US20160361608A1

US20160361608A1 - Process for Thermal Spray Coating of a Golf Club Head and Golf Club Head with Thermally Sprayed Coating

Info

Publication number: US20160361608A1
Application number: US14/735,729
Authority: US
Inventors: Klaus John Eisenmenger
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-06-10
Filing date: 2015-06-10
Publication date: 2016-12-15

Abstract

The disclosure relates to a process for coating a club face or striking surface of a club head of a golf club and also relates to a golf club. A coating is applied to a metallic substrate of the club head on at least a portion of the club face or striking surface by means of a thermal spray coating process. According to the disclosure, the process comprises processing the portion of the club face or striking surface with a laser beam before and after the application of the coating in order to provide the surface of the uncoated substrate and the surface of the coating with a predefined surface roughness, such as one having a roughness depth Rz of 50 μm±10%.

Description

BACKGROUND

1. Field of the Disclosure
The invention relates to a process for coating a club face or striking surface of a club head of a golf club, wherein a coating is applied to a metallic substrate of the club head on at least a portion of a club face or striking surface by means of a thermal spray coating process. The invention also relates to a golf club having a club head, the club head comprising a metallic substrate and a club face or striking surface, wherein the metallic substrate is provided with a thermally sprayed coating on at least a portion of the club face or striking surface.
2. Description of Related Art
Golf clubs in the form of irons or wedges are provided with a metallic club head having a generally flat club face or striking surface that is inclined with respect to a vertical plane at a defined loft angle. Generally the loft angle is approximately from 48 to 60 degrees. In order to achieve a better contact with the golf ball and to provide the golf ball with a spin when hitting the golf ball with the club head the club face is provided with a number of parallel grooves that extend generally horizontally across the club face or a portion thereof.
Some time ago the specification of golf clubs for golf professionals was changed in order to restrict the spin that can be given to the golf ball. The new specification stipulates a V-shaped cross section and a maximum depth of the grooves, which makes it more difficult to impart a high amount of spin to the golf ball. A high amount of spin is of advantage in order to better control the trajectory of the golf ball and to reduce the length of the rolling path after its contact with the ground.
In order to impart a higher amount of spin to a golf ball it has already been suggested in the past to roughen the metallic substrate of the club head in the area of the club face or striking surface by suitably processing the metallic substrate. However the roughened surface of the metallic substrate tended to be worn in use within a comparatively short time by the impact of the golf balls, with the result that the surface roughness was lost or became irregular. Therefore the life time of club heads with such a roughened club face or striking surface was rather limited.
Documents DE 19757736 A1, DE 19929116 A1, DE 10037213 A1 and DE 102006012207 A1 already disclose golf clubs where the club face of the club head is at least partially provided with a coating of a metal or metal alloy that is applied by flame spraying or high-velocity flame spraying onto the metallic substrate of the club head.
Of these documents DE 102006012207 A1 further teaches a golf club where the coating of the club face or striking surface of the club head has a defined surface roughness Ra of 1.4 to 1.9 μm in order to increase the spin of golf balls that are hit with the golf club. In this document the surface roughness Ra is the mean surface roughness and indicates the mean distance of measurement points on the surface from the mean value of the surface height and thus the arithmetic mean value of the deviation. This surface roughness Ra of less than 2 μm is achieved by using a powder with a very fine grain or particle size of 0.8 to 1 μm in the flame spray or high-velocity flame spray process.
WO 97/20961 A1 discloses a process for coating the club face of a golf club to increase the friction between the club face or striking surface and the golf ball in order to obtain a higher degree of control over the golf ball. Before coating the club face or striking surface the latter is subject to a texturing procedure, such as by grit or sand-blasting. The texturing procedure is aimed at establishing a textured surface to insure a proper bonding of the hard coating to the metallic substrate. Once the striking surface has been subject to texturing the resulting textured surface has roughness in one example ranging from approximately 140 to 160 microinches, which is equal to about 3.5 to 4 μm. Here the surface roughness is measured according to the American National Standard for roughness measurement, as set forth in Thermal Spraying, Practice, Theory, and Application: Surface Preparation, Ch. 3, p. 17, (1985).
In trials with golf clubs having a club face or striking surface with such a prior art coating it was however found that only a comparatively limited spin could be imparted to a golf ball. Therefore the control over the trajectory of the golf ball and the length of the rolling path after its first contact with the ground were not yet satisfactory. A further problem encountered with such golf clubs was a rather short durability or life time of the coating. Due to these reasons prior art golf clubs with a coated club face were not economically successful.

