International Journal of Research in Engineering and Science (IJRES)

ISSN (Online): 2320-9364, ISSN (Print): 2320-9356

www.ijres.org Volume 10 Issue 6 ǁ 2022 ǁ PP. 1160-1169

Hard Chrome Plating Inside Of Barrel Bore Of Small

Arms Weapons By Using Forward – Reverse Current
Technique.
(AMIT KUMAR YADAV, IOFS. DY.GENERAL MANAGER
PRASHANT KUMAR SHRIVASTAVA, Jr. WORKS MANAGER
SMALL ARMS FACTORY, KALPI ROAD, KANPUR-208009 (A UNIT OF ADVANCED WEAPONS &
EQUIPMENT INDIA LTD.)
MINISTRY OF DEFENCE (MoD)

---------------------------------------------------------------------------------------------------------------------------------------
Date of Submission: 05-06-2022 Date of acceptance: 20-06-2022
---------------------------------------------------------------------------------------------------------------------------------------

The present invention relates to advanced Hard Chrome Plating Process inside Barrel bore of Small Arms
Weapon by using forward – reverse current. In existing technologies hard chrome plating operation is carried
out by using following process sequence:

S.NO. OPERATION REMARK IF ANY

01 S/R Before Electro polishing
02 Electro polishing Current & time will vary as per components surface area
03 Hot Water Rinsing
04 Cold Water Rinsing
05 Passivation
06 Cleaning With Hot Water & Pull Through
07 Bore Inspection No any wire mark
08 Cleaning With Solvent & Pull Throw
09 Ultra Sonic Cleaning Time will vary as per components surface area
10 Component Inspection component should be clean
11 Batch Formation 08 components for each batch with same gauge
12 Anodic Cleaning Current & time will vary as per components surface area
13 Neutralization
14 Etching Current & time will vary as per components surface area
15 Chrome Plating Current & time will vary as per components surface area
16 Water Rinsing
17 S/R (Dehydrogenation)
18 Quality Control Inspection

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

www.ijres.org 1160 | Page

 Hard Chrome Plating Inside Of Barrel Bore Of Small Arms Weapons By Using..

x. Pitting

A lot of trials at different parameters have been conducted to remove aforesaid defects. 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.NO 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 No- 159/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:

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 To remove traces of adhered Electro polish chemicals on the inner surface of Barrel.
Through
06 Organic solvent Ultra sonic cleaner is used, in which cleaning solvent is used.
degreasing

www.ijres.org 1161 | Page

 Hard Chrome Plating Inside Of Barrel Bore Of Small Arms Weapons By Using..

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).
(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.

iii. 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.

BENEFITS OF THE NEW PROCESS:

A. The following operations are obviated after implementation of hard chrome Plating inside the barrel
bore of Small Arms Weapons by using forward reverse current technique:

01 Electro polishing

02 Hot Water Rinsing

03 Cold Water Rinsing
04 Passivation
05 Cleaning with Hot Water & Pull Through
06 Bore Inspection

B. Zero Chip off, while in existing process chip off percentage is 15-20%.
C. Reduce the Cycle time (50% reduction).
D. Minimum Load on Effluent Treatment Plant.
E. No customer complaint.
F. Shining/lusture is better than existing process.
G. No rework is required.
H. Fulfill all quality all aspect.
I. No any issue of Hydrogen embrittlement.
J. Applicable to all type of Small Arms Weapons.

www.ijres.org 1162 | Page

 Hard Chrome Plating Inside Of Barrel Bore Of Small Arms Weapons By Using..

EXISTING PROCESS FLOW DIAGRAM:

www.ijres.org 1163 | Page

 Hard Chrome Plating Inside Of Barrel Bore Of Small Arms Weapons By Using..

Steps of Process Flow Diagram

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.
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 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, 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.

www.ijres.org 1164 | Page

 Hard Chrome Plating Inside Of Barrel Bore Of Small Arms Weapons By Using..

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: 60 0C) 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, 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)

www.ijres.org 1165 | Page

 Hard Chrome Plating Inside Of Barrel Bore Of Small Arms Weapons By Using..

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.

CHROME PLATING CURRENT – 35 AMP/dm2(Each MAG Barrel)

TIME -- 2.20 HOURS(7.70 RUN)
TEMP. (OC) -- 55
SP. GRAVITY ( Be) – 21 - 22
O

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

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.
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 (200 0C) 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.

www.ijres.org 1166 | Page

 Hard Chrome Plating Inside Of Barrel Bore Of Small Arms Weapons By Using..

INVENTED PROCESS FLOW DIAGRAM:

www.ijres.org 1167 | Page

 Hard Chrome Plating Inside Of Barrel Bore Of Small Arms Weapons By Using..

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
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: 60 0C) 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
SP. GRAVITY ( Be) – 21 - 22
O

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 Tank No. – B-13(II)
to Chargeman Log Book) Forward Current – 20 minutes
Reverse current - 10 second
Dead Time - 05mS
Barrel No. BA-9422,9438,9454,9450,8819,9426
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

www.ijres.org 1168 | Page

 Hard Chrome Plating Inside Of Barrel Bore Of Small Arms Weapons By Using..

(i)4196(17783643) 04/03/22
(ii)4197(17783650) 07/03/22
(iii)4198(17783814) 04/04/22

I/Note No.

k. DRAG OUT IN D.M. WATER: To remove adhered chrome solution on the surface of barrels.
l. 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.
m. COLD WATER RINSE: For cleaning the components.
n. UNLOADING & CHECKING BY GAUGES: To ensure that plating thickness is achieved as per
required.
o. 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 (200 0C) is
driven the hydrogen out from the metal surface & relieve stresses.
p. BORE ADJUSTMENT: Bore is adjusted as per process layout.
q. GLOSSING: To make shining in the chamber of the Barrels, Glossing is done from breach end side of
the Barrel.
r. Q.C.INSPECTION: Q.C. Examiner checks the Barrel’s quality as per drawing & layout.
s. SAND BLASTING: Before crack detection test, barrels are shined by sand blasting operation.
t. 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.
u. PROOF FIRING: To check ability of barrels to wear pressure load, one high pressure proof firing is
done in each barrel.
v. 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.
w. BURNISHING: To clean the Barrel bore.
x. Q.C. INSPECTION: Q.C. Examiner checks the Barrel’s quality as per drawing & layout.
y. DISPATCH: Barrels are collected by CWD(Component Work Depository Section) & it is sent to next
section by CWD.

Conclusion:
03nos of guns (06 nos of barrels) have been passed by the invented process. Final inspection Note has
been issued to Indian Army depot which is proof evidence of invented process to comply all the acceptance
criteria of Director General Quality Assurance (DGQA) inspection which is started from in house Quality
Control inspection followed by DGQA Estt i.e. Senior Quality Assurance Estt(SA), Kanpur. the inspection
procedure followed as High Pressure Proof of Barrels, Pre Inspection, Proof Range Firing & Final Acceptance
Inspection before issue to inspection Note. All the three guns meeting all the standards and issued to Indian
Army Depot (COD) Jabalpur.

www.ijres.org 1169 | Page