Multi-layered roller with high corrosion resistance

Abstract

The present invention relates to a multi-layered roller structure which includes an intermediate layer for that the inner layer adapts to the high chromium containing composition of the outer layer for high corrosion resistance, and rolls material compositions thereof.

Description

[0001] MULTI-LAYERED ROLLER WITH HIGH CORROSION RESISTANCE Technical Field

[0002] The present invention relates to a new roller structure and alloy that allow rolls obtained by centrifugal casting to be produced with high corrosion and high abrasion resistance.

[0003] More specifically, the present invention relates to a multi-layered roller structure which includes an intermediate layer for that the inner layer adapts to the high chromium containing composition of the outer layer for high corrosion resistance, and rolls material compositions thereof.

[0004] Prior Art

[0005] Centrifugal casting called as spin casting has many advantages including homogeneous hardness and thickness, long life, less abrasion and less service cost compared to static casting. Rolling mills perform the function of the rollers which are significant elements at the important production facilities in the field of food such as pellet feed, oil, chocolate, coffee, in very different working environments compared to the sector. The corrosion they are exposed due to the need of the environment in the sector they are used, shortens greatly the life of the conventional rollers compared to the normal working conditions. Therefore, the rollers produced by the existing techniques cannot be used in the high corrosive environment.

[0006] Due to the apprehension about production costs, iron-based alloys are preferred in the rollers produced todays. The use of high alloyed white cast irons becomes crucial especially in the production of hard surfaces requiring high abrasion resistance.

[0007] The chromium element provides a high corrosion resistance and abrasion resistance to the roller made of alloy where it is included in. Thus, high rate of chromium should be preferred for alloying the roller. The microstructure of these materials is mainly perlite-cementite, and it contains significant amount of M7C3 type chromium carbide. These types of carbides are found within the eutectic structures.

[0008] The currently produced rollers consist of two layers. They comprises an outer layer which has the above-mentioned abrasion and corrosion resistance and is formed in a vertical or horizontal centrifugal mold. After said outer layer is formed, there is an inner layer that allows a shaft to be driven in it by filling the space within the outer layer. Therefore, in the current technique, a roller consists of two layers with different physical expectations as being an inner layer and an outer layer. However, the presence of high amount of Chromium within the outer layer alloy for higher corrosion resistance of a roller produced in this structure, prevents its usage with the prior inner layer alloys. In the other words, when it is desired to increase the corrosion resistance more, the outer and inner layer alloys used in the production of current roller show incompatibility and, significant deformations and cracks occur after production and they cause the roller to become unusable in a short time.

[0009] In the patent document EP0560210B1 , a roller composition and a production method thereof are mentioned. In the solution, a shell (outer) part with a high level of abrasion and surface hardness resistance, a hard core (inner) part, the composition of them and a method for producing them are described. However, an intermediate layer that allows a possible outer layer with high Chromium ratio required for high corrosion resistance to be combined with an inner layer and, a multi-layered roller consisting of them are not mentioned.

[0010] In the patent document EP0852162B1 , steel roller production at high quality and speed is mentioned without carbide segregation even in centrifugal casting and high abrasion resistance. In the solution described here, it is stated that the outer layer contains: 2.4 - 2.9% C, at most 1% Si, at most 1% Mn, 12 - 18% Cr, 3 - 9% Mo, 3 - 8% V and 0.5 - 4% Nb. However, the high corrosion resistance and, to achieve this, a multiple layer structure consisting of outer layer, intermediate layer and inner layer are not mentioned.

[0011] In the patent document EP2770073B1, a roller surface material produced by centrifugal casting is mentioned. In the centrifugal casting, the roller surface material consists of the following elements and a composition in the specified proportions: 2.3 - 2.9% C, 0.2 - 0.8% Si, 0.2 - 1.0% Mn, 5.0 - 7.5% Cr, 4.4 - 6.5% Mo, 5.3 - 7.0% V, 0.6 - 1.5% Nb and 0.1 - 4.0% Co. It is claimed that the fatigue resistance of the surface layer is increased in this way.

[0012] In the patent document US2019352753A1, a composition regarding a roller which comprises an outer layer with excellent abrasion (wear, aging) resistance is suggested. In the centrifugal casting, the roller’s outer layer material consists of the following elements and a composition in the specified proportions by weight: 2.2 - 3.2% C, 10 - 3.0% Si, 0.3 - 2.0% Mn, 3.0 - 7.0% Ni, 0.5 - 2.5% Cr, 1.0 - 3.0% Mo, 2.5 - 5.0% V, 0 - 0.5% Nb and a remaining portion containing Fe and inevitable impurities.