SUMMARY

Therefore it is the aim of the present invention to provide an improved process and golf club so that the amount of spin that can be imparted to the golf ball is increased. This will result in an enhanced ability of the golf player to control the trajectory and rolling path of the golf ball. It is a further aim of the present invention to enhance the durability of the coated club face or striking surface in order to increase the life time of the club head.
In order to achieve these aims in the process according to the invention the club face is processed with a laser beam before and after applying the coating in order to provide the surface of the uncoated substrate and the surface of the coating with a predefined surface roughness.
In the golf club according to the invention the surface of the coating and the surface of the uncoated substrate beneath the coating have the same predefined surface roughness.
In one example, the predefined surface roughness is expressed by the term roughness depth Rz which according to DIN EN ISO 4287:2010 is the vertical distance from the highest peak to the lowest valley within a single sampling length when measuring the surface roughness. According to DIN EN ISO 4287:2010 the roughness depth Rz is the vertical distance from the highest peak to the lowest valley within a single sampling length. The sampling length is also referred to as measured length. Rz is also referred to as maximum height of the roughness profile.
In one example, the roughness depth Rz can be 50 μm±10%, and may preferably be 50 μm+10%. In one example, not only the roughness depth Rz but also the mean roughness depth Rzm can be 50 μm±10%, and may preferably be 50 μm+10%. According to DIN EN ISO 4287:2010 the mean roughness depth Rzm is the arithmetic mean value of the vertical distances from the highest peak to the lowest valley within five sampling lengths.
The aforementioned mean roughness depth Rzm of 50 μm±10% corresponds to an arithmetic mean surface roughness Ra of about 16 μm. The arithmetic mean surface roughness Ra according to DIN EN ISO 4287:2010 is the arithmetic mean value of the absolute values of the ordinate values or vertical heights of the surface roughness profile within a single sampling length and indicates the mean or average deviation of the peaks and valleys from an arithmetic mean elevation of the profile.
Thus the arithmetic mean surface roughness Ra of the coated club face of the golf club according to the invention is about four times the surface roughness Ra of the coated club face of the golf club described in WO 97/20961 A1 and about eight times the surface roughness Ra of the club face of the golf club described in DE 102006012207 A1.
By means of the aforementioned inventive roughness depth Rz the surface of the coating will be provided with a relatively high but nevertheless very regular or even surface roughness. This will increase the amount of spin of the golf ball: When hitting the golf ball with the club head the golf ball will remain in contact with the club face some thousandths of seconds longer and therefore will practically roll somewhat across the club face. This will result in an increase of the rotary speed and the angular momentum of the golf ball and therefore in a larger spin rate.
Due to the inventive roughness depth Rz of the surface of the substrate beneath the coating the durability and life time of the coating will increase because the meshing between the substrate and the coating will be increased and therefore prevent any delamination or damage of the coating.
In particular when the golf club has a club face or striking surface that is inclined with respect to a vertical plane, like a wedge, a golf ball having a higher amount of spin will leave the club face with a trajectory that is considerably less steep and more aggressive compared with prior art golf clubs. As a result the trajectory will be less affected by wind or other environmental or weather conditions, like rain. This will also enhance the golf player's control over the golf ball's trajectory.
Another result of a higher amount of spin imparted to the golf ball will be a shorter rolling path of the golf ball after hitting the ground. Thus the golf player can better control or determine the end point of the rolling path, i.e. the point where the golf ball will come to a rest.
In addition to that the very regular or even surface roughness according to the invention will prevent or mitigate any lateral deviations of the trajectory of the golf ball that might result from irregularities of the surface roughness. Furthermore the very regular or even surface roughness of the club face will prevent damages to the golf ball and to the club face when the club head hits the golf ball. This will also result in a longer life time of the club face.
In tests with the inventive golf club it has been further found out surprisingly that it is easier to perform a tee-off in high grass. In view of the flatter trajectory this was rather not to be expected.
In the process according to the invention the very regular or even surface roughness is achieved by the laser processing of the surfaces of the substrate and of the coating. The laser processing of the substrate surface will also contribute to improve the adhesion of the coating to the substrate surface. The laser processing of the coating surface will remove any residues of the thermal spray coating process. The combined laser processing of the substrate surface and of the coating surface will result in a repeating surface pattern on these two surfaces.
