US3888028A

US3888028A - Digger tooth

Info

Publication number: US3888028A
Application number: US504697A
Authority: US
Inventors: Kenneth M White
Original assignee: Western Rock Bit Co Ltd
Current assignee: Western Rock Bit Co Ltd
Priority date: 1973-05-29
Filing date: 1974-09-10
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10

Abstract

A digger tooth having a cutting portion the lateral crosssection of which is defined by two curved surfaces, these being forming the upper and lower tooth surfaces, and varying in profile such that the thickness of the lateral section of the tooth varies from the center of the tooth outwardly at approximately a ratio of 1:4. Thus, since the edges of the tooth are thicker and therefore stronger, wear tends to take place in such a manner that the primary cutting portions of the tooth, defined by the edges, precede the excavating portion by a distance dependent upon the angle of attack of the tooth into the formation being dug.

Description

United States Patent White June 10, 1975 1 1 BIGGER TOOTH 3,326,302 6/1967 Washbond et a1. 172/713 3,396,671 8/1968 Roseber 172/771 x [75] Inventor: Kenneth Calgary 3,534,818 10/1970 Mascaro 172/540 x Albefla- Canada 3,624,827 11/1971 Liess.......... 37/142 R [731 Assign: 9?" Company FOREIGN PATENTS OR APPLICATIONS Calgary Alberta Canada 421,899 1/1935 United Kingdom 37/142 R 22 Filed: Sept. 10, 1974 455,459 3/1949 Canada .1 172/372 1,139,312 1/1969 United Kingdom 172/713 App]. No.: 504,697

Related U.S. Application Data Continuation of Ser. No. 373,939, June 27, 1973, abandoned.

[30] Foreign Application Priority Data May 29, 1973 Canada 172630 [52] US. Cl 37/142 R; 172/713; 299/79 [51] Int. Cl E02i 9/28 [58] Field of Search 37/141 R. 142 R. 142 A. 37/189,191 A; 172/713, 719, 765, 699, 604, 540; 294/54, 55; 299/79, 88, 91-93 [56] References Cited UNITED STATES PATENTS 1,395,048 10/1921 McKee 37/142 R 3,103,752 9/1963 Rockwell 172/771 X Primary ExaminerE. H. Eickholt ABSTRACT A digger tooth having a cutting portion the lateral cross-section of which is defined by two curved surfaces, these being forming the upper and lower tooth surfaces, and varying in profile such that the thickness of the lateral section of the tooth varies from the center of the tooth outwardly at approximately a ratio of 1:4. Thus, since the edges of the tooth are thicker and therefore stronger, wear tends to take place in such a manner that the primary cutting portions of the tooth, defined by the edges, precede the excavating portion by a distance dependent upon the angle of attack of the tooth into the formation being dug.

7 Claims, 9 Drawing Figures PATENTEDJUN 10 1975 3 888 28 SHEET 2 PATENTEUJUH 10 I975 SHEET FIG.6

FIELD OF THE INVENTION This invention relates to a replaceable digger tooth for cutting and excavating hard, ice encrusted formations as would be encountered in permanently frozen ground. The invention is also useful for excavating any hard, layered formation exhibiting aclotropic grain characteristics such as sandstone and limestone. The aforementioned formations can be failed by a scraping action as opposed to the harder isotropic granite and quartzite formations which are best failed by compressive force.

DESCRIPTION OF THE PRIOR ART Known digger teeth suffer primarily from the disadvantage that wear takes place rapidly, especially at the corners of the teeth. As wear progresses, the tooth becomes less able to penetrate the terrain upon which they are working, leading to an increase in the time used for excavating a given amount of material.

SUMMARY OF THE INVENTION The primary feature of this invention is the utilization of the undercutting principal at the tooth point. This tooth undercuts a small portion of the formation on each side of the material to be removed. The primary cutting portions of the tooth point precede the excavating portion by a distance dependent upon the angle of attack of the tooth into the formation. More specifcally, according to the invention a digger tooth comprises a mounting portion for attachment to an excavating machine, and a cutting portion formed by two curved surfaces as viewed in transverse cross-section, the surfaces forming the upper and lower tooth surfaces and varying in profile such that the outer longitudinal edges are thicker than the central portion. Thus, in use, wear of the tooth takes place initially in the thinner central portion so that the outer edges become the primary cutting portions.

By the above means, the life of the tooth is increased and therefore the efficiency of the machinery upon which such teeth are mounted is in turn increased.

Further advantages and features will become apparent from the following description of a preferred embodiment when read with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a tooth and holder mounted on the bucket lip of an excavating machine;

FIG. [A shows the relationship between the two curves on the forwardmost point of the cutting portion of the tooth;

FIG. 1B is a longitudinal section of the preferred tooth design taken along line D-D of FIG. 1;

FIG. 2 is a vertical plan view of the tooth and holder shown in FIG. I when the tooth is partially worn;

FIG. 3 is a side view, partially in section, of the worn tooth and holder shown in FIG. 2;

FIG. 4 is. a frontal view of the tooth and holder combination of FIGS. 2 and 3 taken parallel to the formation being excavated.

FIGS. 5 and 5A show a comparison between the prefe rred tooth and a conventional tooth at the same angle of attack.

FIG. 6 shows a partial longitudinal section of the preferred cutting structure adapted to a different type of tooth and holder combination.

