Patent Description:
Reamer bits for raise boring operations are used for drilling a raise by reaming a pilot hole to the desired final diameter. The drill bit is usually composed of a number of rolling cutters which are arranged in an annular pattern on a raise bit body and are rotated at the same time as the bit is fed upwardly, thus disintegrating the rock around the pilot hole. During the drilling the stem is located in the pilot hole, which has been drilled in advance.

However, there is a problem that known sealing solutions are not sufficient and still some cuttings, water and particles do enter the bearing system which, causing damage to and reducing the lifetime of the components of the roller cutter. Replacing these components is costly and time consuming and so it is desirable to reduce the frequency this is required to be done. Inadequate sealing also has the risk that there is a leakage of grease from the roller cutter which would lead to a loss of lubrication.

<CIT> discloses an exemplary roller cutter with a sealing system comprising a primary cutter seal and a secondary cutter seal. <CIT> discloses an exemplary roller cutter for a drill head for raise boring. <CIT> discloses a sealing system comprising O-rings made of a resilient material that forms a further radial seal, however the problem with this is that too much heat is generated which leads to accelerated degradation of the sealing system, thereby reducing the effectiveness of the seal.

Therefore, the problem to be solved is how to provide an improved sealing solution that is capable of effectively sealing without generating excessive heat and therefore increasing the lifetime of the components in the rotary cutter.

It is an objective of this invention to provide a novel and improved sealing assembly for a roller cutter.

The objective is achieved by providing a roller cutter for a drill head for raise boring as defined by independent claim <NUM>; said roller cutter having a shaft with a longitudinal centre line; a hub rotatably mounted on the shaft; a seal retainer located between the axial ends of the hub and the shaft at least arranged at one end of the roller cutter; the seal retainer supporting a primary cutter seal providing sealing between the shaft and the hub in both axial and radial directions, a secondary cutter seal is located between the seal retainer and the hub, and that the secondary cutter seal provides sealing in the axial direction.

Advantageously, by providing a seal between the seal retainer and the hub in an axial direction this protects the primary seal from damage. If damage to the primary seal is prevented or reduced this will mean that there is less chance of cuttings entering the roller cutter and wearing at its components. There is also a reduced risk of leakage of grease from the roller cutter which would lead to a loss of lubrication. This will ultimately reduce the time and cost spent replacing worn or damaged components of the roller cutters. If the primary cutter seal fails, this could lead to a complete system failure and reduction in the lifetime of the drill bit.

Preferably, the seal retainer has a radially upward projecting region having an axially outermost end and an axially innermost end and wherein the radially upward projecting region is stepped such the axially outermost end projects radially upwards more than the axially inner most end. Advantageously, the presence of the step in the seal retainer means that a secondary cutter seal can be accommodated therein. The presence of the step means that the secondary cutter seal is held stationary relative to the seal retainer, so that correct alignment with respect to the rotating hub is maintained even as the roller cutter rotates and vibrates. The presence of the step in the seal retainer also reduces the surface area of the secondary cutter seal being exposed to cuttings and therefore reduces the risk of damage to the secondary cutter seal occurring.

Preferably, the secondary cutter seal is made of a resilient material. By using a resilient material, it means that the secondary cutter seal is flexible and able to maintain a good seal against the hub even when the components of the drill bit move and vibrate.

Preferably, the secondary cutter seal is a v-ring, wiper or lip seal. Advantageously, these types of seal can form seal between and the seal retainer and the hub in the axial direction. Additionally, the contact area between the secondary cutter seal and the hub is kept to a minimum which reduces the amount of heat created from friction at the contacting surface. The generation of heat is preferably avoided as it accelerates the degradation of the seal and lubricants. Therefore, avoiding the build-up of heat will improve the lifetime and effectiveness of the seal.

Furthermore, a first surface the secondary cutter seal is supported by the upper surface of the axially innermost end of the seal retainer and a second surface of the secondary cutter seal is supported by a side surface of the radially outermost part of the seal retainer and wherein the secondary cutter seal comprises a flexible lip which presses against a supporting face of the hub providing sealing in an axial direction. Advantageously, an axial seal is created. The axial seal generates less friction and therefore less heat than a secondary seal that seals in a radial direction, thereby preventing premature failure of the sealing components and lubricants.

Z r The J Z side surface of the radially outermost part of the seal retainer comprises a groove. Advantageously, the addition of the groove means that the secondary cutter seal is even more rigidly held in place so that the quality of the seal is maintained. Furthermore, a larger surface area of the secondary cutter seal is protected from exposure to damage from cuttings, therefore increasing the lifetime of the seal.

