|Soil Block Presses (GTZ, 1988, 38 p.)|
Development of Soil Block Presses
Since the quality and durability of soil constructions was generally compared with that of burnt brick masonry and more recently with concrete block structures, the compressive strengths achieved by manual compaction (by throwing or ramming) were not always satisfactory. In order to achieve higher compaction, mechanical devices were developed, both in the form of tampers, as well as in the form of block presses (first made out of wood, later out of iron or steel). The first documented block press was developed in France in 1789.
The earlier presses functioned mainly as ramming devices for dynamic compaction, eg with heavy covers (30 kg) which close down with great force, displacing the excess soil. Since the beginning of the 20th century press makers have been devising manual and motorized presses that make use of static force. One of the earliest machines, LA MADELON, is still being manufactured in Belgium, although with several modifications and under different names. But most of the older machines have disappeared from the market.
All these machines were relatively large, heavy and expensive, so that their use was limited. What was needed, was a small, light, simple and cheap block press, which could be used on the remotest building sites in the Third World.
According to these requirements, the Chilean engineer, Raul Ramirez, developed such a machine in 1956. He was then working with CINVA, the Inter-American Housing Center in Bogota, Colombia. The press was, therefore, called CINVA-Ram, whereby "Ram" was derived either from Ramirez, or from the English word for a compacting device.
The CINVA-Ram is now by far the best-known and most widely used block press. Numerous variations of it have been manufactured in many countries, but, in its original form, it still is the lightest and least expensive block press available - every improvement, in terms of handling, output and sturdiness, invariably means an increase in price.
In the 1950s and 60s, interest in soil constructions was generally low. In the 1970s, research work and implementation of soil technologies in development projects steadily increased, largely on account of the world-wide energy crisis. Apart from several other publications, Hassan Fathy's "Architecture for the Poor", which was published in 1973, did a great deal to revive interest in soil construction systems.
In the course of these developments, a new generation of soil block presses came into existence in the 1970s, namely complete production units on wheels. The equipment generally required for blockmaking, apart from the press, are a sieve, a mixer and a measuring scoop for charging the mould, although quite often these are substituted by manual operations and estimation of appropriate soil mix proportions and required quantity of mould filling. The new, partially or fully automatic machines accomplished all these tasks in quickly repeating operation cycles, thus achieving higher outputs of uniform, superior quality bricks.
Soil Block Presses Today
There are basically four types:
Manual presses: the moulding and turning out operations are carried out by the machine which is operated manually.
Motorized presses: the moulding and turning out operations are carried out by the machine which is power driven.
Mobile production units: the production unit is easily transportable and the moulding and turning out operations, the preparation of the raw material and/or the evacuation of the finished product are entirely automated.
Industrial production units: these production units are particularly difficult to transport but the entire process is automated. These units are not included in the Product Information.
Corresponding to the great diversity of these machines, the prices range between 500 and 75.000 US$. The following "extremely generalized) compilation of the respective advantages and problems clearly shows that each system caters for a certain range of needs and thus has a valid place to fill. Grossly simplified, the cheaper devices are taken to be manually operated, while the expensive machines are referred to as motor-driven and automated.
Advantages of manually operated presses:
· Low capital and operational costs.
· Quick delivery.
· Low weight (devices like the CINVA-Ram can, if necessary, be taken along as unaccompanied flight luggage; easy to transport on wheelbarrows or bullock-carts).
· Small size, thus little storage space required.
· Simple to use, even for unskilled workers.
· Apart from cleaning the mould and lubrication of moving parts, low maintenance requirements.
· Possibility of repairs in local workshops, no special spare parts required, except for compression rings special hard steel (45 - 50 Rockwell).
· No additional costs of energy.
· No time loss due to failure of energy supply.
Problems of manually operated presses:
· Low rate of production per machine (on average between 40 and 150 blocks per hour), thus requiring a number of machines to achieve a reasonable output.
· Low compaction pressure (averaging 0.5 to 2.5 N/mm²), hence poor soils are likely to produce weaker blocks (in lower compressive strength, higher moisture absorption, susceptibility to disintegration).
· Tendency to produce irregular block sizes or compaction, depending on compressing system, if filling the mould is done manually.
· Tiring operation; thus, in the course of a series production, tendency of gradual drop in quality and uniformity of blocks produced, if the pressure is continuously exerted by the same person.
Advantages of automatic, motor-driven presses:
· High rate of production (on average between 200 and 1500 blocks per hour).
· High compaction pressure (between 4 and 24 N/mm²), hence good quality of soil blocks (optimum dimensional uniformity, stability of edges and high compressive strength, low moisture absorption, saving of costly and tedious surface treatment).
· Continuously uniform quality of blocks, since no muscle power is applied.
· Requirement of only small proportions of binder (thus saving costs), on account of the high compaction pressure.
· Reduction of manual work, thus saving costs, where wages are high.
Problems of automatic, motor-driven presses:
· High capital and operational costs.
· Relatively long delivery time.
· Usually very heavy, requiring powerful lifting gear and vehicles for transportation, ie transports are troublesome and expensive.
· Large size, requiring large working area, making safe storage under lock and key difficult.
· Requirement of high insurance cover.
· Necessity of skilled labour for operation of machines.
· Maintenance requirements (eg some hydraulic machines) comparable or more complex than for motor vehicles.
· Requirement of specialists for repairs; spare parts possibly expensive and difficult to get, or only after long delivery time.
· Dependancy on local energy supply.
The above list of advantages and disadvantages of the different categories of soil block presses lead to the following conclusions:
Small, manually operated machines are best suited:
· in case of limited capital resources;
· for projects in remote areas, or those that lack the necessary infrastructure;
· on small building sites, with limited working space;
· in areas of low precipitation, thus excluding the danger of excessive water absorption;
· for small building projects with single-storeyed structures, for which the quality of soil blocks is of less importance;
· in places, where the potential for self-help inputs is high;
· or where entrepreneurs, with a small capital base and a team of unskilled workers, produce soil blocks for the local market.
Powered, high capacity machines are advantageous:
· where sufficient financial resources are available;
· in cases where high production rates are needed and there is a high demand over a long period;
· for projects that specify better qualities of soil blocks;
· in working environments with sufficient energy supply, as well as maintenance and repair facilities;
· in cases, where labour is expensive or not easily available;
· or in case of disaster aid operations, which necessitate efficient and quick help, and good, cheap material in large quantities. (Quite often, tents and other temporary accommodations are provided at high costs, requiring more permanent substitutes later on. It is wiser to help disaster victims to build stable, permanent houses straight away. Thus it could be a far better bargain, to invest the money, which usually is spent on provisional measures, in the procurement of a high capacity soil block press.)