JPH10202345A - Continuous casting apparatus for current collecting grid body for lead battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate such trouble as the occurrence of a cold shut between an upper frame skeleton and lug parts of a cast current collecting body and the occurrence of a defective product. SOLUTION: On the bottom surface of lug part forming recessed part 10CPY communicated with an upper frame skeleton forming groove 10C1 for casting the upper frame skeleton of a current collecting grid body 10P in each grid body forming part 10C, at least one piece of projecting line 10 extended by crossing at the right angle to the turning direction of a turning drum mold 1 is arranged. A continuous casting apparatus is composed of the turning drum mold 1 engraving plural grid body forming parts forming at least two lines of recessed grooves 11, 11 along the projecting line so as to continue the grid body forming part 10C for casting the current collecting grid body 10P on the whole periphery of the outer peripheral surface 1a, and a molten metal supplying part 2 for continuously supplying into this grid body forming part 10C. Further, on the inner peripheral surface, ribs parallel engraved so as to provide each lug part forming recessed part 10 for cast the lug part of the current collective grid body 10P on the whole periphery of the outer peripheal surface of the turning drum mold and fitted to each forming grooves 10CP1, 10CP3, 10CP2 in the turning direction, are arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting apparatus for a current-collecting grid for a lead-acid battery.

[0002]

2. Description of the Related Art Conventionally, an apparatus for continuously casting a current-collecting grid for a lead-acid battery using a rotary drum mold and a molten metal supply unit is known. FIG. 11 to FIG. 13 show an example thereof. The rotary drum mold A includes a grid body forming portion C for continuously casting the current collecting grid body P shown in FIG. Ear forming recess CPY for casting ear PY of grid P
Are formed along the axis a2 of the rotary drum mold A, and a plurality of them are continuously engraved. On the other hand, the molten metal supply section B is formed such that its inner surface is formed on the outer peripheral surface a1 of the rotary drum mold A.
Is formed on an arcuate surface b1 that matches
1 is provided with a rectangular opening recess b2 extending in the width direction thereof, that is, extending parallel to the axial direction of the rotary drum mold 1, and a housing of the molten metal supply unit B is provided on the bottom surface of the opening recess b2. Gates b3, b that communicate between the tube D that supplies the molten lead through the left and right side surfaces in the width direction and the inside of the opening recess b2
The upper frame bone forming groove CP1 for casting the upper frame bone P1, the lower frame bone P2, the intermediate frame bones P3, P3,. Are arranged at positions corresponding to the lower frame bone forming grooves CP2, the intermediate frame bone forming grooves CP3, CP3,... Further, the upper inner surface area of the arc-shaped inner surface b1 of the molten metal supply section B has The upper frame bone forming groove CP1, the lower frame bone forming groove CP2, the intermediate frame bone forming grooves CP3, CP3,.
It is preferable that ribs b4, b4,... Having the same cross-sectional shape as P2, CP3, CP3,... Are arranged such that the lower end of each rib b4 extends to the upper edge of the elongated rectangular opening recess b2. These ribs b4, b4, ...
Is generally prevented from flowing from the gates b3, b3,... Into the respective forming grooves in the vertical direction in the direction opposite to the rotation direction indicated by the arrow of the rotary drum A.

[0003]

However, the above-described conventional apparatus has the following disadvantages. That is, while the rotating drum A is rotated, the gate b of the molten metal supply unit B is rotated.
The molten lead is supplied from the elongated hole b2 to the outer peripheral surface of the rotary drum mold A at a required pressure through the slots b2,. 15 (indicated by oblique lines), and each current collector grid P is
And the molten metal supply unit B are sequentially cast, and the current collecting grids P, P,. It is continuously cast as a strip E composed of a series of current collecting grids P by pulling and peeling through a guide roller, and thereafter, each of the continuously cast current collecting grids is filled with an active material paste.
Between the current collecting grids P, P is cut at a cut portion indicated by n in FIG. 15 and used as a lead storage battery electrode plate. In the above continuous casting step, one end of the opening recess b2 is cut. As shown by the imaginary line in FIG. 15, the lead molten metal discharged from the sprue b3 corresponding to the upper bone frame forming groove CP1 goes straight into the upper frame bone forming groove CP1 in front of the molten metal and flows into the upper frame bone. Ear forming recess CPY having a wider surface area than upper frame bone forming groove CP1 communicating with the side of forming groove CP1.
The molten lead flowing into the upper frame forms a turbulent flow such as circulating flow, and collides from the side with the flow of the molten metal that has flowed straight into the upper bone frame forming groove CP1. As a result, the cast current collecting grid body P is
As shown in FIG. 16, a defective product having a crack K due to a hot junction was likely to occur between the ear PY and the upper frame bone P1.