Advantageously the laser beam is generated or emitted by a high power laser source, such as one with a laser power of 150 to 200 Watt, like a diode laser or a fiber laser. With such a laser power the material of the metallic substrate and of the coating will be evaporated when the laser beam impinges onto the surfaces of the metallic substrate or the coating. This will result in an ablation of the metallic substrate material and of the coating material respectively.
In one example, the laser beam is moved along a predetermined path across the surface of the uncoated substrate and across the surface of the coating during the laser processing of the two surfaces. In one example, the surface of the uncoated substrate and the surface of the coating laser beam are scanned with the laser beam in corresponding or superimposed parallel lines in order to create a plurality of small parallel grooves with a depth of less than 100 μm where the laser beam impinges onto the surface.
Advantageously the scanning lines are disposed in a small distance from each other so that the small grooves that are generated will be separated from each other by small parallel ribs or ridges. When the scanning lines on the surface of the uncoated substrate and on the surface of the coating are concurrent, i.e. when the former scanning lines are exactly beneath the latter scanning lines then the points where the laser beam impinges onto the surface of the substrate and onto the surface of the coating respectively coincide and do not have any lateral offset. In this case the roughness peaks on the surface of the uncoated substrate and on the surface of the coating are exactly on top of each other.
In one example, the orientation of the scanning lines and therefore of the small grooves and ridges is horizontal. In this context “horizontal” shall mean generally parallel to a lower edge of the club face or club head and parallel to the ground and to the deeper grooves, if the golf club is a wedge, so that the lines and therefore the small grooves and ridges are perpendicular to the direction of the movement of the club face with respect to the golf ball during the ball contact. This will result in a larger amount of spin when hitting the golf ball. Furthermore this will avoid any lateral deviation of the desired trajectory of the golf ball that might be caused by another orientation of the small grooves and ribs or ridges.
According to another embodiment of the invention the thermal spray coating process is either a flame spray coating process or a high-velocity flame spray coating process. In both processes a powdery coating material is applied to the surface of the substrate after the latter has been subject to the laser beam treatment in order to increase its surface roughness as described above. Advantageously the powdery coating material is a ceramic-metal-composite, such as WC/Co/Ni or WC/Co/Cr. However it is also possible to use a metal, like Ni or Cr, or a metal alloy, like Cr3C2/Ni/Co.
By the use of one of the aforementioned coating materials the coated club face or striking surface will preserve its surface roughness over a longer time span and will therefore guarantee a longer life time of the golf club or the club head respectively.
The amount of powdery coating material or coating powder that is sprayed onto the club face or striking surface during the thermal spray coating process is such that the thickness of the coating applied to the metallic substrate of the club head is between 0.2 and 0.5 mm, and can be between 0.3 and 0.4 mm.
Advantageously before processing of the surface of the coating with the laser beam the surface roughness and the roughness depth of this surface should be at least similar to the surface roughness and the roughness depth of the uncoated surface of the metallic substrate in order to reduce the amount of the coating material that has to be removed or evaporated by the laser beam. In order to achieve this, the coating powder can have a particle or grain size of about 40±10 μm.
According to a further embodiment of the inventive golf club the final coating has a thickness of 0.2 to 0.5 mm, or even a thickness of 0.3 to 0.4 mm and comprises a coating material that is a ceramic-metal-composite, which can consist of WC/Co/Ni or WC/Co/Cr. However it is also possible to use a metal alloy like Cr3C2/Ni/Co or a metal like Ni or Cr.
The club face or striking surface of the inventive golf club, i.e. the surface of the coating and the surface of the metallic substrate beneath the coating, can be provided with a plurality of small parallel grooves having a depth of less than 100 μm and extending horizontally across the club face or striking surface. It is particularly suitable when the grooves of the metallic substrate and the grooves of the coating are superimposed to each other in a front view of the club face or striking surface.
The inventive golf club can be a wedge having a club face or striking surface that is inclined with respect to a vertical plane when the club head hits the golf ball. The club face or striking surface of wedges is provided with a number of parallel grooves in a usual manner and the coating is provided on the portions of the club face or striking surface wedge that are disposed between the grooves.
However the invention may as well be used on other golf clubs with metallic club heads especially on any iron in a set of irons from a 1 iron to a 9 iron.

