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1. Roller ReconditioningQuality-conscious printers know from experience that rollers must be in top condition to obtain top quality printing results. Reconditioning of rollers at regular intervals not only maintains quality reproduction but actually extends the useful life of rollers. Reconditioning includes removal of rule cuts when the operating diameter of the roller can be maintained removal of case-hardened ink, deep cleaning of the surface or precision grinding and polishing.
Veteran pressmen know that a well seasoned roller, which has been properly reconditioned, is better than a new roller.
Roller reconditioning, of which regrinding is just one part depends on how well the rollers are cared for. If a roller is cleaned properly, thoroughly and completely and properly maintained, reconditioning will be required at less frequent intervals. On the other hand, if a roller becomes dirty and glazed, if dried ink is allowed to accumulate, theme reconditioning is an absolute necessity as a "super washup."
If a regular roller washup, such as The Rapid Procedure is used on rubber rollers before the ink starts to dry, roller life will be prolonged and the hardening effect minimized. If, on the other hand, the ink is allowed to dry on the roller, a more powerful roller washup is required. This kind of washup tends to harden rollers more rapidly, thus requiring more frequent reconditioning by a roller manufacturer. However, even under optimum conditions, continuous washup has a tendency to harden the roller. Factory reconditioning will restore the roller, re-move the outer surface and permit the natural plasticizers to return to their proper state.
For urethane rollers, once again the regular use of The Rapid Procedure Washup before ink starts to dry on the roller is recommended. Hardening of the rollers is not so much of a problem with urethanes since most urethanes tend to soften over the long term. However, urethanes are somewhat susceptible to attack by washup systems containing appreciable quantities of water and strong detergents. Thus, extra care must be taken to select a wash that is free of these materials. Your Rapid representative can advise you on this subject.
The hardness of rubber and other elastomeric materials is expressed in durometers. The durometer is checked by use of two different styles of gauges. Both push a stylus Into the roller surface and measure the resistance. Our gauge is the pencil type; the other the quadrant style. Durometer is measured as Shore A hardness.
Two to three additional points of hardness is not critical, but when it gets up to 5 or 6 points, that's when the trouble starts. Most authorities suggest 25 to 30 durometers for the ink form rolls. Properly and carefully handled, they might go up to 30-35 durometers in it's normal life cycle and if not property handled, the hardness might go as high as 40 durometer. At that hardness, the surface of the roller, for approximately 1/32 of an inch in depth, may be as hard as 60 durometer.
That's when the surface of the roller is really slick and glazed. The only way to restore that roller to proper condition, everything else being equal is by factory reconditioning.
Westland Rubber's roller reconditioning process
* Rollers received for Reconditioning are carefully inspected as they are booked.
- Covering is checked for size, cuts, rule marks, cracking, other mechanical damage and adhesion to core,
- Core is checked for damage or excessive wear on journals. Bearings (if furnished) are checked for trueness and free running.
* If cover inspection indicates that the roller cannot be reground within required tolerances, the customer is immediately advised that the roller should be recovered.
* Metal defects are normally repaired and undersize journals metalized. This will not be done if repairs are expressively extensive as compared with the value of the roller and core. In this case, the customer is advised so that he may decide what is most economical.
* Roller is reground, removing the absolute minimum consistent with adequate cleanup. While still on the grinder, it is inspected for diameter, taper, run out and surface finish.
* It is then polished at high speed with fine sandpaper until the surface is brought to the desired smoothness.
* While on the polisher, shoulders are sanded to remove excess dried ink. The core and the journals are also cleaned.
* Surface of roller is then carefully washed with solvent to remove polishing dust and inspected again for size and surface defects.
* Exposed metal parts are painted, and journals protected with a rust inhibitor.
* Roller is then wrapped in special protective paper for shipment to Customer.
