FI123316B - Heat transfer roller and manufacturing method for a heat transfer roller - Google Patents

Abstract

The roll (1) has an inner wall (2) for receiving a load. An outer casing part (4) comprises a surface for treatment of a fiber web. The outer casing part rests against the inner wall to form a longitudinal flow channel (5) for a heat transfer medium, at a boundary surface between the inner wall and the outer casing part. The outer casing part comprises curable steel, which is cured and annealed at temperature of about 300-350 degree Celsius, so that the hardness of the outer casing part is 450 HV. The outer casing part is made of forged steel tube or heat treatable steel. An independent claim is also included for a method for manufacturing a heat transfer roll.

Description

HEAT TRANSFER ROLL AND HEAT TRANSFER MANUFACTURING TECHNIQUES

The present invention relates to a heat transfer roll, such as a thermal roll or cylinder, which can be used in fiber web machines to process a web-like web of fibrous material, such as pressing, drying or calendering paper or board. The invention further relates to the manufacture of a heat transfer roll. More particularly, the invention relates to, but not limited to, a double-rolled thermal roller in which the outer shell 10 is rigidly secured around an inner axis forming the roll body.

BACKGROUND OF THE INVENTION

15 In paper, board, and pulp machines, web-like material can be heated, dried, calendered, wet pressed and / or cooled by heat transfer rollers. Particularly in calendering applications, the heating power required by the web is produced by more efficient thermo rolls using high temperature (nearly 300 ° C) heat transfer oil as the heat transfer medium.

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In order to achieve the required heating and drying effect, the surface temperatures of the thermal rolls need to be raised to 200-250 ° C or even more in demanding process applications. As known, the heat output from the roll depends on the nature of the heat transfer contact between the heated web and the roll and the material being heated, such as the length of the contact, the basis weight of the web and the moisture.

o High travel speed combined with long contact delay, wet web and for a high surface temperature of the thermal roller means that the heat output from the thermal roller must be very high, o

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As is known in the art, the heat of a thermal roll is produced by passing a fluid or gas acting as a heat transfer medium into the flow channels within the thermal roll, and in particular the 2 boreholes in the jacket that transfer the heat to the jacket.

Utility Model Publication FI U8407 discloses a heat transfer roller comprising 5 cylindrical inner shafts, a metallic outer layer surrounding the inner shaft and heat transfer fluid flow channels, for example flow grooves. The roll is made by assembling the inner shaft and outer layer together. The flow channels of the roll consist of flow grooves formed before the assembly of the inner shaft and outer layer, which are formed on the outer surface of the inner shaft and / or on the inner surface of the outer layer 10.

One known surface structure of a heat transfer roller is a hard coating formed by welding to achieve surface hardness. Welding is laborious and requires special equipment. In addition, welding poses a quality risk because the change zone formed in the welding process weakens the material. The welded material may remain damaged, for example from the cavity and inclusions. The cavities exposed on the surface of the roll form visible cavities during machining. Welded structures must be inspected for non-destructive methods with particular care for welding defects.

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Also, surface hardening of the surface of the heat transfer roller can achieve high hardnesses. The surface annealing can cause an unfavorable (uneven) stress distribution in the roll casing in terms of cm stress on the roll.

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However, by welding and surface hardening to the roll surface, only a hard layer of limited thickness can be economically achieved, for example 2-8 | mm. Welding and surface hardening form an additional work step in the manufacturing process, which σ> increases the manufacturing cost and time. When the surface of the heat transfer roller

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cd is removed during maintenance, the roll has to be re-coated after a thin hard layer has been worn off.

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SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a heat transfer roll 5 comprising an inner shaft for carrying a load, an outer jacket portion comprising an outer surface for handling the fibrous web, and an outer jacket member secured 300-350 ° C so that the outer shell portion has a hardness of 10 throughout at least 450 HV.

Preferably, the outer sheath portion is released at an outlet temperature higher than the highest operating temperature of the heat transfer medium during use of the heat transfer roll.

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Preferably, the outer jacket member is made of hardening machine-building steel.

Preferably, the outer sheath portion is made of annealing steel.

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Preferably, the outer shell portion is made of forged or otherwise made seamless steel tube.

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Preferably, the heat transfer roller comprises heat transfer fluid flow passages at the interface between the inner shaft and the outer jacket portion.

m o | Preferably, the inner shaft is made of a material substantially more tough than the outer shell portion, such as ferritic cast iron or structural steel.

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Preferably, the inner shaft is made of an economically advantageous material such as cast iron.

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Preferably, the heat transfer roll is a thermal roll for the calender.

In another aspect of the invention, there is provided a method of manufacturing a heat transfer roll 5 comprising an inner shaft for carrying a load, an outer jacket portion comprising an outer surface for handling a fibrous web, and an outer jacket portion secured against 10, the outer jacket member is discharged at a temperature of 300 to 350 ° C so that the outer jacket member has a hardness throughout of at least 450 HV.

