GB/T 5779.3-2000 Fasteners surface defects - Particular requirements for bolts, screws and studs
Some standard content:
GB/T 5779. 3--2000
This standard is equivalent to the international standard ISO6157-3:1988 "Surface defects of fasteners Part 3: Special requirements for bolts, screws and studs".
This standard is a revision of GB/T5779.3--1986, with the following major revisions: a) Change "wrinkles" on the thread to "folds", change "H,--actual thread height" to "H---tooth profile height" (Article 3.6); b) Add a list of allowable surface defects (Table 1); c) Comprehensively stipulate the inspection and judgment procedures and sampling plans for surface defects (Chapter 4 and Appendix A). This standard replaces GB/T5779.3--1986 from the date of implementation. Appendix A of this standard is the appendix of the standard.
This standard was proposed by the State Machinery Industry Bureau. This standard is under the jurisdiction of the National Fastener Standardization Technical Committee. This standard was drafted by the Mechanical Science Research Institute. This standard is interpreted by the Secretariat of the National Technical Committee for Standardization of Fasteners. 389
GB/T5779.3--2000
ISOForeword
ISO (International Organization for Standardization) is a worldwide federation of national standard bodies (ISO member bodies). The development of international standards is usually carried out through ISO technical committees. Each member body can also participate in the committee if it is interested in the project carried out by a technical committee. Governmental and non-governmental international organizations related to ISO can also participate in this work. ISO has close ties with the International Electrotechnical Commission (IEC) in the field of electrotechnical standardization. Draft international standards adopted by the technical committee are distributed to all member bodies for voting. The formal publication of international standards requires at least 75% of the member bodies to vote in favor.
International Standard ISO6157-3 was developed by ISO/TC2 Technical Committee for Fasteners. Users must note that all international standards are revised from time to time, and any other international standards referenced here should be confirmed as the latest version unless otherwise stated.
1 Scope
National Standard of the People's Republic of China
Fasteners-Surface discontinuitiesBolts, screws and studs for special requirementsGB/T 5779.3—2000
idt ISO 6157-3:1988
Replaces GB/T5779.3--1986
1.1 The limits specified in this standard apply to various types of surface defects of bolts, screws and studs for special requirements. Applicable bolts, screws and studs:
thread nominal diameter equal to or greater than 5mm;
product grade A and B;
nominal length l≤10d (or longer according to special provisions); performance level 12.9;
performance levels 8.8, 9.8 and 10.9, but it should be specified in the product standard or the agreement between the supplier and the buyer. 1.2 Even if the surface defects reach the allowable limit specified in Chapter 3, the mechanical and working properties of the product shall still meet the minimum requirements of GB/T3098.1. In addition, it shall meet the dimensional requirements of the corresponding product standard. When fatigue strength is required, its fatigue strength shall not be lower than the level that can be achieved by defect-free bolts in the same batch of products. Note
1 The figures in Chapter 3 are only examples and are also applicable to other types of bolts, screws and studs accordingly. 2 For the sake of clarity, some surface defects are exaggerated in the figures. 2 Reference Standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T90--1985 Fastener acceptance inspection, marking and packaging (eqvISO3269:1984) GB/T1031-1995 Surface roughness parameters and their values (neqISO468:1982) GB/T2828-1987 Batch inspection counting sampling procedures and sampling tables (applicable to continuous batch inspection) GB/T3098.1-2000 Fastener mechanical properties bolts, screws and studs (idtISO898-1:1999) GB/T15239-1994 Isolated batch counting sampling inspection procedures and sampling tables 3 Types, causes, appearance characteristics and limits of surface defects 3.1 Cracks Cracks
Cracks are a clear (crystalline) fracture along the metal grain boundary or across the grain, and may contain inclusions of foreign elements. Cracks are usually caused by excessive stress in the process of forging or other forming processes or heat treatment of metals, and may also exist in the raw materials. When the workpiece is heated again, the cracks usually change color due to the peeling of the oxide scale. Approved by the State Administration of Quality and Technical Supervision on September 26, 2000 and implemented on February 1, 2001
3.1.1 Quench cracks Original
GB/T5779.3-2000
During the heat treatment process, due to excessive thermal stress and strain, quench cracks may occur Quench cracks are usually irregular and irregular in direction. Quench cracks appear at the corners of the surface of the fixture
The depth of the ear
The braided cracks
The quenching of the head corners
||Braid cracks at the tooth bottom
Horizontal cracks
Quenching cracks on the tooth top
Cut surface cracks
Longitudinal cracks
Quenching cracks that cross the top of the head
To the opposite side of the head or the back
Quenching cracks that extend radially into the fillet
Quenching cracks
Braid cracks of any depth, length or position are not allowed to exist 3.1.2 Forging Cracks cracks
GB/T5779.3-2000
Forging cracks may occur during the cutting or forging process and are located on the top surface of the majority of the head surface of bolts and screws.
