WO2007058803A2

WO2007058803A2 - Wear tip for rotary mineral breaker

Info

Publication number: WO2007058803A2
Application number: PCT/US2006/043122
Authority: WO
Inventors: Damian Rodriguez
Original assignee: Damian Rodriguez
Priority date: 2005-11-16
Filing date: 2006-11-02
Publication date: 2007-05-24
Also published as: US20090014569A1; NZ569074A; EP1971440A4; EP1971440A2; US7607601B2; AU2006315852A1; AU2006315852B2; BRPI0618673A2; US20070108327A1; WO2007058803A3; ES2533720T3; US7427042B2; EP1971440B1

Abstract

A wear tip for a rotary mineral breaker comprises a carrier 12 having at least one wear edge 40 having a recess 50. An insert 14 of abrasion resistant material disposed in the recess 50 has an outer wear surface 52 in generally parallel relation with a wear face 48 of the carrier 12 and an inner surface 54 having an arcuate profile for more effective consumption of the insert material.

Description

WEAR TIP FOR ROTARY MINERAL BREAKER

TECHNICAL FIELD

[ 001] The present invention relates to the field of mineral breakers, and more particularly, to replaceable wear tips for rotors in centrifugal mineral breakers. BACKGROUND ART

[ 002] Centrifugal mineral breakers, such as that described in U.S. Pat. No. 3,970,257, operate by feeding mineral material axially into a rotor from which it is expelled outwardly at high speeds into a housing surrounding the rotor. Some of the expelled material forms a protective rock lining in the housing. Mineral material subsequently ejected through discharge ports in the rotor impacts the protective rock lining. Similarly, a protective rock lining forms inside the rotor protecting most of the inside surfaces of the rotor, except for surfaces located near the discharge ports through which mineral material is ejected from the rotor. The parts of the rotor near the discharge ports are subjected to severe wearing forces from the stream of mineral material being ejected. Accordingly, discharge ports are normally provided with wear tips to protect the port edge from rapidly deteriorating. Typically, a wear tip is placed vertically across the width of each discharge port. The wear tip forms a hardened lip which protects the rotor from erosion caused by the rock exiting with extreme force and velocity.

[ 003] Commonly, wear tips have a generally square profile and can be dropped or bolted into place. In the drop-in style, a square-shaped socket is provided in the bottom ring of the rotor in which the wear tip is seated. A top part of the wear tip is held in place in a square aperture in the top ring of the rotor. For bolted designs, numerous arrangements are possible to fix the wear tip in place. The wear edge of the tip is that corner most exposed to abrasion from streaming mineral material. The wear edge is generally provided with an abrasion resistant insert, typically made from tungsten carbide, which is much more effective at withstanding the wear forces of the stream of material. The main body, or carrier portion, of the wear tip is constructed of steel or cast iron which is much more susceptible to erosion than the insert. The insert generally bears a uniform rectangular profile through its longitudinal dimension and fits in a conforming channel or recess in the wear edge of the tip. To prevent the insert from slipping out of the insert, it is held in place with an industrial adhesive. Frequently, as an added measure of assurance, a bead of weld is applied in the recess the top and bottom of the insert in case the adhesive fails. Often an insert is assembled from several pieces which are fitted in end-to-end abutment in the recess. Unfortunately, this leaves joints between the individual pieces which weakens the bond of each piece to the carrier and leaves a space into which fine particulate matter inserts itself between adjoining pieces. As a result individual pieces of insert material have been known to separate and creep out of the recess thereby exposing the wear tip to erosive damage. [ 004] The primary objective for wear tips is to provide sufficient longevity that the rotor will be protected until it can be observed during a regular maintenance check that the tips have become damaged so that they may be replaced. Wear tips experience greatest wear near the middle of the span across the discharge port and it has been found that unused portions at the top and bottom of the tungsten carbide insert are routinely discarded when the center of the insert becomes fully eroded or loses its usefulness through breakage or detachment. Applicants have observed that under typical wear patterns, approximately forty to fifty percent of the original tungsten carbide is not utilized and is discarded as waste in this manner when the middle of the insert is no longer useful. Since tungsten carbide is relatively expensive, discarding nearly half of the insert is economically inefficient. DISCLOSURE OF THE INVENTION

