Abstract:
This article focuses on the research and development of high hardness roller teeth steel castings, which are core components of drum-type crushers. The study addresses technical challenges such as complex structure, high hardness requirements, and tight dimensional tolerances. Through innovative casting processes, alloy composition control, and heat treatment techniques, the production of roller teeth that meet customer specifications has been achieved.
1. Introduction
Roller teeth, as the critical components of drum-type crushers, play a vital role in material crushing. Due to their harsh operating environment and the need for non-replaceable wearing parts, roller teeth must possess dense internal quality, high hardness, and precise tooth profiles to ensure a long service life and perfect engagement during operation. This study presents the research and development of high hardness roller teeth steel castings for a foreign client.
2. Technical Requirements and Challenges
Table 1: Chemical Composition Requirements of Roller Teeth (Mass Fraction, %)
| Element | Customer Requirement |
|---|---|
| C | 0.25 – 0.29 |
| Mn | 1.00 – 1.20 |
| Si | 0.20 – 0.40 |
| P | ≤ 0.025 |
| S | ≤ 0.015 |
| Cr | 1.25 – 2.00 |
| Ni | 3.20 – 4.00 |
| Mo | 0.25 – 0.50 |
Table 2: Main Technical Requirements
| Requirement | Description |
|---|---|
| UT Inspection | Not applicable due to roller body design; instead, CAE simulation results and magnetic particle inspection (MPI) per GB/T 9444-2019 are required. |
| Hardness | The hardness of the casting body shall not be less than 400 HBW. |
| Dimensional Tolerance | CT12 grade per GB/T 6414-2017; all 864 teeth must pass the template inspection. |
Technical Challenges:
- Complex casting structure with dispersed hot spots and difficult feeding.
- High hardness requirements necessitating precise alloy composition control and tailored heat treatment.
- Large height-to-diameter ratio, tight dimensional tolerances, and challenging molding operations.
3. Casting Process Design
3.1. Solution to Solidification Shrinkage
- Table 3: Casting Process Design Details
| Measure | Description |
|---|---|
| Heating Risers | Three heating risers at the top of the casting to ensure effective feeding. |
| Pouring System | Buffered stepped gate with five layers of horizontal runners and four variable-diameter slot gates per layer; external chills placed at the gate intersections to prevent shrinkage defects. |
| Casting Weight | Gross weight of 2,500 kg; pouring weight of 3,200 kg; process yield of 78.1%. |
| Covering Agent | 2.5 kg of heating covering agent evenly applied to each riser after pouring. |
3.2. Alloy Composition Control
To meet the high hardness requirements, the alloy composition was strictly controlled within the following ranges:
- Cr: 1.6% – 2.0%
- Ni: 3.6% – 4.0%
- Mo: 0.4% – 0.5%
- Mn: 1.1% – 1.2%
- Si: 0.3% – 0.4%
3.3. Heat Treatment Process
Due to the inability of conventional normalization and tempering to meet the high hardness requirements, and the high risk of deformation and cracking during quenching and tempering, a customized heat treatment process was adopted:
4. Key Production Control Measures
4.1. Pattern Making
- Iron frame plates for core boxes to enhance stiffness and prevent deformation.
- Precise tooth dimensions and reasonable mold-splitting design to ensure smooth mold release without damaging tooth profiles.
4.2. Molding Operations
-Baozhu furan resin sand for cores; accurate placement of external chills.
-Welded core bones to prevent pouring leakage.
-Two coats of alcohol-based paint applied evenly, especially on tooth positions.
4.3. Pouring Process Control
- Pouring temperature of 1,560 °C.
- Moderate initial pouring speed for impurity removal and better tooth filling; slower pouring later to prevent false filling of risers.
4.4. Post-Processing
- Final inspection using templates.
- Precision grinding and finishing of the casting.
5. Research Results
The high hardness roller teeth steel castings were successfully developed after thorough preparation. Over ten pieces were subsequently produced, meeting customer specifications. Additional roller teeth of different specifications are under preparation.
6. Conclusions
The successful development of roller teeth represents a significant technological innovation, contributing positively to the company’s export market expansion. Key lessons learned include:
- Application of simultaneous solidification principles and ProCAST simulation for optimized casting design without compromising yield.
- Precise alloy composition control to ensure mechanical strength.
- Customized heat treatment to achieve the required hardness.
- Comprehensive size control methods addressing complex influencing factors.
- Effective quality control plans to prevent and monitor quality issues throughout the process.