P= 0.160 %)

BOF uses pure oxygen having purity more than 99.9%. This oxygen oxidizes the impurities preferentially over iron. Calcined lime is used as a fluxing agent. This helps in formation of suitable slag which keeps P2O5 in slag. The typical slag formed at turndown is as follows:

FeO SiO2 CaO MgO MnO Al2O3 TiO2 P2O5 S Basisity
28.43 10.72 49.9 4.1 0.87 0.6 0.59 3.11 0.24 4.65

At SMS 1 of applicants steel plant maintain slag basicity (ratio of CaO / SiO2) at around 4.0.The typical slag generated is around 8 Tons per blow. Slag pots are being used in Basic Oxygen Furnace Shop for collection of liquid and semi solid slag. Slag pot volume is 11 cubic meter. At the blow end liquid slag is formed and this slag is partially collected in slag pot by tilting the converter in deslagging direction. As slag is lighter than metal it flows over metal and slight inclination of the converter is sufficient to pour slag in slag pot. At this time liquid steel sample and temperature are collected from converter. After this the converter is tilted in tapping direction for taking out liquid steel through the tap hole of converter. The retained slag inside converter is subjected to splashing. During this calcined dolomite is added to increase the slag MgO content. At the end of splashing we get semi solid slag. This semi solid slag is again dumped in slag pot. After every two such blows the slag pot is sent to dumping yard for vacation of slag pot.

For easy removal of slag form slag pot it is coated with a mixture of graphite powder, water and sodium silicate.

Existing spray coating machines at steel melting shop is having top charging and bottom slurry discharging system. The Mixing of water, sodium silicate and graphite powder has been comes out of slag coating machine in the form of slurry under pressure of compressed air. The slurry mixture is taken out through a nozzle placed at the bottom by pressurizing the vessel by compressed air. Another compressed air pipe is connected to this slurry discharge pipe through a “Y” nozzle, to create spray of material for coating purpose. This machine has two main problems.
• Bottom sedimentation of spraying mixture leading to frequent jamming of outlet nozzle. This results in wastage of mixture and poor quality of spray
• Handling of two numbers of flexible hoses and their frequent raptures leads to poor spray.

There has been thus a persistent need in the steel melting shop to develop an improved slag pot coating machine which would be user friendly and easy to operate avoiding any problem of jamming or chocking so that the slag pot coating function can be accomplished in an uninterrupted manner.

OBJECTS OF THE INVENTION

The basic object of the present invention is thus directed to provide a spray coating system for spray coating of slag pot in a user friendly manner using only one flexible hose without the problem of bottom sedimentation of spray mixture within the machine and jamming/chocking of spray nozzle.

A further object of the present invention is directed to provide a slag pot coating machine for spray coating of slag pot wherein spray mixture is more homogeneous resulting in improvement in spray quality and no wastage of mixture material due to jamming of outer nozzle.

A still further object of the present invention is directed to provide a slag pot coating machine for spray coating of slag pot with spray mixture which would help sharp improvement in damages or rejection of slag pots due to drastic reduction of Jamming of slag pot.

A still further object of the present invention is directed to provide a slag pot coating machine for spray coating of slag pot with spray mixture which would favour eliminating damage due to hammering of slag pot and wastage of coating material due to jamming and thus effecting substantial financial saving.

Another object of the present invention is directed to a slag pot coating machine for spray coating of slag pot with spray mixture which would ensure easy dumping of slag from slag pot due to improved coating and thus increased availability of slag pots.

Yet another object of the present invention is directed to a slag pot coating machine for spray coating of slag pot with spray mixture which would avoid loss/wastage of coating materials due to jamming of outlet pipe or bottom jamming of mixing vessel.

An yet further object of the present invention is directed to a slag pot coating machine for spray coating of slag pot with spray mixture which would avoid slag pot hammering and consequent need for stringent maintenance of hammering crane engaged for long hammering operation.

A still further object of the present invention is directed to a slag pot coating machine for spray coating of slag pot with spray mixture favour improved safety and housekeeping avoiding any spillage of spraying mix or rupture of compressed air hose in case of jamming/chocking.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a spray coating system for steel melting shop such as for slag pot coating comprising:
a main vessel;

a charging port positioned on top of said main vessel for charging coating material comprising sodium silicate, graphite and water in a predetermined ratio in the machine to obtain a spray of the mixture;
a substantially vertically upright discharge pipe located spaced from the base of the main vessel which cooperates with a outlet discharge pipe line for spraying purposes;

a compressed air source operatively connected to said main vessel via cooperative compressed air pipelines enabling (i) compressed air supply at the bottom of the vessel such as to generate a circular movement of the spray mix liquid avoiding sedimentation and force the spray mix liquid through said substantially vertically upright discharge pipe towards the top and (ii) forcing the spray liquid mix form said substantially vertically upright discharge pipe via said outlet discharge pipe line for spraying purposes;

said compressed air pipe line and outlet discharge pipe line provided with stop valves to close or open the flow through said lines for desired operating requirements;

a vent valve to release pressure when spraying is over.

