Count Everything: What Gets Measured, Gets Improved

Unit sent back for service after taking a swim in some coating.

In the 1999 baseball movie, For Love of the Game, there is an exchange between Kevin Costner (Billy) and Kelly Preston (Jane):

Jane: Do you lose very much?

Billy: I lose. I’ve lost 134 times.

Jane: You count them?

Billy: We count everything.

 

In UV, we also need to count or measure everything because, as Lord Kelvin said, “If you cannot measure it, you cannot improve it.”

Food Waste Data
Figure 1. Food Waste Data

This column was inspired by a customer in India. The whiteboard (see Figure 1) in the cafeteria tracked food waste. When they weighed the daily food waste, there was a decrease. We encouraged them to extend this approach to the UV curing lines.

Determine the “mandatory” and “nice” things to track in your UV process. The equipment, process stability and value of the products being manufactured will determine how often each parameter needs to be counted or checked. Use common sense.

To get you started, this column offers parameters to count or check. These parameters also are provided as tables that can be downloaded for reference via the QR code provided at the end of the column. Decide if other key process parameters need to be counted or checked for your process. If you are not sure about a parameter, track it for a month and decide if it is important to your process. The goal is improvement, which saves time and money.

UV Source and Process Parameters

At a minimum, record the Joules/cm2 and Watts/cm2. Tracking the applied power and speed/exposure time also is suggested.

  1. Applied Power Setting. Increasing the applied electrical power normally increases the power Watts (W/cm2) of the UV delivered to the cure surface. Understand the settings on the system and the lowest usable setting. Record the W/cm2.
  2. Belt Speed or Exposure Time. The belt speed/exposure time impacts the amount of energy (J/cm2) reaching the cure surface. Independently confirm the belt speed. Record the J/cm2.
  3. Spectral Output. Make sure your UV source(s) can deliver the spectral output needed for the photoinitiator package. If your application requires multiple/different sources, make sure that each source is in the correct position. Not all sources/bulbs are created equal, so buy the bulbs based on their value to you. Put purchasing controls in place to ensure you are only getting what is expected.
  4. Supplied Electrical Power. The uniformity of electrical power coming into the facility can vary. Brownouts and demand from large users, such as data centers, can impact supplied power. Determine whether someone needs to monitor and/or if you need to condition the incoming electrical power.
  5. UV System Optimization. Confirm that the UV system being used is suitable for the process. Is an “available UV system” being used instead of a solution optimized for the process? Confirm that the UV source(s) used deliver the needed power (W/cm2), energy (J/cm2) and spectral output. Determine if the system provides or minimizes intensity.
  6. UV Delivery Pattern. Confirm that the UV energy reaching the cure surface is being delivered (focused, unfocused) as expected. Is it uniform across the entire width of the UV source? Is a profiling radiometer needed? Is there anything – such as a quartz plate – between the UV source and the cure surface? (See Figure 2.)
  7. Comparison of focused (red) and unfocused (blue) system. How the UV is delivered could impact final product qualities.
    Figure 2. Comparison of focused (red) and unfocused (blue) system. How the UV is delivered could impact final product qualities.

    Check to make sure the cooling system is performing as designed and that there is proper air flow. If used, replace the air filters as required. High-power LED systems may use chillers.

  8. Establish a maintenance schedule for inspections and preventive maintenance. The frequency will depend on the conditions of the process and the equipment. Be sure to have the necessary maintenance items available. Maintenance can include:
    • Routine Maintenance: Cleaning of reflectors, quartz plates, air filters, bulbs; inspection and adjustment of all equipment
    • Regular Maintenance: Replacement of bulbs, reflectors, power supply components, quartz plates, air filters and any other consumable items, such as RF screens/magnetrons
  1. Process Window. What are the process conditions that maximize yield and minimize scrap? Were these identified when the process was developed? Risks include:
    • Waiting until there is an issue to define the process window.
    • Failure to monitor the process and catch potential issues.
    • Having a tight process window that is tough to maintain.

