A Review of Press-Maintenance Procedures

Maintenance-free operation does not exist—no matter how much you spend on your press. The reality check is costly when you assume that a problem can wait until you get around to it. The correct way to think of taking care of your machinery is to believe that friction and wear do exist and the mission is to slow down this process by implementing a maintenance plan. Taking care of your press is like taking care of your car. Good maintenance results in longer life, less downtime, less costly repairs, and top performance.

Maintenance-free operation does not exist—no matter how much you spend on your press. The reality check is costly when you assume that a problem can wait until you get around to it. The correct way to think of taking care of your machinery is to believe that friction and wear do exist and the mission is to slow down this process by implementing a maintenance plan. Taking care of your press is like taking care of your car. Good maintenance results in longer life, less downtime, less costly repairs, and top performance.

The more expensive the car, the more attention people tend to give it. Ironically, printing machines costing the same or more money are often ignored. No time is spent understanding how the machine actually works, so parts and potential wear points are often not identified or understood. Many neglect to even consider reading the manual and buying the supplies needed to service the machine.

Shop variables influence maintenance
Figuring out how much downtime costs you is helpful. This stress test of how much downtime your shop can afford can help you determine how serious your action plan of maintenance should be. Do your demands require production with critical deadlines every day? Do you have additional production capacity, such as a second machine or a subcontract relationship, if a problem occurs? Do you run more than one shift occasionally or regularly? Do the characteristics of your shop conditions or operation put stress on your need to maintain 100% capacity of 100% of your machinery all the time? The more stress, the greater the need for a proactive plan that entails trained manpower and a plan.

Extra capacity, such as a second machine, may relieve some of this stress—but a second shift does not. Instead, second and third shifts add to this stress for multiple reasons. Aside from the obvious effect of double or triple losses during a single 24-hour downtime period is the less tangible effect of neglect and abuse that can occur when multiple operators run a machine. Feeling less individually responsible for a machine can tempt some operators to misuse the machine knowing blame can be difficult to assign. Also, when a problem does arrive or builds to a point of failure, there may be a reluctance to identify the problem for fear of being blamed for its existence or perhaps the task of correcting it. Thus, the unidentified problem may fester into a larger problem that becomes more costly to fix with greater downtime.

Ideal programs
A small or a big shop that relies on quick turns while at the same time working at near capacity is ripe for a maintenance program. The more stress or demands placed on productivity, the more comprehensive the program should be. An ideal program should have the following components:

Record keeping This involves tracking when service was last done last and when it is due again. Tracking ensures that service was completed, who did it, and when, as well as assigning responsibility. These records will also help in the resale of the machine should you decide to replace it with something newer, larger, or with more capabilities. Potential buyers always feel better when proof of maintenance is available. Maintenance can be tracked with charts, checklists, or software. Software is helpful in ensuring better tracking when alarm functions are used, letting you know that an interval is coming up or has passed, as well as for better communication in the correct location of inspection areas, procedures, and materials needed.

Part identification This involves an understanding of where the wear points are and how to check them, as well as knowing the cleaning, oiling, greasing, and tightening points and how to perform the maintenance procedures. These include details as simple as how to take a cover off to get access to a maintenance point, such as a grease fitting, to knowing the right type of grease to use along with the right type of grease gun and how much to add. Manuals, drawings/schematics, and videos.

Support parts and supplies Having critical spare parts and supplies on hand when they are needed rounds out a good maintenance program but requires knowledge of your machine and what parts wear or fail the most. Additionally, this ties back to record keeping and pinpointing the last time you checked or replaced these items, how many were used, and the number of press cycles that have passed since replacement. The overall age and condition of your machine impacts the need for spare parts.

Supplies are also important, as they are needed to carry out maintenance. Included in this list are things like lubricants and tools. Buy and label a grease gun for each type of grease you have in your shop. This way, the high-temperature dryer grease is not used by mistake on the printing press. Additionally, the amount of pressure delivered by the grease gun is determined by the size and type of the grease gun. Large-handled guns can inject grease at much higher levels of force than small ones. This may be good in some applications and bad in others. You can over grease or pump too much pressure into a bushing or bearing. Really cranking a high-pressure gun can cause damage. Normally, watching for some grease movement signifies it is filled.

