Offset press: a general method of machine failure identification

7.10 General methods of machine failure identification

Some troubleshooting methods are briefly introduced above. But for machine failure, what is more important is what method to use to identify it. There are many types of machine failures, and they are often multi-cause, multi-cause or multi-cause. Therefore, how to accurately grasp the connection between the cause and result of machine failure is the main purpose of machine failure identification.

1. Causality diagram. Causality diagram is to connect all possible interrelationships between causes and results in a graphical way, so that finding faults is simple and clear.

(Figure 7.1 Fishbone diagram)

(1) The fishbone diagram connects each of the above-mentioned faults with the cause of the occurrence in the shape of a fishbone, the middle trunk is the fault (ie, the result), and the fishbone on both sides is the cause. Taking overprinting as an example, the fishbone diagram is shown in Figure 7.1. Other malfunctioning fishbone diagrams can also be drawn here.

(2) The rectangular table draws the above faults and their causes in the form of a rectangular table. One side of the rectangle is the fault (ie, the result), and the other side is the cause. Where there are connections between each other are indicated by round black dots or other symbols; where there is no connection, they are left empty or indicated by an ×. The following uses the inaccuracy of overprinting and ghosting as examples to draw a rectangular table of the relationship between them and their causes.

The short form of other faults can also be drawn here. The advantage of the short form is that it can see the cross relationship between the cause and the result.

2. Benchmark test method. All the components on the machine are connected in the form of benchmarks, so if we can find the absolute benchmark and the relative benchmark, then we can test the corresponding status between them according to the benchmark relationship diagram. If it does not match the standard status, we should give Adjustment. The benchmarks on a machine are generally divided into two categories: position benchmarks and time benchmarks. Seizing this essential relationship, many faults can be easily eliminated.

3. Replacement method (exclusion method). Due to the intricate complexity between the cause and the result, this poses great difficulties for fault identification. Therefore, in order to accurately identify the source of the fault, the non-fault source should be eliminated first. An effective method for troubleshooting is the replacement method. The same before and after replacement means that it is not the source of the failure, and any changes indicate that it is likely to be the source of the failure (of course, there are other failure sources not excluded).

(1) The final result of the paper replacement method is shown on the paper, so many sources of failure can be detected by replacing the paper. Here are two examples to illustrate the application of this method.

â‘  Thick paper for thin paper: If the rules are not correct in both states, it is likely that the rules are not adjusted properly and has nothing to do with the paper; if the two states are different, one set is accurate and the other is not. That indicates that the fault is related to paper. Adjust the card according to the standard state so that the rules and the paper are in the best fit.

â‘¡Coated paper to replace offset paper: If the ink color is still uneven before and after replacement, it is likely that the ink path is not adjusted properly and has nothing to do with the paper path; if there is a change before and after replacement, one ink color is uniform and one ink color is uneven, then the paper is probably The cause of the failure.

(2) The ink replacement method reduces the ink powder. If the paper still sticks to the blanket after replacement, it means that the paper sticks to the rubber market and has nothing to do with the viscosity of the ink; if the paper is no longer stuck to the blanket after replacement, Then the ink viscosity is probably the cause of the failure.

(3) The fountain solution replacement method increases the acidity of the fountain solution. If the printing plate still wins, it means that the victory on the printing plate has nothing to do with the acidity of the fountain solution; if the printing plate is no longer dirty, it means that the dampening solution The acid of the plate solution is probably the cause of the failure.

(4) The printing plate replacement method replaces the printing plate. If the ink color is still uneven, it indicates that the fault is not related to the printing plate; if the ink color is uniform after the replacement, the printing plate is the fault.

(5) After replacing the village, if the paper is still stuck on the rubber coat, it means that the paper is stuck on the blanket and it has nothing to do with the village; if after the replacement, the paper is no longer stuck on the blanket, then It shows that the rubber market is the source of failure. Generally speaking, the old rubber market is more viscous than the new rubber market.

The above-mentioned replacement methods are all first-level replacement. If you want to further eliminate non-faulty sources, you need to perform second-level or higher-level replacement. If the paper sticks to the rubber coat, replace the paper first. If it still sticks to the blanket, it means that the paper is not the source of failure; then change the ink. If it still sticks to the blanket, it means that the ink is not the source of failure. ; Replace the blanket, if it is still the same, it means that the blanket is not the source of failure; in this case, the printing pressure can be reduced, if it is still not effective, it means that the tooth row of the cylinder is the source of failure. In the end, what part of the dental row is broken, can also be detected by similar methods.

In short, a fault can be replaced in multiple stages. If the replacement is unchanged, it will be removed, and if the replacement is changed, it will be retained, and then replaced after debugging. This is the basic guiding ideology for troubleshooting using the replacement method.

4. The principle of symmetry. The principle of symmetry is a very important method for machine installation, debugging and troubleshooting. The content of the principle of symmetry has been described before. The following uses several examples of faults to illustrate the use of the principle of symmetry.

(1) Check whether the size of the bite is in a symmetrical state when the printed sheet is cut horizontally. If it is in a symmetrical state, it means that the start Tao has nothing to do with the amount of gripping paper.

(2) Check the printing pressure of each contact surface for uneven ink color on the left and right sides of the printed sheet. If they are in a symmetrical state, it means that the fault has nothing to do with the printing pressure.

(3) The printed sheet is fast and slow while checking the tightness of the paper feeding belt and the pressure of the paper pressing roller above, if they are all symmetrical, it means that the tightness of the paper feeding belt and the pressure of the paper pressing roller are not related to the fault .

The above briefly describes the use of the principle of symmetry. But how to grasp the content of the principle of symmetry in the use process, this requires the establishment of a symmetric function:

F (x1, x2, ..., Xn) = F (y1, y2, ..., yn)

If the two places are completely symmetrical, then x1 = y1, x2 = y2, ..., Xn = yn. x1, X2, ..., Xn and y1, y2, ..., yn represent symmetric content. Taking the row of teeth as an example, you can use x1 to indicate the left and right positions of the dental pad, X2 to indicate the height of the dental pad, X3 to indicate the friction coefficient of the dental pad, X4 to indicate the hardness of the dental pad, X5 to indicate the time to open and close the tooth, and so on.

There are different symmetric functions in different places, so when using the principle of symmetry, a symmetric function must be established first.

5. Visual method. The amount of water on the surface of the inking roller can be observed visually. If the inking roller reflects light, it means that the water is large. There are many faults that can be ruled out by visual non-fault sources.

6. Ear listening method. Through the ear to analyze whether there is abnormal sound inside the machine, if there is abnormal sound, you need to stop and check, this method can be used to find unobvious failures.

7. Touch method. You can check the flexibility of the components or the size of the suction force of the air cushion by touching. This method is particularly suitable for checking hidden faults in the force closing mechanism.

8. Signal analysis method. Lift the vibration signal on the machine through the sensor, and then analyze and process it with the computer to find the source of the fault. When using this method, it is best to collect the new and old signals, which is convenient for comparative analysis.

The general methods for troubleshooting are briefly described above. Of course, there are other methods. When troubleshooting, these methods should be applied in a comprehensive manner to select the best path for troubleshooting.

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