Consistent and regular tracking of your parameters is key. Whatever method is used (spreadsheet, clipboard, profiler files), be consistent in collecting and recording the data.

  1. Utilize suppliers and their training programs and websites for information. Incorporate this information and the ”tribal knowledge” of key employees in a training program on the UV process, equipment operation and maintenance.

Note: Parameters 1 (Watts/cm2), 2 (Joules/cm2) and 3 (Spectral Output) work together to allow the formulation to cure to the desired properties. In simple terms, the Watts provide the ability for the UV photons to penetrate through the coating to provide adhesion. Joules provide the energy for the total cure of the material. The Spectral Output of the source interacts with the photointiators in the formulation to help achieve the desired properties. If any of the parameters change significantly, the desired results also may change. It is important to collaborate with both the coating and equipment supplier to optimize the formulation and UV sources for the specific product in use.

UV Instrument Selection

Select a measurement solution matched to your application and process. Use consistent data collection techniques and follow the manufacturer’s guidelines for handling and cleaning the instrument for the best results.

  1. Physical Size. Select an instrument that will physically work/fit into the process.
  2. Band(s)/Spectral Response. The spectral response of an instrument is determined by the manufacturer.
    • Instruments with a single or four-band response are available.
    • Select the band based on the source type, photoinitiator package and desired final product properties.
    • An instrument designed for broadband (mercury) sources may not provide accurate values for an LED.
    • If surface properties (scratch or stain resistance) are important, monitoring UVC in addition to UVA is important.
    • Instruments are a communication tool, and using the same instrument response as others in the supply chain allows users to communicate effectively.
  1. Dynamic Range. Dynamic range refers to the range of irradiance values that an instrument is optimized to measure. Use the correct range unit for accurate values.
  2. Sample Rate. How fast is the line running? Confirm that the instrument has an adequate sample rate to capture the peak intensity and associated irradiance profile.
  3. UV sources generate visible and infrared energy, which can be helpful in some applications. Most UV instruments can be exposed to the intense UV for short periods of time without damaging the optics and/or electronics. Extended UV exposures and/or running the instrument through a thermal oven or infrared system are not recommended and can quickly damage the instrument. Understand the limitations of the instrument to avoid damaging it.
  4. Physical Damage. Manufacturers work to make durable, long-lasting instruments. Customers continue to find creative and new ways to physically damage (abuse) instruments. Please treat the radiometer as an electro-optic instrument and not an indestructible “hockey puck.” (See Figure 3.)
  5. Unit sent back for service after taking a swim in some coating.
    Figure 3. Unit sent back for service after taking a swim in some coating.

    Maintenance and Calibration. Follow the manufacturer’s guidelines for calibration, handling, storage and cleaning of the instrument optics.

  6. UV, visible and infrared energy can be tough on an instrument. Follow the manufacturer’s guidelines for regular service and calibration.
  7. Have realistic expectations:
    • Understand the instrument and its spectral response.
    • Don’t set the process window tighter than the instrument’s stated performance.
    • Keep the instrument calibrated.
  1. Instrument Settings, Data Techniques. Use the same instrument settings, data collection and recording in all company facilities.

Summary

Count Everything: What Gets Measured, Gets Improved. Measurement led to reduced food waste in the cafeteria. The same is true for UV. The two tables give you a start that will lead to improvements in your UV process. Work with your formulator and substrate supplier to identify additional areas to measure and check. Improvements mean savings of time, money or both.

Parting Shot

I single-handedly managed the successful upgrade and deployment of a new environmental illumination system with zero cost overruns and no safety incidents. Translation: I changed a light bulb!

The parameters outlined in this column are provided as tables that can be downloaded in PDF form for reference.

Jim Raymont
Director of Sales
EIT 2.0 LLC
jraymont@eit20.com

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