Moulding Equipment Options for Concrete Block Production
The production of concrete blocks consists of four basic processes: mixing, moulding, curing, and cubing. In moulding process, the concrete mix is fed into the appropriate mould which is then subjected to vibration and compaction. This process results in a dense, high-strength concrete block.
Concrete blocks can be moulded by several methods, ranging from simple small scale hand-operated ones to complex, medium and large-scale production equipment, 'egg-laying' mobile machines and fully automatic stationary machines. The simpler machines are generally mechanically operated using electric, petrol or diesel power, while the larger machines are usually electrically operated. In most of the block making machines, the concrete is compacted by vibration. The quality of blocks generally increases with the degree of mechanization.
Manual or Hand-Operated Moulding Equipment
These are relatively inexpensive, simple and robust devices, which are especially suited for on-site production of concrete blocks. Depending on the block size, efficiency of the machine, rate of supply of concrete and number of workers involved; output rates for this equipment can range from 10 to 80 blocks per hour. There are basically three types of hand operated equipment:
• Steel moulds that can be carried around by one person and used on a raised working surface (eg. table) or on the ground; the mix is tamped with the help of special tampers that fit on the mould, but is more usually compacted by means of a vibrator fixed to the mould or to the working surface (vibrating table).
• Stationary machines with the block mould (into which a wooden pallet is inserted) at about table height; the mix is usually compacted by the tamper lid-plate, which is brought down with a few sharp blows; after compacting, the sides of the mould fold back to release the block, or it is ejected by means of a lever, which pushes the base plate upwards, so that the fresh block can be taken away on the pallet for drying. Some of these machines are equipped with a tray above the mould for preparing the mix and filling it directly into the mould.
• Stationary machines that are similar to the previous type, but have an engine operated jolting mechanism or vibrator for more efficient compaction.
Advantages of hand-operated equipment:
• Low capital and operational costs.
• Quick delivery (possibly available locally).
• Low weight and small size, thus easy to transport, requires little storage space.
• Simple to use with a little training.
• Low maintenance needs, apart from regular cleaning and lubrication of moving parts.
• Possibility of repairs in local workshops, no special parts required.
Problems of hand-operated equipment:
• Low rate of production.
• In case of manual tamping, possibility of non-uniform compaction of concrete; since production rate is low and the use of fresh concrete mixes is limited to the setting time, relatively few blocks are produced per mix, which can differ in quality each time.
• Tiring operation; this can lead to a drop in the quality of blocks if the work is carried out by a single person for too long.
"Egg-laying" Mobile Machines
These are machines designed for medium-scale production, either on-site or in a factory. Production of bricks occurs on a flat concrete surface (slab). The machinery is not stationary - instead it moves along on wheels. Aggregate is fed into the machine & the blocks are compacted in place, after which the machinery is moved forward (or backwards depending on perspective) off the blocks to produce the next batch of blocks, and so on. This system has been compared to a chicken laying eggs; hence the term "egg-laying." The machines, which can be manually operated or fully automatic, have output rates from 60 to 400 blocks per hour, depending on the size of block and machine, the degree of automation, availability of continuous supplies of concrete and production site organization.
Advantages of egg-laying machines:
• Relatively high output of blocks than manual machine
• Uniform quality of blocks than manual machine, since more blocks are made from each concrete mix and most of the operations are mechanized.
• Fairly easy to operate with a little training.
• Suitability for use on-site or in a factory.
Problems of egg-laying machines:
• Higher capital and operational costs than those of hand-operated equipment.
• Requirement of large flat production area.
• Require costly concrete slabs that are thick enough to prevent vibration travel to the bricks behind
• Dependency on the weather, if not under a roof: in dry regions, if the blocks are not covered with plastic sheets, premature drying and cracking are inevitable; if it rains, production must cease, otherwise the green blocks will disintegrate.
• The higher the degree of automation, the greater the dependency on energy supplies.
Fully Mechanized Stationary Machines
These are automatic and very versatile machines used for the medium and large-scale production of superior quality concrete blocks. They can be of various sizes, but are generally far more expensive than egg-laying machines of comparable sizes. The filling of the moulds, the compaction (vibration) and ejection of the blocks is done automatically, and output rates can range from 200 to 800 blocks per hour, depending on block size and machine capacity. These high output rates are only possible with sophisticated ancillary equipment for transportation, handling, stacking etc, a well-trained staff, efficient management and sound financial base. Space is saved by stacking the green blocks in shelves, where they are usually steam cured for better product quality and quicker turnover.
Advantages of fully mechanized machines:
• Very high output rates.
• Superior and uniform quality of products.
• Greater adaptability to the production of special concrete products.
Problems of fully mechanized machines:
• Very high capital and operational costs.
• Dependency on uninterrupted energy supplies, high standard of ancillary equipment, skilled labour, good management and, above all, continuous high demand for the products.
• Limited mobility.
• Need of specialists for maintenance and repairs; spare parts usually expensive.