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1. WO2003018239 - SOUDAGE D'UNE PIECE D'USURE SUR UNE PIECE METALLIQUE

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

WELDING OF A WEARING PIECE TO A METAL WORK PIECE

FIELD OF INVENTION

The present invention generally relates to welding. More particularly, the present invention relates to a method and an arrangement for welding of a wearing piece to a metal work piece, and to a use of a nickel based welding wire.

BACKGROUND

It has long been desired to be able to in a straightforward way weld wearing pieces of hard metal to steel work pieces, since hard metal is much more durable than steel but more expensive than steel. With a base of steel and an edge of hard metal a reasonably inexpensive work piece with a durable edge is achieved.

Present solutions for achieving a hard metal wearing edge to a steel work piece are cumbersome, time consuming and hard metal consuming and are thus expensive. These present solutions are based on brazing of hard metal material to a work piece.

Brazing of a hard metal wearing piece to a steel work piece has a lot of disadvantages. Brazing is usually performed in an oven, by a high frequency brazing or under a gas flame, which heats both the steel work piece and the hard metal wearing piece as well as the brazing material. The surface of a steel work piece that is to be brazed needs to be purified and grooves need to be milled into it to provide reasonable adherence of the hard metal, further the surface needs to be perfectly planar. As hard metal and steel have different linear expansions stress arise in the joint when hard metal brazed to steel cools off. Further, a flux agent or a protective gas is usually used during brazing.

There is also known through Derwent abstract of JP 7-116 919 A, Derwent abstract of JP 1-2141 376 A and US 5413016 to use resistance welding, or spot welding, to adhere cemented carbide to certain specific metal pieces. To achieve a resistive layer between the cemented carbide and the metal piece it is suggested to use nickel. The resistive layer is applied to the cemented carbide by means of a coating process. Such a process is expensive and not desirable. Also, spot welding only works satisfactory on cemented carbide pieces that are smaller than the welding electrode. A larger piece of cemented carbide may be spot welded by several spots along the cemented carbide but will result in internal stress in the cemented carbide. Even if the internal stress not necessarily is large enough to crack the cemented carbide directly it will at least greatly reduce the durability of the cemented carbide and probably crack the cemented carbide immediately when put to use.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome the above-mentioned disadvantages when applying a wearing piece to a metal work piece .

This object, among others, is according to the present invention attained by methods and uses, respectively, as defined in the appended claims.

With a wearing piece welded to a work piece, by means of a TIG, a MIG, a MIG/MAG, or a plasma transferred arc technique, a less amount of wearing material, such as hard metal, is needed compared to prior art methods and a more durable wearing surface is achieved, providing a lower cost for a hard metal reinforced product. With a welded joint less heat disperse into a work piece compared to a brazed joint, providing less stress on the joint. Further, a brazed joint has lower structural strength than a welded joint. Also, a spot welded joint has lower structural strength than a joint welded by one of the following techniques: TIG, MIG, MIG/MAG and plasma transferred arc. Especially a joint welded by the MIG technique may be obtained under very low temperatures, which is important when welding thin parts of hard metal.

Further, welding of a joint is a less complex manufacturing method of available products, compared to brazing of a joint. A welding process may be performed by an uncomplicated automated welding process. A welding process needs less complex machining to provide a ready product, compared to a brazing process. Oxide on a surface has to be removed before welding is performed, but the surface need not be planar.

If the steel work piece accidentally is weakened due to heating during welding it is possible to anneal the steel without altering the welding joint or the hard metal. It is not possible to anneal the steel work piece if a brazing process has been utilized for applying hard metal as wearing material, unless special materials have been utilized in the wear piece and special fixing devices holds the brazed pieces together during a low temperature anneal process.

As an example it is with the present invention possible to weld a hard metal rod with a diameter of less than 1.2 mm onto an edge of less than 0.5 mm. It is further possible to obtain joints with a length of more than 600 mm without internal stress noticeably reducing the durability.

Further features and advantages of the present invention will be evident from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description of embodiments given below and the accompanying figures, which are given by way of illustration only, and thus, are not limitative of the present invention, wherein:

Fig. 1 schematically shows a plan view of a hard metal wearing piece applied to a steel work piece;

Fig. 2 shows a cut along the line II-II in Fig. 1;

Fig. 3 schematically shows a grinded hard metal wearing piece;

Fig. 4 schematically shows a saw tool; and

Fig. 5 shows a side view of a cut along the line V-V in Fig. 4.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, for purpose of explanation and not limitation, specific details are set forth, such as particular techniques and applications in order to provide a thorough understanding of the present invention. However, it will be apparent for a person skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed description of well-known methods and apparatuses are omitted so as not to obscure the description of the present invention with unnecessary details.

A first embodiment of the present invention will now be described with reference to Figs. 1-3.

