How To Set Up A Business Unit For Wirewound Resistors Manufacturing

Increasing demand for electronic devices and equipment is driving the increasing growth of the wirewound resistors market.

Wirewound resistor is a type of passive component in which metal wires are used to reduce or restrict the flow of electric current to a certain level. It is of two types: power wirewound resistor and precision wirewound resistor.

Power wirewound resistor. This is a non-inductive wirewound resistor that operates at high temperature. It is commonly used for high power applications.

Precision wirewound resistor. This operates at low temperature with high accuracy. It is used as a precision resistor in instrumentation because of its high accuracy.

Wirewound resistors are used only for low frequencies, and are not suitable for high frequencies. At high frequencies, these act as inductors. Hence, for high frequencies, non-inductive wirewound resistors are used.

Wirewound resistors find use in almost all major electronic circuits, and are widely used in applications such as telecommunications, computers, audio and video equipment, medical electronic equipment, defence and space, telephone switching systems, transducers instrumentation, current and voltage balancing, and current sensing.

Market potential

There are many units in India that manufacture different types of wirewound resistors, including silicon-coated, ceramic-encased and aluminium-wound resistors. But, there is an incremental growth of electronic industries in the country, which has created further scope for new industries in the field of wirewound resistors.

Increasing demand for electronic devices and equipment is the key factor driving the increasing growth of the wirewound resistors market. Most consumer electronics have inbuilt wirewound resistors to avoid or minimise the flow of excessive electric current.

Wirewound resistors provide high protection to electronics equipment by reducing fluctuations in the flow of extra current near their threshold voltage. Home appliances and electronic devices such as cellphones, LCD monitors and digital cameras are escalating the demand for wirewound variable resistors.

Growing adoption of circuit-breaking applications is another factor boosting the growth of the wirewound variable resistors market. Use of pure metals and alloys that have high temperature coefficient of resistance is increasing significantly, thereby increasing the demand for wirewound variable resistors, to prevent excess electric current transfer.

Due to an abundance of opportunities, a number of players are entering the market. And, existing players are investing heavily in research and development to improve the functionalities of wirewound variable resistors.

Production of wirewound variable resistors is increasing due to low technology barriers and an abundance of raw materials in the market. However, adoption of alternative technologies (such as chip resistors) and macroeconomic conditions (such as economic slowdown and global recession) may hamper the growth of the wirewound variable resistors market.

Precision resistors are expected to grow rapidly owing to the number of benefits provided by these, such as better short-term and long-term stability, faster frequency response, low noise and high performance. Manufacturers are focusing on providing enhanced precision resistors.

Manufacturing process

The wirewound resistor manufacturing process varies widely. The manufacturing process and choice of materials to be used depend on the way the resistor will be used in a circuit. However, all wirewound resistors are made by winding the resistance wire in a spiral around a non-conductive core.

The resistance wire is usually a nickel-chromium alloy, and the core is often ceramic or fibre-glass. A coating such as vitreous enamel is used for protection. Spiral winding has capacitive and inductive effects that make it unsuitable for applications higher than 50kHz. Often, other winding techniques are used to reduce the undesired high frequency effects.
For high tolerance requirements, resistance value is measured to determine the exact cut-to-length of the wire. To create a high resistance, wire diameter needs to be small and the length long. Therefore wirewound resistors are mainly produced for lower resistance values.

For low power ratings, a very thin wire is used. Handling of the wire is, for this matter, critical. Any damage may sever contact. After winding, the wire is well protected from access to moisture to prevent electrolytic corrosion.

Next to precision, there are also wirewound resistors with high power rating for 50W or more. These have a different construction. Compared to other resistor types such as metal film, wire diameter is relatively big and therefore more robust.

Raw materials and equipment

A wirewound resistor is an electrical passive component that limits current. The resistive element exists out of an insulated metallic wire, which is wound around a core of non-conductive material. The wire material has high resistivity, and is usually made of an alloy such as nickel-chromium (nichrome) or a copper-nickel-manganese alloy called manganin.

Common core materials include ceramic, plastic and glass.

Wirewound resistors are the oldest type of resistors that are still manufactured today. These can be produced very accurately, and have excellent properties for low resistance values and high power ratings.

These are mainly produced with alloys, since pure metals have a high temperature coefficient of resistance. However, for high temperatures, pure metals such as tungsten are used.

Temperature coefficient is a sign of how much the resistance will change as temperature changes. TCR (temperature coefficient of resistance) is measured in units of ppm/°C. If a manufacturer rates a resistor at 50ppm/°C, the resistor will not change more than 50 in resistance for each 1M of the resistor’s given value, for a temperature change of 11°C. Typical alloys that are used as resistor wire are copper, silver, nickel-chromium, iron-chromium and iron-chromium-aluminium. Properties of the most common alloys are given in Table I.

Following raw materials are required for wirewound resistors:

• Viterous enamel/silicon-based resin
• Strips
• Resistance wires
• Caps and beads
• Consumables like hardener, rubber sheet and packaging

Machinery and equipment required are:

• Toggle action press of ½-ton capacity
• Automatic coil winding machine
• Lead cutting machine grinder
• Lead straightening machine
• Lead tinning machine
• Spot welding machine
• Oven (temp.)
• Stirrer (ball mills)
• LCR – Q meter
• Digital temperature indicator
• 4½-digit bench micro-ohm meter
• Dimmer stat (4A)
• 4½-digit digital multimeter
• Load tester and brake tester
• Fusing tent machine
• Tension tester
• Marking machine with accessories
• Resistance oil standards

Financial analysis

Table II shows fixed capital, that is, land and building, and machinery and equipment.

Table III shows the cost of working capital per month.

Total capital investment is given in Table IV. Cost of production per annum is shown in Table V. Turnover per annum is shown in Table VI.

Profit before taxes = Turnover per annum – Cost of production per annum
= 7,200,000 – 5,839,184 = ₹ 1,360,816