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Downtime is still a critical issue for most adhesive applications, however, especially on high-volume packaging lines. The end-of-line packaging process must run smoothly in order to process the most product in the least amount of time and with the least amount of waste. Downtime can cost companies many thousands of dollars per hour. To avoid these added costs, process improvements may need to be considered in equipment upgrades, adhesive optimization, preventive maintenance or operator training.
Improving the Application ProcessThe adhesive application process is an area where problems can occur in many carton-erecting and case-sealing processes. Most automated packaging lines use some type of hot-melt adhesive application process consisting of a heated adhesive supply unit (ASU), a heated hose to transfer the hot adhesive and a heated applicator for applying the adhesive onto carton flaps. Operators routinely fill the ASU with a hot-melt adhesive in the form of chips, pellets or pillows.
Equipment failure, poor adhesion, no adhesion, adhesive dripping, stringing, over- or under-shooting, and often too much adhesive (which leads to glue-caked machine components) are issues observed in many packaging plants. Simple adhesive equipment upgrades can make a noticeable improvement in the adhesive application process and can result in fewer hours of downtime and reduced machine maintenance.
First, downtime due to hose failure should be eliminated. No cost-effective preventive maintenance program exists for hot-melt adhesive hoses. When a hose heater or temperature sensor fails, production stops. Common practice is to keep a spare hose and change it after a failure occurs. In many plants, this often results in several hours of downtime and lost productivity. Backup taping systems are found on some lines, but even starting a backup system can waste valuable time.
Dual-circuit hoses incorporating two heaters and two sensors-with an automatic method for switching between the first and second circuits-virtually eliminate line downtime due to hose failure. The ITW Dynatec Gemini Automatic series contains a flashing illuminated control box that lets the operator know that the second circuit has been activated, providing time for a new hose to be ordered and then replaced at the next scheduled production downtime.
Air open/air close modules also improve adhesive cut-off. Over time, adhesive applicator modules that use an air open/spring close system can lose spring tension, which then results in dripping, stringing and poor adhesive cut-off. Air open/air close applicator modules, which are readily available but not commonly used on many packaging lines, do not rely on a spring to close the orifice during operation. The result is both cleaner cut-off and better operation over a longer operating life span. Zero- and reduced-cavity modules that are still air open/spring close provide improved adhesive cut-off to minimize stringing, but still suffer from loss of spring tension.
Automatic bulk adhesive feed systems can help reduce waste as well. As reported in an article in Adhesives & Sealants Industry magazine in April 2010, automatic adhesive fill systems offer many manufacturing benefits.1 Adhesive fill systems reduce labor and raw material costs, prevent nozzle clogging, and improve safety. Adhesive fill systems continuously monitor the adhesive level in hot-melt adhesive hoppers. Without a bulk feed system, operators constantly have to monitor hopper levels by opening the lid and looking at the current volume. This process introduces many variables into the manufacturing process, such as labor costs to monitor and fill the hopper, failure to fill the hopper, and even the chance of spillage or thermal shock to the adhesive.
With an automatic feed system, adhesive levels and temperatures remain steady, reducing the risk of char and other degradation. Adhesive feed systems virtually eliminate contaminants that lead to char and nozzle clogging by reducing adhesive exposure to the environment. Fewer replacement parts are required, and downtime and maintenance are also reduced. ITW Dynatec manufactures a drop-in, easily integrated hot-melt adhesive delivery system that requires virtually no maintenance and seamlessly allows the user to reduce contaminants, downtime, and labor.
Adhesive OptimizationMany companies look only at adhesive cost per pound to decide which product to use for a packaging operation. The lower cost conventional ethylene-vinyl acetate (EVA) hot melts have limitations as packaging adhesives. Superior performing hot-melt products, like metallocene and polyolefin products, offer many benefits in spite of a higher per pound cost. While EVAs are still in use today, more companies are choosing higher performing, clean-machining, more precise, versatile and aggressive products that lower total costs.
Using superior performing adhesives can lower costs. According to studies by H.B. Fuller, even though metallocene hot melts might have a higher cost per pound than EVAs, use of H.B. Fuller’s Advantra technology can lower costs over the long run.2 Advantra hot melts can reduce total packaging costs by up to 40% vs. standard EVAs through higher mileage, reduced downtime, less maintenance, increased yield and greater throughput. Superior performing adhesives’ application precision and consistency, thermal stability and no-char formulation optimizes packaging processes by minimizing line interruptions and downtime.
Another significant cost savings comes from reducing the amount of adhesive used. When using superior performing adhesives, manufacturers can see a 30% reduction in the amount of adhesive applied to a case or carton. In addition to switching to the air open/air close applicator valve, customers often downsize nozzles by one or two sizes, which can yield substantial adhesive savings. One gram less adhesive per carton can yield a daily savings of 21 lb of adhesive based on production output of 20 cartons per minute, eight hours per shift each day. At $2.50 per pound, adhesive optimization can yield close to a $20,000 savings per year for just one shift of production.
