AfriCart – a handcart for Africa

ED302 – design & technology

02.1 Research – Materials

The choice of material is limited to what is suitable for use in the rural areas of SSA: suitability is judged on

  • Availability of material
  • Availability of skills & tools
  • Repairability

Aluminium

My first choice as it is light but also very strong and therefore has a high strength-to-weight ratio: 222kN·m/kg. However: as a raw material it is not usually available in rural areas and welding it requires more specialist equipment than welding mild steel. Aluminium requires specialist knowledge and equipment, eg: TIG, to weld successfully. Rivetting is not an option as there is little or poor access to aluminium “pop” rivets and rivet guns in rural areas. Bolting would be an option though, however I feel that this would not be a successful solution owing to the harsh terrain and subsequent strain on all joints and fixings as Aluminium does have a tendancy to “fatigue” if continually stressed in the same place.

If the material is hard to find in the rural areas and if it is hard to create sufficiently strong joints, it seems reasonable to assume that it will be hard to repair with any degree of longetivity, and so is no longer considered a suitable material.

Mild Steel

My second choice as it is stronger than aluminium, with a strengh to weight ratio of 254 kN·m/kg, it is easily available in various forms (round bars or rod, square bars, rectangular or flat bars etc), and it can be easily welded using Electric Arc or Oxy-Acetalelyne – the skills and equipment for which are often found in urban/semi-urban areas of SSA where vehicles are repaired, and fences, gates and Scotch Carts built. Mild steel can also be successfuly bolted and most importantly repaired with simple equipment, however it’s failure is it’s weight: mild steel is heavy and therefore to make the whole of this cart using steel would be illogical.

However when I started this project I envisaged a 2 part construction: a wood cart body attached to a metal framework – rather like a LandRover: an aluminium body resting on a steel ladder chassis – however after consultation with a development worker from Practical Action (formerly known as ITDG) I decided to go with a monocoque wooden construction. The points that were brought to my attention were that however well made the steel frame was – it could still break and immediate ad-hoc repairs could not be made, and that if my target market were women and children, then every weight saving I could achieve in construction would be reflected in ease of use.

Wood

After eliminating both aluminium and steel I was left with wood, but what type of wood was both available and practical? There are many different varieties of wood grown in Africa and all these woods have different properties and so which would be suitable? Many indigenous hard woods such as African Ebony and Ironwood are hard and strong but very difficult to work with hand tools. Rhodesian Teak and many species of the Acacia family produce hard and durable wood however this indigineous “found” wood is hard to find in communal rural areas – much has already been cut down by craftsmen and builders and it is not grown, in communal areas, on a sustainable basis.

Bamboo

This would also be a great material, however it is not indigenous and is only found in localised highland areas.

Some examples of these woods are:

Sapele Mahogany

  • Hardwood
  • Native of West Africa
  • Durable
  • Uses – paneling, furniture, boat building, shop and window fittings

Iroko

  • Hardwood
  • Coarse texture
  • Uses – veneers, flooring, high quality interior and exterior joinery

Mahogany (African)

  • Hardwood
  • Native of West Africa
  • Uses – Interior and Exterior joinery and veneers

Afromosia (Mahogany)

  • Hardwood
  • Close grained appearance
  • Uses – high quality joinery, furniture and veneers

Mopane

  • Hardwood – one of southern Africa’s heaviest used timbers
  • Termite resistant – or this reason it has long been used for building houses and fences, as railway sleepers and as pit props.
  • Traditionally used for all bush carpentry inc axe handles and roof trusses.

In rural areas of SSA people will make use of whatever is available and because there are so many different species of tree in SSA it is very hard to specify a particular wood to use – each area will have it’s own specific tree (such as the use of Mopane in Zimbabwe) denoted by availability, culture and tradition for the construction of things such as tool handles or as in this case, a hand cart. However, one non-indigenous wood that has made inroads into African joinery is Pine. With it’s swift lifecycle it is often grown throughout Africa as a “cash-crop” and therefore often displaces indigenous hardwoods, it is used in every form of African woodwork. Due to this omnipresence of pine products, it is a rich source of “found” and recycled wood. One of the great sources of “found” or recycled woods has been the Aid and Transport industries: here I mean the ubiquitous wooden pallet .

The cheapest pallets are made of a softwood such as pine and are often considered expendable, to be discarded as trash along with other wrapping elements, at the end of the trip. This is the reason one finds pallets popping up in all sorts of places especially in areas where fly-tipping is prevalent. So in Europe these pallets are treated as waste, however in Africa they are a much prized resource. Personally I have seen stray pallets in the middle of bush in Tanzania and Kenya but they more reularly occur in the major urban centres, cities and transport hubs such as Mombassa, Nairobi, Harare etc.

wooden_pallet_with_glove


The great thing about pine pallets is that the european pine is produced on a sustainable basis and to a standard size:

The most popular British pallet is the 1200 x 1000mm, 9-block, with a full-perimeter base. That design is considered by many as the National UK pallet, though it is only one of many UK designs and does not even have a dedicated British Standard to formalise it. It is simply listed as one of five permitted modular sizes in ISO 6780 and EN 13382. (The British 1200 x 1000mm footprint originally came from the 1960s metric conversion of the dominant North American 48″ x 40″ 2-way stringer/bearer pallet). From the outset the UK mainly used the 9-block design with a full perimeter base, much as shown in the illustration, with the fastenings, thicknesses and wood species evolving over time.

British Pallets

800px-tidy_stacks_of_pallets


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Written by d.TEC@fablab.blog

March 17, 2009 at 4:06 pm

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