A further aspect of the present invention is directed to said spray coating system comprising

a substantially cylindrical shaped main vessel having a detachable cover;

a charging port with a closable lid positioned on top cover of said main vessel for charging coating material comprising sodium silicate, graphite and water in a predetermined ratio in the machine to obtain a spray of the mixture;

an compressed air inlet pipe disposed from top of the main vessel through cover;

a discharging pipe line with a low pressure supporting compressed air line connected thereto at one end, disposed from top of the main vessel through cover, and a flexible hose connected to the other end for spraying;

said compressed air line and discharge line provided with stop valves to close or open the flow through said lines for desired operating requirements;

a vent valve to release pressure when spraying is over.

A still further aspect of the present invention is directed to said spray coating system comprising said compressed air inlet pipe cooperatively connected to a substantially circular shaped pipe at the inside bottom of said main vessel to favour thorough mixing and homogenization of the spray mix by developing a circular motion of the mix under the action of compressed air.
Another aspect of the present invention is directed to said Spray coating system wherein the open bottom end of discharge pipe line is disposed inside the main vessel through top cover positioned 70mm above the bottom of the vessel so that the spray mixture rises through the discharge pipe because of the air pressure inside the vessel.
Yet another aspect of the present invention is directed to said Spray coating system wherein said low pressure supporting compressed air line is connected to discharge pipe line through stop valve to provide sufficient pressure required for spraying of coating mixture in a uniform manner.

A further aspect of the present invention is directed to a method of spray coating such as for slag pot coating comprising the steps of

(i) Providing the desired spray mix into said main vessel;
(ii) Operating the said compressed air pipelines connected to said compressed air source and cooperative valves such as to enable (i) compressed air supply at the bottom of the vessel to generate a circular movement of the spray mix liquid avoiding sedimentation and force the spray mix liquid through said substantially vertically upright discharge pipe towards the top and (ii) forcing the spray liquid mix form said substantially vertically upright discharge pipe via said outlet discharge pipe line for spraying purposes.

A still further aspect of the present invention is directed to said method of spray coating comprising,
(i) providing sodium silicate, graphite and water in a predetermined ratio in side main vessel of the machine through the charging port and closing the lid;
(ii) closing the stop valve on discharge line and closing the
pressure release vent valve;
(iii) opening the stop valve on the compressed air inlet line to allow entry of compressed air inside the main vessel to enable thorough mixing of coating materials;
(iv) opening the stop valve on supporting compressed air line followed by opening the stop valve on the discharge pipe line after allowing some time for desired mixing of the spray mix inside the main vessel, thus obtaining desired spray of homogenized coating mix for coating of slag pot.

A still further aspect of the present invention is directed to said method of spray coating wherein the compressed air is supplied at pressure range of 4 to 6 kg/cm2, preferably 5kg/cm2.
A still further aspect of the present invention is directed to said method of spray coating wherein after spraying is over the spraying valve is put off and pressure release valve is opened and the inlet valve is throttled to a lower pressure, to ensure that the remaining mixture inside the vessel keeps on moving and therefore no sedimentation takes place in bottom.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

Figure 1: shows a schematic diagram of existing spray coating machine for slag pots.
Figure 2: shows a schematic diagram of prior art machine indicating the problematic area.
Figure 3: shows the schematic diagram of the modified and improved slag pot spray coating machine according to the present invention indicating various components used in the machine.
Figure 4: is a photographs of the spray coating machine according to the present invention for coating of slag pots showing an outside view of the actual machine.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS
The present invention is directed to a spray coating system for spray coating of slag pot in a user friendly manner using a single flexible hose with nozzle for spraying coating material without the problem of bottom sedimentation of spray mixture within the machine and jamming/chocking of spray mix inside vessel/nozzle.

Existing spray coating machines at steel melting shop is having top charging and bottom slurry discharging system. Figure 1 shows the schematic diagram of the spraying machine before modification. The Mixing of water, sodium silicate and graphite powder is done within the vessel that comes out of slag coating machine in the form of slurry under pressure of compressed air. The Pressure of compressed air is about 5 Kg/cm2. The slurry mixture is taken out through a nozzle placed at the bottom by pressurizing the vessel by compressed air. Another compressed air pipe is connected to this slurry discharge pipe through a “Y” nozzle. For the operation of machine first Valve no 4 is made off. Then the charging lid is opened to put water, sodium silicate and graphite powder in a pre determined ratio.

The existing machine thus suffers from the following two main problems:
(i) Bottom sedimentation of spraying mixture leading to frequent jamming of outlet nozzle. This results in wastage of mixture and poor quality of spray.
(ii) Handling of two numbers of flexible hoses and their frequent raptures leads to poor spray.

Accompanying Figure 2 shows a schematic diagram of prior art machine indicating the problematic area showing bottom sedimentation and resultant chocking of the outlet nozzle and delivery pipe creating interruption in slag pot spray coating process.