BRIEF DESCRIPTION OF THE DRAWINGS

Other novel features and advantages of the present invention will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:

FIG. 1 is a perspective view of parts of a golf club in the form of a wedge;

FIG. 2 is another perspective view of the same parts;

FIG. 3 is partial cross-sectional view similar to FIG. 2;

FIG. 4 is an enlarged cross-sectional view of the detail IV in FIG. 3;

FIG. 5 is a further enlarged cross-sectional view of the detail V in FIG. 4 before processing the uncoated club face or striking surface with a laser beam;

FIG. 6 is a view similar to FIG. 5 after having processed the uncoated club face or striking surface with the laser beam;

FIG. 7 is a view similar to FIG. 6 after having applied a coating to the laser processed club face or striking surface;

FIG. 8 is a view similar to FIG. 7 after having processed or treated the coated club face or striking surface with a laser beam.

DETAILED DESCRIPTION

The golf club 10 as depicted in the drawing is a wedge that is particularly suited for shorter strikes around the green or for strikes in complicated situations, like strikes from bunkers, from ditches or from high grass.
The golf club 10 is made up of a shaft 12 (only partially depicted) and a metallic club head 14 that is mounted at the lower end of the shaft 12. The club head 14 has a generally flat club face or striking surface 16. When the club head 14 hits a golf ball the club face or striking surface 16 is inclined with respect to a vertical plane E, as shown in FIG. 2. The angle of inclination α of the club face or striking surface 16 with respect to the vertical plane E is referred to as loft angle and ranges normally from 48 to 60 degrees, depending on the type of wedge.
A portion of the flat club face or striking surface 16 is provided with a plurality of grooves 20. The drawings show exemplarily six grooves 20, however normally there will be more than six grooves 20. The grooves 20 are parallel to each other and to a slightly curved lower edge 22 of the club face or striking surface 16. The grooves 20 have a generally horizontal orientation so that they are parallel to the ground when the club head 14 hits a golf ball while the club face or striking surface 16 is inclined with respect to the vertical plane E, as shown in FIG. 2.
The grooves 20 extend across a central portion 34 of the club face or striking surface 16. At their opposite ends the grooves 20 and the central portion 34 of the club face or striking surface 16 are delimited by two straight lines 24 and 26 that are perpendicular to the grooves 20.
In the central portion 34 between the lines 24 and 26 on one hand and between the lower edge 22 and an opposite upper edge 30 of the club face or striking surface 16 the club head 14 is provided with a coating 32 as shown in FIGS. 3 to 8. The coating 32 is a thermally sprayed coating 32 that covers the metallic substrate material 36 of the club head 14 in the central portion 34 between the grooves 20. The coating 32 has a thickness of about 0.35 mm and may consists of a hard and durable ceramic-metal-compound, such as WC/Co/Ni or WC/Co/Cr.
In order to increase the spin of a golf ball when hitting the golf ball with the club head 14 the coating 32 has a coating surface 42 with an even or regular surface roughness. The surface roughness of the coating surface 42 is such that a roughness depth Rz and a mean roughness depth Rzm according to DIN EN ISO 4287:2010 are Rz=50 μm+10%, whereas the arithmetic mean surface roughness Ra according to DIN EN ISO 4287:2010 is Ra=12 to 20 μm and, in one example, can be about 16 μm. DIN EN ISO means that the noted standard is according to German Industry Standard (Deutsche Industrie Norm DIN), European Standard (Europaische Norm EN), and International Standard by the International Organization for Standardization (ISO).
Such a club head 14 is fabricated from a club head body where the metallic substrate material 36 in the central portion 34 of the club face or striking surface 16 between the two straight lines 24, 26 has a smooth surface 40 and where the grooves 20 are milled into the smooth surface 40, as shown in FIG. 5.
In a first processing step the smooth surface 40 is scanned with a laser beam from a high power laser source where the laser beam is moved across the surface 40 line by line. The lines are parallel to the grooves 20 and extend from one of the two straight lines 24, 26 to the other one 26, 24 respectively.
The laser beam is emitted from a diode laser source or from a fiber laser source having a laser power of 150 to 200 W. With a laser power of 200 W and a diameter of the laser beam at the surface 40 of about 50 μm the power density of the laser beam at the surface 40 is about 10⁷W/cm². Such a power density will cause a local evaporation and ablation of practically every metallic substrate material, like steel, at the target point of the laser beam. Due to the line by line movement of the laser beam across the central portion 34 of the club face or striking surface 16 the result of the laser processing is a laser processed surface 50 having a plurality of small shallow grooves 44 that are disposed between each pair of neighboring grooves 20 and that are parallel to the grooves 20. The small shallow grooves 44 have a depth of about 40 to 45 μm and are separated from neighboring small shallow grooves 44 by ribs or ridges 46 where the metallic substrate material 36 is not ablated by the laser beam, as shown in FIG. 6.
