Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 18685-2002 The bar diameters for rolling general purpose metric screw threads. In addition to editorial changes, the following main technical changes have been made with respect to GB/T 18685-2002:
——22 thread specifications (M8×0.75, M10×0.75, M18×1, M20×1, M22×1, M24×1, M27×1, M30×1, M39×4, M42×4, M45×4, M45×3, M45×2, M45×1.5, M48×4, M48×3, M48×2, M48×1.5, M52×4, M52×3, M52×2 and M52×1.5) are added in this standard (see Table 1);
——When the blank is processed by turning process, this standard uses "twice the arithmetic mean deviation value of surface roughness profile (2Ra)" to correct the blank diameter; the 2002 edition standard uses "the maximum height of surface roughness profile (Rz)" to correct the blank diameter (see 7.1 of this edition, paragraph 1 of Clause 7 in 2002 edition);
——This standard recommends that the ratio of the blank diameter tolerance to the pitch diameter tolerance of the thread should not be less than 0.20; the maximum diameter of Grade 4 thread blank of 11 specifications that do not meet this condition is adjusted (the shrinkage factor fT of the pitch diameter of the through-end thread ring gauge is not considered in the calculation) (M18×2.5, M20×2.5, M22×2.5, M30×3.5, M33×3.5, M36×4, M39×4, M42×4, M45×4, M48×4, M52×4); the 2002 edition standard specifies the condition that the blank diameter tolerance is not less than 0.01mm, and it has not adjusted the maximum blank diameter (see Clause 7 and Table 1 of this edition, A.3 and Table 1 of 2002 edition);
——The method for determining the thread length (B) of the through-end thread ring gauge in this standard is different from that in the 2002 edition (see A.1 of this edition, A.1 of 2002 edition).
This standard was proposed by and is under the jurisdiction of SAC/TC 108 National Technical Committee on Screw Threads of Standardization Administration of China.
The previous edition of this standard is as follows:
——GB/T 18685-2002.
The blank diameters for rolling general purpose metric screw threads
1 Scope
This standard specifies the blank diameters for rolling general purpose metric screw threads. The nominal diameter of general purpose metric screw threads ranges from 1mm to 52mm (the first and second series diameter; the maximum pitch is 4mm); there are five thread tolerances: 4h, 6h, 6g, 6f and 6e.
This standard is applicable to the general purpose metric screw threads of carbon steel and alloy steel materials processed with full-profile extrusion process.
Note: "Full-profile extrusion process" refers to the processing method in which the thread materials completely fill the thread bottom space of the cutting tool when the thread is extruded.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 971-2008 Thread rolling cylindrical dies
GB/T 972-2008 Thread rolling flat dies
GB/T 3934-2003 Specification of gauges for general purpose screw threads
GB/T 14791 Screw threads - Vocabulary
3 Terms and definitions
For the purpose of this document, the terms and definitions specified in GB/T 14791 apply.
4 Calculation formula of blank diameter
The calculation formula of blank diameters for rolling screw threads shall meet the requirements of Annex A.
5 Limit dimensions of blank diameter
The limit dimensions of blank diameters for rolling general purpose metric screw threads shall meet the requirements of Table 1.
6 Precision grade of thread cutting tool
The precision grade of thread rolling flat dies or thread rolling cylindrical dies shall be selected according to the corresponding relation of thread tolerance grade and precision grade of cutting tool specified in Table 2.
The dimensions of thread rolling flat dies and the thread rolling cylindrical dies of general purpose metric screw threads shall meet the requirements of GB/T 972-2008 and GB/T 971-2008 respectively.
7 Adjustment of blank diameter
7.1 It is recommended to use wire drawing or grinding process to process the blank diameter. If the blank is processed by turning process, its diameter shall be the dimension specified in Table 1 plus twice the arithmetic mean deviation value of surface roughness profile (2Ra).
7.2 When the thread is processed by non-full-profile extrusion process, the minimum blank diameter can be smaller than the value specified in Table 1.
7.3 When the blank diameter tolerance calculated by the formula is too small (the ratio of the blank diameter tolerance to the corresponding pitch diameter tolerance of thread is less than 0.20), the following methods are recommended to increase the maximum blank diameter:
a) Improve the precision of the pitch and flank angle of cutting tool, and calculate the maximum blank diameter according to the actual error value of the pitch and flank angle of cutting tool used;
b) Recalculate the maximum blank diameter after ignoring the internal shrinkage of the through-end pitch diameter of the new thread ring gauge (deleting the fT item in the formula).
7.4 When using the thread rolling flat dies, thread rolling cylindrical dies and thread gauge specified in other standards, the blank diameter shall be recalculated according to the parameter precision of the corresponding standard.
