Rapier-to-Air-Jet Replacement: Payback Before Commitment
A mill weaving 63-inch 20 × 20 / 60 × 60 cotton sheeting on 48 rapier looms (190 cm, 450 rpm, 88% efficiency) is offered 24 air-jet looms (190 cm, 1,000 rpm, 94% efficiency) to replace them. Power: rapier 2.2 kW per loom; air-jet 3.5 kW per loom plus a 3.0 kW share of compressor and air treatment. Tariff Rs 8/kWh. Labour: one tenter per 12 rapier looms, one per 24 air-jet looms, three shifts, wage Rs 18,000/month including benefits. The mill runs 7,000 loom-hours per year and earns Rs 10/m contribution. The installed package is Rs 3.4 crore, and the old rapier looms have a resale offer of Rs 40 lakh. Air-jet weaving needs a cleaner warp: the present warp runs 3.4 breaks per 10⁵ picks and has high hairiness. The order book is currently firm for 3.2 million m/year.
1. Calculate hourly production for each installation, the annual output at 7,000 hours, and the energy consumption per metre.
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Rapier installation
- Picks/min = 450 × 0.88 = 396
- At 60 picks/inch: 396/60 = 6.60 in/min = 0.1676 m/min = 10.06 m/h per loom
- 48 looms = 482.9 m/h
- Annual: 482.9 × 7,000 = 3.38 million m
- Power: 48 × 2.2 = 105.6 kW → 105.6/482.9 = 0.219 kWh/m
Air-jet installation
- Picks/min = 1,000 × 0.94 = 940
- 940/60 = 15.67 in/min = 0.398 m/min = 23.88 m/h per loom
- 24 looms = 573.1 m/h
- Annual: 573.1 × 7,000 = 4.01 million m
- Power: 24 × (3.5 + 3.0) = 156 kW → 156/573.1 = 0.272 kWh/m
Comparison
- Extra output: 90.2 m/h, or 18.7%; 0.63 million m/year
- Energy per metre rises by 24.5%
- Annual power bill: rapier 105.6 × 7,000 = 739,200 kWh = Rs 59.1 lakh; air-jet 156 × 7,000 = 1,092,000 kWh = Rs 87.4 lakh; increase Rs 28.2 lakh/year
The energy result is the one that surprises people: the air-jet loom is more productive but uses more energy per metre, because compressed air is expensive. The extra output is real only if the market takes it.
2. Calculate the simple payback on the investment, including the energy penalty and labour saving, using the resale value of the old looms.
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Annual benefits and costs
- Extra output: 0.63 million m × Rs 10/m = Rs 63.1 lakh
- Labour: rapier 48/12 = 4 per shift; air-jet 24/24 = 1 per shift; saving 3 per shift × 3 shifts = 9 workers. At Rs 18,000/month × 12 = Rs 2.16 lakh per worker/year → Rs 19.4 lakh
- Extra energy: −Rs 28.2 lakh
- Net annual benefit: 63.1 + 19.4 − 28.2 = Rs 54.3 lakh
Investment
- Package Rs 3.4 crore less resale Rs 40 lakh = Rs 3.0 crore net
- Simple payback = 3.0 crore/54.3 lakh = 5.5 years
Sensitivity
The result is sensitive to three assumptions, so test them before committing:
- If contribution falls from Rs 10 to Rs 8/m, the extra output is worth Rs 50.5 lakh and payback stretches to about 6.7 years.
- If air-jet efficiency is 90% rather than 94%, output falls to 549 m/h and the output benefit shrinks by about Rs 8 lakh/year.
- If the extra 0.63 million m cannot be sold, the output benefit disappears and the project cannot be justified on labour and energy alone.
A payback of 5.5 years is at the long end for weaving machinery, where 4 years is a common hurdle. It is acceptable only with a firm order book and a warp quality upgrade already budgeted.
3. Recommend whether to proceed, and state the conditions that must be met before the order is placed.
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Recommendation: proceed only conditionally, and phase the decision.
The engineering case is sound: 24 air-jet looms replace 48 rapiers with 18.7% more output, half the labour and half the floor space. The financial case is thinner: 5.5 years payback, with the output benefit carrying most of the value and the energy penalty working against it. The project is therefore a market decision as much as a machinery decision.
Conditions to meet before ordering
- Order cover. The firm book is 3.2 million m/year, below the 4.0 million m the air-jets can make. Secure at least 3.8 million m/year, or plan to run fewer than 24 looms in the first year; an air-jet loom idle at 94% efficiency is still consuming compressor power.
- Warp quality. 3.4 breaks per 10⁵ picks is too high for air-jet, where a stop is more costly and the reed and relay nozzles are less forgiving. Target below 1.5 breaks per 10⁵ picks through sizing add-on, hairiness control and yarn clearing. Budget this cost in the project, not after it.
- Utilities. Confirm the compressor capacity, air quality (dry, oil-free) and power supply can carry 156 kW continuous; a voltage dip stops all 24 looms at once.
- Skills and spares. Air-jet nozzles, valves and electronics need trained technicians and a spares policy; a single unavailable valve can idle a loom.
- Residual value and phasing. Verify the Rs 40 lakh resale offer in writing, and consider replacing 24 rapier looms first, then deciding on the rest after twelve months of actual efficiency, energy and break-rate data.
If the order book cannot be secured, the correct answer is to keep the rapiers running and invest in warp preparation and maintenance instead; that route improves efficiency without a 3 crore commitment.