Preferably, the outer sheath portion is heat shrunk over the inner shaft.

Preferably, the release temperature of the outer shell portion is selected based on the hardness target of the outer shell portion while maintaining good material strength properties.

Preferably, the outlet temperature of the outer jacket portion is selected to be higher than the highest operating temperature of the heat transfer medium during operation of the heat transfer roller.

Preferably, in addition to the release temperature, the release time is selected such that the hardness of the outer cm of the shell portion is at least 450 HV.

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Preferably, the inner shaft is made of a material that is substantially tougher than the outer shell portion of the i 0.

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o) When the outer sheath layer is hard throughout its thickness, a heat transfer roller may be provided

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co increase service life compared to prior art. With roll maintenance o 30, more material than known can be removed before the outer sheath layer of the heat transfer roller needs to be replaced. The outer sheath layer can be renewed by removing the worn outer sheath layer and a new outer sheath layer can be installed over the original inner shaft. The original worn outer sheath layer can be removed, for example, by dividing the outer sheath layer into two parts along the length of the heat transfer roll.

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The residual stresses of the outer jacket layer can be kept low and the residual stress peaks of the prior art can be avoided.

Various embodiments of the present invention will be described or described only in connection with some or some aspects of the invention. One skilled in the art will appreciate that any embodiment of an aspect of the invention may be applied to the same and other aspects of the invention, alone or in combination with other embodiments.

The invention will now be described with reference to the accompanying diagrammatic figures, without, however, limiting the invention to those shown in the figures.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 is a longitudinal cross-sectional view of a heat transfer roll according to an embodiment of the invention.

Fig. 2 is a perspective view of the heat transfer roller of Fig. 1 without dj shaft ends.

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DESCRIPTION OF THE PREFERRED EMBODIMENTS

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σ> In the following description, like references are meant

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co similar parts. It should be noted that the figures shown are not to scale in their entirety, and that they serve primarily the purpose of illustrating embodiments of the invention.

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Figures 1 and 2 show a heat transfer and / or cool heat transfer roll 1 provided with a thin steel outer jacket member 4 and an inner inner shaft 2 of the outer jacket member having flow grooves 5 for forming flow channels for the heat transfer medium.

The heat transfer roller 1 comprises shaft ends 3 attached to the ends of the inner shaft 2 and the inner shaft 2 for carrying the load. The heat transfer roller 1 is designed as a double jacket structure, the inner shaft 2 forming an inner jacket part (e.g. The outer jacket member 4 is secured to the inner jacket member 2 by, for example, heat-shrinking or molding, or other connection method such as end-welding. Longitudinal channels 5 are formed in the inner jacket portion 2 as flow paths of the heat transfer medium 15 to the outer surface 2a of the inner jacket member.

The outer sheath portion 4 comprises an outer surface for treating the fibrous web. In heating roller applications, heat is transferred from the heat transfer medium through the outer sheath portion 4 to the fibrous web, in cooling roller applications, heat is transferred from the fiber web W through the outer sheath portion 4 to the heat transfer medium. The heat transfer medium is preferably an oil used at hot temperatures. The heat transfer medium may also be water or steam or other liquid.

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dj When the outer jacket member 4 is secured to the inner jacket member 2, flow channels are formed between longitudinal channels 5 0 on the outer surface of the inner jacket member for the heat transfer medium.

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σ> The heat transfer roller 1 can be used as a thermal roller for different types of calenders

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cd for example in the super calender, multi roll calender and soft calender.

In the calender, the fibrous web can be pressed and heated in a nip between the thermo roll and a contact member in contact therewith, which can be a 7 coated or uncoated roll or belt, especially a metal belt, or dry the fibrous web on the surface of the thermo roll. The heat transfer roller 1 can also be used on the drying section as a hot drying cylinder, against the surface of which the fiber web is dried.

5 The outer sheath portion 4 of the heat transfer roller 1 is formed of hardening steel, which can achieve a hardness of 450 HV at an emission temperature of 300 to 350 ° C. In this case, no separate surface hardening is required and the entire material thickness becomes hard.

Preferably, the outer sheath portion is formed of forging steel. Blanks made of forged steel are commercially available. The forged steel tube is preferably seamless. Forging steel can be commonly used tempering machined steel with good availability. 42CrMo4 and 36CrNiMo6 are examples of such steels. For example, such annealed machine building steel 15 can achieve a uniform microstructure.

When the outer jacket portion is made of annealing steel, the normal annealing emission at high temperature will not be made, leaving the hardness at a lower level (for example, about 300 HV), but the final discharge at 20 low temperatures, which can then exceed 500 HV.

