【発明の詳細な説明】[Detailed description of the invention]
この発明は、焼結金属部材のメツキ方法に関
し、特に、３段階からなる前処理を施すことを特
徴とする、焼結金属部材のメツキ方法に関する。
一般に焼結金属は原料粉を加圧成形後に焼結す
るという工程によつて製造されるために、その組
織内には空孔が残留し、このような空孔を含む焼
結金属部材の表面に一般の溶融材と同様な方法で
メツキを施しても、その空孔を通してメツキ液が
表面から内部へ浸入してメツキが均一に付着でき
なくなると共に、生成したメツキ層は脆弱で、強
固な被膜とはならない。したがつて、空孔を含ま
ない一般の溶融材に施すような通常のメツキ方法
では、従来、焼結金属部材の表面に満足なメツキ
を設けることはできなかつた。
そこで本発明者は、焼結金属部材においても、
溶融材で得られるようなメツキ層と較べて遜色の
ないメツキ層を得べく鋭意研究を重ねた結果、焼
結金属部材に一連の水蒸気処理、酸洗処理および
予備メツキ処理からなる前処理を施すことによつ
て、その後の本メツキが順調に遂行され、それに
よつて焼結金属部材表面に強固なメツキ層を設け
ることができるという知見を得た。
この発明は、上記知見にもとづいてなされたも
のであつて、焼結金属部材にメツキを施す際に、
その前処理として、焼結金属部材に順次水蒸気処
理、酸洗処理および予備メツキ処理を施した後
に、本メツキ処理を施すことによつて、強固なメ
ツキ層を焼結金属部材表面に形成させることを特
徴とするものである。
例えば、鉄を含む焼結金属部材に水蒸気処理を
施すと、その表面に四三酸化鉄（Fe3O4）の被膜
が生じて表面の空孔は封じられ、メツキ液の浸入
は阻止されるけれども、その水蒸気処理を施した
部材に、そのまま本メツキ処理を施すと、四三酸
化鉄は電気の良導体でないために、メツキ膜形成
時に電気の流通が妨げられて電解反応が不活発に
なるという不都合を生じる。ところが本発明の前
処理によると、最初の水蒸気処理によつて生成し
た平均膜厚10μm程度の比較的厚い四三酸化鉄被
膜は、次の酸洗処理によつて一部溶解除去され、
平均膜厚0.5〜10μm程度の被膜となり、焼結金属
部材表面は通電性が回復して、電気反応に対して
活性化される。更に本発明の前処理ではその活性
化された四三酸化鉄被膜上に予備メツキを施し
て、予め強固な薄いメツキ層を形成させておくの
で、その後の本メツキにおいて、それを土台に強
固なメツキ層が形成される。
このように本発明の前処理においては、最初の
水蒸気処理によつて生成した酸化物被膜が焼結金
属部材を封孔し、次の酸洗処理で部材表面の酸化
物被膜の一部が除去されてその表面が活性化さ
れ、更に最後の予備メツキ処理によつて、後の本
メツキ処理における強固なメツキ層の形成の基と
なる強固な薄いメツキ層が形成するので、本メツ
キ処理の前にこのような３段階からなる前処理を
配している本発明は、結局焼結金属部材表面に強
固なメツキ層を形成することができるという効果
を奏するものである。
本発明における水蒸気処理は種々の条件下で遂
行することができ、鉄系の焼結金属部材の場合に
は、例えばそれを450℃の水蒸気に30分間曝した
後、550℃の水蒸気に60分間曝すという水蒸気処
理を利用するのが有利であり、水蒸気処理によつ
て形成させる酸化物被膜の平均膜厚は例えば約
10μm程度とするのが好都合であるが、このよう
な処理条件は焼結金属およびメツキ層の種類や性
格等に応じて適宜変更できることは言うまでもな
い。
また、酸洗処理後の酸化物被膜の平均膜厚が
0.5μm未満では、封孔が不完全となつてメツキ液
の侵入が懸念され、他方それが10μmを超えると、
酸化物被膜の絶縁作用の増大によつて陽イオンの
誘引が妨げられるので、一般に酸洗後のその平均
膜厚は0.5〜10μmであるのが好ましい。
一般に酸洗処理は、酸化鉄被膜の平均膜厚が上
記の範囲に入るように、例えば温度：30℃±２℃
を有するPH：１以下の塩酸溶液のような強酸浴中
に被メツキ部材を３〜４分間浸漬することによつ
て遂行される。
酸洗後の予備メツキ処理においては、例えばニ
ツケルメツキの場合、55〜60℃において、電圧２
〜５ボルト、電流密度２〜7A／ｄm2の条件下で、
PH：１以下の塩化ニツケル―硼酸溶液からなるメ
ツキ浴中に２〜５分間保持することによつて、平
均膜厚１〜5μmの強固な薄いニツケル層が形成さ
れる。
前処理を施した後の本メツキ処理は、一般の溶
融材のメツキ処理において使用されている当該技
術で周知のメツキ方法によつて遂行することがで
きる。
つぎに、この発明のメツキ法を以下の実施例に
よつて具体的に説明する。
実施例
焼結金属部材として、外径25mm×内径10mm×高
さ15mmの寸法を有し、かつｃ：1.0重量％を含有
し、残りがFeおよび不可避不純物からなる成分
組成を有する、焼結体密度6.8g／cm2のリング部材
を用意した。
(1) これを、450℃の水蒸気に30分間、つづいて
550℃の水蒸気に60分間曝し、その表面に平均
膜厚10μmの四三酸化鉄被膜を形成させ、この
水蒸気処理ずみのリング部材に下記の手順でニ
ツケル・クロムメツキを施した。
(2) PH：10以上のアルカリ溶液による脱脂：１分
間、
(3) 水洗：１分間、
(4) 酸洗：PH：１以下の塩酸溶液に温度：30℃に
て３分間浸漬
(5) 水洗：１分間、
(6) 予備ニツケルメツキ：PH：１以下の塩化ニツ
ケル―硼酸溶液からなるメツキ浴に、温度：60
℃、電圧：３ボルト、電流密度：3A／ｄm2の
条件で３分間浸漬、
(7) 水洗：0.5分間、
(8) ニツケルメツキ：ワツト浴（硫酸ニツケル：
300g／、塩化ニツケル：45g／、ホウ酸：
40g／、光沢剤：10g／、PH：４）中、温
度：55℃、電流密度：3A／m2で２分間処理、
(9) 水洗：0.5分間、
(10) クロムメツキ：サージエント浴（クロム酸―
硫酸―３価クロム形成剤の混合液中、温度：50
℃、電流密度：30A／ｄm2の条件で１分間浸
漬、
(11) 水洗：0.5分間、
(12) 湯切乾燥：熱湯（90〜100℃）中に２〜３分
間浸漬し、引上げ後乾燥。
上記(1)〜(12)の工程のうち、(1)、(4)、(6)工程が本
発明の前処理に相当し、(8)、(10)工程が本メツキ処
理に相当している。(4)工程では酸洗によつて水蒸
気処理被膜が一部溶解し、その平均膜厚は10μm
から5μmに減少して、リング部材表面は活性化す
ると共に導電性が改善され、(6)工程で生成した平
均層厚2.5μmの強固で薄いニツケル層は、リング
部材表面を一層良好な導体とすると共に陽イオン
の誘引を円滑にして(8)工程のニツケルメツキ：平
均層厚9μmと(10)工程のクロムメツキ：平均層厚
11μmの形成を容易にしている。
つぎに、(i)上記(1)〜(12)工程のメツキ方法（本発
明例）によつてメツキされたリング部材と、(ii)リ
ング部材に直接上記(8)〜(12)工程のニツケル・クロ
ムメツキを施す方法（比較例１）によつて得られ
