JP5657402B2 - Induction heating device - Google Patents

Description

  The present invention relates to an induction heating device for a billet that can be arranged in a space-saving manner.

  A technique is known in which a cylindrical billet made of a metal material is heated by induction heating and used for casting or forging. In induction heating of a billet, as a method for improving productivity, a method of heating while conveying a plurality of billets arranged in series in the axial direction is known (see, for example, Patent Document 1). Moreover, the structure described in patent documents 2-4 is known as a technique which handles a billet.

Japanese Patent Laid-Open No. 11-6016 JP-A-9-118429 JP-A-9-287018 JP 2001-129610 A WO2004 / 018130

  In the method of performing induction heating while conveying billets arranged in series in the axial direction, the length in the conveying direction becomes long, so that a long space is required for arranging the equipment. For this reason, arrangement | positioning of an induction heating apparatus is restrict | limited. Further, the method of performing the induction heating while conveying the billet in series in the axial direction has a limited position where the billet is carried into the induction heating coil.

  In such a background, the present invention is an induction heating apparatus capable of simultaneously heating a plurality of billets and continuously discharging the billets in a heated state. It aims at providing the structure with the high freedom degree of the position which carries in the billet to a coil.

The invention according to claim 1 is a solenoid structure induction heating coil having a shape in which a cross section is elongated in a longitudinal direction in a direction perpendicular to an axis, and the longitudinal direction is inclined with respect to a horizontal plane, The billet movement comprises: an inclined surface for rolling a plurality of billets in the inclined downward direction inside the induction heating coil; and a billet moving means for moving the billet from the axial direction toward the inside of the induction heating coil. means is a movable along a direction which is stretched in the longitudinal shape of the induction heating coil, in this movable range, Ri can der moving the billet toward the inside of the induction heating coil, wherein On both sides of the induction heating coil in the axial direction, the billet moving means can move the billet within the movable range of the billet moving means. It is an induction heating device according to claim in which retractable insulation plate is disposed to be.

According to the first aspect of the present invention, the billet moves along the longitudinal direction flattened in the direction perpendicular to the axis of the induction heating coil inside the induction heating coil. Then, the billet is carried into the induction heating coil and the billet is discharged from the induction heating coil along the axial direction of the induction heating coil. For this reason, the dimension of the longitudinal direction of an induction heating apparatus can be restrained, and space saving can be achieved. In addition, by allowing the billet moving means to move along the lengthwise direction of the induction heating coil, the billet can be pushed into the induction heating coil in this moving range. According to the invention described in claim 1, the heat insulating plate is opened when the billet is carried into the induction heating coil at a predetermined position or the billet is discharged from the induction heating coil, and the heat insulating plate is opened in other situations. By closing, the reduction in billet heating efficiency can be suppressed.

  According to a second aspect of the present invention, the billet moving means can discharge the billet stored inside the induction heating coil to the outside of the induction heating coil within the movable range of the billet moving means. It is an induction heating apparatus of Claim 1 characterized by the above-mentioned. According to the second aspect of the present invention, the billet can be discharged from the induction heating coil in a range in which the billet moving means can move. In addition, the billet in the induction heating process moves by its own weight along the slope, and its direction is orthogonal to the axial direction of the induction heating coil. The billet can be easily discharged from the induction heating coil. That is, by pushing out the billet in the axial direction perpendicular to the moving direction of the billet that rolls and moves during heating, only the defective billet can be removed from the row.

The invention according to claim 3 is the invention according to claim 1 or 2 , wherein the lowest billet inside the induction heating coil is discharged in a state where a plurality of billets are housed in the induction heating coil. After that, the remaining billet stored is rolled down the inclined surface by its own weight, and a new billet is inserted into the vacant space generated by the rolling by the billet moving means. .

According to the third aspect of the present invention, when the billet heated from the lowermost part inside the inclined induction heating coil is discharged, a slope corresponding to the gap in which the remaining billets are vacated by gravity along the inclination. Roll down. Then, a new billet is carried into the uppermost part where the gap is generated. By repeating this cycle, the billet inside the induction heating coil is heated while gradually rolling downward, and is sequentially discharged from the induction heating coil.

The invention according to claim 4 is the invention according to any one of claims 1 to 3 , wherein a plurality of billets are heated by induction heating while rolling on the inclined surface inside the induction heating coil. It is characterized by.

