Title of Invention

"A PROCESS FOR SUBSTRATE PREPARATION FOR POWDER COATING OF GALVANIZED SHEET"

Abstract A process for the manufacture of substrate for powder coating of the galvanised sheet for use in a refrigeration appliance comprising a two stage process of degreasing and rinsing. The process involves two pair of tanks. Tank I & II contains the solution of Iron Phosphate and demineralized water in a particular temperature and concentration. Tank III contains raw water for rinsing off the extraneous Iron Phosphate and tank IV contains demineralized water to meet all the quality specifications.
Full Text FIELD OF INVENTION:
The present invention relates to the process for the manufacture of substrate for powder coating of the galvanised steel used in the refrigeration appliance.
More specifically, it is a 2-stage process for the manufacture of substrate for powder coating of the galvanised steel used in the refrigeration appliance.
Prior Art:-
Conventionally, a process for the manufacture of substrate for powder coating of the cold rolled cold annealed (CRCA) or galvanised (Gl) steel is a 7-stage process to be used for refrigeration appliance. The 7-stages of the conventional process are:
1. Knock -off degreasing
2. Normal water rinsing
3. Activation
4. Zinc phosphating
5. DM water rinsing
6. Passivation
7. DM water rinsing
The knock off degreasing in the conventional process of the sheet is done in a tank with the alkaline base caustic free - Tri-Sodium Phosphate (Ridoline -1352-WI) at a temperature of 50-60°C having a concentration of 2-3% kg/volume. This sheet is again degreased in an adjacent tank with the caustic (Ridoline - 1352-h6) at a temperature of 50-60°C. having a concentration of 2-3% kg/vol. The degreased sheet is then rinsed twice in two different tank with raw water for a time period of 1 minute. The degreased and rinsed sheet is surface activated by the chemical base titanium phosphate (KEM Activator & D.M. water) at a concentration of 0.3% kg/vol. at a pH of 9.0 to 10.5 at an

ambient temperature. The sheet is further put in a phosphating bath containing the chemical base-di-cation phosphate (Ni) acid (KEM-KOTE-315 W and an accelerator (sodium nitrite base) at a concentration of 3% and a temperature of 30°C. The rinsing III is done maintaining the contamination level 5.0 ml max and rinsing IV is done maintaining the contamination level at 1.5 ml max. These rinsings are done with a neutraliser (caustic soda) to decrease the 0.1 ml free acid. The sheet is then passivated by the chromium salt (Cr3+) at a concentration of 0.1% vol. at a pH 3-4. The sheet is again rinsed in demineralised water for 1 minute. The 7 stage process is then followed by water drying, powder coating and curing of powder paint.
In the traditional process the zinc phosphating step generates lots of industrial effluent which needs to be subsequently treated in Effluent Treatment Plant.
The conventional process also gives very less bare metal salt spray and low humidity life of the components, is susceptible to corrosion and is a tedious process.
The conventional process also has a major constraint of increasing the conveyor speed. The existing line speed of 3 m/min generates 1.5 min max. time (due to tank size restriction) for substrate preparation in degreasing/activation/zinc phosphating, which is the minimum time required for desired surface treatment to meet all the quality specifications. Any increase in conveyor speed would result in further decrease in substrate preparation time thus deteriorating the treatment quality or it will require a major modification in the complete pre-treatment line resulting in huge investment.
Therefore, there is a need to develop a process to overcome the above mentioned drawbacks.

Therefore it is an object of the subject invention to increase the capacity by making it a 2 step process of degreasing and water rinsing and deleting the steps of activation, phosphating and passivation steps inturn increasing the conveyor speed .
It is an object of the present invention to reduce the industrial effluent generation to minimum. The present invention eliminates the use of zinc phosphate, activation and passivation which reduces the effluent generation to 90%.
It is also an object of the present invention to increase the Bare Metal Salt spray and humidity life of refrigerator cabinet and door panel.
The subject invention ensures a good bare metal corrosion salt spray life of about 200hrs. as compared to 24hrs. (for CRCA) & 72 hrs. (for Gl) as in the traditional process. This is made possible by doing a trivalent chromium organic coating on the sheet prior to substrate preparation followed by a 2-stage process including only degreasing and water rinsing and also making the subsequent changes in powder coating and curing process to achieve better results.
In the present invention the conventional 7 step process has been reduced to a 2 step novel process of degreasing and water rinsing thus increasing the conveyor speed by 15-20%.
In the said invention only degreasing chemical iron phosphate (Duridine) is used with 3-5% concentration in DM water and does not require any major waste treatment process. The tank can be discarded once in a month and the daily load on the ETP (effluent treatment plant) is in turn reduced to almost nil form the paint shop.

