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GB/T 39542.3-2025Mechanical pencils for technical drawings - Part 3: Black leads - Bending strengths of HB leads (English PDF)

技术制图活动铅笔第3部分：黑铅芯 HB铅芯弯曲强度

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Issued by

State Administration for Market Regulation, China National Standardization Administration

Level / Type

National · Recommended

Issue date

May 30, 2025

Implementation date

May 30, 2025

Scope

GB/T 39542.3-2025 is the English-translated version of 技术制图活动铅笔第3部分：黑铅芯 HB铅芯弯曲强度.

GB/T 39542.3-2025 is the Chinese national standard that fixes how strong the HB black lead of a technical-drawing mechanical pencil must be in bending, and how that strength is measured.

Bending strength is the value obtained by loading a lead to its breaking point under the prescribed test method and formula.

Minimum values are set by lead type and nominal diameter: for resin leads 240 MPa at 0.35 mm, 190 MPa at 0.5 mm, 160 MPa at 0.7 mm and 95 MPa at 1 mm, and for clay leads 70 MPa at 2 mm, with a note that 0.35 mm and 1 mm leads are commonly marked 0.3 and 0.9.

Lead makers and testing laboratories use it to release product. Identical to ISO 9177-3:2022, it replaces GB/T 39542.3-2020 and was issued and came into force on 30 May 2025.

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Document preview — GB/T 39542.3-2025

National Standard of the People's Republic of China

ICS: 97.180
Classification: Y 50

Issued by: State Administration for Market Regulation, China National Standardization Administration

Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Bending strength

Foreword

This document is in accordance with the provisions of GB/T 1.1-2020 "Guidelines for standardization work Part 1: Structure and drafting rules for standardization documents" Drafting.

This document is part 3 of GB/T 39542 "Mechanical pencils for technical drawing". GB/T 39542 has published the following parts.

--- Part 1: Classification, dimensions, performance requirements and tests;

--- Part 2: Classification and dimensions of black lead cores;

--- Part 3: Bending strength of black lead core HB lead.

This document replaces GB/T 39542.3-2020 "Mechanical pencils for technical drawing - Part 3: Bending strength of black lead HB lead" Compared with GB/T 39542.3-2020, in addition to structural adjustments and editorial changes, the main technical changes are as follows.

--- The lead type has been changed (see 4.2, 4.2 of the 2020 edition).

This document is equivalent to ISO 9177-3:2022 "Mechanical pencils for technical drawing - Part 3: Bending strength of black lead HB".

Introduction

Mechanical pencils are one of the most popular writing tools among consumers. Mechanical pencils are divided into general-purpose mechanical pencils according to different usage occasions. and technical drawing mechanical pencils to meet the evolving market needs. The third edition of ISO 9177-1 in 2016 changed the main elements of the standard name to The second edition of ISO 9177-2 and ISO 9177-3 in 2022 also made the same adjustment, and the technical content is only Limited to technical drawing mechanical pencils and their leads to distinguish them from general purpose mechanical pencils.

GB/T 39542 is intended to consist of three parts.

--- Part 1: Classification, dimensions, performance requirements and tests. The purpose is to establish the quality requirements for mechanical pencils suitable for technical drawing and test methods.

--- Part 2: Classification and dimensions of black lead. The purpose is to establish the basic quality of black lead for mechanical pencils suitable for technical drawing Require.

--- Part 3: Bending strength of HB black lead. The purpose is to establish the HB black lead suitable for technical drawing mechanical pencils Requirements and test methods for flexural strength.

1 Scope

This document specifies the bending strength and test method of black lead with hardness grade HB for use in technical drawing mechanical pencils.

2 Normative references

This document has no normative references.

3 Terms and definitions

The following terms and definitions apply to this document.

ISO and IEC maintain terminology databases used for standardization at the following websites.

3.1 Bending strength

The lead core strength is obtained by measuring the lead core from bending to the breaking point using the prescribed test method and calculation formula.

4 Bending strength

4.1 General

The bending strength of HB lead cores used in mechanical pencils shall be tested in accordance with Chapter 5 and shall comply with the requirements of 4.2.

4.2 Bending strength of HB black lead of mechanical pencil

The bending strength (sigma) should not be less than the corresponding value of each nominal diameter specified in Table 1.

0.35a 240 0.5 190 0.7 160 1a 95 Clay (C) 2 70 a Usually, the pencils and packaging can be marked as 0.3 and 0.9. Users should note that the new standardized mark is fully applicable to the old mark.

For a mechanical pencil, the reverse is true, i.e. 0.35 and 1 correspond to 0.3 and 0.9 respectively.

......
This preview omits tables, figures, formulas and parts of the technical clauses. The complete document — 17 pages — is available in the English PDF.

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