[0013] As a result, the require for production of a roller that is durable as well as having high corrosion resistance and the insufficiencies in the current technique led this present innovative solution to emerge. Objectives and Short Description of the Invention

[0014] The aim of the invention is to present a multi-layered roller with high corrosion and high abrasion resistance.

[0015] Another aim of this invention is to present a three-layered roller increasing the corrosion resistance to the highest levels by containing a high rate of chromium (Cr) in the rollers produced by centrifugal casting method and hence, comprising an intermediate layer which provides a seamless combination of the inner layer with high carbon level at different technical properties with the outer layer without any cracking or physical deformation.

[0016] Another aim of this invention is to present a three-layered roller which comprises an outer layer containing 15 - 20% Cr and 0.5 - 1.5% C by weight, an inner layer containing 0 - 0.5% Cr and 2.5 - 3% C by weight and an intermediate layer containing 0 - 1% Cr and 0.5 - 1.5% C by weight between them.

[0017] Description of the Figures

[0018] In Figure 1 , a representative view showing layers of present innovative roller is given.

[0019] Reference Numbers

[0020] 10. Outer layer 20. Intermediate layer 30. inner layer

[0021] Detailed Description of the Invention

[0022] Present invention is a multi-layered roller (1) with high hardness levels and high corrosion resistance by means of the centrifugal casting method.

[0023] Basically, rollers (1) comprise an outer layer (10) obtained by centrifugal casting process at the desired hardness values in accordance with the field of usage, and an inner layer (30) which is obtained from a different alloy and in which ultimately the shaft is driven in. However, when it is desired that the desired hardness values of roller (1) are higher than expected as well as having high corrosion resistance, a significant incompatibility problem between the outer layer alloy and inner layer is emerged, and a result of this, cracks and deformations occur in the rollers produced with traditional approaches. This present invention comprises an intermediate layer (20) between the outer layer (10) and the inner layer (30) to solve this technical problem.

[0024] In the present invention, the hardness values desired from the outer layer (10) of the roller (1) are between 500 - 550 HB. important researches have been carried out in order to reach this hardness value without any problem and to present a roller (1) with high corrosion resistance values and thus to reveal the present invention.

[0025] For example, high alloyed white cast irons are preferred in the production of these hard surfaces that are expected to have high abrasion resistance. Since the chromium element gives to the structure a high corrosion resistance and a high abrasion resistance, the chromium ratio has been kept high in the outer layer (10) of the present invention. However, keeping the chromium ratio too high (for example 25%) causes incompatibility with the inner layer and cracks during firing process for driving the shaft in. A high carbon ratio in addition to the high chromium ratio can cause cracks in the outer layer (10) of the roller (1). Therefore, an optimization is required between the chromium and carbon ratios in the compositions that will be used in the production of the outer layer (10). Besides, for the outer layer (10) to reach the desired hardness values, it must be subjected to heat treatment process after casting. During a destabilization heat treatment, austenite in the matrix turns into martensite. However, in this case, the accumulated energy in the roller (1) can become even more dangerous and finally the roller (1) may crack along the outer surface during application of heat treatment process.

[0026] Unlike the prior art rollers (1), the outer layer (10) composition required by a more special roller (1) with high hardness value, abrasion and corrosion resistance values, is not compatible with the conventionally produced inner layer (30) compositions. In research, GG25 lamellar graphite cast iron, and in another research, the spherical graphite cast iron in the GGG40 alloy were use as the inner layer, however the compatibility with the outer layer was not achieved in both cases.