Forging cracks
Length of forging cracks 1:
Depth or width b of forging cracks:
b≤0.04d;
This limit for forging cracks does not apply to recessed head screws (Clause 3.1.5). Nominal thread diameter
3.1.3 Forging brusts
Forging brusts
Forging brusts may occur during the forging process, such as on the diagonal of the hexagonal head of bolts and screws, or on the circumference of the flange surface or round head products, or on the raised part of the head of the recess. Forging brusts
Linked to
Forging brusts
Hexagonal head and hexagonal flange bolts and screws Forging brusts on the flange surface of hexagonal flange bolts and screws should not extend to the top circle (chamfered circle) of the top surface of the head or the bearing surface under the head. Forging brusts on the diagonal should not reduce the diagonal width to less than the specified minimum size. Forging brusts on the raised part of the head of the recess of bolts and screws should not exceed 0.06d in width or be less than the recess in depth. Forging cracks on the flange surface and round head circumference of round head bolts and screws and hexagonal flange bolts shall not exceed the following limits: the width of forging cracks
≤0.08d (or d) (when there is only one forging crack); ≤0.04d. (or d) (when there are two or more forging cracks, one of them is allowed to be up to 0.08d or dk). Depth of forging burst:
Nominal thread diameter; d.—head or flange diameter; dk-head diameter
3.1.4 Shear bursts
GB/T 5779.3—2000
Shear bursts may occur during the forging process, such as on the circumference of the round head or flange surface of round head or flange surface products, usually at an angle of about 45° to the product axis
Shear bursts may also occur on the opposite side plane of hexagonal head products
Shear bursts
Do not crack
Hexagonal head and hexagonal flange bolts and screws: The limit of shear bursts at the wrench head: width ≤0.25mm+0.02s
depth ≤o.04d.
