The present invention relates to advanced Hard Chrome Plating Process
inside Barrel bore of Small Arms Weapon by using forward – reverse
current.
Following defects is always occurred in existing technology:
i. Coating peeled off
ii. Coating chip off
iii. Insufficient coating thickness
iv. Absence of coating
v. Uneven coating thickness
vi. Rough coating deposition
vii. Dual color coating
viii. Scratches in coating
ix. Dent
x. Pitting
A lot of trials at different parameters have been conducted to remove
aforesaid defects.
…….3.
16 Water Rinsing
17 S/R (Dehydrogenation)
18 Quality Control Inspection

……..4.
SUMMARY OF THE NEW INVENTION:-
The present invention relates to advanced Hard Chrome Plating Process
inside Barrel bore of Small Arms Weapon by using forward – reverse current
Finally it is found that when current is given in forward-reverse direction in
following sequence, these defects don’t occur after processing and proof
firing. Process sequence is given below:
S.N
O
OPERATION REMARK IF ANY
01 S/R Before Electro polishing Bore Inspection : Found O.K.
02 Electro polishing Not Done
03 Hot Water Rinsing Not Done
04 Cold Water Rinsing Not Done
05 Passivation Not Done
06 Cleaning with Hot Water &
Pull Through
Not Done
07 Bore Inspection Not Done
08 Cleaning With solvent & Pull
Throw
Bore Inspection : Found OK
09 Ultra Sonic Cleaning
10 Component Inspection Bore Inspection : Found OK
11 Batch Formation 7.70 Gauge enters up to
10mm from Breech End.
7.70 Gauge enter up to
10mm from Muzzle end.
12 Anodic Cleaning All Parameters are
maintained
13 Neutralization All Parameters are
maintained
14 Etching All Parameters are
maintained
15 Chrome Plating All Parameters are
maintained.

Forward Current
Reverse Current
16 Water Rinsing All Parameters are
maintained
17 S/R (Dehydrogenation) All Parameters are
maintained
18 Quality Control Inspection Found O.K.
I/Note No159/S2/EP/21;Dtd:
29/01/22
Wt. No. – 132/0, Operation
No:
1430:Proof Chamber
1450: Stamp Proof Mark
19 Burnishing, Chamber Polish,
Bore View, Gauging
Found O.K.(01/02/22)
20 Q.C. Submission All Barrels are passed
I/Note No- 164/F/EP/21; Dtd:
02/02/22
Wt. No. – 132/0
a. 06 numbers of MAG Barrels had been chrome plated by using Reversal
Unit with Conventional Chrome Bath. All Barrels were finally passed by
QC. Three numbers of Gun was made by using these six Barrels. These
guns were passed in assembly, Proof Firing and Final Stage Inspection.
b. In this process, Electro polish operation was omitted. As per existing
process Barrels to be chrome plated, should be electro polished prior to
plating for maintaining conversant. Since Electro Chemical solution is
highly viscous so that high temperature (850C) is required & after
Electro Polish operation following operation is also required to obtain
some properties as given below:
…….5

S.
No.
PROCESS Description
01 Electro
Polish
Electro polishing takes place as a result of the
electro chemical removal of a surface layer &
the principles of electro polishing are similar
to those for electroplating. The major
difference concerns the polarity of the work
piece being treated. This process is used for
making convergent of barrel bore.
02 Hot Water
Rinse
Since chemical (highly acidic ) used in electro
polish is very viscous, so a thick layer is
formed inside the bore during operation. To
remove such layer, it is washed by hot water.
03 Cold Water
Rinse
It is used for cleaning.
04 Passivation To protect the surface from corrosion, this
operation is used.
05 Cleaning by
brush & Pull
Through
To remove traces of adhered Electro polish
chemicals on the inner surface of Barrel.
06 Organic
solvent
degreasing
Ultra sonic cleaner is used, in which cleaning
solvent is used.
i. Since there is no need to Electro Polish Operation, so all operations as
mentioned in aforesaid tables are not required.
ii. (a) Saving of electrical energy (to maintained process temperature of
Electro
Polish & Hot water Bath.
(b) Saving of water (no need of cold water, hot water & passivation
Bath).
…..6.

