It has been established from experience that most electroplating accidents are traceable to carelessness, inexperience, failure to follow instructions, poor engineering of equipment, inadequate layout of plating tanks and ventilation systems, bad housekeeping, improper shop flooring and drainage arrangement, confusion regarding chemicals and poor labelling of tanks and chemicals. Such neglect may result in explosion, fires and the release of toxic gases which are harmful to health.
The common types of hazardous chemicals used in an electroplating shop are:
a Hydrogen;
a Cyanides;
a Chlorinated solvents;
a Sulphuric acid; and a Chromic acid;
Hydrogen: A hydrogen explosion occurs with electro-cleaners that produce foam. The foam blanket created by wetting agents sometimes traps the hydrogen and oxygen generated at electrical contact points. It can be prevented by keeping electrical contact points away from foam levels and proper exhaust arrangements.
Cyanides: When cyanide baths are used for electroplating, a separate drainage arrangement and exhaust system are recommended. Safety masks for the operators are necessary.
Chlorinated Solvents: These solvents are used in vapour/aqueous de-greasing units. These solvents can affect the brain when the operator or maintenance people inhale this vapour for long periods.
Alkali (caustic soda) vapours exposed to chlorinated materials can cause an explosion. So the de- greasing section should have a proper exhaust and ventilation system and should be separated from the other process. A separate cleaning and rinsing tank is needed when chlorinated solvents are being used. Improper design and maintenance of de-greasing units is hazardous to life.
Acids: In electroplating shops, acids like sulphuric acids, hydrochloric acid and nitric acid are used for preparing electroplating solutions. When mixing these materials, protective clothing, aprons, gloves and chemical goggles should be used for safety. Otherwise any accident can harm the face and clothes.
Always add acid to the water slowly, stirring the solution as the acid is being poured. Water should not be added to the acid. This causes an immediate violent reaction which can splash up and result in severe burning of the exposed skin of operators.
The spilled acids and acid vapour also affect the operator and lead to a polluted atmosphere.
Proper exhaust, ventilation systems, proper layout and acid-resist flooring are necessary in the plating shop.
8.8.1 Plating Shop Layout
The layout requirement for an electroplating shop depends upon the process, which is of three types:
a Automatic plating process;
a Semi-automatic plating process; and a Manual plating process.
The above plating systems have the following sequences:
a Racking or wiring system;
a Pre-treatment including rinsing system;
a Electroplating system;
a Post-treatment including final rinsing and drying system; and a Unloading system.
Regardless of whether the process is automatic, semi-automatic or manual, the arrangement of the above five can be in one unit or in different units. The overall system is connected with a central exhaust system.
The plating room floor should be water-proof and with acid/alkali resist coating (either an epoxy layer or a bitumen layer). During processing, spilling of some drag-out of plating solutions or cleaning solutions on the floor is unavoidable. If the floor is made of cement, it will be rapidly affected and needs to be protected with a protective coating.
Plating Processes 345
Water used for plating and rinsing should be pure water like distilled water or de-mineralized water. All the exposed metal fittings in the room should be protected from the acid and alkali corrosion. For this purpose, the points used should be bitumastic paints “chlorinated rubber paints”
vinyl paints or epoxy resin type paints. In the plating shop, the information chart on safety and first aid treatment kits should be displayed prominently.
The used water should be discharged directly from the floor or tanks and connected to drainage channels. The floor should be laid such that there is a slight natural slope towards drainage channels.
The collected waste water should be treated in different treatment plants and the treated water must be neutralized upto 7-8 pH. The drainage must be connected to the open evaporator system as shown in Figure 8.13.
Waste water collection tank (2m*2m)
Neutralized water tank
(2m*3m)
Drainage (open tank)
Reaction tank
(pH)
Effluent transfer chemical pump Mixer
Settlement tank (2m*3m)
Cleanedeffluent
Reaction tank [add acid or alkali upto required pH level (2m*2m)]
Sludge tank (2m*2m)
Fig. 8.13 Drainage system for pollution treatment
8.8.2 Equipment
Plating solutions are highly corrosive. Precautions should be taken to protect the walls and bottom floors of the tanks and filters. Solutions of plating tanks, heating elements, filters and filter aids depend upon the type of metal plating solution. The materials used for construction for electroplating equipment are given in Table 8.3.
Table 8.3 Materials Used for Construction of Electroplating Equipment
Bath Tank Lining Heaters Filters Filter Aids
Copper PVC, rubber Stainless steel Stainless steel, Cellulose fibre,
pyrophosphate polypropylene epoxy asbestos fibre
Acid copper PVC, rubber, Carbon Hard rubber Non-silicated
sulphate polypropylene filter aid
Acid gold PVC, pyrex, Quartz PVC lined Asbestos
quartz, Teflon diatomaceous earth
Alkaline gold PVC, pyrex Titanium PVC lined Asbestos fibre polypropylene, Teflon
Tin lead PVC, rubber Not required PVC rubber Non-silicated lined filter aid
Nickel PVC, Not required PVC rubber Asbestos fibre
sulphomate polypropylene lined
Bright acid tin PVC, Not required 316 stainless Asbestos fibre
polypropylene steel, hard
rubber
Bright cyanide Hard rubber Not required 316 stainless Asbestos fibre
silver steel,
polypropylene