Web Coating Blog

“Reducing Energy Usage in Your Process Dryers”

“Reducing Energy Usage in Your Process Dryers”
Dan Bemi
MEGTEC Systems, Inc.

There are many ways to limit the energy used in your process dryers. Most are focused on either reducing heat loss or exhaust air volume.

Some approaches can be low cost efforts that involve mostly labor and material expenditures (i.e. best practices oriented efforts). These include; sealing leakage points (doors and windows etc.), re-insulating hot spots, adjusting air flow balancing dampers, properly maintaining heat sources, greasing roller bearings and aligning rolls.

Often, simply analyzing your process operational requirements can lead to energy reduction opportunities by insuring that your thermal resources are applied proportionately to your raw material and end product drying requirements. For example, by instituting recipe management you can insure that dryer temperatures, line speeds, and impingement velocities are optimized to the specific needs of each product. This will ensure that only the energy required to produce a quality product is expended. Don’t be afraid to experiment with raising operating temperature rather than lowering it. Remember, efficiency is a measure of energy input per unit of production output, therefore, if a small increase in temperature results in a large increase in throughput, this may well result in an overall lower cost product.

Other energy saving approaches may involve modest capital investments; such as automating air flow control dampers, adding exhaust recirculation loops, or adding web IR sensors to control burner output. These latter suggestions can be more difficult and expensive if the process is not already equipped with PLC controls.

The installation of process monitoring and database collection systems can allow plants to analyze energy data and use it to implement cost saving maintenance and standard operating procedures. For instance, many converting processes have machine uptime in the 50-80% range. Something as simple as knowing when to bring processes on and off-line can save thousands of dollars of energy otherwise wasted as processes idle needlessly.

Of course, there are also technology-based opportunities for improving dryer/process efficiency that involve more significant capital investments. For instance, in water-based applications, dryer exhaust temperatures of 275 – 400˚F are not uncommon. Adding a heat exchanger to the exhaust air in order to preheat the dryer make-up air will often provide a financial payback of less than two years on the investment.

Using feedback from humitdity sensors installed in the process exhaust stream can reduce energy usage by allowing the operator to adjust the exhaust volume control damper/s to maintain a humidity level that insures both full drying of the product and a minimum exhaust rate. With feedback to a PLC and the addition of modulating damper/s this type of system can run in a closed-loop mode, eliminating operator intervention.

For solvent-based drying systems, this same concept of exhaust volume reduction can be achieved by substituting LEL monitors for humidity controls.

Solvent-based converters often have additional opportunities available to “close the energy loop” through the installation of oxidizer secondary heat recovery technologies. Depending on the application, the thermal oxidizer can often provide all the heat necessary for the process dryers, eliminating the need for burner systems or electrical induction heating coil systems. Sometimes, there is still energy leftover for other process and/or building heating or cooling requirements.

The Importance Of Accurately Quantifying Defect Losses

37. The Importance Of Accurately Quantifying Defect Losses

There are many essential factors in the effective running of a high quality and economically effective web coating process. One of these factors is to maintain a quantitative detailed accurate database of defect losses in the process. This analysis should provide an ongoing:

• Accurate summary of product yield losses
• What caused the specific losses, streaks, bubbles scratches coverage etc?
• Summary of losses by product and defect type type.
• Specific losses for coating line down, product change, start-up losses
• The ability to calculate dollar losses for each defect
• Easy access to the data for all personnel

Utilization of this database will provide:
• Understanding of defect types in process and where they occur
• The ability to compare product performance and identify better performing products
• The ability to dentify process elements that need upgrading
• With accurate yield loss number the economic Justification for programs and new hardware can be calculated
• A priority list to work on
• An aid in understand mechanisms and

A barrier to developing this database is that often, the yield data collected can be rudimentary and does not accurately reflect the total losses and is not very helpful in identifying the potential causes for defects. The losses are characterized by where they are detected, i.e. in slitting or sheeting process and when the customer uses the product and return the product because it is defective. The classification also can be very general categories, which are not very helpful in finding the sources of the defect, and quantifying losses.