The invention according to claim 5 is the invention according to any one of claims 1 to 4 , wherein the inclined angle is 3 ° to 10 ° with respect to a horizontal plane.

According to the first aspect of the present invention, in the induction heating apparatus capable of simultaneously heating a plurality of billets and continuously discharging the billets in a heated state, space saving is possible and induction is performed. A configuration with a high degree of freedom in the position of carrying the billet into the heating coil is provided. Moreover, according to invention of Claim 1, the fall of the efficiency of induction heating is suppressed.

  According to the invention described in claim 2, since a mechanism for carrying in the billet into the induction heating coil is used as a mechanism for discharging the defective billet, the defective billet can be obtained without complicating the configuration. The structure which can be discharged | emitted from an induction heating coil is obtained. Further, since billets to be discharged can be selected within a range in which the billet moving means can move, a plurality of billets can be selected as discharge targets.

According to the third aspect of the present invention, the plurality of billets that are heated at the same time are moved inside the induction heating apparatus by rolling due to their own weight, so that the transport mechanism can be omitted and the configuration is simplified.

According to the invention described in claim 4 , since the billet rolls in the heated state, uniform heating is realized.

According to the fifth aspect of the present invention, there is provided a condition in which billet self-running due to its own weight occurs and the billet is free from deformation and damage due to excessive momentum of the self-running billet.

It is the top view (A) and side view (B) of the induction heating apparatus of embodiment. It is a perspective view of an induction heating coil. It is a side view of an induction heating coil. It is a side view which shows an example of the procedure which carries in a billet in the inside of an induction heating coil.

(Configuration of induction heating device)
FIG. 1 shows an induction heating apparatus 100 according to an embodiment. Here, FIG. 1A is a top view, and FIG. 1B is a side view as viewed from the negative Y-axis direction in FIG. The induction heating device 100 includes an induction heating coil 101. FIG. 2 is a perspective view of the induction heating coil 101. The induction heating coil 101 has a solenoid structure in which a cross-section is elongated in a direction perpendicular to the axis and the elongated direction is inclined with respect to a horizontal plane, and a magnetic flux is generated in the Y-axis direction in the interior 101a. When viewed in cross section, a flat solenoid coil-shaped winding portion 101b having a U-shape at both ends and a straight portion connected therebetween is provided.

  The induction heating coil 101 is installed at an angle of 5 ° with respect to the horizontal plane (XY plane in the figure). This angle is suitably about 3 ° to 10 °. If this angle is less than 3 °, the possibility of difficulty in rolling due to the billet's own weight increases. On the other hand, when the angle exceeds 10 °, the momentum of rolling due to the billet's own weight becomes strong, and the possibility that the billet is damaged or deformed due to collision with the end portion or collision with another billet increases. If this angle exceeds 10 °, when the billet is inserted into the induction heating coil 101 and discharged from the induction heating coil 101, the speed of the billet rolling from the adjacent position increases, and the billet The problem that the retraction of the pushing piston is not in time becomes apparent.

  A plurality of billets 102 (seven in the illustrated example) to be heated can be stored in the interior 101a of the induction heating coil 101 arranged in an inclined manner. The billet has a cylindrical shape. The billet material is not particularly limited as long as it is a metal material to be subjected to induction heating, and for example, aluminum, iron, stainless steel, copper, and other alloys can be used. The number of billets that can be stored in the induction heating coil 101 is not limited to seven, and may be any other number as long as it is plural.

  The outside of the induction heating coil 101 is covered with a heat insulating material, and in particular, a heat insulating plate made of a heat resistant ceramic material is attached to the side surface thereof. This heat insulating plate will be described with reference to FIG. FIGS. 3A and 3B show the appearance of the induction heating coil 101 viewed from the negative Y-axis direction in FIG. On the side surface of the induction heating coil 101 viewed from this viewpoint (the lower side surface in FIG. 1A), a heat insulating plate 201 that is vertically slidable is provided. FIG. 3 shows a state in which all billable billets (in this case, a total of seven) are housed inside the induction heating coil 101. Further, FIG. 3 shows an inclined surface 301 arranged inside the induction heating coil 101. The inclined surface 301 extends along the flat direction of the induction heating coil 101, and is inclined from the horizontal plane at the same angle as the induction heating coil 101. A billet is disposed on the inclined surface 301.

  FIG. 3A shows a state in which the heat insulating plate 201 is closed and the billet insertion hole 202 provided in the heat insulating plate 201 can be seen from the outside, and the uppermost billet 210 accommodated therein can be seen from there. Yes. The upper portion refers to a portion in the relatively upward direction of the induction heating coil in a tilted state, and the lower portion refers to a portion in the relatively lower direction. Further, FIG. 3A shows a billet push-out hole 205 for pushing out the lowest billet by a piston in the positive Y-axis direction of FIG. Further, a state where a part of the end face of the lowermost billet 205 is visible from the billet extrusion hole 205 is shown. FIG. 3B shows a state where the heat insulating plate 201 is slid upward and the inside 101a of the induction heating coil 101 is opened to the outside. In the state of FIG. 3B, the end surfaces of the fifth billet from the top stored inside are exposed to the outside. In addition, although detailed description is abbreviate | omitted, parts other than the heat insulation board 201 are also made into the heat insulation structure.

  FIGS. 3C and 3D show the appearance of the induction heating coil 101 as viewed from the positive Y-axis direction in FIG. On the side surface of the induction heating coil 101 viewed from this viewpoint (the side surface on the upper side in FIG. 1A), a heat insulating plate 203 that is vertically slidable is provided. FIG. 3C shows a state in which the heat insulating plate 203 is closed and the billet discharge hole 204 provided in the heat insulating plate 203 can be seen from the outside, and the lowermost billet 211 accommodated therein can be seen from there. Yes. FIG. 3D shows a state where the heat insulating plate 203 is slid upward and the inside 101a of the induction heating coil 101 is opened to the outside. In the state of FIG. 3D, the end faces of the fifth billet from the top stored inside are exposed to the outside.

  As shown in FIG. 1, a heating coil part billet pushing device (heating coil part work pushing device) 103, which is an example of a billet moving means, is arranged on the side surface of the induction heating coil 101. The heating coil part billet extrusion device 103 has a structure capable of moving along the tilt direction of the tilted induction heating coil 101, and inserts the billet into the induction heating coil 100 from a plurality of positions, and the billet induction heating coil. 100 has a function of discharging from 100.

  Hereinafter, the heating coil part billet extrusion apparatus 103 will be described. The heating coil unit billet extrusion apparatus 103 includes a gantry 104 serving as a base. FIG. 1 shows a state in which a billet 105 in a stage before being inserted into the induction heating coil 101 is arranged on the gantry 104. A cylinder 106 is fixed on the gantry 104. A piston 107 can be inserted and removed from the cylinder 106 in the Y-axis direction in the figure, and the billet 105 can be pushed out in the direction of the induction heating coil 100 (positive direction of the Y-axis) by the piston 107. The piston 107 is driven by an electromagnetic actuator or hydraulic pressure.

  The gantry 104 can move in parallel along the inclination direction of the induction heating coil 101 with the two rails 108 arranged along the inclination direction of the induction heating coil 101 inclined in the same manner as the induction heating coil 101. It is in a state. Note that a description of the engagement relationship between the two rails 108 and the gantry 104 is omitted. Between the two rails 108, similarly, a male screw rod 109 arranged along the inclination direction of the induction heating coil 101 is arranged. The male screw rod 109 is rotated by a motor 110. FIG. 1B omits the description of the configuration related to the rail 108 to show the drive mechanism of the gantry 104, and the drawing shows the male screw rod 109 constituting the drive mechanism of the gantry 104. .

  The male screw rod 109 is rotated by a motor 110. A screwing portion 111 having a female screw portion inside is fixed to the lower portion of the gantry 104. The female screw portion of the screwing portion 111 is engaged with the male screw rod 109. When the motor 110 rotates, the male screw rod 109 rotates, and a driving force is generated that moves the screwing portion 111 engaged with the male screw rod 109 along the inclination direction of the induction heating coil 101. By this driving force, the gantry 104 moves in parallel along the inclined longitudinal direction of the induction heating coil 101 (extending direction of the male screw rod 109). By the movement of the gantry 104, the heating coil part billet extrusion device 103 can be moved to an arbitrary position between the position A of the solid line and the position B of the broken line in FIG.