……7.
(c)Saving of Sodium di-chromate (Na2Cr2O7) chemical, which is used
for passivation (Na2Cr2O7 is a hazardous chemical).
(d) Saving of solvent which is used as a cleaning agent after Electro
polish operation.
(e)Reduced load on E.T.P.
(f) Saving of SMH, Cycle time is reduced, Shinning is better.
In this process twenty minutes time is given for forward current (forward
current is responsible for plating) & then after mode is automatically
changed in reverse manner for ten second. After plating reverse current
cleans the surface & it is tendency to escape out the trapped hydrogen on
the surface, so problem of Hydrogen embrittlement will reduced.
Hydrogen Embrittlement is a main cause of chip off inside the Barrel
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF
THE DRAWINGS
BLOCK DIAGRAM
(a. ANODIC CURRENT)
i. BARREL RECEIVED FROM
C.W.D.
ii. BURNISHING
iii. CHAMBER ADUSTMENT
iv. CLEANING BY SOLVENT
vi. ELECTROPOLISH
v. STRESS RELIEVING
vii. HOT WATER RINSE

DETAILED DESCRIPTION OF THE SEVERAL VIEWS OF
THE DRAWINGS
i. BARRELS RECEIVED FROM CWD : There is a section in factory
named as CWD(Components work depository Section), which
collects different components from different sections & distributes
such components in respective sections where next operation to be
carried out.
ii. BURNISHING: For cleaning inside the barrels there are burnishing
machine. It works on reciprocating motion principle. Emery paper of
grit size-80 is used for this purpose.
……..8.
viii. PASSIVATION
ix. COLD WATER RINSE
x. OILING
xi. CLEANING BY SOLVENT
xii. BATCH MAKING
xiii. LOADING IN FIXTURE
xiv. ANODIC CLEANING
xv. RINSING IN COLD WATER
xvi. NEUTRALIZATION
xvii. DM WATER RINSING
xviii. ETCHING

……..9.
iii. CHAMBER ADJUSTMENT: Prior to chrome plating inside the barrels,
chamber gauges are maintained.
iv. CLEANING BY TCE: To remove oil, grease etc prior to plating,
components are cleaned by degreasing solvent.
v. STRESS RELEIVING: Stress developed by machining operation is
released by baking the components at the temperature 2000C for
two hours.
vi. ELECTROPOLISH: Electro polishing takes place as a result of the
electro chemical removal of a surface layer & the principles of
electro polishing are similar to those for electroplating. The major
difference concerns the polarity of the work piece being treated.
When electro polishing , the work piece is positively charged, which
is achieved by electrically connecting the item being processed to a
source of direct current whilst immersed in a chemical
solution(Mainly ortho phosphoric acid). This solution, usually acid
based, is referred to as an electrolyte & its composition will depend
on the metal being treated. The electro chemical circuit is
completed by metal cathodes (negative), which are also immersed
in the electrolyte solution.
A rectifier which converts alternating current into direct current
is the usual means of providing the anodic & cathodic current.
Metal is dissolved from the anodic part. Almost immediately large
quantities of oxygen are liberated at the surface of the part,
forming a dense gaseous layer. Because of the tendency of
electrical current to flow from points & projections, these areas are
dissolved preferentially. Resulting in a smoothing of the surface.
The viscous boundary layer that forms as a result of the gaseous
contributes to the preferential dissolution of peaks & the
projections. The process is optimized by control of the solution
chemistry, temperature, current density & time. Electro polishing

…….10.
solutions are highly acidic & corrosive, requiring the use of
corrosion resistant equipment & close attention to worker safety.
vii. HOT WATER RINSE: This process is carried out after electro
polishing operation. In electro polishing operation, solution used is
very viscous & it makes a thick film layer on the surface of bore.
Since this chemical should be removed for next operation.
Components is dipped in hot water tank so that solution adhered on
the surface can be removed.
viii. COLD WATER RINSE: the purpose of this operation is only for
cleaning. This is process requirement for next operation.
ix. PASSIVATION: After electro polish, surface is free from any oxide
layer. It is chance to form corrosion layer when components will put
in any environment. To protect the surface from corrosion,
components are dipped in sodium dichromate solution (2% w/v &
Temp. – 550C). This solution gives nascent oxygen & since nascent
oxygen having tendency of high reactivity so it makes a uniform
layer of oxide inside the bore. This is why no corrosion will occur in
any environment.
x. OILING: To protect the components from environmental corrosion.
xi. CLEANING BY SOLVENT: To remove oil, grease etc prior to plating,
components are cleaned by degreasing solvent.
xii. BATCH MAKING: To maintain coating thickness, a batch of eight
barrels are made having same bore size.
xiii. LOADING IN FIXTURE: Components are loaded in fixture for plating
operation.
xiv. ANODIC CLEANING: Alkaline cleaners remove organic type soils and
have less effect on inorganic soils such as oxides, scale and rust,
though many of these may also be removed if they are embedded in
the organic soils because they are lifted out with them. Alkaline
cleaners work through the processes of saponification,