When the surface roughness of the laser processed surface 50 (FIG. 6) is measured in a direction that is perpendicular to the grooves 20 and parallel to the straight lines 24, 26 in five sampling lengths of 2.5 mm each the measured arithmetic mean surface roughness Ra according to DIN EN ISO 4287:2010 is Ra≈15 to 17 μm whereas the roughness depth Rz and the mean roughness depth Rzm according to DIN EN ISO 4287:2010 are Rz=50 μm+10% because some of the evaporated substrate material is deposited on the ribs and ridges 46 between the grooves 44.
In a second processing step the coating 32 is applied to the laser processed surface 50 by means of a flame spray coating process or a high-velocity flame spray coating process. The grooves 20 can be masked before the second processing step in order to avoid a deposition of coating material within the grooves 20. Alternatively any coating material deposited within the grooves 20 can be removed afterwards by grinding or the like.
In the flame spray coating process or high-velocity flame spray coating process a suitable burner system is fed with the powdery coating material in a carrier gas and a burnable gas mixture, which in one example is a mixture of acetylene and oxygen. When the carrier gas with the powdery coating material and the burnable gas mixture are fed into the burner system and ignited the hot combustion gases together with the carrier gas will be accelerated to a supersonic velocity. At the same time the hot combustion gases will partially melt the powder particles of the coating material. When the partially melted powder particles hit the surface 50 they will be mechanically bonded together and to the surface 50. The coating process is carried out until the coating 32 has a thickness of approximately 0.35 mm and a surface 52, as shown in FIG. 7.
The powdery coating material is a ceramic-metal-composite that comprises an oxide-free ceramic component and a metal component and has a particle or grain size of about 45±10 μm. The ceramic component comprises a metal carbide, such as tungsten carbide (WC), while the metal component comprises cobalt (Co) and/or nickel (Ni) and/or chrome (Cr). The metal carbide provides for a high surface hardness while cobalt (Co) increases the resistance against wear and nickel (Ni) enhances the thermal conductivity, the adhesion to the metallic substrate material 36 and the cohesion within the coating 32. In total the ceramic component is more than 80% of the ceramic-metal-composite while the metal component is less than 20%.
Instead of a ceramic-metal-composite, such as WC/Co/Ni or WC/Co/Cr, alternatively the coating can consist of Cr3C2/Ni/Co or Ni or Cr.
After having applied the coating 32 to the laser processed surface 50 of the metallic substrate material 36 in a subsequent third processing step the surface 52 of the coating 32 is scanned or processed with the laser beam from the same high power diode or fiber laser source. The laser beam is also moved across the surface 52 line by line where the lines are parallel to the grooves 20 and extend between the two straight lines 24 and 26 across the central portion 34 of the club face or striking surface 16. The resulting evaporation of coating material again generates a plurality of small shallow grooves 54 that are disposed between each pair of neighboring grooves 20, are parallel to the grooves 20, have a depth of about 40 to 45 μm and are separated from neighboring small shallow grooves 54 by ribs or ridges 56 where the coating 32 is not ablated by the laser beam, as shown in FIG. 8.
The paths of movement of the laser beam during the first and the third processing steps are identical so that the shallow grooves 54 in the coating surface 42 will be superimposed to the shallow grooves 44 in the substrate surface 50 and the ribs or ridges 56 of the coating surface 42 will be superimposed to the ribs or ridges on the substrate surface 40, as can be best seen in FIG. 8.
When the surface roughness of the laser processed coating surface 42 is measured in a direction that is perpendicular to the grooves 20 and parallel to the straight lines 24, 26 in five sampling lengths of 2,5 mm each the measured arithmetic mean surface roughness Ra according to DIN EN ISO 4287:2010 is Ra≈15 to 17 μm whereas the roughness depth Rz and the mean roughness depth Rzm according to DIN EN ISO 4287:2010 are Rz=50 μm+10% because some of the evaporated substrate material 36 is deposited on the ribs and ridges 56 between the small shallow grooves 54.

