Method for enhancing the casting performance of a nodular iron core centrifugal roll neck
By incorporating ferrochrome powder into the coating on the sand box surface during the centrifugal roll casting process, the problem of precise control of alloying elements in the centrifugal roll neck was solved, thereby improving hardness and toughness and reducing costs and operational difficulty.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SINOSTEEL XINGTAI MACHINERY & MILL ROLL
- Filing Date
- 2023-11-10
- Publication Date
- 2026-06-30
AI Technical Summary
Existing technologies make it difficult to precisely control the addition and diffusion depth of alloying elements at the neck of centrifugal rolls, resulting in insufficient hardness or the need to pour additional high-alloy risers, which increases costs and affects processing efficiency.
During the casting process, ferrochrome powder is mixed into the coating on the sand box surface as a reinforcing agent to control the element content and diffusion depth of the alloy layer on the roll neck surface. Specific methods include determining the target mass fraction of Cr and the depth of the hardened layer, and ensuring that the hardened layer is retained after the finished product through mold size control. The ferrochrome powder grade is FeCr55C600 or FeCr55C1000, with a mesh size of 100-800, and it is applied to the contact surface between the sand box and the roll surface.
Precise control of the alloy layer elements on the roll neck surface was achieved, which improved hardness and maintained central toughness, reduced the difficulty of operation and the amount of alloy added, and improved processing efficiency and surface quality.
Abstract
Description
Technical Field
[0001] This invention relates to the field of roll casting, and in particular to a method for enhancing the casting performance of roll necks. Background Technology
[0002] The neck of a centrifugal roll is subjected to bending or torsional forces during use, and must ensure good strength and toughness. At the same time, the neck is assembled in the bearing housing and rotates relative to the cylinder during use. There is a risk of frictional contact when lubrication is poor, and the main shaft neck needs to have a certain surface hardness.
[0003] Centrifugal roll cores and necks are typically made of ductile iron. Core filling is usually done vertically. During the core filling process, the outer layer of the core is melted and mixed with alloying elements, which strengthens the roll. However, these alloying elements form carbide deposits and settle downwards before solidification due to gravity. Therefore, the neck (the upper part of the roll during casting) is less likely to benefit from the strengthening effect of the melted alloy. Generally, a high-alloy riser needs to be cast separately, or surface treatment is required near the finished product stage. The former increases the additional smelting and casting process and costs, while also affecting the neck's toughness. The latter reduces processing efficiency and, because the strengthening layer is shallow, requires near-finished product treatment, which can easily lead to surface quality problems. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to provide a method for enhancing the casting performance of the neck of a centrifugal roll with ductile iron core. During the molding process of the neck, reinforcing elements are added to the coating that comes into contact with molten iron, so as to achieve precise control of the surface composition of the neck after core filling and enhance the strengthening effect.
[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:
[0006] A method for enhancing the casting performance of centrifugal roll necks with ductile iron cores involves first determining the target mass fraction of Cr based on the hardness requirements of the hardened layer of the roll neck, then controlling the molding dimensions to ensure that the hardened layer is retained after processing into the finished product, and mixing ferrochrome powder into the coating on the sand box surface as a reinforcing agent.
[0007] A further improvement of the technical solution of the present invention is that: when the roll neck requires 30-35HS, the target mass fraction of Cr on the surface is 0.2%-0.4%; when the roll neck requires 35-40HS, the target mass fraction of Cr on the surface is 0.4%-0.5%; and when the roll neck requires 40-45HS, the target mass fraction of Cr on the surface is 0.5%-0.6%.
[0008] A further improvement to the technical solution of the present invention is that the depth of the hardened layer after the roll is cast is 20-25mm.
[0009] A further improvement of the technical solution of the present invention is that: the reinforcing agent uses ferrochrome powder of grade FeCr55C600 or FeCr55C1000. After the ferrochrome is crushed, the residue is screened and the mesh size is consistent with the surface coating of the molding sand box, which is 100-800 mesh. The ferrochrome powder is mixed into the surface coating of the sand box and brushed onto the contact surface between the sand box and the roller before use after molding.
