CN107979203A - Slot wedge, Stator and electrical machine and the method for manufacturing the slot wedge - Google Patents

Abstract

The invention provides a slot wedge, a stator and a motor as well as a method for manufacturing the slot wedge. The slot wedge used for the stator core of the motor includes a laminated body formed by stacking a plurality of magnetically conductive sheets, and the laminated body is in the shape of a strip, wherein the slot wedge is provided with a plurality of ventilation slots, the The ventilation slots are formed through the laminated body along the radial direction of the stator core. The use of the slot wedge for the stator core of the motor can effectively reduce harmonics and improve the distribution of air gap magnetic flux, so as to improve the working efficiency and rated power of the motor, and at the same time reduce the heating of the motor and prolong the service life of the motor .

Description

Slot wedge, stator and electric machine and method of manufacturing same

technical field

The present invention relates to the technical field of wind power generating sets, and more specifically, to a slot wedge, a stator, a motor and a method for manufacturing the slot wedge.

Background technique

At present, the slot wedges usually used in the motors of wind turbines are insulating slot wedges. This is because the insulating slot wedges can only fix the windings, and the performance is single, and the insulating slot wedges have the characteristics of large no-load current of the motor and high core loss of the motor. , Stator temperature rise and other shortcomings. In addition, most of the existing slot wedges have a rectangular structure or an inverted triangular structure, and the contact friction force is small, and the slot wedges are easy to detach.

Therefore, there is a need for a slot wedge that can reduce the loss of the motor core, reduce the temperature rise and prevent detachment.

Contents of the invention

In order to solve the above technical problems, the present invention provides a slot wedge for a stator core of a motor, a stator, a motor and a method for manufacturing the slot wedge, which can reduce the core loss and temperature rise of the motor.

According to one aspect of the present invention, there is provided a slot wedge for a stator core of a motor, the slot wedge includes a laminated body formed by stacking a plurality of magnetically conductive sheets, and the laminated body is in the shape of a strip, wherein The slot wedge is provided with a plurality of ventilation slots, and the ventilation slots are formed by penetrating through the stacked body along the radial direction of the stator core. Since the slot wedge includes a plurality of magnetically conductive pieces, when the magnetic flux passes through the slots of the stator core, the amplitude of the magnetic flux in the core teeth is reduced, the pulse vibration loss is reduced, the magnetic density is more uniform, and the no-load additional loss. In addition, since the slot wedge is provided with the ventilation slot, the temperature rise of the motor can be reduced. The temperature rise of the motor is reduced, and the high-order harmonics of the air-gap magnetic field are reduced, so that the no-load current is reduced, and the vibration and noise of the motor can also be reduced.

According to an exemplary embodiment of the present invention, the position and number of the ventilation slots correspond to the position and number of the ventilation grooves of the stator core respectively, and the slot wedges are installed in the notches of the stator core In the state, the ventilation groove communicates with the corresponding ventilation groove to better dissipate heat, thereby further effectively reducing the temperature rise of the motor.

According to an exemplary embodiment of the present invention, the magnetic permeable sheet may include a silicon steel sheet. Silicon steel sheet slot wedges can reduce harmonics, pulse vibration loss and iron core loss, so it can reduce loss and reduce motor temperature rise. In addition, the magnetically permeable sheet is a silicon steel sheet with strong magnetic permeability, so that the magnetic permeability of the teeth is increased, so that the starting torque and the maximum torque are reduced. According to an exemplary embodiment of the present invention, the magnetically conductive sheet can be a self-adhesive silicon steel sheet, so that the plurality of magnetically conductive sheets can be conveniently stacked and bonded to each other to form a laminated body without other fasteners. Fasten the plurality of magnetic permeable sheets.

According to an exemplary embodiment of the present invention, the two adjacent magnetic conductive sheets in the laminate are combined by pressing and buckling; or the corresponding positions of the plurality of magnetic conductive sheets are provided with through holes, through which the bolts pass through. The plurality of magnetically conductive sheets are fastened together through the through holes of each magnetically conductive sheet, so that the magnetically conductive sheets can be designed more flexibly, and the selection range of the magnetically conductive sheets is expanded.

According to an exemplary embodiment of the present invention, the end portion of the slot wedge in the axial direction of the stator core may be formed with an inclined guide surface for guiding the end portion of the slot wedge to be easily inserted into the stator iron core. in the notch of the core.

