GOST 1759.3-83 Nuts. Surface Defects and Methods of Control

GOST 1759.3-83 applies to hexagon nuts with nominal thread diameters from 1 to 48 mm and establishes the permissible limit values of surface defects and methods for their control.

The requirements of this standard may be extended to nuts of other shapes.

The standard fully complies with ST SEV 3682-82.

Nuts. Surface defects and methods of control Nuts. Surface defects and methods of control	GOST 1759.3-83 (ST SEV 3682-82) Supersedes GOST 1759-70 with respect to surface defects of nuts and methods of their control

1. Types of surface defects

1.1. Cracks

Cracks are fractures occurring at the boundaries and within crystals, as well as at locations of non-metallic inclusions, as a result of metal overstressing during processing. If products with cracks are subjected to heating, the crack surface is usually covered with scale.

1.1.1. Stress cracks

They occur during heat treatment as a result of thermal and deformation stresses. They are located randomly on the surface of the product: in the thread, on the wrench surface, extending to the end face, side surface, and flange (collar).

1.1.2. Forming cracks

They occur during blanking of the workpiece, subsequent deformation, and punching of the hole. They are located on the bearing surface of nuts or at the transitions from the bearing surface to the chamfer and thread. Cracks from non-metallic inclusions occur when such inclusions are present in the raw material. They are found on the bearing surface and thread (from non-metallic inclusions), on the end face, on the internal chamfer of the nut hole on the flange side, in the thread, and on the outer surface of the locking element.

1.1.3. Shear cracks

They occur as a result of metal deformation on the wrench surfaces, chamfers, and the side surface of the flange or collar. They are located at an angle of 45° to the nut axis.

1.1.4. Cracks from rolled-in blisters

Cracks from rolled-in blisters in the raw material are in most cases straight, and are located on the side and bearing surfaces, as well as on the collar and flange.

1.1.5. Cracks from scratches

Cracks from scratches on the raw material may occur as a result of deformation of the workpieces on the wrench surfaces, collar, and flange.

1.2. Tears

Tears are open ruptures in the metal occurring at locations subjected to the greatest deformation.

1.3. Folds

They occur as a result of burrs formed during the stamping of nuts being pressed in. They are located on the bearing surface and at the transitions from the bearing surface to the thread and side surface: on the bearing surface, on the wrench surface, at the transitions, and on the bearing surface of nuts with a flange.

1.4. Pitting

Shallow recesses on the surfaces of nuts that are not filled with metal during stamping. They occur due to chips being pressed in or corrosion of the raw metal.

1.5. Tool marks

Longitudinal or circular scratches of small depth occurring as a result of the movement of the processing tool over the nut surface: circular scratches on the bearing surface, longitudinal scratches on the wrench surface.

1.6. Thread damage

Tears or chipping along the thread profile, formed during thread cutting or rolling.

1.7. Burrs

A thread surface defect in the form of a sharp comb-like protrusion formed during cutting.

2. Permissible limit values of surface defects

2.1. Stress cracks

Stress cracks of any size are not permitted.

2.2. Forming cracks

Forming cracks are permitted on the bearing surfaces, end faces, and the surface of the locking element: no more than two cracks on each bearing surface, extending over their full width. If the cracks extend into the thread, they may extend no more than one thread turn. The crack depth shall not exceed 0.5P (P — thread pitch), and the width shall not exceed 0.3 mm.

A crack is permitted on the internal chamfer of the nut hole on the flange (collar) side, provided it does not extend into the thread.

2.3. Shear cracks, cracks from rolled-in blisters, and tears

Cracks or tears shall not extend onto the bearing surface of the hexagon. If cracks or tears are present on opposite flats, the minimum width across flats and the minimum circumscribed circle diameter shall not be less than permitted. The width of a crack or tear shall not exceed 0.02 S + 0.25 mm, where S is the width across flats. On the side surface of the flange or collar, no more than one crack or tear with a width of 0.08 dc is permitted, along with several with a width not exceeding 0.04 dc (dc — the diameter of the collar or flange).

The depth of a crack or tear shall not exceed 0.04d (d — nominal thread diameter of the nuts).

2.4. Cracks from scratches on the raw material

Cracks from scratches with a width not exceeding 0.013d are permitted for nuts with a nominal thread diameter d up to 36 mm, and 0.02d for nuts with a nominal thread diameter d over 36 mm.

2.5. Folds

Folds are not permitted on the bearing surface of nuts with a flange or collar, nor simultaneously on both bearing surfaces of other nuts.

2.6. Pitting

Pitting is permitted if its dimensions do not exceed those specified in Table 1.

Table 1

Nominal thread diameter	Depth	Total area of bearing surface, %
Up to M14	0.25 mm	5
Over M14 to M24	0.017d	7
Over M24	0.02d	10

2.7. Tool marks

Tool marks are permitted if their depth does not exceed the roughness parameters specified in Table 2.

Table 2

Name of surface with tool marks	Product grade	Roughness parameter Ra, μm
Bearing surfaces	A	6.3
	B	12.5
	C	Not regulated
Side surface of thread profile	A; B; C	12.5
Wrench surfaces	A	25
	B; C	Not regulated

2.8. Thread damage

Not permitted:

• burrs and dents on the thread that prevent the GO thread gauge from screwing in;
• chipping of thread turns if their length exceeds half a turn.

3. Methods for control of surface defects

3.1.

The dimensions of defects are calculated using the formulas given in items 2.2–2.4, 2.6, to the second decimal place.

3.2. Visual inspection

To detect surface defects as per items 1.1–1.7, nuts are subjected to visual inspection without the use of magnifying devices.

3.3. Metallographic inspection

If surface defects are present, nuts are subjected to metallographic testing using the deep-etching method.

For testing, a microsection is prepared at the location of the defect. If a crack, tear, or pitting is located on the wrench surface or on the thread, the microsection for determining the depth is prepared perpendicular to the nut axis.

If a crack or pitting is located on the bearing surface or locking washer, the microsection for determining the depth is prepared parallel to the nut axis.

Magnetic methods, such as magnetic particle inspection, may be used to control surface defects of nuts.