Foreword II 1 Scope 2 Normative references 3 Terms and definitions 4 Calculation formula of blank diameter 5 Limit dimensions of blank diameter 6 Precision grade of thread cutting tool 7 Adjustment of blank diameter Annex A (Normative) Calculation formula of blank diameter
ICS 21.040.01 J 04 中华人民共和国国家标准 GB/T 18685—2017 代替GB/T 18685—2002 普通螺纹搓制和滚制前的毛坯直径 The blank diameters for rolling general purpose metric screw threads 2017-09-29发布 2018-04-01实施 中华人民共和国国家质量监督检验检疫总局 中国国家标准化管理委员会 发布 前言 本标准按照GB/T 1.1—2009给出的规则起草。 本标准代替GB/T 18685—2002《搓、滚制普通螺纹前的毛坯直径》。与GB/T 18685—2002相比，除编辑性修改外，主要技术变化如下： ——本标准增加22个螺纹规格(M8×0.75、M10×0.75、M18×1、M20×1、M22×1、M24×1、M27×1、M30×1、M39×4、M42×4、M45×4、M45×3、M45×2、M45×1.5、M48×4、M48×3、M48×2、M48×1.5、M52×4、M52×3、M52×2、M52×1.5)(见表1)； ——采用车削工艺加工毛坯时，本标准用“表面粗糙度轮廓算术平均偏差值的两倍(2Ra)”修正毛坯直径；2002版标准用“表面粗糙度轮廓最大高度值(Rz)”修正毛坯直径(见7.1，2002年版的第7章第1段)； ——本标准推荐毛坯直径公差与螺纹中径公差之比不小于0.20，对不满足此条件11个规格的4级螺纹毛坯最大直径进行了调整(计算时不考虑螺纹通端环规中径的内缩因素fT)(M18×2.5、M20×2.5、M22×2.5、M30×3.5、M33×3.5、M36×4、M39×4、M42×4、M45×4、M48×4、M52×4)；2002版标准给出毛坯直径公差的条件是其不小于0.01 mm，它没有调整过毛坯的最大直径(见第7章和表1，2002版的A.3和表1)； ——本标准确定螺纹通端环规螺纹长度(B)的方法与2002版标准不同(见A.1，2002版的A.1)。本标准由全国螺纹标准化技术委员会(SAC/TC 108)提出并归口。 本标准所替代标准的历次版本发布情况为： ——GB/T 18685—2002。 普通螺纹搓制和滚制前的毛坯直径 1 范围 本标准规定了普通螺纹搓制和滚制前的毛坯直径尺寸。普通螺纹公称直径范围为1 mm～52 mm(第1、2系列直径；最大螺距为4 mm)；螺纹公差带有4h、6h、6g、6f和6e五种。 本标准适用于全牙型挤压工艺加工碳素钢和合金钢材料的普通螺纹。 注：“全牙型挤压工艺”是指在螺纹挤压成形时，螺纹材料完全充满刀具牙底空间的加工方法。 2规范性引用文件 下列文件对于本文件的应用是必不可少的。凡是注日期的引用文件，仅注日期的版本适用于本文件。凡是不注日期的引用文件，其最新版本(包括所有的修改单)适用于本文件。 GB/T 971—2008 滚丝轮 GB/T 972—2008搓丝板 GB/T 3934—2003普通螺纹量规 技术条件 GB/T 14791螺纹 术语 3术语和定义 GB/T 14791界定的术语和定义适用于本文件。 4毛坯直径计算式 搓制和滚制螺纹毛坯直径计算式应符合附录A的规定。 5毛坯直径极限尺寸 普通螺纹搓制和滚制前的毛坯直径极限尺寸应符合表1的规定。 6螺纹刀具精度等级 搓丝板或滚丝轮的精度等级应按表2规定的螺纹公差等级与刀具精度等级对应关系进行选择。 普通螺纹搓丝板和滚丝轮尺寸应分别符合GB/T 972—2008和GB/T 971—2008的规定。 7毛坯直径调整 7.1 推荐采用拉丝或磨削工艺加工毛坯直径。当采用车削工艺加工毛坯时，其毛坯直径应在表1规定基础上再加上其表面粗糙度轮廓算术平均偏差值的两倍(2Ra)。 7.2 采用非全牙型挤压工艺加工螺纹时，其毛坯最小直径可采用比表1规定更小的数值。 7.3 当公式计算出的毛坯直径公差过小时(毛坯直径公差与相应螺纹中径公差之比小于0.20)，推荐采用下列方法增大毛坯最大直径： a) 提高刀具的螺距和牙侧角精度，按所用刀具的实际螺距和牙侧角误差值重新计算毛坯最大直径； b)忽略新螺纹环规通端中径的内缩量(删除公式内的fT项)后重新计算毛坯最大直径。 7.4 当采用其他标准所规定的搓丝板、滚丝轮和螺纹量规时，应按照相应标准的参数精度重新计算毛坯直径。 表1 普通螺纹搓制和滚制前的毛坯直径 单位为毫米 公称 直径 d 螺距 P 毛坯直径d0 4h 6h 6g 6f 6e max min max min max min max min max min
