82 CHAPTER 3 DEVELOPMENT OF ELECTROPLATING SETUP FOR PLATING ABS AND POLYAMIDES 3.1 BACKGROUND OF ELECTROPLATING 83 3.2 DETAILS OF THE DEVELOPMENT OF ELECTROPLATING SETUP 83 3.2.1 Polypropylene Tank for Electroplating 85 3.2.2 Heating Elements 85 3.2.3 Electroplating Anode Bags 89 3.2.4 Copper and Nickel Anodes 89 3.2.5 Transformer 90 3.2.6 Demineralized Water 91 3.2.7 Chemicals for Preparation of Electrolytic Solution 92
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82
CHAPTER 3
DEVELOPMENT OF ELECTROPLATING SETUP FOR
PLATING ABS AND POLYAMIDES
3.1 BACKGROUND OF ELECTROPLATING 83
3.2 DETAILS OF THE DEVELOPMENT OF ELECTROPLATING SETUP
83
3.2.1 Polypropylene Tank for Electroplating 85
3.2.2 Heating Elements 85
3.2.3 Electroplating Anode Bags 89
3.2.4 Copper and Nickel Anodes 89
3.2.5 Transformer 90
3.2.6 Demineralized Water 91
3.2.7 Chemicals for Preparation of Electrolytic Solution 92
83
CHAPTER 3
DEVELOPMENT OF ELECTROPLATING SETUP FOR
PLATING ABS AND POLYAMIDES
3.1 BACKGROUND OF ELECTROPLATING
Electroplating involves using electrical current to form a
coherent metal coating on an electrode. Electrolyte used in the
electroplating process acts as a conducting medium for the passage of
electricity between the anode and the cathode [82]. The sample to be
coated is the cathode, which is connected to the negative terminal.
The anode (positive) is the metal that dissolves and gets deposited on
the cathode. When the electric current passes through the electrolyte,
the negatively charged ions start to move towards the anode and the
positively charged ions move towards the cathode. The exodus of ions
through the electrolyte constitutes the flow of electric current in the
circuit. The metallic ions with a positive charge in the electrolyte are
drawn by the cathode. Due to this process the substrate gets plated
[83]. Fig. 3.1 illustrates a typical line diagram of the plating unit for
plating with Copper (Cu) and Nickel (Ni). Part description has been
shown in the Table 3.1.
3.2 DETAILS OF THE DEVELOPMENT OF ELECTROPLATING
SETUP
The entire electroplating setup (fig. 3.2) is established at Alpha
College of Engineering, Bengaluru, India. The details of the
developments have been discussed in the ensuing paragraphs.
84
3
4
5
6
21
7
8
9
Fig. 3.1: Line diagram of the plating unit
Table 3.1: Part description Table
Part
No Description
Part
No Description
1 Anode (+) 6 Temperature display
2 Cathode (-) 7
Transformer 0-12 Volts, 0-30
Amps
3
AC supply to heater (0-
230V) 8
AC supply to transformer (0-
230V)
4 Heater with glass cover 9 Air pipe from compressor
5 Electrolyte temperature sensor
Fig. 3.2: Electroplating setup at Alpha College of Engineering, Bengaluru
85
3.2.1 Polypropylene Tank for Electroplating
The polypropylene (pp) tank (fig. 3.3) is fabricated at “Keyan
reinforced plastics”, Bengaluru, India. Two tanks, one each for Cu and
Ni electroplating of dimensions 20 cm x 20 cm x 30 cm are fabricated.
A 10 mm thick PVC coat is provided on the inner side of the tank to
protect it from the chemicals / acids attack.
Fig. 3.3: Polypropylene Tank used in the Study
3.2.2 Heating Elements
The heat sensing thermocouple, indicator and controller and
heater [figs. 3.4 (a-d)] are procured from „Thermo measure‟,
(manufactures of thermocouples, RTD sensors and instruments),
Bangalore.
The universal temperature controller of type AOB508-A21 is
used for display and control of temperature. The size of the
instrument is 96 mm x 96 mm x 90 mm. A21 actually
86
represents one relay contact switched output and one alarm
output channel. The instrument is capable of handling 0-20 mA
of current and a power supply of 220V. The instrument is
capable of measuring 0-120 oC of temperature.
K type thermocouple is used to sense the temperature. This
thermocouple gives a very broad range of temperature detection.
Type K covers the widest range from −200 °C to 1,260 °C. These
thermocouples are usually made of Ni with excellent resistance
towards corrosion. In order to measure uniform temperature
within the electroplating bath the thermocouple is inserted in a
glass tube filled with water.
