Field of invention

The present invention relates to a shank adapter for top hammer rock drilling having a corrosion and / or wear protection layer.

Shank adapters are used in rock drills as the main component which transfers the impact energy from the piston to the drill string while being rotated. Further, shank adapters are used to transfer flushing media from the rock drill into the drill string. Since shank adapters need to have high impact resistance, they are typically made from high strength carburized steel. However, the drawback of this material is that it is corroded by the flushing media, which may for example contain chloride, sulphide or other ions which accelerate the corrosion. If the shank adapter is corroded, its functionality decreases. The steel may for example have issues with stress corrosion cracking as the mechanical strength of the material is decreased.

Further, it is important to maintain the integrity of the seals inside the flushing housing for preventing leakage of the flushing water and maintaining good flushing pressure. For the seals to not wear out prematurely, it is important that the surface of the shank adapter in contact with the seals remains in a good, non-corroded condition. A corroded surface is highly abrasive and leads to premature failure of the seals in the flushing housing of the rock drill.

Therefore, it is advantageous to provide a corrosion protection coating on the surface of the shank adapter.

A known method of corrosion protection on shank adapters is to provide a layer of hard chrome plating on its surface. However, the hard chrome layers contain pores and microcracks which can act as channels for the water to penetrate through and reach the surface of the shank adapter therefore removing the corrosion protection. Therefore, the problem to be solved is how to provide methods of improving the corrosion and / or wear resistance of surfaces of the shank adapter.

Summary of the Invention

It is an objective of the present invention to provide means to increase the corrosion and / or wear resistance of shank adapters. This objective is achieved by providing a shank adapter to form part of a drilling assembly, the shank adapter comprising: a longitudinal axis; an external surface; an internal surface; a threaded part provided at a forward end and a plurality of splines provided at a rearward end; and a machine part extending axially between the threaded part and the splines; wherein at least part of the external surface is coated with a first corrosion protection layer comprising nickel; characterized in that: at least part of the first corrosion protection layer is coated with a polymer based sealant top layer.

Advantageously, the combination of the nickel based corrosion protection layer with the polymer based sealant top sealant results fewer open cracks and flaws between the atmosphere and steel substrate and so improved resistance against corrosion is achieved. This coating combination provides a corrosion protective layer on the shank adapter and around the flushing slots thus delaying radial crack propagation of the shank diameter and hence delaying transversal fractures of thread or machine part. Further, this coating combination provides a low friction surface. The low friction coating is beneficial for reducing wear on the flushing seals and other rock drill components thereby further increasing the service life of the seals. Additionally, this solution provides high wear resistance and reduced galling.

In one embodiment, additionally at least part of the internal surface is coated with the first corrosion protection layer and / or the polymer based sealant top layer. Advantageously, this provides protection against cavitation and resistance against corrosion on the inside of the shank adapter as well as the outside, therefore extending the lifetime of the shank adapter. In one embodiment, the thickness of first corrosion protection layer is between 5-200 pm. Advantageously, this thickness provides the optimal balance between providing sufficient corrosion and wear protection without adding excessive costs.

In one embodiment, the thickness of the polymer based sealant top layer is between 0.5 - 10 pm. Advantageously, this provides the optimal balance between having sufficient thickness to be effective whilst not unnecessarily adding cost or adding the risk that streaks are formed as the coating dries. The polymer based sealant top layer may also penetrate into the cracks therefore providing extra adhesion and corrosion protection.

In one embodiment, the first corrosion protection layer is a nickel phosphorous alloy. Advantageously, nickel phosphides provide a hard coating and therefore increased wear resistance.

In one embodiment, the phosphorus content of the nickel phosphorus alloy is 6-9 wt%. Advantageously, this phosphorus content provides increased wear without undesirable brittleness.

In one embodiment, the polymer based sealant top layer comprises a polymer having a friction coefficient of between 0.05 - 0.15. Advantageously, the low friction coating is beneficial for reducing wear on the flushing seals and other rock drill components thereby further increasing the service life of the seals.

In one embodiment, the first corrosion protection and the polymer based sealant top layer are located on the machine part. Advantageously, this provides corrosion protection to the region of the shank adapter that is most exposed to corrosion and most important to be protected from corrosion.

In one embodiment, the first corrosion protection layer and the polymer based sealant top layer are located on all parts of the shank adapter. Advantageously, this provides highly comprehensive corrosion resistance. In one embodiment, the rearward end, otherwise known as the striking face, of the shank adapter is uncoated. Advantageously, this avoids unwanted peel off in this region which could adversely block up the circulation system.