Claims

What is claimed is:

1. Process for coating a club face or striking surface of a club head of a golf club, wherein a coating is applied to a metallic substrate of the club head on at least a portion of the club face or striking surface by means of a thermal spray coating process comprising processing the portion of the club face or striking surface with a laser beam before and after the application of the coating in order to provide the surface of the uncoated substrate and the surface of the coating with a predefined surface roughness.

2. Process according to claim 1, wherein the surface of the uncoated substrate and the surface of the coating are provided with a roughness depth Rz according to DIN EN ISO 4287:2010 of Rz=50 μm±10%.

3. Process according to claim 1, wherein the surface of the uncoated substrate and the surface of the coating are provided with an arithmetic mean surface roughness Ra according to DIN EN ISO 4287:2010 of Ra from 12 to 20 μm.

4. Process according to claim 1, wherein the laser beam is emitted from a laser source having a laser power of 150 to 200 Watt.

5. Process according to claim 4, wherein the laser source is a diode laser or a fiber laser.

6. Process according to claim 1, wherein the laser beam is moved along identical predetermined paths across the surface of the uncoated substrate and across the surface of the coating.

7. Process according to claim 6, wherein the laser beam is moved in parallel horizontal lines across the surface of the uncoated substrate and across the surface of the coating.

8. Process according to claim 1, wherein the thermal spray coating process is a flame spray coating process or a high-velocity flame spray coating process.

9. Process according to claim 1, wherein the coating is applied to a thickness of 0.2 to 0.5 mm.

10. Process according to claim 1, wherein the coating comprises a coating material that is selected from the group consisting of WC/Co/Ni, WC/Co/Cr, Cr3C2/Ni/Cr, Ni und Cr.

11. Process according to claim 1, wherein the coating material is a particulate powder having a particle size of 45±10 μm.

12. Golf club having a club head, the club head comprising a metallic substrate and a club face or striking surface, wherein the metallic substrate is provided with a thermally sprayed coating on at least a portion of the club face or striking surface and wherein the surface of the coating and the surface of the uncoated substrate beneath the coating have the same surface roughness.

13. Golf club according to claim 12, wherein the surface of the coating and the surface of the uncoated substrate have a roughness depth Rz according to DIN EN ISO 4287:2010 of Rz=50 μm±10%.

14. Golf club according to claim 12, wherein the surface of the coating and the surface of the uncoated substrate have an arithmetic mean surface roughness Ra according to DIN EN ISO 4287:2010 of Ra from 12 to 20 μm.

15. Golf club according to claim 12, wherein the coating has a thickness of 0.2 to 0.5 mm or a thickness of 0.3 to 0.4 mm.

16. Golf club according to claim 12, wherein the coating comprises a coating material that is selected from the group consisting of WC/Co/Ni, WC/Co/Cr, Cr3C2/Ni/Cr, Ni und Cr.

17. Golf club according to claim 12, wherein the surface of the coating, the surface of the metallic substrate beneath the coating, or both the surface of the coating and the surface of the metallic substrate beneath the coating have a plurality of small parallel grooves with a depth of less than 100 μm.

18. Golf club according to claim 12, wherein the surface of the coating, the surface of the metallic substrate beneath the coating, or both the surface of the coating and the surface of the metallic substrate beneath the coating have a plurality of small parallel grooves that extend horizontally across the club face or striking surface.

19. Golf club according to claim 12, wherein the golf club is a wedge or an iron from a 1 iron to a 9 iron.

20. Golf club according to claim 19, wherein the club face or striking surface has a number of parallel grooves and wherein the coating is provided on portions of the club face or striking surface wedge that are disposed between the grooves.