EP0490664A1

EP0490664A1 - An aluminium alloy for heating rollers

Info

Publication number: EP0490664A1
Application number: EP91311539A
Authority: EP
Inventors: Tadashi Aiura; Kazuhiro Kaida; Osamu Takezoe; Masaya c/o Osaka Works of Nishi
Original assignee: Kobe Steel Ltd; Sumitomo Electric Industries Ltd
Current assignee: Kobe Steel Ltd; Sumitomo Electric Industries Ltd
Priority date: 1990-12-12
Filing date: 1991-12-11
Publication date: 1992-06-17
Also published as: JPH04210445A

Abstract

An alloy for heating rollers consisting essentially of, by weight, 0.4 to 0.6% of Fe, 0.15 to 0.6% of Cu, 0.6 to 1.5% of Mn, and 3.0 to 4.5% of Mg; and the Si content being restricted to less than 0.5% by weight; and aluminum and inevitable impurities for the remaining part. Preparing an alloy of this concentration, it is possible to provide an aluminum alloy which is excellent in strength, machinability, and formability, and where blackening process for improving the heat absorption efficiency can be completed by oxidizing the surface thereof at a high temperature.

Description

The present invention relates to an aluminum alloy for heating rollers, the alloy which is suitable for the material for heating rollers in a copying machine, printer and the like.
A heating roller for use in a fixing portion of a copying machine, printer or the like comprises an aluminum alloy pipe with its peripheral surface being coated with a resin paint, and is heated to a high temperature by a heater disposed therein.
As a material for heating rollers, there has been conventionally used JIS 5056 alloy which is excellent in heat resistance since a heating roller is required to have a high strength in high temperatures. Moreover, there have been disclosed alloys in Japanese Provisional Publication No.11640/1988, Japanese Provisional Publication No.11642/1988 and Japanese Provisional Publication No.179047/1988 in which the above mentioned alloys are improved in heat resistance or surface smoothness. Particularly the alloy disclosed in Japanese Provisional Publication No.11640/1988 is an aluminum alloy consisting essentially of, by weight, 1 to 8% of Ni, 0.05 to 3% of Mn, 0.05 to 0.5% of Zr and one or more element selected from a group consisting of 0.05 to 3% by weight of Fe, 0.05 to 1.5% by weight of Cu and 0.05 to 1.5% by weight of Mg. On the other hand, the alloy disclosed in Japanese Provisional Publication No.11642/1988 is an aluminum alloy consisting essentially of, by weight, 4 to 13% of Si, and one or more than one element selected from a group consisting of 0.05 to 3% by weight of Fe, 0.05 to 1.5% by weight of Cu, 0.05 to 3% by weight of Mn, 0.05 to 1.5% by weight of Mg, 0.05 to 0.5 % by weight of Zr and 0.05 to 0.5% by weight of Cr. The alloy disclosed in Japanese Provisional Publication No.179041/1988 is an aluminum alloy consisting essentially of, by weight, 0.5 to 13% of Si, and one or more element selected from a group consisting of 0.05 to 2% by weight of Fe, 0.05 to 7% by weight of Cu, 0.05 to 1.5% by weight of Mn, 0.05 to 7% by weight of Mg, 0.05 to 0.5% by weight of Zr, 0.05 to 1.0% by weight of Cr and 0.05 to 8% by weight of Zn.
In the case where a heating roller is formed with any of these alloys, the inner surface of the heating roller is made to be baked to form a black coat (hereinafter referred to blackening) for the purpose of increasing the heat absorption efficiency and thus shortening the warming-up time for the equipment. This inner black coat is formed by coating a paint on the inner surface of the aluminum pipe of about 250mm in length and thereafter baking the painted surface. Further it should be noted that the coat on the inner surface of the pipe made by the baking need to have heat resistance since the pipe is subjected to high temperatures in the following-step where a resin is coated on the outer peripheral surface of the pipe.
There is however a problem that the JIS 5056 alloy which has been used exhibits insufficiency in comprehensive characteristics for heating rollers such as strength, machinability and formability.
Moreover, the case where a black paint coating is to be formed on the inner surface of a pipe which is made of any of JIS 5056 alloy, or alloys disclosed in the above-noted Japanese Provisional Publications, gives rise to drawbacks that not only the material used for the heat resistance paint is expensive but also the painting work for the inner surface of the pipe is complicated and thus makes the cost become high. Moreover, there is a fear of the paint running and falling, thus bringing about a difficulty to manufacture products in high quality.
Hence, an aluminum alloy has been desired to develop where the black coat can be easily formed and machinability and formability are excellent.
We will describe
an aluminum alloy for heating rollers which is easy to effect the blackening for increase in heat absorption efficiency and which is excellent in strength, machinability and formability.
The aluminum alloy for heating rollers according to the present invention consists essentially of 0.4 to 0.6% by weight of Fe, 0.15 to 0.6% by weight of Cu, 0.6 to 1.5% by weight of Mn and 3.0 to 4.5% by weight of Mg, the content of Si being restricted to less than 0.5% by weight; and aluminum and inevitable impurities for the balance.
Since the aluminum alloy of the present invention contains predetermined amounts of Mg, Fe, Cu and Mn, it can be blackened by oxidizing its surface at a high temperature and is excellent in strength and workability. Consequently the aluminum alloy of the present invention is markedly useful for the material for the heating rollers of copying machines, printers and the like.
The inventors of the present invention made various studies and experiments in order to develop an aluminum alloy which is easy to effect the blackening for increase in heat absorption efficiency and which is excellent in strength, machinability and formability and is easy to manufacture. As a result of the research, it was found that an oxide film mainly consisting of Mg was black or gray, having an excellent heat absorption efficiency and could be formed easily by oxidizing an Mg containing-alloy at a high temperature. In other word, when a member made of Mg containing-aluminum alloy is heated at a predetermined temperature, it is blackened rapidly by forming on its surface an oxide film mainly containing Mg. Since this oxide film is formed by natural oxidation, no trouble such as paint running or painting unevenness is brought about. The present invention has been achieved based on the experimental result, and is intended to improve the aluminum based alloy in workability and blackening performance by adding to the alloy respective components of Mg, Cu, Mn and Fe in proper amounts.
Now, explanation will be made on the reasons for additions of individual components and the reasons for restrictions on respective compositions.