Glazed rollers contribute to much of the trouble in everyday production. This condition comes about gradually and eventually induces faint areas on the printed sheet. Glazing is due to an accumulation of a dried ink film, and if not corrected, roller surface lose their affinity for ink. Skidding, streaking and stripping can also be traced to this cause. A glazed form roller loses its frictional potential and slows down due to poor traction. When it strikes the plate whose cylinder speed is greater than that of the slower glazed roller. a skid is produced. This in turn causes a streak across the plate.
If rollers are not factory reconditioned at regular intervals, the ink that remains on the surface will cause the rollers to crack. This will seriously affect the quality of printing.
Even under the best operating conditions, using extreme care and the best materials in washups. the roller ends are frequently not washed up. This leads to cracking at the shoulders. If the shoulders crack, the crack will go further in the roller, leading to progressive and complete destruction.
When the roller surface is badly glazed, factory reconditioning is the only way to restore the roller to the proper durometer and remove the glazed surface. In the most practical terms, regular factory reconditioning of rollers is a form of printing insurance. The cost of reconditioning rollers regularly, and keeping them in the best condition, is an extremely small part of the total printing job. Care of the rollers is a most effective means of maintaining the quality of the printing. We suggest that you have your highly qualified Rapid Sales Engineer check your rollers for reconditioning every time he visits you. Many of your rollers can be reconditioned locally at Rapid plants saving time and trouble.
How to check if a roller needs recovering
* Check the ends for dried ink.
* Make a visual inspection.
* A clean rubber roller should have a dull, velvety surface which can be seen and felt.
* Inspect the shoulders for ink buildup and cracks. Also carefully inspect the ends of each roller for the same thing.
* Inspect the surface of the roller for signs of abrasion, damage or unevenness.
* Measure durometer of rollers. Your Westland Rubber representative can perform this check for you.
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2. Proper Roller SettingAccurate roller setting is one of the most important functions of a pressman. Pressmen know that if rollers are not properly set, the very efficient operation of inker units will he partially lost and they will not perform at operating capacity. Ductors, distributors and forms are driven from the surfaces of power driven rollers.
Therefore, the settings must be exact.
Improper setting of rollers may cause costly damage to plates and forms and cause lack of uniformity in the wear of the rollers themselves. It also adversely affects the quality of the printing Improperly set rollers cannot perform to their fullest efficiency because friction speeds wear. Rollers should be set as lightly as possible to still accomplish their intended function, namely, to transfer ink to the plate.
Press manufacturers have made it easier to set rollers through fewer and more accessible adjustments. However, great care must still be given to the proper" setting of rollers.
A successful offset press operation must start with setting inking rollers properly. Unless the plate cylinder diameter is changed or replacement of a roller is required, once adjustments have been completed and the adiustment screws locked, no further adjustments are required.
An irregular roller surface will affect ink transfer. All rollers, except gear driven steel rollers are driven by contact. This means an irregular roller surface will adversely affect ink transfer. All rollers must contact the driving rollers over their entire length.
Form rollers must contact the plate evenly. Poor distribution of ink will result from the least loss of contact between rollers because of the thinness of the ink film.
Most streaks can be avoided if the inker is timed to accommodate the gap of the cylinder. Older and worn presses may require an earlier start (on the back of the plate if the form will permit).
Streaks are most prominent on the gripper edge and by starting earlier, the slack created by excessive wear is taken up before 'the cylinder reaches the gripper.
Proper Setting
Sockets that have become worn should, of course, be replaced. Worn spindles should be built up.
Any roller, regardless of its roller materials, should be set as lightly as possible in order to effect proper ink distribution. This setting is often referred to as the "kiss."
Keep in mind that a substantial portion of downtime may be caused by improper roller setting. Since the cost of downtime can run into hundreds of dollars per hour it can readily be seen that improper roller setting can be very costly. indeed. Rollers that are not properly set can be the cause of and can add to many troubles to be encountered in the pressroom. including scum, streaks, filled halftones, filled screens and reverse type, lined page images. ragged solids, retarded ink drying, variation of print values and set-off problems. These can be direct results.