According to another aspect of the present application is a method for providing corrosion protection on a shank adapter as described hereinabove or hereinbelow comprising the steps of:

- depositing a first corrosion protection layer comprising nickel on at least part of the external surface of the shank adapter;

- depositing a polymer based sealant top layer on top of the first corrosion protection layer;

- heat treating the coated shank adapter.

Advantageously, this method provides a means to provide a highly effective corrosion resistance protection to the shank adapter, as well as a low friction and high wear resistant coating.

In one embodiment, the first corrosion protection layer is applied using an electroless nickel bath. Advantageously, this method is quick and less harmful to the environment compared to chrome plating. A further benefit of this method is that it is able to provide a coating having more uniform thickness with high reproducibility.

In one embodiment, the polymer based sealant top layer is sprayed on. Advantageously, this method provides a coating having a uniform thickness.

In one embodiment, the heat treatment is conducted at a temperature of between 150 - 300°C for 30 - 120 minutes. Advantageously, this temperature range provides the balance between having a high enough temperature and heating time that a hard and wear resistant surface is formed and not having too high a temperature and time that case hardened properties of the steel substrate are adversely affected. In one embodiment, the surface of the shank adapter is shot peened or blasted before the nickel based corrosion protection layer is applied. Advantageously, this step provides improved adhesion of the corrosion protection layer to the surface of the shank adapter. of drawings

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

Figure 1 is a schematic drawing of a shank adapter.

Figure 2 is a schematic drawing of one embodiment of the corrosion protection layer.

Detailed

Figure 1 shows a shank adapter 2 to form part of a drilling assembly, the shank adapter 2 comprising, a longitudinal axis 4; an external surface 6; an internal surface 8; a threaded part 10 provided at a forward end 12 and a plurality of splines 32 that project radially outward provided at a rearward end 14; and a machine part 16 (otherwise known as a main body) extending axially between the threaded part 10 and the splines 32. The splines 32 are configured to be engaged by corresponding splines of a drive bushing in a rotational motor (not shown) to induce rotation of the shank adaptor 2 about axis 4 during drilling operations. The threaded part 10 could be either a male or female thread. The shank adapter further comprises a flushing slot 26 providing entrance to a flushing hole or bore (not shown) that extends radially through the machine part 16 in the form of an internal cavity. The shank adaptor 2 is configured for coupling to an elongate drill string and to allow transmission of a stress wave to a drill bit (not shown) located at the deepest region of the drill hole to impart the percussion drilling action. In particular, the forward end 12 may be coupled to a rearward end of a rearwardmost elongate drill rod forming a part of the drill string or to a coupling (not shown). The rearward end 14, otherwise known as the striking face, is configured to be contacted by a hydraulically driven piston (not shown) that creates the stress wave within the shank adaptor 2 and the drill string. Optionally the forward end 12 also comprises an annular shoulder 28 from which the threaded part 10 axially projects. Optionally, a slim 30 is positioned axially between the machine part 16 and the threaded part 10.

Figure 2 shows that at least a part of the external surface 6 of the shank adapter 2 is coated with a first corrosion protection layer 18 comprising nickel. At least part of the first corrosion protection layer 18 is coated with a polymer based sealant top layer 20. Areas of the external surface 6 of the shank adapter 2 that are not coated with the first corrosion protection layer 18 may also be coated with the polymer based sealant top layer 20. Part or all of the first corrosion protection later 18 could be coated with the polymer based sealant top layer 20.

At least part of the internal surface 8 of the shank adapter 2 may also be coated with the first corrosion protection layer 18 and / or the polymer based sealant top layer 20. The internal surface 8 of the shank adapter 2 includes the flushing slot 26 and the flushing hole / bore that extends radially through the machine part along to the thread opening. At least part or all of the internal surface 8 may be coated with only first corrosion protection layer 18. At least part or all of the internal surface 8 may be coated with only the polymer based sealant top layer 20. At least part or all of the internal surface may be coated with both the first corrosion protection layer 18 and the polymer based sealant top layer 20. Any combination of these options is possible.

In one embodiment the thickness of first corrosion protection layer 18 is between 5-200 pm, more preferably between 7-100 pm, even more preferably between 10-50 pm.

In one embodiment the thickness of the polymer based sealant top layer 20 is between 0.5 - 10 pm, preferably between 0.5 - 5 pm.

The first corrosion protection layer 18 could be nickel alloyed with sulphur, phosphorus, boron or any other suitable element. Preferably, the first corrosion protection layer 18 is a nickel phosphorous alloy. Preferably, the phosphorus content of the nickel phosphorus alloy is 6-9 wt%. In one embodiment the polymer based sealant top layer 20 comprises a polymer having a friction coefficient of less than 0.05 - 0.15, preferably 0.1 - 0.13. For example, the polymer could be a Teflon or a fluorinated polymer (e.g. Polytetrafluoroethylene (PTFE)) or a non-fluorinated crystalline polymer (e.g. Poly ether ether ketone (PEEK)) or a high density polymer (e.g. Ultra-high-molecular-weight polyethylene (UHMWPE)).

