At Auroville I took the work on automating their CSEB manufacturing machine – Auram 6000. Compressed Stabilized Earthen Blocks are fast becoming popular for their obvious benefits. These blocks have superior thermal insulation than concrete. With proper design, they compare well with Concrete on earthquake tolerance. These are normally made from locally available material, thus reducing transportation cost. Curing time for earthen block is low. As these blocks have better dimensional accuracy, it is possible to use these blocks without using mortar. These help to improve productivity and at the same time is the technology is friendly to environment.
Aureka makes manual and semi-automatic CEB presses. These can make around 65 types of normal and specialized bricks. It has now come with fully automatic machine that will be able to produce around 500 full size (1′ x 1′) blocks in a hour. An average size 2500 Sq.ft building will normally require 15000 blocks. Automatic CEB machine can produce these bricks in 30 Hrs. At this rate CEB will rival the construction speed of concrete. In order to use mortar-less construction the blocks need to be within +/- 1 mm accuracy. Molding sand and soil to this level accuracy proved to be a challenge.
In this machine I am using PIC 16f4877a microcontroller to control the hydraulics. Micro-controller helps to automate movement of different rams. These speeds up the process and relives the operator from monotonous lever shifting work. First day when we tried, the operator pointed out that for some specialized blocks, machine needs to be stopped at a certain stage for manual intervention. So I had to modify the microcontroller program. Next we tried a small sample batch. Position variations were very high. I noticed that the sensors were placed in a manner that is responds to change in position quite slowly. Oriented sensor positions to improve the sensitivity issue. Next issue was the problem of inertia in the control circuit. As sensor detects position, it responds by closing a relay in hydraulic. How much the ram will travel after receiving stop signal depends on:
- Response time of solenoid
- Viscosity of oil
- Plasticity of soil
These three variables depend on ambient temperature, humidity, condition of machine, amount of water added in soil. In simple words, it is impossible to control the inputs to provide consistent output purely on sensor feedback. Solution was to introduce some physical limiters at vantage points. This CEB press operates at around 100 bar pressure. In these pressures it is quite easy to damage structures unless proper design precautions are taken. These physical limiter, in turn required modifications in the structure. After taking care of all these, machine started producing blocks with proper dimensional control. Here you see the trial run on the prototype setup.
With 65 different types of blocks to produce, next challenge was to find a convenient process to set the block height and mold depth. Each block require different setting. Sometime setting may need to be changed to take care of type of soil being pressed. For this I found it best to consult the person who will actually do the setting. After some brainstorming we settled on a process that is easy to use in field with minimal equipment. The process was documented.
Next stage was to take the machine for a full scale trial. CEB press works with auxiliary equipment – crusher is used to break solid lumps of soil and dry mixture is used to mix sand and cement uniformly with the soil. These are required to feed CEB press at its required speed. Here you see the full setup for production trial.