KR20150123235A - Protective system for use in induction heating - Google Patents

Abstract

The invention relates to a protection system for an induction heating element, the induction heating element comprising an induction coil and a coupling element connecting the induction coil to a power source, the protection system comprising a polyimide insulation material, a silicone rubber insulation material, An insulating material selected from the group consisting of PTFE insulating material and PVC insulating material, and optionally insulating means.

Description

PROTECTIVE SYSTEM FOR USE INDUCTION HEATING [0002]

FIELD OF THE INVENTION The present invention relates to a member protection system for use in induction heating of a substance, e.g., metal, to prevent electrical sparks and arcing and to prevent wear by plasma attack and irradiative heat.

The heating and melting of one or more metals or metal alloys in the induction heating of materials, and more particularly in the heating of metals, such as physical vapor deposition (PVD) processes, is preferred between equipment components with different potentials It can cause sparks and arcs. Spark and arc generation depend on the voltage and current used for induction heating, the geometry of the process components, the gas pressure and composition of the process, and the gas partial pressure and composition associated with the volatile system components. In the event of a spark, the disruptive discharge of electricity means that it occurs between two positions with large potential differences. Spark occurs after path ionization precedes. When an arc occurs, the luminous electric gas discharge means that the electric density is high and the potential gradient is low. The ionization required to maintain a large current is mainly provided by evaporation of some material of the equipment members between locations. In PVD, both sparking and arcing can cause damage to the equipment, which will interrupt the process, and therefore, will be detrimental to productivity.

Another factor that can cause damage to equipment components is the generation of plasma. Plasma can occur between points where a potential difference exists and an electric field is generated. The stronger the electric field, the higher the conductivity of the gas and the sensitivity to the ionization of the gas, the easier the formation of the plasma. The conductivity of the gas and its sensitivity to ionization depends on the gas composition, the gas pressure, and the distance between the points where the potential difference is present. Plasma can wear a protective coating applied to prevent sparks or arcing, thereby increasing the risk of sparks or arcing.

Finally, the temperature realized by induction heating, for example the temperature of the molten metal in the crucible, causes damage by irradiation. Such damage can be, for example, damage to the protective coating applied to prevent sparks or arcs.

One way to minimize the risk of sparking of the induction coil is to place the crucible and induction coil outside the vacuum chamber under atmospheric conditions. In this situation, the spark will occur when the potential difference is very large, to the order of a few kilovolts (kV) (F. Paschen, 'Ueber die zum Funkenubergang in Luft, Wasserstoff und Kohlensaure bei verschiedenen Drucken erforderliche Potentialdifferenz, Annalen der Physik 273 ): 69-75. However, placing the induction coil with the crucible outside the vacuum chamber introduces a need for a vacuum sealing that can cope with the large temperature difference between the crucible compartment and the remainder of the vacuum chamber, which greatly complicates the process. The generated set-up will be more capital-intensive than in an improved coil system.

It is an object of the present invention to provide a protection system for members used for induction heating of a material to prevent sparks.

It is another object of the present invention to provide a protection system for members used for induction heating of materials to prevent arcing.

It is yet another object of the present invention to provide a protection system for an element used for induction heating of a material to prevent or minimize the formation of a plasma.

It is a further object of the present invention to provide a protection system for a member used for induction heating of a material to prevent damage caused by radiant heat.

It is still another object of the present invention to provide a member protection system used for induction heating of a material which can be easily applied.

It is another object of the present invention to provide a low cost, low cost protection system for use in induction heating of materials.

According to a first aspect of the present invention, one or more objects of the present invention are realized by providing a protective system for the protection of an induction heating element, the induction heating element comprising an induction coil and a connection element Wherein the protective system comprises an insulating material applied to the member, wherein the insulating material is a polyimide insulating material, a silicone rubber insulating material, a polytetrafluoroethylene (PTFE) insulating material, and a polyvinyl chloride (PVC) insulating material. And is selected from the group of insulating materials made of a material.