According to an exemplary embodiment of the present invention, the cross-section of the slot wedge may be trapezoidal, so that the slot wedge matches the shape of the notch, and the contact area is increased to provide strong resistance, thereby preventing the slot wedge from out of the notch.

According to an exemplary embodiment of the present invention, the angle formed by the extension lines of the sides forming the two waists of the trapezoid of the slot wedge may be between 45° and 70°, so that the sides of the slot wedge The edge matches the shape of the notch of the stator core, and the surface of the slot wedge can be provided with an anti-rust film to prevent the slot wedge from rusting and prolong its service life.

According to another aspect of the present invention, a stator is provided, the stator includes the stator core and the above-mentioned slot wedge, and the slot wedge is inserted into the slot of the stator core.

According to another aspect of the present invention, there is provided an electrical machine comprising the above-mentioned stator.

According to another aspect of the present invention, there is provided a method for manufacturing the slot wedge as described above, the method comprising: punching the plurality of magnetically permeable sheets; stacking the punched plurality of magnetically conductive sheets into a mold to form the stacked body; fasten the stacked mold with mold bolts to compact the stacked body; send the compacted stacked body into an oven for curing; After the laminated body is cooled, demoulding is performed; and the ventilated slot is formed by punching the demolded laminated body to obtain the slot wedge, wherein the magnetically conductive sheet is a self-adhesive magnetically conductive piece.

According to an exemplary embodiment of the present invention, the method may further include: after fastening the stacked mold with mold bolts to compress the laminated body, detecting the height, lamination coefficient and flatness of the end face of the laminated body ; and/or after obtaining the slot wedge, detecting the height of the stack.

According to an exemplary embodiment of the present invention, the plurality of self-adhesive magnetic permeable sheets are self-adhesive silicon steel sheets.

According to an exemplary embodiment of the present invention, the method may further include: forming an inclined guide surface at an end portion of the slot wedge in an axial direction of the stator core.

According to an exemplary embodiment of the present invention, the method may further include: forming an antirust film on a surface of the wedge.

According to another aspect of the present invention, there is provided a method for manufacturing the slot wedge as described above, the method comprising: punching the plurality of magnetically conductive sheets, and opening through holes in the plurality of magnetically conductive sheets; Laminating the punched magnetically conductive sheets, using bolts to pass through the through holes of each magnetically conductive sheet to fasten the multiple magnetically conductive sheets together to form the laminate; and The laminate performs punching to form the ventilation slots to obtain the slot wedges.

According to another aspect of the present invention, there is provided a method for manufacturing the slot wedge as described above, the method comprising: punching the plurality of magnetically conductive sheets, and The buckle and the corresponding buckle groove are provided on the opposite side; the buckle and the buckle groove of two adjacent magnetic conductive sheets are pressed and combined, so that the multiple magnetic conductive sheets are laminated and pressed to form the laminated body; and performing punching on the laminated body to form the ventilation slot to obtain the slot wedge.

The use of the slot wedge for the stator iron core of the motor can effectively reduce harmonics and improve the distribution of air gap magnetic flux, so as to improve the working efficiency and rated power of the motor, and at the same time reduce the heat generation of the motor and prolong the service life of the motor .

Description of drawings

Exemplary embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, and the above and other features and advantages of the present invention will become clearer. In the accompanying drawings:

FIG. 1 is a schematic perspective view of a slot wedge according to an exemplary embodiment of the present invention;

FIG. 2 is a schematic left side view of the slot wedge shown in FIG. 1 according to an exemplary embodiment of the present invention;

3 is a schematic front view of the slot wedge shown in FIG. 1 according to an exemplary embodiment of the present invention;

4 and 5 show schematic views of installing a slot wedge into a slot of a stator core of an electric motor according to an exemplary embodiment of the present invention.

Explanation of reference numbers:

1: slot wedge; 2: stator core; 21: core teeth; 3: slot; 11: laminate; 12: ventilation slot.

