Hob-type cutting tool with improved sealing

Abstract

A roller cutter for a drill bit for raise boring, the roller cutter having a shaft with a longitudinal centerline; a hub rotatably mounted on the shaft; a seal holder located between an axial end of the hub and an axial end of the shaft, the seal holder supporting a primary cutter seal that provides sealing between the shaft and the hub in both axial and radial directions, and an auxiliary cutter seal located between the seal holder and the hub and that provides sealing in the axial direction.

Description

Technical Field

[0001] The present invention relates to a roller cutter for a drill bit used for drilling earth and rock formations, particularly for raise boring operations. Background Art

[0002] Reaming drill bits used in raiseboring operations are used to drill a raisehole by reaming the pilot hole to the desired final diameter. The drill bit typically consists of multiple cutters arranged in a ring on the raisebit body. These cutters rotate as the drill bit is fed upward, breaking up the rock surrounding the pilot hole. During drilling, the drill rod is positioned in the pre-drilled pilot hole.

[0003] However, there is a problem: known sealing solutions are insufficient, and some chips, water, and particles still enter the bearing system, causing damage to and reducing the life of the hob components. Replacing these components is both expensive and time-consuming, so it would be desirable to reduce the frequency of replacement. Inadequate sealing also carries the risk of grease leaking from the hob, which would result in a loss of lubrication.

[0004] EP2781684 discloses a sealing system comprising an O-ring made of an elastomeric material which forms a further radial seal, however this has the problem of generating excessive heat which leads to accelerated degradation of the sealing system, thereby reducing the effectiveness of the seal.

[0005] Therefore, the problem to be solved is how to provide an improved sealing solution which is able to seal effectively without generating excessive heat and thus increase the life of the components in the rotary cutter. Summary of the Invention

[0006] An object of the present invention is to provide a new and improved seal assembly for a hob cutter.

[0007] This object is achieved by providing a roller cutter for a drill bit for raise boring; the roller cutter has a shaft with a longitudinal centerline; a hub rotatably mounted on the shaft; a seal holder located between an axial end of the hub and an axial end of the shaft arranged at least at one end of the roller cutter; the seal holder supports a main tool seal, which provides a seal between the shaft and the hub in both an axial direction and a radial direction, characterized in that a secondary tool seal is located between the seal holder and the hub, and the secondary tool seal provides a seal in the axial direction.

[0008] Advantageously, by providing an axial seal between the seal holder and the hub, the main seal is protected from damage. Preventing or reducing damage to the main seal means there's less chance of chips entering the cutter and wearing out its components. It also reduces the risk of grease leaking from the cutter, which could lead to a loss of lubrication. This ultimately reduces the time and cost of replacing worn or damaged parts of the cutter. If the main cutter seal fails, it can lead to system failure and shorten the life of the drill bit.

[0009] Preferably, the seal holder has a radially upwardly projecting region having an axially outermost end and an axially innermost end, and wherein the radially upwardly projecting region is stepped so that the axially outermost end projects radially upwardly further than the axially innermost end. Advantageously, the presence of the step in the seal holder means that the auxiliary tool seal can be accommodated therein. The presence of the step means that the auxiliary tool seal remains stationary relative to the seal holder, thereby maintaining correct alignment relative to the rotating hub even when the hob rotates and vibrates. The presence of the step in the seal holder also reduces the surface area of the auxiliary tool seal exposed to chips and, therefore, reduces the risk of damage to the auxiliary tool seal.

[0010] Preferably, the auxiliary cutter seal is made of an elastomeric material. By using an elastomeric material, this means that the auxiliary cutter seal is flexible and can maintain a good seal to the hub even when components of the drill bit move and vibrate.

[0011] Preferably, the auxiliary tool seal is a V-ring seal, a wiper seal, or a lip seal. Advantageously, these types of seals can form a seal in the axial direction between the seal holder and the hub. In addition, the contact area between the auxiliary tool seal and the hub is kept to a minimum, which reduces the heat generated by friction at the contact surfaces. It is preferable to avoid heat generation because heat can accelerate the degradation of the seal and lubricant. Therefore, avoiding heat accumulation will increase the lifespan and effectiveness of the seal.

[0012] Preferably, a first surface of the auxiliary tool seal is supported by an upper surface of the axially innermost end of the seal holder, and a second surface of the auxiliary tool seal is supported by a side surface of a radially outermost portion of the seal holder, wherein the auxiliary tool seal includes a flexible lip that presses against a support surface of the hub to provide an axial seal. Advantageously, an axial seal is created. Axial seals generate less friction and, therefore, less heat than auxiliary seals that seal in a radial direction, thereby preventing premature failure of sealed components and lubricant.

[0013] Optionally, the side surface of the radially outermost portion of the seal retainer includes a groove. Advantageously, the inclusion of the groove means that the secondary tool seal is held in place even more rigidly, thereby maintaining the quality of the seal. Furthermore, a greater surface area of the secondary tool seal is protected from damage from chips, thereby increasing the life of the seal.