The shear burst on the flange surface of hexagonal flange bolts and screws shall not extend to the top circle (chamfered circle) of the top surface of the head or the bearing surface under the head. The shear burst on the diagonal shall not reduce the diagonal width to less than the specified minimum size. The width of the shear burst on the raised part of the head of the bolt and screw recess shall not exceed 0.06d or the depth shall be lower than the recess part. Round head bolts and screws and hexagonal flange bolts: The width of the shear burst on the flange surface and round head circumference of the bolt and screw shall not exceed the following limits: ≤0.08d. (or d) (when there is only one shear burst) ≤0.04d. (or dx) (when there are two or more shear bursts, one of them is allowed to reach 0.08d. Or dk) --- width across flats; d
—nominal thread diameter; d. ————Head or flange diameter; dk——Head diameter GB/T 5779.3-2000
3.7.5 Forging cracks socket head screws Cause
During the process of forging and processing the groove, due to the effect of shear and extrusion stress, cracks may occur on the circumference, top surface and inner and outer surfaces of the groove (such as hexagon socket)
Cracks not exceeding half the distance between the circumference of the head
tt
Allowed ... Can
- Not allowed
Allowed
- Allowed
Cracks connecting the groove and the head
edges are not allowed
Allowed
Cracks that may
intersect are not allowed
- Allowed
Allowed
Cracks that may
intersect are not allowed
Allowed depth:
GB/T 5779. 3--2000
Table (end)
For fitting parts
Transverse cracks in rounded corners are not allowed
hi≤0.03dk (maximum value is 0.13mm);hz≤0.06d (maximum value is 1.6mm)). 0. 3
Allowed
Number of cracks within 0.37 of the bottom of the bend or
The diameter of the head: t—groove depth
Cracks extending from the inside of the groove to the outer surface and possibly intersecting in the transverse direction are not allowed. Cracks are not allowed within 0.3t of the bottom of the groove. Cracks located in other parts of the groove are allowed, but the length should not exceed 0.25t. The depth should not exceed 0.03dk (maximum value 0.13mm) A longitudinal crack with a depth not exceeding 0.03d (maximum value 0.13mm) is allowed at the junction of the head and the top surface of the head. Longitudinal cracks with a depth not exceeding 0.06dl (maximum value 1.6mm) are allowed on the circumference. GB/T5779.3--2000
3.2 Cracks and streaks in raw materials Row material seams and laps Cracks or streaks in raw materials are usually a thin straight line or smooth curve extending longitudinally along the thread, polished rod or head. Causes of defects
Cracks and streaks are usually inherent defects in the raw materials used to manufacture fasteners. Cracks or marks are often straight lines or smooth curves extending longitudinally
Double lines or streaks, usually longitudinal
thick lines or smooth lines
The depth of cracks or streaks:
≤0.015d+0.1mm (maximum value 0.4mm). If the crack or streak extends to the head, it shall not exceed the permissible limits of width and depth specified for forging burst (Article 3.1.3). d—Nominal diameter of thread
3.3 Voids
GB/T5779.3--2000
A dent is a shallow pit or depression on the surface of a bolt or screw due to the failure of metal to fill the surface during forging or upsetting. Cause
A dent is a mark or impression caused by chips or shear burrs or rust layer of raw materials, and the marks cannot be eliminated during the forging or upsetting process
The depth of the dent h:
h≤0.02d (maximum value is 0.25mm).
Area of the dent:
The sum of the dent areas on the bearing surface shall not exceed 5% of the total area of the bearing surface. Nominal thread diameter
3.4 Folds
GB/T 5779. 3-2000
Folds are metal folds that appear on the surface of fasteners during the forging process. Causes: During an impact of upsetting, wrinkles are generated due to displacement of material caused by insufficient volume and different shapes. Shape: Typical: Wrinkles are allowed at the junction of flange and wrench part. Wrinkles are not allowed on inner corners. Wrinkles are allowed on outer corners. Wrinkles on end surface. Wrinkles are allowed on outer corners. Wrinkles are not allowed on inner corners. Wrinkles are not allowed on inner corners located at or below the supporting surface. However, wrinkles are allowed on outer corners with the exception of those specially allowed in the above diagram or product standards. 3.5 Cut marks: Tool marks are shallow grooves in longitudinal or circumferential direction. Causes
Cut marks are caused by the movement of the manufacturing tool beyond the surface of the bolt or screw
Cut marks formed by the trimming process are allowed—
On the polished rod, fillet or supporting surface, the cut marks caused by processing shall not exceed Ra=3.2μm (as specified in GB/T1031)
GB/T5779.3—2000
3.6 Laps on the thread Laps are metal wrinkles on the thread surface, usually appearing in the same pattern in each product. That is, on the same batch of products, folds appear at the same position and in the same direction of movement. Reasons
3.7 Damage
During the cold forming process of rolled threads, folds or wrinkles are generated on the threads. Unallowed folds and cracks
Allowed folds and cracks
Allowed double cusps
Tooth profile height
Folds of any depth or length are not allowed in the following locations: thread bottom;
Load direction
The stressed side of the thread below the mid-diameter, even if its starting point is above the mid-diameter. The following folds are allowed:
Folds within 0.25H1 of the thread crest; the incompletely rolled thread crest within half a turn on each thread; folds below the mid-diameter on the unstressed thread side and extending in the direction of the major diameter, with a depth not exceeding 0.25H1 and a length not exceeding half a turn of thread length on each thread.
