How to Produce Calcarb
The first step is to have a stable and constant feed stock of fibers. Our technology was based upon an expensive precision-cut rayon monofilament fiber about one eight inch long. This fiber is cooked slowly in the absence of air to produce carbon. Rayon is about 45% carbon and 55% water by chemical analysis, and rayon is wet when received by up to 10% water. If it is cooked too fast and in too large a mass the outer portion turns to carbon and the inner part still has water to convert the outer carbon layer to water gas. The yield is down in this case and the fibers are very brittle. This brittle fiber breaks into fine powder, which caused us major problems. In the early days we depended upon carbon cloth scrap made from high strength fibers we purchased from the American scrap market place. This cloth was ground in a mill that produced fines and various lengths. We did not have enough retort capacity to cook rayon because the Scots refused to close down the welding shop to install the equipment.
The second step is to have about 65% of the recycled material of consistent size and quality. A major use at that time was for insulating silicon crystal growing furnaces and a spill box under the furnace. These parts were machined to give a high volume of recycle for future production. We did not have the necessary numerically controlled milling machines to make these products and this work was sent to Rancocas, which left us with a shortfall of recycled material.
The third step is to mix the recycle and fibers with a starch like finely ground resin and the proper amount of water. We had six plastic tanks with mixers that looked like oversized cake mixers you use in the kitchen. The water line that fed the Bellshill factory was too small, so we had to recycle the water during this time. This water and problems with very fine and unfired feed stock caused us fits for several months.
The fourth step is to make a filter cake while slowly sucking the water/fiber mix through a filter screen, leaving the fiber and recycle in a consistent filter cake in the mold. Fines and dirty filter screen cause the filter system to blind and it is necessary to suck harder. We made a few tons of mistakes due to this simple problem. We compounded the error when we used a portion of these failures to recycle directly in the wet phase. The wet recycle caused the dry resin to ball into what Joe Lona called chocolate chip quality. Old filter screens caused a washboard effect on the bottom as the screen wrinkled. Holes in the screen if large enough let all the mix go into the sewer. This happened with regularity in Bellshill in those days.
The fourth step is to dry the filter cake. This step is critical to melt the resin and bond the fibers together. If the cake is allowed to get too hot it will catch fire from the vapors coming from the resin. We had a forty foot container with heat exchanger tubes along the side through which stem was passed. Good drying requires airflow, like a clothing dryer in your home. We did not remember the air flow requirement in the beginning, and we were to find that Scotland's weather is not the best for drying.
The fifth step is firing to at least 700 degrees C. Our retort was overfilled due to lack of installed capacity. This material is an insulator so the middle of the stack was not fired enough.
The final step is firing to at least 1800 degrees C. We had vacuum capability so this step worked fine except when the furnace failed, which was much too often in those days.