|Product Information: Micro Concrete Roofing Equipment - Fibre or Micro Concrete Tiles (BASIN - GTZ GATE - SKAT, 1997, 38 p.)|
Apart from a set of ordinary masonry implements (e.g. spades pans, wheelbar-rows, sieves, trowels, sand and cement batching boxes, balance and the like), the production of FCR and MCR elements requires some special equipment:
· screeding machines
· testing equipment
· This comprises a vibrating screeding surface and interchangeable, hinged frame (for products of different shapes and thicknesses). The machine can be a small, portable "mini plant", or a stationary workstation.
· The vibrating mechanism requires an energy source, which can be electricity (from a mains outlet, converted to 12 volt DC power by a transformer-rectifier, or from a car battery), hand-power (crank with pulley system or metal springs), foot-power (treadle or bicycle pedal system), or flywheel energy (hand-operated).
Advantages and problems of the various screeding machines
· Electric machines:
+ relatively quiet, do not tire out the user, produce uniform, good quality elements, recommended for a sustainable business;
- dependent on reliable power supplies for operating the machines or recharging batteries, risk of production setback due to bad battery maintenance.
· Hand-powered machines:
+ independent of power supplies and can thus be used in remote rural areas;
- relatively noisy and tiring and needs 2 people to operate, uniformity of vibration dependent on the way the handle is turned, thus possibility of non-uniform quality of products.
· Foot-powered machines:
± more or less the same advantages and disadvantages as hand-powered machines, except that, depending on the design, the second worker can be omitted, as the hands remain free to spread the mortar during vibration.
· Flywheel-powered machines
+ incorporate all the advantages of electric and hand-powered machines and can be operated by a single person;
- cost about the same as electric machines.
· These can be of various shapes and sizes, depending on the local requirements and are needed in large numbers - at least as many as the number of components produced in two working days, because the tiles are demoulded after 24 hours.
· The moulds can be made of different materials, such as vacuum formed PVC (polyvinyl chloride) and fibreglass. FCR and MCR producers in developing countries have devised methods of making moulds out of concrete. These are produced in 3 stages: first making a concrete "mother mould" from which several concrete "mother moulds" are formed and sold to local tilemakers, who make the actual concrete moulds themselves. More recently, plywood "mother moulds" have been devised, eliminating the "grandmother mould"
· The PVC and fibreglass moulds are designed for self-stacking; in most cases, the concrete moulds are placed in special wooden racks for initial curing, but self-stacking concrete moulds (either entirely concrete or with metal frames) have also been developed.
Advantages and problems of the various types of setting moulds
· PVC moulds:
+ produced industrially and hence uniform and of good quality, extremely lightweight and easy to handle, can be stacked airtight (vital requirement for curing) and save storage space;
- most expensive moulds, production in developing countries limited.
· Fibreglass moulds:
+ similar advantages as PVC moulds, can be produced locally if the materials and skills are available
- tend to be less accurate than PVC moulds.
· Concrete moulds (not recommended):
+ cheap and can be produced by the tilemaker himself;
- heavy and less accurate than PVC, and if not self-stacking and not airtight, the rack in which they are placed has to be well covered with a plastic sheet (which is often not done carefully, causing the green tiles to crack due to non-uniform drying)
· Several tests should be carried out before, during and after the production process to ensure the MCR products are of consistently good quality. The tests are generally very simple and only a few need special equipment.
· Some MCR machines are equipped with a demoulding jig, on which the 24 hour old tiles are placed upside down, together with the setting mould, which can be lifted off. Subsequently, the plastic sheet can be peeled off carefully and the rough edges trimmed off. A close fit of the tile and the edges being in line with those of the jig show that the tile has exactly the right shape.
· After curing and drying, random samples of tiles from each batch produced should be tested.
· These and many other tests are described in greater detail in the FCR/MCR toolkit No. 23, Quality Control Guidelines, which can be obtained from the Roofing Advisory Service of SKAT, Vadianstr. 42, 9000 St. Gallen, Switzerland.
