WO2014108727A2

WO2014108727A2 - A passivation method

Info

Publication number: WO2014108727A2
Application number: PCT/IB2013/002950
Authority: WO
Inventors: Ebru OEZEL; Azra MARTIN; Zuehre VAROL OEZGUER
Original assignee: Robert Bosch Gmbh; Bosch Sanayi Ve Tic. A. S.
Priority date: 2012-12-31
Filing date: 2013-12-20
Publication date: 2014-07-17
Also published as: EP2938748A2; WO2014108727A3; CN104981550A

Abstract

The subject matter invention is a passivation process against the nitriding process in the parts where the hardness, toughness and fatigue strength are not desired to be changed after the nitriding process of any injector component (10). Accordingly said process is characterized by comprising the steps of: a. Subjecting the injector component (10) to a grinding process, b. Subjecting the injector component (10) to the chemical washing process, c. Subjecting the injector component (10) to the electrochemical washing process, d. Subjecting the injector component (10) to the nickel coating process.

Description

SPECIFICATION A PASSIVATION METHOD

TECHNICAL FIELD

The present invention relates to a passivation method for protecting steel-based materials against the nitriding process.

PRIOR ART

For protecting steel-based materials against physical affects during usage, the hardness and toughness values of the material surface should be increased. One of the methods for increasing hardness and toughness of the surface is the nitriding method. During the nitriding method, some regions on the piece (for instance the regions whereon tooth is formed) are not desired to be subject to the nitriding process. In these cases, a paste is applied to said regions comprising various chemical substances. Said process is realized by the operator manually in an inhomogeneous manner. By means of the application, the regions, remaining under the paste, are passivated during the nitriding process, in other words, the region is prevented from being subject to the nitriding process. After the nitriding process is completed, the paste, provided on the passivated region, is cleaned. If this cleaning process is not realized in a correct manner, there occur problems like deposition on the surface. Moreover, if the paste application process is realized manually in an inhomogeneous manner, some regions are subjected to nitriding process. In the application US4746376A, a slurry is disclosed which functions as a protective against the nitriding process.

As a result, because of the abovementioned problems, an improvement is required in the related technical field.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a passivation process for providing passivation against the nitriding process, in order to eliminate the abovementioned problems and to bring new advantages to the related technical field. The main object of the present invention is to provide a passivation process for providing passivation of the injector component, which will be subject to nitriding process, against nitriding.

In order to realize all of the abovementioned objects and the objects which are to be deducted from the detailed description below, the present invention is a passivation process against the nitriding process in the parts where the hardness, toughness and fatigue strength are not desired to be changed after the nitriding process of any injector component. Accordingly, the method is characterized by comprising the steps of: a. Subjecting the injector component to a grinding process,

b. Subjecting the injector component to the chemical washing process,

c. Subjecting the injector component to the electrochemical washing process, d. Subjecting the injector component to the nickel coating process.

Thus, in the regions where nickel coating is realized, nitrogen entry into the injector component during the nitriding process is prevented.

In a preferred embodiment of the subject matter invention, in said step (a), the grinding process is realized by means of at least one magnetic paper. Thus, the surface is cleaned in a mechanical manner.

In another preferred embodiment of the subject matter invention, in said step (a), different magnetic papers are utilized having different porosity values.

In another preferred embodiment of the subject matter invention, in said step (a), magnetic papers are utilized having Allegro (between 7 and 10) pm, Doc (between 2 and 4) pm, Chem (between 0,03 and 0,05) pm porosity values. Thus, the process is repeated from a high porosity value to a low porosity value, and a cleaner surface is obtained.

In another preferred embodiment of the subject matter invention, in said step (b), the injector component is cleaned in an ultrasonic manner inside the acetone in the range of 8-12 minutes.

In another preferred embodiment of the subject matter invention, in said step (b), the injector component is kept in H₂S0₄ solution in the range of 8-12 percent in volume for duration between 25 and 35 seconds. In another preferred embodiment of the subject matter invention, in said step (b), the injector component is kept in H₂S0₄ solution in the range of 4-6 percent in volume for duration between 25 and 35 seconds.

