Transmission Chain Testing

Transmission chain inspection mainly conducts scientific testing and analysis on the geometric dimension and precision testing, tensile property, fatigue life testing, hardness testing, pre-loading and measurement, and appearance and surface quality inspection, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Geometric dimension and precision testing: The precise measurement is carried out on the key dimensions such as the chain pitches, roller diameters, inner link plate heights and pin diameters, ensuring that they meet the design drawings and standard tolerance requirements. This is the basis of evaluating the chain manufacturing precision and interchangeability, directly affecting the engagement performance between the chains and sprockets.

Tensile property (breaking strength) testing: On the dedicated tensile testing machines, the continuously increasing tensile loads are applied to a section of chain or a single link until the fracture occurs. The maximum breaking loads are recorded, to verify whether the chain material strengths and the load-bearing capabilities of the overall structures meet the design and standard provisions.

Fatigue life testing: Simulating the working conditions of the chains bearing the periodic alternating loads in the actual transmission, the fatigue testing machines are used to make them run at the high-speed cycles under the specific loads. The numbers of cycles when the fatigue cracks appear or the complete fractures occur in the chains are recorded, to evaluate their durability and reliability for the long-term use.

Hardness testing: The Rockwell or Vickers hardness testers are used to measure the hardnesses of the surfaces or cross-sections of the key parts such as the pins, bushings, rollers and link plates of the chains. The appropriate hardness values are crucial for ensuring the wear resistance, fatigue strength of the parts and preventing the brittle fractures.

Pre-loading and measurement: The pre-tensions of about 1/3 of the breaking strengths are applied to the new chains, eliminating the initial clearances generated during the manufacturing processes, and then their lengths are precisely measured. This testing is used to determine the initial length precision of the chains, and is the basis of ensuring the accurate tension setting of the transmission systems.

Appearance and surface quality inspection: Through the visual inspection or with the help of the magnifiers, whether the chain surfaces have the defects such as the cracks, laps, rust, burrs and indentations is checked. At the same time, the stamping qualities of the link plates, rivet head shapes, as well as the uniformity and adhesion of the surface treatment layers such as the electroplating and blackening are checked.

Testing Scope

Short-pitch precision roller chains for the transmission: This is the most widely applied chain type. The testing scope covers all the specifications specified by the standards such as ISO 606 (GB/T 1243) and ANSI B29.1, from the 04C to 48A series, mainly applied to the medium and low speed transmission occasions such as the motorcycles, agricultural machinery and industrial conveying.

Heavy-duty cranked link roller chains for the transmission: For the cranked link chains under the heavy-load working conditions such as the petroleum, metallurgy and mines, the testing follows the standards such as ISO 3512 and GB/T 15390. The testing emphases are the bending strengths of the link plates, wear resistance of the large-size pins and bushings, as well as the overall impact resistance.

Silent chains (inverted tooth chains): The testing is according to the standards such as ISO 606 and GB/T 10855. In addition to the routine items, the special attention is paid to the tooth profile precision of the link plates, guide forms (inner guide or outer guide), clearances of the hinge pairs, as well as the noise level testing during the operation.

Roller chains and bushing chains for the motorcycles: This type of chains needs to meet the harsh requirements of the high speeds, high loads and wear resistance. In addition to the general items, the testing scope also includes the strict lateral flexibility inspection, wear resistance testing, as well as the sealing property and grease retention testing for the O-ring sealed chains.

Flat-top chains and side-bending chains for the conveying: Mainly used for the automated conveying lines. The testing scope includes the top surface flatness of the link plates, lateral bending flexibility of the hinges, as well as the turning radius testing of the chains in the horizontal and vertical planes, ensuring that they can smoothly and flexibly run along the predetermined tracks.

Chains for the special environments: Covering the corrosion-resistant chains such as the stainless steel chains and nickel-plated chains, as well as the special material chains for the high or low temperature environments. The testing scope needs to be extended to the salt spray testing, mechanical property testing under the high and low temperatures, as well as the material metallographic analysis.

Testing Methods

Contact measurement method: The measuring tools such as the micrometers, vernier callipers, height gauges and pitch gauges are used for the direct contact measurement of the chain geometric dimensions. This method is intuitive with the low costs, but has the high requirements for the operator skills, suitable for the fast inspection of the single pieces or small batches at the production sites.