Other considerations Other factors include the type of environment in which your machine is required to perform. Are your conditions extremely hot or cold, damp or dry? Does the air in your region have contaminates such as salt, sand, or dust? How do these environmental issues affect the parts on your machine, and what can be done to protect your machine from these contaminants? Lastly, how many ship days are you from receiving parts?

Because the job of maintenance is multifaceted and ongoing with a variety of procedures, it is handled more easily if it is divided into segments/categories that make the job easier to comprehend and simpler to carry out and track.

Air
The type of machine you have and the amount of air your machine consumes influences the importance of your air-delivery system to overall machine performance. If your machine consumes more that a few CFM, then the water and air filtration or pretreatment of air going into your machine is critical. Trapping and filtering contaminants is made more difficult when your air compressor and storage tanks change air out rapidly. In these scenarios the airborne contaminants do not have a chance to settle out and instead are passed through the system more easily into areas that cause performance problems.

Machine manufacturers most always provide an FRL (filter, regulator, and lubricator) on the machine to filter some of these contaminants out of the air supply and introduce a small amount of clean oil into the air/machine. However, the FRL is not designed to handle large amounts of moisture or contaminants. Other air pretreatments should be part of your system—mainly an aftercooler and refrigerated dryer, as well as additional filters.

The aftercooler is the part of the compressor (optional when purchasing the compressor) that is responsible for cooling the air (heated by compression) so that the air exiting the compressor is lowered to a temperature within the working range of the refrigerated dryer. Aftercoolers are usually no more than metal or aluminum fin strips that help to radiate heat away from the pipes that the air flows through.

The refrigerated dryer uses actual electricity to power a refrigeration system. All refrigerated dryers specify the max inlet temperature of incoming air and warn that the unit will not perform if recommended limits are exceeded. Therefore, an aftercooler is required when a refrigerated dryer is used. More recently, however, some companies have made combination aftercooler/refrigerated dryers that are contained in one cabinet. These units look like a slightly larger refrigerated dryer but with a fan to provide the function of the aftercooler. Purchasing this unit eliminates the need for the aftercooler. I like the idea of both for areas that experience high humidity.

These units need to be monitored periodically to make certain that they are performing correctly and stop the transfer of any significant amounts of water or oil through to the FRL. A regular maintenance procedure includes draining these supply lines to make note of how much water is making its way through the air-line routing. Drops that allow you to shut off, as well as open up, and drain the lines prior to air coming into your press are essential.

Other issues are poorly mapped air systems where the compressor is located outside, sucking in 100% relative humidity when it is raining, as well as all airborne contaminants. Long runs of pipe or hose that allow for water to condense in the pipe without a drop or loop in the line to drain this accumulation before entering the press are also problematic. A local air-service rep can help spot and correct these issues and stop by on occasion to keep your system operating correctly. Compressors are so important to the health of your press that a quarterly check up by an expert in your area is necessary.

Operators should check the FRL every morning when the machine is turned on to verify that the pressure is correct, the water trap is not full of water, and the oiler has oil in it. The pressure regulator is used to control and set the optimum pressure for the machine. Regulating it at the machine allows for a higher pressure to run to the press, which helps to maintain adequate air volume. Check this pressure, often set to around 90 psi, to make sure it is maintained. Drops in pressure indicate a compressor or demand issue that can impact proper press operation. Insufficient air supply starves components of air and can result in lack of pressure or speed of devices furthest from the air supply. Larger garment presses with several printheads are susceptible to this problem, especially when the original manufacturer doesn’t equip the machine with effective air-distribution systems. Even a slight drop in air supply can create a loss of print pressure.