…….11.
emulsification, solubilization, and preferential wetting. Alkaline
cleaners should be water-soluble and their solutions should wet the
surface being cleaned, and preferentially wet and penetrate the soil
to be removed. They should be temporarily able to emulsify and
suspend solid particles in solution without re-depositing them on
the metal surface; and they should be able to solubilize or bring into
solution those soils capable of dissolving in a reasonable length of
time. They should be able to soften water, rinse freely, not attack or
tarnish the metal surface being cleaned, have a high buffering
capacity, i.e., tolerate drag-in of acid substances introduced with
the metal without change of pH; and they should not form excessive
foam during cleaning or rinsing. In alkaline soak cleaning, the parts
are immersed in tanks of hot alkaline cleaning solution.
Concentration and temperature of the cleaner should be as high as
possible considering the nature of the work, in order to minimize
the time for satisfactory cleaning.
xv. RINSING IN COLD WATER: water rinse is used for cleaning of
components.
xvi. NEUTRALIZATION: Since Alkaline solution has tendency to convert
hexavalent chrome into trivalent chrome so before reverse etching,
components are dipped in sulfuric acid (1% v/v & temp: 600C) so
that traces of alkaline solution could be neutralized.
xvii. D.M. WATER RINSING: To remove last traces of impurities.
xviii.ETCHING: Reverse etch is used for the final removal of oxides
before chrome plating. The final operations before chrome plating is
usually a reverse etch in either a chromium plating solution or a
solution of sulfuric acid. This operation removes the last traces of
oxides, left on the surface after the cleaning operation; activates the
surface of the metal (remember that the initial layer of chrome
plate is sometimes very difficult to deposit, and, most importantly,

………12.
contributes to good adhesion of the chrome plate.) Chromic acid
reverse etches are operated at the temperature and concentration
of the plating bath. There is danger on some parts of producing a
rough deposit if the etch is prolonged much beyond the desired
time, which is dependent upon the base metal alloy being plated.
BLOCK DIAGRAM:
(b. CATHODIC CURRENT)
A. CHROMIUM PLATING
B. DRAG OUT IN DM WATER
C. CHROME KILL
D. COLD WATER RINSE
E. UNLOADING AND CHECKING BY GAUGE
F. STERSS RELIEVING (DEHYDROGENATION)
G. BORE ADJUSTMENT
H. GLOSSING
I. QC INSPECTION
J. SAND BLASTING
K. CD IN QC (HT)
L. PROOF FIRING (SQAE)
M. CD IN PROOF RANGE
N. BURNISHING

A. CHROME PLATING: Chromium is the hardest of the most commonly
deposited metals. Hard chrome is used as a wear resistant coating not
only on steel but also on a wide variety of other metals.

B. DRAG OUT IN D.M. WATER: To remove adhered chrome solution on
the surface of barrels.
C. CHROME KILL: Chrome-Kill (Sodium meta bi sulphide Na2S2O5) can be
used in the final rinse tank to remove the last traces of the chrome
bath, which can later bleed out and stain the parts. Time of contact
between the work and the rinse must be sufficient to remove all
chemical films; for immersion rinses with air agitation this is usually
around 30 - 60 seconds. Another advantage of using Chrome-Kill as the
final rinse is that it operates hot and therefore the parts will air dry
quickly without requiring a separate drying operation.
D. COLD WATER RINSE: For cleaning the components.
E. UNLOADING & CHECKING BY GAUGES: To ensure that plating
thickness is achieved as per required.
………13.
CHROME PLATING CURRENT – 35 AMP/dm2
(Each MAG
Barrel)
TIME -- 2.20 HOURS(7.70
RUN)
TEMP. (OC) -- 55
SP. GRAVITY (OBe) – 21 - 22
Bath Composition CrO3 225-275g/l
SO4
-- 2.25 – 275g/l
Iron Oxide 0-20 g/l
Cr2O3 0-18 g/l
Total Oxide 0-38 g/l
O. QC INSPECTION
Q. DISPATCH