; ^
Moreover the phosphate and chromium content in the total effluent generation will be very small and within the acceptable limits of pollution norms. The present invention will result in annual financial savings on account of pre-treatment chemical cost saving, energy (fuel and electricity) savings, effluent treatment plant savings, there is no rust in press shop due to inceased bare metal corrosion properties, enhances the capacity, demineralised water savings, decrease in line rejections due to better process control.
SUMMARY OF THE INVENTION:-
The present invention relates to the process for the manufacture of substrate for powder coating of the galvanised steel sheet used in the refrigeration appliance. It is a 2-stage process involving :
i) Knock off- Degreasing I and II ii) Rinsing I and II
to be conducted in two pairs of tanks having the overhead conveyor belt system.
The process starts with the degreasing of the galvanised steel in Tank 1 which contains the acidic base iron phosphate and demineralised water in 3-5% concentration at a temperature of 40 - 60° C for about 1 -2 mins. The degreased sheet is again degreased in an adjacent tank II containing the acidic base iron phosphate and demineralised water in 4% concentration at a temperature of 40 - 60 °C for about 1 -2 mins to minimize the contamination level of the galvanised steel sheet. This degreased sheet is then rinsed with raw water for a time period of about .2 - .7 mins in the Tank III. In Tank IV it is further rinsed with demineralised water for a time period of .5 mins and dried in the drying oven.
the subject invention may better be understood with reference to accompanying drawings. However, the same should not be construed to restrict the scope of the application as they are for illustrative purposes only.
BRIEF DESCRIPTION OF THE DRAWINGS:-1. Fig. 1 Block diagram of the subject invention DETAILED DESCRIPTION OF THE INVENTION:-
The invention describes a process for the manufacture of substrate for powder coating of the galvanised steel used in the refrigeration appliance. The subject invention reduces the industrial effluent generation by almost 90%. Iron phosphate imparts corrosion resistance to the galvanised steel. The invention involves 2-step process which includes - Knock-off Degreasing and rinsing and requires two pairs of tanks having overhead conveyor belt system.
Knock-off Degreasing I & II involves the washing of the refrigerator cabinet and door panel made of galvanised steel moving on a conveyor belt in a chamber connected to the tank through a pipe. The acidic bath containing the iron phosphate (trade name Duridine 3965) at a temperature of 40-60°C. having the concentration of 3-5% kg/volume at a pointage 25+/- 5 ml with addition per pointage is 5.5 kg is pumped and sprayed through the nozzels over the refrigeration appliance moving in a conveyor belt for a time period of about 1-2 minutes. The temperature is controlled in the tank by plurality of heaters having the temperature indicator. This step reduces the impurities of the sheet to some extent. This is verified by taking 10 ml sample and adding to this 2-3 drops of methyl orange indicator and further titrated with N/10 H2SO4 to pink end point. The frequency of verification is twice per shift. To ensure the minimum contamination level the degreasing of the refrigerator
appliance is repeated with the same parameters of the solution, temperature, concentration, time, pointage .process steps and verification.
The degreased sheet free of contamination is the rinsed with raw water for a time period of 0.5 minutes in a tank to remove the acidic base Iron Phosphate. The raw water is sprayed from Tank III through a pipe fitted with a pump. The contamination level is 5.0 ml maximum. This is verified by taking 100 ml sample and adding to this 2-3 drops of methyl orange indicator and further titrated with N/10 H2SO4 to pink end point . The frequency of verification is once per day.
Rinsing II involves washing of the degreased and rinsed refrigerator cabinet and door panel with demineralised water for a time period of 0.5 minute in another tank in the same manner. The contamination level is 2.5 maximum.This is verified by taking 100 ml sample and further adding white phenolphathalien indicator with N/10 NaOH to red end.
The 2 pair of tanks are connected in series.
The subject invention would require only knock of degreasing and rinsing as substrate preparation prior to powder coating resulting into excellent bare metal salt spray life organic coated galvanised sheet as compared to existing bare CRCA sheet resulting into no rust issue during monsoon (press shop scrap reduction), 90% reduction in effluent generation due to 2-stage pre-treatment process, excellent exposed surface corrosion resistance properties with the use of Gl sheet and much better process control due to simplicity of the pretreatment process. It is also excellent in terms of financial gains and introduction of new technology for the first time in white good industry worldwide.
Accordingly, the subject invention relates to a process for the manufacture of substrate for powder coating of the galvanised sheet for used in refrigeration
appliance comprises a two stage process wherein the stage one the galvanised sheet is first degreased in a acidic bath having iron phosphate of 3 to 5% kg/volume concentration at a temperature of 40-60°C for a period of 1 to 2 minutes, and then the said degreased sheet is again degreased in an adjacent acidic bath having a iron phosphate composition of 3-5% kg/volume concentration at the temperature of 40-60°C for a period of 1-2 minutes, in stage two the twice degreased sheet is rinsed in bath for a period of 0.4 to 1.0 minute with raw water, the rinsed sheet is further rinsed in another bath for a period of 0.4 to 1.0 minute with demineralised water to obtain the substrate.
In the present process the concentration of the iron-phosphate is preferably 4% kg/volume.
In the present process the pointage of said sample is maintained at 25+7-5 ml with addition per pointage is 5.5 kg and the time required for degreasing the sheet is preferably 1-1.5 minutes and that for rinsing is preferably 0.5 minute.
Accordingly the present invention is relates to a process for the preparation of substrate for powder coating of the galvanised sheet for used in refrigeration I appliance comprises a two stage process wherein stage one the galvanised sheet is first degreased in a acidic bath having iron phosphate of 3 to 5% kg/volume concentration at a temperature of 40-60°C for a period of 1 to 2 minutes, and then the said degreased sheet is again degreased in an adjacent acidic bath having a iron phosphate composition of 3-5% kg/volume concentration at the temperature of 40-60°C for a period of 1-2 minutes, in stage two the twice degreased sheet is rinsed in bath for a period of 0.4 to 1.0 minute with raw water, the rinsed sheet is further rinsed in another bath for a period of 0.4 to 1.0 minute with demineralised water to obtain the substrate.
EXAMPLE I:-
The refrigeration appliance is taken to the tank with overhead conveyor belt system containing the 2-5% kg/volume concentration of acidic base iron phosphate in DM water at a temperature of 52°C. for .5-1.5 minute for knock-off degreasing. The degreased galvanised refrigeration appliance is again degreased in an adjacent tank containing the 4% kg/volume concentration of acidic base iron phosphate in DM water at a temperature of 52°C. for .5-1.5 minute. The degreased appliance is then rinsed in a tank containing the raw water for a time period of 0.5 minutes which is further rinsed in an adjacent tank containing the DM water.
EXAMPLE 2:-
The refrigeration appliance is taken to the tank with overhead conveyor belt system containing the 3-6% kg/volume concentration of acidic base iron phosphate in DM water at a temperature of 55°C. for 1-2.5 minute for knock-off degreasing. The degreased galvanised refrigeration appliance is again degreased in an adjacent tank containing the 4% kg/volume concentration of acidic base iron phosphate in DM water at a temperature of 55°C. for 1-2.5 minute. The degreased appliance is then rinsed in a tank containing the raw water for a time period of 2.5 minutes which is further rinsed in an adjacent tank containing the DM water for .5 minutes.




