GB2428709A

GB2428709A - Retainer sleeve for a rotary bit

Info

Publication number: GB2428709A
Application number: GB0608487A
Authority: GB
Inventors: Kenneth S Monyak; Daniel Mouthaan
Original assignee: Sandvik Intellectual Property AB
Current assignee: Sandvik Intellectual Property AB
Priority date: 2005-07-26
Filing date: 2006-04-28
Publication date: 2007-02-07
Also published as: AU2006201769A1; CA2543514A1; GB0608487D0; US20070024104A1; DE102006029388A1

Abstract

A retainer sleeve for retaining a rotary bit includes a longitudinally split cylindrical portion 72 defining a longitudinal axis, and at least four circumferentially spaced tabs 74 deformed generally radially inwardly from the cylindrical portion. The sleeve is formed from a sheet of spring steel having a thickness of at least 0.12cm (0.048 inches). Each tab comprises a connector section 74a inclined from the cylindrical portion in a generally radially inward and longitudinally rearward direction and a keeper section 74b extending rearwardly from a free end of the connector section. The keeper section includes a first flat surface 74b' facing the axis and oriented parallel thereto, and a second flat surface 74b'' facing rearwardly and oriented perpendicularly to the axis. The retainer sleeve may be used to retain a rotary bit used in the mining of soft rock formations such as asphalt and sandstone, and also hard materials such as rock and ice.

Description

I

RETAINER SLEEVE FOR A ROTARY BIT

1] The present invention relates primarily to the retention of rotary bits which are comprised of a hardened steel body with a hard tip and retained by a hardened steel retainer sleeve. These bits are mounted to a holder such as drums, chains and wheels in various orientations arid quantity. The bit is then engaged in soft rock formations ranging from asphalt to sandstone. The hard tip fixed to the end of the body directly engages the material being mined or cut.

2] The retainer sleeve permits the bit to rotate freely relative to the holder about the bit's center axis, while being restrained against axial dislodgment from the holder. Due to being freely rotatable, the tip is basically self-sharpening.

(0003] It should be understood that cutting mechanisms of the type described above have been used to cut through hard materials, such as rock and ice, in addition to cutting through softer materials such as asphalt. During the cutting of rock, the highest rate of bit wear occurs at the carbide tip, so the wear life of the bit is determined by the life of the carbide tip. However, during the cutting of relatively softer material, such as asphalt, coal, and salt, the highest rate of wear occurs at the bit head, i.e. erosion caused by cut asphalt rubbing and impacting against the head.

4] Thus, when cutting asphalt during a road resurfacing operation, the wear life of the cutting bit is determined by the life of the bit body rather than by the bit tip. Efforts have been made to increase the life of the bit body, such as, for example, disclosed in US 200510035649 wherein a ring is provided on a shoulder of the body rearwardly of the tip. The ring is formed of a material harder than the bit body and functions to deflect the substance bertg cut (e.g., asphalt) in a manner minimizing wear of the bit body. Thus, the life of the bit body is increased.

5] One consequence of the increased life of the bit body is that the tool life is now often determined by the life of the retainer sleeve (also called a keeper).

The sleeve is typically formed from a sheet of spring steel having a thickness no greater than 0.045 inches. A plurality of tabs are deformed radially inwardly from the cylindrical portion and are received in an annular groove of the bit shank.

The tabs are usually formed by a punching operation, resulting in each tab being generally U-shaped or V-shaped as viewed in a direction parallel to the axis (see Fig. 7). Due to rotary friction occurring between the sleeve and the bit shaft during a cutting operation, the sleeve eventually becomes worn thin, and becomes more susceptible to deformation. Thus, the sleeves gradually lose their bit-retention properties, enabling the bits to become dislodged. Therefore it would be desirable to provide a retainer sleeve which has a longer bitretention life.

SUMMARY OF THE INVENTION

6] One aspect of the present invention pertains to a retainer sleeve for retaining a rotary bit. The sleeve comprises a longitudinally slit cylindrical portion defining a longitudinal axis, and at least four circumferentially spaced tabs deformed generally radially inwardly from the cylindncal portion. The sleeve is formed from a sheet of spring steel having a thickness of at least 0.048 inches.