The invention will be further illustrated by the example shown in the figures as follows:
Figure 1 schematically illustrates the fields induced by an induction coil provided from an AC power source,
Figure 2 shows a diagram showing the breakdown voltages for uncoated induction coils and coated induction coils in various gas environments,
Figures 3a, 3b and 3c schematically show the capture system for free charge carriers around the induction coil.

In a series of tests, the breakdown voltage at which sparks occur is the pressure in the chamber used in the PVD, the setup of the induction heating system, the shape of the heating element, the type and size of the heating element, and the type of electric field (AC / DC) . It has also been determined that in a physical vapor deposition test on a substrate of zinc, the breakdown voltage at which sparks occur increases in the chamber due to the low pressure rise in the vacuum chamber during the evaporation process. Nevertheless, in order to continuously and sufficiently supply metal vapors or vapors of metals, it is necessary to maintain power at such a level that sparks and arcs can easily occur without any protective means.

The spark can draw a lot of energy from the power supply, even tripping the power supply's overload system and turning off all the power supplies. The risk of sparking is enhanced by the release of hot electrons from the heated member surface, which increases the conductivity of the gas at this point.

According to a first aspect of the present invention, one or more objects of the present invention are realized by providing a protective system for the protection of an induction heating element, the induction heating element comprising an induction coil and a connection element Wherein the protective system comprises an insulating material applied to the member, wherein the insulating material is a polyimide insulating material, a silicone rubber insulating material, a polytetrafluoroethylene (PTFE) insulating material, and a polyvinyl chloride (PVC) insulating material. And is selected from the group of insulating materials made of a material.

Of these insulating materials, the polyimide insulating material can withstand the highest temperature. The term polyimide insulating material refers to an insulating material comprising polyimide or made of polyimide. This applies equally to the above-mentioned other insulating materials in that each of these insulating materials is partially or entirely made of a specific material.

In an induction heating system using a vacuum chamber, such as a system considered for use with a PVD system, the induction heating element may be located inside or outside the vacuum chamber. If the induction heating element is inside the vacuum chamber, feedthrough means is provided to couple the induction heating element inside the vacuum chamber to the power source through the vacuum chamber wall. These through connection means are part of the connection element.

By using one of the insulating materials as an insulating material on the surface of the member, the generation of sparks and arcs is largely prevented.

In the test, very good results were obtained by using the polyimide insulating material. The properties of the polyimide insulation are provided as follows:

- Low electrical conductivity to prevent sparks / arcs,

- Compared to the upper insulating layer, a high thermal conductivity,

Good thermal contact with the induction heating element,

- flexibility to prevent cracking or fatigue of the insulating material, and

- High breakdown voltage or dielectric strength.

In a further aspect of the invention, the polyimide is a thermosetting polyimide. The polyimide insulation may be applied as an insulating tape, but preferably the polyimide is applied as a thermosetting coating. In this way, a polyimide insulating coating is obtained that is in close contact with the induction heating element without leaving any free space, which has good thermal contact with the induction heating element.

Coils coated with a polyimide insulated coating have been demonstrated to withstand currents of up to 6 kA in an atmospheric pressure range of 0.001 Pa - 2 kPa and an applied AC potential difference of 1000 V RMS with a connector spacing of 8 mm. This is more than twice the potential difference that can be achieved when there is no insulating material on the coil surface.

Since the insulating material is exposed to radiant heat resulting from the melting or evaporation of metals or metals used in the PVD process, the insulating material may wear and eventually crack. Also, due to the large potential difference, a plasma, which can be either inductively coupled plasma (ICP) induced by the azimuthal electrical field of the induction coil, or capacitively coupled plasma (CCP) induced by the axial field of the induction coil, Lt; / RTI > Plasma and more specifically ICP also eventually degrade the insulating material, resulting in spark / arcing again.

In order to prevent wear due to radiant heat and plasma attack, insulation is provided for the induction heating element. Preferably, a heat insulating material is provided between at least the member and an object to be heated by induction heating. However, the insulating material is preferably applied as a second layer surrounding the insulating material.

