Equipment for concrete block production is available for various methods and scales of production, so that newcomers to this technology may find it difficult to decide which type of equipment is best suited for a particular situation. However, by considering the following points, it should be possible to narrow down the choice, and avoid problems and disappointments after purchasing the equipment.
Type of Blockmaking Equipment
· Just as the second and third categories of blockmaking machines described above are generally more expensive than the previous category, there is also a roughly proportionate increase in output rates, variety and quality of products, dependency on special skills in manufacturing concrete products and maintaining the machines. Similarly, there is a distinct increase in the need for sophisticated additional equipment for batching, mixing, transporting, storing, curing, etc. Thus, even if the difference in the capital costs of the machines is not very large, their respective operational costs can differ considerably.
· Each type of machine has different spatial requirements, depending on the method and speed of production. Whether in a factory or on a building site, the available space is an important determining factor. The largest area is normally needed by egg-laying machines, the most suitable surface being that of a smooth concrete slab (thickness and width depending on the weight and operating width of the machine), with a minimum slope of 1 in 100 (for drainage), and contraction joints at intervals of 3 to 4.5 m (depending on the slab thickness). The production area may also have to be covered if intense sunshine or rains are to be expected, both of which would damage the fresh blocks.
· The versatility of the machine is a further important criterium, that is, the possibility of providing a variety of moulds (even special ones made to order) which are easy to change in a short time (say less than one hour), the possibility of adjusting output rates to the local conditions, the possibility of switching from automatic control to manual operation in case of power failure, etc.
·For machines that require energy sources other than manual labour, their use is dependent on the local availability and cost of such energy. For instance, power failures may occur frequently or engine fuel may not be supplied regularly, as can be the case in many rural areas in developing countries.
· As with all production equipment, the rate of output claimed by the manufacturer is usually a theoretical figure for production under ideal conditions. However, problems, such as shortage of energy supplies or raw materials, breakdown of machines, shortcomings of the operators, harsh weather conditions and several other factors, can greatly influence the productivity of a machine, so that the real output rate in the field can be up to 50 % less than expected.
· Before aiming for a high output rate, it is essential to investigate the market potential of concrete blocks. If it is a new product in that area and its acceptance difficult to judge, it will be safer to begin with a low output, manually operated machine, and change to higher output machines when the demand increases and is likely to remain at a high level.
Operation and Maintenance
· The posture of the operator, the distances he has to move and the kind of movements needed are all factors that influence the efficiency of operation, which in turn depends on the design of the machine. This is also of importance with regard to the accessibility of vital parts for cleaning, servicing and repairs.
· Special attention should be given to safety measures, such as avoidance of projecting moving parts, clearly marking and/or protecting dangerous points, incorporating thermal fuses, secuity pins, etc. With egg-laying and stationary machines it is important that guards are positioned around mechanically moving parts, and that these guards cannot easily be removed. Automatic machines must at all cost be equipped with an emergency stop switch, which is easily accessible.
· Hand tamping is not likely to lead to the superior values for the strength, density, durability and consistency of blocks obtained by vibration. However, for many construction applications, such as basic housing, these values would not need to be especially high.
· Apart from the method of compacting the concrete, the method of extruding and transporting the fresh blocks also influences their quality. Jerky movements of the compacting head and moulds can cause cracks or deformations. Pallets must therefore be moved smoothly. But the less the green blocks are handled before developing strength the better. In this respect, an egg-laying machine has a distinct advantage. However, if the slab on which it works is not properly constructed, there is a risk that too much of the vibration used to compact one drop of blocks is transmitted to other recently demoulded blocks.
· Equipment suppliers for concrete blockmaking plants range from small to large companies, with varying degrees of commercialization, offering a very diverse choice of products and services. The larger companies are usually better known, experienced in international trade and consequently reliable business partners. Small firms or their machines are often not so well-known, because of small advertising budgets, hence their list of references can be small in spite of a good product.
· Personal visits to the manufacturer and/or sites at which their machines are in use should be undertaken as far as possible. The value of reference lists is to be able to meet or correspond with users, to learn about their experiences. If such lists do not contain addresses, these should be specifically asked for.
· Of special advantage are training courses, offered by some manufacturers. To be effective, they should not only include the production of blocks and other concrete products, as well as handling and maintenance of the equipment, but also the testing and use of the raw materials, as well as production management and design guidelines for building construction. Trainees should also learn to dismantle and assemble complicated machines, in order to understand their function and conduct repairs by themselves.
Purchase of Machine
· The "FOB" price (free on board) includes packaging, transportation and insurance costs of the machine within the retailer's country, This price can be artificially inflated in order to compensate for the reduction offered on the factory price.
· As regards sales or rental conditions, one must be suspicious of contracts providing for price indexing based on the number of blocks, etc produced or for payment of royalties for patent use, which is often not justified. A patent is not necessarily a proof of guaranteed quality and constructors often apply for patents for processes that are already of the public domain,
· It is advisable to include a penalty clause in the contract, to safeguard against late delivery.
· In the case of an after sales service contract, the waiting period for repairs and maintenance must be clearly indicated. A detailed handbook should be provided, including specifications of all spare parts and a maintenance plan, indicating operations necessary and expected maintenance frequency.