Printing machine test
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
More and more printers recognize the value of measuring and analyzing the performance of a press because it is one of the most expensive equipment and the highest cost center in print production. Due to purchase/installation acceptance and quality control and color management reasons, the size of the model should be tested. The real benefit of this press test is that it is a comprehensive, systematic job and requires the production process to be evaluated as a whole. The following elaboration will help the printing company to successfully complete this task.
Anomalies found by analyzing press test data can indicate existing mechanical failures, even printer failures that will occur. In addition to being used to diagnose faults, press testing can be used as a calibration and process control tool to determine current print performance and collect color management profile data.
Reasons to test multicolor presses
1. Purchase / installation acceptance
The printer will not buy a press that does not know if it can achieve the print quality he expects. Many companies use structured test behavior as part of the acceptance criteria for new press purchases and installations, as well as for previously owned presses. Diagnostic verification can determine if the press's performance meets the factory's nominal specifications and industry-accepted quality tolerances. Press testing is the first step in optimizing and extending the lifecycle of a major investment device.
2. Process review
Testing the printer's primary color ink density and tonal value increases helps determine current print performance and can be compared to industry specifications. Print tests can also be used to inspect materials such as inks, tapes, fountains, plates and papers to make better choices.
3. Diagnosis
Press testing can help identify the causes of associated quality failures such as matching proofs, mechanical smear and ghosting, registration faults, and color cast faults.
4. Maintenance and correction of the annual quality system
In order to comply with recognized quality control requirements, such as ISO 9000 and Total Production Quality Inspection (TPM) programs, more and more printing companies are testing their presses every year or even half a year; these tests can also be given to the factory during production shutdowns. The technician provides the information.
5. Printing machine performance characterization
The increase in the tonal value of each press (the dot gain) is different, which affects the printing effect. Know the specific printing The machine's dot gain feature and the use of a compensation curve when outputting the film and plate will give the press operator better control over the print quality.
Press testing should focus on the following issues
1. Is the main printing parts of the press such as rollers and gears damaged or aged?
2. Can the printing press print out the ink density and dot gain values accepted by the industry?
3. Can the printing machine accurately achieve stable image registration?
4. Can the press maintain consistent ink density and tonal values throughout the printing process?
Three stages of press testing
Performing press test analysis requires the use of a test target and a test form. The process consists of three phases, in the following order:
1. Material stage
Since press testing is the best measure of press performance, not the worst, first choose the material that best optimizes press performance. If tested with a low standard material, it will not effectively reflect the mechanical failure of the press. Ensure that the materials used in the press test meet the specific requirements of printability.
Plate
First, the plate is tested by drying the plate exposure control strip to determine the resolution of the image, which is the sharpness that can be measured, and can be used to create a halftone dot. Second, test the registration grids of the suction drying rack or the continuous drying equipment to determine if they meet the accepted registration accuracy. The registration accuracy should be ±0.01mm.
Tape
Use a cushioned, quick-recovery tape to get the clearest possible dots on the press.
Paper
Paper used for press testing should be of good quality. For example, powder paper commonly used by commercial printers, and powder ash paper commonly used by packaging printers for testing.
Ink
Use inks that optimize the performance of your press. At a reasonable thickness of the ink layer, the dots produced by the ink increase and the overprint ratio are within an acceptable range.
Dampening solution
Make sure the fountain solution is compatible with inks and plates; incompatible fountain solutions can cause larger dot gains. It is also important to determine the pH and conductivity of the fountain solution. Please ask the fountain solution supplier for assistance.
*The above requirements for materials are mainly for the accuracy of the test. Of course, it is impossible to make all the top materials in actual production.
2. Printing machine setup and specification stage
Once the material has been selected and inspected, the next step is to determine if the operating components of the press are set up and maintained according to the manufacturer's and material supplier's specifications, and then verify that they are properly operated. This can be done by a series of checks based on the specified test sample. Inspections and tests include the following:
Ensure that the condition and settings of the ink cartridge are in accordance with the manufacturer's specifications, and measure the Shore hardness of the ink cartridge with a durometer; the Shore hardness of the new ink cartridge should conform to the printer manufacturer's specifications. Roller placement and manufacturing techniques play an extremely important role in reducing water mark problems. The width of the embossed surface is set correctly according to the specifications of the printing machine manufacturer; for example, the printing machine for the open side is often set to 3 mm (1/8"), and the width of the embossed surface to the printing plate is usually set to a maximum of 4 mm (3). /6"). Make sure the press roller is in good condition and that it is properly contacted during press-fitting; to inspect the flat-sheet press, use a thumb to apply a thin layer of ink onto the two rollers of the press plate cylinder, spaced 6 inches apart. Run 4 to 5 sheets of paper at the same pressure, and then check if the amount of ink transferred to the blanket roller is the same. Sheetfed presses that do not go to the bolster need to be inspected with a probe; please consult the press manufacturer.