In one embodiment the first corrosion protection layer 18 and the polymer based sealant top layer 20 are located on the machine part 16. In one embodiment the first corrosion protection layer 18 and the polymer based sealant top layer 20 are limited to being only located on the machine part 16. In other words, the first corrosion protection layer 18 is not positioned on the splines 32 or the threaded part 10. Alternatively, the entire external surface 6 of the shank adapter 2 is coated with a first corrosion protection layer 18 and the polymer based sealant top layer 20.

In one embodiment the first corrosion protection layer 18 and the polymer based sealant top layer 20 are located inside the flushing slot 26, this results in less breakages on the machine part.

In one embodiment the first corrosion protection layer 18 and the polymer based sealant top layer 20 are located the threaded part 10.

In one embodiment the rearward end / striking face 14 of the shank adapter 2 is left uncoated. In other words, the rearward end / striking part 14 of the shank adapter is free of the first corrosion protection layer 18 and the polymer based sealant top layer 20. In one embodiment all parts of the shank adapter 2 apart from the rearward end / striking face 14 are coated with the first corrosion protection layer 18 and the polymer based sealant top layer 20.

The present application further relates to a method for providing corrosion protection on a shank adapter 2 comprising the steps of: a) depositing a first corrosion protection layer 18 comprising nickel on at least part of the external surface 6 of the shank adapter 2; b) depositing a polymer based sealant top layer 20 on top of the first corrosion protection layer 18; c) heat treating the coated shank adapter 20.

In one embodiment, the first corrosion protection layer 18 is applied using an electroless nickel bath. The nickel or nickel based alloy adheres to the substrate, the substrate being the metal of the shank adapter. In electroless nickel plating the object reacts to the plating bath chemistry, creating a uniform and smooth, layer with very little surface porosity. The even deposition makes it an ideal choice for complex, non-line of sight, geometries and often eliminates grinding after plating. Alternatively, the first corrosion protection layer could be applied via electroplating or any other suitable method.

In one embodiment, the polymer based sealant top layer 20 is sprayed on. Alternatively, the polymer based sealant top layer 20 could be applied through dipping or any other suitable method.

The purpose of the heating step is to enable the formation of Ni-P intermetallic phases, improve the adhesion to the substrate and to cure the polymer based sealant top layer. Typically, the heat treatment is conducted in furnace.

In one embodiment the heat treatment is conducted at a temperature of between 150 - 300°C, preferably between 225 - 260°C. In one embodiment the heat treatment is conducted for between 30 - 120 minutes, preferably between 45 - 75 minutes.

The same method can be used to apply the first corrosion protection layer 18 and / or the polymer based sealant top layer 20 to the internal surface 8 of the shank adapter 2.

In one embodiment, the surface of the shank adapter (2) is shot peened or blasted before the nickel based corrosion protection layer (18) is applied.

The shank adapter as described hereinbefore or hereinafter could be part of a drill string and / or a drill rig arrangement. Examples

Summary of shank adapter tested

Table 1 shows the corrosion protection applied to shank adapters used in the field trails:

Table 1 : Shank adapter coating summary

Field Trial 1

A field trial was performed at a mine in Sweden. The drilled meters and drilling duration was recorded for each of the tested shank adapters. In this test both shank adapters failed after a similar number of drilled meters, however the cause of the failure was different. The chromed comparative shank adapter B had observations of delaminated abrasive corroded spots, therefore indicating that corrosion was the primary reason for the failure. Inventive shank adapter A did not have any delaminated abrasive corroded spots and showed significantly less general corrosion compared to shank adapter B. Instead, inventive shank adapter A failed because of worn out threads. Therefore, the corrosion was the limiting factor for the lifetime of the shank adapter for comparative shank adapter B but not for inventive shank adapter A after approximately the same number of drilling hours.

Field trial 2

A further field trial was performed at a mine in Australia. Table 2 shows the number of hours drilled before the shank adapters failed.

It can be seen that inventive shank adapter A significantly outperformed comparative shank adapter B in terms of number of meters drilled before failure and therefore proves the lifetime of the shank adapter having the corrosion protection according to the present invention is significantly increased.

Field Trial 3

A further field trial was performed at a mine in India which does not typically have significant issues with corrosion. It was found that the lifetime of the shank adapter improved by 27% for the inventive shank adapter A compared to comparative shank adapter C. It was observed that inventive shank adapter A did not break inside the rock drill and the service life of the seals in the rock drill were improved.