Harrel, Incorporated has for years been preaching that American industry and that of other developed countries, cannot afford to build labor into their product. If they do, sooner or later, the extrusion line is going to end up overseas, in some country where labor is cheaper.
The answer, of course, is automation. It doesn't matter how high your labor costs are if you don't build labor into your product. In the techniques of installing and maintaining automated equipment, American manufacturers actually have an advantage, because of their larger pool of technically trained personnel.
In line with this philosophy, Harrel offers a complete line of sheet lines with completely automated control systems. Instead of the agonizingly slow and tedious process of trial and error involved in getting a conventional line on target, with a Harrel system, the operator needs simply to key in the dimensions of the final sheet and press a button. The Harrel SHEETROL II system will bring the sheet into spec in a matter of minutes, and keep it there hour after hour, day after day -- without operator intervention being required!
Harrel SHEETROL monitoring and control systems are available for upgrade of existing sheet lines, of course, as discussed elsewhere on this web site. But it makes far better economic sense to install them at the start. SHEETROL III upgrade systems can add the advantages of a melt pump to an existing sheet line, of course, but it is far better to build the melt pump in as an integrated part of the extruder -- in other words, to use a Harrel GEARTRUDER, as Harrel turnkey sheet lines do.
THE GEARTRUDER ®
The Harrel GEARTRUDER, described in detail elsewhere on this web site, is the heart of the Harrel turnkey sheet extrusion system.
- The melt pump is fully integrated into the extruder system -- not added on as an afterthought.
- Harrel has been making precision melt pumps specifically designed for use with extruders since 1978. They are thoroughly field-proven.
- Exclusive Harrel control technique controls not just the inlet pressure to the melt pump, as other controllers do, but also controls the differential pressure across the pump. This stabilizes the leakage around the pump. It increases the throughput stability to 0.1%!
- Special forms of the melt pump for PVC and for fluoropolymers.
THE DIE
Harrel does not make its own sheet dies but rather uses those of well-established specialists in the field.
- Harrel uses automated dies in its SHEETROL II automatic sheet profile control system. These dies can take either of two forms:
- THERMALLY HEATED die bolts. Individual die bolts are encased in a temperature controlled jacket. Increasing or decreasing the temperature of an individual bolt causes the same effect as adjusting the bolt manually.
- The exclusive Harrel ULTRATHERM automatic profile control system uses separately heated zones in the lower lip of the die, opposite each die bolt. Increasing or decreasing the temperature of the die lip at a given die bolt position changes the friction characteristics of the plastic at that point and has the same effect as adjusting the corresponding die bolt.
- Another contribution Harrel makes to the die is to apply its control expertise to the tightest possible control of temperatures -- a major factor in the die performance. Harrel introduced the very first 3 mode (PID) temperature controllers to the plastics industry in 1967, and has improved that capability ever since.
- THERMALLY HEATED die bolts. Individual die bolts are encased in a temperature controlled jacket. Increasing or decreasing the temperature of an individual bolt causes the same effect as adjusting the bolt manually.
CONTROL OF SHEET THICKNESS AND PROFILE WITH THE HARREL SHEETROL® SYSTEM.
The Harrel systems for control of the thickness of the sheet and for automated control of the cross-machine profile are described in detail elsewhere on this web site:
- For description of the SHEETROL I system, click here SHEETROL I: CLOSED LOOP CONTROL OF AVERAGE THICKNESS PLUS DISPLAY OF CROSS-MACHINE PROFILE.
- For description of the SHEETROL II system, click here: SHEETROL II: FULLY AUTOMATED SHEET PROFILE CONTROL IN BOTH THE MACHINE DIRECTION AND THE CROSS-MACHINE DIRECTION.
TOTAL CONTROL OF THE REST OF THE SHEET EXTRUSION LINE
Harrel has a longer experience in the TOTAL control of the extrusion line than any other manufacturer in the business.
- The Harrel DIGIPANEL controller.
- Harrel introduced the very first PID temperature controllers to the plastics industry in 1967. This made possible deep well sensing for greatly improved accuracy.