Infrared quartz heating element is used for heating of the
electrolyte in the electroplating bath. The detailed specification
of the heating element is summarized in Table 3.2. The
advantages of using this type of heating elements are,
Most of the energy is passed on as Infrared heat,
With high precision the output can be controlled
By-products are not give off.
Maintenance is very less and requires very less space for
setting up.
87
(a) Temperature Controller
With Universal Input
(Model no: AOB508-A21)
(b) K Type thermocouple with
protective glass tube.
(c) Quartz Heating Element (d) PP Tank installed with heater,
heat sensor and air blower
Fig. 3.4: Temperature controller, Thermocouple and Heating element
88
Table 3.2: Specifications of Infrared Quartz Heating Element (Source: Thermo measure)
Infrared Quartz Heating Element
Items Medium wave
Diameter 18mm
Max. overall
length 3,500 mm
Quartz tube 99.99% purity quartz which ensures high transparency, great shock heating resistance
and high strength
Ceramic base High heat-resistant and non-deformable
Filament Fe-Cr-Al or Ni-Cr
With special protective coating and is firmly
burnt-in
Filament temp. 600°C - 900°C
Wave length 2.3-4 μm
Max. power 30 W/cm
Average lifespan 20,000 hrs
Response time 1-3 min
Wire connection Two side connection for single tube
Voltage 230V
3.2.3 Electroplating Anode Bags
The anode bag (fig. 3.5) is basically a filter that avoids Solid
Anode Particles (SAPs) from entering into the electroplating solution. It
is usually observed that SAPs in the electroplating solution will
cause roughness on the plated parts [84].
Electroplating anode bags used in the study are made up of „PP‟
material procured from „Keyan Reinforced Plastics‟, Bengaluru, India.
These bags are double needle sewn at the top and bottom. Sides of the
bags are also double stitched to prevent the bags from being torn by
the rough action created by air agitation in the plating bath. PP
89
material has an excellent resistance towards alkalies, mineral acids,
organic acids, organic solvents and oxidizing agents. The maximum
safe temperature up to which they can be used in the electroplating
bath is 93 oC.
Fig. 3.5: Electroplating Anode Bags Used In Copper and Nickel Plating
3.2.4 Copper and Nickel Anodes
The Cu and Ni anodes [Figs. 3.6 (a-b)] are procured from
Lakshmi Industries, Bengaluru, India. Cu anodes available with them
are of two types viz, Electrolytic Copper (EC) and Phosphorous De-
Oxidised (PDO). EC is a pure form of copper and finds its use in
cyanide copper plating solutions. PDO anodes have low traces of
phosphorus, on an average 0.05 % phosphorus. PDOs are important
in acid Cu plating solutions that use organic additives. Since organic
90
additives are used in electroplating, the latter type of anode is used in
the study.
(a) Copper anode (b) Nickel anode
Fig. 3.6: Copper and Nickel Anodes used in the study
Electrolytic Ni anodes are used in the study. These are the
purest type of Ni anodes and are usually less expensive. They are
usually available in strips or small pieces ('F' - flats, 'R' - rounds). Flat
type of Ni anode is used in the study.
3.2.5 Transformer
The transformer used for electroplating, as shown in the fig. 3.7,
has the following specifications: AC to DC variable transformer, Input
230V AC, single phase, output 0V to 230V DC, capacity 30 Amps, is
procured from Universal Electricals, Bengaluru, India. The
transformer is custom made, as the specifications depend on the size
of the plating tank. The transformer is suitable for the research with
precision amperage regulation. The control panel has an amp meter
91
and an on/off switch. The transformer is designed for continuous duty
with solid state circuitry and full range of power.
Fig. 3.7: Transformer used in the Study
Some of the exclusive features of the built transformer are:
Industrial grade, heavy duty, high output transformer.
Oversized heat sinks and built-in cooling fans prevent
overheating.
Output current is 99% filtered assuring consistent results.
Voltage is adjustable from 0 to 12 volts.
3.2.6 Demineralized water
Fifty litres of demineralized water is supplied by
Sri. Manjunatha Chemicals, Bengaluru, India. According to
Subramanian Ramajayam and Ted Mooney [85], demineralised water
92
is generally used in all plating rinses, as hard water contains a large
amount of dissolved solids. Also, the presence of iron, nitrate and
large amount of chloride in the underground water may cause
problems in plating. The water sample used in plating has to be
analysed first, otherwise, plating problems like roughness, dullness,
low cathode efficiency etc. may arise. But for post plating processes,
soft water is generally preferred.
3.2.7 Chemicals for Preparation of Electrolytic Solution
Chemicals like Copper sulphate salts, Chrome salts, Nickel