F. STRESS RELEIVING(DEHYDROGENATION): A proven method of
removal of hydrogen is baking after plating. Thermal treatment of
metals for specified times (16 to 18 hrs.) & temperature (2000C) is
driven the hydrogen out from the metal surface & relieve stresses.
G. BORE ADJUSTMENT: Bore is adjusted as per process layout.
H. GLOSSING: To make shining in the chamber of the Barrels, Glossing is
done from breach end side of the Barrel.
I. Q.C.INSPECTION: Q.C. Examiner checks the Barrel’s quality as per
drawing & layout.
J. SAND BLASTING: Before crack detection test, barrels are shined by
sand blasting operation.
K. CRACK DETECTION TEST: To ensure that there are no any cracks on the
outer surface of barrel before high pressure proof, crack detection test
is required.
L. PROOF FIRING: To check ability of barrels to wear pressure load, one
high pressure proof firing is done in each barrel.
M.C.D. IN PROOF RANGE: To ensure that there are no any cracks on the
outer surface of barrel after high pressure proof, crack detection test is
required.
N. BURNISHING: To clean the Barrel bore.
O. Q.C. INSPECTION: Q.C. Examiner checks the Barrel’s quality as per
drawing & layout.
P. DISPATCH: Barrels are collected by CWD(Component Work Depository
Section) & it is sent to next section by CWD.
…….14

INVENTED PROCESS FLOW DIAGRAM:

(b. ANODIC CURRENT)
n. STRESS RELIEVING
b. SOLVENT CLEANING
d. LOADING IN FIXTURE
a. STERSS RELIEVING
g. NEUTRALIZATION
C. BATCH MAKING
e. ANODIC CLEANING
f. RINSING IN COLD WATER
h. DM WATER RINSING
i. ETCHING
j. CHROMIUM PLATING (By Forward-Reverse current)
w. BURNISHING
k. CHROME KILL
l. COLD WATER RINSE
m. UNLOADING AND CHECKING BY GAUGE
o. BORE ADJUSTMENT
p. GLOSSING
q. QC INSPECTION
s. SAND BLASTING
t. CD IN QC (HT)
j. DRAG OUT IN DM WATER
u. PROOF FIRING (SQAE)
v. CD IN RANGE

………..15.
a. STRESS RELEIVING: Stress developed by machining operation is released
by baking the components at the temperature 2000C for two hours.
b. SOLVENT CLEANING: To remove oil, grease etc prior to plating,
components are cleaned by degreasing solvent.
c. BATCH MAKING: To maintain coating thickness, a batch of eight barrels
are made having same bore size.
d. LOADING IN FIXTURE: Components are loaded in fixture for plating
operation.
e. ANODIC CLEANING: Alkaline cleaners remove organic type soils and have
less effect on inorganic soils such as oxides, scale and rust, though many
of these may also be removed if they are embedded in the organic soils
because they are lifted out with them. Alkaline cleaners work through
the processes of saponification, emulsification, solubilization, and
preferential wetting. Alkaline cleaners should be water-soluble and their
solutions should wet the surface being cleaned, and preferentially wet
and penetrate the soil to be removed. They should be temporarily able
to emulsify and suspend solid particles in solution without re-depositing
them on the metal surface; and they should be able to solubilize or bring
into solution those soils capable of dissolving in a reasonable length of
time. They should be able to soften water, rinse freely, not attack or
tarnish the metal surface being cleaned, have a high buffering capacity,
i.e., tolerate drag-in of acid substances introduced with the metal
without change of pH; and they should not form excessive foam during
x. QC INSPECTION
y. DISPATCH

……16.
cleaning or rinsing. In alkaline soak cleaning, the parts are immersed in
tanks of hot alkaline cleaning solution. Concentration and temperature
of the cleaner should be as high as possible considering the nature of the
work, in order to minimize the time for satisfactory cleaning.
f. RINSING IN COLD WATER: For cleaning the components.
g. NEUTRALIZATION: Since Alkaline solution has tendency to convert
hexavalent chrome into trivalent chrome so before reverse etching,
components are dipped in sulfuric acid (1% v/v & temp: 600C) so that
traces of alkaline solution could be neutralized.
h. D.M. WATER RINSE: To remove last traces of impurities.
i. ETCHING: Reverse etch is used for the final removal of oxides before
chrome plating. The final operations before chrome plating is usually a
reverse etch in either a chromium plating solution or a solution of
sulfuric acid. This operation removes the last traces of oxides, left on the
surface after the cleaning operation; activates the surface of the metal
(remember that the initial layer of chrome plate is sometimes very
difficult to deposit, and, most importantly, contributes to good adhesion
of the chrome plate.) Chromic acid reverse etches are operated at the
temperature and concentration of the plating bath. There is danger on
some parts of producing a rough deposit if the etch is prolonged much
beyond the desired time, which is dependent upon the base metal alloy
being plated.
j. CHROME PLATING(BY FORWARD-REVERSE CURRENT): Chromium is the
hardest of the most commonly deposited metals. Hard chrome is used as
a wear resistant coating not only on steel but also on a wide variety of
other metals.
CHROME PLATING CURRENT – 35 AMP/dm2(Each
MAG Barrel)
TIME - 2.20 HOURS(7.70
RUN)
TEMP. (OC) - 55

