How to Make Concrete Blocks with Steel Moulds: A Guide from Design to Production
Making concrete blocks with steel moulds is a precision-driven process that transforms raw materials into durable building units. As a manufacturer of brick machines and moulds since 2010, Fujian Unik mould Technology Co., Ltd. has evolved alongside the industry, particularly in Quanzhou, Fujian-a hub known for its manufacturing capability and global connectivity. This guide outlines the entire workflow, from mould selection and material preparation to the finishing steps that ensure consistent, high-quality output.
1. Selecting and Preparing the Steel Mould
Matching the Mould to the Machine and Material
The process begins with the right mould. It is a precision tool, not a generic accessory. A proper mould must be specified for the block type (standard bricks, hollow blocks, pavers, kerbs, or custom profiles) and, critically, for the specific block-making machine model. Moulds are engineered to mount seamlessly onto machines from major brands like HESS, MASA, ZENITH, and BESSER, with custom interfaces available. The material and treatment of the mould are chosen based on production demands. For standard mixes, 42CrMo steel may be used, but for highly abrasive mixes or high-volume production (exceeding 200,000 cycles), alloy tool steel like Cr12MoV or 9CrSi is preferred. These undergo carburizing heat treatment, achieving a surface hardness of HRC58-62 to resist abrasion, while maintaining a tougher core to absorb vibration.
Cleaning and Applying Release Agent
Before the first pour, the steel mould must be prepared. This typically involves:
Cleaning: Ensuring the cavity is free of dust, debris, or old concrete.
Applying a Release Agent: To prevent concrete from sticking to the mould walls. This is particularly important for complex shapes like interlocking blocks. Options range from a simple oil to specialized sprays, or for smoother performance, choosing a mould with chrome-plated cavities can significantly reduce adhesion.
2. Preparing the Concrete Mix
The concrete mix is a crucial factor in block quality and mould longevity. The typical mixture for concrete blocks is a 1:3:6 ratio (cement:sand:aggregate) with a maximum aggregate size of 10mm, or a cement-sand mix in ratios like 1:7 or 1:9. A stiff or plastic consistency is recommended for block-making to minimize water content, reduce shrinkage, and achieve the necessary strength. The use of proper, clean materials not only ensures the block's structural integrity but also reduces the abrasive wear on the steel mould cavity.
3. The Moulding Process
Filling the Mould
The prepared concrete is placed into the mould cavities. In manual or semi-automated setups, this is often done in layers to ensure even distribution. For instance, the mould can be filled to about half, then compacted before adding the remaining concrete. In fully automated systems, the filling is controlled by the machine.
Compaction and Vibration
This is the most critical step for achieving a dense, strong block. Compaction removes air voids and ensures a uniform product.
Vibration: Modern machines use high-frequency vibration to consolidate the concrete. The mould transfers this vibration directly to the mix.
Pressing: A tamper plate or press head comes down on the mix, applying pressure to form the final shape. The clearance between the presser foot and the mould cavity is precise, often between 0.2mm and 0.4mm, to prevent concrete from escaping.
Manual Methods: In simpler setups, manual tamping using a rammer or a tamper lid-plate is used for compaction.
4. Demoulding and Curing
Demoulding: Removing the Fresh Block
After compaction and a very short initial setting period (often immediately in automated lines), the block is removed from the mould. This can happen in several ways:
Ejection: The mould's base plate pushes the block upwards and out of the cavity onto a pallet.
Folding Moulds: For some manual machines, the sides of the mould fold back or are removed to release the block.
The precision of the mould, including its surface finish (Ra 1.6 or better) and tapered walls, is vital here to ensure the block releases cleanly without sticking or damage.
Curing: Strengthening the Block
Freshly demoulded blocks are fragile and need a controlled curing process to gain strength. This involves:
Initial Curing: The blocks should be kept moist and covered for at least 24 hours. In dry or hot conditions, they are often sprinkled with water.
Main Curing: For approximately two weeks after production, the blocks are periodically wetted to allow the cement to fully hydrate and develop its maximum strength.
Drying: After curing, the blocks must be dried before use. If placed in a wall while still damp, they will shrink and cause cracks. Blocks are stacked with space between them to allow for air circulation, and hollow blocks are stacked with cavities horizontal for better drying.
5. Quality Control and Maintenance
Ensuring Mould Quality
Quality steel moulds from China have improved significantly. Leading manufacturers like UNIK now employ CNC machining for precise dimensions and vacuum quenching and tempering for consistent hardness, minimizing warping and ensuring a long, predictable lifespan. Modern moulds can achieve a dimensional tolerance of ±0.3mm.
Maintenance and Lifespan
A well-maintained steel mould is a long-term asset. The expected lifespan varies:
Standard Use: A quality alloy tool steel mould typically lasts 80,000 to 120,000 cycles.
High-Volume Use: For fully automated lines, a mould can last 150,000 to 250,000 cycles.
Regular maintenance is crucial. This includes cleaning the mould after each use, inspecting for wear, and applying rust-preventative coatings for storage. Worn moulds can often be refurbished through re-machining or re-plating to restore their performance.
Conclusion
Making concrete blocks with steel moulds is a systematic process that blends material science, precision engineering, and practical skill. The journey-from selecting a high-quality steel mould that matches your specific machine and production needs, to preparing the right concrete mix, mastering compaction, and performing proper curing and maintenance-directly influences the quality, efficiency, and profitability of your operation. By adhering to these steps, producers can achieve consistent, high-strength blocks that meet the demands of modern construction.