[0004]

SUMMARY OF THE INVENTION The present invention provides an apparatus for continuously casting a current-collecting grid for a lead-acid battery, which solves the above-mentioned disadvantages of the conventional apparatus. A rotary drum mold in which a plurality of grid body forming portions are continuously formed, and a molten metal supply that slidably contacts the molten lead with the outer peripheral surface of the rotary drum mold and continuously supplies the molten metal to the grid body forming portion. On the inner peripheral surface of the casing of the molten metal supply unit, and on the entire outer peripheral surface of the rotary drum mold, there are formed ear molding concave portions for casting the lugs of the current collecting grid body along the axial direction thereof. In a continuous casting apparatus for a lead-acid battery grid body, which is provided with ribs that are cut in parallel so as to have and fit into respective forming grooves in the rotation direction, the current-collecting grid body of each grid body forming portion is formed. On the bottom surface of the ear molding concave portion communicating with the upper frame bone molding groove for casting the upper frame bone, Provided with at least one ridge extending perpendicular to the rotational direction of the rotary drum mold, characterized in that to form at least two rows of grooves extending along the convex strip. Further, the present invention provides a method for continuously casting a current-collecting grid for a lead-acid battery having a foot, wherein a rotating direction of the rotary drum mold is provided on a bottom surface of a foot forming recess for casting a foot of each grid body forming part. At least one ridge extending perpendicular to the ridge, and at least two ridges extending along the ridge
The groove of the strip is arranged in the rotating direction of the rotary drum.

[0005]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIGS. 1 to 5 show a continuous apparatus for a current-collecting grid for a lead-acid battery according to an embodiment of the present invention. The configuration of a rotary drum mold and a molten metal supply unit is continuously formed on the peripheral surface of the rotary drum mold. Excluding the mold of the formed lattice body molding part,
There is no change from the conventional one. That is, according to the present invention, as clearly shown in FIG. 3, each of the current-collecting grid bodies continuously cut along the entire outer peripheral surface of the rotary drum mold 1 is continuously cast. Lattice forming parts 10C, 10C, ...
Are provided with the ridges 10 as described in detail below. More specifically, FIG. 1 shows a rotating drum mold 1 and the rotating drum 1.
FIG. 2 is a side view of a part of an example of a continuous casting apparatus for a current-collecting grid for a lead-acid battery according to the present invention, comprising a molten metal supply unit 2 for supplying molten lead to an outer peripheral surface 1a of the rotary drum mold. 1, a plurality of grid forming parts 10C for sequentially and continuously casting a current collecting grid 10P, which will be described in detail later, as shown in FIG. Engraved. 1b shows a rotation axis.