Thread height
Damages
Damages are marks on any surface of the bolt or screw. Causes
Damages such as dents, abrasions, notches and gouges are caused by external influences during the manufacturing and transportation of the bolt or screw. The above damage does not have an accurate geometric shape, position or direction, and it is impossible to identify the factors of external influence. The above damage should not be rejected unless it can be proved that the function or usability is impaired. Depressions, abrasions, notches and gouges located in the first three turns of the thread shall not affect the passage of the thread gauge, and the torque when screwing in shall not be greater than 0.001d\N*m.
If necessary, special agreements, such as packaging requirements, shall be made to avoid damage during transportation. d Nominal diameter of thread5Forging cracks socket head screwsCauses
During the process of forging and processing the groove, due to the effect of shear and extrusion stress, cracks may occur on the circumference, top surface and inner and outer surfaces of the groove (such as hexagon socket).
Cracks not exceeding half the distance between the circumference of the head ||tt| ... Can
- Not allowed
Allowed
- AllowedbzxZ.net
Cracks connecting the groove and the head
edges are not allowed
Allowed
Cracks that may
intersect are not allowed
- Allowed
Allowed
Cracks that may
intersect are not allowed
Allowed depth:
GB/T 5779. 3--2000
Table (end)
For fitting parts
Transverse cracks in rounded corners are not allowed
hi≤0.03dk (maximum value is 0.13mm);hz≤0.06d (maximum value is 1.6mm)). 0. 3
Allowed
Number of cracks within 0.37 of the bottom of the bend or
The diameter of the head: t—groove depth
Cracks extending from the inside of the groove to the outer surface and possibly intersecting in the transverse direction are not allowed. Cracks are not allowed within 0.3t of the bottom of the groove. Cracks located in other parts of the groove are allowed, but the length should not exceed 0.25t. The depth should not exceed 0.03dk (maximum value 0.13mm) A longitudinal crack with a depth not exceeding 0.03d (maximum value 0.13mm) is allowed at the junction of the head and the top surface of the head. Longitudinal cracks with a depth not exceeding 0.06dl (maximum value 1.6mm) are allowed on the circumference. GB/T5779.3--2000
3.2 Cracks and streaks in raw materials Row material seams and laps Cracks or streaks in raw materials are usually a thin straight line or smooth curve extending longitudinally along the thread, polished rod or head. Causes of defects
Cracks and streaks are usually inherent defects in the raw materials used to manufacture fasteners. Cracks or marks are often straight lines or smooth curves extending longitudinally
Double lines or streaks, usually longitudinal
thick lines or smooth lines
The depth of cracks or streaks:
≤0.015d+0.1mm (maximum value 0.4mm). If the crack or streak extends to the head, it shall not exceed the permissible limits of width and depth specified for forging burst (Article 3.1.3). d—Nominal diameter of thread
3.3 Voids
GB/T5779.3--2000
A dent is a shallow pit or depression on the surface of a bolt or screw due to the failure of metal to fill the surface during forging or upsetting. Cause
A dent is a mark or impression caused by chips or shear burrs or rust layer of raw materials, and the marks cannot be eliminated during the forging or upsetting process
The depth of the dent h:
h≤0.02d (maximum value is 0.25mm).
