Coating processes – Electrical product produced – Cellulosic or fibrous base
Reexamination Certificate
2002-01-10
2003-08-05
Paschall, Mark (Department: 3742)
Coating processes
Electrical product produced
Cellulosic or fibrous base
Reexamination Certificate
active
06602542
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a device for cleaning a product which has a substrate chamber in which there is a substrate guide and which has a substrate holder.
U.S. Pat. No. 5,238,752 describes a thermal barrier coating system with an intermetallic bond coat. The thermal barrier coating system is applied to a metallic base body, in particular to a Cr—Co-steel for an aircraft engine blade. An intermetallic bond coat, in particular of nickel aluminide or a platinum aluminide, is applied directly to this metallic base body. This bond coat is adjoined by a thin ceramic layer of aluminum oxide, to which the actual thermal barrier coating, in particular of yttrium stabilized zirconium oxide, is applied. This ceramic thermal barrier coating of zirconium oxide has a rod-like structure, the rod-like columns being oriented substantially perpendicular to the surface of the base body. The intention of this is to improve the ability to withstand cyclic thermal loads. The thermal barrier coating is deposited on the base body by means of an electron beam PVD (Physical Vapor Deposition) process, zirconium oxide being vaporized from a metal oxide body by an electron beam gun. The process is carried out in a corresponding device, in which the base body is preheated to a temperature of approximately 950° C. to 1000° C. During the coating operation, the base body is rotated at a constant rate in the jet comprising the metal oxide.
An electron beam PVD process for producing a ceramic coating is also described in U.S. Pat. No. 5,087,477. The ceramic coating produced in this case has a layer thickness of between 250 and 375 &mgr;m.
To provide good adhesion between the coating and the base body, it is advantageous for the base body to be cleaned prior to the coating operation. It has become known from British patent specifications GB 2 323 855 and GB 1 447 754 to clean a product which is to be coated prior to the coating. The cleaning in those cases takes place by means of a sputtering process, in which firstly a plasma is generated and the positive ions of the plasma are accelerated toward the base body. The device for cleaning the base body is integrated in the device for coating the base body. In order for the base body to be heated to a suitable coating temperature, the base body is heated with the aid of an electron beam. There is provision for it to be possible to switch between the heating phase by means of the electron beam and the cleaning phase by means of ion sputtering. To do this, it is necessary for the relationship of potential between the base body and the electron source or the positive ions of the plasma to be adjusted or controlled. To do this, GB 2 323 855 provides for the base body to be connected to a voltage source, in order to set the base body to a suitable potential. In GB 1 447 754, a voltage source and a monitoring device are also provided, in order to be able to influence the relationships of potential between base body, electron source and plasma. Therefore, to set a suitable relationship of potential, according to both literature sources an active voltage supply is required.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a device for cleaning an article.
With the above and other objects in view there is provided, in accordance with the invention, a method of cleaning a surface of an article having a metallic base body, the method which comprises:
generating a plasma with electrically positively charged ions, accelerating the ions towards the article, and bringing ions into contact with the base body for cleaning the base body;
directing an electron beam onto the base body; and
controlling an outgoing flow of electrons coming into contact with the base body by connecting the base body to a reference potential via a switch at a given frequency, which may be fixed preset, adjustable, or regulated.
In other words, the object relating to a process for cleaning the surface of a product which has a metallic base body is achieved by the fact that a plasma with electrically positively charged ions is generated and the ions are accelerated toward the product, so that they come into contact with the base body for cleaning purposes, an electron beam being directed onto the base body, and that the outgoing flux of electrons which come into contact with the base body is controlled as a result of the base body being connected to a reference potential via the switch with a fixedly preset, adjustable or regulated frequency.
With this process, the surface of the product, in particular a component in a plasma, undergoes preliminary cleaning in such a manner that the adhesion of layers which are to be vapor-deposited is significantly improved compared to a process involving thermal cleaning. The latter may, for example, lead to gases escaping.
Compared to the processes which are known from the prior art, the process described here has the crucial advantage of being significantly simpler and therefore also less susceptible to faults.
This is primarily due to the fact that the connection of the base body to the reference potential which is, for example, frame potential or ground potential, can be switched on and off makes it easy to suitably adjust the relationship of potential between base body and plasma and the electrons of the electron beam. Therefore, the electrical potential of the base body is controlled by means of the connection to the reference potential. The outgoing flux can in this case be controlled between a maximum value and a minimum value, the minimum value preferably being zero, i.e. there is no outgoing flux of electrons. In the latter case, the electrons do not flow out and an electron build-up is produced around the product, which negatively charges the product. In the presence of the plasma, the positively charged ions are accelerated toward the product; they come into contact with the product at a parameter-dependent velocity. Contaminants present on the surface of the product are removed by means of a pulse exchange with this surface.
On the other hand, if the outgoing flux is set to a maximum value, i.e. the switch is closed and the base body is connected to the reference potential, for example, frame potential, the electrons can flow out of the electron beam without obstacle. Consequently the positive ions of the plasma are not accelerated toward the base body. Therefore, when the switch is closed, the product is substantially only exposed to the electron beam, which heats the product. Therefore, by actuating the switch it is simple to switch over between a cleaning phase and a heating phase. The switch can be suitably actuated with a fixedly preset, adjustable or regulated frequency.
The outgoing flux of electrons preferably takes place via an electrical outgoing line, which is alternately opened and closed by means of the switch. This outgoing line produces a current path which is constantly switched between passing and blocking. The alternating switching between passing and blocking of the current path can take place at a constant, possibly temporally variable frequency. Alternating switching allows alternating charging and discharging of the product, as a result of which, in the presence of a gas, an alternating voltage discharge (plasma) can be ignited or maintained. In this way, it is possible to continuously clean the component.
The frequency at which the outgoing flux of electrons is controlled may in this case lie between a few hertz and frequencies up to the megahertz range, in particular, the frequency may be approximately 50 kHz or approximately 27 MHz. The high-frequency switching has the crucial advantage that, at suitable high frequencies, the cleaning effect is not dependent upon the component geometry. Therefore, the high-frequency switching allows reliable and in particular homogenous cleaning of the product.
There is a potential difference, i.e. an electric voltage, between the plasma and the base body, which potential difference can be influenced, in particular, set, by
Greenberg Laurence A.
Locher Ralph E.
Paschall Mark
Siemens Aktiengesellschaft
Stemer Werner H.
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