New process for manufacturing and repairing corrug

New process for manufacturing and repairing alloy steel corrugating rollers

corrugating rollers are the most expensive heart components in the corrugated cardboard production line. Its corrugating shape rationality and manufacturing accuracy, wear resistance and pressure resistance, service life and running speed are the main technical indicators to measure its quality and economy, and meet the needs of the imported and domestic corrugated cardboard production lines of China's carton industry, which tend to be wider and faster, It is directly related to the product quality and economic benefits of carton enterprises

during the ironing and bending forming process of high-speed continuous feeding, the corrugating base paper continuously moves relative to the top of the corrugating roll under the action of pressure, resulting in friction and extrusion. The impact of inclusions and mineral hard particles in the base paper makes the top of the corrugating roll severely worn, gradually changing from arc to flat head, so that the height of the corrugating teeth is slowly lower than the lower limit of the standard. At the same time, some corrugating rolls with low hardness of the corrugating roll will cause pits and depressions on the top of the corrugating roll. Because the production line is often not full of paper, resulting in uneven wear on the surface of the corrugating roll, resulting in concave roll shape. Under the condition of continuous high-speed single tooth meshing and directional operation, the corrugated roll with low hardness will appear corrugation, inclination, distortion, Ovality and runout errors due to plastic deformation, which will affect the service life and economy of the corrugated roll

how to improve the sharp wear and deformation phenomenon of the corrugating roller in operation, prolong the service life of the corrugating roller in high-speed operation, and improve the economy of the corrugating roller has been an important topic that China's corrugated cardboard box industry has been paying attention to for many years

alloy steel precision forging materials with stable chemical composition, wear resistance and pressure resistance are used. The hardened layer with a uniform depth of about hrc58 (hs80) is obtained by advanced heat treatment process. The reasonable ridge shape is designed by computer-aided. The ridge shape and drum shape are accurately ground by computer-controlled grinding machine, and the surface is coated with high-quality micro crack wear-resistant hard chromium. It is introduced in this paper that after years of hard research, it has been carefully developed and repaired for wear resistance, corrosion resistance New technological achievements of high-precision and durable high-quality corrugated roller products

I. selected materials

the current steel standards adopted in China have a wide range of chemical components of the same brand, and its upper and lower limits are often connected with adjacent brands (for example, the upper and lower limits of carbon content and other chemical components of 35CrMo commonly used in domestic corrugating rollers are within the middle and lower limits of 42CrMo). The large error of chemical components of steel of the same brand brings great harm to the quality control of heat treatment

we all know that the carbon content will directly affect the hardness of quenched martensite of corrugated roll alloy steel. For example, the carbon content of alloy steel is 0.3%, and the hardness of martensite is (HRC) 49 ~ 55. The carbon content is 0.4%, and the hardness of martensite is (HRC) 54 ~ 60. The carbon content is 0.5%, and the hardness of martensite is (HRC) 58 ~ 62

therefore, strict material selection, selection of high-quality 42crm south is the neither hot nor cold season O and 50crmo precision forgings, strict control of the chemical composition of the material, and control the indicators of the main components such as carbon, chromium, silicon, manganese and aluminum within a certain range, so as to create basic conditions for the stability of the quality of future preparation heat treatment and quenching

II. Advanced heat treatment process

corrugated roll adopts alloy steel 42CrMo and 50crmo precision forgings with good hardenability, but its special geometry and size of roll surface bring great difficulty and quality instability factors to heat treatment, so it has always been the main problem to be tackled by peers at home and abroad

