Replacing Ceramic Emitter Array with Casso-Solar FB Heaters to Improve Quality, Energy Efficiency, and Production Rate
The Challenge
A customer reached out to us regarding a new HDPE embossing application that they were struggling with. They were running a continuous web made from HDPE through a pre-heating station to soften it prior to passing through embossing rolls. The difficulty they faced was that their existing pre-heating setup was yielding inconsistent quality across the width of the web, as well as being inconsistent over the course of a production run.
Casso-Solar was tasked with recommending a replacement setup that would yield more consistent quality product both across the width of the web and throughout the course of a day’s production.
Previous Setup
The customer had purchased a series of ceramic infrared emitters they then installed in 5 rows each with 12 emitters across. This arrangement was mirrored above and below the web for a total of 120 emitters. The emitters were approximately 5” square and similar to those pictures in Figure 1 (photo courtesy of Tempco). This type of ceramic emitter is commercially available from various suppliers.
Figure 1 (photo courtesy of Tempco)
To control these emitters, the customer was monitoring the face temperature of a sampling of them via a thermocouple. In order to get acceptable embossing, the emitters needed to be run at their maximum temperature (about 500C) at all times. However, because of the buildup of heat within the emitters over time, the product started to overheat as a production run’s length increased. This appears to be due to the emitters’ output not being consistent with the measured face temperatures. To counteract this, the customer had to manually adjust the emitter output continuously to prevent overheating.
In addition to the overheating problem, the arrangement of multiple emitters across the width of the web created a pattern of cold and hot spots that led to most of the finished product being unusable. This was compounded by semi-frequent failures of the individual emitters that required consistent maintenance to troubleshoot and replace.
The Solution
When the customer presented this application to the Casso-Solar team, we identified 3 main problems that needed to be addressed:
1. The current emitter arrangement consists of a total of (120) individual emitters, which creates both maintenance problems and issues with inconsistent quality due to cold spots where the emitters meet.
a. We addressed this issue by proposing a total of 2 Casso-Solar Technologies FB heaters, one for above the web and one for below the web. Each FB heater would replace 60 of the ceramic emitters. This reduces both the complexity of the wiring and the likelihood of maintenance issues while also eliminating cold spots across the web width.
2. The customer’s objective is to heat a thin surface layer of the HDPE web to soften it for embossing. Heating the entire thickness of the web is undesirable for the process, as it causes the web to sag and deform. HDPE absorbs infrared energy best at a wavelength of approximately 3.25 microns. The ceramic emitters primarily used operated at an average wavelength of 4 microns. At 4 microns, nearly 80% of the infrared energy passes through the surface of the HDPE to the interior. So to achieve the target surface temperature, the interior had to be heated much higher than necessary.
a. Utilizing both our experience with HDPE heating and an analysis of the infrared transmission curve, Casso-Solar designed the FB heaters to operate at the target wavelength of 3.25 microns.
3. The existing control scheme relied on measuring heater face temperature to achieve a consistent surface temperature on the HPDE web. This measurement strategy led to the surface temperature slowly increasing throughout a production run.
a. To provide more reliable results, Casso-Solar designed and built a new control system that utilizes infrared pyrometers to separately measure the top and bottom web surface temperature as it exits the heating zone. The control system then regulates the heater output as required to maintain a consistent surface temperature.
The Results
1. The original set of emitters had a total wattage rating of 48kW and ran close to maximum power to achieve adequate embossing results. The replacement FB heater system has a total wattage rating of 32kW and runs between 60-70% output, resulting in significant energy savings.
2. The Casso-Solar Type FB Heaters reach the specified temperature faster than the ceramic emitters, reducing wasted time during the warm-up period.
3. Product quality has greatly improved.
“With the previous ceramic emitters, the embossing quality was often patchy, creating ‘cold’ and ‘hot’ spots … across the width of the sheet. This has rendered all previous testing runs as scrap since acceptable embossing could not be achieved.
The new Type FB heaters form continuous heating zones across the web, eliminating the striping and patchy texture that previously occurred.
Advancing to being able to control the sheet temperature using pyrometers has stabilized the process and made the resulting texture much more consistent from edge to edge and from run to run, significantly improving overall visual and tactile quality.”
4. The customer is now able to achieve their production speed goals, where previously they had to slow down the line to compensate for the difficulties caused by using the ceramic emitters.
“Because the heat distribution is now uniform and the sheet quickly reaches and holds the correct embossing temperature throughout product/climate temperature swings, the line can run at the intended production speed without sacrificing surface quality or needing to slow down to ‘nurse’ cold areas or compensate for failing individual heaters.
This preserves our high production lbs/hr throughput, which aligns exactly with operational goals. Changeovers between different colors and products have also become faster and more predictable, since the operators adjust directly to the required sheet temperature setpoints rather than experimenting with heater temperatures and waiting for the system to stabilize.”
5. Simplified use and maintenance of equipment.
“The new heater banks are easier to operate because the control strategy is straightforward: operators monitor and control actual sheet temperature using pyrometers, instead of inferring it from multiple heater readings and making frequent manual adjustments, reducing guesswork across shifts.
From a maintenance standpoint, having two solid heating banks instead of roughly 120 individually wired 4″x4″(+/-) elements has simplified troubleshooting, reduced ‘mystery’ defects from single failures, and cut spare-parts inventory needs. It also eliminates high-voltage electrician calls for heater changes or rewiring and requires a smaller overall footprint.”
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