Area of the dent:
The sum of the dent areas on the bearing surface shall not exceed 5% of the total area of the bearing surface. Nominal thread diameter
3.4 Folds
GB/T 5779. 3-2000
Folds are metal folds that appear on the surface of fasteners during the forging process. Causes: During an impact of upsetting, wrinkles are generated due to displacement of material caused by insufficient volume and different shapes. Shape: Typical: Wrinkles are allowed at the junction of flange and wrench part. Wrinkles are not allowed on inner corners. Wrinkles are allowed on outer corners. Wrinkles on end surface. Wrinkles are allowed on outer corners. Wrinkles are not allowed on inner corners. Wrinkles are not allowed on inner corners located at or below the supporting surface. However, wrinkles are allowed on outer corners with the exception of those specially allowed in the above diagram or product standards. 3.5 Cut marks: Tool marks are shallow grooves in longitudinal or circumferential direction. Causes
Cut marks are caused by the movement of the manufacturing tool beyond the surface of the bolt or screw
Cut marks formed by the trimming process are allowed—
On the polished rod, fillet or supporting surface, the cut marks caused by processing shall not exceed Ra=3.2μm (as specified in GB/T1031)
GB/T5779.3—2000
3.6 Laps on the thread Laps are metal wrinkles on the thread surface, usually appearing in the same pattern in each product. That is, on the same batch of products, folds appear at the same position and in the same direction of movement. Reasons
3.7 Damage
During the cold forming process of rolled threads, folds or wrinkles are generated on the threads. Unallowed folds and cracks
Allowed folds and cracks
Allowed double cusps
Tooth profile height
Folds of any depth or length are not allowed in the following locations: thread bottom;
Load direction
The stressed side of the thread below the mid-diameter, even if its starting point is above the mid-diameter. The following folds are allowed:
Folds within 0.25H1 of the thread crest; the incompletely rolled thread crest within half a turn on each thread; folds below the mid-diameter on the unstressed thread side and extending in the direction of the major diameter, with a depth not exceeding 0.25H1 and a length not exceeding half a turn of thread length on each thread.
Thread height
Damages
Damages are marks on any surface of the bolt or screw. Causes
Damages such as dents, abrasions, notches and gouges are caused by external influences during the manufacturing and transportation of the bolt or screw. The above damage does not have an accurate geometric shape, position or direction, and it is impossible to identify the factors of external influence. The above damage should not be rejected unless it can be proved that the function or usability is impaired. Depressions, abrasions, notches and gouges located in the first three turns of the thread shall not affect the passage of the thread gauge, and the torque when screwing in shall not be greater than 0.001d\N*m.
If necessary, special agreements, such as packaging requirements, shall be made to avoid damage during transportation. d Nominal diameter of thread5Forging cracks socket head screwsCauses
During the process of forging and processing the groove, due to the effect of shear and extrusion stress, cracks may occur on the circumference, top surface and inner and outer surfaces of the groove (such as hexagon socket).
