For a long time, there are large amounts of worldwide study on technology that manufacture and maintain squeeze roller. Now for the manufacturing of roller press, the common materials are alloy of Cr, W, Mo, V and forge piece such as 45＃steel. The casting is also used abroad. On the whole, the forge piece has better performance than casting one.
Inblock cast, overlaying and stud welding of cemented carbide are different manufacturing methods in different periods. Inblock cast is the technology used in early times and is no longer widely used at present. Stud welding of cemented carbide is hard to be generalized due to the reason that it’s very sensitive to the foreign matter in the materials or too expensive costs.
Taking wear resistance, adaption to working condition, convenient usage and maintenance into account, overlaying is considered to be the best process at present.
The working condition of squeezing roller is very poor. When manufacturing squeeze roller, the high-intensive, good-ductile low alloy and high-strength steel by refined-smelting ladle furnace, such as 34CrNiMoA forge steel, should be chosen as roller material. Due to costs, medium carbon steel with grade ZG45 or ZG40Cr are used to be roller materials. For these steel there is no refining and even casting roller is applied. Due to high impurity content, poor toughness and ductility, and many latent defects of the roller made by such materials, internal crack will appear and may cause peeling off in large quantity and even the abnormal failure of roller. Therefore, for the manufacturing of new roller, the roller must be forged according to design requirements, and then overlain on its surface.
According to references, various welding materials are used to overlay squeeze roller (consist of Cr, W, Mo, V alloy) when manufacturing roller press. There are 3 types of material: the bottom layer with low carbon alloy, which joins the parent roller directly, the transition layer with low carbon and medium alloy and the top hardfacing layer. The top layer is wear resistance layer with medium-carbon high alloy. According to design requirements, there are different roller surface such as smooth surface, ZIG-ZAG lines, cross lines, short crossing and wear-resistant dots.
The overlaying manufacturing process of squeeze roller is shown as bellow:
(1) After rough turn, the forge piece of squeeze roller is placed in the furnace with 700℃ to preheat treatment. The temperature is 300℃, rate of temperature increase is 5℃/min, and soaking time is 4 hours.
(2) After the roller is discharged it should be overlain immediately by submerged arc welding.
(3) Welding parameters: welding current 600A～650A , arc voltage 32V～34V , welding speed 18mm/min～22mm/min .
(4)During the welding, the temperature of the roller should not be lower than 250℃. Thermo detector is used to supervise the temperature of roller in welding. The welding should stop immediately once the temperature is lower than 250℃.When it occurs the roller should be placed to the furnace and heated to 300℃ again . Then the roller can be discharged and the welding operation starts again. The thickness of the weld bead should be strictly controlled. The lowest point of weld bead should meet the thickness requirements of drawing design.
(5) For the end face of squeeze roller, There are little overlaying work .The welding parameters are as follows:400A～welding current 450A and arc voltage 34V～40 V. The welding speed can be adjusted according to the thickness of overlaying layer.
(6) When the temperature of squeeze roller is not lower than 200℃, the roller should be placed into furnace to eliminate welding stress. The parameter is shown as bellow: rate of temperature increase is 50℃/h. After the temperature is increased to 550℃, it should be kept for 5 hours. Followed by the soaking process, the roller is taken out of the furnace and cool down to 80℃. The cooling rate is 50℃/h.
(7) To ensure the stability of the roller’s hardfacing layer microstructure and performance, the roller should be processed by lathe work after it’s been taken out from the furnace and cooled to room temperature. The weld bead of the transition layer should be lathed until the size and roughness of roller should meet the requirements of the drawing.
(8) After that the roller should be placed into heat treatment furnace to preheat. The temperature of furnace is 300℃. The rate of temperature increase is 50℃/h and soaking time is 4 hours.
(9) Overlaying for hardfacing layer of roller: welding current 600～680A, arc voltage 32～34V. The welding speed is adjusted appropriately according to the required thickness. Other requirements are the same with the buffer layer.
(10) After welding, the roller should be wrapped with aluminum silicate heat insulation blanket to cool slowly to room temperature, and hardness is no less than HRC55. |
