GB5779.1-86标准（英文版）

National Standard of the Peoples Republic of China UDC 621. 882: 620. 191 GB 5779.1-86Surface discontinuities of fasteners on bolts, screws and studs for general requirements 1. Introduction 1.1 This standard is applicable to types, names, appearance characters, allowable minimum limits and examination and inspection methods of surface discontinuities on bolts, screws and studs whose requirements on surface discontinuities are general requirements (product quality). 1.2 Applicable fasteners shall meet conditions as follows: nominal thread diameters from 5 mm to 64mm;product grade A and B (GB 3103.1-82 Fastener Tolerance Bolts, Screws and Nuts;property classes equal to or lower than 10.9 (GB 3098.1-82 Fastener Mechanical Properties Bolts, Screws and Studs).1.3 This standard is mainly applicable to standard fasteners. It also could be used for non-standard fasteners. 1.4 When it is required to more strictly control surface discontinuities of bolts, screws and studs, it shall follow related product standards or agreement made by both interested parties according to GB 5779.3-85 Surface Discontinuities of Fasteners-Bolts, Screws and Studs-Special Requirements.Note: figures in this standard are used as examples only. They could also be applicable to other types of bolts, screws and stubs. They are exaggerated in some cases for clarity.2 Types, causes, appearance and limits of surface discontinuities2.2 Cracks A crack is a clean fracture passing through or across the grain boundaries and may possibly follow inclusions of foreign elements. Cracks are normally caused by overstressing the metal during forging or other forming operations, or during heat treatment, where parts are subjected to significant reheating, cracks usually are discolored by scale. Issued by China State Bureau of Standards on 01-17-1986 Implemented on 10-01-1986GB 5779.1-86 2.1.1 Quence cracksCauseQuence cracks may occur during heating due to excessively high thermal and transformation stresses. Quench cracks usually follow an irregular and erratic course on the surface of the fastener. Appearquench crack circumferential and adjacent to filletquench crack cross the gasketsanceusually an extension of crack in shank or side of headquench crack across top of headquench crack on the headquench crack at corner of headtransverse quench crackquench crack at rootX enlargedlongitudinal quench crackquench crack at rootquench crackLimitsQuench cracks of any depth, any length, or in any location are not permitted.2.1.2 Forging cracks Causeforging cracks may occur during the cut-off or forging operations and are located on the top of the head of screws and bolts.Appearanceforging crack Limitslength of forging cracks: 1d;Depth or width of forging cracks: 0.04d;nominal thread diameter 2.1.3 Forging bursts Cause forging bursts may occur for example during forging on the flats or comers of the heads of bolts and screws, at the periphery of flanged or circular head products or on the raised periphery of indented head bolts and screws.Appearance forging burstsforging burstsforging burstsforging burstsLimits forging bursts1 Hexagon head boltsa No forging burst in the flats of hexagon bolts and screws shall extend into the crown circle on the top of the head surface (chamfer circle) or into the underhead bearing surface.b Forging bursts occurring at the intersection of two wrenching flats shall not reduce the width across corners below the specified minimum.2. Circular head bolts and screws and Hexagon flange face bolts Width of forging bursts on the circumference:0.08dc (or dk)（with only one forging burst）0.04dc (or dk)（with two or more forging bursts, one of which may extend to 0.08dc ）。3. Forging bursts on the upheaval parts, whose width shall not exceed 0.06d or whose depth shall not extend under the peck. dnominal thread diameter; dchead of flange diameter; dkhead diameter 2.1.4 Shear burstsCauseshear bursts may occur, for example during forging, frequently at the periphery of products having circular or flanged heads, and are located at approximately 450to the product axis.Shear bursts may also occur on the sides of hexagon head products. Appearanceshear bursts shear bursts shear bursts Limits1 Hexagon head boltsc Noshear burst in the flats of hexagon bolts and screws shall extend into the crown circle on the top of the head surface (chamfer circle) or into the underhead bearing surface.d. Shear bursts, occurring at the intersection of two wrenching flats, shall not reduce the width across corners below the specified minimum.2. Circular head bolts and screws and Hexagon flange face bolts The width of shear bursts on the circle shall not exceed the following limits:0.08dc (or dk)（for only one shear burst）0.04dc (or dk)（with two or more forging shear bursts, one of which may extend）。 3. Shear bursts on the upheaval parts, whose width shall not exceed 0.06d or whose depth shall not extend under the peck. dnominal thread diameter: dchead of flange diameter; dkhead diameter2.2 Raw material seams or lapsA seam or lap is a narrow, generally straight or smooth curved line discontinuity running longitudinally on the thread, shank or head.Causeinherent in the raw materials from which fasteners are madeAppearanceseams or laps seams or laps seams or laps Limits1 Permissible depth of seams and laps0.03d；2 If laps or seams extend into the head, they shall not exceed the permissible limits for width and depth specified for bursts (see 2.1.3).dnominal thread diameter 2.3 Voids A void is a shallow pocket or hallow on the surface of a bolt or screw.Causevoids are produced by marks and impressions due to chips or by rust formation on the raw material. Appearancevoids Limits1Depth, h, of voids :0.02d( maximum value is 0.25mm)；2 Area of voids:The combined surface area of all voids on the bearing face shall not exceed 10 % of the total area.dnominal thread diameter 2.4 FoldsA fold is a doubling over of metal which occurs at the surface of the fastener during forging.Causefolds are produced by materials displacements. They always occur on the places when sections changeAppearancepermissible typical “clover leaf” fold in non-circular shoulder fastenerpermissible, at the surface of the bolt end; permissible, at the intersection between flange and driving part; non permissible, fold at interior corner; non permissible, fold at interior corner; permissible, fold at exterior corner;permissible, fold at exterior corner;Limits1 Folds at interior concerns at or below the bearing surface are not permissible, unless specifically permitted in the product standard 2 Folds at exterior corners are permissible.2.5 Tool marks Tool marks are longitudinal or circumferential grooves of shallow depth.Causetool marks are produced by the movement of manufacturing tools over the surface of the bolt or screw. Appearancetool marks tool marks tool marks Limits1 Tool marks produced by machining in the shank, fillet or bearing surface shall not exceed a surface roughness of Ra=3.2 m （in according with GB1031-83）2 Other surface tool marks are permissible. 2.6 Damages Damages are indentations of any surface of a bolt or screwCausedamages, for example dents, scrapes, nicks and gouges, are produced by external action during manufacture and handling of bolts and screws, for example during loading.AppearanceNo precise geometrical shape, location or direction, identifiable as external action.Limits1. Damages as described above shall not cause rejection unless it can be shown that they impair function or usability,2. Dents, scrapes, nicks and gouges on the first three threads shall be such that they allow the screwing on of a go-ring gauge with torque values of 0.001 d3 max., in Newton meters.3. If necessary, both parties shall reach into special agreement, including packing requirements to avoid any damage during the transport.dnominal thread diameter3 Inspection and evaluation procedure3.1 Non-destructive testingA random sample shall be taken subjected to either visual tests or other suitable tests, e.g. magnetic techniques or eddy current.3.2 Destructive testing If defective pro