[ 005] A wear tip for a rotary mineral breaker according to the invention comprises a carrier having at least one wear edge disposed transversely to the path of the mineral material being ejected out of one of the discharge ports of the rotor. The wear edge has a wear face angularly disposed to the inward face of the carrier. A recess in the wear face receives an insert of abrasion resistant material. The insert has an outer wear surface which is in general planar alignment with the wear face of the wear edge. An inner surface of the insert has an arcuate profile such that the center portion of the insert has a greater depth than that of its top and bottom portions. Since the wear pattern on the wear edge of the tip is greater in the middle portion than the top or bottom portions of the insert, the greater depth of the insert in its center permits more efficient overall utilization of the insert material and reduces wastage of the expensive abrasion resistant insert.

[ 006] In another aspect of the invention, the tip comprises a carrier having a generally square profile and at least two wear edges disposed transversely to the path of the mineral material being passed out of the rotor. A first wear face is disposed at the intersection of the inward face and a forward face of the carrier, whereas a second wear edge is disposed at the intersection of the inward face and a following face. Each wear edge has a recess in which is received an insert of abrasion resistant material. The inner surface of each of the inserts has an arcuate profile. The carrier is bisected by a middle plane parallel with the forward face and following face of the carrier, defining a forward half and a following half. The forward and following halves form mirroring symmetrical halves of the carrier about the middle plane. Accordingly, once one of the inserts has been worn away, the carrier may be inverted about a horizontal axis perpendicular to the inside face of the carrier to place the other unused insert of the carrier into the former position of the used insert. [ 007] The invention has the distinct advantage that the shape of the insert material is consistent with the wear pattern on the insert caused by the streaming mineral material, resulting in substantially improved consumption of the tungsten carbide insert material. The second embodiment of the invention combines that advantage with the ability to flip over the carrier in which one insert has been used to quickly replace it with the unused insert. Thus, a single wear tip may be used twice rather than replacing it with an entirely new wear tip when the insert has lost its usefulness. The cost of the insert material in the arcuate shape is approximately the same as conventional inserts, yet provides the potential for nearly double the wear. BRIEF DESCRIPTION OF THE DRAWINGS [ 008] Fig. 1 is a perspective view of a wear tip according to the invention shown in exploded relation to a representative rotor of a rotary mineral breaker. [ 009] Fig. 1A is a plan view taken along lines 1 A-1A of Fig. 1 of the interior of the rotor shown in Fig. 1 depicting a rock bank built up behind each wear tip installed in the rotor. [ 010] Fig. 1 B is a sectional elevation view taken along lines 1 B-1 B of Fig. 1 of the wear tip and portions of the rotor shown in Fig. 1. [ 011] Fig. 2 is a close up perspective view of the wear tip shown in Fig. 1. [ 012] Fig. 2A is a perspective view of a wear tip according to the invention showing a typical wear pattern across the wear edge of the carrier.

[ 013] Fig. 3 is a sectional elevation view taken along lines 3-3 of the wear tip shown in Fig. 2. [ 014] Fig. 3A is a sectional elevation view taken along lines 3A-3A of the wear tip shown in Fig. 2A.

[ 015] Fig. 4 is a sectional plan view taken along lines 4-4 of the wear tip shown in

Fig. 2.

[ 016] Fig. 4A is a sectional plan view taken along lines 4A-4A of the wear tip shown in Fig. 2A.

[ 017] Fig. 5 is a perspective view of an alternate embodiment of a wear tip according to the invention shown in exploded relation to a representative rotor of a rotary mineral breaker.

[ 018] Fig. 6 is a perspective view of the wear tip shown in Fig. 5. [ 019] Fig. 7 is a sectional view taken along lines 7-7 of the wear tip shown in Fig. 6, showing a rock bank built up against one wear edge.

[ 020] Fig. 7A is a sectional plan view of a wear tip similar to that shown in Fig. 7 depicting a typical wear pattern on one of the wear edges.

[ 021] Fig. 7B is a sectional plan view taken along line 7B-7B of the wear tip shown in Fig. 6 depicting the second wear edge in worn condition.

[ 022] Fig. 8 is a perspective view of a third embodiment of a wear tip according to the invention showing straight-sided recesses for straight-edged inserts extending the full length of the wear tip.