The inspection of the pressed B-B type press roller by the blanket cylinder can be carried out using a special strip-shaped metal foil. The strip metal foil is placed between the plate cylinder and the roller of the blanket cylinder to be pressed and rolled. Then use a magnifying glass to compare the width of the strip of metal foil. If the width is not the same, then the pressure on both sides of the drum is inconsistent. The pressure adjustment should be consistent before proceeding with the subsequent processing.
Make sure that the pressure between the plate cylinder and the blanket cylinder is appropriate for the type of tape used; conventional tapes typically have a embossed surface width of 0.05 mm to 0.1 mm; and air cushion tapes should be between 0.1 and 0.125 mm. The pressure of the B-B press against the pressure of the blanket cylinder usually depends on the thickness of the paper.
Dry solid printing and decompression testing were carried out with cyan ink in each unit, and the streak and printing pressure were determined by dry inspection. A dry decompression test can reveal damage or repair of the drum. Dry solid ink density should be consistent with the cyan density used in current plants or industry accepted specifications or guidelines. The cyan ink density should be as even as possible between each sheet. Using a densitometer to measure from the mouth to the end of the print will help determine if the amount of ink is consistent.
Dry field printing test, check dry and can determine streak and printing pressure
Field decompression testing can reveal damage or repair of the drum
On a sheet-fed press, a dry-down decompression test was performed on each unit to evaluate the printing pressure, check whether the impression cylinders were parallel, and find out the abnormality of the impression cylinder. For every 0.05 mm reduction of the impression cylinder pressure, 25 sheets of paper were run.
Continue the decompression test until the paper is just pressed onto the tape or the paper is finally removed from the tape roller. If the different units start to show that the pressure of the paper is different from the blanket cylinder, the pressure gauge setting of the impression cylinder may be incorrect. Make proper corrections and reset the pressure gauge to prevent excessive roller pressure.
Wet solid printing was performed on each unit to evaluate the performance of the wetting system and water marks; the wet solid plate image should cover the entire paper (with a 25 mm margin). If water marks appear on wet ground, it is usually the cause of the wetting unit. Check and correct the setting of the wetted leeches, the condition of the leeches, and the concentration of the fountain solution.
After completing the press setup and specification testing, determine if there are any mechanical parts of the press that need to be repaired or replaced. This must be done before the diagnostic printing process or before the diagnostic process reveals the characteristics. Once the press setup and specification conditions are adequate, the diagnostic process can be performed.
3. Printing process diagnosis and analysis
There are three steps in the diagnostic process of the printing process. The first step is to check the Ghosting caused by the machine. The second step is to test the registration accuracy of each unit using the register checkered film and the printing plate. The last step is to use Test samples to determine registration accuracy and printing performance of the press.
Check mechanical ghosting
This test was performed on each unit using a mechanical ghost test plate using the dark brown color of Pantone477. If the difference in ink density displayed on the ghost plate from the intersection of the longest vertical bar and the level bar is greater than 0.1 (measured with a densitometer), then some correction to the machine is required. The ink transfer of the inking system may need to be reset, or older printer designs may hinder acceptable printing.
Check the registration of the printing unit
This test uses a registration grid tool with a film negative with precise lines and shallow mesh blocks. Plates made with this film also have original color control strips. This test can find registration errors as small as 0.025 mm.
Install the plate according to the keyhole positioning system. Test different colors of ink in each unit: CMYK, as well as spot colors orange and green. Run the press until the ink density between the sheets is uniform, then print at least 50 sheets. The first extracted sheet, the registration accuracy at the end of the plate should be within ±1 grid width. If the set of meshes exceeds ± tolerance, then check the lockhole positioning system, the flatness of the plate, and the zero setting of the plate cylinder.
The printing plate/roller registers the mouth and the press has no standard for image registration accuracy. The opposite press can achieve point-to-point registration accuracy at the mouth and a 2% point size error at the end of the print. For larger full-open presses, a half-size 2% dot size error may occur at the end of the print. If the registration error in the vertical direction of the tail is too large, the drum circumferential direction may be inconsistent. Replace the plate cylinder and blanket pad as needed to achieve acceptable tolerances. The press may need to replace the drum due to previous damage.