To overcome the above problems, a modified and improved slag pot coating machine is developed by way of the present invention.

Accompanying Figure 3 shows the schematic diagram of the modified and improved slag pot spray coating machine according to the present invention indicating various components used in the machine.
It can be seen from Figure 3 that the machine contains a substantially cylindrical shaped main vessel(7) made of steel founded on floor on supporting legs and having an openable cover(7a).

In this modified machine, provision is made for both charging and discharge of spray mix material through top cover. The charging port(8) with lid is provided at top cover of main vessel to put water, sodium silicate and graphite powder in a pre determined ratio. Then this lid is tightly closed. To operate the machine, the vent valve (1) is also closed and compressed air inlet stop valve (2) on inlet air pipe (5) is opened. Then after 10 minutes stop valve (3) is opened which enable entry of compressed air in the main vessel at bottom portion through a circular shaped pipe(9) favouring through mixing and homogenization of the spray mix materials and followed to this the stop valve (4) on discharge pipe is also opened. Then spray coating is started.

Thus to improve the performance of the machine following modification have been made:

Modification No.1:-

The inlet compressed air pipe(5) has been modified. It has been given a circular shape(9) at bottom to generate a circular movement of the spray mix liquid. This results in more homogenization of mixture. After spraying we put off the spraying stop valve(4) on discharge pipe line(10) and open the pressure release vent valve(1) and throttle the inlet valve(2) to a lower pressure. This ensures that the remaining mixture inside the vessel keeps on moving and therefore no sedimentation will take place in bottom.

Modification No. 2:-

The outlet nozzle at the bottom has been removed and outlet pipe(10) has been put through top. The outlet pipe(10) has a clearance of 70 cm from bottom of vessel. Because of the pressure in the vessel, the mixture rises through the discharge pipe(10). There is also connected a low pressure pipe(11) to the outlet pipeline(10) just above spray machine which is supporting compressed air line to facilitate discharge of spray mix. This provides sufficient pressure required for spraying. This arrangement has also eliminated the requirement of another compressed air hose which was joined in existing machine to the slurry pipeline through a “Y” nozzle. This arrangement has eliminated the problem of handling two hoses and coating material can be sprayed by using only one hose(12). Through this discharge pipe(12) a mixture of water, sodium silicate, graphite powder, and air, is obtained as spray favouring uniform and durable spray coating of slag pot in an uninterrupted manner.

Thus by way of the present invention following benefits can be achieved:
(a) TECHNICAL/TECHNOLOGICAL BENEFITS: Spray mixture is more homogeneous. No wastage of mixture material due to jamming of outer nozzle. Spraying of mixture can be performed using only one flexible hose. So the job becomes very easy to carry out. Jamming of slag pot has drastically reduced thus there is a sharp reduction in damages or rejection of slag pots.

(b) ECONOMIC ADVANTAGE: The spray mixture has become more uniform thus the quality of spray has improved drastically. Cost of one slag pot is about 45 Laks. Hammering of slag pot has drastically reduced after innovation and modification. The wastage of material has been eliminated completely. In old machine we have to clean the bottom jam of approx 50 kg after handling 300 to 400 kg of graphite powder. The cleaning requires at least 5 hrs of shut down. If the jamming took place during spraying then complete mixture has to be thrown away before cleaning.

(c) IMPACT IN INDUSTRY: Slag pot can be easily dumped so the availability of slag pot has been improved. There is less damage to hammering crane and slag pot. Similar usage of slag pot can be adopted in other steel industries.

(d) MATERIAL LOSS: At many instances the jamming of outlet pipe causes wastage of entire coating mixtures as it has to be thrown away for cleaning of tank and pipeline. Also in old machine the bottom jam of approx 50 kg need to be cleaned after handling 300 to 400 kg of graphite powder.

(e) EQUIPMENT LOSS: Because of poor homogenization of mixture material and frequent breakdown / choakage of spraying machine in existing practice, there are a large number of instances where there occurred insufficient or no coating of slag pot. In that case the pots are subjected to severe hammering. This leads to damages or even rejection of slag pots. Also the slag pot hammering crane needs more stringent maintenance for long hammering operation.

(f) HOUSEKEEPING & SAFETY: In conventional machine, two hoses are required to be handled for spraying and in case of any jamming in spraying the compressed air pipe line hose get burst causing spillage of spraying mixture while cleaning the discharge outlet needs separate attention for housekeeping. This type of problems are eliminated by the new machine.

It is thus possible by way of the present invention to provide a slag pot spray coating machine which can be used for spray coating of mixed coating material at room temperature in a user friendly manner involving single flexible hose for delivery of coating material comprising sodium silicate, graphite and water charged in the machine to prepare a spray of the mixture aided by compressed air to favour easy removal of slag from slag pot. The machine can be operated and used without any interruption or jamming and free of bottom sedimentation of spray mixture.