As shown in FIGS. 1 and 2, the molten metal supply unit 2 is composed of a fixed mold casing, and an inner surface 2a of the molten mold supply unit 2 has a radius of curvature so as to match the outer peripheral surface 1a of the rotary drum mold 1. In addition to being formed in an arc-shaped surface, a central portion of the arc-shaped inner surface extends in the width direction, that is, extends in parallel with the direction of the axis 1b of the rotary drum mold 1, and each of the lattice body forming portions 10C is formed. Ear forming recess 10CPY and foot forming recess 1
It has a long rectangular opening concave portion 2b long enough to cover including the 0CPL, and has a tube 3 for supplying the molten lead through the left and right side surfaces in the width direction of the housing. However, the openings at both ends are connected to a molten metal lead supply source, and the molten lead passes through the molten metal supply section 2 at a predetermined pressure by the operation of a supply pump interposed in the tube 3 from one open end thereof. From the open end to the molten metal supply source. Opening recess 2
b and the tube 3 are opened in the bottom surface of the opening concave portion 2b and the side surface of the tube 3 facing the opening and communicate with each other, and are cut into the rotary drum mold 1 as shown by a chain line in FIG. Forming grooves 10CP1,1 which are arranged in parallel in the set axial direction
Gates 2C, 2C, 2C,..., 2C are provided at positions corresponding to 0CP3, 10CP3,.
Further, the opening concave portion 2 of the arc-shaped inner surface 2a of the molten metal supply portion 2 is formed.
In the upper inner surface area b, each of the vertical moldings arranged in parallel in the axial direction of the rotary drum mold 1 in a state where the arc-shaped inner surface 2a is in sliding contact with the outer peripheral surface 1a of the rotary drum mold 1 Grooves 10CP1, 10CP3, 10CP3, ..., 10C
Each of the molding grooves 10CP1 and 10CP fitted in the respective P2.
Each of the ribs 2d, 2d, 2d,..., 2d for preventing the molten lead supplied to 3, 10CP3,..., 10CP2 from flowing in the direction opposite to the rotation direction and solidifying beforehand. . The configuration of the molten metal supply unit 2 is the same as that of the conventional one. The cross-sectional shape of each of the above-mentioned forming grooves is not limited to a square as shown in the drawing, but may be a desired cross-sectional shape such as a polygonal shape or an arc shape. It goes without saying that the groove is formed in a sectional shape that matches and fits in accordance with the sectional shape of the groove.

[0007] Specifically, as shown in FIG. 3, each grid body forming portion 10 C is provided with a current collector grid 10 P shown in FIG. 7 to be manufactured.
Are formed with upper frame bone 10P1 and lower frame bone 10P2 forming part of the outer peripheral frame bone, and a plurality of horizontal bones 10P3, 10P3,... Forming part of the internal vertical and horizontal lattices therebetween. Are formed at predetermined intervals in parallel with the axial direction of the rotary drum mold 1 and the lugs for casting the lugs 10PY. The upper frame bone forming grooves 10CP1 and 10CP2 and the lateral bone forming grooves 10CP3, 10CP3,. The molding recesses 10CPY are oriented in parallel and carved. Also, the left and right side frame bones 10d and 10e of the outer peripheral frame bone of the current collecting grid body 10P, and a plurality of vertical bones 10f and 10f of the internal lattice therebetween. Are formed in parallel with the left and right side frame forming grooves 10Cd, 10Ce and the vertical bone forming grooves 10Cf, 10Cf,. Carved, and the upper frame 1 Molding groove casting the P1 10CP1
In the meantime, the ear forming recess 10CPY for casting the ear 10PY of the current collecting grid body 10P is cut in connection with this, and further formed in the forming groove 10CP2 for casting the lower bone 10P2. Is a foot forming recess 10CP for casting the two feet PL, PL of the current collecting grid P in connection with this.
L, 10CPL are formed by engraving, respectively, and each of the lattice body forming portions 10C, 10C,... Formed on the outer peripheral surface 1a of the rotary drum mold 1 over its entire peripheral surface, and each adjacent lattice is formed. It is formed so as to be continuous at the forming grooves 10Cd and 10Ce of the body forming portions 10 and 10. In the figure, n indicates an intermediate position where the adjacent lattice forming portions 10C, 10C are to be cut thereafter.

The configuration of the lattice forming grooves 10C, 10C,... Formed continuously on the outer peripheral surface 1a of the rotary drum mold 1 is the same as that of the conventional one, but according to the present invention,
Each of the ear forming recesses 10CPY, 10CPY,... Of each of the lattice body forming portions 10C, 10C, and so on has a continuous or discontinuous ridge on its bottom surface in a direction orthogonal to the rotation direction of the rotary drum 1. At least one groove 10 is formed, whereby at least two concave grooves 11, 11 are formed in the concave space of each of the lug forming concave parts 10CPY. In the embodiment shown in FIG. 3, as is clear from FIGS. 4 and 5, three continuous linear ridges 10 extending in the horizontal direction perpendicular to the direction of rotation of the rotary drum 1 in the vertical direction indicated by arrows are provided. Four recessed grooves 11, 11, 11, 11 were formed between the ridges 10, 10, 10 on the bottom surface of the ear-shaped recess 10CPY at regular intervals in the width direction. Show things.

