Boring or penetrating the earth – Bit or bit element – Rolling cutter bit or rolling cutter bit element
Patent
1997-08-12
1999-11-02
Bagnell, David
Boring or penetrating the earth
Bit or bit element
Rolling cutter bit or rolling cutter bit element
761082, E21B 1046
Patent
active
059752238
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rock drill bit for rotary crushing machining of rock, which comprises at least one leg carrying a journal provided with bearing races in order to cooperate via a bearing element with bearing races in a rotatable roller provided with crushing means. The leg is made from a parent material with substantially homogenous hardness and comprises a leg tail provided to resist entrance of drill cuttings into the bearings. The invention further relates to a method for hardening a rock drill bit.
2. Description of Related Art
It is previously known to protect a roller drill bit leg end from wear by providing it with protective inserts and/or hard facing. The hard facing is necessary especially at the leg tail, where there is not enough space to mount the protective inserts. If the leg tail wears away, drill cuttings will quickly enter into the bearing races, which leads to bearing breakage or blocking of the bearings. The legs of a roller drill bit are carburized and hardened in order to achieve sufficient case depth and hardness of about 60 HRC on the bearing races. The core hardness on the other hand, lies about 30 HRC, in order to maintain suitable toughness and to decrease the risk for cracks and breakage. The low hardness of the legs however, wears the steel away too fast, unless protective inserts and hard facing are used.
OBJECTS OF THE INVENTION
In order to avoid the problems and the increased manufacturing costs that hard facing mean when producing roller drill bits, the present invention aims to provide a simple method of selectively hardening the legs during the heat treatment of the bit.
Another object of the present invention is to provide a roller drill bit with hardened portions, which have a good wear resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a roller drill bit according to the present invention;
FIG. 2 shows a leg in a side view according to II--II in FIG. 1; and
FIG. 3 shows the leg in cross section according to the line III--III in FIG. 1.
FIG. 4 shows a part of a drill bit, in cross section, according to the present invention in an alternative embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIG. 1, a rock drill bit according to the present invention is shown, for rotary crushing, drilling of rock, referred to as a roller drill bit. The drill bit comprises three legs 10, whereof one is shown in section, on which journals 11 are provided. In some constructions of drill bits it is possible to provide only one or two legs. A roller 12 equipped with inserts 13, is rotatably mounted on each journal by means of roller bearings 14, a system of ball bearings 15, a radial bearing 16 and an axial bearing 17. The inserts can alternatively be replaced by other crushing means, such as chisel teeth integrated with the roller. The legs 10 are evenly distributed about the periphery of the bit with 120.degree. partition. The journal 11 is provided with a channel 18 for introducing the balls 15, in which a plug 19 is received in order to retain the separate balls 15. The cylindrical roller bearing 14 receives a major part of the reactional force from the rock while the major object of the ball bearing 15 is to retain the roller 12 on the journal 11. The roller 12 has a shoulder 20 to abut against a collar 21 on the journal for receiving axial forces, which are not received by a support disc 22 cooperating with the axial endsurface 25 of the journal. The bit is provided with channels 23, 24 for a flush medium, such as pressurized air with an addition of water for cooling and cleaning of the bearing system. The above-mentioned bearings can be sealed and lubricated by a lubricant system integrated with the bit. A frictional bearing 14' can be provided in instead of roller bearing 14 on a substantially corresponding position according to FIG. 4.
It has been shown that the leg tails wear out during drilling and that drill cuttings, enter into the bearing races and destroy the
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Bagnell David
Sandvik AB
Singh Sunil
LandOfFree
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