Print test sample
Plates made with press test samples can now be installed for the actual press testing process. The objectives designed on the test sample are used to collect information on press diagnostics, process performance studies, process control, and standardization.
Printing preparation
The printing preparation begins with the installation of the checked plates on the press. Check the registration of all color groups on the first drawn sheet, and use the registration grid on the test sample to determine the registration accuracy of the positioning key. The inking system is adjusted to achieve the desired ink distribution for production. The initial distribution density of CMYK and spot color orange and green can be based on typical printer or industry accepted specifications or guidelines for ink density.
After the ink balance is adjusted, the test sample can be printed. Use the color control strip at the end of the test sample to determine that the ink density is stable within ±0.05 (hand-held densitometer or scanning densitometer). During the test, the speed (rev/h) of the press should be between 80% and 85% of the rated speed. For example, if a flat sheet press is rated at 15,000 iph, then the test speed should be at least 12,500 iph. Let the press run at 500 to 700 rpm at the test speed to ensure that the ink is in balance so that all test sheets reach the target density. With the least amount of operational intervention, continue to run, and the sheetfed press will print another 2,000 sheets.
Analyze the diagnosis target
After the end of printing, when the ink is completely dried early, the analysis of the diagnostic target is performed. The targets on the test coupons are designed to reveal the characteristics of the mechanical system and printing. The following explanation focuses on the characteristics of the mechanical system.
Ladder targets
Place on both sides of the test sample, from the mouth to the end of the print. The main elements of the ladder are the vertical and horizontal lines of 50% coverage. Vertical movement will cause the horizontal line to expand or smear causing the image to be darker in the horizontal direction. The movement in the horizontal direction also affects the vertical line. Ladders can be sensitive to mechanical printing failures such as excessive dot gain, poor paper and paper transfer, tape slack, gear wear bars, gear eccentricity, poor roller contact, and ghosting and smear. The density difference between the vertical and horizontal lines at the same place should be less than 0.07 (CMY) and 0.1 (K and a particularly black color) measured by a densitometer.
Star targets
Provides a quick diagnosis of visually increasing excess tone values (dots increase). In good printing conditions, the center of the star shows a small dot. An abnormally large dot in the center indicates that the ink layer is too thick or the dot is severely enlarged. The central elliptical point indicates that the dot produces a smear whose direction is perpendicular to the direction of the smear. The 8 character or bow at the center of the star indicates a ghosting.
Vernier targets
Measurement and evaluation help determine changes in print length and paper stability between units. The extension of the paper and the length of the print length were measured at the mouth and the end of the print. The registration between the printing units is measured within 200 mm from the mouth. Accuracy errors over 0.02mm usually show a visual contrast on the cursor.
The registration grid is in four areas, two in the mouth and two in the end, helping to determine the accuracy of the registration between the units. The registration box helps to indicate that the printing unit has been overprinted.
The increase in the tonal value (the dot gain) can be measured with a densitometer on the color control strip at the end of the print. It is more suitable to measure on the important screen color blocks in the center of the test sample.
Use a densitometer to check again if the density is close to the target density. If the density is too heavy or too light, then the tonal value no longer represents what the test is going to determine. High density will result in severe dot gain, and low density will result in a slight dot gain. Refer to some typical industry specifications for acceptable dot gain. A properly set press is mechanically suitable for operation and uses high quality The material, then the printed image dot gain should be acceptable.
The change in ink density throughout the test is another factor to analyze. During the test, at least 50 sheets were continuously or randomly drawn, and the density of the same place of each sheet was measured with a densitometer.
Analysis of 50 consecutive sample sheets will show if the ink fountain roller and the transfer roller are properly handled. Analysis of at least 50 randomly sampled sheets will help determine if a stable ink-and-wash balance is achieved. If the ink density changes by more than ±0.05, then the inking system, the type and concentration of the fountain solution, and the suitability of the material should be examined.
in conclusion:
The entire diagnostic analysis of the press is critical to determining if its mechanical system requires maintenance. The press acceptance test results will show whether the press can print acceptable results and whether the printer signs a new or old press. Press testing can also help to find the quality and suitability of printed materials and has become a standardized procedure in quality control and maintenance systems. Press testing can also help optimize the lifecycle of major investment products.
Finally, Process Contro1 is an essential part of the color management workflow, and comprehensive press diagnostic testing can establish process control benchmarks. Many color management efforts have failed because they did not consider that the entire workflow and previous work conditions will affect the final product. If the color management work is to be effective, the key is to stabilize the mechanical and technological elements so that their state maintains the original features.