as we all know, the corrugating roller with excellent heat treatment quality should ensure full quenching, reach the required hardening layer depth, have uniform hardness, no soft belt and no cracking. In addition to the material with stable composition and sufficient and reasonable preliminary heat treatment (such as quenching and tempering. Repeated removal of machining and welding stress), the conditions of sufficient and uniform hardening and prevention of quenching crack also require that during the quenching and cooling process, the measured value of cold D ear making rate at each temperature stage must be distributed within the allowable cooling rate zone of this kind of quenching, so as to realize the cooling rate distribution of "water quenching and oil cooling", That is, the high and medium temperature cooling stage has a cooling rate as fast as water to avoid the non martensitic transformation zone. In the low temperature stage, the cooling speed should be as slow as possible, especially at about 300 ℃, so as to avoid deformation and cracks

the new process has reformed the traditional heat treatment method. The first is to move the allowable zone of cooling rate by adjusting the material, stabilizing and narrowing the range of chemical composition, and adjusting the heating method and heating temperature. The second is to move the cooling curve into the allowable cooling rate zone by selecting the quenching medium with superior performance and adjusting the cooling mode

so far, polyvinyl alcohol solution is generally used as the quenching medium for medium frequency quenching of alloy steel in China. Polyvinyl alcohol was used as an additive for water in the mid-1950s. It is widely used in China at present. Because it is afraid of freezing in winter, it is easy to deteriorate and stink in other seasons, and it is easy to agglomerate and block the spray hole during use, which is difficult to maintain, and has short effective service life. At the same time, it is difficult to accurately detect and control the concentration because of the low use content (usually the use concentration is about two to three thousandths, and the change of one thousandth of its concentration can cause a great difference in performance). Therefore, most operators can only control it by experience (such as looking at the amount of foam and judging the viscosity by hand feeling), so the stable quenching quality cannot be guaranteed. Because it is not conducive to concentration management, it has been rarely used abroad

the new process introduces SZ water-based quenching solution and quenching process for the quenching of corrugated rollers and other alloy steels, which effectively ensures the stability of quenching quality. SZ water-based quenchant is a kind of polyalkeneglycols quenchant. With inverse solubility, quenching cooling speed faster than oil and slower than water can be obtained by adjusting to a certain concentration. When the workpiece is quenched, the sprayed quenchant will attach a desolved polymer film to the working surface, which can effectively destroy the steam film formed by water on the workpiece, thus improving the high-temperature cooling rate of water and making the cooling rate of different parts of the workpiece tend to be uniform. The existence of this layer of polymer film also reduces the low-temperature cooling rate of water and reduces the risk of quenching deformation and cracking. At the same time, the concentration of the quenching medium is easy to detect and control, ensuring the stability of the process. Secondly, within a certain range, the temperature of the quenching medium is controlled by changing the stirring conditions to ensure that the cooling characteristic curve of the quenching medium falls into the allowable cooling rate zone, so that the quenching workpiece can achieve high and uniform quenching hardness, no cracking, and ensure a stable quenching layer depth. Due to the strict control of each process layer by layer, the deformation of quenched workpiece can be stably less than 0.15 mm

why are there grooves in a pair of corrugating rollers (including paper guide grooves, vacuum external suction and internal suction grooves) easy to crack and have obvious soft bands, so quenching tends to be soft. This is because the medium frequency induction quenching is the instantaneous heating of the induction ring moving at a uniform speed. During quenching, with the upward movement of the induction ring, the ridge teeth at the lower end of the groove are easily quenched and cracked due to the instantaneous overheating of the magnetic field blocked by the groove and the heat transmitted upward, and the concentration of power and heat. At the same time, because the upper end of the groove blocks the heat transfer at the lower part, the temperature has not reached the phase transition temperature, but the induction coil has risen, so it cannot be hardened, forming an obvious soft band. In order to reduce the risk of quenching crack, the quenching temperature is often reduced or 35CrMo material with relatively low carbon content is selected at the expense of quenching hardness

corrugating roller is similar to pinion with modulus below 2.5, and the common medium frequency quenching frequency is generally between 2500 ~ 8000Hz. The frequency of corrugated roll with large diameter is between 2500 ~ 4000Hz. Therefore, there is an obvious temperature difference between the tooth top and the tooth groove during quenching, which often leads to soft tooth top and hard tooth groove after quenching, and a large tensile stress is concentrated near the tooth groove, which is easy to cause axial cracking

