This standard specifies the technical requirements, inspection methods, inspection rules and marking, packaging, transportation, storage, etc. of forged steel connecting rods for internal combustion engines (including connecting rod bodies, connecting rod caps and connecting rod bushings). This standard applies to forged steel connecting rods for reciprocating piston internal combustion engines with a cylinder diameter of less than or equal to 200 mm. JB/T 6721-1993 Technical conditions for connecting rods for internal combustion engines JB/T6721-1993 Standard download decompression password: www.bzxz.net

Mechanical Industry Standard of the People's Republic of China
JB/T 6721-1993
Technical Conditions for Connecting Rods of Internal Combustion Engines
Published on July 29, 1993
Ministry of Machinery Industry of the People's Republic of China
Implementation on January 1, 1994
Mechanical Industry Standard of the People's Republic of China
Technical Conditions for Connecting Rods of Internal Combustion Engines
1 Subject Content and Scope of Application
JB/T6721-1993
This standard specifies the technical requirements, inspection methods, inspection rules and marking, packaging, transportation, storage, etc. of forged steel connecting rods (including connecting rod bodies, connecting rod caps and connecting rod bushings) for internal combustion engines. This standard applies to forged steel connecting rods of reciprocating piston internal combustion engines with a cylinder diameter of less than or equal to 200mm. Cited standards
GB1958
GB2828
GB2829
GB3077
GB 6397
GB/T13320
JB/T6722
ZBJ92005
3 Technical requirements
Metal tensile test method
Metal Charpy (U-notch) impact test methodMetal Brinell hardness test method
Technical conditions for high-quality carbon structural steel
Shape and position tolerance inspection regulations
Batch inspection counting sampling procedure and sampling table (applicable to inspection of continuous batches) Periodic inspection counting sampling procedure and sampling table (applicable to inspection of production process stability) Technical conditions for alloy structural steel
Metal tensile test specimen
Standard rating diagram and evaluation method for metallographic structure of steel die forgingsMagnetic particle inspection of connecting rods for internal combustion engines
Rolled connecting rod bushings for internal combustion engines
Technical conditions for connecting rod bushings
Technical conditions
3.1 Connecting rods shall be manufactured in accordance with product drawings and technical documents approved through prescribed procedures3.2 Connecting rod roughening and heat treatment
3.2.1 Connecting rod body and connecting rod cap shall be manufactured of 45 steel (selected carbon content is 0.42%~0.47%) specified in GB699 or 40Cr, 35CrMo alloy structural steel specified in GB3077, and may also be manufactured of other steels with mechanical properties not lower than those of the above grades. 3.2.2 The hardness of the connecting rod body and connecting rod cap after quenching and tempering is: 45 steel
217~293 HBS
223~280HBS
35CrMo
250~320HBS
The hardness difference on the same connecting rod body or connecting rod cap should not be greater than 35HBS. 3.2.3 The fiber direction of the metal macrostructure of the longitudinal section of the connecting rod body and connecting rod cap should be along the center line of the connecting rod and consistent with the shape, without disorder and discontinuity. Folding, cracks, delamination, slag inclusion and other defects are not allowed. 3.2.4 The microstructure of the connecting rod should comply with Grades 1~4 in GB/T13320. The depth of the decarburization layer of the connecting rod shall be in accordance with the provisions of the product drawing. 3.2.5 The unprocessed surface of the connecting rod should be smooth, and cracks, folds, creases, scars, oxide scales and defects caused by the metal not filling the forging die are not allowed. The rod body is not allowed to have cutting edge scratches, and the flash of the parting surface should not be greater than 0.8mm in height. It is allowed to have no more than 2 pits with a diameter of no more than 5mm and a depth of no more than 1mm, but the positions shall not be on the same cross section. The connecting rod is allowed to be trimmed within the range of dimensional tolerances approved by the Ministry of Machinery Industry on July 29, 1993 and implemented on January 1, 1994. The trimmed parts should have a smooth transition. Welding repair is not allowed for connecting rods. JB/T6721-1993 The roughness of the connecting rod should be shot peened or other surface strengthening treatments. The roughness R of the main processing surfaces of the connecting rod shall comply with the provisions of Table 1. Table 1