The following is an example of a basic yield loss summary, which provides insufficient information:

• Finishing yield loss 9-62 % of square feet processed
o Pattern length loss 2-14%
o Pattern width loss 1.5-35 %
o Quality yield loss 0-22 %
• Customer returns 10-15 %

For example, what is needed is the exact defects, which resulted in the loss. In regard to pattern width loss there are several potential losses and each may require different corrective action:

• Poor coating weight profile in either machine or transverse direction
• A streak or scratches which prevents using optimum slitting pattern
• Substrate defect such as gauge bands
• Poor edge coverage profile
• Quality Defects
• Missing coating

The database must be maintained in a computer system with intranet access for all company personnel. With advent of computer process control systems, on-line thickness gauges and on-line inspection systems; a significant amount of the data required can be added to the database without requiring personnel costs to add data.

The following is some of the typical data that is needed for an effective database:

• Identification information
• Roll number
• Raw material batches
• slit location
• Defect type
• Amount lost in sq.ft. for each defect type
• Segregated according to product
• Type classification
• Downtime losses,
• Time lost
• Causes such as
• Mechanical failure
• Product change
• Start-up times
• Getting on target for coverage and drying conditions
• Best estimate of defect origination, not where detecte
• Bubble detected in sheeting is coating defect
• Data for each product

The sources of data for the database are:
• Coater logs & inspection data
• Losses from slitters and sheeting
• Customer complaints
• Quality control testing
• On-line inspection data
• On-line thickness gauges

Another requirement of the database design is the ability to interact with other quality control and process databases so that losses can be correlated with process variables to determine defect causes.

One of the difficulties with this database is that there are no standard names and occasionally jargon names are used. This can result in different names for the same defect. One way to minimize this effect is to classify defect by attributes as well as the name. Figure 1 is an example of a classification scheme. An advantage of this approach is that the loss from general defect classes can be identifies and the cost of losses identified, such as streaks, chatter, base defects, etc. In addition, coater losses for operational variables can be determined.

Figure 1

DEFECT CLASSIFICATION

1. Linear Continuous
a. Machine direction
i. STREAKS
ii. RIBBING
b. Transverse direction
i. CHATTER
c. Diagonal
i. DIAGONAL CHATTER
2. Linear Intermittent
a. Machine direction
i. SCRATCHES
b. Transverse direction
c. Diagonal
3. Discrete point defect
a. Spot
i. BUBBLE SPOTS
ii. GELS
b. Contamination coating
i. REPELLENT SPOTS
ii. DIRT
c. Contamination substrate
i. REPELLENT SPOTS
d. Other types
i. REPEAT SPOTS

4. Pattern & diffuse defects
a. MOTTLE
b. DRYER BANDS
c. ORANGE PEEL
5. Process specific defects
a. Raw Materials
i. REPELLENTS
ii. BENARD CELLS
b. Coating
i. AIR ENTRAINMENT
c. Drying
i. MOTTLE
ii. DRYER BANDS
d. Web Transport & winding
i. WRINKLES
ii. SCRATCHES
iii. REPEAT SPOTS
e. Metallizing process
i. BLOOMING
6. Substrate defects
a. Plastic
i. GAUGE BANDS
ii. POLYMER SPOTS
iii. COATING NON-UNIFORMITY
b. Paper
i. WRINKLES
c. MEtalized

T

Response to question on Gravure ink pick-up

In answer to your question about change in color of a gravure coater with a speed increase. Within normal operation the laydown from a gravure cylinder should not vary with a reasonable speed increase. However, the clean out of the cells and hence the coverage and color density may be effected by many things. The degree of cell cleanout depends on things like viscosity, surface tension and other rheology properties. Increasing speeds can also cause pressure on a wiper blade and change the degree of wipe.

Changes in the substrate surface energy from upstream web treatment might also be a factor. Cell cleanout is typically not better than 80%. I would suggest you test a sample at two different speed for coating weight and color density. If you are using organic solvents (evaporation) or high viscosity fluids there may be some issues.