BEST MODE FOR CARRYING OUT THE INVENTION [ 023] A wear tip for a rotary mineral breaker according to the invention, indicated generally at 10 in Fig. 1 , is shown in an exploded position relative to a representative rotor for a mineral breaker. With additional reference to Figs. 2 and 3, the wear tip 10 comprises a carrier 12 and an insert 14. The carrier 12 has a generally square profile as seen in Fig. 4, and has a forward face 16, an inward face 18, a following face 22, and an outer face 24. As seen in Fig. 1 , the bottom 26 of the carrier 12 drops into a socket 28 in the bottom ring 30 of the rotor 32. The top 34 of the carrier 12 is held in place in an aperture 36 in the top ring 38 of the rotor 32. As the rotor 32 spins in the direction indicated by arrow A, the forward face 16 of the carrier 12 is facing generally towards the direction of travel of the rotor 32, the inward face 18 is oriented towards the center of the rotor 32, the following face 22 is facing away from the direction of travel of the rotor 32, and the outer face 24 is positioned towards the outer edge of the rotor 32.

[ 024] Referring again to Fig. 2, a wear edge 40 is located at the intersection of the forward 16 and inward 18 faces. During operation of the mineral breaker, mineral material is discharged from the spinning rotor 32 along the path indicated by arrows B in Fig. 1 A through discharge ports 42. Most of the mineral material passes generally parallel to the wear edge 40 on its discharge path. Even though carriers are typically manufactured of steel or cast iron, it is well known that they will erode rapidly under the severe abrasive forces resulting from the discharging mineral material. Therefore, as shown in Fig. 3, wear edges are provided with an abrasive-resistant insert 14 disposed in a recess 44 in the wear edge 40. The insert 14 is preferably positioned in the recess 44 with its side surfaces 46 at a thirty degree angle to the forward face 16 of the carrier, and hence, at a sixty degree angle to the inward face 18. See Fig. 4. The carriers are positioned in the rotor so that the inserts are nearly perpendicular to the path of the mineral material being ejected from the discharge port thus making the most effective use of the insert material to protect the wear edge 40. Nevertheless it will be understood by those of skill in the art that orientation of the insert may be established at many different angles in the carrier or in the rotor according to the structural characteristics of the breaker and the nature of the mineral material being processed. [ 025] It is known in the art to extend the insert through the entire longitudinal dimension of the carrier, as seen in the embodiment shown in Fig. 8. Inserts have typically been straight-edged with a uniform cross-sectional profile throughout their full length, one commonly used insert having a depth of .88 inches and a width of .38 inches. As mentioned above, however, the typical wear pattern caused by the abrasive action of the mineral material discharging transversely across the wear edge results in greater wear in the center portion of the insert. As a consequence, when the center of the insert is worn away, even though a substantial amount of the top and bottom portions of the insert remain, the entire insert is usually discarded. Applicants have determined that a typical wear pattern such as this results in approximately forty to fifty percent of the insert being discarded. [ 026] With reference now to Figs. 1 , 1 A, 2, 3 and 4, a carrier 12 according to the invention includes a wear edge 40 (see Fig. 2) having a wear face 48 disposed in general planar alignment with the path of the mineral material passing across the wear edge 40. A recess 44 in the wear face 48 has an inner edge 50 having a generally convex profile. An insert 14 disposed in the recess 44 has an outer wear surface 52 generally in planar alignment with the wear face 48 of the wear edge 40. An inner surface 54 of the insert 14 has a convex profile conforming to the inner edge 50 of the recess 44. According to the nature of the minerals being feed into the rotor and the degree of particle size reduction required, rotors are provided in different sizes defined generally by the distance C between the top surface 56 of the top ring 38 and the bottom surface 58 of the bottom ring 30: 9.25", 12.25", and 14.25". Applicants have determined that an 1 1.81 " radius R defining an arcuate profile for the inner surface 54 of the insert 14 yields a center portion-to-top and bottom portions depth ratio in a 12.25" carrier that is consistent with a typical wear pattern on the wear edge 40. See Fig. 1 B. The insert having a 11.81 " radiused inner surface 54 preferably has a maximum center depth D₁ of 1.25 inches tapering to a relatively shallow depth D₂ at the top 60 and bottom 62 ends of the insert. It will be understood by those of skill in the art that the invention is not limited to an insert having a 11.81 " radiused inner surface and that a range of convex profiles of the insert's inner surface 54 are intended to fall within the scope of the invention. It should be noted that a small portion of the top and bottom ends 60, 62 of the insert are truncated as a safety measure to eliminate the sharp edges which would otherwise result from intersection of the outer wear surface 52 and inner surface 54.