[0027] Besides, the high tension and low toughness of cast iron emerge as a continuous problem in our researches. Rough carbide structure of the white iron and residual stresses are the main reasons for this change. At this point, the steel system which stands out with higher toughness values has been preferred. Steel materials stand out with their high toughness and high corrosion resistance. However, their hardness is lower than the hardness values desired from the rollers. Martensitic stainless steel is a class that combines properties of hardenability and corrosion resistance. At this point, the focus has been on the martensitic stainless steels. However, this approach alone is not sufficient for the compatibility between the outer layer (10) and the inner layer (30). The outer layer (10) composition of the present innovative roller (1) achieves the targeted technical properties as a result of using the following elements at a certain intervals. Accordingly, the outer layer (10) composition contains by weight: 0,5 - 1,50% C, 0 - 1% Si, 0 - 1% Mn, 15 - 20% Cr, 0 - 1% Mo and 0 - 1% Ni. These rates can be expressed in a table as follows:

[0028] The roller obtained as a result of casting was taken for rough machining process before it is sent to heat treatment. After rough machining process was completed, the hardness value was taken from the roller. In a casting carried out under normal conditions, 270 HB hardness values can be obtained at maximum. The hardness values obtained by the centrifugal casting process used in the present invention vary between 360 - 400 HB. However, on the other hand, the hardness values expected from the roller (1) are between 500 - 550 HB. In order to achieve this, heat treatment, quenching and tempering processes were applied on the roller (1) and, the desired hardness values were reached in the present innovative roller (1).

[0029] The outer layer (10) obtained by the centrifugal casting process is a hard layer exposed to corrosion and abrasion, it can have an average thickness of 30 mm from the outer surface of the mold; if required to give a value in terms of sampling. In the two-layered structure in the previous applications, there is a soft layer from the outer layer (10) to the shaft driving gap, namely covering the majority of the casting. The transition zone between these two materials (outer layer (10) and inner layer (30)) is the point where these two metals are connected to each other. However, applications done with these two metals (bimetallic) were insufficient. In the present invention, the number of casting layers has been increased to solve this technical problem.

[0030] An outer layer (10), an inner layer (30) and an intermediate layer (20) in order to form the transition region between these two layers and to eliminate the incompatibility problem between them and consequently the cracking problems, are formed in a preferred embodiment of the present innovative roller (1).

[0031] The chemical composition of mentioned intermediate layer (20) contains by weight: 1 - 2% C, 0 - 1% Si, 0 - 1% Mn, 0 - 1% Cr, 1 - 3% Mo and 1 - 3% Ni. These rates can be expressed in a table as follows: The intermediate layer (20) has been formed with the specified inner layer (30) composition without the need for changing the outer layer (10) and inner layer (30) compositions described above and, the present innovative multi-layered roller (1) was obtained without any cracking in the final result achieved. After both rough machining, heat treatment stages and shaft driving process, the present innovative roller (1) could be produced at the expected hardness values and corrosion resistance without any problem.

[0032] Thus, a roller (1) which, comprising an outer layer (10) made of stainless steel and an inner layer (30) made of cast iron, has a high corrosion resistance and is produced by the centrifugal casting method, and comprises an outer layer (10) containing 15 - 20% Cr and 0.5 - 1.5% C by weight, an inner layer (30) containing 0 - 1% Cr and 2.5 - 3.5% C by weight and an intermediate layer (20) containing 0 - 1% Cr and 1 - 2% C by weight between them.

[0033] Besides, mentioned inner layer (30) contains the following chemical composition by weight: 2,5 - 3,5% C, 2 - 2,5% Si, 0 - 1% Mn, 0 - 1% Cr, 0 - 1% Mo and 0 - 1% Ni. These rates can be expressed in a table as follows:

Claims

CLAIMS1. A roller (1) which, comprising an outer layer (10) made of stainless steel and an inner layer (30) made of cast iron, has a high corrosion resistance and is produced by the centrifugal casting method, and characterized by; comprising an outer layer (10) containing 15 - 20% Cr and 0.5 - 1.5% C by weight, an inner layer (30) containing 0 - 0.5% Cr and 2.5 - 3.5% C by weight and an intermediate layer (20) containing 0 - 1% Cr and 1 - 2% C by weight between them.

2. A roller (1) according to claim 1 and characterized in that mentioned intermediate layer (20) contains 1 - 2% C, 0 - 1% Si, 0 - 1% Mn, 0 - 1% Cr, 1 - 3% Mo and 1 - 3% Ni by weight.

3. A roller (1) according to claim 1 and characterized in that mentioned outer layer (10) contains 0,5 - 1,50% C, 0 - 1% Si, 0 - 1% Mn, 15 - 20% Cr, 0 - 1% Mo and 0 - 1% Ni by weight.

4. A roller (1) according to claim 1 and characterized in that mentioned inner layer (30) contains2,5 - 3,5% C, 2 - 2,5% Si, 0 - 1% Mn, 0 - 1% Cr, 0 - 1% Mo and 0 - 1% Ni by weight.

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