A coalescing filter is used to physically extract water vapor from the incoming air when the air is regulated
at the press. This is accomplished by forcing the air to pass through a filter similar to what is used in fish tanks to make air bubbles. In our application, it is designed to rake the water droplets from the air. This system works for smaller quantities of moisture, but your refrigerated dryer does the bulk of the moisture extraction upstream by cooling the air and forcing the moisture to condense and fall out of the air before entering the FRL at the machine.

The water trapped or physically extracted from the coalescing filter is expected to collect in a clear plastic bowl until either the machine operator pushes a button to drain it out or a internal float is pushed up by the accumulating water (similar to a toilet float) and the water is pushed out. The float then resets itself and air no longer passes out of the bottom. The filter will leak air continuously when a contaminant prevents the floats from reseating themselves. You’ll likely have to cut the air supply and drain any air trapped in the lines before removing the filter. Once the filter is removed, you may only have to tap on the bowl to dislodge the dirt or particle that may be in the way of the float reseating itself.

The oiler follows the filter and regulator (Figure 1). The oiler is designed to add a drop of lightweight oil into the air so that the inside of pneumatic parts, such as valves and air cylinders, move freely. This oil addition can be a problem when too much oil is let in. It is always better to have too little than too much. Manufacturers suggest a drop after so many indexes. This is a bit of a guess and should be checked occasionally or metered up or down based on the setting’s effects on your press. The most important and often missed maintenance step is filling the bowl with the right type of oil when it runs out.

Air that exits the FRL is distributed to parts on the press. In some cases, an incoming air line feeds a large manifold that serves as a reservoir and a distribution center for several airlines that feed multiple points on the machine. If this manifold has a drain, it is good to drain it once or twice a year. Doing so tells you whether a lot of oil and/or water are getting into the press.

Check the air system past the manifold for leaks and kinks in the air lines. Kinks in air lines can cut off air supply, which results in a slow or non-working component. For example, a squeegee may not be pushing down on the substrate at the regulated pressure until mid-stroke when a restricted air line prevents proper pressure buildup. This can lead to problems with ink deposit at the beginning of the stroke, and you’ll notice that print quality improves as the squeegee travels further and further back.

Replacing mufflers on valves isn’t a widely recognized maintenance issue. These bronze mufflers help to quiet the noise of air escaping from the air valve when the valve is actuated. When these mufflers expel air, the contaminants block or restrict the air flow over time, which in turn slows the speed at which the parts operate. These mufflers cost only a few dollars. The closer the valves are to the base of the machine, the more likely they will clog sooner. Replace them every few years.

Evaluate valves that are slow to react or make a humming noise when they attempt to switch. Humming indicates that the electromagnet is having difficulty overcoming the friction in the valve when it tries to pull in the spool. This added friction might be sludge in the valve (oil and water mixture) that is overworking the electrical solenoid. Be prepared to replace the solenoid and/or valve if you don’t attend to this problem. A cleaning of the valve may solve the problem, but some valves are not designed to be serviced. If you take the valve apart, you should use new seals when putting it back together. Repair kits are available for many valves.

Air cylinders on a machine also affect performance. Cylinders that leak do not fill with air as quickly and do not pressurize to their full capability. If air is leaking past the seals, then full pressure is impossible. For example, if a cylinder used for squeegee pressure were leaking, it would not press down as hard as normal—and cranking down the squeegee location would not correct the problem. Cylinders may leak because the rubber O-rings have dried out and cracked, thereby allowing air to pass. They can also move in the cylinder, causing intermittent leaks.

Electric
Proper grounding and surge protection is important. Its purpose is to guard your machine from acting unpredictably or losing its programming. Electrical storms and power surges have been known to cause machines to cycle on their own or to lose the memory stored in the PLC. Proper grounding and surge protection are important.

Safety is the most important reason to inspect your electrical systems (Figure 2). Most people assume that electrical service never changes and therefore should never need inspecting. They are wrong. Check to make sure that your equipment is fed power through the appropriate wire type and gauge and that the machine is properly grounded.

Inspect all power-feed connections for a solid connection, especially in flash applications where wires heat up and cool down a lot. Tighten these connections on occasion. Strain reliefs that hold the electrical cords as they enter electrical boxes should be inspected to make sure they have not come loose from moving a flash around. The stress these reliefs encounter can cause them to loosen.