[0010] A further improvement to the technical solution of this invention is that the amount of ferrochrome powder added is calculated based on the required mass fraction of Cr and the weight of the molten iron in the hardened layer: ① Required mass fraction of Cr = Target mass fraction of Cr - Mass fraction of Cr in the core, ② Weight of molten iron in the hardened layer = Surface area of the reinforced part of the roll neck Enhanced depth ③ The Cr yield of the ferrochrome powder is 45%-55%; ④ The amount of ferrochrome powder added = (the mass fraction of Cr to be added × the weight of the molten iron in the hardened layer) / (the mass fraction of Cr in the ferrochrome powder × the Cr yield).
[0011] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows:
[0012] This invention relates to a method for enhancing the performance of the roll neck during the casting process of centrifugal rolls. It aims to precisely control the content of alloying elements and their diffusion depth on the roll neck surface, thereby achieving precise control over the hardened layer depth and hardening effect. Compared to other strengthening methods, this method is easier to operate, reduces costs, and improves efficiency. This method is applicable to the alloy strengthening of the surface layer of the roll neck in centrifugal rolls. Through reinforced composition design, reinforcing elements are added to the coating in contact with molten iron during the roll neck molding process. After core filling and casting, the alloying elements melt and expand to the roll neck surface, providing a hardening effect.
[0013] The centrifugal rolls cast using the method of this invention can achieve the expected surface strengthening depth and hardness of the roll neck, while not compromising the core toughness. This solves the problem of insufficient hardness in the neck casting of traditional casting methods, which requires special strengthening in the later stages of processing. At the same time, compared with the additional pouring of molten iron into the neck, it reduces the difficulty of operation, saves the total amount of alloy added to the core, and maintains the core toughness. Detailed Implementation
[0014] The present invention will be further described in detail below with reference to embodiments:
[0015] A method for enhancing the casting performance of centrifugal roll necks with ductile iron cores involves first determining the target Cr mass fraction based on the hardness requirements of the hardened layer of the roll neck. Then, by controlling the molding dimensions and ensuring the hardened layer is retained after machining, ferrochrome powder is mixed into the surface coating of the sand box as a reinforcing agent. The specific steps are as follows:
[0016] The target composition is designed based on the hardness requirements of the hardened layer of the roll neck. Generally, when the roll neck requires 30-35HS, the target surface Cr mass fraction is 0.2%-0.4% (the core composition can usually directly reach this level without additional reinforcement); when the roll neck requires 35-40HS, the target surface Cr mass fraction is 0.4%-0.5%; and when the roll neck requires 40-45HS, the target surface Cr mass fraction is 0.5%-0.6%.
[0017] By controlling the dimensions of the molded parts, the hardened layer is ensured to remain after machining to the finished product. Using this method, the hardened layer depth after roll casting is 20-25mm. Therefore, the machining allowance for the areas requiring reinforcement should be at least 2-3mm less than the hardened layer depth to ensure uniform hardening.
[0018] The reinforcing agent uses ferrochrome powder, with the grade FeCr55C600 or FeCr55C1000. The mass fraction of C and Cr is C: 6%-10% and Cr: 52%-60%. In addition, P≤0.06% and S≤0.06%, and the other components are Fe or impurities. After the ferrochrome is crushed, the residue is sieved to a mesh size consistent with the surface coating of the molding sand box, which is 100-800 mesh. The ferrochrome powder is mixed into the surface coating of the sand box and brushed onto the contact surface between the sand box and the roller before use after molding.
[0019] The amount of ferrochrome powder to be added is calculated based on the required Cr mass fraction and the weight of the molten iron in the hardened layer: ① Required Cr mass fraction = Target Cr mass fraction - Core Cr mass fraction. The Cr mass fraction in the core composition is designed according to the requirements of the bottom neck (lower roll neck). The lower roll neck can generally obtain a certain alloy by eroding the outer layer. If the target composition is A and the furnace front composition is B, estimate the alloy increment C obtained by eroding the outer layer, then B = AC; C = weight of eroded outer layer. Outer layer alloy content / total weight after melting. ② Weight of molten iron in the hardened layer = surface area of the reinforced part of the roll neck. Enhanced depth ③ The Cr yield of ferrochrome powder is 45%-55%, which can be adjusted appropriately according to actual production conditions; ④ The amount of ferrochrome powder added = (the mass fraction of Cr to be added × the weight of the molten iron in the hardened layer) / (the mass fraction of Cr in the ferrochrome powder × the Cr yield).
