Self-tapping thread inserts in steel stainless and carbon steel are screwed into preformed or predrilled holes and cut their own threads into the wall for permanent installation. Eliminates the time and expense of tapping. Provides a strong wear and vibration resistant thread. Stainless Steel Insert,Screw Locking Thread Inserts,Stainless Steel Threaded Inserts,Stainless Steel Keylocking Threaded Inserts Shenyang Helisert Technology Co., Ltd , https://www.helisert.comBearing Steel Quality Requirements and Shortcomings (4)
Uneven annealing schedules can significantly affect the quality of bearing steel. The goal is to achieve a uniform or spheroidal pearlite structure. However, if the cooling process after casting and rolling is not properly managed, or if the annealing procedure is incorrect, this can lead to uneven microstructures. In severe cases, the carbon-poor regions may experience overheating, resulting in coarse lamellar pearlite. Additionally, slow cooling after casting can cause network-like structures or irregularly distributed coarse carbides.
If the original structure of the steel is normal but the annealing temperature is too high, it can result in coarse lamellar pearlite. Conversely, if the temperature is too low, the structure may appear as fine-grained or very fine pearlite. These inconsistencies in the annealing process can reduce the machinability of the steel and lead to uneven microstructures after quenching, ultimately shortening the service life of bearing components.
**Quality Inspection Methods for Bearing Steels**
1. **Surface Appearance Inspection**:
The surface quality of steel is typically checked with the naked eye. For annealed and non-annealed hot-rolled steels, a pneumatic or electric grinding wheel may be used if necessary. Cold-drawn annealed strip steel and tubes can be inspected by twisting them into smooth surfaces using a thin flat boring tool. For wire discs, visual inspection is standard, and sometimes pickling is performed. A 250mm section from each end is pickled in a low-acid solution to check for surface defects.
2. **Scale and Dimensional Inspection**:
For hot-rolled round steel, a vernier caliper with 0.1mm precision or a micrometer with 0.01mm accuracy is used. Cold-drawn steel and wire are measured using a micrometer with 0.01mm precision. The outer diameter and wall thickness of steel tubes are also measured with similar tools. Thickness of cold-rolled sheets and strips is measured with a micrometer, while length and width are checked with a steel ruler. Bending is assessed using a double ruler or feeler gauge.
3. **Steel Type Identification**:
Portable spectrometers and spark testing are commonly used to identify the type of steel. Spectrometers provide semi-quantitative analysis of key alloy elements such as chromium, manganese, nickel, molybdenum, tungsten, and vanadium. Spark testing helps determine the steel grade based on its spark characteristics.
4. **Hardness Testing**:
Brinell hardness tests are conducted on cold-drawn and annealed steels. The test follows the GB231-84 standard, ensuring accurate measurement of material hardness.
5. **Fracture Inspection**:
For steels with a diameter of 30mm or less, fracture testing is performed. A notch is cut using a hammer or press, and the cross-section is examined under the naked eye for shrinkage cavities, white spots, cracks, and overheating.
6. **Low-Magnification Microstructure Inspection**:
For steels larger than 30mm in diameter, low-magnification inspection is required. A 12–15mm thick sample is cut from one end, ground, and then hot-etched in a 50% hydrochloric acid solution at 70±5°C for 30–40 minutes. After washing with alkaline water and hot water, the sample is examined for segregation, porosity, white spots, cracks, and overburning.
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Bearing steel quality requirements and shortcomings (4)
Source: China Bearing Network | Time: 2013-04-10