Criteria for Selection and Purchase
MCR being relatively new technologies, the number of equipment suppliers are still very few. In the early stages of development, the equipment used was locally made by research institutes and appropriate technology groups, which mainly experimented with the production of large sheets. No equipment was commercially available.
ITW of Cradley Heath, U.K., who were the first to develop small roofing components and a method to produce them by vibrating, were also the first to supply equipment on a commercial basis. The earliest equipment was the portable "Mini Plant" (1983), which was followed two years later by an "Industrial" version of the same production process, and a series of other modified and improved equipment later on.
While this equipment was principally available all over the world, the relatively high capital and transport costs, prohibitive currency exchange rates and import restrictions in many developing countries led to the local production of equipment. Thus there are several types of FCR/MCR equipment on the market and it may be difficult for a newcomer to this technology to decide which one should be bought. The following points will help the potential buyer to make a good choice.
Due to quality reasons, SKAT/RAS has decided in 1993 to promote MCR tiles of at least 8 mm thickness only. The production of FCR tiles and sheets is very delicate and therefore not recommended. In spite of this, there are still many producers who promote semisheets and FCR tiles.
Design of Screeding Machine
· The design of a screeding machine is the result of several stages of development:
· Development and design of prototype
· Testing and modification of prototype
· Field testing of 5 to 10 prototypes for at least 1 year
· Modifications resulting from field tests
· Finalization of design, production manual, accessories, etc.
These steps can only be followed if appropriate workshop facilities, qualified engineering capacity, qualified production and quality control capacity and sufficient funds are available. Depending on the extent to which these requirements are met, there are great differences in the quality of machines available.
· If a MCR tile production plant is to operate successfully in a developing country, the equipment must be capable of withstanding rough use. If possible, machines that have been in use under such conditions for a reasonably long time (say 3 to 4 months) should be inspected to check, for example, whether the screeding surface and/or the hinged frame is warped of damaged, handles or switches are broken off, and so on.
· Special consideration should be given to the working conditions for the production team, especially with regard to operation procedures and handling of products, that is, avoidance of dangerous or exceptionally hard manual work and activities that have to be done in a bent position.
· A balance must be found between the desired output rate, quality standard and level of sophistication. Complicated mechanical devices often necessitate special training and experience for maintenance and repairs. Spare parts can be expensive and, if imported, may be difficult and take long to procedure.
· The choice of screeding machine will also depend on the tile size required, which is basically a choice between the pantile (or Roman tile, depending on the mould) of 50 to 60 cm length, 25 to 29 cm width and 6 mm thickness (requiring 8 to 12 tiles to cover 1 m2), and the larger semisheet, which is 60 x 60 cm and 8 mm thick (requiring 4 elements to cover 1 m2).
· The type of energy required to operate the vibration mechanism is one of the most important selection criteria. Hand or foot operated machines can be used anywhere, and are the only viable option in remote areas, where power supplies are unreliable or not available. If electric machines with car batteries are used in such areas, it may be possible to recharge the batteries with a pholtovoltaic solar energy system, but such devices have so far not proved successful.
· The vibration mechanism normally consists of rapidly rotating eccentric weights. With two shafts rotating in opposite directions, the horizontal component of vibrations can be neutralised, so that the screeding surface is subjected to a simple harmonic motion in the vertical direction only.
· A less common vibration method is with flat metal springs, which hit the underside of the screeding plate at a rate of about 2000 times per minute, by turning a rattle wheel. With this method it is more difficult to achieve uniform vibration frequency, but the machine is very cheap to construct and easy to repair, but on the other hand very noisy.
Design of Setting Moulds
· Since a very large number of moulds are needed, they represent the highest single cost factor. The industrially produced PVC moulds are the best in all respects, but the most expensive. World-wide experience shows that the quality of tiles is strongly linked with the quality of moulds. Hence, SKAT/RAS recommends the use of PVC moulds only.