Detailed ways

Embodiments of the invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

A slot wedge 1 and a manufacturing method thereof according to an exemplary embodiment of the present invention will be described below with reference to FIGS. 1 to 5 . Fig. 1 is a schematic perspective view of a slot wedge 1 according to an exemplary embodiment of the present invention; Fig. 2 is a schematic left view of a slot wedge 1 shown in Fig. 1 according to an exemplary embodiment of the present invention; Fig. 3 is a schematic diagram of a slot wedge according to the present invention A schematic front view of a slot wedge 1 shown in FIG. 1 of an exemplary embodiment of the invention; FIGS. 4 and 5 show how the slot wedge 1 is installed to the stator core 2 of a motor according to an exemplary embodiment of the invention Schematic diagram of the inside of notch 3. The slot wedge 1 according to the exemplary embodiment of the present invention may be used at the notch 3 between the adjacent core teeth 21 of the stator core 2 of the motor.

The slot wedge 1 for the stator core 2 of a motor according to an exemplary embodiment of the present invention may include a laminated body 11 formed by laminating a plurality of magnetic permeable sheets. A plurality of ventilation slots 12 are also provided on the slot wedge 1 , and the ventilation slots 12 are formed through the laminated body 11 along the radial direction of the stator core 2 .

Since the magnetically permeable sheet is made of magnetically permeable material, the slot wedge 1 is a magnetic slot wedge. According to an example of the present invention, each of the plurality of magnetically permeable sheets is a silicon steel sheet with strong magnetically permeable capability. The hysteresis loop of the silicon steel sheet is small, which reduces the hysteresis loss and greatly reduces the degree of heat generation. By laminating a plurality of silicon steel sheets to form the slot wedge 1, the eddy current loss can also be reduced, and when the magnetic flux passes through the slot 3 of the stator core 2, the amplitude of the magnetic flux in the core teeth 21 is reduced, the pulse vibration loss is reduced, and the magnetic flux is reduced. The density is more uniform, and the no-load additional loss can be reduced.

In addition, since the slot wedge 1 is provided with ventilation slots 12 penetrating the laminated body 11 along the radial direction of the stator core 2, and the positions and numbers of the ventilation slots 12 correspond to the positions and numbers of the ventilation grooves of the stator core 2 respectively , and when the slot wedge 1 is installed in the notch 3 of the stator core 2, the ventilation groove 12 communicates with the corresponding ventilation groove, thereby effectively reducing the temperature rise of the motor. The temperature rise of the motor is reduced, and the high-order harmonics of the air-gap magnetic field are reduced, so that the no-load current is reduced, and the vibration and noise of the motor can also be reduced. As an example, the ventilation slots 12 may be symmetrically provided in two sides of the slot wedge 1 that are opposite to each other in the radial direction of the stator core 2 or formed in only one of the two sides.

As shown in Figure 1, the slot wedge 1 is elongated as a whole, and as shown in Figure 2, the cross section of the slot wedge 1 taken along the radial direction of the stator is trapezoidal, and the slot along the axial direction of the stator When the wedge 1 is installed at the notch 3 of the stator core 2 of the motor, the shape of the slot wedge 1 matches the notch 3, so that the contact area is increased to provide strong resistance, thereby preventing the slot wedge 1 from falling out of the notch 3. break away.

Preferably, the corners of two adjacent sides of the slot wedge 1 are rounded and transitioned to avoid damage to the stator core 2 and the winding coil when the slot wedge 1 is installed in the notch 3 of the stator core 2 of the motor. cause damage.

The angle α formed by the extension lines of the sides of the two waists forming the trapezoidal section of the slot wedge 1 can be between 45° and 70°. Preferably, referring to Fig. 2, when the angle α' of the dovetail portion of the dovetail-shaped notch 3 of the stator core 2 is 60 degrees, the included angle α can be set to 60 degrees. However, the present invention is not limited thereto. In practical applications, the angle α can be reasonably designed according to the shape of the slot 3 of the stator core 2, so that the slot wedge 1 can match the slot 3, and contact as large an area as possible. For example, the angle α can be designed according to the angle α' of the dovetail portion of the dovetail slot 3 of the stator core 2 (refer to FIG. 5 ).

