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.

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(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

salts, Sodium Hydroxide, Sodium Potassium Tartarate [figs. 3.8 (a-e)],

Sulphuric acid, Hydrochloric acid, Silver Nitrate [fig. 3.8 (h)], Tin

Chloride and Formaldehyde are purchased from Sri. Manjunatha

Chemicals, Superchem Finishers and Lakshmi Industries, Bengaluru,

India. Barium carbonate [fig. 3.8 (g)] for chrome flash is procured from

M/s. Mehta Sons, Bengaluru, India. Brighteners 2793 and leveller

2794 [fig. 3.8 (f)] are supplied by Swathi chem-Plast, Bengaluru, India.

93

(a) Copper

Sulphate Salts (b) Chrome Salts (c) Nickel Salts

(d) Sodium

Hydroxide

(e) Sodium

potassium

Tartarate

(f) Brightener

2793 (left) and

Leveller 2794

(right)

Solutions

(g) Barium Carbonate (h) Silver Nitrate Solution

Fig. 3.8: Chemicals used in Electroplating process