In another preferred embodiment of the subject matter invention, the injector component is rinsed with pure water after every stage of step (b).

In another preferred embodiment of the subject matter invention, in step (c), the injector component is kept in a solution comprising NaOH, Na₂S0₄ and Na₂C0₃ by applying current in the range of 8-12 mA/cm² for duration of 18-22 minutes.

In another preferred embodiment of the subject matter invention, in step (c), the injector component is rinsed with pure water after it is kept in the solution comprising NaOH, Na₂S0₄ and Na₂C0₃.

In another preferred embodiment of the subject matter invention, in step (d), the injector component is subject to watts type nickel coating process.

In another preferred embodiment of the subject matter invention, in step (d), the injector component is coated by nickel with a thickness 3,4-3,6 pm with a current density between 0,33-0,39 mA/cm² in a solution with a pH value between 3,3-3,6.

In another preferred embodiment of the subject matter invention, the nickel coating is provided at a thickness of 3,5 pm.

In another preferred embodiment of the subject matter invention, an injector component, produced after passing said passivation process, is an injector comprising said injector component.

BRIEF DESCRIPTION OF THE FIGURES

In Figure 1 , a representative view of the application of step (d) of the subject matter passivation process is given.

REFERENCE NUMBERS

10 Injector Component 20 Vessel

30 Solution

40 Anode

50 Power Supply

THE DETAILED DESCRIPTION OF THE INVENTION

In this detailed description, the passivation process against the nitriding process is explained with references to examples without forming any restrictive effect in order to make the subject more understandable.

In diesel injectors, the nitriding process is realized for increasing the hardness and toughness values of the injector. During the nitriding process, nitrogen is diffused into an injector component (10) and the hardness, toughness and fatigue values of the injector are improved. However, the nitriding process is not desired to be applied at every region of the injector component (10). Therefore, the regions, which are desired to be subjected to the nitriding process, are kept active and the other regions are passivated. For providing said passivation, the passivation process whose details are described below is realized.

In step (a) of the passivation process, the injector component (10) is subject to a grinding process.

In the first step of step (a) where the grinding process is realized, a magnetic paper (Allegro- 9 m) is utilized whose porosity value is at a high level.

In the second step of step (a) where the grinding process is realized, a magnetic paper (Doc- 3 pm) is utilized whose porosity value is lower than the porosity value utilized in the first step. In the third stage of step (a) where the grinding process is realized, the injector component is cleaned by means of the grinding process by utilizing a magnetic paper (Chem-0,04 μηη) with a porosity value lower than the porosity value in second step.

In step (b) of the passivation process, the injector component (10) is subject to chemical washing process.

In the first stage of step (b) where the chemical washing process is realized, the injector component (10) is cleaned in an ultrasonic manner inside acetone for duration of 10 minutes. In the second stage of step (b) where the chemical washing process is realized, the injector component (10) is rinsed with pure water. In the third stage of step (b) where the chemical washing process is realized, the injector component (10) is kept for 30 seconds inside the H₂S0₄ solution having a portion of 10 percent in volume.

In the fourth stage of step (b) where the chemical washing process is realized, the injector component (10) is rinsed with pure water.

In the fifth stage of step (b) where the chemical washing process is realized, the injector component (10) is kept for thirty seconds inside the H₂S0₄ solution having a portion of 5 percent in volume.

In the sixth stage of step (b) where the chemical washing process is realized, the injector component (10) is rinsed with pure water.

In step (c) of the passivation process, the injector component (10) is subject to the electrochemical washing process. During the electrochemical washing process, a current of 10 mA/cm² is applied to the injector component (10) for duration of 20 minutes, and afterwards, it is kept in a solution including NaOH, Na₂S0₄ and Na₂C0₃. After the electrochemical washing process, the injector component (10) is rinsed with pure water.

