Several common methods of carburizing process

1. One-time heating and quenching low temperature tempering, carburizing temperature 820 ~ 850oC or 780 ~ 810oC

Features: For those with high core strength requirements, quenching at 820 ~ 850oC, low-carbon martensite in the core structure; high hardness on the surface, using 780 ~ 810oC heating quenching can refine the grains

Scope: carbon steel after solid carburization and low alloy steel workpiece. Coarse grain steel after gas and liquid carburizing, parts that are not suitable for direct quenching after carburizing, and parts that need to be machined after carburizing

2, carburizing, high temperature tempering, one heating quenching, low temperature tempering, carburizing temperature 840 ~ 860oC

Characteristics: high temperature tempering decomposes martensite and retained austenite. Carbon and alloying elements in the layer are precipitated as carbides, which facilitates the reduction of retained austenite in the layer after work-shaping and quenching.

Scope of application: mainly used for carburizing workpieces of CR-NI alloy steel

3, secondary quenching low temperature tempering

Features: The first quenching (or normalizing) can eliminate the reticulated carbide and refine the heart tissue. The second quenching mainly improves the microstructure of the layer, but it should be quenched above the core AC3 when the performance of the core is high.

Scope of application: It is mainly used for important carburized parts with high mechanical properties, especially for coarse grain steel. However, after carburizing, two high-temperature heating is required to increase the deformation and oxidative decarburization of the workpiece, and the heat treatment process is complicated.

4, secondary quenching cold treatment low temperature tempering

Features: Temperature quenching above AC1 or AC3 (heart), high austenitic steel has more retained austenite on the surface layer, and cold treatment (-70 ~ 80oC) promotes austenite transformation, thereby improving surface hardness and wear resistance

Scope of application: mainly used for high alloy steel workpieces that do not require machining after carburizing

5, direct quenching low temperature tempering

Features: Can not refine the grain of steel. The quenching distortion of the workpiece is large, and the amount of retained austenite on the surface of the alloy steel carburized part is large, and the surface hardness is low.

Scope of application: simple operation and low cost. The pit furnace is used to treat parts that are not deformed and subjected to impact loads, and is suitable for gas carburizing and liquid carburizing processes.

6, pre-cooling direct quenching low temperature tempering, quenching temperature 800 ~ 850oC

Features: It can reduce the quenching distortion of the workpiece. The amount of retained austenite in the carburized layer can also be slightly reduced, the surface hardness is slightly improved, but the austenite grains are not changed.

Scope of application: Simple operation, small oxidation, decarburization and quenching deformation of the workpiece. Widely used in a variety of workpieces made of fine grain steel.

Use 3

Thrust roller bearings


Thrust roller bearings includes self-aligning thrust roller bearings, tapered roller thrust bearings, cylindrical roller thrust bearings and needle roller thrust bearings.


1. 29000 type thrust self-aligning roller bearings, this type of bearings can carry both axial and radial load in which mainly is axial load. And it has low friction coefficient and fine self-aligning property. The roller of this bearing is unsymmetrical spherical roller, which can reduce relatively slip between roller and raceway in the operating. Also the long roller has big diameter and much quantity, so the load capacity is high. Generally it adopts oil lubrication, but under low speed circs will be grease lubrication.

NXZ mainly produce the following structures:

2.80000 type thrust cylindrical roller bearings and 90000 type thrust tapered roller bearings, this type can accommodate single-direction axial load, they have much higher axial carrying-capacity than thrust Ball Bearings; in additional, they have high rigidity and take up smaller space.. The thrust cylindrical roller bearings are applied in operation with low rotation speed; the rotation speed of thrust tapered roller bearings is a little higher than thrust cylindrical roller bearings.

3.350000 type double-directions thrust tapered roller bearings (SKF code), this type can accommodate larger double-direction axial load.

4. TTSV and TTSX type thrust full tapered roller bearings used on pressing-down device of mill, this type is full complement roller, can accommodate larger single-direction axial load.

Cage materials

Brass, brozen or steel solid cages are adopted.

Permissible tilt angle

The bearing axis of thrust tapered roller bearings and thrust cylindrical roller bearings are not permitted to be inclined. The bearing axis of thrust self-aligning Roller Bearing is permitted to be inclined, when the equivalent static load P0a≤0.05C0a, and when the shaft washer is slewing, the permissible tilt angle is: 

Bearing series   Permissible tilt angle

292 series        1.5°

293 series          2°

294 series        2.5°

The permissible tilt angle will decrease with the increase of the load.

Minimum axial load

When the bearings are slewing, as the rolling bodies are acted by centrifugal moment, the rolling bodies will slid with reference to the raceway, which will cause the shaft washer and housing washer to be separated. In order to ensure the normal operation of the bearings, certain axial load must be put on the bearing. The minimum axial load required is:  

Thrust tapered roller bearings and thrust cylindrical roller bearings


Thrust self-aligning roller bearings


In the equation: Famin   Minimum axial load (kN)

             Fr        Radial load (kN)

             C0a    Basic static load rating (see bearing dimension table) (kN)

             A     Minimum load constant (see bearing dimension table)

             n      Rotational speed (r/min)

When the actual load acted on a bearing is less than the minimum axial load computed, a spring or other measures must be used to preload the bearing.

Dynamic equivalent axial load

Pa=Fa        (Thrust tapered roller bearings and thrust cylindrical roller bearings)

When Fr≤0.55Fa      Pa=Fa+1.2Fr    (Thrust self-aligning roller bearings)

Static equivalent axial load

        P0a=Fa         (Thrust tapered roller bearings and thrust cylindrical roller bearings)

When Fr≤0.55Fa   P0a=Fa+2.7Fr   (Thrust self-aligning roller bearings)

Thrust Roller Bearing

Thrust Spherical Roller Bearing,Thrust Spherical Roller Bearing,Thrust Tapered Roller Bearing,Full-Type Tapered Roller Thrust Bearing

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