Cracks not exceeding half the distance between the circumference of the head ||tt| ... Can
- Not allowed
Allowed
- Allowed
Cracks connecting the groove and the head
edges are not allowed
Allowed
Cracks that may
intersect are not allowed
- Allowed
Allowed
Cracks that may
intersect are not allowed
Allowed depth:
GB/T 5779. 3--2000
Table (end)
For fitting parts
Transverse cracks in rounded corners are not allowed
hi≤0.03dk (maximum value is 0.13mm);hz≤0.06d (maximum value is 1.6mm)). 0. 3
Allowed
Number of cracks within 0.37 of the bottom of the bend or
The diameter of the head: t—groove depth
Cracks extending from the inside of the groove to the outer surface and possibly intersecting in the transverse direction are not allowed. Cracks are not allowed within 0.3t of the bottom of the groove. Cracks located in other parts of the groove are allowed, but the length should not exceed 0.25t. The depth should not exceed 0.03dk (maximum value 0.13mm) A longitudinal crack with a depth not exceeding 0.03d (maximum value 0.13mm) is allowed at the junction of the head and the top surface of the head. Longitudinal cracks with a depth not exceeding 0.06dl (maximum value 1.6mm) are allowed on the circumference. GB/T5779.3--2000
3.2 Cracks and streaks in raw materials Row material seams and laps Cracks or streaks in raw materials are usually a thin straight line or smooth curve extending longitudinally along the thread, polished rod or head. Causes of defects
Cracks and streaks are usually inherent defects in the raw materials used to manufacture fasteners. Cracks or marks are often straight lines or smooth curves extending longitudinally
Double lines or streaks, usually longitudinal
thick lines or smooth lines
The depth of cracks or streaks:
≤0.015d+0.1mm (maximum value 0.4mm). If the crack or streak extends to the head, it shall not exceed the permissible limits of width and depth specified for forging burst (Article 3.1.3). d—Nominal diameter of thread
3.3 Voids
GB/T5779.3--2000
A dent is a shallow pit or depression on the surface of a bolt or screw due to the failure of metal to fill the surface during forging or upsetting. Cause
A dent is a mark or impression caused by chips or shear burrs or rust layer of raw materials, and the marks cannot be eliminated during the forging or upsetting process
The depth of the dent h:
h≤0.02d (maximum value is 0.25mm).
Area of the dent:
The sum of the dent areas on the bearing surface shall not exceed 5% of the total area of the bearing surface. Nominal thread diameter
3.4 Folds
GB/T 5779. 3-2000
Folds are metal folds that appear on the surface of fasteners during the forging process. Causes: During an impact of upsetting, wrinkles are generated due to displacement of material caused by insufficient volume and different shapes. Shape: Typical: Wrinkles are allowed at the junction of flange and wrench part. Wrinkles are not allowed on inner corners. Wrinkles are allowed on outer corners. Wrinkles on end surface. Wrinkles are allowed on outer corners. Wrinkles are not allowed on inner corners. Wrinkles are not allowed on inner corners located at or below the supporting surface. However, wrinkles are allowed on outer corners with the exception of those specially allowed in the above diagram or product standards. 3.5 Cut marks: Tool marks are shallow grooves in longitudinal or circumferential direction. Causes
Cut marks are caused by the movement of the manufacturing tool beyond the surface of the bolt or screw
Cut marks formed by the trimming process are allowed—
On the polished rod, fillet or supporting surface, the cut marks caused by processing shall not exceed Ra=3.2μm (as specified in GB/T1031)
GB/T5779.3—2000
3.6 Laps on the thread Laps are metal wrinkles on the thread surface, usually appearing in the same pattern in each product. That is, on the same batch of products, folds appear at the same position and in the same direction of movement. Reasons
3.7 Damage
During the cold forming process of rolled threads, folds or wrinkles are generated on the threads. Unallowed folds and cracks
Allowed folds and cracks
Allowed double cusps
Tooth profile height
Folds of any depth or length are not allowed in the following locations: thread bottom;
Load direction
The stressed side of the thread below the mid-diameter, even if its starting point is above the mid-diameter. The following folds are allowed:
Folds within 0.25H1 of the thread crest; the incompletely rolled thread crest within half a turn on each thread; folds below the mid-diameter on the unstressed thread side and extending in the direction of the major diameter, with a depth not exceeding 0.25H1 and a length not exceeding half a turn of thread length on each thread.
Thread height
Damages
Damages are marks on any surface of the bolt or screw. Causes
Damages such as dents, abrasions, notches and gouges are caused by external influences during the manufacturing and transportation of the bolt or screw. The above damage does not have an accurate geometric shape, position or direction, and it is impossible to identify the factors of external influence. The above damage should not be rejected unless it can be proved that the function or usability is impaired. Depressions, abrasions, notches and gouges located in the first three turns of the thread shall not affect the passage of the thread gauge, and the torque when screwing in shall not be greater than 0.001d\N*m.