More specifically, each ear-shaped recess 10CPY
Has a depth of, for example, 0.8 mm.
The protrusion height of each ridge 10 of the ridges 10, 10, 10 of the book is:
The depth t of the recess 10CPY is preferably t / 2 or more, for example, 0.6 mm, and the upper space 12 of the recess 10CPY of 0.2 mm remains above the depth t. , Depth 0.6mm, width 1-2m
Four concave grooves 11, 11, 11, 11 having a length of about m are formed. The length of each ridge 10 extends from the inner end of the base of the ear-shaped recess 10CPY, and its outer end does not reach the inner-end wall surface of the ear-shaped recess 10CPY but extends in the width direction therebetween. Extending, the respective grooves 11, 11,.
A communication groove 13 communicating with the outer ends of the eleventh and eleventh is formed. In addition, thus, each of the concave grooves 11, 11,
Of course, the inner ends of 11, 11 communicate with the side surfaces of the upper bone frame forming groove 10CP1. The cross-sectional shape of each ridge 10 may be a desired shape such as a triangle, a quadrangle, or an arc, but in the illustrated example, the cross-section was a quadrangle.

As described above, the protruding ridges 10, 10, 10 are provided on the bottom surface of each ear forming concave portion 10CPY, and the concave grooves 11, 1 are formed.
Next, the operation of the continuous casting apparatus provided with the rotary drum mold 1 of the present invention in which the respective grid body forming portions 10C formed with 1, 11, 11 are engraved on the entire peripheral surface will be described. When the rotary drum mold 1 is rotated in a direction indicated by an arrow in FIG. 1 by a driving device (not shown) and a molten lead is supplied to the molten metal supply section 2 through a tube 3 at a predetermined pressure, the molten lead at a predetermined pressure is supplied to each gate. 2C,
2C, 2C,..., 2C, the vertical forming grooves 10CP1, 10CP3, 10CP arranged in the axial direction of the rotary drum mold 1 corresponding to them via the opening concave portions 2b.
,..., 10CP2, respectively. At this time, the molten lead flows into the respective ribs 2d, 2d, 2d,.
2d prevents backflow above the opening recess 2b. Thus, the forming grooves 10CP1, 10CP3,
10CP3,..., 10CP2, and at the same time, the lateral forming grooves 10Cd, 10Cf, 10Cf,. The molten lead that has flowed into the recesses 10CPL and thus has flowed into the entire lattice forming part 10C is cooled by the surface of the rotary drum 1 and is cooled by the molten metal shown in FIG.
Solidified as shown by hatching, and with the rotation of the rotary drum mold 1, the continuous cast strip 10E is pulled and separated from the outer peripheral surface 1a by a pulling device via an external guide roll (not shown). This series of current-collecting grid bodies is filled with an active material paste and cut at cutting locations indicated by n in FIG. 3 to continuously obtain an electrode plate. FIG. 7 shows a current-collecting grid obtained by the present invention. Show body 10P.

In the above casting operation, according to the present invention, the ear forming recesses 10 of each grid body forming section 10C are previously determined.
Since the ridges 10 and the concave grooves 11 are formed in the CPY as described above, the molten lead a flowing out from the gate 2C is, as shown in FIG. 10C
As shown in FIGS. 6 (a), 6 (b), 6 (c), and 6 (d), the lubrication molding flows into P1 and, as shown in FIGS. Recess 10C
The first groove 11, the second groove 11, the third groove 1 in the PY
1, since it flows into the fourth concave groove 11 regularly in a branched manner as shown by oblique lines, the conventional ear-shaped concave portion 10CP
Since the molten lead does not flow freely and irregularly into the wide space of Y and does not wrap around, the upper bone frame groove 10CP1
There is no boundary between the molten lead and the molten metal. .. Flows into the small space in each of the narrow grooves 11, 11,. Thus,
The lug 10CPY cast by solidification of the molten lead filled in the concave groove 10CPY space is shown in FIGS. 7 (a), (b),
As shown in (c), it is cast into a high-quality product without cracks due to hot water. In this case, each of the ridges 10, 10, 10
The ear 10PY in which the concave strips 10 ', 10', 10 'are formed correspondingly is obtained. Therefore, since the surface area of the ear 10CPY increases, the contact area with the strap lead when the strap is formed by COS or the like increases, and an effect that more reliable welding can be obtained is brought. In addition, since there is no hot water boundary K as in the prior art, there is no risk of early failure such as local corrosion or breakage of the base of the ear during use of the battery, which is advantageous. The cast portion 12 'corresponding to the upper space 12 of the ear forming recess 10CPY is formed in a thin ear plate. Further, the communication groove 1 of the ear molding recess 10CPY.
Since the cast portion 13 'corresponding to No. 3 is formed on a flat surface, it is used as a welded portion of the strap, and good welding is obtained.