[0014] Preferably, the distance between the hub's support surface and the axially outermost side surface of the seal holder is less than the width of the auxiliary tool seal before installation in the hob. Advantageously, this means that the auxiliary tool seal is slightly compressed while held in place, preventing it from moving axially, thereby ensuring that the seal against the hub's support surface is maintained. This means that the auxiliary tool seal is held in place by axial pretension, which prevents chips and dust from entering the hob.

[0015] Preferably, the auxiliary tool seal is held in place by pre-tensioning, glue or clamping. Advantageously, this means that the auxiliary tool seal will stay in the correct position so that it is immobile relative to the seal holder and can maintain a good seal against the rotating bearing surface of the hub. More preferably, the auxiliary tool seal is held in place only by pre-tensioning. Using pre-tensioning alone to hold the auxiliary tool seal in place means that the auxiliary seal can be easily replaced if necessary. Furthermore, assembling the seal using pre-tensioning means that no additional components will become damaged if the seal is exposed to a harsh environment.

[0016] Preferably, the secondary cutter seal and seal holder are stationary. This means a good seal is maintained to prevent chips from entering the hob. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Specific embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings:

[0018] Figure 1 : Schematic illustration of an axial cross section through the raise boring head.

[0019] Figure 2 : Schematic diagram of the hob.

[0020] Figure 3 : A cross section through one of the hobs.

[0021] Figure 4 : Figure 3 An enlarged view of the seal holder is shown in greater detail.

[0022] Figure 5a : Magnified view of the hob in the seal retainer position before installing the auxiliary tool seal.

[0023] Figure 5b : Magnified view of the auxiliary tool seal before installation into the seal holder.

[0024] Figure 6 : Alternative version of the seal holder with grooves. DETAILED DESCRIPTION

[0025] Figure 1 A pilot hole 11 is shown pre-drilled in a known manner between an upper and lower level (not shown). The drill bit 10 is connected to a drive drill rod 12 and then rotated and pressed against an annular surface 13 surrounding the pilot hole 11.

[0026] The drill bit 10 includes a main body 16 and a plurality of roller cutters 14 rotatably mounted on the main body 16 using saddles 15 (also referred to as fasteners). The saddles 15 are mounted on the main body 16. The drive drill rod 12 is connected to the main body 16. The main body 16 has a mounting surface 17 on which the saddles are carried.

[0027] Figure 2 Each hob 14 is shown to include a row of circumferential balls or cutting members 25 formed of cemented carbide, mounted in a known manner. The saddle 15 includes a bottom surface 18 that is intended to be connected to the mounting surface 17 of the body 16, for example, by bolting or welding. The saddle 15 also includes two saddle tool mounts 19, 20, between which the hob 14 is mounted. The saddle tool mounts 19, 20 are formed with arms 21 at their ends facing away from the bottom surface 18. The arms 21 are of varying lengths from the bottom surface 18. Fastening means in the form of bolts 22 and nuts 23 are used to hold the hob 14 and the saddle 15 together.

[0028] Figure 3A cross-section of a hob 14 is shown having a shaft 33 with a longitudinal centerline 40. Directions throughout this specification refer to the centerline 40. Axial directions are directions along the centerline 40, as indicated by a first arrow 42, and radial directions are directions along the radius of the cross-section of the hob 14, as indicated by a second arrow 44. The end of the shaft 33 along the longitudinal centerline 40 has a square shape machined therein for abutting against a support surface (not shown) in the arm 21 of the saddle 15. A hub 24 (also referred to as a cutter housing) is rotatably mounted on the shaft 33 by bearing members 26, 28. The bearing members 26, 28 are received in circumferential grooves in the hub 24. The hub 24 is axially locked relative to the shaft 33. The bearing member 26 is received in a circumferential groove in the hub 24. The hub 24 is axially locked relative to the shaft by a locking member 28, preferably in the form of a ball that cooperates with circumferential grooves in both the shaft 33 and the hub 24. Between the axial ends of the hub 24 of the cutter hob 14 and the axial ends of the shaft 33, there is a seal retainer 46 at at least one end, and preferably at both ends.

[0029] Figure 4 An enlarged view of the hob 14 at the location of the seal retainer 46 is shown. Figure 5a An enlarged view of the hob 14 is shown at the location of the seal retainer 46 prior to installation of the secondary cutter seal 62 . Figure 5b An enlarged view of the auxiliary tool seal 62 is shown before it is installed on the seal holder 46. The seal holder 46 is typically equipped with a relief hole with a plug installed in the hole to prevent lubricant from leaking out through the hole (not shown), and the seal holder 46 is typically made of mild steel. The seal holder 46 supports the main tool seal 48. The main tool seal 48 typically includes two O-rings 50 made of an elastomeric material and two sealing rings 52 made of cast iron. The main tool seal 48 forms a seal between the hub 24 and the shaft 33 in both the axial direction and the radial direction. The main tool seal 48 is intended to prevent drill cuttings and other impurities from entering the hob 14 and the bearing system, and to prevent lubricant from leaking out of the hob 14.