In order to facilitate the installation of the slot wedge 1 into the notch 3 of the stator core 2, an inclined guide surface may be formed at the end of the slot wedge 1 in the axial direction of the stator core 2 for guiding the end of the slot wedge 1. The part is easily inserted into the slot 3 of the stator core 2. For example, the inclined guide surface may be formed by forming a chamfer β of about 15° at an end portion of the top surface of the wedge 1 in the axial direction of the stator core 2 . The inclined guide surface can only be formed on one end of the slot wedge 1, obviously, it can also be formed on both ends of the slot wedge 1, so that any one end of the slot wedge 1 can be inserted into the notch 3 during installation, so that the installation direction is not affected. restrictions for more flexible installation. In addition, the size of the chamfer β is not limited to the above-mentioned approximately 15°. In actual use, the chamfer β can be flexibly designed according to the shape of the notch 3, as long as it facilitates the installation of the slot wedge 1 into the notch 3 That's it.

In addition, in order to prevent the slot wedge 1 from rusting and improve the service life of the slot wedge 1, an anti-rust film can be provided on the surface of the slot wedge 1. According to an example, the anti-rust film can be formed by spraying anti-rust paint.

As shown in FIG. 4 , the slot wedge 1 according to the exemplary embodiment of the present invention can be inserted into the motor by inserting its end having the inclined guide surface into the motor while keeping the inclined guide surface facing the axial center of the stator core 2 . In the notch 3 between the core teeth 21 of two adjacent stator cores 2 , and then use a suitable tool to push the slot wedge 1 into the notch 3 .

By comparing the performance of using the magnetic slot wedge according to the exemplary embodiment of the present invention with the performance of the existing non-magnetic slot wedge for a 1.5MW motor and comparing it with the analysis and calculation of the finite element software Magnet, the effect of using the magnetic slot wedge is verified . From the actual measurement and calculation results, no matter using the magnetic slot wedge according to the exemplary embodiment of the present invention or using the existing non-magnetic slot wedge, both of them have little influence on the no-load back electromotive force of the motor, which is mainly Since the 1.5MW motor adopts a slotted winding and the rotor is skewed by 2.5mm, the cogging harmonics in the back electromotive force are cancelled. In addition, the magnetic slot wedge and non-magnetic slot wedge also affect the loss and noise of the motor. The loss of the motor caused by the slot wedge is mainly manifested in the surface loss of the stator core and the eddy current loss of the rotor magnet and yoke. The influence of the slot wedge on the iron loss of the stator is mainly due to the hysteresis and eddy current loss generated by the high-order space harmonics on the tooth surface of the stator core. For a 1.5MW motor, calculated by the finite element software Magnet, using the motor of the existing non-magnetic slot wedge, the eddy current losses of the magnetic steel and the yoke are respectively 2411.2W and 380W, while using the magnetic The eddy current losses of the slot wedge motor, magnet and yoke are 1152.8W and 224W respectively. Compared with the existing non-magnetic slot wedge motor, the magnetic slot wedge motor according to the exemplary embodiment of the present invention reduces the eddy current loss of the magnet and the yoke by more than 50%. In addition, the use of silicon steel type magnetic slot wedges can also effectively reduce the noise of the generator.

Therefore, according to the slot wedge 1 of the stator core 2 of the motor according to the exemplary embodiment of the present invention, the motor can reduce the excitation current, improve the power factor, and improve the work efficiency by 1%-2%; the slot wedge 1 can reduce The iron core loss is about 40%, which reduces the temperature rise of the motor and reduces electromagnetic noise and vibration, thereby prolonging the life of the motor; in addition, because the slot wedge 1 is made of laminated magnetic sheets, the magnetic permeability of the motor is enhanced, thereby reducing starting torque.

A stator according to another exemplary embodiment of the present invention includes a stator core 2 and a slot wedge 1 as described above, wherein the slot wedge 1 is inserted into the slot 3 between adjacent core teeth 21 of the stator core 2 middle.

A motor according to another exemplary embodiment of the present invention includes the stator as described above.

The magnetically conductive sheet used in the slot wedge 1 as described above can be a self-adhesive magnetically conductive sheet, or a buckle-type or perforated magnetically conductive sheet. The method for making the slot wedge 1 by using the self-adhesive magnetic conductive sheet and the buckle-type or perforated magnetic conductive sheet will be described respectively below. As an example, in order to produce a slot wedge with an overall thickness between 5mm-7mm, a length between 300-350mm and a trapezoidal cross-section, approximately 15-20 pieces with a thickness of 0.35mm may be used in the method described below silicon steel sheets.