A steel work tool, such as a debarking tool 1, a bore crown or a saw tooth, wears out fast in an industrial environment due to a large amount of use. By applying a wearing piece 2 of a harder material than steel on the parts of the work tool 1 that are subject to wear a more durable work tool is obtained. Hard metal and materials having similar properties, such as materials sold under the trademark Stellite, are materials that are harder than steel and are regularly used as wearing materials. Hard metal, contrary to Stellite, comprises above all wolfram carbide (WC) to obtain its hardness.

Preferably, the wearing material comprises at least of 50% wolfram carbide, more preferably at least 80% wolfram carbide and most preferably at least 95% wolfram carbide. However, Stellite or other materials having similar properties may alternatively be used with a slightly less wearing resistance compared to hard metal.

By welding a weld joint 3 at a contact surface between the wearing piece 2 and the work tool 1 , where the welding wire is based on nickel (Ni), the wearing piece 2 is securely fastened to the work tool 1. It is due to the choice of welding wire material that it is possible to weld a hard metal to steel.

The welding wire consists of at least 95% nickel, preferably at least 99% nickel and more preferably at least 99.4% nickel.

Due to the manufacturing process of the welding wire trace elements may unintentionally be added to thereto. The welding wire may contain trace elements such as: chrome (Cr), cobalt (Co), manganese (Mn), iron (Fe), phosphorous (P), silicon (Si), carbon (C), copper (Cu), sulfur (S) and titanium (Ti) .

Cobalt may further be added to the welding wire as an additive. With a content of 0.05-0.3% cobalt, preferably 0.1-0.2% cobalt and more preferably about 0.12% cobalt in the welding wire an improved joint is obtained.

Also manganese may be added to the welding wire as an additive. With a content of 0.05-0.3% manganese, preferably 0.1-0.2% manganese and more preferably about 0.14% manganese in the welding wire an improved joint is obtained.

By providing the above-described additives of both cobalt and manganese a further improved joint is achieved. The traditional way of using iron as an additive in the welding wire is not necessary as when welding a joint between a wearing piece of a non hard metal and a work piece.

Yet a further additive that may be useful is copper. With a contents of 0.05-2% copper, preferably 0.1-1% copper and more preferably about 0.5% copper in the welding wire a lower melting point of the joint is obtained. Further, the cooling period is extended, obtaining a reduced tension, with such an additive.

The hard metal wearing piece 2 welded to the steel work piece 1 may now easily be grinded to provide a sharp wearing piece 2' for e.g. debarking, drilling or sawing.

A second embodiment of the present invention will next be described with reference to Figs. 4 and 5.

A saw tool comprises a saw blade 4 with an exchangeable saw tooth 5. The saw blade 4 is made of steel and the saw tooth such as Stellite. As mentioned above, hard metal comprises above all wolfram carbide (WC) and cobalt (Co) to obtain its hardness.

By welding a joint 6 along a contact surface between the saw tooth 5 and the saw blade 4, where the welding wire is based on nickel (Ni), the saw tooth 5 is securely fastened to the saw blade 4. It is due to the choice of welding wire material that it is possible to weld a hard metal to steel. The choice of material is identical to that described above in the first embodiment of the present invention.

Welding as described above may be performed by one of the following types: TIG (Tungsten Inert Gas), MIG (Metal Inert Gas), MIG/MAG (gas metal arc welding) and plasma transferred arc. It is also possible to utilize the newly developed techniques where plasma transferred arc is combined with MIG or where laser is combined with MIG. Each welding process is easily performed as the work piece as well as the wearing piece may be of room temperature when the welding process is begun. Preferably, the traditional initial melting of the work piece and the wearing piece, during welding, is not performed, i.e. the welding process has some resemblance to braze welding. Further, the welding process may easily be performed by an automatic welding machine.

An example of a welding process will now be described, performed by TIG or plasma welding. A welding electrode is held at an angle of approximately 50-70° to the work piece, preferably at an angle of around 60°. When welding the wearing piece to a thin work piece the welding arc is ignited against the wearing piece and when welding the wearing piece to a thicker work piece the welding arc is ignited against the work piece. There should not arise any melt in either the work piece nor the wearing piece, as porosity than may arise in the welding joint.

The temperature in the work piece and the welding piece should be high enough to provide wetting of surfaces, which the nickel based welding wire is to be welded to, prior to applying the nickel based welding wire. The welding wire is applied at an angle of approximately 15-30°, preferably at an angle of around 15°, and is gently brought into the welding arc against the wetted surfaces until a melt of nickel arise. Thereafter the thread is moved in a continuous process such that the nickel flow out and forms a joint.

At the beginning and ending of the welding process a protective gas should flow before the arc is ignited and after the arc is extinguished. When a high speed automatic plasma welding is performed the electrode may be applied at an angle of 90° to the work piece.

Welding wires with a diameter from 0.6 mm to 1.5 mm have been utilized and excellent results have been achieved.

It will be obvious that the present invention may be varied in a plurality of ways. Such variations are not to be regarded as departure from the scope of the present invention. All such variations as would be obvious for a person skilled in the art are intended to be included within the scope of the present invention.