Monday, October 8, 2012

CEB Automation

In order to make a large number of blocks of very uniform size, a machine must be automated. While the block machine in the picture can be manually operated, automation frees up one individual who does not have to stand there in mind-numbing repetitive motion trying to get exact movements every few seconds. But getting this thing automated has not been easy.

First, I paid an electronics/computer guy to wire up an Arduino sensor and control program for the machine. It was supposed to work by sensing tiny magnets as each hydraulic cylinder moved. It did not work to my satisfaction. On the second round, the new and improved Arduino system also failed, so I went to commercial control assemblers in Fort Worth who previously built all the septic controllers installed during my "wetlands" career.

System Program and Controller

What you see in the pictures now is a robust, complex but easy to read and easy to use system that controls the high-pressure cylinders in very rapid and precise movements. An industrial strength, proximity sensor reads bolt head buttons as they pass by it. As the sensor “reads” the button, it tells the program what to do next.

The controller program not only signals each stage of operation with LED lights, it gives a read-out on the LCD screen of exactly what is occurring. I can operate the system with the two red buttons in the controller box or turn it loose for totally automatic “stepping.”

One important feature that I added was a high-pressure release valve that senses pressure to the main cylinder and when it reaches a maximum pressure it triggers a release and sends the cylinder on to the next step. The importance of this pressure sensor is that a load of dirt may be just a little too much and prevent the cylinder head from reaching its next sensor stop because it cannot compress the over-load quite enough. Potentially the machine could get “confused” and not know when to move on since it failed to reach its next trigger stop. With this pressure sensor, the machine moves on when it reaches maximum pressure at any stage. Yes, the block coming from such an over-ride would have to be visually checked to see if it is good enough or send it back for recycling.

Safety around very hot, extremely high-pressure (2200 psi at 120-150oF) hydraulic hoses cannot be exaggerated. To ensure safety, the hydraulic pump and its cooler and reservoir stand some distance from the people working to remove blocks as they are ejected. All the hydraulic hoses are built below deck and a skirt of plywood will be bolted to the frame to be sure that no one will be burnt or cut by any accidental rupturing of hoses. Safety “Kill” buttons are located where anyone for any reason can push them to stop the entire system instantly.

Solar Power

The entire machine’s electronics are powered by an 80 watt solar panel that keeps all three batteries charged. A battery back-up is located below deck to ensure consistent power to the automation/controller on the press on a cloudy day. A battery on the hydraulic rover must also stay charged. And the water tank has a 12 volt remote control operated pump and mister powered by its own battery. I don’t have to get off the tractor to spray water on the soil-cement mixture—if it should need a little moisture.

How Many Blocks a Minute?

While automation makes this machine very fast and accurate, it does not translate into so many blocks a minute—which is how most machines are advertised. That figure is meaningless when you consider that you have to dig up soil, screen it, mix in cement or lime, add water, and then press the blocks, move them to a pallet and shrink wrap them. Thus, a far more reasonable estimation of any block-press efficiency might be how many blocks a crew of two can produce in one hour, averaged from what they produced over the last eight or ten of steady work.

Block Testing

The next step on our journey to a CEB house is to make a series of test blocks from the soil we have aggregated/mixed on the dam. We will make test loads of 30 blocks adding 5% 7% and 10% cement. We will then try the same with lime fractions. Then we will repeat the same formulas for stabilization but also add 5, 7 and 10% Bentonite (70% Montmorilinite clay) to see if this compensates for our excess silt fraction. Adding some clay powder will effectively raise our level of clay to 40% from 30%. [See previous soil triangle]

When these blocks have cured for 14 to 28 days, a random sample of 4 from each test pallet will be taken to a certified soil testing lab for carefully recorded testing. Two will be crushed to discover the crush (compression) strength and the other two the modulus of rupture—how easily a point load will cause it to crack. We will publish the results of these tests in future blogs, but obviously we are interested in which block will meet the required standard of 800 psi crush and 30 lbs. for rupture that we have set for the minimum safety of this house.

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