- Harrel introduced the industry's first microprocessor controller for extrusion lines in 1975.
- Harrel developed and patented the Harrel DUOSENSE® control -- a barrel temperature controller using cascaded deep and shallow well sensing to combine the fast response to external conditions of a shallow well, and the fast response to process changes of the deep well.
- Harrel pioneered in the use of a melt pump built onto an extruder to stabilize the throughput to 0.1% (the Harrel GEARTRUDER®).
- All temperatures are controlled. DUOSENSE deep-and-shallow well sensing optional.
- All RPM's are controlled, and roll stack speed is synchronized exactly to the melt pump or extruder screw speed with a Harrel DIGISYNCH® -- 0.000% steady state synchronization error. This in turn stabilizes the cross sectional area of the sheet.
- Melt pressure is controlled at the die if no melt pump is used. If a melt pump is employed, differential pressure across the pump is controlled to increase the stability of throughput.
- Melt temperature is controlled from an immersion type temperature sensor. (Combination pressuree/temperature sensors do not indicate melt temperature accurately!)
- Full color schematic diagram of entire system. All out-of-tolerance values are in red.
- Trend plots -- a plot of the values of any 4 parameters of the line for the past hour.
- Alarm logging -- The last 232 alarms on the system can be displayed. Includes zone number, time and date, and alarm description.
- Line startup check list. Safety interlocks can be very frustrating if the operator is inexperienced. The CP- 873 calls up a checklist of actions which must be taken before the system can be started, indicating those already done.
- Speaks 4 languages. Displays in English and any of 3 other languages.
- Unlimited recipe storage on 3 1/2" computer disks.
- "KEEP WARM" mode drops all temperatures into standby mode.
- TEL-CHECK® allows Harrel factory Engineers to monitor the performance of your line from the Harrel plant. TEL-CHECK has been a feature of Harrel extrusion control systems since 1979.
- Temperature plots. The touch of a button calls up a plot of all temperatures.
- Optional heater power monitoring of each heater.
THE HARREL RS-600 ROLL STACK
- Meets mandates of new ANSI/SPI B151.20, 1999 standard.
- Nips open 4" in less than 3 seconds.
- Highly polished 12" diameter chill rolls.
- Rolls temperature controlled by the DIGIPANEL controller to 1 degree tolerances
- Downstack configuration is standard. Upstack on special order.
- 8" rubber covered pull rolls
- Pull rolls tension driven.
- Separate speed control and precision motor drive on each chill roll. Separately settable from DIGIPANEL controller for thick sheet.
For many years sheet extrusion systems were covered only by a basic extrusion safety standard. In August of 1999, however, the America National Standards Institute (ANSI) published a comprehensive safety standard for sheet lines. This new standard was made mandatory for all new and rebuilt sheet lines after August 2000, and on all existing machinery in the field after August 2002.
The most dramatic change in the new standard has to do with the nip opening on the roll stack. Most units in the field can open to 1" or 1 1/2" on a relatively relaxed time frame.
The new requirements are significantly more stringent. They require that the nips open to a 4" gap within 3 seconds of tripping the emergency release. It is obvious that most roll stacks in the field will have either to be replaced or completely rebuilt to comply.
How serious is ignoring the new requirement? Well, ANSI is not a goverment body, so the recommendations do not have the force of law. They are, however, used as guidelines by OSHA inspectors, and a company which is not in complience can receive a safety citation or a fine. And, of course, if an accident occurs on a machine in violation of safety standards, the management will have a problem, to say the least. The only activity of equal rank which comes to mind is Russian Roulette!
COST SAVINGS WHEN UPGRADING
The 3 chill rolls in the traditional 3-roll stack typically represent 30% or more of the total cost of the roll stack. The raises the possibility that, if the rolls on the existing stack are in good condition, it may be possible to salvage them and build them into a new roll stack frame. Harrel is always willing to check the possible savings here when quoting on a new roll stack.
You can't buy a finer sheet extrusion line than a Harrel SHEETROL line!
FOR FULL DETAILS FILL OUT inquiry form, or call Harrel at (203) 866-2573.