  By enabling the heating coil portion billet pusher 103 to move between the position A and the position B, the billet is inserted into the induction heating coil 101 by the piston 107 in this movement range, and from the induction heating coil 101. Billet can be discharged.

  Corresponding to the billet storage position at the bottom of the induction heating coil 101 arranged at an inclination, the heating coil part billet extrusion device 112 is arranged. The heating coil part billet extrusion device 112 includes a cylinder 113 and a piston 114 that enters and exits from the cylinder 113. As the piston 114 moves in the Y-axis direction in FIG. 1, the billet 211 stored in the lowermost portion of the induction heating coil 101 is pushed out to the billet receiving portion 115. Although not shown, the billet receiving part 115 is inclined in the same manner as the inclination of the induction heating coil 101, and the billet pushed out from the induction heating coil 101 to the billet receiving part 115 by the piston 114 due to this inclination is as follows. Furthermore, it rolls down on the billet receiving portion 116.

  The billet receiving portion 116 is disposed between the uniform heating coil portion extrusion device 117 and the uniform heating coil 120. The uniform heating coil unit extrusion device 117 includes a cylinder 118 and a piston 119. The piston 119 pushes the billet disposed in the billet receiving portion 116 into the uniform heating coil 120. The uniform heating coil 120 is an induction heating coil constituted by a solenoid coil. The uniform heating coil 120 makes the final billet heated uniformly, and the billet is fed to a casting apparatus, a forging apparatus, or the like disposed at the subsequent stage of the induction heating apparatus 100. Auxiliary induction heating is performed to absorb heating state changes (billette temperature changes) due to supply timing fluctuations and the like.

  Reference numeral 121 denotes a billet positioning device 121. The billet positioning device 121 includes a pressing part 122, an arm part 123, a piston 124, and a cylinder 125. The pressing part 122 presses the tip end surface of the billet pushed by the piston 119 toward the inside of the uniform heating coil 120. Thereby, the billet accommodated in the uniform heating coil 120 is positioned. The piston 124 can be moved in and out of the cylinder 125 and can be rotated. The arm part 123 moves the pressing part 122 back and forth in the Y-axis direction by moving the piston 124 in the Y-axis direction. Further, the holding portion 122 is retracted from the axis of the uniform heating coil 120 by the rotation of the piston 124.

  On the outlet side of the uniform heating coil 120 (upper side in FIG. 1A), a rolling conveyance unit 126 having a plurality of rollers is arranged. The billet pushed out from the inside of the uniform heating coil 120 by the piston 116 moves on the transport unit 126 in the positive direction of the Y axis by the rotation of the roller. For example, an injection molding apparatus (not shown) that performs injection molding using a billet that has been heated and made into a semi-molten state is disposed at the tip of the rolling conveyance unit 126. The apparatus arranged in the subsequent stage of the induction heating apparatus 100 is not limited to the injection molding apparatus, and may be another apparatus as long as it uses the billet after heating.

(Induction heat treatment)
Hereinafter, an example of a procedure for performing induction heating of the billet will be described. First, an example of a procedure for storing a plurality of billets in the induction heating coil 101 will be described. FIG. 4 shows an example of a process for storing the billet in the induction heating coil 101 step by step. First, as shown in FIG. 1, the induction heating coil part billet extrusion apparatus 103 in a state where the billet is arranged on the gantry 104 is moved to the lowest position (FIG. 4A).

  Next, as shown in FIG. 3B, the heat insulating plate 201 is slid upward to open the inside of the induction heating coil 101. Next, the piston 107 in FIG. 1 is advanced, the billet on the gantry 104 is pushed in the positive direction of the Y axis, and the billet is pushed into the induction heating coil 101 and inserted. The billet inserted into the induction heating coil 101 in the positional relationship of FIG. 4A rolls down the inclined surface 301 by the action of gravity, and becomes the state of FIG. FIG. 4B shows a billet 302 that is positioned at the bottom of the induction heating coil 101 by rolling the inclined surface 301 by a distance corresponding to two billets from the state of FIG.

  After inserting the first billet, a high-frequency current is passed through the induction heating coil 101 to start induction heating. Next, the heating coil part billet extrusion apparatus 103 is returned to the position shown in FIG. 1A, and the next billet is placed on the gantry 104. And the heating coil part billet extrusion apparatus 103 is moved to the same position as FIG. 4 (A), the same operation | work as the case of the 1st billet is performed, and the 2nd billet is inserted. Since the second billet already has the first billet 302, the second billet rolls the distance of one billet and stops at the position where it touches the billet 302.