According to a further aspect of the present invention, the insulation comprises a heat resistant material and a carrier for the refractory material. The carrier for the refractory material is not so important as long as it can withstand at least a high temperature. Although the induction coil consists of a hollow tube through which the cooling liquid circulates, the temperature outside it can rise much higher than the temperature of the cooling liquid. The carrier may comprise a mineral wool, which may be a glass wool or a stone wool.

According to a further aspect of the present invention, the refractory material is a ceramic material applied to the carrier. The ceramic material is, for example, a magnesium oxide-based ceramic material. The magnesium oxide-based ceramic material comprises the following characteristics:

- high temperature capability, and

- low electrical conductivity.

The magnesium oxide-based ceramic material is preferably applied to the carrier material as a paste to facilitate easy application.

Even in a layered protection system with a first layer of insulating material and a second layer providing insulation, it appears that inductively coupled plasma can still be generated when high voltage is used.

According to yet a further aspect of the present invention, a trapping system for a free charge carrier is provided for the induction heating element. The trapping system may be a system comprising a conductive element that follows at least a portion of turns or turns of the induction coil.

In a further aspect of the present invention, the free charge carrier trapping system comprises at least one conductive member positioned in the radial direction of the induction coil and parallel to the axis of the induction coil. It has been found that by means of said member, for example a flat plate, the voltage and current applied to the induction coil can be significantly increased before the inductively coupled plasma again occurs.

By grounding the free charge carrier capture system, the effect of the capture system is further improved.

As an alternative to this carrier capture system, a non-conductive member that physically occupies a free space directly around the induction coil may be used, thus capturing any free electron carriers moving along the periphery of the coil and forming a plasma Thereby preventing ignition of the battery.

In a further aspect of the invention, the induction heating element is used in a chamber having a reduced pressure in the range of O.OOlPa - 2.5 kPa, wherein a maximum of IkV voltage and a maximum of 6 kA current at a frequency of up to 20 kHz are supplied to the induction coil do.

The above-described protection system can be effectively used in an induction coil system that operates not only in AC but also in DC.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention will be further described by the embodiments shown in the drawings.

In Fig. 1, the axial cross section of the induction coil 1 is shown on the left, and the radial cross section of the induction coil is shown on the right. In this embodiment, the induction coil 1 has a limited number of turns 2, with a potential difference of about 600 V between the last turn of the coil 1 and the first turn.

Field lines 3 of magnetic B-fields induced by currents passing through the induction coils are schematically shown in the figure. The axial field E _z and the azimuthal electric field E _{? Are} also represented by the respective field lines 4 and 5, respectively. The capacitively coupled plasma (CCP) is related to the axial electric field (E _z ) and the inductively coupled plasma (ICP) is related to the azimuthal electric field (E _θ ). On the right side, the direction 6 of the current in the induction coil is indicated by the dotted line and the arrow.

The induction coil 1 and its connecting parts were made of copper for good electrical conductivity. Copper, in the form of a hollow tube, allows the coils to be adequately cooled by a cooling liquid pumped through the inside of the coils.

Figure 2 is a diagram showing the minimum breakdown voltage of an uncoated induction coil and a coated induction coil in various gas environments, with the vertical axis plotted versus voltage and different coil and gas environments along the horizontal axis. The minimum value was determined at a pressure range of ~ 10 mbar to 10 ^-4 mbar. Conventional PVD processes can occur somewhere in this region.

In an uncoated induction coil (in this case, a non-coated copper induction coil), the spark-free regime varies from less than 200V for a coil used in an argon gas environment to about 400V for air. There is a small region where sparks can occur above these spark-free occurrence regions, and a spark necessarily occurs above the small region. From this plot, the breakdown voltage can be said to be relatively high in the Zn atmosphere when it occurs in the vacuum chamber during the Zn PVD process.

For coated coils (coils with a layer of insulating material but no insulation), the breakdown voltage in the same gaseous environment was much higher than the uncoated copper induction coil.