[0020] In actual production, due to slight differences in core casting temperature and solidification time, rolls with higher casting temperature, larger specifications, and longer solidification time have a higher Cr iron powder recovery rate and a deeper hardened layer. Appropriate adjustments need to be made based on the production and testing results of the first roll.
[0021] Example 1:
[0022] A centrifugal work roll for hot continuous rolling finishing has a neck spindle diameter of 700mm and a neck length of 950mm, with a required neck spindle hardness of 35-40HSD. Based on these dimensions, the inner wall dimensions of the neck molding section are selected as a diameter of 730mm and a length of 980mm. According to its outer layer composition and corrosion resistance, the designed Cr% composition of the core molten iron before the furnace is 0.2%-0.25%, and the designed surface Cr% after strengthening is 0.4%-0.5%. It is calculated that 1.76Kg of chromium powder (containing 52% Cr) needs to be added to strengthen the neck. 1.76Kg of the chromium powder meeting the composition is sieved and mixed with cavity coating in the same proportion, then evenly brushed onto the inner surface of the neck cavity and allowed to dry for 24 hours before use. The centrifugal and core-filling production processes remain unchanged. After demolding, the surface Cr of the blank neck (0-950mm) is tested and found to be 0.44%, meeting the expectations. When the final spindle is machined to a diameter of 700mm, the hardness is tested at 36-38HS, meeting the expectations.
[0023] Example 2:
[0024] A centrifugal work roll for hot continuous rolling finishing has a neck spindle diameter of 420mm and a neck length of 1000mm, with a required neck spindle hardness of 40-45HSD. Based on these dimensions, the inner wall dimensions of the neck molding section are selected as a diameter of 450mm and a length of 1030mm. According to its outer layer composition and corrosion resistance, the core molten iron composition before the furnace is designed to have a Cr% of 0.3%-0.35%, and the surface Cr% after strengthening is designed to reach 0.5%-0.6%. It is calculated that 1.13Kg of chromium powder (containing 52% Cr) needs to be added to strengthen the neck. 1.13Kg of the chromium powder meeting the composition is sieved and mixed with cavity coating in the same proportion, then evenly brushed onto the inner surface of the neck cavity and allowed to dry for 24 hours before use. The centrifugal and core-filling production processes remain unchanged. After demolding, the surface Cr of the 1000mm diameter of the blank neck is tested and found to be 0.53%, meeting the expected result. When the final spindle is machined to a diameter of 420mm, the hardness is tested at 41-44HS, also meeting the expected result.
[0025] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A method for enhancing the casting performance of the neck of a centrifugal roll with a ductile iron core, characterized in that... First, determine the target mass fraction of Cr based on the hardness requirements of the hardened layer of the roll neck. Then, control the molding dimensions and ensure that the hardened layer can still be retained after processing into the finished product. Mix chromium iron powder into the coating on the sand box surface as a reinforcing agent. When the roll neck requirement is 30-35HS, the target surface Cr mass fraction is 0.2%-0.4%; when the roll neck requirement is 35-40HS, the target surface Cr mass fraction is 0.4%-0.5%; when the roll neck requirement is 40-45HS, the target surface Cr mass fraction is 0.5%-0.6%. The depth of the hardened layer after the roll is 20-25mm; The reinforcing agent uses ferrochrome powder with the grade FeCr55C600 or FeCr55C1000. After the ferrochrome is crushed, the residue is screened and the mesh size is the same as that of the surface coating of the molding sand box, which is 100-800 mesh. The ferrochrome powder is mixed into the surface coating of the sand box and brushed onto the contact surface between the sand box and the roller before use after molding. The amount of ferrochrome powder to be added is calculated based on the required Cr mass fraction and the weight of the molten iron in the hardened layer: ① Required Cr mass fraction = Target Cr mass fraction - Core Cr mass fraction; ② Weight of the molten iron in the hardened layer = Surface area of the reinforced part of the roll neck Enhanced depth ③ The Cr yield of the ferrochrome powder is 45%-55%; ④ The amount of ferrochrome powder added = (the mass fraction of Cr to be added × the weight of the molten iron in the hardened layer) / (the mass fraction of Cr in the ferrochrome powder × the Cr yield).