WE CLAIM:
1. A process for the preparation of substrate for powder coating of the
galvanised sheet for used in refrigeration appliance comprises a two stage
process wherein stage one the galvanised sheet is first degreased in a acidic
bath having iron phosphate of 3 to 5% kg/volume concentration at a
temperature of 40-60°C for a period of 1 to 2 minutes, and then the said
degreased sheet is again degreased in an adjacent acidic bath having a iron
phosphate composition of 3-5% kg/volume concentration at the temperature
of 40-60°C for a period of 1-2 minutes, in stage two the twice degreased
sheet is rinsed in bath for a period of 0.4 to 1.0 minute with raw water, the
rinsed sheet is further rinsed in another bath for a period of 0.4 to 1.0 minute
with demineralised water to obtain the substrate.
2. A process for preparation of substrate for powder coating as claimed in
claim 1 wherein the concentration of the iron-phosphate is preferably 4%
kg/volume.
3. A process for preparation of substrate for powder coating as claimed in
claim 1 wherein the pointage of said sample is maintained at 25+/--5 ml.
4. A process for preparation of substrate for powder coating as claimed in
claim 1, wherein the acid point of the sample is maintained at pink end point.
5. A process for preparation of substrate for powder coating as claimed in
claim 1 wherein the time required for degreasing the sheet is preferably 1-1.5
minutes.
6. A process for preparation of substrate for powder coating as claimed in
claim 1, wherein the time taken for rinsing is preferably 0.5 minute.
7. A process for preparation of substrate for powder coating as claimed in
claim 1, wherein the acid point of the sample is maintained at red end.
8. A process for preparation of substrate for powder coating of the
galvanised sheet for used in refrigeration appliance, substantially as
hereinbefore described with reference to the foregoing examples and
accompanying drawings.

Documents:

533-del-2002-abstract.pdf

533-del-2002-claims.pdf

533-del-2002-correspondence-others.pdf

533-del-2002-correspondence-po.pdf

533-del-2002-description (complete).pdf

533-del-2002-drawings.pdf

533-del-2002-form-1.pdf

533-del-2002-form-19.pdf

533-del-2002-form-2.pdf

533-del-2002-form-26.pdf

533-del-2002-form-3.pdf


Patent Number 197399
Indian Patent Application Number 533/DEL/2002
PG Journal Number 51/2007
Publication Date 21-Dec-2007
Grant Date 08-Oct-2007
Date of Filing 06-May-2002
Name of Patentee WHIRLPOOL OF INDIA LIMITED
Applicant Address 7TH FLOOR, ATMA RAM HOUSE, 1, TOLSTOY MARG, NEW DELHI - 110001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 RITESH BHATIA WHIRLPOOL OF INDIA LIMITED, 28, N.I.T. FARIDABAD-121001, HARYANA, INDIA.
2 VIJAY SABHARWAL WHIRLPOOL OF INDIA LIMITED, 28, N.I.T. FARIDABAD - 121001, HARYANA, INDIA.
PCT International Classification Number C09D5/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA