Paper Tear Index
Compute the paper tear index, index = tear force (mN) / grammage (g/m²), in mN·m²/g, normalizing the tear resistance by the grammage. Tearing depends greatly on fiber length (long fibers resist more) — which is why packaging papers use long softwood fibers. It is a property that often competes with tensile (more refining raises tensile but lowers tear). Enter the tear force and the grammage.
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Índice de rasgo do papel
O índice de rasgo = força de rasgo (mN) / gramatura (g/m²), em mN·m²/g, mede a resistência do papel a continuar um rasgo já iniciado (no ensaio Elmendorf, um pêndulo rasga várias folhas e mede a energia gasta), normalizada pela gramatura. É uma propriedade governada por um fator dominante: o comprimento das fibras. Fibras longas (de coníferas/softwood — pinus, abeto) atravessam a linha de rasgo e precisam ser arrancadas ou quebradas uma a uma, dissipando muita energia → alto rasgo. Fibras curtas (de folhosas/hardwood — eucalipto) se descolam facilmente → baixo rasgo. Por isso embalagens, sacos e papéis que sofrem esforço de rasgo usam fibra longa, enquanto papéis de impressão (onde lisura e formação importam mais) usam fibra curta de eucalipto. Há uma tensão clássica entre rasgo e tração: o refino aumenta a tração (mais ligações entre fibras) mas reduz o rasgo (fibras mais ligadas quebram em vez de deslizar e dissipar energia) — o papeleiro precisa encontrar o ponto de refino que equilibra as duas conforme o uso final. Curiosamente, o rasgo costuma ter um máximo em refino intermediário. Informe a força de rasgo e a gramatura.
Related Tools
Paper Tensile Index
Compute the paper tensile index, index = tensile strength (N/m) / grammage (g/m²), in N·m/g, normalizing the strength by the grammage to allow comparing papers of different weights. It is one of the most important mechanical properties, linked to fiber strength, inter-fiber bonding and refining. Packaging and sack papers require a high tensile index. Enter the tensile strength and the grammage.
Paper Breaking Length
Compute the breaking length (self-rupture) of paper, L = tensile index / 9.80665, in km — the length of a paper strip that, hung from one end, would break under its own weight. It is an intuitive, classic way to express tensile strength, independent of grammage. Common papers break around 3–8 km; high-strength papers, more. Enter the tensile index (N·m/g).
Paper Burst Index
Compute the burst index of paper, index = burst strength (kPa) / grammage (g/m²), in kPa·m²/g, normalizing the bursting pressure by the grammage. The Mullen test applies increasing pressure with a rubber diaphragm until the sheet ruptures. It is the most used strength property in packaging papers, sacks and corrugated board, reflecting combined tensile and stretch. Enter the burst strength and the grammage.
Box Compression Strength (McKee)
Estimates the vertical compression strength of a corrugated box with the simplified McKee formula, BCT = 5.87 × ECT × √(board caliper × box perimeter), where ECT — the edge crush resistance measured per TAPPI T 811 (ISO 3037) — is in newtons per millimetre and both dimensions are in millimetres. The result, in newtons, is the load an empty box withstands in the laboratory compression test, with the board conditioned at 23 °C and 50% relative humidity. Because strength grows with the square root of the perimeter and linearly with ECT, doubling the perimeter buys only 41% more, while switching to a flute with 30% higher ECT buys the full 30% — upgrading the board usually beats reshaping the box. For real pallet stacking, divide the BCT by a safety factor of 3 to 5, which covers the stiffness lost to ambient humidity, the creep of board under load over weeks and the misalignment between boxes in the column. Enter the ECT, the board caliper and the box perimeter.
Cobb (Paper Water Absorption)
Compute the Cobb value of a paper, Cobb = mass gain (g) / area (m²), in g/m², the amount of water absorbed by one face of the paper in a standardized time (usually 60 s). It measures resistance to water penetration, crucial in packaging papers, printing (glue/ink control) and products that contact liquids. A low Cobb indicates good sizing. Enter the mass gain and the tested area.
Paper Bulk (Specific Volume)
Compute the bulk (apparent specific volume) of paper, bulk = thickness (µm) / grammage (g/m²), in cm³/g, the inverse of density. A high bulk means a 'fluffier', more voluminous paper for the same weight (book papers, boards, tissue), giving stiffness and softness; a low bulk gives dense, thin paper (high-quality printing papers, glassine). It is a key paper-design parameter. Enter the thickness and the grammage.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.