Textile Machinery, Instrumentation and Maintenance
This domain tests machine mechanisms - gearing, change wheels, cams, shedding and picking systems - together with production calculations and the basics of instrumentation and maintenance management. Expect one or two numerical items on draft constant, twist constant or machine output, and short definitions of MTBF, MTTR and availability.
Gearing and calculation
- Draft = draft constant ÷ draft wheel; twist = twist constant ÷ twist wheel. Changing the wheel changes the result proportionally.
- Production (kg/h) = delivery surface speed (m/min) × 60 × efficiency × linear density (ktex) ÷ 1000, where 1 ktex = 1 g/m.
- Efficiency accounts for doffing, creeling, repairs and stoppages; always apply it last.
Mechanisms
- Shedding by tappet, dobby or jacquard; picking by cone underpick, projectile, rapier, air-jet or water-jet; let-off positive or negative; take-up through change wheels to set picks per inch.
- Brakes, clutches, variable-frequency drives and servo let-off systems control starting marks and tension.
Instrumentation
- Sensors: photoelectric weft detectors, proximity switches, encoders, tacho-generators, load-cell tension meters, thermocouples in dyeing machines.
- Control: PLC logic, PID loops for temperature, tension and moisture; online monitoring gives production, stops per shift and OEE.
Maintenance
- Preventive and predictive maintenance (lubrication schedules, vibration analysis, thermography) versus breakdown maintenance.
- MTBF = mean time between failures; MTTR = mean time to repair; availability = MTBF ÷ (MTBF + MTTR).
Worked example
Card doffer 0.6 m diameter at 30 rpm, sliver 5 ktex, efficiency 85%. Delivery speed = π × 0.6 × 30 = 56.5 m/min. Per hour = 56.5 × 60 × 0.85 = 2884 m. Production = 2884 m/h × 5 g/m = 14 420 g/h ≈ 14.4 kg/h. Note the doffer, not the cylinder, sets delivery rate.
Traps
- Using cylinder speed in output calculations.
- Forgetting efficiency, or treating ktex as tex.
- Inverting the availability formula.
- Assuming a larger draft wheel always means more draft - check whether the wheel is driver or driven.