FIG. 8 shows another embodiment of the present invention. In this embodiment, each ridge 10 has a long length reaching the outer end wall surface of the lug forming recess 10CPY. In the same manner as in the embodiment, the lead molten metal is sequentially branched from the upper bone frame forming groove 10CP1, and the grooves 11 and 1 are regularly distributed.
1, 11, 11 so that the casting of the ear without border is obtained, and thus, the ear 10PY of the cast current collecting grid body 10P is, as shown in FIG. The concave strip 10 'formed corresponding to the strip 10 is obtained in the one formed in the opening at the upper end surface.

In many cases, a plurality of continuous or discontinuous ridges 10 formed in the ear-shaped concave portion 10CPY are provided in a plural number. Particularly, in the case of a relatively small current collecting grid to be cast,
Since the width of the ear portion is reduced, one ridge 10 is sufficient.
FIG. 10 shows an example of the embodiment, in which continuous linear convex portions are provided.
That is, the case where one ridge 10 is provided is shown.

As described above, in any of the above-described embodiments, the large space of the lug forming recess 10CPY is formed by the at least one ridge 10 extending in the horizontal direction.
A plurality of grooves 11 extending in the horizontal direction in the direction of rotation
As the rotary drum mold rotates, the lead molten metal flowing out of the molten metal port is not allowed to flow into the grooves 11 and 11 arranged in the rotation direction in the lug forming recess 10CPY. Since a regular flow is prevented from occurring, and a regular inflow is performed, the ear portion is cast without forming a conventional hot water boundary, and a loss that causes a defective product of the current collecting grid body can be eliminated. It can be manufactured efficiently and economically.
In addition, since the concave portion 10 'is formed in the ear portion, a lightweight current collecting grid body 10P can be obtained.

In the case of continuously casting a current collecting grid body having a foot portion 10PL, each of the grid body forming portions 10C formed on the entire outer peripheral surface of the rotary drum mold 1 is provided with a lower frame thereof. Foot forming groove 1 communicating with forming groove 10CP2
0CPL is formed in each pair.
During the casting process, the CPL also forms a hot junction similarly to the ear-shaped recess 10CPY. As shown in FIG. 14, the current-grating body is formed between the foot 10PL and the lower frame P2. A crack K may be generated between the hot water boundaries, resulting in product loss. Therefore, as shown in FIG. 3, a direction perpendicular to the rotation direction of the rotary drum mold 1 is provided on the bottom surface of each foot-shaped recess 10CPL in the same manner as applied to the ear-shaped recess 10CPY in each of the above embodiments. By providing at least one continuous or discontinuous ridge 10 on the
The formation of a hot water boundary is prevented, and therefore, a predetermined current-collecting grid body without a crack K can be continuously cast without loss. In the case of the embodiment shown in FIG. 3, continuous linear ridges, that is,
Each of the foot forming recesses 10CPL is arranged at intervals in the width direction, and three recessed grooves 11, 11, 11 are formed therebetween. By performing continuous casting by this, FIG.
As shown in the figure, a current collecting grid body 10P having no crack K in the foot 10PL due to the hot water boundary is obtained. In addition, the foot portion 10PL is a lightweight one in which the concave ridge 10 'is formed with respect to the convex ridge 10.

