CA1071439A - Brazing alloy - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
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Silver-containing brazing alloys are provided which are suitable for use in the fabrication of cutting tools, for example, the brazing of a cutting tip to a shank of a rock drill. One particular silver-containing brazing alloy in accordance with an aspect of this invention comprises, apart from impurities, 15-40 wt.% zinc, 15-45 wt.% silver, 0,2-15 wt.% manganese, 0.2- 10 wt,% nickel and the balance copper. This brazing alloy is thus com-patible both with the steel shank material and the cobalt-bonded tungster carbide cutting tip material.

Description

` ~7~3g This inventlon relates to alloys and especially to silver-contain-ing brazing alloys.
A brazing alloy for uge in forming a brazed joint between the shank and cutting tip of a rock drill should ideally possess the ability to wet steel (the shank material) and a cobalt-bonded tungsten carbide tthe cutting tip material) as well as being metallurgically compat:Lble with these materials~
A brazing alloy should be of relatively low intrinsic cbst and have the abili-ty to be fabricated in the form of a wire and strip by standard production methods. A brazing alloy should also possess a relatively high plasticity in a temperature range between the solids of the brazing alloy and, say, 300C.
This plasticity feature reduces the risk of cracking which tends to occur in large size drills during cooling due to the widely differing contraction ..
characteristics of steel and tungsten carbides. Further, a brazing alloy should have a sufficiently high strength at room temperature, for example, a U.T.S. of 20-30 tons/square inch, to reduce the risk of premature failure of a drlll due to fatique of the brazed joint between the shank and the tip.
It is an ob~ect of an aspect of this invention to provide a silver-containing brazing alloy for use in the fabrication of cutting tools, for ex-ample, the brazing of a cutting tip or cutting insert on to a shank of a rock drill.
By a broad aspect of this invention, a silver-containing brazing alloy is provided comprising copper, zinc, silver, manganese, and nickel;
wherein the proportion of zinc is 15-40 wt.%; wherein the proportion of silver is 15-45 wto%; wherein the proportion of manganese is 0.2-15 wt.%; wherein the proportion of nickel is 0.2-10 wt.%; and wherein the balance is substantially copper.
According to one variant of this invention a silver-containing braz-ing alloy comprises, apart from impurlties, 33 wt.% zinc9 25 wt.~ silver, , ', , ' '' .

~C171439

2 wt.% manganese, 2 wt.% nickel and 38 wt.% copper, and melts within a tem-perature of 710-810C.
By another aspect of this invention a cutting tool is provided hav-ing at least one cutting tip or at least one cutting insert secured to a shank of the tool by a silver-containing brazing alloy as described above.
By yet another aspect of this invention, a rock drill is provided comprising: a steel shank; a groove in one end of the shank; a carbide cutting tip inserted in ~he groove; the dimensions of the groove providing a joint gap between the tip and the walls of the groove; and a silver-containing brazing alloy as described above disposed in the joint gap and brazing the tip to the shaft.
By a variation thereof, the rock drill includes two or more cutting tips.
By another variation, the joint gap is not less than 0.004 inch.

Reference has been made above to reducing the risk of cracking in brazed joints iD carbide-tipped tools. This risk increases in pro-portion to the joint length which governs the magnitude of stresses produced by the differential contraction of the various materials present, ,.~