[ 027] Similarly, since the top 34 and bottom 26 of the carrier 12 are disposed in the top and bottom rings 38, 30 of the rotor 32, protected against wear from discharging mineral matter, it has been found needless to extend the insert into the top 34 and bottom 26 of the carrier 12. Therefore, as shown in Fig. 1 B, the insert 14 according to the invention has a longitudinal extent E delimited by the spacing S between the top and bottom rings 38, 30 of the rotor 32. Applicants have determined that an insert having a length of 9.53", and the curved inner edge 50 with an 11.81 " radius R as discussed above, results in substantially more efficient usage of insert material in a 12.25" carrier. It will be appreciated that the invention is not limited to inserts having a length of 9.53" in a 12.25" carrier and that modifications in the length of the insert are intended to fall within the scope of the invention. Nevertheless, it can be stated generally that an insert according to the invention has a longitudinal extent E substantially coextensive with the spacing S between the top and bottom rings 38, 30 of the rotor 32 and, hence, the width of the discharging mineral material as it traverses the wear edge 40. In the case of the 12.25" carrier, the typical insert used in the prior art was 12.25" long, .88" deep, and .38" wide, and had a total weight of 1.79 pounds. By reshaping the insert material as described above to be consistent with the wear pattern on the wear edge 40, the same amount of insert material will be more efficiently used, resulting in a longer performing carrier and less waste of the expensive insert material. Approximately .79 lbs, or about 45%, of a typical straight- edged insert is discarded when the middle of the insert has been worn nearly through by the usual wear pattern shown in Figs. 2A and 3A. In comparison, applicants have determined that, by using a reshaped insert according to the invention weighing 1.76 lbs, approximately .50 lbs, or only 28%, of the insert will need to be discarded after full utilization of the insert under exposure to the same wear pattern. The insert is held in place in the insert with industrial adhesive. Since the insert is constructed of one single piece, applicants have found adhesion of the insert to the carrier 12 to be more positive. In addition, it has been found unnecessary to add beads of weld in the insert at the top and bottom of the insert.

[ 028] Referring again to Figs. 1A, 2 and 4, a mineral retaining recession 66 formed in the inward face 18 of the carrier has a forward boundary formed by a mineral retaining surface 68 that is generally in parallel relation with the side surfaces 46 of the insert. In normal operation of the mineral breaker during which the rotor may spin at up to 3000 rpm, a rock bank 70 builds up behind the mineral retaining surface 68 protecting the carrier 12 and portions of the rotor 32 from the impact of mineral material being flung outward from the center of the rotor 32. The mineral material also fills small gaps between the top 34 of the carrier 12 and the perimeter of the aperture 36 in the top ring 38 of the carrier 12 and between the bottom 26 of the carrier 12 and the walls of the socket 28 in the bottom ring 30 of the carrier 12, helping to anchor the carrier 12 in position in the rotor 32. Removal of the carrier 12 from the rotor 32 involves chipping the rock away from the carrier and inserting a pry bar into pry bar channel 72 to lever the carrier upwards out of the socket 28. [ 029] Referring now to Figs. 5, 6, and 7A-7C, a second embodiment of the invention comprises a carrier 80 having two wear edges 82, 84. Similarly to the embodiment discussed above, the carrier 80 has a generally square profile having a forward face 86, an inward face 88, a following face 90, and an outer face 92. A first wear edge 82 is located at the intersection of the forward 86 and inward 88 surfaces of the carrier, and a second wear edge 84 is located at the intersection of the inward 88 and following 90 faces of the carrier 80. The bottom 93 of the carrier 80 drops into a socket 94 in the bottom ring 96 of a rotor 98, and the top 100 of the carrier 80 is held in place by an aperture 102 in the top ring 104 of the rotor 98. [ 030] A recess 106 is located in the wear face 108 of each of the wear edges 82, 84 of the carrier 80. In the embodiment shown in Figs. 6 and 7A-7C, the recess 106 has an inner edge 110 having a convex profile and the inserts 112 received in the recesses have an inner surface 114 having a convex profile conforming to that of the inner edge 110 of the recess 106 as discussed in respect to the first embodiment above shown in Figs. 1-4A. Each recess 106 is disposed at approximately a sixty degree angle with respect to the inward face 88 of the carrier 80. A middle plane 116 bisects the carrier longitudinally into a forward half 118 including the first wear edge 82 and a following half 120 which includes the second wear edge 84. The forward 118 and following 120 halves of the carrier 80 form mirror images of each other such that the carrier may be flipped over about a horizontal axis to position the following half 120 in place of the forward half 118. This has a significant practical advantage because each carrier having two wear edges effectively takes the place of two carriers having only one wear edge. Moreover, at a point during operation of the breaker when the first wear edge 82 has been worn down such that it has lost its functional value, such as is shown in Fig. 7A, a "replacement" is readily at hand in the second wear edge 84. This has the added advantage that the mineral breaker need not suffer an extended and expensive period of down time while a replacement wear tip is located. Moreover, the second wear edge 84 acts as a de facto safety backup for the first wear edge 82. Due to the extreme environment in which wear tips must function, it is not uncommon for an insert to fall out, break or otherwise fail, leaving the surrounding carrier material exposed to erosion from the mineral material streaming out of the port edge. If there is only wear edge in the carrier, the entire carrier may rapidly fail exposing the rotor and other parts of the breaker to potential damage. However, if a second wear edge is provided, it will essentially "take over" as a second line of defense for the first even if the failure of the first wear edge is not noticed for some time.