The outer sheath portion is quenched to the desired hardness and released at low cm temperature. The material of the outer jacket portion is preferably discharged at a temperature higher than the maximum operating temperature of the heat transfer medium flowing in the heat transfer roller 1, preferably 300-350 ° C. The material of the outer jacket portion o is released at such a low temperature that the quenching achieved hardness will not fall below 450 hp. In some cases, the material is discharged at a temperature such that a hardness of 450 to 500 HV or

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cd more. The temperature and the release time are preferably selected so as to avoid g? 30 brittleness.

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During tempering of the outer jacket portion 4 and subsequent release treatment, the impact toughness of the material can be compromised. The inner shaft 2 of the heat transfer roller 1 is formed of a material which is substantially tougher than the outer shell part, for example ferritic cast iron or structural steel, which is cheap and easy to machine. Despite the impingement on the outer sheath portion, the outer sheath portion of the heat transfer roller 1 can be fabricated with an impact shear strength greater than 10 times that of the surface layers of the molding rolls currently in use.

The outer mantle portion is formed throughout the thickness of 10 through hardening and subsequent discharge. Thus, the outer jacket layer can be machined (e.g., maintenance grinding) deeper than known hard surface layers of heat transfer rollers without losing surface hardness properties. This increases the service life of the heat transfer roller and allows the heat transfer roller to be repaired for longer at a paper mill maintenance workshop, for example, before the heat transfer roller has to be transported to a roll manufacturer for replacement of the outer sheath.

It is previously known to use hardening steel which can achieve a hardness of 450 HV because it is thought that high hardness will also lead to a brittle structure. Typically, neither the product range, nor the product program, of commercial forged steel manufacturers, 20 or the product program, provides such hardness values for large tubular pieces. Typically, forged steel tube suppliers' manufacturing program provides hardness values for materials that have been achieved at significantly higher release temperatures than 300 ° C, whereby hardness remains relatively low.

Examples of some embodiments of the invention are given above. Alan | however, it will be clear to one skilled in the art that the invention is not limited to the particulars σ> shown, but that the invention may also be implemented in other equivalent ways.

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Some features of the embodiments shown may be utilized without the use of other features. The foregoing description is to be construed as merely describing the principles of the invention and not limiting the invention. Thus, the scope of the invention is limited only by the appended claims.

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Claims (13)

A heat transfer roller (1) comprising an inner shaft (2) for carrying a load, an outer sheath portion (4) comprising an outer surface for handling the fibrous web 5 and an outer sheath portion secured against the inner shaft to form a flow space (5) for the heat transfer medium. (4) is made of a hardening steel hardened and released at a temperature of 300 ° C to 350 ° C such that the outer shell portion has a hardness of at least 450 HP throughout. Heat transfer roller according to Claim 1, characterized in that the outer sheath portion (4) is released at an outlet temperature higher than the highest operating temperature of the heat transfer medium during use of the heat transfer roller (1). 15 Heat transfer roller according to claim 1 or 2, characterized in that the outer jacket part (4) is made of forged steel tube. Heat transfer roller according to one of Claims 1 to 3, characterized in that the outer jacket part (4) is made of tempering steel. Heat transfer roller according to one of claims 1 to 4, characterized in that the cm heat transfer roller (1) comprises heat transfer fluid flow channels (5) at the interface of the inner axis ° (2) and the outer sheath part (4). S 25 i Heat transfer roll according to one of Claims 1 to 5, characterized in that | the inner shaft (2) is made of a material which is substantially tougher than the outer shell part (4), such as ferritic cast iron or structural steel. CM o CD o 30 7. Heat transfer roll according to one of Claims 1 to 6, characterized in that the heat transfer roll (1) is a thermal roll for the calender. A method of manufacturing a heat transfer roller (1) comprising a inner shaft (2) for carrying a load, an outer jacket member (4) comprising an outer surface for handling a fibrous web, and an outer jacket member secured against the inner shaft to form a flow making the outer jacket member (4) of hardening steel, quenching the outer jacket member and releasing the outer jacket member at a temperature of 300 to 350 ° C so that the outer jacket member has a hardness of at least 450 HP throughout. 10 Method according to claim 8, characterized in that the outer sheath portion (4) is heat shrunk over the inner shaft (2). Method according to claim 8 or 9, characterized in that the release temperature of the outer shell portion (4) is selected based on the hardness target of the outer shell portion while maintaining the good strength properties of the material. A method according to any one of claims 8 to 10, characterized in that the outlet temperature of the outer jacket portion (4) is selected to be higher than the highest operating temperature of the heat transfer medium 20 during operation of the heat transfer roller (1). cm 12. A method according to any one of claims 8 to 11, characterized in that, in addition to the release temperature, the release time is chosen so that the hardness of the outer jacket portion 10 is at least 450 HV. i m o | Method according to one of Claims 8 to 12, characterized in that the inner shaft (2) is made of a material which is substantially tougher than the outer cd shell part (4). δ CM