· The most successful locally made moulds are concrete moulds (as described above). However, great care is needed in production and handling. The usual practice for initial curing is to put the moulds with the fresh tiles in special wooden racks, which have been covered with plastic sheets to retain the moisture in the tiles. If this is not done properly, parts of the tiles may dry out earlier, causing cracks. Therefore, self-stacking concrete moulds should be preferred.
· With good equipment, good tiles can be produced, but if the ingredients are of poor quality or prepared incorrectly, good equipment is not likely to produce good tiles. Therefore, quality control must begin with the selection and preparation of the ingredients.
· Broken tiles, leaking roofs and other serious problems associated with FCR in the early stages of development have shown the extreme importance of strict quality control during all phases of tile production, roof construction and installation of tiles. A tile testing kit, as described under Testing Equipment, is essential in every MCR production plant.
· But above all, the main prerequisite for good quality products is a thorough professional training of the production team and supervisory staff, and efficient management.
· Equipment suppliers are basically of two types:
· private, commercial producers
· non-government organisations (NGO's) based in developing countries.
The advantages of private producers are:
+ their dependency on good sales, and hence the need to produce good equipment, as failures of bad service would seriously harm their reputation and ultimately stop business;
+ their experience in international trade and good administrative backing, making them reliable business partners.
However, the need to support a qualified technical and administrative staff with modern equipment, to maintain a consistently high standard and respond to changing needs, makes their products expensive. Importing these into a developing country not only increases the costs considerably (high exchange rates, transport costs, insurances, duty, etc.) but also can be extremely difficult (due to import facilities and restrictions, long delivery time, problems due to breakage in transit, etc).
The advantages of NGO's are:
+ their high motivation and closeness to the target group, enabling them to adapt their methods and products to local requirements, and provide assistance and advice whenever needed;
+ their low overhead and production costs, and if their equipment is sold locally, the additional savings on foreign exchange, transport costs, duty, the trouble with important formalities and delivery time, and the like.
However, these groups do not always have required funds, technical staff and workshop facilities to carry through all the tests and modifications that the maturing of a new product need. Unfortunately, this problem is sometimes underestimated.
· 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 specially asked for.
Professional Training Courses
· Of special importance are training courses offered by all good equipment suppliers. As far as possible, these courses should be conducted at a place where the whole production team can participate.
· There should be no preconditions for participating in the courses, other than knowledge of the language used. The method and content must be understandable for people without special skills or formal school education, and the course should cover all phases of tile production, roof construction and laying of the tiles, as well as administration and marketing.
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 tiles 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 frequently 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.
Checklist for Potential Buyers
The following is a summary of the main points to be considered when selecting MCR tile production equipment:
· Available financial resources (budget restraints can limit the choice to locally available equipment).
· Required size and shape of MCR tiles (smaller components are easier to produce and handle, and suitable for all sloped roofs; pantiles are less sensitive to inaccuracies than Roman tiles; semisheets are quicker to produce and install per unit area, but less suitable for complex roofs, as semi-sheets are more wasteful to cut than tiles).
· Required production rate (this depends on the expected market demand and determines the quantity of equipment needed).
· Available energy sources (not only the costs must be considered, but also the frequency of power failures; manual operation is always appropriate, but can be very tiring).
· Availability of spares and skilled technicians for maintenance and repairs (machines with standardized parts create less problems).
· Professional training (this is a must to guarantee a successful business)
· Operational safety (this is not usually a problem in FCR/ MCR tile production).
· References (contacts with equipment users should be sought whenever possible).
· Conditions of purchase (since machines of similar types are available, comparisons of prices, discounts for large orders, delivery time, etc. are urgently recommended, but also - if applicable - import restrictions, after sales service, guarantee period, etc. should be taken into account).
· After sales services (not only should the manufacturers be fair enough to rectify defects of their machines by providing technical assistance or supplying spare parts at minimum or no-costs; users should also take the trouble to send accounts of their experiences and suggestions for improvements to the manufacturers, for without this feedback, no effective development is possible).