|ROCK CRUSHER (LITE)|
Labour Intensive Technology and Engineering (LITE) is working on civil works projects in Limpopo Province in South Africa using hand operated Rock Crushers and Concrete Mixers.
They have good long term data (4 years) on production from the New Dawn Engineering's Rock Crusher (Pat. SA 97/3141).
It goes like this:
The larger the pieces you want, the higher the throughput. Normally the stone is first broken with a large sledge-hammer to pieces smaller than 150mm x 150mm. The smaller, the better. It takes less effort to break a large stone with a 10 or 14 pound sledge hammer than with the crusher. The machines are best at producing the small stones , which is the most difficult task for a hand held hammer. The large pieces are first crushed to about 40mm and stored in a pile. This can be done with a team of 7 at a rate of about 5 cubic metres per day. This is a size is suitable for railway sleeper beds, drains and 'stone pitching' beside the road. LITE reports they get 0.7 cubic metres of such stone per person per day, using a team of 7 people in one team is optimal.
The division of labour is:
- 2 people pulling rocks out of the ground or hillside
- 2 people hauling them to the work site
- 3 people operating the Rock Crusher, taking turns at the handle.
LITE has been using 2 teams of 7 on one site for several years. They produce about 10 cubic metres of product per day. The organization of labour took time to optimize however they have maintained this level for the past 3 years.
When a customer requires, for example, 20mm stone, the 40mm material is re-crushed. This double process is faster and takes less total work than trying to do it all during the initial stage. In some cases, it is best to have one crusher making 40mm stone, then feed that into 2 machines set at 16mm. There are a number of variables that affect such decisions including the initial size of the rock, the hardness, the desired size and whether the machine has one or two (or more) people operating it.
Using quartzite, and setting the jaws to make 25mm pieces, the Rock Crusher can make about 1 litre of crushed stone per minute, or more than ½ a cubic metre per day. Some crews make 1 cubic metre of 25mm stone per day (15 wheelbarrows). It's about 30 to 50 times faster than using a hammer and anvil.
To make small stones in the 12mm range it is faster and easier to two more stages at smaller settings. The jaws can be adjusted closer to each other at the top and bottom giving more than 20 sizes of stone. To do this, pull out the top pin on the fixed jaw and move it closer to the swing jaw, and put the pin in again. The top has 3 positions: 150mm, 100mm and 50mm. When using a 100mm setting, a larger proportion of the jaw is used at a time. This reduces wear on the lower portion of the jaws and increases output. It is easier to break the small pieces than the large ones so the machine should be set to do as much work as people can handle.
Experience to date shows that operating the machine (only) with a group of 3 people is best. Stones still have to be dug and transported to the machine by additional people ift hey are not crushed at the source. The three take turns on the handle in 15-20 minute shifts. Three or four people having a business in Swaziland or South Africa about 100km from a large scale crusher would share out R200-700 per day (there area lot of variables that affect this figure).
Solomon Radzilani working at Mohlaletsi, Limpopo Province, RSA. The roadside drain in the upper left of the picture is made from hand crushed stone.
Using the crushed stone to make road culverts with a hand operated concrete mixer