[ 031] A longitudinally extending groove 122 between the first 82 and second 84 wear edges forms a mineral retaining recession for retention of a rock bank 126 during operation of the breaker. The groove 122 has a V-shaped profile the side walls of which form a first mineral retaining surface 124 adjacent the first wear edge 82 and a second mineral retaining surface 128 adjacent the second wear edge 84. In a first position seen in Fig. 7A in which the first wear edge 82 is in position on the discharge port edge, the first mineral retaining surface 124 acts as the forward boundary for the rock bank. In a second position seen in Fig. 7B in which the carrier has been flipped over to position the second wear edge 84 adjacent the port edge, the second mineral retaining surface 128 takes over the function of being the forward boundary for the rock bank. Whichever wear edge is positioned on the port edge, the other wear edge becomes buried in the rock bank during operation of the breaker such that it is substantially protected from erosion.

[ 032] When it is necessary to remove the carrier from its seat in the rotor, the rock bank 126 is chipped away from the carrier 80 and a pry bar is fitted into a transversely extending lower pry bar channel 130 in the bottom of the carrier to lever it up. An upper pry bar channel 132 is provided at the top 100 of the carrier 80 for use when the carrier has been flipped over to make use of the second wear edge 84. [ 033] The outer face 134 of the carrier has a semi-circular profile as seen in Figs. 7A-7C which makes the carrier easier to handle, reduces the amount of raw material needed for manufacturing each unit, and presents an aesthetically pleasing appearance even after heavy use of the part. [ 034] A third embodiment of the invention is shown in Fig. 8 which is similar to the second embodiment described above except that each recess 136 extends through the full length of the carrier 138 and has a uniform rectangular profile to accommodate a standard straight-edged insert.

[ 035] There have thus been described certain preferred embodiments of a wear tip for a rotary mineral breaker. While preferred embodiments have been described and disclosed, it will be recognized by those with skill in the art that modifications are within the true spirit and scope of the invention. The appended claims are intended to cover all such modifications.

Claims

We claim:

1. A wear tip for the rotor of a centrifugal mineral breaker of the type having discharge ports through which mineral material is passed out of the rotor, the wear tip comprising: a carrier having at least one wear edge, said wear edge disposed transversely to the path of the mineral material being passed out of the rotor, said wear edge having a wear face and a recess in said wear face, and an insert of abrasion resistant material disposed in each said recess, said insert having an outer wear surface and an inner surface, said outer wear surface of said insert in general alignment with said wear face of said wear edge, said inner surface of said insert having an arcuate profile.

2. The wear tip as recited in claim 1 wherein: each said insert has a top portion, a bottom portion, and a middle portion, and said middle portion of said insert has a depth greater than that of said top and bottom portions.

3. The wear tip as recited in claim 1 wherein: said recess has an inner edge having a generally convex profile.

4. The wear tip as recited in claim 3 wherein: said inner edge conforms to said arcuate profile of said inner surface of said insert.