  The above operations are repeated, and the third (FIG. 4C), fourth (FIG. 4D), and fifth (FIG. 4E) and billets are sequentially inserted. From the third, the operation is to insert a new billet on the billet that has already been inserted, and the inserted billet does not roll. In this way, billets are sequentially inserted, and seven billets are stored in the induction heating coil 101. Thereafter, the heat insulating plate 201 shown in FIG. 3 is closed, and the state shown in FIGS. 3 (A) and 3 (C) is obtained. Further, the gantry 104 is moved to the position shown in FIG. 1A, and the billet to be loaded next is placed on the gantry 104 to prepare for the reloading operation.

  Thus, the heat treatment in the state of FIG. When the initially stored billet (bottom billet) reaches the prescribed heating state, the piston 114 in FIG. 1 is advanced, and the piston 114 is inserted into the induction heating coil 101 from the billet extrusion hole 205 in FIG. Then, the lowest billet 211 (see FIG. 1) is pushed out to the billet receiving portion 115, and then the piston 114 is retracted. At this time, the next billet located on the upper side of the adjacent slope rolls down due to the action of gravity at the portion where the extruded billet was present.

  The billet pushed to the billet receiving portion 115 rolls down to the billet receiving portion 116. The billet that has moved to the billet receiving portion 116 is inserted into the uniform heating coil 120 through which a high-frequency current is flowing as the piston 119 advances. At this time, the position of the billet on the Y-axis in the uniform heating coil 120 is adjusted by the function of the billet positioning device 121. In the uniform heating coil 120, the billet whose heating uniformity is adjusted moves in the positive direction of the Y axis in FIG. 1 by further advancement of the piston 119, and is transported on the rolling transport unit 126. Sent to the outside.

  In addition, after the billet located at the bottom in the induction heating coil 101 is pushed out to the billet receiving portion 115 by the piston 114, the billet that has become six in the induction heating coil 101 rolls down by one billet. A space for one billet is created at the top. The piston 107 is advanced at the timing when the uppermost empty space is generated, and a new pre-heating billet is inserted into the uppermost portion of the induction heating coil 101 from the billet insertion hole 202 of FIG. The newly inserted billet gradually rolls down and moves each time the bottom billet is sequentially discharged, and is heated in the induction heating coil 101 in the process.

  Thus, the cycle of (1) discharge of the heated billet from the lowermost part of the inclined induction heating coil 101 → (2) insertion of a new billet at the uppermost part where a space is created when the billet rolls down the slope. Repeatedly, a continuous billet heat treatment is performed.

(Defect handling processing)
During the induction heating, there may be a problem that the billet is in a heated state or a problem that makes it difficult to move due to its own weight. An example of how to deal with this problem will be described. For example, assume a case where a defect occurs in the billet 401 in FIG. In this case, the heat insulating plates 201 and 203 in FIG. 3 are opened, and the billet 401 is exposed on the side surface of the induction heating coil 101. In this way, the states shown in FIGS. 3B and 3D are obtained. Next, the heating coil part billet pushing device 103 in FIG. 1 is moved to the billet 401 part in FIG. 3, and the side surface of the billet 401 on the side shown in FIG. Thereby, the billet 401 having a defect is pushed out in the positive direction of the Y axis in FIG. 1 and is forcibly discharged from the induction heating coil 101 halfway.

(Superiority)
In the above-described configuration, the induction heating coil 101 having a solenoid structure having a flat structure when viewed from the axial direction is arranged so as to be inclined from the horizontal plane. Here, the induction heating coil 101 includes an inclined surface 301, and a plurality of billets 102 housed in the induction heating coil 101 are disposed on the inclined surface 301. And the heating coil part billet extrusion apparatus 103 is made into the structure which can move along the inclination direction of the inclined induction heating coil 101, The billet to the induction heating coil 101 inside between the position A and the position B is carried out. Can be brought in.

  According to this configuration, the final billet discharge direction (Y-axis direction) and the billet conveyance direction during heating (the direction of self-running while rolling) (X-axis direction) are orthogonal to each other. Occupied space is reduced as compared to a structure that is heated while moving in the direction and further discharged. Further, the billet can be carried into the induction heating coil 101 between the positions A and B, and the degree of freedom of the position where the billet is carried into the induction heating coil is high.

