Common problems and solutions in the use of the ho

Common problems and solutions in the use of printing cots

cots are an important part of the printing press, but in actual production, the maintenance of COTS is often ignored, resulting in shortened service life of cots, increased maintenance costs, and difficult to improve product quality. The author believes that there is a quality problem of the cots themselves, but the most important thing is the use method of the operators. In this regard, the author, combined with his years of practical experience, briefly analyzes several problems that should be paid attention to in the use of cots

problems that should be paid attention to during installation and adjustment of cots

1. Install new cot bearings correctly

first clean the impurities at both ends of the new cots, then select bearings with specifications and models that meet the design requirements, apply lubricating oil on each mating surface, and hammer the special bearing sleeve correctly and evenly until the bearings are installed in place. Do not apply force directly to the bearing and knock it at will to avoid damage to the bearing before it is used

2. ensure the lubrication of the bearings and shaft seats of the cots

before installing all cots, the surfaces of the bearings at both ends of the cots and the cot bearing sleeves and supports on the machine should be coated with lubricating grease to minimize the rotational impact friction between them caused by the back movement of the inking roller. It is often found that some inking rollers, shaft sleeves and both sides of the shaft seat have been seriously worn in a very short time in order to effectively and accurately control the dosage of epoxy raw materials before the mixture is injected into the mold, so they have to be re welded and processed. Moreover, the inking roller bearings are often damaged and replaced, and even the roller surface is damaged after the bearing is broken, causing greater losses. The main reason is that the lubrication of the contact surface of each workpiece is not done well

3. regulate the pressure of water and ink rollers

after the water and ink rollers are installed on the machine, they must be strictly regulated. If the pressure is adjusted too lightly, it is easy to cause poor water and ink transmission; If the pressure is adjusted too heavily, it will artificially increase the friction between rollers, heat up the ink roller, increase the extrusion and expansion between rubber rollers, and accelerate its wrinkle and aging. At the same time, the product quality will also be affected, and the harm is self-evident. An operator once mistakenly adjusted the pressure between the hard roll and the rubber roll too heavily when changing the rubber roll, so that the new rubber roll cracked and was scrapped as soon as it was started up for a shift. In addition, if alcohol fountain solution is used, the pressure relationship of the water roller should be adjusted carefully to prevent the service life from being reduced due to passive transmission

cots often have problems in the printing process because the expansion speed is not directly related to the stretching speed

1. Cot surface crystallization and calcification

the surface of high-quality cots should be fine, smooth, slightly sticky, and have good ink transfer performance. However, due to the influence of fountain solution, ink, paper and other factors on the cots for a long time, and the impossibility of complete cleaning each time, various substances accumulate on the surface of the cots layer by layer. Over time, the original pores on the surface of the cots will be closed, forming a smooth crystalline layer similar to calcium, which will seriously affect the ink transfer and water transfer performance, and cannot stably control the ink color of printed matter. In order to solve this problem cost effectively, at first, special build-up paste and accumulated water were used to clean it, but it was time-consuming and laborious, and the production cost was virtually increased. Later, try to wash it with citric acid water after each washing, so that some calcium impurities on the surface of the cot can react chemically to form soluble substances for cleaning. Practice has proved that this method works well and saves money and effort

2. The surface of the cot is easy to have scars and numbness

because the cot is relatively soft, a little hard object will be scratched during high-speed operation, especially when the alcohol fountain solution relies on the water roller, once there is a scratch, it can no longer be used. There are two main reasons: one is that the printing plate is not pulled tightly or the plate clamp is not clamped tightly, and there are often cracks and cracks at the trailing tip of the printing plate, which scratch against the plate water and ink roller; Second, the ink roller is not maintained in time, and there are many impurities such as ink skin and ink residue on the rubber roller, which accelerates the friction, heating and aging of the rubber roller, and makes the surface of the rubber roller full of hemp eyes. Generally, the two ends of the rubber roller are more serious

3. the cots are chapped and aged too early

there are many reasons for this problem, such as excessive dry oil in the ink, which makes the ink dry and heat on the cots; The cleaning agent used to clean the rubber roller is improperly selected, and the cleaning time is too short, so that the impurities on the rubber roller can not be completely cleaned; The ambient temperature of the workshop is high, and the cooling system of the fountain plate works poorly, so that a large amount of heat generated during the operation of the rubber roller cannot be dissipated in time, and the cohesive temperature of the rubber roller is very high: the performance of the rubber roller bearing is poor, and it is rotated by the inking roller, resulting in jumping friction, extrusion, etc. These factors will accelerate the early chapping and aging of cots

strengthen the regular maintenance of cots

nowadays, all printing plants attach great importance to machine maintenance, among which water and ink rollers are one of their key maintenance contents. According to production experience, the following problems should be paid attention to when maintaining cots: India will become the second largest PE importer in the Asia Pacific region after China in 2023

(1) check whether the bearings at both ends of the rubber roll move freely and are in good condition. If they are loose or worn, they should be replaced in time to avoid greater harm

(2) scrub the surface of the rubber roller to remove impurities such as ink skin and ink residue

(3) check whether the rubber on the surface of the cots is good, especially the version cots must be the best, and the cots with peeling surface and more pockmarks should be re polished or cast in time

(4) before installing the rubber roller, be sure to apply lubricating grease on the mating surface of each rubber roller bearing to prevent these parts from being damaged

reprinted from: Printing Technology