Mg

Mg is added to the aluminum alloy, because Mg is a main component of the black oxide film layer. That is, Mg added to the aluminum alloy is oxidized to form an oxide film containing Mg as a main component on the surface of the aluminum alloy. If the Mg content is less than 3.0% by weight, the black oxide film excellent in heat absorption efficiency can not be formed stably requiring a prolonged period of time for the blackening process and makes it impossible to provide a required strength for heating rollers. On the other hand when the Mg content exceeds 4.5% by weight, workability of the alloy is decreasing. As a result, the Mg content is to be specified to a range of from 3.0 to 4.5% by weight.

Fe

Fe is a component which improve, like the Mn component hereinafter, the machinability of the alloy. Fe also works for improving the drawing workability of the aluminum alloy. Moreover, the more is the Fe content, the more the blackening is promoted. When the Fe content is less than 0.4% by weight, these effect stated above are not achieved enough, particularly the blackening effect becomes unstable, to thereby require a prolonged period of time for the blackening process, thus inhibiting the efficiency for mass production. On the other hand, if the Fe content is more than 0.6% by weight, the alloy is lowered in corrosion resistance. As a result, the Fe content is to be specified to a range of from 0.4 to 0.6% by weight.

Cu

Cu is a component to improve the strength of the aluminum alloy. When the Cu content is less than 0.15% by weight, improvement in strength is not sufficiently achieved. On the other hand increase in the Cu content provides improvement in strength but entrails a deterioration of the extrusion performance of the alloy. Subsequently, when the Cu content exceeds 0.6% by weight, the alloy is low also in corrosion resistance. Accordingly, the Cu content is to be specified to a range of from 0.15 to 0.6% by weight.

Mn

Mn increases the strength of the aluminum alloy, improves together with Fe the etching performance by alkali aqueous solution, so that the heat absorption efficiency is improved. When Mn content is less than 0.6% by weight, the effects of Mn exhibits insufficiency. On the other hand, the Mn content is more than 1.5% by weight, large-crystallization arise resulting in a deterioration of cold formability. Consequently, the Mn content is to be specified to a range of from 0.6 to 1.5% by weight.

Zr

Zr, which plays a role to improve the strength of the aluminum alloy by fining the crystal grains of aluminum alloy, is added as required. In order to ensure the effect of improvement in strength, the Zr content is needed to be 0.05% by weight or more. On the other hand, the effect becomes saturated when the Zr content exceeds 0.2% by weight, so that the augmentation in the content of more than this is of no use. As a result, the Zr content is preferably 0.05 to 0.2% by weight.