Each tab comprises a connector section inclined from the cylindrical portion in a generally radially inward and longitudinally rearward direction. Each tab further includes a keeper section extending rearwardly from a free end of the connector section. The keeper section includes a first fiat surface facing the axis and oriented parallel thereto, and a second flat surface facing rearwardly and oriented perpendicularly to the axis.

1] Another aspect of the invention pertains to a cutting assembly which comprises a rotary bit and the above described retainer sleeve for rotatably holding the rotary bit.

BRIEF DESCRIPTION OF THE DRAWINGS

8] The objects and advantages of the invention will become apparent from the following detailed description of a preferred embodiment thereof in connection with the accompanying drawings in which like numerals designate like elements.

Fig. I is a side elevational view of a cutting assembly according to the present invention which includes a cutter bit and a retainer sleeve therefore, Fig. IA is a fragmentary longitudinal sectional view of Fig. I depicting the manner in which the retainer sleeve engages a shank of the bit.

Fig. 2 is a side elevational view of the retainer sleeve in a relaxed state.

Fig. 3 is a longitudinal end view of the retainer sleeve.

Fig. 4 is an enlarged fragmentary view of Fig. 3.

Fig. 5 is a view taken in the direction of arrow B of Fig. 4.

Fig. 6 is a sectional view taken along the line 6-6 in Fig. 3 Fig. 7 is a view similar to Fig. 4 of a prior art retainer sleeve.

DESCRIPTON OF A PREFERRED EMBODIMENT

10009] Depicted in FIG. 1 and IA is a tool holder 40 adapted to be mounted, e.g., bolted or welded, to a vehicle (not shown), and a cutting tool or bit 42 mounted in the holder. There would normally be a plurality of holders 40 and bits 42 mounted on a carrier, such as a rotary drum disposed on the vehicle.

0] The holder can be formed of steel and includes a cylindrical bore 44 extending through a front face 46 of the holder.

[00111 The bit 42 includes a body formed for example of hardened steel, the body including a front head 50. A hard cutting tip 52 (e.g., formed of cemented carbide) is mounted in a front end of the head 50. The body defines a longitudinal center axis A. (0012] The head 50 includes a front annular flange 64 ci larger diameter than the bore 44. The body further includes a shank 56 extending rearwardly from the head 53, the shank 56 having a smaller diameter than the bore 44.

(0013] The body further includes a rear cyhndrical flange 58 situated at a rear end of the shank 56 and having a diameter no greater than (preferably equal to) that of the rest of the shank. Thus, an annular radial gap is formed between an outer cylindrical surface of the rear flange 58 and the cylindrical wall of the bore 44. A rear end 61 of the flange 56 is chamfered to facilitate entry into the bore.

(0014] The head 50 may include a ring 59 that is harder than the body and attached rearwardly of the tip 52 to reduce erosion of the head as disclosed in U.S. Published Application No. 2005/0035649.

5] The shank includes an annular groove 60 formed therein immediately in front of the rear flange, the groove 60 including a bottom surface 65.

(0016] A retainer sleeve 70 formed preferably of hardened steel is disposed between the shank 56 and the cylindrical wall of the bore 44. The retainer sleeve includes a cylindrical portion 72 which includes a longitudinal slit 75. The cylindrical portion 72 is long enough to cover substantially all of the shank 56.

[0011 In a relaxed state (Fig. 2), the cylindrical portion has an outer diameter larger than that of the bore 44. Thus, after being radially compressed and positioned in the bore (Fig. 1), the cylindrical portion attempts to rebound outwardly and makes tight contact with the bore wall, while the inner diameter of the compressed cylindrical portion 72 only loosely engages (or avoids engaging) the shank 56 to minimize any obstwction to free rotation of the tool.

