The 30s Hank That Tested 28.8s
A knitting unit near Guwahati supplies 1,800 kg of white cotton hosiery fabric a month to a Kolkata buyer. It knits from 30s combed hosiery yarn bought in 1.8 kg hanks. A new supplier delivers 600 kg with a mill certificate showing 30s count and CSP 2,450, and offers a 3% discount on the previous supplier's rate. Production needs 500 kg this week. The unit's own tests on 20 leas give an average lea count of 28.2s and a lea strength of 68 lb. A moisture meter reads 10.8% regain, because the yarn store is unventilated in the June humidity; cotton's standard regain is 8.5%. On the machine, the new yarn runs with frequent dropped needles and needle lines, and the knitter reports tight loops and high tension at the positive feeder. The previous lots, certified 30s at CSP 2,300, knitted cleanly at identical settings. The supplier refuses a return but will negotiate on price.
1. Calculate the lot's CSP and its count corrected to standard regain, then decide whether to accept, reject, or accept with a claim. Justify each step.
Read the worked answer
Step 1 – CSP. CSP = lea count x lea strength = 28.2 x 68 = 1,918. That is 16.6% below the proven 2,300 of earlier lots and 22% below the 2,450 on the certificate. CSP is the single number a knitter uses for spinnability, so a drop of this size is a quality failure, not a normal lot-to-lot variation.
Step 2 – count correction. The yarn was weighed damp, so the measured count is biased. Correct to standard regain: C(std) = C(meas) x (100 + R(meas)) / (100 + R(std)) = 28.2 x 110.8 / 108.5 = 28.8s. The lot is therefore about 1.2 counts coarser than 30s, roughly a 4% shortfall in length per kilogram - a commercial loss, but smaller than the raw 28.2s suggests.
Step 3 – machine behaviour. A coarser, weaker yarn at unchanged stitch length and feeder tension is over-stressed: loop formation needs more yarn than the cam setting supplies, so tension rises, needles flex, and dropped needles and needle lines follow. The 10.8% regain also means about 2% of the invoice weight is water.
Decision. Accept only with a price claim covering the 4% length shortfall, the 17% strength deficit and the excess regain - or reject and buy elsewhere. If the 500 kg must be used, re-set stitch length and tension and run it on a coarse, low-stress product, never on the Kolkata order.
2. The supplier argues the certificate is a mill average and offers 3% off. How would you answer him, and what would you write into the purchase order next time?
Read the worked answer
Answer to the supplier. A 3% discount does not touch the real loss. Three separate costs sit in the lot: about 4% fewer metres per kilogram (count 28.8s instead of 30s), a 17% CSP deficit that shows up as needle-line seconds and machine downtime, and roughly 2% of paid weight that is water at 10.8% regain. On 600 kg the usable-yarn loss alone is about 24 kg of length, before any fabric seconds are counted. A certificate quoting 2,450 when an independent lea test gives 1,918 is also a documentation problem, not a tolerance - ask for the mill's test method, the number of leas tested, and whether the strength was on a conditioned or a dry lea.
Purchase order clauses to add. (1) Count and CSP stated with the test method, number of leas, and standard regain, with an acceptance band (e.g. CSP not below 2,250, count within +/-0.5s). (2) Price based on conditioned weight at 8.5% regain, with a regain correction clause. (3) Retest at receipt, with rejection rights and freight at supplier's cost. (4) Yarn store dehumidified or stock rotated weekly so damp-season regain does not distort count, weight or knitting tension.