Paper cores and cardboard tubes: sizes, strength and uses

A paper core is a cylinder made of strips of board, usually wound in a spiral and glued ply on ply. At the centre of a roll or reel it carries film, paper, textiles, tape or metal strip through winding, transport and unwinding. It is specified by inside diameter, wall thickness, flat and radial crush strength, moisture content and tolerances. Cardboard tube and winding core mean the same thing. Read more

Mostly as winding cores for industrial rolls: stretch and flexible film (usually 3", where radial strength counts), paper, tissue and board (3" to 6", heavy reels), textiles and nonwovens (thin walls, clean surface), adhesive tapes and labels (25 to 76 mm, clean cut) and aluminium and metal strip (thick walls, high loads). Large tubes of 150 to 1,200 mm are used as single-use formwork for round concrete columns. Read more

Strips of core board, mostly from recycled fibre, are wound around a steel mandrel and glued ply on ply. In spiral winding, the most common method, the strips go in at an angle to the axis and the seams run in a helix; the tube comes off the line continuously and is cut to length. Convolute (parallel) winding rolls a sheet into concentric layers: stiffer in bending and smoother, but it costs more and the sheet width limits its length. Read more

ISO 13542 lists 17 inside diameters from 10 to 400 mm, each with a plus-only tolerance. For industrial rolls the most common are 3" (76 mm) and 6" (152 mm), which the standard treats as 76 and 150 mm. Core makers usually cover inside diameters from about 10 to 500 mm, walls from under 1 mm to 15-25 mm and lengths up to 10 m; non-standard sizes are made to order. Read more

None in substance: both are a cylinder of board strips wound and glued ply on ply. "Core" is used when the tube carries a roll; "tube" also covers mailing and packaging.

Yes, they go into the paper and board recycling stream. Our recycling guide lists the waste codes and the PPWR rules. Read more

It is the resistance to flat crushing: a 100 mm sample is squeezed between two parallel plates until it first gives way. The standard is ISO 11093-9 (published in the UK as BS ISO 11093-9; the US equivalent is CCTI T-108). The result is given in kN/m or N/100 mm. Read more

Flat crush squeezes the core between two plates, along a line. Radial crush squeezes it with uniform pressure over the whole surface, as a wound film does, and is measured in bar (CCTI T-158 with steel balls, T-159 with an inflatable bladder). The two values correlate poorly: for film rolls, radial strength is what counts. Read more

Usually between 6% and 8%. Below 4–5%, paper turns brittle, because the bonds between fibres need a little water; above 9–10%, strength drops fast. The humidity in the customer’s warehouse matters more than at the production site: the core reaches equilibrium with the air within days. Read more

Under ISO 13542 the tolerance is plus only: +0.5 mm up to 60 mm, +1.0 at 70, +1.2 at 76, +1.4 at 100, +1.6 at 120 and 150, +2.0 at 200, up to +3.0 at 300 and 400. The difference between two perpendicular diameters must not exceed 0.5 mm below 70 mm and 1.5 mm from 70 mm up. Read more

Seven things: inside diameter with tolerance, wall thickness (or outside diameter), length with tolerance, minimum strength with the test method (flat crush ISO 11093-9, radial crush CCTI T-158 or T-159), maximum moisture on delivery, edge and surface finish, and packing. Without the test method, a strength figure cannot be compared. Read more