Connecting rod small end hole
Connecting rod bushing hole
Connecting rod big end hole
Connecting rod big end two end surfaces
Connecting rod big end separation surface
Bolt hole supporting end surface
With bushing
Without bushing
The tolerance grade of the dimensional tolerance of each main processing part of the connecting rod shall not be lower than that specified in Table 2. Table 2
Connecting rod bushing hole
Connecting rod big end hole
Connecting rod small end hole
Connecting rod big and small end hole center distance
3.5 The parallelism of the axis of the connecting rod small end hole and the connecting rod bushing hole to the axis of the connecting rod big end hole is:
a. The parallelism in the vertical direction of the plane determined by the axis of the big and small head holes is level 6; b. The parallelism in the parallel direction of the plane determined by the axis of the big and small head holes is level 7. 3.6
The tolerance grades of the shape and position tolerances of the following processing parts of the connecting rod are as follows: a. The cylindrical tolerance grade of the connecting rod bushing hole is not less than Grade 6; b. The cylindrical tolerance grade of the connecting rod big head hole is not less than Grade 6; c. The cylindrical tolerance grade of the connecting rod small head hole is not less than Grade 7; d. The perpendicularity tolerance grade of the two ends of the connecting rod big head to the axis of the connecting rod big head hole is not less than Grade 8;
e. The parallelism tolerance grade of the bolt hole support end face on the connecting rod body and the connecting rod cover to the connecting rod big head separation surface is not less than Grade 8; f. The perpendicularity tolerance grade of the connecting rod bolt guide hole or screw hole axis to the connecting rod big head separation surface is not less than Grade 9. 3.7 The connecting rod shall be inspected by flaw detection in accordance with the provisions of JB/T6722. μm
The weight of the connecting rod and the weight difference of a group of connecting rods on the whole internal combustion engine, and the distribution of the weight of the large and small heads of the connecting rods shall be in accordance with the provisions of the product drawings. 3.8
The connecting rod bushing shall comply with the provisions of NJ19 and ZBJ92005. 3.9
Life.
When the user complies with the provisions of the internal combustion engine manual, the life of the connecting rod shall not be less than the use of the internal combustion engine equipped with the connecting rod. Warranty period of connecting rod: When the user complies with the installation, maintenance and use rules specified in the internal combustion engine manual, within 12 months from the date of manufacture
, or the cumulative working time of 1000h for automotive diesel engine connecting rods and 2000h for other diesel engines, if the connecting rod is damaged and there are technical records available, the manufacturer shall replace it for the user free of charge. Note: The warranty period shall terminate if either of the two warranty conditions expires. 2
Testing method
4.1 Hardness
4.1.1 Mechanical test
JB/T6721-1993
4.1.1.1 Test location: The processing location of the big or small end of the connecting rod, see A in Figure 1. Figure 1
4.1.1.2 Test method: According to the provisions of GB231. 4.1.2 Non-destructive hardness test method
4.2 Mechanical properties
4.2.1 Tensile strength and yield strength
4.2.1.1 Test location: After cutting the metallographic specimen from the rod body, process the plate-shaped specimen according to the dimensions of Figure 2 and Table 3, or the circular specimen according to the provisions of GB6397. When sampling cannot be carried out according to the above dimensions, non-standard specimens are allowed. R
Specimen number
Testing method: According to the provisions of GB228.