Add to this, decreased roller life and increased costs. and you can readily see the importance of proper roller setting. The ductor roller is the start because distribution can be no better than the source of supply. The ductor timing, which times the flow of ink, can be set on most presses to bring down the majorpart of the ink charge wherever it is desirable. It will be found, for example, that it is desirable on some forms to have a much heavier flow of ink on the back half of the sheet than on the front half. The ductor must be set parallel with the steel roller, usually a vibrator, contact with which starts the distribution chain. If a ductor is set so it strikes too hard upon contact. it can send reverberations throughout the inking system and cause roller streaks.
The ink ductor should be set very lightly to both points of contact and its action should be set so it contacts the ink fountain roller at the extreme height of its stroke. Distributing rollers must accept and transfer the ink in a position parallel to the rollers which they contact. Form rollers, at the end of the distribution chain, supply the ink to the image of the plate or blanket. A good way to check form rollers after inking up is to drop them on the plate and be sure you "stripe up" about 1/4 to 5/16 inches wide on the larger presses and 1/8 to 3/16 inches on the smaller presses. Keep in mind that rollers on the larger presses are ground with a crown to compensate for "whip" created in the long rollers at high speeds. Setting form rollers too hard is a common and faulty practice. Overloaded rollers. especially during make-ready, will not lift the ink uniformly resulting in a scumining condition which will eventually work into the grain of the offset plate.
Rollers should always be positioned without jarring, so as to avoid springing the core, causing the roller to run out of true.
Testing Roller Settings
* Take a "picture" of the contact by washing the plates clean, then locking the inked rollers against them to print. Check several places around each roller determine till contact at both high and low areas to interpret the roller stripe. Refer to Chart 1
* Use strips of paper one narrow between two wider ones. Place these between the roller and the surface against which it is to be set. Change the adjustment until the proper contact is felt on the middle or narrow strip.
* On flatbed presses, a quick and satisfactory picture can be made and checked by running the inked plate plate under the roller backing the roller sockets off on both sides and then bringing the socket back one at a time to just touch the roller shafts.
* In setting a roller, the lowest roller area must touch the lowest form area. See illustration for proper setting ink form rollers.
* Fountain rollers should not be set in such a way as to be allowed to stop in the same position each time. To observe whether or not it is stopping in the same spot, dent a little impression or smear some ink on the end of a fountain roller and see if these marks move. Proper adjustment of the brake will take care of the problem and correction will result in a more uniform supply of ink.
* After a roller has been set and is running for a short time, check setting again and reset if necessary.
Things to Remember
* For high speed newspaper printing, very light settings are recommended, especially for ROP colour.
* When setting rollers, there must be uniform tension on both ends. This is very important.
* After roller has been set and is
running for a short time, check setting, reset if necessary.
* Composition rollers must be set more carefully and reset more frequently because humidity and atmospheric conditions expand these rollers. -
3. Proper Maintenance of RollersThere is an old saying, "An ounce of prevention is worth a pound of cure." This is particularly applicable to the printing industry with an annual output of many billion dollars a year ...and has special application to the proper maintenance of rollers.
Properly maintained rollers, the "heart" of the printing press, will go far to insure top quality printing. But if they are mishandled or ignored, they will be blamed for costly downtime, and they will also, be blamed for inferior work.
In summarizing, it is important to remember that roller costs can be reduced and printing quality can be improved by a consistent roller care program. It has frequently been proved that rollers is less than 5% of the cost of ink and paper consumed in a specific print run. In-fact many printers and lithographers spend more for waste rags than for rollers. But the rollers are the "heart" of the printing press and unless they are in A-1 condition at all times, top quality printing is not only unlikely but impossible.
The alternate success of the printing process can be no better than the control or ink distribution. A good roller has the ability to pick up a film or ink and deposit what is necessary for a proper impression. This establishes the necessity to always have the right roller used and maintained under the best possible operating conditions. Many roller problems will never occur if there is proper roller maintenance.
