| Boiling Point No. 20- December 1989 |
by Tim Jones, ITDC, UK
This very basic manual crusher was seen by ITDG in a small tile works in Tamil Nadu. It is used to crush down to 3 to 4 mm any stones occurring in the clay, though this does depend on how worn out the machine is. The two so far found are quite old and have had a very hard life but are still in use. The clay once dug and roughly mixed is passed through the crusher a couple of times. The crusher is operated by three people, two turning the rollers and one feeding the clay through.
It is a very simple machine consisting of two parallel rollers, each of which is directly attached to one of the very large wooden wheels which have large horizontal handles positioned at the circumference. The rollers are made of cast iron tubes six inches in diameter by eighteen inches long. The shafts from the driving wheels are cemented into the rollers. There are two heavy steel plates supported by the frame on the outside of the rollers and angling in to make contact with the wider sides of the rollers. These act as scrapers removing the clay from the rollers to allow it to fall along with the clay passing through the rollers. The scrapers can be removed to allow for cleaning. The whole unit of wheels, rollers and scrapers is mounted on a very strong wooden framework with four wooden legs positioning the rollers three to four feet above the ground so they are easy to turn.
It is quite strenuous to operate the crusher despite the advantage of the very large driving wheels because of the direct drive from the wheels to the rollers without gear wheels. Having said this the crusher does not have to be operated for very long to process a large quantity of clay. Clay processing by hand is slow and laborious, the crusher takes only a quarter of the time. For ceramic stoves use it produces a better material.
The clay is passed through the crusher twice and does three very valuable things to the clay at the same time.
1) it crushes down the stones to produce a coarse sand of three to four millimetres which is good for the mixture as it opens out the clay during drying and prevents pre-drying cracks;
2) the clay is mixed thoroughly by being passed through the rollers twice and is well homogenized; 3) the small dried lumps of clay that are slow to mix in properly and difficult to process by hand are crushed and mixed well by this simple machine.
Disadvantages are the initial cost which would be far too much for a single potter but could certainly be covered by a group of potters working in a village or cooperative. This would also mean that the three people required to operate the crusher will not present a problem. The machine should be under group ownership so that there will be free access by all the contributing potters. This is not always as straightforward as it should be mainly because the crusher has to be kept somewhere.
The crushers are used at present to produce clay for roof and floor tiles (not bricks) for which the clay has to be fine (less coarse material) and well mixed to prevent drying distortion. This is also very important in the production of ceramic cooking stoves. These crushers are relatively cheap compared to powered crushers; they can be made in country with skills and materials readily available and are maintenance free apart from the occasional greasing. One suitable and last advantage is that their use may open up clay reserves that are easily accessible but have not been used up to now because they are too stony.
The question now is will the potters think that it is worthwhile to change the habits of a lifetime and to make the necessary investment in a crusher. We here at ITDG will help them to give it a trial to find out.