If necessary, special agreements, such as packaging requirements, shall be made to avoid damage during transportation. d Nominal diameter of thread2 Cracks and streaks in raw materials Row material seams and laps Cracks or streaks in raw materials are usually a thin straight line or smooth curve extending longitudinally along the thread, polished rod or head. Causes of defects
Cracks and streaks are usually inherent defects in the raw materials used to manufacture fasteners. Cracks or marks are often straight lines or smooth curves extending longitudinally
Double lines or streaks are usually longitudinal
banana lines or smooth lines
Depth of cracks or streaks:
≤0.015d+0.1mm (maximum value is 0.4mm). If the crack or streak extends to the head, it shall not exceed the permissible limits of width and depth specified for forging burst (Article 3.1.3). d—Nominal diameter of thread
3.3 Voids
GB/T5779.3--2000
A dent is a shallow pit or depression on the surface of a bolt or screw due to the failure of metal to fill the surface during forging or upsetting. Cause
A dent is a mark or impression caused by chips or shear burrs or rust layer of raw materials, and the marks cannot be eliminated during the forging or upsetting process
The depth of the dent h:
h≤0.02d (maximum value is 0.25mm).
Area of the dent:
The sum of the dent areas on the bearing surface shall not exceed 5% of the total area of the bearing surface. Nominal thread diameter
3.4 Folds
GB/T 5779. 3-2000
Folds are metal folds that appear on the surface of fasteners during the forging process. Causes: During an impact of upsetting, wrinkles are generated due to displacement of material caused by insufficient volume and different shapes. Shape: Typical: Wrinkles are allowed at the junction of flange and wrench part. Wrinkles are not allowed on inner corners. Wrinkles are allowed on outer corners. Wrinkles on end surface. Wrinkles are allowed on outer corners. Wrinkles are not allowed on inner corners. Wrinkles are not allowed on inner corners located at or below the supporting surface. However, wrinkles are allowed on outer corners with the exception of those specially allowed in the above diagram or product standards. 3.5 Cut marks: Tool marks are shallow grooves in longitudinal or circumferential direction. Causes
Cut marks are caused by the movement of the manufacturing tool beyond the surface of the bolt or screw
Cut marks formed by the trimming process are allowed—
On the polished rod, fillet or supporting surface, the cut marks caused by processing shall not exceed Ra=3.2μm (as specified in GB/T1031)
GB/T5779.3—2000
3.6 Laps on the thread Laps are metal wrinkles on the thread surface, usually appearing in the same pattern in each product. That is, on the same batch of products, folds appear at the same position and in the same direction of movement. Reasons
3.7 Damage
During the cold forming process of rolled threads, folds or wrinkles are generated on the threads. Unallowed folds and cracks
Allowed folds and cracks
Allowed double cusps
Tooth profile height
Folds of any depth or length are not allowed in the following locations: thread bottom;
Load direction
The stressed side of the thread below the mid-diameter, even if its starting point is above the mid-diameter. The following folds are allowed:
Folds within 0.25H1 of the thread crest; the incompletely rolled thread crest within half a turn on each thread; folds below the mid-diameter on the unstressed thread side and extending in the direction of the major diameter, with a depth not exceeding 0.25H1 and a length not exceeding half a turn of thread length on each thread.
Thread height
Damages
Damages are marks on any surface of the bolt or screw. Causes
Damages such as dents, abrasions, notches and gouges are caused by external influences during the manufacturing and transportation of the bolt or screw. The above damage does not have an accurate geometric shape, position or direction, and it is impossible to identify the factors of external influence. The above damage should not be rejected unless it can be proved that the function or usability is impaired. Depressions, abrasions, notches and gouges located in the first three turns of the thread shall not affect the passage of the thread gauge, and the torque when screwing in shall not be greater than 0.001d\N*m.
