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D4826-88 – Standard Test Method Technical Guide
📐 Scope and Significance
This standard practice (ASTM D4826-88) specifically addresses the application of the International System of Units (SI) within the pulp, paper, and paperboard field. It codifies the recommendations of ISO/TC6 as detailed in ISO 5651 to overcome confusion caused by the various ways SI units can be applied to paper properties. The primary goal, as stated in Section 4, is to provide “uniformity in expressing the results of testing and in quoting property values” to improve communication in commerce and research. The practice is harmonized with ASTM Practice IEEE/ASTM SI 10 and ISO Standards 31 and 1000.
⚠️ Importance of Uniformity
Confusion in reporting test results can arise because “some properties cannot at this time be expressed in SI, some can be expressed in various units all within SI, and various multiples can be used” (Section 1.2). This practice directly addresses these issues by providing a single set of preferred units.
Confusion in reporting test results can arise because “some properties cannot at this time be expressed in SI, some can be expressed in various units all within SI, and various multiples can be used” (Section 1.2). This practice directly addresses these issues by providing a single set of preferred units.
⚙️ Conversion Procedure and Rounding Rules
Section 5.1 of the standard provides a clear procedure for converting test values. To convert a measurement, simply multiply the value in customary units by the specific conversion factor found in the standard’s table. The standard gives a detailed rounding rule to maintain significant precision:
“Generally, the converted value should be rounded to the same number of significant figures or one more than in the value in customary units, depending, respectively, on whether the first digit of the new value is more or less than that of the original value.”
💡 Practical Example from Section 5.1
Thickness of paper determined to be 5.3 mils.
Conversion factor (mil to µm) = 25.4 (exact).
5.3 × 25.4 = 134.62 µm.
First digit of new value (1) is less than original (5), so round to one more significant figure (3 sig figs). Result: 135 µm.
Thickness of paper determined to be 5.3 mils.
Conversion factor (mil to µm) = 25.4 (exact).
5.3 × 25.4 = 134.62 µm.
First digit of new value (1) is less than original (5), so round to one more significant figure (3 sig figs). Result: 135 µm.
📊 Key Conversion Factors
The table below summarizes common conversions found in the pulp and paper industry as recommended by this standard. Factors marked with an asterisk (*) in the source document are exact conversions.
| 🟦 Property | 📏 Customary Unit | 🎯 Recommended SI Unit | ⚡ Conversion Factor |
|---|---|---|---|
| Thickness | mil (0.001 in) | micrometre [µm] | 25.4* |
| Grammage (Basis Weight) | lb / 1000 ft² | gram per square metre [g/m²] | 4.882 |
| Bursting Strength | psi | kilopascal [kPa] | 6.895 |
| Tensile Strength | lbf / in | kilonewton per metre [kN/m] | 0.1751 |
| Tearing Resistance | gram-force [gf] | millinewton [mN] | 9.807 |
❓ Frequently Asked Questions
🔍 What is the designation and status of this standard?
This is ASTM D4826 – 88 (Reapproved 2007). The original adoption was in 1988, and it was last reaffirmed in 2007. It holds the status of an American National Standard.
💡 Are all conversion factors provided exact?
No. As stated in Section 3.1, the table marks exact conversion factors with an asterisk (*). For example, the factor for thickness (mils to micrometres) is exactly 25.4. Factors without an asterisk are sufficiently rounded for practical commercial use.
⚡ How does this standard handle non-preferred SI units?
Section 3.2 explains that units recommended by ISO 5651 are marked with (+) or (#). The hash mark (#) specifically indicates that while the unit is recommended for the pulp and paper industry, it is not a preferred SI unit according to the general rules of ISO 1000.
📌 Which ASTM committee oversees this standard?
This practice is under the jurisdiction of ASTM Committee D06 on Paper and Paper Products and is the direct responsibility of Subcommittee D06.92 on Standardization. It serves as a key resource alongside Practice IEEE/ASTM SI 10 for metric usage.