A method for manufacturing the above-mentioned slot wedge using self-adhesive magnetically conductive sheets will be described, the method comprising: punching the plurality of magnetically conductive sheets; stacking the punched self-adhesive magnetically conductive sheets in a stacked mold, to form the stacked body 11; fasten the stacked mold with mold bolts to compact the stacked body 11; send the compacted stacked body 11 into an oven to perform curing; after the solidified stacked body 11 is cooled, perform demolding; and performing punching on the demolded laminated body 11 to form ventilation slots 12 to obtain slot wedges 1 .

The plurality of self-adhesive magnetic conductive sheets are self-adhesive silicon steel sheets.

In the process of punching a plurality of self-adhesive silicon steel sheets, the width of the plurality of self-adhesive silicon steel sheets can be gradually reduced, so that the plurality of self-adhesive silicon steel sheets can be formed into elongated strips with a trapezoidal cross section.

The method may further include: after using mold bolts to fasten the stacked mold to compress the laminated body, detecting the height, lamination coefficient and flatness of the end face of the laminated body to check the Whether the bonding between them is smooth and dense, if the height, lamination coefficient and end surface flatness of each place are inconsistent, it can be adjusted by adjusting the mold bolts at the corresponding positions. As an example, the pressure for compressing the laminated body can be controlled between 3.5MPa-3.6MPa.

In the process of sending the compacted laminate into an oven for curing, the temperature of the oven can be set at 200°C±5°C, and the constant temperature baking time can be 2h. Then, demoulding is performed when the cured laminate is cooled to 50° C. or lower.

In addition, the method may further include: after obtaining the slot wedge 1 , detecting the height of the laminated body, so as to check whether the bonding between the silicon steel sheets is smooth and compact.

During the process of punching holes to form the ventilation slots in the laminated body after demoulding, preferably, holes can be punched symmetrically in the sides of the two waists of the trapezoid of the slot wedge 1 to form the ventilation slots. 12.

In addition, the method may further include the steps of: forming a chamfer of 15° at the end of the slot wedge 1 in the axial direction of the stator core 2 to form an inclined guide surface; Rounding is performed on the corners of two adjacent sides.

The method may further include: spraying anti-rust paint on the surface of the slot wedge 1 to form an anti-rust film.

The method of making the above-mentioned slot wedge by using a snap-on type or a perforated magnetic sheet will be described below, and the steps of forming ventilation slots in the following method are the same as those formed in the above-mentioned method of using a self-adhesive magnetic sheet to manufacture the above-mentioned slot wedge. The steps of ventilation slots and the like are similar or identical, and their similar or identical descriptions will be omitted here. Therefore, only the steps different from the above-mentioned method of using self-adhesive magnetic permeable sheets to manufacture the above-mentioned slot wedges will be described below.

The method for manufacturing the above-mentioned slot wedge by adopting a buckle-type magnetically conductive sheet may include the following steps: punching the plurality of magnetically conductive sheets, and opening through holes in the plurality of magnetically conductive sheets; The magnetically conductive sheets are stacked, and the plurality of magnetically conductive sheets are fastened together by bolts passing through the through holes of each magnetically conductive sheet to form a laminated body 11; and the laminated body 11 is punched to form a ventilation slot 12 , to obtain slot wedge 1.

The method for manufacturing the above-mentioned slot wedge by using a perforated magnetic sheet may include the following steps: punching the plurality of magnetically conductive sheets, and setting buckles on one side of each magnetically conductive sheet and on the other side opposite to the one side sheet and the corresponding buckle slot; the buckle and the buckle slot of two adjacent magnetic conductive sheets are combined by pressing, so that the plurality of magnetic conductive sheets are stacked and pressed to form a laminated body 11; and the laminated body 11 performs punching to form ventilation slots 12 to obtain slot wedges 1 .

Using the slot wedge for the stator core of the motor according to the exemplary embodiment of the present invention and the slot wedge manufactured by the above method, the stator and the motor including the slot wedge can effectively reduce harmonics and improve the air gap magnetic flux distribution, In order to improve the working efficiency and rated power of the motor, it can also reduce the heating of the motor and prolong the service life of the motor.

While the invention has been particularly shown and described with reference to exemplary embodiments of the invention, it should be understood by those skilled in the art that modifications may be made thereto without departing from the spirit and scope of the invention as defined by the claims. Various changes in form and detail.