Si

An excessive amount of Si in the alloy inhibits the blackening on its surface to be brought about by Mg, so that the content is necessarily restricted to less than 0.5% by weight.

Ti

Adding Ti to the aluminum alloy enables the crystal grains in the ingot to become fine, to thereby prevent the ingot from cracking when the alloy is cast. Hence, Ti may be added optionally to the alloy if necessary. In this case the additive of Ti is to be within a range of from 0.005 to 0.1% by weight.
The examples of the present invention will be described with reference to the comparative examples which deviate from the scope of the invention.
Billets each having a 200mm in diameter were cast by melting in the ordinary way the aluminum alloys having respective compositions shown in Table.1 below.
The aluminum alloys of the examples and the comparative examples were examined and evaluated in the following characteristics on the basis of the obtained billets.

1. Workability

Billets were subjected to the drawing, and drawing workability was examined based on each processing precision of the obtained article. In addition, the machinability was examined by observing the parting state of the chip forming while each billet was being machined.

2. Etching performance

The member can be improved in heat absorption efficiency by etching its surface to be roughened and matted. Hence, each aluminum alloy of the examples and the comparative example was examined in the etching performance by the method as follows.
Firstly, each of the billets was shaped into a pipe, and then was subjected to a 5-minutes immersion in a 10% by weight NaOH aqueous solution which was heated and kept at 50°C, so that the surface of the pipe was etched. After this process, the glossiness of each pipe surface was examined.

3. Heat absorptivity

The pipes were subjected to the blackening treatment. Specifically, each of the pipes was heated and kept at 550°C for 2 hours to be oxidized at a high temperature, so to form an oxide film on its surface. Then a heater was disposed inside the pipe, to heat the pipe from within. The period of time (warming-up time) for which the outer peripheral surface of the pipe reached 100°C, was measured.

4. Strength

A testing piece was cut out from each of the pipes which were blackened as described above, and was subjected to the tensile test (JISZ2241). The results examined on these characteristics are collectively shown in Table.2 below.
In this table, the workability are indicated according to the following bases: "excellent" is shown where a billet can be shaped with a good precision into a designated shape by drawing and where disposal of chips formed in machining is excellent; "good" is shown where a billet can be shaped with a good precision by drawing and where disposal of chips formed in machining is good; and "bad" is shown where a billet cannot be shaped with precision by drawing, or where disposal of chips formed in machining is bad.
In relation to the etching performance, "good" is allotted where the surface of the etched pipe is matted, and "bad" is shown where the surface of the etched pipe has a gloss.
In relation to the heat absorption efficiency, "excellent" is shown when the period of time for the outer peripheral surface of the pipe to reach 100°C is markedly short; "good" is shown when the period of time for the outer peripheral surface of the pipe to reach 100°C is short; and "bad" is shown when a long period of time is taken for heating the outer peripheral surface of the pipe to 100°C. For the case between the cases "good" and "bad", "little bad" is allotted.
For the strength, when the yield strength is 15kgf/mm² or more, "good" is allotted; and when the yield strength is less than 15kgf/mm², "bad" is shown.
Furthermore, based on these results, the applicability to the member for heating rollers were comprehensively evaluated. In the evaluation, "good" is shown when an alloy is markedly suitable for heating rollers; "bad" is shown when an alloy is less suitable for heating rollers; and "little bad" is allotted for there-between.
As is apparent from Table.2, all the aluminum alloys in the examples 1 to 3 of the present invention were good (excellent) in their strength and workability for drawing and machining, and could be readily roughened by the NaOH aqueous solution. Furthermore, each roughened surface of these examples could be easily oxidized at a high temperature to be blackened, and thus the blackened pipes had a short warmingup time, indicating excellent suitability for heating rollers.
In contrast, the aluminum alloys in the comparative examples 1 through 8 which deviate from the scope of the present invention were unsatisfactory in any of workability, etching performance, heat absorption efficiency or strength, to indicating unsuitability for heating rollers.

Claims

An aluminum alloy for heating rollers consisting essentially of 0.4 to 0.6% by weight of Fe, 0.15 to 0.6% by weight of Cu, 0.6 to 1.5% by weight of Mn, and 3.0 to 4.5% by weight of Mg; and the Si content being restricted to less than 0.5% by weight; and aluminum and inevitable impurities for the balance.
An aluminum alloy according to claim 1, containing 0.05 to 0.2% by weight of Zr
An aluminum alloy according to claim 1 or 2, containing 0.005 to 0.1% by weight of Ti.