[0030] The seal retainer 46 has a radially upwardly projecting region 54 having an axially outermost end 56 and an axially innermost end 58. The radially upwardly projecting region 54 is stepped such that the axially outermost end 56 projects radially upward to a greater extent than the axially innermost end 58, thereby forming a stepped region 60. The axially outermost end 56 is axially and radially further away from the primary tool seal 48 than the axially innermost end 58.

[0031] The axially innermost end 58 of the axially upwardly projecting region 54 of the seal holder 46 houses a secondary tool seal 62. The secondary tool seal 62 protects the primary tool seal 48. The secondary tool seal 62 must be able to form an axial seal between the seal holder 46 and the hub 24 using a relatively small contact area relative to the size of the seal. The secondary tool seal 62 may be in the form of, for example, a V-ring seal, a pressure seal, a lip seal, or any other seal that is capable of creating a seal against the rotating surface of the hub 24 using only a relatively small contact area relative to the size of the seal.

[0032] The auxiliary tool seal 62 is housed in the stepped area 60 of the seal holder 46 so that a first surface 64 of the auxiliary tool seal 62 is supported by an upper surface 66 of the axially innermost end 58 of the seal holder 46, and a second surface 68 of the auxiliary tool seal 62 is supported by a side surface 70 of the axially outermost end 56 of the seal holder 46. The auxiliary tool seal 62 also has a flexible lip 72 that presses against a support surface 74 of the hub 24 and then slides against the support surface 74 of the hub 24, thereby forming a seal in the axial direction. The auxiliary tool seal 62 is fixedly located on the seal holder 46. The auxiliary tool seal 62 is made of a heat-resistant and wear-resistant elastic material (e.g., rubber). The auxiliary tool seal 62 is held in place by pre-tensioning, glue, or a clamp. Preferably, the secondary cutter seal 62 is held in place solely by radial pretensioning by the seal retainer 46 being slightly larger in size than the secondary cutter seal 62 so that it fits into place by being stretched onto the seal retainer 42 .

[0033] The distance (D) between the support surface 74 of the hub 24 and the side surface 70 of the axially outermost end 56 of the seal holder 46 is slightly smaller than the width (W) of the secondary tool seal 62 before being mounted on the seal holder 46, so that when the secondary tool seal 62 is inserted, it compresses to ensure a constant seal against the support surface 74. The secondary tool seal 62 forms a seal between the seal holder 46 and the hub 24 in the axial direction and is intended to protect the primary tool seal 48 from wear and damage.

[0034] Figure 6 Optionally, a groove 76 is shown in the side surface 70 of the seal holder 46, with the secondary cutter seal 62 positioned in the groove 76. The secondary cutter seal 62 abuts the outer diameter 78 of the groove 76, the upper surface 66 of the axially innermost end 58 of the seal holder 46.

Claims

1. A roller cutter (14) for a drill bit (10) for raise boring; The hob has a shaft (33) with a longitudinal centerline (40); a hub (24) rotatably mounted on the shaft (33); a seal retainer (46) located between an axial end of the hub (24) and an axial end of the shaft (33) disposed at least at one end of the hob (14); The seal holder (46) supports a primary tool seal (48) that provides sealing between the shaft (33) and the hub (24) in both axial and radial directions; Its characteristics are: A secondary tool seal (62) is located between the seal holder (46) and the hub (24), and the secondary tool seal (62) provides sealing in the axial direction, The seal retainer (46) includes a radially upwardly projecting region (54) having an axially outermost end (56) and an axially innermost end (58), and wherein the radially upwardly projecting region (54) is stepped such that the axially outermost end (56) projects radially upward to a greater extent than the axially innermost end (58), Furthermore, the first surface (64) of the auxiliary tool seal (62) is supported by the upper surface (66) of the axially innermost end (58) of the seal holder (46), and the second surface (68) of the auxiliary tool seal (62) is supported by the side surface (70) of the radially outermost portion of the seal holder (46), and wherein the auxiliary tool seal (62) includes a flexible lip (72) that presses against the support surface (74) of the hub (24) to provide sealing in the axial direction.

2. The hob (14) according to claim 1, wherein The auxiliary tool seal (62) is made of elastic material.

3. The hob (14) according to any one of claims 1-2, wherein: The auxiliary tool seal (62) is a V-ring seal, a pressure seal or a lip seal.

4. The hob (14) according to any one of claims 1 to 3, wherein: The side surface (70) of the radially outermost portion of the seal retainer (46) includes a groove (76).

5. The hob (14) according to any one of the preceding claims, wherein A distance (D) between the support surface (74) of the hub (24) and the side surface (70) of the axially outermost end (56) of the seal retainer (46) is less than a width (W) of the auxiliary cutter seal (62) prior to installation on the cutter hob (14).

6. The hob (14) according to any one of the preceding claims, wherein The secondary cutter seal (62) is held in place by pre-tensioning, glue or clamping.

7. The hob (14) according to any one of the preceding claims, wherein The secondary cutter seal (62) and the seal retainer (46) are stationary.

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