たリング部材と、(iii)前処理として上記(1)〜(3)工程
の水蒸気処理のみを施した後、上記(8)〜(12)工程の
ニツケル・クロムメツキを施す方法（比較例２）
によつて得られたリング部材と、(iv)溶融材
（s45c）から製作したリング部材に上記(8)〜(12)工
程のニツケル・クロムメツキを施したもの（参考
例）について、それぞれ発錆試験と剥離試験を実
施した。その発錆試験はJIS Z2371の塩水噴霧試
験に準拠して遂行し、赤錆発生までのサイクル数
を測定し、また剥離試験はナイフで傷をつけたメ
ツキ被膜に粘着テープを接着―剥離させる操作を
５回繰返す方法によつて遂行し、メツキ被膜剥離
までの回数を測定することによつて、それぞれメ
ツキの防錆能と密着性を調べた。これらの測定結
果を合わせて第１表にした。
The present invention relates to a method for plating a sintered metal member, and particularly to a method for plating a sintered metal member, which is characterized by performing a three-stage pretreatment. Generally, sintered metal is manufactured through a process in which raw material powder is pressure-formed and then sintered, so pores remain in its structure, and the surface of the sintered metal member containing such pores. Even if plating is applied using the same method as general melted materials, the plating liquid will penetrate from the surface to the inside through the pores, making it impossible for the plating to adhere uniformly, and the resulting plating layer will be brittle and will not form a strong coating. It is not. Therefore, it has not been possible to provide a satisfactory plating on the surface of a sintered metal member by conventional plating methods applied to general molten materials that do not contain pores. Therefore, the inventor of the present invention has also found that in sintered metal members,
As a result of intensive research in order to obtain a plating layer that is comparable to the plating layer obtained with molten metal, we performed a pretreatment process on the sintered metal parts consisting of a series of steam treatments, pickling treatments, and pre-plating treatments. In particular, it has been found that the subsequent main plating can be carried out smoothly, thereby making it possible to provide a strong plating layer on the surface of the sintered metal member. This invention was made based on the above knowledge, and when plating a sintered metal member,
As a pretreatment, the sintered metal member is sequentially subjected to steam treatment, pickling treatment, and preliminary plating treatment, and then main plating treatment is performed to form a strong plating layer on the surface of the sintered metal member. It is characterized by: For example, when a sintered metal member containing iron is subjected to steam treatment, a film of triiron tetroxide (Fe 3 O 4 ) is formed on the surface, sealing the pores on the surface and preventing the plating liquid from entering. However, if the main plating treatment is applied to the steam-treated member as is, triiron tetroxide is not a good conductor of electricity, so when the plating film is formed, the flow of electricity is blocked and the electrolytic reaction becomes inactive. cause inconvenience. However, according to the pretreatment of the present invention, the relatively thick triiron tetroxide film with an average thickness of about 10 μm generated by the first steam treatment is partially dissolved and removed by the subsequent pickling treatment.
