Identifying unlabelled board stock and choosing folder materials for a humid-season order
Your unit is attached to a vocational centre that trains candidates with locomotor disabilities. In late June a donor sends three lots of stock kept for months in a leaky godown: 300 sheets marked only "2 mm", 200 sheets of cream-coloured paper, and 150 sheets of 300 gsm duplex board. A school orders 250 certificate folders, finished 22 × 31 cm when folded, to be delivered on 12 August. The workshop owns a steel rule, a kitchen scale reading to 0.1 g, a micrometer, two bone folders, a 90 cm manual guillotine and no dehumidifier; relative humidity has stayed between 78% and 84% for three weeks. A trial batch of 40 folders made last week from the duplex board curled inward about 6 mm at the fore-edge within three days, and the board cracked and delaminated along the score line. The centre can spend at most ₹3,500 on fresh stock this month. Two trainees work four hours a day; one has limited grip strength in the left hand.
1. Identify the three donated lots and decide which becomes the folder cover and which the inner lining. Justify each decision with a test that can actually be run in this workshop.
Read the worked answer
Test before choosing. GSM: cut ten pieces exactly 25 × 40 cm (0.1 m² each, 1 m² in all) and weigh them on the kitchen scale; the mass in grams is the gsm. Caliper: use the micrometer on a stack of ten sheets and divide by ten.
- The lot marked "2 mm" is a caliper figure, not a weight. If it really measures about 2 mm it is roughly 1,500–1,600 gsm, i.e. a binding board, not a folder cover. Confirm with the micrometer before using it anywhere.
- The cream paper, if it weighs about 100 gsm, is a lining paper.
- The 300 gsm duplex board is the only sensible cover stock for a folding folder: stiff enough for a 22 × 31 cm panel, printable, and 300 gsm folds without a press.
Grain (needed in task 2): tear a strip both ways - it tears straight and with less ragged edge along the grain; a fold-and-crease test gives a cleaner crease along the grain; a dampened square curls up across the grain. The "2 mm" board is reserved for rigid-box work and is not used on this order.
Verdict: duplex 300 gsm for the cover, cream paper for the lining, and no money spent on new stock unless the sheet count in task 3 falls short.
2. Explain why the trial folders curled and delaminated, and set out a grain and pasting rule for the whole order.
Read the worked answer
Curl is a two-layer problem, not a bad-glue problem. Paper and board swell and shrink far more across the grain than along it - a change from 80% to 50% RH can move a sheet by 0.2–0.3% across the grain and only a fraction of that along it. If the lining is pasted with its grain at 90° to the board's grain, the two layers fight each other and the panel behaves like a bimetallic strip: it curls toward the layer that shrinks most. A 6 mm lift at the fore-edge on a 31 cm panel is consistent with cross-grain lamination plus a wet paste and no pressing.
Rules for the order:
- Board grain parallel to the spine fold, i.e. running along the 31 cm height.
- Lining grain parallel to the board grain - never crossed.
- Score on the outside of the fold, with a waste sheet over the board, using a blunt scorer rather than a knife; the delamination shows the duplex plies are weakly bonded, so a sharp blade cuts through the plies instead of compressing them.
- Use the thinnest paste that will hold, apply it to the lining only, and dry flat between blotters under a weighted board for at least 12 hours.
- Store finished folders in a closed polythene bag with a sachet of silica gel until dispatch.
3. Calculate how many duplex sheets the 250 folders need, allowing for grain direction and 10% wastage, and say whether the donated 150 sheets are sufficient.
Read the worked answer
Size of one cover panel: 22 cm wide × 31 cm high, with the grain along the 31 cm side (parallel to the spine fold).
On a 70 × 100 cm sheet, keep the grain direction fixed:
- along the 70 cm edge only the 31 cm dimension may be placed: 70 ÷ 31 = 2 rows (62 cm used, 8 cm waste);
- along the 100 cm edge the 22 cm dimension goes: 100 ÷ 22 = 4 columns (88 cm used, 12 cm waste);
- yield = 2 × 4 = 8 panels per sheet.
If the sheet were turned the other way you would get 3 × 3 = 9, but every panel would then be cross-grained, so that layout is not allowed.
Panels needed = 250 folders × 2 panels = 500. Sheets = 500 ÷ 8 = 62.5, round up to 63. With 10% wastage for trimming, damaged corners and the reinforced spine strip: 63 × 1.10 = 69.3, so 70 sheets.
Verdict: 150 donated sheets cover the requirement with a wide margin; the ₹3,500 should not be spent on cover board. Check the cream lining paper separately on the same basis before promising delivery, and keep the surplus duplex as buffer for the 12 August deadline, since re-ordering in this humidity risks a different caliper and fresh warping.