Larry Gogolin
lgogolin@aol.com

Comment on Question about Chatter

Response to Question on Chatter submitted to web coating blog

Mechanical chatter is the defect that you are describing. This appears as straight transverse direction bars across the web. It usually is caused by vibrations being transmitted to the coating bead, inducing vibrations in the coating bead, which leads to differences in coating weight. The vibration sources can be from pumps, drives, building, unwinding rolls, dryer heating and ventilating systems, coater rolls and bearings, and exterior sources.

The first step is to calculate the chatter frequency. The formula for this is:
chatter frequency in cycles/sec = web speed inches/sec* measured cycles/inch
This frequency should help suggest possible vibration sources, For example 60 cycles sec suggests electrical. Vibration frequencies in coater and or specific components can be measured with appropriate equipment

To control vibrations:
• A rigid coating station, isolated from vibrations of the rest of the building, is needed. It should not vibrate and maintain settings.
• There should be uniform tension in the web and no vibrations or surges
• All rolls should be balanced and should not stick, vibrate, or wobble.
• Other vibration sources should be isolated or removed.

Recession Impact on Converting Technology

There is no doubt that the current economic slowdown, recession, or economic adjustment is presenting a major challenge for all businesses, Volume for most converting products are down significantly and profits are only fond memories. Businesses are responding to the changing scenario by the typical reaction of layoffs, reducing forces, and cost
cutting and a little bit of wishful thinking. The federal and local governments are also responding with a variety of actions. The Arizona legislature has taken several steps including reducing funding for all levels of education. It seems ironic that at time when we need more educated people to solve these problems, they are trying to reduce the supply

My interest is to try and ascertain what the effect is going to be on the industries’ manufacturing facilities and particularly on the personnel from R&D to Manufacturing. I expect that there will be:

• A major focus on short-term earnings, by improving quality and productivity and reducing losses
• Modernizing of existing equipment
• A reduction in long term capital projects for new facilities
• A need for personnel to rapidly acquire additional new skills as people in their companies are reduced
• A focus on energy savings in all aspects of the process.
• A reduction in support activities, instruments, analytical tests, education and travel expenses as management views their people as a cost and liability instead of an asset which can be optimized.

There are several technologies that can rapidly be implemented in the coating lines to improve efficiency and reduce costs. On-line coating weight thickness gauges will improve thickness control and can reduce product variability and save on raw material costs, An out of specification thickness can rapidly be determined and corrective action taken immediately. The devices can be used as part of a closed loop control system. Thus reducing amount of scrap produced.

On line-inspection devices can rapidly detect defects and permit rapid corrective actions. A major attribute is that they can detect small defects which are difficult for the human eye to detect, but will result in scrap product when the customer uses. Also, given an accurate position of defects, the final conversion of roll stock to the sizes required by customers can be optimized.

Both of these technologies if utilized correctly can have rapid payoffs and return of investments. They can also be used to develop a true quantitative estimate of real production losses. I have often found that the loss data is not in sufficient detail to identify the root causes. These technologies will rapidly provide reliable information can then permit technical effort on the real problems. These process detection devices can be integrated with computer technology to process data and reduce the burden on people.

Other technologies that should be investigated and upgraded are the ancillary support equipment, such as surface treatment, improved coater line speed and tension control, statistical process control, solution handling equipment and instrument performance and accurate easy to understand procedures. Improvements in these areas often require small expenditures and can resulting rapid process improvement and coat savings.

The process is very dependent on fossil fuels, as a source of energy. There has been an unlimited of fuels at reasonable prices.
However, in recent years the energy costs have increased dramatically, leading to higher energy costs for the convertor. The operating personnel need to focus on the newly available energy conservation technologies. To reduce costs.

One of the issues in the evaluation, selection and installation of the above technologies is that there will be less people to do these functions. In addition, the remaining people may not have expertise in the needed areas. The reduction in travel will reduce the ability of personnel to travel to technical meetings and continuing education courses to learn these technologies. I believe that this need will be met by more effective utilization of the Internet technology in which no one travels. All will have to get more comfortable with the computer and internet technology so they can institute and attend webinars, on-line courses, the use of sharing software. Technical meetings, which are currently almost exclusively face-to-face events will change to include a virtual meeting component. Some of the face-to-face component will gradually be replaced by remote participation by both attendees and presenter. This will permit rapid and less costly information transfer,