Sometimes a pressman will wonder why he had trouble on a plate, why he had streaks, or why a job didn't print clean and sharp or possibly didn't dry the way it should. When you look at his press, you may find that he is trying to print with hard, dry, cracked, dead, dirty rollers.
When a roller gets in this condition it is usually full of tiny surface cracks or a hard glaze. Either of these will prevent its performing properly. The roller has lost its ability to hold on to ink and split the ink film properly. These conditions can ruin even the best plate and cause even the most beautiful, sharp halftone to print muddy. They invite water logging and stripping.
The only way to get the best results from rollers is to keep it in a soft, smooth, tacky, velvety condition just the way, we, the roller manufacturer made it.
Steps for proper maintenance of rollers:
Proper Selection
The type of roller required varies with its function; that is, whether it picks up, distributes or deposits the ink as a ductor, distributor, intermediate or form roller. The best roller also varies with kind of ink, press speed, type of press, and so forth. For example, high speed presses have radically changed roller requirements. Roller manufacturers continually developing new rubber compounds and improved urethane compounds to broaden the types of rollers available as original equipment and for replacement. Therefore, we should be consulted for proper selection of rollers and we can recommend from our broad experience, the roller best suited to your requirements.
Storage
Rollers must always be stored away from dampness and heat. away from sunlight, away from ozone generated by electric motors, switch gear or generators. Give special care to the physical locator, of the storage facilities. Do not store rollers on open racks close to non-ofiset spray guns. or in congested areas where they may be damaged by materials handling equipment. Special care must be taken in storing so that they are supported only by the roller shaft. The roller should never be left in contact with anything that will cause a depression or a mark in the roller surfaces. Storage of rollers should be in racs where, if possible, they can be covered to keep dust and sunlight from the rubber. Rollers should be wrapped in paper or covered.
Spares
Printers and lithographers should always have an adequate supply of spare rollers on hand...a quarter of a set for each press. When new or reconditioned rollers are received, they should be put to immediate use and the ones on the press removed, cleaned properly and thoroughly, and stored. A new rubber roller may not be stress relieved and is apt to start developing high and low spots. Spares should be stored at normal room temperature and in a clean place. Spares should be rotated with the rollers on the presses at least every six months. Spares should be suspended on the journals either horizontally or vertically and the covers should never contact each other or any other surface. Spare rollers should be covered when stored.
Setting
Much down time may be caused L by improper roller setting. All rollers should be set very lightly when cold because, when in use, frictional heat and absorption of ink expands them. After the press reaches operating temperature in 20 or 30 minutes, roller settings should be rechecked and reset if necessary. In all instances, rollers should be set as lightly as possible to transfer ink to plate.
Wash-up
Pressmen should check their rollers every day to watch for and prevent accumulated ink/gum glaze. Stripping, streaking.
hickies, emulsification, excessive plate abrasion, ink glaze and gum glaze are some of the problems caused by improper washup. Preventing a buildup of ink/gum glaze is far superior to attempting to remove it after it has occurred. This method provides clean performance from day to day and would be similar to having a new set of rollers, always on the press. The ink/gum glaze that is imbedded in the roller is impregnated with pigment wax. vamish, lint and acid from the fountain.
No roller can function properly if any part of its surface is clogged with dried oils, solvents or gum.
Reconditioning
Your printing roller manufacturer is your best continuing aid to proper roller maintenance. If the surface of the rollers becomes hard and glazed because of accumulated dried ink, dried oils, solvents or gum, that's the time to send the rollers back to the roller manufacturer 1or roller reconditioning. Reconditioning of rollers at regular intervals not only maintains quality reproduction,but actually extends the useful life of the rollers.
A good pressman takes pride in his press and every part of it. As has been repeatedly emphasised, rollers are the "heart." of the printing press. Unless the rollers are properly maintained, top quality printing is an impossibility. Every good pressman knows it. -
4. Proper Wash-up of RollersPrinting rollers have frequently been referred to as the "heart" of the printing pres. Without rollers there would be no printing. And, for some strange reason, which no one fully understands or can readily explain, the rollers are frequently the most neglected part of the printing press.