the new process has made breakthrough improvements to the heat treatment equipment, the induction coil, the water spray coil, the distance between the induction coil and the water spray coil, the gap between the two coils and the workpiece, the spray angle, the heating method and the moving speed and method of the induction coil, so that the ridge surface can obtain a layer depth of more than hrc58, 6 ~ 7mm, and the start-up experiment is carried out to test the hardness uniformity, and the grooved roller has no obvious hardened layer of soft belt, so as to ensure the stability of the heat treatment quality

III. chromium plating layer with good quality

hard chromium plating of more than 0.1mm on the surface of the corrugated roller after hardening and fine grinding can reduce the friction coefficient of the surface of the corrugated roller, enhance the wear resistance of the corrugated roller, and prolong the service life of the corrugated roller. At present, the traditional hard chromium plating process is applied in China. Due to the low cathode current efficiency, which is generally 12 ~ 14%, the plating solution concentration and plating temperature are roughly controlled, and most of them are adjusted by the operator based on experience, so the coating quality is unstable, mainly as follows: 1 Coating thickness is difficult to control. If a pair of corrugating rollers are not plated in pairs, the thickness error of some upper and lower corrugating rollers is even 50%. 2. The deep plating ability is poor, especially for corrugated rollers with grooves. The corrugated teeth at the groove edge are often not plated with chromium or rarely plated, resulting in uneven wear during the use of corrugated rollers. 3. The hardness is low and uneven. Because the corrugated roller electroplating is a deep well plating tank, if there is no stirring, the temperature difference between the upper and lower parts is very large, resulting in the upper temperature high chromium layer is soft, the lower temperature low chromium layer is brittle, which seriously affects the use quality

the new process adopts the most advanced hbef25 high-efficiency hard chromium plating process in the world. Its advantages are:

1 Using a higher current density than the traditional hard chromium plating process, the cathode current efficiency is 22 ~ 26%, twice that of the conventional chromium plating process, and the deposition speed is 2 ~ 3 times that of the traditional chromium plating process. Therefore, the deep plating ability is greatly improved

2. The microhardness of the coating is HV, which is the traditional process

3. The wear of the hard chromium coating obtained by this process is nearly 25% less than that of the traditional coating

4. 368 enterprises and institutions from home and abroad participated in the exhibition. Due to the reduction of over thick deposition of high current, the coating thickness was uniform

5. The coating is smooth, fine and bright

because microcracks represent a relatively easy corrosion situation. Corrosion occurs along these microcracks. The smaller the number of microcracks, the deeper and longer the crack, and the easier it is to corrode. This process generates many shallow and short microcracks, which improves the anti-corrosion ability and reduces corrosion defects

strict process management shall be carried out during electroplating. Each roller shall set process parameters respectively according to its diameter, length and plated area, strictly keep operation records, continuously circulate and filter the plating solution, strictly control the plating temperature according to the process requirements, strictly detect and control the plating solution concentration and various indicators. Ensure that the hard chromium coating of more than 0.10mm is evenly plated on the top of the most easily worn teeth and a certain proportion of chromium coating is plated on the root and ridge surface, so as to obtain a hard chromium coating that is harder, smoother, brighter and more wear-resistant than the traditional hard chromium process

practice has proved that although the cost of this process is three times that of the traditional process, the quality of the product has been greatly improved, the wear resistance has been increased by 40%, the service life has been extended, and the maintenance cost has been reduced

IV. scientific design of corrugated type

the paper consumption of corrugated roller is an important factor affecting the production technology cost of enterprises for the corrugated board manufacturing industry. Some foreign countries with relatively developed packaging industry attach great importance to the economic index of corrugated roll paper consumption. as