Check wires for heat when the machines have been on for a while to see if excess heat is accumulating. The wire type and size you use must conform to local codes, but on occasion a machine is taken out and another is put in using the same cords. Checking loads with an amp meter when all machines are on at the same time is a good safety precaution. Your electrician should be brought in on occasion to check the load conditions and make sure circuit breakers are appropriate for the machines you have.

Oversized breakers will not show up as a problem until the time comes when they should trip to protect your equipment and don’t. Undersized breakers are a nuisance, but do not be tempted to replace them with oversized breakers. Check your fuses regularly, and be prepared to replace any that may be damaged in a short. Keeping properly rated extras on hand keeps downtime to a few minutes and cuts down the temptation of using the wrong size just to keep production going. You may not remember to replace these quick fixes later. Presses often take fuses that aren’t available from the local hardware store.

Other power-related service issues that top the list include batteries used to backup computer memory. If your press’s PLC uses a battery for memory, then waiting until that battery fails before you replace it will require you to reinstall its software. Imagine the productivity you’ll lose when you send the PLC back to the manufacturer.

Safety systems often fail because they’re exposed to a lot of abuse. Jumping safety systems for any reason other than troubleshooting is a bad idea. When your safety system fails, you should immediately find and fix the problem. Depending on the system and machine used, the diagnostics for finding a short can be frustrating but well worth the effort.

Switches are often the culprit of machine failure. Switches may fail at any time, leaving you down one printhead or an entire machine. Having one or two switches on hand that are common to your machine is a good idea. Like many electrical parts, a physical inspection does not reveal any signs of looming failure. One day they are working; the next they may not. One exception is the leads that run to the switch. Wear and tear can lead to a short that will often ruin the switch entirely. Some proximity switches have short-circuit protection, but when this feature is lacking, one wire touching the other leads to complete failure. Proximity switches used on printheads often fail due to mechanical issues such as the leads getting tangled with a moving part. Normally this causes the squeegee-floodbar carriage to stop at one end or the other and refuse to cycle back. The switch may fail open or closed.

Machines using motors with brushes should be monitored. It’s a great idea to inspect these brushes every six months and write on the motor the last date it was checked. When these brushes wear out, they will ruin the motor quickly by allowing arcing to occur on the armature of the motor. Most motors cost more than a few hundred dollars, so check these brushes regularly.

Housekeeping is important, especially for control cabinets or motors that rely on a certain amount of cooling for their performance. Heat can cause failure, and if cooling weren’t so important, the manufacturer would not have installed a fan. Keeping fans clean and working on motor enclosures and control cabinets is essential. Louvers are sometimes used in addition to fans to allow for passive air flow should the fan stop working. Dirt and atomized spray glue have an easier time working their way into these open designs. Clean the components and enclosures periodically.

Hydraulic
Fewer machines use hydraulics these days, save for shock absorbers or linear decelerators. These devices use the flow of oil within the unit itself to create a resistant force that can be used to slow down or dampen the speed of the part that comes in contact with the shock. Oil flows through or out of multiple orifices in these devices as the plunger is pushed in. As the plunger is forced in, the number of escape holes is reduced, which causes a buildup of backpressure. The effect of backpressure goes unnoticed when the plunger is pushed in slowly because, in this instance, the oil has plenty of time to escape; however, when the plunger is depressed quickly, you should notice the resistance quickly and that it builds as the plunger goes in. Some of these devices are equipped with an adjustment to increase or decrease the port size of the holes within the unit, thereby changing the overall force/speed effect.

Checking the performance of these devices is crucial to the performance of the machine movements they are used to control. Aside from making adjustments to shocks for changes in temperature and changing force ratings, the unit may need to be replaced after awhile due to failure. If the shock is not providing the required impact reduction, then excess wear will occur.