DETAILED DESCRIPTION Referring to FIG. 1, the plan view shows the replaceable digger tooth I mounted in a holder 2 attached to a bucket lip 3. In the preferred embodiment the cutting edge 4 of the tooth l is formed, from the frontal view, of two circular arcs. The circular arcs are of different radius and are offset to one another such that the thickness of the cutting edge 4 increases from the center outwards. FIG. 1A shows a frontal view of the cutting edge of FIG. 1 with the upper radius R and the lower cutting edge radius R optimized when R T and W are set as defined below.

These equations generate the curved cutting edge profile in such a fashion that the tooth section increases from a thickness T in the center to 4T on the outside edge of the cutting point or when X i W/ ,C 4T.

FIG. 1B shows the dimension B as being constant over the majority of the cutting point length and T increasing at the rate of 2.5T per inch of cutting point length. The blend-out radius R, is equal to or greater than R and is dependent upon actual tooth loading conditions. Protection for the leading edge of tooth holder 2 as shown in FIG. I is provided by the blend out radius R, and the raised step 9 on the forwardmost portion of the shaft 10. Provision for retaining means is provided for by recess 11 and a retainer as fully described in US. Pat. No. 3,665,623 granted on May 30th, 1972 to Kenneth M. White or Canadian Pat. No. 890,315 granted on Jan. 11th, 1972 to Kenneth M. White can be used.

FIG. 2 is a plan of the tooth and holder combination and illustrates the worn tooth profile 12 that the aforementioned cutting edge design generates. The leading edges 13 precede the tooth removal portion and under cut the material to be removed. As the tooth proceeds into the formation the curved surface generated by R in FIG. 1A places a lateral shear load on the formation. The lateral shear load combined with the tensile load generated due to the angle of attack of the tooth on the formation causes formation failure.

As shown in FIG. 3, the angle of attack 15 determines the amount of undercut 16. A quick and simple method of varying this angle is described in Canadian Pat. No. 896,423 granted on Mar. 28th, 1972 to Kenneth M. White. Increasing the angle of attack causes the undercut distance 16 to decrease for soft formations such as clay. The cutting edge on the tooth wears sharper and excavates more efficiently than teeth not having the preferred cutting edge profile. Reducing the angle of attack causes the undercut distance to increase and the tooth loading to change from shear to compressive. In permafrost formations, the tendency is for the teeth to slide on the ice. In this type of formation the reduced angle of attack presents a long slender leading edge to penetrate the formation much the same as an ice pick. The cutting edge material on the tooth represented by 13 working under the material being excavated tends to hold the teeth in the formation. This overcomes a major problem with conventional teeth which is rounding of the tooths cutting edge so that the bucket wheel on rotary trenching machines in which the teeth are mounted slides on the formation rather than digging in.

Maintaining B as shown in FIGS. 1A and 1B constant generates two raised areas shown as

flats

17 and 18 in H0. 4. Placing the raised areas along the outer edges of the tooths cutting surface causes the cutting edge to wear straight as shown in FIG. 4 from the front view. in extremely abrasive conditions there is a tendency for the profile to wear as shown by the phantom line 19. This leads to a compound shearing radius on the cutting edge and indicates the angle of attack should be reduced for that particular formation. Maintaining a flat cutting profile with square corners is important in excavating hard layered formations since the sharp corner acts as a stress riser for shearing failure across the formation.

H68. 5 and 5A illustrate the comparison between the sliding surface on the preferred cutting profile and a conventional tooth at the same angle of attack. The conventional tooth shown in FIG. 5A wears according to the phantom line 20 and cuts a rounded bottom groove in the formation which leads to increased sliding and excavating time.

What l claim as my invention is:

l. A digger tooth for releasable attachment to an excavating machine, comprising a mounting portion and a cutting portion having a cutting edge, said cutting portion having an upper concave and a lower convex surface as viewed in transverse section, said surfaces varying in profile such that the outer edges of the cutting portion are thicker than its central part, whereby when said tooth is mounted and working said outer edges undercut a portion of material on each side of the material to be removed.

2. A digger tooth according to claim 1, wherein said central part of the cutting portion gradually increases in thickness rearwardly from the cutting edge.

3. A digger tooth according to claim 2, wherein the increase in thickness rearwardly of the central part is at the rate of approximately 2.5 times the thickness of the central part of the cutting edge per inch of cutting portion length as viewed in longitudinal section.

4. A digger tooth according to claim 1, wherein said outer edges of the cutting portion are substantially parallel.

5. A digger tooth according to claim I, wherein said upper concave and lower convex surfaces as viewed in transvere section are circular arcs.

6. A digger tooth according to claim 1 in which the profile forming the upper surface of the cutting portion is substantially constant over the length of the cutting portion and the profile forming the lower surface of the cutting portion is moving relative to the upper surface such that the thickness of the central portion of a lateral section is increasing at a rate approximately 2.5 times the cutting portion terminal thickness per inch of longitudinal cutting portion length as viewed in longitudinal section, said thickness increasing from the terminus of the cutting portion towards the mounting means.

7. A digger tooth according to claim 1, wherein said thicker outer edges have narrow, flat, upper surfaces. l 1k

Claims

1. A digger tooth for releasable attachment to an excavating machine, comprising a mounting portion and a cutting portion having a cutting edge, said cutting portion having an upper concave and a lower convex surface as viewed in transverse section, said surfaces varying in profile such that the outer edges of the cutting portion are thicker than its central part, whereby when said tooth is mounted and working said outer edges undercut a portion of material on each side of the material to be removed.

5. A digger tooth according to claim 1, wherein said upper concave and lower convex surfaces as viewed in transvere section are circular arcs.

7. A digger tooth according to claim 1, wherein said thicker outer edges have narrow, flat, upper surfaces.