Optical image measurement method: The two-dimensional or three-dimensional image measuring instruments are used. Through the high-resolution cameras to capture the chain profiles, the software automatically analyses their dimensions and geometric tolerances. This method is non-contact, with the high precision and good repeatability, especially suitable for the precision testing of the complex profiles (such as the tooth profiles of the silent chains).

Tensile testing method: According to the standards such as ISO 15654 or GB/T 20736, carried out on the electronic universal material testing machines. The two ends of the chain specimens are clamped with the dedicated fixtures, and the loads are applied at the constant rates. The transducers record the load-displacement curves, finally obtaining the breaking load and elongation data.

Rotary fatigue testing method: According to the ISO 15654 standard, the chains are installed on the two sprockets to form the closed loops, driven by the drive motors, and the constant tensioning forces are applied through the loading devices. The testing is carried out under the closed oil bath or oil spray lubrication conditions, continuously running until the failure, recording the numbers of cycles.

Wear testing method: Usually the bench testing is used to simulate the actual working conditions, making the chains and standard sprockets wear against each other under the set loads and speeds. The chain pitch elongation amounts are regularly measured during the shutdowns, and the wear curves are plotted, to evaluate the wear lives of the chains and the effects of the lubricants.

Non-destructive testing method: Including the magnetic particle flaw detection or fluorescent penetrant flaw detection, used to detect the surface micro cracks of the chain parts (especially the pins and link plates); the ultrasonic flaw detection can be used to detect the internal defects such as the inclusions and porosity of the materials. It is the important means of ensuring the qualities of the high-reliability chains.

Testing Standards

Domestic Standards:

1. GB/T 1243, Short-pitch transmission precision roller chains and chain wheels

2. GB/T 15390, Welded steel type cranked link chains, attachments and sprockets for engineering

3. GB/T 10855, Inverted tooth (silent) chains and chain wheels

4. GB/T 20736, Fatigue test method for precision roller chains for transmission

5. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

6. GB/T 230.1-2018, Metallic materials — Rockwell hardness test — Part 1: Test method

7. GB/T 4340.1-2009, Metallic materials — Vickers hardness test — Part 1: Test method

8. GB/T 10125-2021, Corrosion tests in artificial atmospheres — Salt spray tests

International Standards:

1. ISO 606, Short-pitch transmission precision roller chains, attachments and associated chain sprockets

2. ISO 3512, Heavy duty cranked link transmission chains

3. ISO 15654, Fatigue test machine for transmission roller chains

4. ISO 7500-1, Metallic materials — Calibration and verification of static uniaxial testing machines — Part 1: Tension/compression testing machines

5. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

6. ANSI B29.1, Transmission roller chains, attachments, and sprockets

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Universal material testing machine: Equipped with the dedicated chain tensile fixtures, used for the breaking strength, yield strength and elongation testing. The equipment needs to have the high-precision force transducers and displacement measurement systems. The measuring ranges should cover the full load ranges from the light to heavy chains, and comply with the calibration requirements of ISO 7500-1.

Chain fatigue testing machine: The core equipment used to evaluate the chain durability. Usually the closed-loop structure, including the drive systems, loading systems, lubrication systems and cycle counting devices. The high-end equipment has the load and speed programming control functions, and can monitor the vibration and temperature changes in real time.

Precision measuring instruments: Including the coordinate measuring machines (CMM) and optical image measuring instruments, used to obtain the comprehensive geometric dimension data of the chains with the high precision and efficiency. In addition, the dedicated chain pitch measuring instruments and roller diameter sorting machines are also the key testing equipment on the production lines.

Hardness tester: According to the sizes and heat treatment states of the chain parts, the Rockwell hardness testers (HRC, HRB), Vickers hardness testers (HV) or Leeb hardness testers are selected. For the small parts (such as the pin ends) or the samples needing the hardened layer depth testing, the micro Vickers hardness testers are the more appropriate choices.

Metallographic microscope and preparation equipment: Used for the micro-structure analysis of the chain materials. Through the cutting, mounting, grinding, polishing and etching to prepare the metallographic specimens, the grain sizes, phase compositions, carburized layer or hardened layer depths are observed under the microscopes, thereby determining whether the heat treatment processes are qualified.

Wear and lubrication test bench: The dedicated testing equipment simulating the specific working conditions, which can control the loads, speeds, temperatures and lubrication conditions. Through the measurement of the weight losses, dimension changes of the chains or the wear particle compositions in the lubricating oils before and after the operation, the wear resistance of the chains and the effectiveness of the lubricants are comprehensively evaluated.