4.2.2 Impact toughness
The specimen is cut from the connecting rod body, and the test method is in accordance with GB229. 4.3 Metallographic microstructure
Testing location: Cut at the junction of the small head hole and the rod body of the connecting rod, see the AA section in Figure 3. 4.3.1
JB/T 67211993
4.3.2 Test method: Grind the metallographic specimen and observe the level and decarburization layer depth with a 500x metallographic microscope. 4.4 Metal macrostructure of the longitudinal section of the connecting rod
4.4.1 Test location: Cut and grind according to the BB section in Figure 3. 4.4.2 Test method: Cut open after forging, and check after corrosion with 3%~5% nitric acid alcohol solution. 4.5 Surface roughness
Measured with a surface roughness meter, or other methods can be used. 4.6 Size
Connecting rod big and small head holes: measure with internal diameter micrometer or other measuring instruments. 4.6.1
4.6.2 Center distance of big and small head holes: measure with four equal blocks, lever micrometer and height gauge on the flat plate, and special inspection tools are allowed to be used for measurement. 4.7 Shape and position tolerance
The shape and position tolerance of each processed part on the connecting rod shall be measured in accordance with GB1958. 4.8 Surface quality
The surface quality of the connecting rod shall be observed with the naked eye.
Magnetic particle inspection shall be in accordance with the provisions of JB/T6722.
5 Acceptance rules
5.1 Each pair of connecting rods shall be inspected and qualified by the technical inspection department of the manufacturer before leaving the factory. 5.2 The manufacturer shall sample the mechanical properties and chemical composition of the raw materials in batches. The test bars used for testing shall be materials of the same brand and the same furnace number.
5.3 The manufacturer shall regularly inspect the hardness, mechanical properties, impact toughness (if the test specimen cannot be cut, it is allowed not to conduct this test), microstructure and macrostructure of the connecting rod and 3.3, 3.4, 3.5. 5.4 When the ordering unit samples the quality of the connecting rod, the sampling method shall be carried out in accordance with the provisions of GB2828 and GB2829, or the ordering unit shall negotiate and decide with the manufacturer.
6 Marking, packaging, transportation and storage
6.1 Each connecting rod assembly shall be marked with:
a. Manufacturer name or factory mark;
b. Matching mark of connecting rod body and connecting rod cover; c. Weight or weight group mark.
JB/T 67211993
The position, size and method of marking shall be in accordance with the product drawings, and care shall be taken not to damage the parts. 2 The connecting rod body must be packed together with the connecting rod cover. Before packing, it must be cleaned and oil-sealed or treated with other anti-corrosion treatments, and wrapped with strong and impermeable neutral paper or plastic film, and then packed in a dry packaging box lined with waterproof paper, and ensure that the parts will not be damaged during normal transportation. The total weight of the box shall not exceed 50kg. Www.bzxZ.net
6.3 A packing list signed and stamped by the manufacturer's inspector and packer should be attached to the packaging box, which should indicate the internal combustion engine model, part name, part number, quantity and packaging date.
6.4 Each connecting rod should be accompanied by a product quality certificate signed and stamped by the manufacturer's inspector, and the certificate should indicate: a. Manufacturer name, factory logo and address;
b. Internal combustion engine model, part name and part number; c. Inspection date.
6.5 The outer surface of the packaging box should be marked with:
a. Manufacturer name, factory logo and address;
b. Internal combustion engine model and part name;
c. Packing date, gross weight and quantity;
d. "Handle with care" and "Moisture-proof" signs. 6.6 Connecting rods should be stored in a ventilated and dry warehouse. The manufacturer should ensure that the connecting rods will not rust within 12 months from the date of leaving the factory under normal storage conditions.
Additional instructions:
This standard was proposed and managed by the Shanghai Internal Combustion Engine Research Institute of the Ministry of Machinery Industry. This standard was drafted by the Shanghai Internal Combustion Engine Research Institute of the Ministry of Machinery Industry. The main drafter of this standard is Li Shaoqiu.
From the date of implementation of this standard, NJ20-85 "Technical Conditions for Connecting Rods" will be invalid. 5
People's Republic of China
Mechanical Industry Standard
Technical Conditions for Connecting Rods of Internal Combustion Engines
JB/T 67211993
Published and issued by the China Academy of Mechanical Science
Printed by the China Academy of Mechanical Science
(No. 2 Shouti South Road, Beijing
Postal Code 100044)
Word Count 10.000
1/16 Print Sheet 1/2
Format 880×1230
First Edition in December 1993
First Printing in December 1993
Print Quantity 1-500
Price 2.00 Yuan
Mechanical Industry Standard Service Network: http://www.JB.ac.cn66_9
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