Mechanical
A press’s mechanical functions are often unique to each manufacturer and, perhaps, to each model they make (Figure 3). Understanding how the basic functions work is key to understanding where to find wear and how to service the machine. If, for example, your machine uses a cam, it is likely that it will need grease. If a gearbox is used in conjunction with the cam, it will likely need oil. Knowing all of these grease and oil points is critical so they can be mapped out and assigned numbers. Numbering ensures that none is overlooked or missed.

Grease points are present in places of abundant friction (Figure 4). Reducing friction prolongs the life of the press. What is important to understand is that lubricants are often needed in areas where close tolerances are maintained. If a close tolerance is needed to ensure accuracy—registration, for example—then there may not be a lot of room to hold the needed grease. An example is the central bushings on a garment press. The tight fit of the indexer’s bronze bushings mated to the steel center shaft is critical to print registration. However, the design challenge is getting grease into this area and, more importantly, keep it in play for as long as possible.

In tight-fit scenarios, the grease always gets pushed out of the area where you need it. Operators see an abundance of grease that has been pushed out, and the sight gives them a false sense of security. What they are seeing instead is grease that is no longer useful. It has been pushed out of play.

In the example of the center shaft, a grease gun is required to shoot the grease into the groove cut in the bushing. When this cavity runs out of grease and it all ends up out of play, then the machine endures more wear than necessary until the cavity is filled again. Greasing these bushings properly is important. Check with your manufacturer, but normally I recommend rotating the indexer to 12, 3, 6, and 9 o’clock as grease is pumped into the bushings. This helps to distribute the grease.

Be careful not to use a high pressure grease gun (large pump handle) and then pump with an extreme amount of force as this can sometimes create enough pressure as to distort a bushing to where the machine may not raise and lower freely without removing the grease fittings and relieving the excess pressure.

Other linkages, such and chains and belts, are often responsible for power transfer on presses. Most designers now use timing belts (Figure 5) more often than chains, but chains are still preferable in some instances. Chain wear is described as stretch. The chain becomes longer over time, and it is thought to be from the metal stretching. This does not really happen; instead, each of the holes in the length of the chain where the pins go through grow larger in diameter from wear, thereby lengthening the chain. If you can adjust chain tension, tighten it up. If not, make the necessary replacement. Belts, on the other hand, seem to hold their shape very well and tend to fail mainly from over tightening or from wear due to another mechanical problem.

A worn gearbox (Figure 6) may prevent optimum machine performance. In indexing applications, play in the gear-box may make smooth indexing or movement difficult—if not impossible. In applications where the printhead is lifted and lowered, the wear in the box may allow over or under travel, causing the machine to run roughly or inconsistently. In some cases, the gearbox may be too complex (planetary gears) to rebuild yourself; in other cases, simple boxes with a worm gear may use shims that can be removed to reduce the gap/play that takes place with the wear of the worm gear.

Getting fixed up
A monthly inspection of all knobs, handles, and broken parts is also worthwhile. The extra time spent working around these inconveniences is always more costly than the time, money, and effort needed to replace them. Because today’s machines use a lot of these, they are sometimes easy to overlook until you are setting a job up. If maintenance is performed by a non-operator, he may never notice these broken or missing items. Marking them with a fluorescent sticker or tape may be helpful in remembering what needs attention.

Everything that moves is subject to inspection. Even microadjustments are thought to be bad sometimes when only a lock nut is loose. Operators performing set ups for weeks without the use of a microadjustment may lose a lot of time that could be saved by spending two minutes with a wrench.

This article highlights many of the most common issues that simple maintenance can minimize or prevent. You should consult your equipment rep/tech or your press’s manual should a very specific problem arise. You goal is to keep your press operators in that role and not make them into part-time service techs. Learning even a small amount about your press and how to care for it will allow you to take care
of the things affordably.

Rick Fuqua is the owner of Real Performance Machinery, LLC. He has more than 14 years of experience in graphic arts and 14 years of experience working for screen-press manufacturers. Fuqua holds a teaching degree in graphic communications, a master’s degree in technology education, and 14 screen-printing-machinery patents ranging from complete machine designs of both oval and round presses to flash-cure units, pin registrations systems, and all-over-print platens.