Concrete block moulds withstand long-term high-frequency vibration impact, material friction and demoulding stress during production, requiring extremely high wear resistance, toughness and fatigue strength of materials. Material selection and heat treatment are the two core factors determining mould service life and cost-effectiveness. This article systematically introduces the practical experience and technical key points accumulated by Botuo-Benda in mould manufacturing from material selection to the whole heat treatment process.
1. Analysis of Mould Working Conditions
During the vibration pressing process, block moulds face the following typical failure modes:
- Wear failure of cavity wall caused by high-speed friction of concrete aggregates
- Fatigue cracks and fractures caused by vibration impact
- Local deformation caused by tensile stress during demoulding
- Corner chipping caused by stress concentration at mould edges
Therefore, ideal mould materials must have high hardness (wear resistance), high toughness (impact resistance) and good fatigue strength (cyclic load resistance). These three properties are often difficult to balance in ordinary steels and must be coordinated through reasonable alloy design and heat treatment processes.
2. Comparison of Common Wear-resistant Alloy Steels
Cr12MoV is a high-carbon high-chromium steel with excellent wear resistance, hardness HRC 58-62, suitable for cavity main body and standard working conditions. D2 (SKD11), a high-alloy cold work tool steel, has good comprehensive performance and is suitable for precision moulds and high-frequency vibration pressing under the same hardness range. H13 (SKD61) is a hot work tool steel with good toughness but low hardness (HRC 48-52), ideal for impact-resistant liners. 42CrMo has high comprehensive strength and moderate cost, hardness HRC 35-45, commonly used for mould frame structural parts.
Botuo-Benda recommends differentiated material solutions according to customers' brick machine types and working conditions. For high-frequency heavy-duty conditions (such as MASA/HESS equipment), D2 steel or imported wear-resistant plates are preferred for longer service life.
3. Key Points of Heat Treatment Process
3.1 Preliminary Heat Treatment (Annealing / Quenching & Tempering)
Raw materials are usually annealed or normalized after rough machining to eliminate internal stress, improve machinability, and create a good structure foundation for subsequent finishing and final heat treatment. Spheroidizing annealing (slow cooling at 780-800°C) is generally adopted for Cr12MoV steel to ensure uniform spherical carbides.
3.2 Vacuum Quenching
Vacuum quenching is the most mainstream quenching method in the mould industry, with main advantages including:
- Zero oxidation and decarburization: Heating in vacuum environment avoids surface oxidation, ensuring dimensional accuracy and surface quality
- Small deformation: Controlled cooling rate by gas cooling, low thermal stress, and workpiece deformation much lower than salt bath quenching
- Eco-friendly and safe: No salt bath medium, environmentally friendly
Vacuum quenching parameters for Cr12MoV steel: heating temperature 1000-1020°C, holding time determined by effective section (about 20-30 minutes), nitrogen gas cooling to room temperature. Hardness after quenching shall reach HRC 62-64.