The use of various insulating materials or combinations of these insulating materials was investigated and appeared to produce good results in combination with silicone-rubber and PVC-based tapes or ceramic covers. However, the breakdown voltage and time showed the best performance when using polyimide tape. The same or even better results are obtained by the use of the polyimide applied in a coating that encloses the induction coil in a seamless manner. In a polyimide insulative coating having a thickness of 65 [mu] m, it was established that the breakdown voltage was on the order of 6 kV (order).

Heat is radiated in the object to be heated, so that a heat insulating material is preferably provided on the coating. The heat insulating material includes a heat resistant material and a carrier for the heat resistant material. This insulation also provides some degree of protection against plasma attack.

For insulation, the polyimide layer is covered with an additional layer of glass wool impregnated with MgO-paste. During the Zn PVD test, this protection system can operate for several hours at an AC voltage in the range of 550-600 V RMS to successfully withstand crucible temperatures of 750-770 ° C under vacuum pressures of at least 10 Pa. The coils did not show signs of damage.

3A and 3B respectively show a perspective view and a plan view of an induction coil provided with a protection system, in which the induction coil 1 is provided with an insulating material and a trapping system for free charge carriers so as to further suppress the plasma attack do. The insulation of the coil includes a polyimide coating, and a thermal insulation applied over the polyimide coating. The trapping system includes two grounded metal plates 7, or three grounded metal plates 7 distributed around the induction coil and parallel to the central axis of the coil as shown in Figure 3b.

The trial was run on a coil by a hollow crucible at about 18 kHz, where the induced voltage was stepped up. When nitrogen gas was used without plate 7, the breakdown occurred at 740 V RMS and the coil current was 2150 A. If one grounded plate 7 is added to the set up, this voltage can rise up to 820V RMS and coil current to 2450A before inductively coupled plasma (ICP) occurs. After the addition of the third grounded plate, the setup maintains an ICP-free state at a voltage level of greater than 890 V RMS and a coil current of greater than 2580 A.

3C, the free charge carrier trapping system comprises a plurality of non-conductive elements 8 made of a material such as concrete, BN, Al ₂ O ₃ , or other insulating material, located around the circumference of the induction coil 1 . Due to these elements 8 located adjacent to the coil, movement of the free charge carriers in the field around the coil, and hence the duration of the plasma, is also prevented.

Claims (15)

A protection system for an induction heating member,
The induction heating element including an induction coil and a coupling element connecting the induction coil to a power source,
The protection system comprising an insulating material applied to the induction heating element,
Wherein the insulation material is selected from the group of polyimide insulation material, silicone rubber insulation material, PTFE insulation material and insulation material comprising PVC insulation material. The method according to claim 1,
Wherein the insulating material is a polyimide insulating material. 3. The method of claim 2,
Wherein the polyimide insulating material is applied as a thermosetting coating. 4. The method according to any one of claims 1 to 3,
Wherein the insulation is provided for the induction heating element. 5. The method of claim 4,
Wherein the heat insulating material is provided between at least the induction heating member and an object to be heated by induction heating. 6. The method of claim 5,
Wherein the heat insulating material comprises a heat resistant material and a carrier for the heat resistant material. The method according to claim 6,
Wherein the carrier for the refractory material comprises mineral wool. 8. The method of claim 7,
Wherein the mineral wool is a glass wool. 9. The method according to any one of claims 4 to 8,
Wherein the refractory material is a ceramic material. 10. The method of claim 9,
Wherein the ceramic material is a magnesium oxide-based ceramic material. 11. The method according to any one of claims 1 to 10,
A capture system for free charge carriers is provided for a member used in induction heating. 12. The method of claim 11,
Wherein the trapping system comprises a conductive element along at least a portion of the turn of the induction coil. 12. The method of claim 11,
Wherein the trapping system comprises one or more conductive elements located in a radial direction of the induction coil and parallel to an axis of the induction coil. 12. The method of claim 11,
Wherein the trapping system comprises non-conductive elements located along a circumference of the induction coil. 11. The method according to any one of claims 1 to 10,
Wherein the induction heating element is used in a chamber having a reduced pressure in the range of O.OOlPa - 2.5 kPa and a maximum of 6 kA current is supplied to the induction coil at a pressure of up to lkV and a frequency of at most 20 kHz.

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