Quality Waterjet Newsletter 08/01/2006

AWJ for CRT Disassembly


Glass cutting with AWJs is a very common application. However, cutting cathode ray tubes (CRT) with AWJs requires a special investigation. Geskin et at. * presented such an investigation in their 2002 paper. Here are the highlights.


A CRT consists of a faceplate, made of unleaded or low-leaded glass, and a funnel, made of high-leaded glass. For retired CRTs, there is a need to separate these two parts so that the unleaded or low-lead glass can be used in some other applications (e.g. in architecture and construction).  Two currently commercial technologies for CRT disassembly are water-cooled diamond saw and “hot-wire”, which employs thermal shock to break the glass tube. These two commercial technologies have their limitations in productivity and separation reliability as well as automation.


In evaluation of AWJs for CRT disassembly, the basic requirement is complete separation of a CRT within a time frame of significantly less than 2 minutes. The authors started with an AWJ cutting experiment in the lab. Using 45 kpsi water pressure, a 0.010” orifice, and a 0.060” focusing tube, a separation speed of 60 ipm was achieved. Then further tests were done with these four approaches: (a) multiple nozzles; (b) using glass abrasive; (c) use water-only jets; (d) use low-pressure suspension jets. Multiple nozzles can definitely cut down the cycle time. Using glass abrasive can achieve a reasonable cutting speed at 30 ipm. But nozzle clogging did occur, probably due to inconsistent glass particle sizes and nozzle design. Further processing refining is needed if glass abrasive is to be used. Water-only jets tend to break the glass and did not show promising results. Tests with suspension jets were conducted in a different location and the results did show effectiveness of suspension jets in this job.


Based on these tests, a waterjet-based CRT disassembly prototype system at a laboratory scale was built and tested. This system used two sets of dual nozzle setup, mounted on two cutting stations oriented 90 degrees to each other and linked with conveyor belts. The first set of dual jets cut off two sides, simultaneously, of the rectangular faceplate. The CRT was then transferred to the 2nd cutting station, where the other two sides were cut. The weight of the CRT was enough to secure it for the cutting and transfer. A cushioned bumper may be added to support the CRT to enhance stability (was not used in the prototype system). The conveyor belt speed was set at 32 ipm. The system throughput was 2 CRTs per minute, much higher than the required 1 CRT per two minutes. Therefore the authors concluded that the experiment was successful.


* Geskin, E.S., Goldenberg, B., & Caudill, R. (2002) Development of advanced CRT disassembly technology, In Paul Lake (Ed.), Proceedings of the 16th International Conference on Water Jetting, Aix-en-Provence, France, October 16-18, p583-593.

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