It is also helpful to measure adhesive reduction through glue audits. The primary purpose of a glue audit is to determine the adhesive cost per unit and not simply focus on adhesive cost per pound. Simple glue audits can be conducted to measure the amount of glue actually applied to the case or carton. Place masking tape over the flap where glue is applied. Process the carton through the packaging line. Remove the taped and glued box from the line with great care; the bonded areas will be weak from the applied masking tape. Peel open the flaps, remove the product (if necessary), and remove the applied glue from the masking tape, which acts as a release-coated surface. Prior to removing the glue line, observe the line placement and length. Measure the line length to ensure uniformity from side to side of each carton. Weigh each glue bead to the nearest 0.1 gram. Data recorded includes hot-melt unit, hose and head temperatures, glue pressure, nozzle sizes, glue amount in grams, and line lengths. The procedure may sound more complicated than it really is; this simple yet important procedure is rarely used by manufacturers unless a vendor offers to conduct the audit.
How much adhesive is too much or too little? Companies using conventional EVA products commonly use a lot of adhesive to assure adequate bonding. The use of superior bonding products requires substantially less adhesive, but it is difficult to break the “more is better” mindset. Operators do not want their packages popping open at the end of the line or after they have shipped. The easiest way for an operator to ensure well-sealed cartons is to turn up the glue pressure, use large-orifice nozzles and apply plenty of glue. As mentioned, at several dollars per pound of adhesive, this conventional wisdom can be very costly to manufacturers. Methods for quantifying carton flap adhesion exist but are not often used, especially at smaller manufacturers.
The most common method for measuring carton flap adhesion is a very subjective manual tear test: simply tear the carton open. If the flaps don’t pop open at the end of the line, adhesion is usually adequate. Unless cartons are subjected to environmental extremes, the manual tear test often works. It is the responsibility of the manufacturer to determine optimum bond strength. Trial and error, drop tests, shipping tests, or adhesion testing can all be conducted to determine optimum adhesive amounts. Whatever method is selected for determining adhesive bond strength, it is critical that the proper amount of adhesive is applied consistently and uniformly with no stringing or dripping. Applying too much adhesive becomes a large price to pay.
Preventive MaintenanceMost companies have some type of preventive maintenance (PM) program for the equipment on their packaging lines. In today’s business environment, with reduced staffing and pressure to increase output, preventive maintenance is not always a top priority. A goal of 100% uptime at the packaging line will require a system for PM on adhesive application equipment. Simple-and often neglected-maintenance of a glue machine is necessary to assure trouble-free operation.
Flushing and cleaning the gluing system is essential. This often-neglected step can take three to four hours to complete. Requirements for flushing vary tremendously, depending on the type of adhesive used and the number of hours the machine is in operation annually. With EVA adhesive products, flushing may generally be required every 1,000-2,000 hours of machine use. With metallocene products, flushing may be extended to 5,000-6,000 hours of use. Since it is sometimes difficult to track machine hours, a general guideline might be quarterly for EVA products and annually for metallocene products.
Filters must also be changed, depending on the type of adhesive used and machine hours. The primary manifold filter should be changed at every flushing. Applicator filters may require changing anywhere from monthly to every six months. In-line filters commonly found on packaging equipment require more frequent changing than built-in filters found on ITW Dynatec’s air open/air close applicators.
Manufacturers also need to remember to change nozzles and glue valves (modules). H.B Fuller reports that use of their Advantra hot melts can reduce replacement parts needed by up to 80% due to no char or gel formation. Since so many variables affect nozzle and module function, a very general guideline would be to replace the nozzles and glue modules at every machine flushing and filter change.
Extensive operator training is not required since daily maintenance of hot-melt glue machines is minimal. Normal operation of a glue machine is to turn it on prior to start-up and turn it off at shut-down. Turning off at shut-down is critical to avoid extended heating and degradation of the hot-melt product. Even the metallocene products exhibit degradation over an extended period of heating.
Standard operating procedures should include setting and checking the correct adhesive temperatures for the adhesive supply unit hopper, hose and applicator, as well as correct pressure or motor setting for the pump. Most packaging lines control the glue line length through a PLC or pattern controller. Once set, these parameters should not change.
The primary responsibility of the machine operator is to make sure the glue is applied in the correct location at the correct glue length and appropriate bead size. Operator training should emphasize the importance of conserving glue and using only the glue that is required.
The Bottom LineThe focus on lean manufacturing, productivity, sustainability, green products and cost-cutting will continue for most manufacturers well into the future. Manufacturers can implement several simple and cost-effective steps with their packaging lines to achieve lower costs, minimize waste, and increase packaging line speeds.
For more information, contact HAR Adhesive Technologies at 60 South Park, Bedford, OH 44146; phone (440) 786-7185; fax (440) 786-7186; email firstname.lastname@example.org; or visit www.haradhesive.com.
References1. Hoff, George, “Automatic Bulk Adhesive Feed System Provides Benefits to Manufacturers,” Adhesives & Sealants Industry, April 2010.
2. H.B. Fuller Co., Advantra Adhesives White Paper, October 2010.