Preferably, a distance between the supporting face of the hub and the side surface of the axially outermost end of the seal retainer is less than a width of the secondary cutter seal before installation into the roller cutter Advantageously, this means that the secondary cutter seal is compressed slightly when held in position so that is not able to move axially, thus ensuring that the sealing against the supporting face of the hub is maintained. It means that the secondary cutter seal is held in place by axial pre-tension which will prevent cuttings and dirt from passing into the roller cutter.

Preferably, the secondary cutter seal is held in place by pre-tension, glue or clamping. Advantageously, this means that secondary cutter seal will stay in the correct position, so that it is stationary with respect to the seal retainer and able to maintain a good seal against the rotating supporting face of the hub. More preferably, the secondary cutter seal is held in place by pre-tension alone. By using pre-tension alone to hold the secondary cutter seal in place means that the secondary seal can easy be replaced if necessary. Furthermore, fitting of the seal using pre-tension means there are no additional components that could be compromised if the seal is exposed to harsh environments.

Preferably, the secondary cutter seal and the seal retainer are stationary. This means that a good seal is maintained to prevent the passage of the cuttings into the roller cutter.

A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings:.

<FIG> shows how a pilot hole <NUM>, which is pre-drilled in known way, between an upper and lower level (not shown). A drill head <NUM> is connected to drive stem <NUM>, then the drill head <NUM> is rotated and pressed against the ring-shaped surface <NUM> that surrounds the pilot hole <NUM>.

The drill head <NUM> comprises a body <NUM> and a plurality of roller cutters <NUM> which are rotatably mounted on the body <NUM> using saddles <NUM> (otherwise known as fasteners). The saddles <NUM> are mounted on the body <NUM>. The drive stem <NUM> is connected to the body <NUM>. The body <NUM> has a mounting surface <NUM> on which the saddles are carried.

<FIG> shows that each roller cutter <NUM> comprises circumferal row of buttons or cutting members <NUM> of cemented carbide that are mounted in a known way. The saddle <NUM> comprises a bottom surface <NUM>, which is intended to be connected, for instance by bolting or welding, to the mounting surface <NUM> of the body <NUM>. The saddle <NUM> also comprises two saddle cutter seats <NUM>, <NUM> between which the roller cutter <NUM> is mounted. The saddle cutter seats, <NUM>, <NUM>, are, at the ends thereof facing away from the bottom surface <NUM> formed with arms <NUM>. The arms <NUM> have different lengths from the bottom surface <NUM>. Fastening devices in the form of threaded bolts <NUM> and nuts <NUM> are intended to hold the roller cutter <NUM> and saddle <NUM> together.

<FIG> shows a cross section of the roller cutter <NUM> having a shaft <NUM> with a longitudinal centre line <NUM>. Directions in this description refer to the centre line <NUM>. Axially refers to a direction along the centre line <NUM> illustrated by a first arrow <NUM> and radially refers to a direction along the radius of the cross section of the roller cutter <NUM>, illustrated by a second arrow <NUM>. The ends of the shaft <NUM> along the longitudinal centre line <NUM> have a machined square, which is intended to abut against a support surface (not shown) in the arms <NUM> of the saddle <NUM>. A hub <NUM> (otherwise known as a cutter shell) is rotatably mounted on the shaft <NUM> via bearing members <NUM>, <NUM>. The bearing members <NUM>, <NUM> are received in circumferal grooves in a hub <NUM>. The hub <NUM> is locked axially in relation to the shaft <NUM>. The bearing members <NUM> are received in a circumferential groove in the hub <NUM>. The hub <NUM> is locked axially in relation to the shaft by means of a locking member <NUM>, preferably in the form of balls, which co-operate with circumferential grooves in both the shaft <NUM> and the hub <NUM>. Between the axial ends of the hub <NUM> and the shaft <NUM> of the roller cutter <NUM> at least at one end, preferably both, there is a seal retainer <NUM>.

<FIG> shows an enlargement of the roller cutter <NUM> in the location of the seal retainer <NUM>. <FIG> shows an enlargement of the roller cutter <NUM> in the location of the seal retainer <NUM> before the secondary cutter seal <NUM> is installed. <FIG> shows an enlargement of the secondary cutter seal <NUM> before being installed onto the seal retainer <NUM>. The seal retainer <NUM> are typically equipped with relief holes having plugs mounted in said holes to prevent lubricant from leaking out through said holes (not shown) and are typically made from mild steel. The seal retainer <NUM> supports a primary cutter seal <NUM>. The primary cutter seal <NUM> typically comprises two O-rings <NUM> made of a resilient material and two seal rings <NUM> made of cast iron. The primary cutter seal <NUM> creates a seal between the hub <NUM> and the shaft <NUM> in both axial and radial directions. The primary cutter seal <NUM> is intended to prevent drill cuttings and other impurities from entering into the roller cutter <NUM> and the bearing system and to prevent leakage of the lubricants from the roller cutter <NUM>.