It has often been said, that the care, or the lack of care, given to printing rollers has much to do with the results they give their users. Any misuse or abuse that rollers receive is not so much the result of deliberate carelessness as a lack of information as how best to care for them. Pressmen should check their rollers every day to watch for and prevent accumulated ink and glaze. If a roller starts to accumulate such deposits, it must be cleaned at once.. or it will crack and pit and continue to deteriorate. Glazed rollers often cause an offset pressman to think that there is something wrong with his water solution or ink.
The problem that occurs is caused by the printer working with materials soluble in water and minerals soluble with solvents.
Cleaning the rollers of the types of glaze-causing materials is a difficult task. The recommended method of accomplishing this is a two step procedure. Step one is specially formulated to break down ink making it water miscible. Step two flushes away this solution which has been held in suspension and also flushes away lint and gum. The Rapid Procedure is such a process.
Some products sold for use in the pressroom may have a deleterious effect on rollers and blankets. The prudent pressman can determine the harshness of a solution by soaking a section of blanket or roller covering overnight and checking to see if swelling has occurred. Your Rapid representative can show you how to conduct this test.
It has been truly said that "The more automatic a mechanism becomes, the less attention is given to it". This particularly applies to mechanical washup devices which, while they do a fairly good job, do not accomplish a complete job. Example: most offset presses have automatic washup devices that do not clean beyond the face length of the roller. When this buildup gets heavy. it will begin to flake off into the press, causing "nickles". To prevent this build-up of ink, the roller shoulders beyond the washup device should be cleaned, by hand at least once a week.
Where these ends are inaccessible, a long handled brush will come in handy.
Once each month the washup blade should be examined for wear and replaced if necessary.
With some solutions, when a press is washed up day after, a thin film of ink remains on the rollers after each washup.
Finally the surface of the rubber rollers becomes filled with dried ink and the rollers become hard and glazed, then the rollers do not accept and distribute ink properly.
When this happens, the rollers (rubber or urethane) are typically hand washed with one the stronger proprietary wash-ups. Never use ketones, acetates or anv of the chlorinated hydrocarbons. If the glazing has gone too far, even this may not be effective. In this case, the rollers should be removed from the press and factory reconditioned.
Composition rollers should he cleaned with a recommended roller wash after using. After washup at the end of the day, oil should he applied to the ink plate and the press should be run for a few minutes. Rollers will pick up a film or oil and this procedure will prevent ink drying on the rollers if any is left after the washup.
Stripping of Ink Rollers
Occasionally parts of the ink rollers will refuse to hold ink. This is called stripping. For some reason, the rollers have lost their affinity for ink in these areas. Usually it is the steel rollers which strip, but at times even parts of the rubber rollers refuse to hold ink properly. There are two main reasons for stripping. First, a film of dried ink on the rollers and second, desensitisation of the steel rollers. After these have been explored, it should he easy to prevent or cure roller stripping.
A film of dried ink on the rollers often remains after each washup. Finally, the surfaces of the rollers become hard and glazed and do not accept ink as well as they should. This is probably what the pressman means when he says that his rollers have "oxidised".
Once a glaze has been built up it must be removed!
Basic roller wash-up procedure
* Wash with a good two-step solution. The first step will dissolve the water, grease and contaminants and make them water-miscible. The second step will flush the glaze-causing materials from the roller.
* Wash the metal rollers with Chrome Roller Cleaner and Desensitizer or similar solution.
* Wash rollers with a strong glaze remover.
* If above methods are not completely effective, return printing rollers to the factory for reconditioning or recovering.
A few more helpful hints
* When an offset or letterpress will stand for a long period of time rollers should be washed.
* Give special attention to the ends of the rollers that were beyond the form. Get all the ink off shore leaving the rollers.
* On ofset presses the metal vibrator rollers should be washed approximately every 30 days with a cleaner designed for these rollers.