A film with an average thickness of about 0.5 to 10 μm is formed, and the surface of the sintered metal member regains electrical conductivity and becomes activated for electrical reactions. Furthermore, in the pretreatment of the present invention, preliminary plating is performed on the activated triiron tetroxide film to form a strong thin plating layer in advance, so that in the subsequent main plating, a strong thin plating layer is formed on the basis of this. A plating layer is formed. In this way, in the pretreatment of the present invention, the oxide film generated by the first steam treatment seals the sintered metal member, and a part of the oxide film on the surface of the member is removed by the next pickling treatment. The final pre-plating process forms a strong thin plating layer that forms the basis for the formation of a strong plating layer in the subsequent main plating process. The present invention, which includes such a three-step pretreatment process, has the effect that a strong plating layer can be formed on the surface of the sintered metal member. The steam treatment in the present invention can be carried out under various conditions; in the case of iron-based sintered metal parts, for example, it is exposed to steam at 450°C for 30 minutes, then exposed to steam at 550°C for 60 minutes. It is advantageous to use a steam treatment called exposure, and the average thickness of the oxide film formed by the steam treatment is, for example, approximately
It is convenient to set the thickness to about 10 μm, but it goes without saying that such processing conditions can be changed as appropriate depending on the type and characteristics of the sintered metal and the plating layer. In addition, the average thickness of the oxide film after pickling treatment is
If it is less than 0.5 μm, the sealing will be incomplete and there is a concern that the plating liquid may enter. On the other hand, if it exceeds 10 μm,
Since the increased insulating effect of the oxide film prevents the attraction of cations, it is generally preferred that the average film thickness after pickling is between 0.5 and 10 μm. Generally, pickling treatment is carried out at a temperature of, for example, 30℃±2℃ so that the average thickness of the iron oxide coating falls within the above range.
This is accomplished by immersing the member to be plated in a strong acid bath such as a hydrochloric acid solution having a pH of 1 or less for 3 to 4 minutes. In the preliminary plating treatment after pickling, for example, in the case of nickel plating, at 55 to 60°C, a voltage of 2
Under conditions of ~5 volts and a current density of 2 to 7 A/ dm2 ,
A strong thin nickel layer with an average thickness of 1 to 5 μm is formed by holding the film in a plating bath consisting of a nickel chloride-boric acid solution with a pH of 1 or less for 2 to 5 minutes. The main plating process after the pretreatment can be performed by a plating method well known in the art that is used in general plating processes for molten materials. Next, the plating method of the present invention will be specifically explained with reference to the following examples. Example As a sintered metal member, a sintered body having dimensions of 25 mm outer diameter x 10 mm inner diameter x 15 mm height, and containing 1.0% by weight of c, with the remainder consisting of Fe and unavoidable impurities. A ring member with a density of 6.8 g/cm 2 was prepared. (1) Apply this to steam at 450℃ for 30 minutes.