The seal retainer <NUM> has a radially upward projecting region <NUM> having an axially outermost end <NUM> and an axially inner most end <NUM>. The radially upward projecting region <NUM> is stepped such that the axially outermost end <NUM> projects radially upwards to a larger extent than the axially inner most end <NUM> therefore forming a stepped region <NUM>. The axially outermost end <NUM> is located axially and radially further from the primary cutter seal <NUM> compared to the axially inner most end <NUM>.

The axially innermost end <NUM> of the axially upward projecting region <NUM> of the seal retainer <NUM> accommodates a secondary cutter seal <NUM>. The secondary cutter seal <NUM> protects the primary cutter seal <NUM>. The secondary cutter seal <NUM> must be capable of forming an axial seal between seal retainer <NUM> and the hub <NUM> using a small contact area relative to the size of the seal. The secondary cutter seal <NUM> could for example be in the form of a v-ring, wiper seal, lip seal or any other seal that is able to create a seal against the rotating surface of the hub <NUM> using only a small contact area relative to the size of the seal.

The secondary cutter seal <NUM> is accommodated in the stepped region <NUM> of the seal retainer <NUM>, such that a first surface <NUM> of the secondary cutter seal <NUM> is supported by the upper surface <NUM> of the axially innermost end <NUM> of the seal retainer <NUM> and a second surface <NUM> of the secondary cutter seal <NUM> is supported by a side surface <NUM> of the axially outermost end <NUM> of the seal retainer <NUM>. The secondary cutter seal <NUM> also has a flexible lip <NUM> which presses towards and then slides against a supporting face <NUM> of the hub <NUM> forming a seal in an axial direction. The secondary cutter seal <NUM> sits stationary on the seal retainer <NUM>. The secondary cutter seal <NUM> is made of a resilient material that is resistant to heat and wear e.g. rubber. The secondary cutter seal <NUM> is held in place by pre-tension, glue or clamp. Preferably, the secondary cutter seal <NUM> is held in place by radial pre-tension alone by the seal retainer <NUM> being dimensioned slightly larger than the secondary cutter seal <NUM>, so that it is fitted in place by being stretched onto the seal retainer <NUM>.

The distance (D) between the supporting face <NUM> of the hub <NUM> and the side surface <NUM> of the axially outermost end <NUM> of seal retainer <NUM> is slightly less than the width (W) of the secondary cutter seal <NUM> before being installed onto the seal retainer <NUM>, so that when the secondary cutter seal <NUM> is inserted it compresses to ensure constant sealing against the supporting face <NUM>. The secondary cutter seal <NUM> forms a seal between the seal retainer <NUM> and the hub <NUM> in an axial direction and is intended to protect the primary cutter seal <NUM> from wear and damage.

Claim 1:
A roller cutter (<NUM>) for a drill head (<NUM>) for raise boring;
said roller cutter having a shaft (<NUM>) with a longitudinal centre line (<NUM>);
a hub (<NUM>) rotatably mounted on the shaft (<NUM>);
a seal retainer (<NUM>) located between the axial ends of the hub (<NUM>) and the shaft (<NUM>) at least arranged at one end of the roller cutter (<NUM>);
the seal retainer (<NUM>) supporting a primary cutter seal (<NUM>) providing sealing between the shaft (<NUM>) and the hub (<NUM>) in both axial and radial directions;
wherein
a secondary cutter seal (<NUM>) is located between the seal retainer (<NUM>) and the hub (<NUM>), and that the secondary cutter seal (<NUM>) provides sealing in the axial direction;
wherein a first surface (<NUM>) of the secondary cutter seal (<NUM>) is supported by the upper surface (<NUM>) of the axially innermost end (<NUM>) of the seal retainer (<NUM>) and a second surface (<NUM>) of the secondary cutter seal (<NUM>) is supported by a side surface (<NUM>) of the radially outermost part of the seal retainer (<NUM>) and wherein the secondary cutter seal (<NUM>) comprises a flexible lip (<NUM>) which presses against a supporting face (<NUM>) of the hub (<NUM>) providing sealing in an axial direction;
characterized in that the side surface (<NUM>) of the radially outermost part of the seal retainer (<NUM>) comprises a groove (<NUM>).