k.
l. DRAG OUT IN D.M. WATER: To remove adhered chrome solution on the
surface of barrels.
……17
SP. GRAVITY (OBe) – 21 - 22
Bath Composition CrO3 225-275g/l
SO4-- 2.25 – 275g/l
Iron Oxide 0-20 g/l
Cr2O3 0-18 g/l
Total Oxide 0-38 g/l
Forward – Reverse
current(According
to Chargeman Log
Book)
Tank No. – B-13(II)
Forward Current – 20 minutes
Reverse current - 10 second
Dead Time - 05mS
Barrel No. BA9422,9438,9454,9450,8819,9426
I/Note No. (i)Found O.K.
I/Note No- 159/S2/EP/21;Dtd:
29/01/22
Wt. No. – 132/0, Operation No:
1430:Proof Chamber
1450: Stamp Proof Mark
(ii)All Barrels are passed
I/Note No- 164/F/EP/21; Dtd:
02/02/22
Wt. No. – 132/0
Gun Number Gun No. Date of
Passing
(i)4196(17783643) 04/03/22
(ii)4197(17783650) 07/03/22
(iii)4198(17783814)
04/04/22
I/Note No.

……18.

m. CHROME KILL: Chrome-Kill (Sodium meta bi sulphide Na2S2O5) can be
used in the final rinse tank to remove the last traces of the chrome bath,
which can later bleed out and stain the parts. Time of contact between
the work and the rinse must be sufficient to remove all chemical films;
for immersion rinses with air agitation this is usually around 30 - 60
seconds. Another advantage of using Chrome-Kill as the final rinse is that
it operates hot and therefore the parts will air dry quickly without
requiring a separate drying operation.
n. COLD WATER RINSE: For cleaning the components.
o. UNLOADING & CHECKING BY GAUGES: To ensure that plating thickness
is achieved as per required.
p. STRESS RELEIVING(DEHYDROGENATION): A proven method of removal
of hydrogen is baking after plating. Thermal treatment of metals for
specified times (16 to 18 hrs.) & temperature (2000C) is driven the
hydrogen out from the metal surface & relieve stresses.
q. BORE ADJUSTMENT: Bore is adjusted as per process layout.
r. GLOSSING: To make shining in the chamber of the Barrels, Glossing is
done from breach end side of the Barrel.
s. Q.C.INSPECTION: Q.C. Examiner checks the Barrel’s quality as per
drawing & layout.
t. SAND BLASTING: Before crack detection test, barrels are shined by sand
blasting operation.
u. CRACK DETECTION TEST: To ensure that there are no any cracks on the
outer surface of barrel before high pressure proof, crack detection test is
required.
v. PROOF FIRING: To check ability of barrels to wear pressure load, one
high pressure proof firing is done in each barrel.

w. C.D. IN PROOF RANGE: To ensure that there are no any cracks on the
outer surface of barrel after high pressure proof, crack detection test is
required.
x. BURNISHING: To clean the Barrel bore.
y. Q.C. INSPECTION: Q.C. Examiner checks the Barrel’s quality as per
drawing & layout.
z. DISPATCH: Barrels are collected by CWD(Component Work Depository
Section) & it is sent to next section by CWD.
Novel features of the invention :-
In present time, Chrome Plating Process on different components have been
carried out by existing process (refer process flow diagram “a & b”). After a
lot of trials, a new process (invented process flow diagram) has been
developed. The invented process gives better performance in comparison of
existing process. Present invention has been developed in factory premises.
As per inventor knowledge, the invented process is totally new & unusual.
Its novelty has to be checked in global context as per section-13 (a & b) of
Patent Act 1970

CLAIM:-

The applicant claims on advanced Hard Chrome Plating Process inside
Barrel bore of Small Arms Weapon by using forward – reverse current.
7. Have you sold, offered for sale, publicly used or published anything
related to this invention?
( No )
8. Do you have records or log books documenting the
conception/development of your invention?
(YES)
……..19.