  In addition, by arranging the induction heating coil 110 at an angle and allowing the billet to move while rolling under its own weight, it is not necessary to arrange a billet conveying device in the heating coil, and the structure is simplified. When the transfer device is arranged in the heating coil, the equipment cost becomes high and the transfer device is damaged due to the high temperature, so that the maintenance cost becomes high. However, in the case of this embodiment, the problem does not occur.

  In addition, as shown in FIG. 4, the billet is moved when the billet is carried into the induction heating coil 101 by moving the heating coil part billet extrusion device 103 in parallel along the longitudinal direction of the opening of the inclined induction heating coil 101. The rolling distance can be suppressed, and the problem that the billet rolls over a long distance, thereby causing damage to the billet or the like can be avoided.

  In addition, since the billet moves while rotating around the direction of the applied magnetic flux inside the induction heating coil 110, the uniformity of the heating state inside the billet can be obtained.

  Further, when a problem occurs in the billet inside the induction heating coil 101, the defective billet can be easily discharged from the inside of the induction heating coil 101 by the heating coil part billet pusher 103. In a structure in which billets are linearly arranged in the axial direction and induction heating is performed while being conveyed through the induction heating coil, if a failure occurs in a part of the billet during heating, it is easy to eliminate only the defective billet. And complicated work is required. On the other hand, in the induction heating apparatus of the present embodiment, the defective billet can be selectively eliminated with a simple operation.

  The present invention can be used for an induction heating apparatus.

  DESCRIPTION OF SYMBOLS 100 ... Induction heating apparatus, 101 ... Induction heating coil, 101a ... Inside of induction heating coil, 101b ... Winding part of induction heating coil, 102 ... Billet, 103 ... Heating coil part billet extrusion apparatus, 104 ... Base, 105 ... Billet DESCRIPTION OF SYMBOLS 106 ... Cylinder 107 ... Piston 108 ... Rail 109 ... Male thread rod 110 ... Motor 111 ... Screwing part 112 ... Heating coil part billet extrusion apparatus 113 ... Cylinder 114 ... Piston 115 ... Billet receiving part 116 ... Billet receiving portion, 117 ... Uniform coil portion extrusion device, 118 ... Cylinder, 119 ... Piston, 120 ... Uniform heating coil, 121 ... Billet positioning device, 122 ... Pressing portion, 123 ... Arm portion, 124 ... Piston, 125 ... Cylinder, 126 ... Rolling conveyance unit, 201 ... Heat insulation plate, 202 ... Letting hole 203, heat insulating plate, 204 ... billet discharge hole, 205 ... billet extrusion hole, 210 ... uppermost billet, 211 ... lowermost billet, 301 ... inclined surface, 302 ... billet, 401 ... Billet.

Claims (5)

An induction heating coil of a solenoid structure having a shape in which a cross section is elongated in a longitudinal direction in a direction perpendicular to an axis, and the longitudinal direction is inclined with respect to a horizontal plane;
An inclined surface for rolling a plurality of billets in the inclined downward direction inside the induction heating coil;
Billet moving means for moving the billet from the axial direction toward the inside of the induction heating coil,
The billet moving means is movable along the direction extended in the longitudinal shape of the induction heating coil, and the billet can be moved toward the inside of the induction heating coil within the movable range. The
An induction heat-insulating plate that allows the billet movement means to move the billet within the movable range of the billet movement means is disposed on both sides in the axial direction of the induction heating coil. Heating device.   The billet moving means can discharge the billet stored inside the induction heating coil to the outside of the induction heating coil in the movable range of the billet moving means. The induction heating device described in 1. In a state where a plurality of billets are housed in the induction heating coil,
After the lowest billet inside the induction heating coil is discharged, the remaining billet stored rolls down the inclined surface by its own weight, and a new billet is formed in the empty space generated by the rolling. induction heating apparatus according to claim 1 or 2, characterized in that it is inserted by the billet moving means. The induction heating apparatus according to any one of claims 1 to 3 , wherein a plurality of billets are heated by induction heating while rolling on the inclined surface inside the induction heating coil. The induction heating device according to any one of claims 1 to 4 , wherein the inclined angle is 3 ° to 10 ° with respect to a horizontal plane.

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