Claims (15)

1. A slot wedge for a stator core of an electric motor, characterized in that, the slot wedge (1) comprises a stack (11) formed by stacking a plurality of magnetically conductive sheets, and the stack (11) ) is strip-shaped, wherein, the slot wedge (1) is provided with a plurality of ventilation slots (12), and the ventilation slots (12) penetrate the radial direction of the stator core (2) Laminate (11) is formed. 2. The slot wedge according to claim 1, characterized in that, the position and quantity of the ventilation groove (12) correspond to the position and quantity of the ventilation groove of the stator core (2) respectively, and in the When the slot wedge (1) is installed in the notch (3) of the stator core (2), the ventilation groove (12) communicates with the corresponding ventilation groove. 3. The slot wedge according to claim 1, wherein the magnetic permeable sheet comprises a silicon steel sheet. 4. The slot wedge according to claim 3, wherein the magnetic conductive sheet is a self-adhesive silicon steel sheet. 5. The slot wedge according to claim 3, characterized in that, two adjacent silicon steel sheets in the laminate (11) are combined by pressing and buckling; or The corresponding positions of the multiple silicon steel sheets are provided with through holes, and the bolts pass through the through holes of the silicon steel sheets to fasten the multiple silicon steel sheets together. 6. The slot wedge according to claim 1, characterized in that the end portion of the slot wedge (1) in the axial direction of the stator core (2) is formed with an inclined guide surface. 7. The slot wedge according to claim 1, characterized in that, the cross-section of the slot wedge (1) is trapezoidal, and the extension of the sides of the two waists of the trapezoid formed in the slot wedge (1) The angle formed by the lines is between 45° and 70°, and the surface of the slot wedge (1) is provided with an antirust film. 8. A stator, characterized in that the stator comprises the stator core (2) and the slot wedge (1) according to any one of claims 1-7, the slot wedge (1) is inserted into It is arranged in the notch (3) of the stator core (2). 9. A motor, characterized in that the motor comprises the stator according to claim 8. 10. A method of manufacturing the slot wedge of claim 1, said method comprising: Punching the plurality of magnetically conductive sheets; stacking the plurality of punched magnetic conductive sheets in a stacked mold to form the stacked body (11); Utilizing mold bolts to fasten the stacked mold to compress the stacked body (11); Sending the compacted laminate (11) into an oven for curing; After the solidified laminate (11) is cooled, demoulding is performed; and performing punching on the demolded laminate (11) to form the ventilation slot (12), so as to obtain the slot wedge (1), Wherein, the magnetically conductive sheet is a self-adhesive magnetically conductive sheet. 11. The method of claim 10, further comprising: After tightening the stacked mold with mold bolts to compress the laminated body (11), the height, lamination coefficient and end surface flatness of the laminated body (11) are detected; and/or After obtaining the slot wedge (1), the height of the stack (11) is checked. 12. The method according to claim 10, wherein the plurality of self-adhesive magnetically conductive sheets are self-adhesive silicon steel sheets. 13. The method according to claim 10, characterized in that, the method further comprises: forming an inclined guide surface at the end of the slot wedge (1) in the axial direction of the stator core (2) ; Form an anti-rust film on the surface of the slot wedge (1). 14. A method of manufacturing the slot wedge of claim 1, said method comprising: Punching the plurality of magnetically conductive sheets, and opening through holes in the plurality of magnetically conductive sheets; Laminating the punched magnetically conductive sheets, using bolts to pass through the through holes of each magnetically conductive sheet to fasten the multiple magnetically conductive sheets together to form the laminate (11); and Punching is performed on the laminated body (11) to form the ventilation slot (12) to obtain the slot wedge (1). 15. A method of manufacturing the slot wedge of claim 1, said method comprising: Punching the plurality of magnetically conductive sheets, and setting buckle pieces and corresponding buckle piece slots on one side of each magnetically conductive sheet and the other side opposite to the one side; The button pieces and the button grooves of two adjacent magnetic conductive sheets are press-fitted together, so that the plurality of magnetic conductive sheets are laminated and compressed to form the laminated body (11); and Punching is performed on the laminated body (11) to form the ventilation slot (12) to obtain the slot wedge (1).