* Urethane rollers must be carefully and completely cleaned after each day's run. Dried ink should never be allowed to build up on the roller. Dried films obscure the fine natural tack of urethane and destroy the sharpness of printing.
* Check washup blade for oleanlines, alignment and wear every month.
Remember no roller can function properly, if any part of its surface is clogged with dried oils, solvents or gum.
Always check with your roller manufacturer for proper wash up solutions to fit your requirements.
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5. Troubleshooting and Common Problems in PressroomIndications of worn-out roller covering Glazing of the surface Ink build-up and cal careous deposits or material residues which cannot be removed by careful washing and cleaning.
Hardening of the surface
Increase of the surface hardness in comparison to the hardness of the new roller cover by more than 5 shore A.
Destruction of the surface
Porosity, roughness, break-ups, especially at the ends, sore running, irregular abrasion, orange peel effect, material tears.
Deviations in dimension
Cigar shape, trumpets at the ends, collar build-up at the edges, shrunken or swollen parts.
Heavy diameter shrinkage
Deviations between actual diameter and diameter of the new roller of more than 1.0 mm.
Problems caused by Incorrect roller setting
Setting too high
* Due to partial squeezing insufficient trans ink or dampening solution and consequently bad printed image.
* High energy consumption, heavy temperature increase and cooling problems.
* Premature material fatigue, danger of burst of the cover or separation of the core bonding.
* Higher abrasion of the printing plate by the high pressure of the form rollers.
Setting too low
* Irregular or interrupted transfer of ink and dampening solution.
* Disturbance of the ink-water-balance, leading to scumming or smearing.
* Application of dampening solution too high, leading to faded print-outs and smearing.
* In consequence of bad transport and slippage the form rollers wipe the ink beyond the dot and fill in the open parts of the plates.
* Insufficient compensation of tolerances and vibrations.
Uneven Setting
* Opening on one side too large and squeezing on the other side too strong, leading to one-sided smearing scumming,
* Setting at one side too high leads to local overheating with danger of failure of the roller cover or core bonding.
* The one sided abrasion destroys the cylinder form.
Rest setting
* Lasting deformation and in consequence concentricity deviations of the roller cover.
* Streaks in the print-out.
Problems caused by Incorrect treatment of the roller cover
Too frequent washing
* Shortened service life of the roller cover caused by separation of material particles and excessive chemical stress on the roller cover.
Insufficient washing, cleaning and maintenance
* Filling-in, glazing, and hardening of the roller surface.
* Bad ink splitting.
* Reduced ink storage with danger of ghosting or streaking.
* Enhanced wear or pollution of the printing plate by loosening ink rests.
* Linting and fluffing.
Aggressive or wrong washing agents
* Swelling or shrinkage causing too high or too low setting
* Dissolution or quick abrasion of the cover.
* Hardening or glazing of the roller surface.
Usage of inadequate inks, UV-inks, lacquers etc.
* Swelling or shrinkage causing too high or too low setting.
* Hardening or glazing of the roller surface.
* Dissolution or quick abrasion of the cover.
Dry running at the ends or in the range of reduced transport
* Premature glazing caused by drying of the ink.
* Formation of axial and radial cracks.
* Partial picking of the roller cover.
* Marks in the printed image.
* Locally enhanced accumulation of hickies.
* Local Overheating.
Calcareous dampening water
* Filling and glazing of the roller surface by calcareous deposits.
* Ghosting and streaking.
* Enhanced wear of the printing plate.
Inappropriate cleaning by means of sharp-edged objects like spatula or wire brush
* Mechanical damage or scratching of the roller surface.
* Hickeys accumulation and loosening of rubber particles resulting in pollution of the printing form and marks in the print.
During storage no protection against sun or ozone, influence of temperature and noxious gases
* Glazing of the roller surface.
* Embrittlement and formation of cracks
Stored while laying on it's side
* One-sided deformation and loss of dimensional accuracy.
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- Call On: +91 99998 54440 / 93246 24237
Rollers Knowledge Centre
Rollers Knowledge Centre