[0016]

As described above, according to the present invention, in a continuous casting apparatus for a current-collecting grid for a lead-acid storage battery, comprising a rotary drum mold and a molten metal supply unit slidably contacting the circumferential surface thereof, A continuous or discontinuous projection orthogonal to the rotating direction of the rotary drum mold is formed on the bottom surface of each ear forming recess of the grid body forming recess for casting a plurality of current collector grid bodies continuously engraved on the entire surface. Since at least one groove and at least two grooves along the groove are provided, the continuous casting of the current collecting grid body does not have a hot junction as in the prior art.
It is possible to continuously cast a high-quality current-grating body without any cracks at the boundary between the ear and the upper frame bone without a crack due to a hot water boundary, and at the same time, obtain a lighter-weight current-grating body than before. In the case of continuous casting of a current-collecting grid body provided with a foot portion, at least one ridge and at least two concave grooves along the same are similarly provided on the bottom surface of each grid-forming recess. Thus, a hot junction is not generated, and therefore, a light-weight current collecting grid body having a foot without cracks can be continuously cast without loss.

[Brief description of the drawings]

FIG. 1 is a side view in which a part of a continuous casting apparatus for a current-collecting grid for a lead-acid battery according to an embodiment of the present invention is partially cut away.

FIG. 2 is a perspective view of a molten metal supply section of the apparatus.

FIG. 3 is an exploded view of a part of an outer peripheral surface of a rotating drum mold of the apparatus in an operating state.

FIG. 4 is an enlarged sectional view taken along the line IV-IV of FIG. 3;

FIG. 5 is an enlarged sectional view taken along line VV of FIG. 3;

FIGS. 6 (a) to 6 (d) are plan views of ear-shaped recesses of the lattice-shaped body, illustrating a process of casting the ears.

7 (a) to 7 (c) are current collecting grids, and FIG. 7 (a) is a front view of a current collecting grid cast by the apparatus of the present invention;
7B is an enlarged sectional view taken along line AA of FIG. 7A, and FIG. 7C is an enlarged sectional view taken along line BB of FIG. 7A.

FIG. 8 is a plan view of an ear forming recess of an apparatus according to another embodiment of the present invention.

FIG. 9 is an enlarged perspective view of an ear portion of the current collecting grid body cast according to the embodiment shown in FIG. 8;

FIG. 10 is a plan view of an ear forming recess of an apparatus according to still another embodiment of the present invention.

FIG. 11 is a side view of a part of a conventional continuous casting device for a current-collecting grid for a lead-acid battery.

FIG. 12 is a perspective view of a molten metal supply unit of the apparatus shown in FIG. 11;

13 is a developed view of a part of the outer peripheral surface of the rotary drum mold of the apparatus shown in FIG.

FIG. 14 is a front view of a current collecting grid body cast by the apparatus shown in FIG. 11;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Rotary drum mold 2 Molten metal supply part 2a Arc-shaped surface 10 Convex ridge 11 Concave groove 12 Upper space 13 Communication concave groove 10P Current collecting grid body cast by the present invention 10PY Ear part 10C Grid body forming part 10CP1 upper part by the present invention Frame bone forming recess 10CP2 Lower frame bone forming recess 10CPY Ear forming recess 10CPL Foot forming recess

Claims (2)

[Claims] 1. A rotating drum mold in which a plurality of grid body forming portions for casting a current collecting grid body are continuously engraved around the entire outer peripheral surface, and a lead molten metal slidably contacts the outer peripheral surface of the rotating drum mold. And a molten metal supply section that continuously supplies the molten metal to the grid body forming section, and collects current on the inner peripheral surface of the casing of the molten metal supply section along the entire outer peripheral surface of the rotary drum mold along the axial direction thereof. In a continuous casting apparatus for a lead-acid battery grid body, which is formed by arranging ear-shaped recesses for casting ears of the grid body in parallel with each other and arranging ribs respectively fitted in respective forming grooves in the rotation direction, At least one extending perpendicular to the rotation direction of the rotary drum mold is provided on the bottom surface of the ear forming recess communicating with the upper frame bone forming groove for casting the upper frame bone of the current collecting grid body of each grid body forming section. And at least two grooves extending along the ridge are formed. A continuous casting device for a current-collecting grid for a lead storage battery. 2. The continuous casting of a current-collecting grid for a lead storage battery having a foot, wherein the foot of each grid body forming part is cast on a bottom surface of a foot forming recess in which the rotary drum mold is rotated. A continuous casting apparatus for a current-collecting grid for a lead-acid battery, wherein at least one ridge extending perpendicular to the ridge is provided, and at least two grooves extending along the ridge are formed.