8] The retainer sleeve 70 includes at least four circumferentially spaced tongues or tabs 74 bent generally radially inwardly from the cylindrical portion and received in the annular groove 60 to prevent axial dislodgement of the bit from the sleeve while permitting free rotation of the bit. If four tabs 74 are employed, they are circumferentially spaced apart generally equidistantly by an angle a of about 86 5 .

9] In accordance with the present Invention, the sleeve is formed from a sheet of hardened spring steel having a thickness T greater than that previously used in the making of retainer sleeves, the thickness T being at least 0.048 in.

Prior art retainer sleeves had a thickness no greater than 0.045 in. By increasing the thickness to at least 0.048 in., the sleeve according to the present invention has a longer wear life. Also the sleeve is more robust and exhibits a greater resistance to being compressed when being installed, so that its rebound strength is increased. Accordingly, it bears more tightly against the wall of the bore 44 and thus exerts greater friction force to resist dislodgement from the bore.

(0020] Also, the tabs 74 are shaped in a manner maximizing their bitretention properties. Previously, tabs Ta have been formed with a U.shape or V-shape as viewed in a direction parallel to the axis A (see Fig. 7). In contrast, the present tabs 74 have a generally rectangular shape as viewed parallel to the axis - see Fig. 3. The tabs are formed by being punched before the sheet is rolled into a cylindrical shape. More specifically, each tab 74 includes a connector section 74a which extends from the cylindrical portion 72 in a direction inclined radially inwardly and longitudinally rearwardly (see Fig. 6). and a keeper section 74b which extends rearwardly from a free end of the connector section 74a in a direction parallel to the axis A. Thus, the keeper section includes a flat surface 74b' facing the axis and lying in a plane parallel to the axis, and a flat rearwardly facing stop surface 74b" lying in a plane perpendicular to the axis A. Each tab could have a width W of about 0.21 inches.

1] Due to its increased thickness of at least 0.048 in., each tab has a longer wear life. Due to the increased thickness, and its generally rectangular shape, each tab is less likely to allow the bit shank to slip forwardly therepast as has occurred in connection with prior art V-shaped or U-shaped tabs.

2] It will be appreciated that a retainer sleeve according to the present invention exhibits longer life, greater resistance to dislodgement, and better bit- retention than prior and retainer sleeves.

3] Although the present invention has been described in connection with a preferred embodiment thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS: 1. A cutting assembly comprising: the bit defining a

longitudinal axis of rotation and comprising a body including a head, and a shank projecting longitudinally rearwardly from the head, the bit further including a hard tip mounted at a front end of the head; the shank including at a rear end, and pn annular groove disposed forwardly of the rear end and extending coaxially with the longitudinal axis, the retainer sleeve including a longitudinally split cylindrical portion extending around the shank and extending substantially to the rear end, and at least four circumfereritially spaced tabs deformed generally radially inwardly from the cylindrical portion and received in the annular groove; the sleeve formed of a sheet of spring steel having a thickness of at least 0.045 inches; each tab comprising a connector section inclined from the cylindrical portion in a generally radially inward and longitudinally rearward direction, and a keeper section extending rearwardly from a free end of the connector section, the keeper section including a first flat surface facing the axis and oriented parallel thereto, and a second flat surface facing rearwardly and oriented perpendicularly to the axis.
2. The cutter assembly according to claim I wherein thee are exactly four tabs.
3. A retainer sleeve for retaining a rotary bit, comprising a longitudinafly slit cylindrical portion defining a longitudinal axis, and at least four circumferentially spaced tabs deformed generally radially inwardly from the cylindrical portion, the sleeve formed from a sheet of spring steel having a thickness of at least 0.048 inches; each tab comprising a connector section inclined from the cylindrical portion in a generally radially inward and longitudinaHy rearward direction and a keeper section extending rearwardly from a free end of the connector section; the keeper section including a first flat surface facing the axis and oriented paraflel thereto, and a second flat surface facing rearwardly and oriented perpendicularly to the axis,
4. The retainer sleeve according to claim 3 wherein there are exactly four tabs.
5. A cutting assembly or a retainer sleeve for retaining a rotary bit substantially as any one embodiment herein described with reference to the accompanying drawings.