5. The wear tip as recited in claim 1 wherein: said arcuate profile has a radius of approximately 11.81 inches.

6. The wear tip as recited in claim 5 wherein: said carrier has a longitudinal dimension of approximately 12.25 inches, and said insert has a length of approximately 9.53 inches.

7. The wear tip as recited in claim 1 wherein: said carrier has a longitudinal dimension and said insert extends substantially the length of said longitudinal dimension.

8. The wear tip as recited in claim 1 , the rotor of the type having a top ring and a bottom ring spaced from the top ring, wherein: said arcuate profile of said inner surface of said insert extends substantially the entire distance between the top and bottom rings of the rotor.

9. The wear tip as recited in claim 1 wherein: said carrier has a generally square profile and an inward face, and said insert has generally parallel side surfaces disposed at approximately sixty degrees to said inward face.

10. The time as recited in claim 9 wherein: said inward face has a mineral retaining recession having a forward portion bounded by said wear edge, said forward portion including a material retaining surface disposed in generally parallel relation with said side surfaces of said insert.

1 1. The wear tip as recited in claim 1 wherein: said carrier has at least two wear edges.

12. The wear tip as recited in claim 11 wherein: said carrier has a generally square profile, an inward face, a forward face and a following face generally parallel to said forward face, and said at least two wear edges includes a first wear edge disposed at the intersection of said inward face and said forward face, and a second wear edge disposed at the intersection of said inward face and said following face.

13. The wear tip as recited in claim 12 wherein: said inward face of said carrier includes a longitudinally extending groove between said first and second wear edges.

14. The wear tip as recited in claim 13 wherein: said groove has a V-shaped cross-section.

15. The wear tip as recited in claim 12 wherein: each insert in said recesses in first and second wear edges has an inner surface having an arcuate profile.

16. The wear tip as recited in claim 15 wherein: each said insert has generally parallel side surfaces disposed at approximately sixty degrees to said inward face.

17. The wear tip as recited in claim 15 wherein: said carrier has a middle plane disposed in generally parallel relation to said forward and following faces, said middle plane longitudinally bisecting said carrier into a forward half and a following half, said forward and following halves forming mirroring symmetrical halves of said carrier about said middle plane.

18. The wear tip as recited in claim 11 wherein: said carrier has a generally square profile and an outward face, said outward face having an upper portion and a lower portion, and said upper and lower portions each having a transversely extending pry bar channel.

19. The wear tip as recited in claim 18 wherein: said outward face has a generally semi-circular profile intermediate said upper and lower portions.

20. The wear tip as recited in claim 1 wherein: said insert consists of a single piece of material.

21. A wear tip for the rotor of a centrifugal mineral breaker of the type having discharge ports through which mineral material is passed out of the rotor, the wear tip comprising: a carrier having an inward face, a forward face, a following face generally parallel to said forward face, a middle plane disposed in generally parallel relation to said forward and following faces, and at least two wear edges each disposed transversely to the path of the mineral material being passed out of the rotor, said at least two wear edges including a first wear edge disposed at the intersection of said inward face and said forward face, and a second wear edge disposed at the intersection of said inward face and said following face, said inward face having a longitudinally extending groove between said first and second wear edges, said wear edges each having a wear face and a recess in said wear face, said middle plane longitudinally bisecting said carrier into a forward half and a following half, said forward and following halves forming mirroring symmetrical halves of said carrier about said middle plane, and an insert of abrasion resistant material disposed in each said recess, each said insert having an outer wear surface, an inner surface, and generally parallel side surfaces disposed at approximately sixty degrees to said inward face of said carrier, said outer wear surface of each said insert generally in planar alignment with said wear face of one of said wear edges, said inner surface of each of said inserts having an arcuate profile.

22. The wear tip as recited in claim 21 wherein: said recess in said wear face of each of said wear edges has an inner edge having a generally convex profile conforming to said arcuate profile of said inner surface of said insert.

23. The wear tip as recited in claim 21 wherein: said carrier has a generally square cross-sectional profile.

24. The wear tip as recited in claim 21 wherein: said groove has a V-shaped cross-section.

25. The wear tip as recited in claim 21 wherein: said inner edge conforms to said arcuate profile of said inner surface of said insert.