It was exposed to steam at 550°C for 60 minutes to form a triiron tetroxide film with an average thickness of 10 μm on its surface, and the steam-treated ring member was then plated with nickel chrome according to the following procedure. (2) Degreasing with an alkaline solution with a pH of 10 or higher: 1 minute, (3) Washing with water: 1 minute, (4) Pickling: Immersing in a hydrochloric acid solution with a pH of 1 or lower at a temperature of 30°C for 3 minutes (5) Washing with water: 1 minute (6) Preliminary nickel plating: In a plating bath consisting of a nickel chloride-boric acid solution with a pH of 1 or less, temperature: 60
℃, voltage: 3 volts, current density: 3 A/dm 2 for 3 minutes, (7) Water washing: 0.5 minutes, (8) Nickel plating: Watt bath (nickel sulfate:
300g/, Nickel chloride: 45g/, Boric acid:
40g/, brightener: 10g/, PH: 4), temperature: 55℃, current density: 3A/m 2 for 2 minutes, (9) water washing: 0.5 minutes, (10) chrome plating: sergeant bath (chromic acid ―
In a mixed solution of sulfuric acid and trivalent chromium forming agent, temperature: 50
℃, current density: 30A/dm 2 for 1 minute, (11) washing with water: 0.5 minutes, (12) draining and drying: immersing in hot water (90-100℃) for 2-3 minutes, pulling up and drying. . Among the steps (1) to (12) above, steps (1), (4), and (6) correspond to the pretreatment of the present invention, and steps (8) and (10) correspond to the main plating treatment. ing. (4) In the process, the steam treated film is partially dissolved by pickling, and the average film thickness is 10μm.
The ring member surface is activated and its conductivity is improved, and the strong and thin nickel layer with an average layer thickness of 2.5 μm produced in step (6) makes the ring member surface an even better conductor. At the same time, the attraction of cations is facilitated, and the nickel plating in step (8) has an average layer thickness of 9 μm and the chrome plating in step (10) has an average layer thickness of 9 μm.
It facilitates formation of 11μm. Next, (i) the ring member plated by the plating method of steps (1) to (12) above (example of the present invention) and (ii) the ring member directly plated by the plating method of steps (8) to (12) above. A ring member obtained by the method of applying nickel chrome plating (Comparative Example 1) and (iii) after applying only the steam treatment of the above steps (1) to (3) as pre-treatment, the above (8) to (12) Method of applying nickel/chrome plating in the process (Comparative Example 2)
The ring member obtained by (iv) and the ring member manufactured from molten material (S45C) that was plated with nickel and chrome in steps (8) to (12) above (reference example) were tested for rusting. Tests and peel tests were conducted. The rusting test was carried out in accordance with the JIS Z2371 salt spray test, and the number of cycles until red rust appeared was measured.The peeling test was carried out by adhering and peeling the adhesive tape to the plating film that had been scratched with a knife. The rust prevention ability and adhesion of each plating were investigated by repeating the test five times and measuring the number of times until the plating film peeled off. These measurement results are shown in Table 1.
【表】
第１表に示される結果から、この発明の方法に
よつて焼結金属部材上に形成されたメツキ層は、
前処理を施さない比較例１や、前処理として水蒸
気処理しか施さなかつた比較例２によつて得られ
たメツキ層よりも遥かに強力な防錆能を有すると
共に、優れた密着性を有し、更にこの発明の方法
によれば、溶融材に施される普通のメツキ層（参
考例）に匹敵あるいはこの以上の防錆能と密着性
を具備するメツキ層を焼結金属部材の表面に形成
できることがわかる。
なお、上記実施例ではニツケルメツキを施した
場合について述べたが、亜鉛、カドミウム、銀、
および金などのメツキについても同様に実施でき
ることは勿論である。
上述のように、この発明のメツキ方法によれ
ば、空孔を有するために従来満足なメツキを施す
ことができなかつた焼結金属部材表面に、一般の
溶融材の表面に施されるメツキ層に匹敵、あるい
はこれ以上の強固な密着性を有するメツキ層を形
成することができ、それによつて多種多様の焼結
金属部材に強力な防錆能を与えることができると
いう効果を奏するから、この発明が広範囲の産業
分野において多大の貢献をなすことは明らかであ
る。[Table] From the results shown in Table 1, the plating layer formed on the sintered metal member by the method of the present invention is
It has a much stronger anti-corrosion ability and excellent adhesion than the plating layer obtained in Comparative Example 1 which was not subjected to pre-treatment or Comparative Example 2 which was only subjected to steam treatment as pre-treatment. Furthermore, according to the method of the present invention, a plating layer is formed on the surface of the sintered metal member, and the plating layer has rust prevention ability and adhesion that are comparable to or better than the ordinary plating layer applied to molten material (reference example). I know what I can do. In addition, in the above example, the case where nickel plating was applied was described, but zinc, cadmium, silver,
Of course, the same method can be applied to plating with gold or the like. As described above, according to the plating method of the present invention, the plating layer applied to the surface of a general molten material can be applied to the surface of a sintered metal member, which previously could not be satisfactorily plated due to the presence of pores. It is possible to form a plating layer with strong adhesion comparable to or even stronger than that of sintered metal parts, which has the effect of imparting strong anti-corrosion properties to a wide variety of sintered metal parts. It is clear that the invention will make a significant contribution to a wide range of industrial fields.