In step (d) of the passivation process, the injector component (10) is subject to the nickel coating process. During the nickel coating process, the method, called Watts type nickel coating process, is utilized in the present art. Nickel, having a thickness of 3,5 pm and having a current density of 0,36 mA/cm², is coated inside a solution (30) having pH of 3,5 and having nickel sulphamate therein [Ni(S0₃NH₂)]. As can be seen in Figure 1 , during said coating process, the injector component (10) is immersed into a solution (30) provided in a vessel (20). Moreover, a vessel (20) is connected to a power supply (50) together with the anode (40) provided therein, and thereby the circuit is completed and the nickel, provided inside the solution (30), is provided to be coated onto the injector component (10) provided in the cathode position.

As a result of the nickel coating process performed, the passivation of the injector component (10) against the nitriding process is realized. In the preferred embodiment of the present invention, a coating with a thickness of 3,5 pm is realized for providing full passivation together with the smallest coating thickness. In alternative embodiments, thicker or thinner coating thicknesses can be provided.

In the preferred embodiment of the present invention, the injector component (10) is made of 50CrMo4 material. In the alternative embodiments, any kind of steel-based material can be utilized. The protection scope of the present invention is set forth in the annexed Claims and cannot be restricted to the illustrative disclosures given above, under the detailed description. It is because a person skilled in the relevant art can obviously produce similar embodiments under the light of the foregoing disclosures, without departing from the main principles of the present invention.

Claims

1. A passivation process against the nitriding process in the parts where the hardness, toughness and fatigue strength values are not desired to be changed after the nitriding process of any injector component (10), characterized by comprising the steps of:

a. Subjecting the injector component (10) to a grinding process,

b. Subjecting the injector component (10) to the chemical washing process, c. Subjecting the injector component (10) to the electrochemical washing process, d. Subjecting the injector component (10) to the nickel coating process.

2. A passivation process according to Claim 1 , characterized in that in said step (a), the grinding process is realized by means of at least one magnetic paper.

3. A passivation process according to Claim 2, characterized in that in said step (a), different magnetic papers are utilized having different porosity values.

4. A passivation process according to Claim 3, characterized in that in said step (a), magnetic papers are utilized having Allegro (between 7 and 10) μηη, Doc (between 2 and 4) prn, Chem (between 0,03 and 0,05) μιτι porosity values.

5. A passivation process according to Claim 1 , characterized in that in said step (b), the injector component (10) is cleaned in an ultrasonic manner inside the acetone in the range of 8-12 minutes.

6. A passivation process according to Claim 1 , characterized in that in said step (b), the injector component (10) is kept in H2SO₄ solution in the range of 8-12 percent in volume for duration between 25 and 35 seconds.

7. A passivation process according to Claim 1 , characterized in that in said step (b), the injector component (10) is kept in H₂S0₄ solution in the range of 4-6 percent in volume for duration between 25 and 35 seconds.

8. A passivation process any of the claims between Claim 5 and 7, characterized in that the injector component (10) is rinsed with pure water after every stage of step (b).

9. A passivation process according to Claim 1 , characterized in that in step (c), the injector component (10) is kept in a solution comprising NaOH, Na₂S0₄ and Na₂C0₃ by applying current in the range of 8-12 mA/cm² for duration of 18-22 minutes.

10. A passivation process according to Claim 9, characterized in that in step (c), the injector component (10) is rinsed with pure water after it is kept in the solution comprising NaOH, Na₂S0₄ and Na₂C0₃.

1 1. A passivation process according to Claim 1 , characterized in that in step (d), the injector component (10) is subject to watts type nickel coating process.

12. A passivation process according to Claim 1 1 , characterized in that in step (d), the injector component (10) is coated by nickel with a thickness 3,4-3,6 pm with a current density between 0,33-0,39 mA/cm² in a solution (30) with a pH value between 3,3-3,6.

13. A passivation process according to Claim 12, characterized in that the nickel coating is provided at a thickness of 3,5 pm.

14. A passivation process according to any one of the preceding claims, characterized in that, an injector component (10), produced after passing said passivation process, is an injector comprising said injector component (10).