If necessary, special agreements, such as packaging requirements, shall be made to avoid damage during transportation. d Nominal diameter of thread2 Cracks and streaks in raw materials Row material seams and laps Cracks or streaks in raw materials are usually a thin straight line or smooth curve extending longitudinally along the thread, polished rod or head. Causes of defects
Cracks and streaks are usually inherent defects in the raw materials used to manufacture fasteners. Cracks or marks are often straight lines or smooth curves extending longitudinally
Double lines or streaks are usually longitudinal
banana lines or smooth lines
Depth of cracks or streaks:
≤0.015d+0.1mm (maximum value is 0.4mm). If the crack or streak extends to the head, it shall not exceed the permissible limits of width and depth specified for forging burst (Article 3.1.3). d—Nominal diameter of thread
3.3 Voids
GB/T5779.3--2000
A dent is a shallow pit or depression on the surface of a bolt or screw due to the failure of metal to fill the surface during forging or upsetting. Cause
A dent is a mark or impression caused by chips or shear burrs or rust layer of raw materials, and the marks cannot be eliminated during the forging or upsetting process
The depth of the dent h:
h≤0.02d (maximum value is 0.25mm).
Area of the dent:
The sum of the dent areas on the bearing surface shall not exceed 5% of the total area of the bearing surface. Nominal thread diameter
3.4 Folds
GB/T 5779. 3-2000
Folds are metal folds that appear on the surface of fasteners during the forging process. Causes: During an impact of upsetting, wrinkles are generated due to displacement of material caused by insufficient volume and different shapes. Shape: Typical: Wrinkles are allowed at the junction of flange and wrench part. Wrinkles are not allowed on inner corners. Wrinkles are allowed on outer corners. Wrinkles on end surface. Wrinkles are allowed on outer corners. Wrinkles are not allowed on inner corners. Wrinkles are not allowed on inner corners located at or below the supporting surface. However, wrinkles are allowed on outer corners with the exception of those specially allowed in the above diagram or product standards. 3.5 Cut marks: Tool marks are shallow grooves in longitudinal or circumferential direction. Causes
Cut marks are caused by the movement of the manufacturing tool beyond the surface of the bolt or screw
Cut marks formed by the trimming process are allowed—
On the polished rod, fillet or supporting surface, the cut marks caused by processing shall not exceed Ra=3.2μm (as specified in GB/T1031)
GB/T5779.3—2000
3.6 Laps on the thread Laps are metal wrinkles on the thread surface, usually appearing in the same pattern in each product. That is, on the same batch of products, folds appear at the same position and in the same direction of movement. Reasons
3.7 Damage
During the cold forming process of rolled threads, folds or wrinkles are generated on the threads. Unallowed folds and cracks
Allowed folds and cracks
Allowed double cusps
Tooth profile height
Folds of any depth or length are not allowed in the following locations: thread bottom;
Load direction
The stressed side of the thread below the mid-diameter, even if its starting point is above the mid-diameter. The following folds are allowed:
Folds within 0.25H1 of the thread crest; the incompletely rolled thread crest within half a turn on each thread; folds below the mid-diameter on the unstressed thread side and extending in the direction of the major diameter, with a depth not exceeding 0.25H1 and a length not exceeding half a turn of thread length on each thread.
Thread height
Damages
Damages are marks on any surface of the bolt or screw. Causes
Damages such as dents, abrasions, notches and gouges are caused by external influences during the manufacturing and transportation of the bolt or screw. The above damage does not have an accurate geometric shape, position or direction, and it is impossible to identify the factors of external influence. The above damage should not be rejected unless it can be proved that the function or usability is impaired. Depressions, abrasions, notches and gouges located in the first three turns of the thread shall not affect the passage of the thread gauge, and the torque when screwing in shall not be greater than 0.001d\N*m.
If necessary, special agreements, such as packaging requirements, shall be made to avoid damage during transportation. d Nominal diameter of thread
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