Process Troubleshooting Services
Whether it is a problem with a continuous process involving temperature, flow, pressure, or motion, or a manufacturing process that has a hunting problem (up and down quality sinusoid), Burns Bridge can help with the majority of your process hunting and drift problems. As examples of process solutions, Burns Bridge offers the following examples:
1. A glass bottle plant with new 
BHF forehearth technology had a 3 degree fahrenheit sinusoid hunting problem (circa 1986): At the time this temperature variation was such that it was impossible to run seven bottlemaking machines for a loss of $170,000 per day. After review of valve motions for 1. heating (PID burner control) and 2. cooling valve motion control (step motion), it was recommended the cooling valve be reprogrammed for PID control with a 5 degree overlap of the heating and cooling valves to ensure no dead area. Within two weeks 7 fore hearths had been reprogrammed reducing the temperature variation from three degrees fahrenheit to less than one half degrees. All seven bottle lines started to run at standard.
Instrument drift was reduced to practically zero over a six month period. Temperature control variation during production was reduced to a fraction of a degree fahrenheit at 1300 degrees C.
3. In an aluminum jobbing foundry, there was a problem having process controllers on crucible furnaces melt and then hold the aluminum at the required pouring temperature. Burns Bridge after brief investigation, concluded that melting is an on-off control scheme requiring a burner to be at high fire, where as holding is a variable PIV style control scheme. The two control schemes are mathematically exclusive. This means that simple PIV single loop temperature controllers are not capable of melting and holding due to the need for very different sets of PIV parameters for each control mode.
Initially, changes were made to use the single loop controller deviation alarms to drive a burner to high fire, with the alarm circuitry restoring control of the combustion air valve to the controller once the process approached set point. On subsequent furnaces, as fuzzy logic controllers became available, the need to use the deviation alarms to shift from melting to holding modes became unnecessary. With these improvements, variation in holding metal temperatures was reduced from 100 F to less than 25 F.
4. In a crimping process in an automotive fuel tube assembly and test plant a mechanic was being kept busy making unnecessary size adjustments every day all day to 20 or so crimping presses. After assessing the process and the measured data, it was ascertained that the quality engineers had been too enthusiastic in their use of statistically derived process control limits which resulted in a green band of only +- 10 microns.
After review it was established that the green (produce) band could be opened to +-25 microns without jeopardizing product quality (leakers). Process control charts were created with green (go), yellow (adjust), and red (stop and contain) bands. Subsequently the crimp presses would run for several months without need for adjustment and the mechanic was able to work on solving real problems in the shop. Crimp press up time was improved by at least 40 hours per week minimum.
5. A Blanchard style connecting rod grinding process in an automotive OEM engine plant had been experiencing excessive rejects (up to 600 pieces) for a period going back 25 years (hearsay). An initial attempt to solve this problem by a Shainin problem solving team identified excessive operator adjustment as the problem. A lock was put on the caliper (gauge) and all operators were given a key. Unfortunately the gift of a key to each operator completely negated the lock solution and rejects continued at a somewhat lower, but still economically wasteful level. Excessive operator adjustment is almost always a symptom of the problem and rarely the root cause of an oscillating process.
Subsequently, a statistical graphic analysis of the rod thicknesses by fixture, was conducted, taking one shift to complete. It was found that one fixture was too low by five microns and one fixture was too high by the same amount. After a tool and die maker took one shift to adjust the problem fixtures, the rejects were reduced to less than 5 out of 4000 rods per shift. The five rejects were gauge type 1 errors (part is good, gauge rejects the part). Approximately $2 million per year was saved.
6. In an automotive OEM piston casting cell having pouring robots with three axis controlled by Parker proportional hydraulics spool valves, there was a problem with excessive motion faults resulting in much downtime, cold moulds and poor product quality (lots of scrap). An electrical engineer had spent months attempting to tune the PIV parameters in the controls to eliminate the motion defects without success.
Burns Bridge after analyzing the process speeds and hydraulic flows needed, concluded that all three valves on the three axis were too large to the point where less than 10% of the valve capacity on each axis was being used. This meant that it was unlikely that stable motion control could be achieved with such over sized valves. The valve in each axis was replaced by a smaller unit sized to use roughly 60% of the valve capacity. With reprogramming of the tuning parameters, the motion control faults were eliminated achieving a substantial increase in throughput and product quality.
8. Finally a set of offices in a manufacturing plant, serviced by a common central HVAC unit and each having a separate electrical resistance heater were freezing in the summer from excessive A/C and also freezing in the winter in spite of the baseboard heaters being run continuously. Each baseboard had its own thermostat on the wall just inside each office door. The HVAC unit thermostat was installed in one of the offices adjacent to that office's baseboard thermostat. After a brief assessment of the problem, Burns Bridge recommended the HVAC unit be relocated to the hallway side of the wall, a task which took a contract electrician two hours to complete. With this minor change, the cat fight between the two thermostats was eliminated and comfort was restored to all four offices. Thousands of dollars per month in electrical A/C and natural gas heating bills were saved. Most importantly, four senior managers now had reasonably comfortable offices in which to work and became more productive. This condition had existed for at least 15-20 years.
9. In a small shared engineering office with four employees and a second office for the general manager of a turbine repair facility, there had been an ongoing need for several years to use an assortment of portable electric heaters to keep the offices warm. Electrical circuits were being constantly overloaded with many circuit breaker trips.
In the first week as the site leader, Burns Bridge asked a local HVAC contractor to troubleshoot this issue. An hour later the contractor had identified and replaced a broken fusible link ($10.00 part) which had allowed a fire damper to drop and block the main duct.
10. Burns Bridge has had experience to troubleshoot dozens of PID control loop and accordingly has an intuitive knowledge of frequency response methods related to process control and vibration dynamics. Further Burns Bridge has also troubleshooted dozens of programmable logic controller controlled processes. To this end, Burns Bridge has taken three college level PLC programming courses.
Summary: These are just a few examples of process control problems. Burns Bridge's experience is that there are almost always simple cost effective (practically free) solutions to the majority of process control problems. Examples eight and nine above are provided to add a little tragic humor and also to point out that even solutions to "perplexing" HVAC problems can actually be brutally simple.
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