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-`"" 1C17~439 namely, steel (the drill shank)~ the brazing alloy, and tungsten carbide (the cutting tip).
The invention will be hereinafter more Eully described with refer-ence to the accompanying drawing in which:
Figure 1 shows a side elevation of a drill fitted with a tungsten carblde insert, and Figure 2 shows an end view of the drill seen in the direction of the arrow P of Figure 1.
As shown in the drawing, the drill 10 comprises a steel shank 12 10 formed at one end with a rectangular groove 14 in which is inserted a tungsten, carbide tip 16, the groove being dimensioned to provide a narrow gap 18 for receiving the brazing alloy forming the joint.
Brazing tests were carried out on rock drills with carbide tips 1.75 inch long ( which is almost the maximum siæe used in industry) of the type shown in Figure 1.
Another factor affecting the risk of cracking is the joint gap width, rock drills with wider joint gaps being generally less susceptible to cracking under the influence of stresses due to differential contraction.
The width of the joint gap is quite an important factor and, generally speak-2Q ing, the minimum admissible joint gap, that is, the smallest gap ensuring the freedom from crack formation during the cooling cycle of a brazing opera-tion, varies depending on the length of the carbide ins~rt 16, the com-.. . .
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po~ition of the steel shank 12 and on the cooling site a~ter brazing.
'~he nominal joint g~p in ~ll the experimental roclc drills brazed during this investi~ation was 0O004 inch.
'l`h.is ~igure is ne~r the lower limit of the joint gap range ecommended ~or, and used in such.brazed joints, and experience has~sho~n that such a gap is sufficiently small to promo-te cracking. of joints with unsuitable alloys.
Each bra~ing test ~as carried out under conæitions simulating the brazing cycle currently used in the manu-facture of rock dr.ills. In this procedure the brazing ~peration is combined with the heat treatment of the steel sha~. ~his is done by heating -the worhpiece tc.
the brazi~g temperature, cooling or heating it (as necess- .
ary) depending on the melting point of the allo~r, to 850~
transferrlng it to an oven at 3~0C, holding it at. 350C
ior one hol1r, and then coolin~ i-t in air ~o room tempera-. ture.
- - ~o ascertain that tests carried out und.er the condit- ::
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ions chosen ~Jould provide a reliable mean~ of re~realing the potential usefulness of the alloys tested, a p~elimin- -ary series of e~periments was carried ou~ with a Cu-2.5 ~i-Oo 6% Si alloy refer;ed to as "A" 3ronze", kno~m to pro- ;
4 d.uce joints susceptible to cracking and with 2 ductile --5-- . -.
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alloy Cu-3~Ni referred to as "~" Bronze, known to produce crack-free joints (but not used in the manufacture of rock drills because of its low strength).
E~tensive cracks were, in fact, formed in joints made with "A" Bronze whereas little or no evidence of cracking was found in joints made with "B" Bronze.
This was regarded as a sufficient proof of the reliability of the test.
Medium-frequency heating was used for brazing. Sufficient brazing alloy to form the joint was placed at the bottom of a wall of the groove fo~med in the steel shank of the rock drill. A coat of paste known by the Trade Mark of Tenacity No~ 5 Flux paste was next applied to the joint area which was then sprinkled with a liberal quantity of boric oxide to increase the stability of the flux at elevated temperatures. Asbestos tape was wrapp~c round the drill to contain the molten flux in the joint gap.
The compositions of the alloys tested included various combinations of the constituents zinc, silver, manganese, nickel, copper and silicon, i.e.
alloys both within ambit of aspects of this invention and outside the scope of this invention. Zinc and silver were used as melting point depressants;
manganese was added to improve the wetting characteristics of the alloys on tungsten carbide; nickel was introduced to act as a hardener to improve the joint filling properties of the alloys and to reduce the extent of erosion of tungsten carb.ide by molten brazing alloys, whilst silicon was added to improve the wettability and the flow characteristics of the alloys.
Typical of the large number of alloys tested are those referred to in Table 1 as Alloys Nos. 1, 2 and 3.
The melting ranges of the alloys tested were determined by spread-ing tests carried out in a continuous brazing furnace at temperatures pro-gressively increasing in steps of 20C. ;~
The hardness of the alloys (in the as-cast condition and after a heat treatment simulating the bra7ing cycle) was measured to get a rough es-timate of their relative strength.

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3~3 Vls~al exami-.latioll alone of ~oiDts in brazed rock drill specimens could tlO~: be relied on tr- de~ermine the presence or the extent of cracking except i-n the case of large open cracks visible on both the vertical and horizontal ~oint faces. In other cases there was a possibility of hair cracks bein~, concealed as a result of the cleaning operation (sand blasting~, or of surface defects (e.g., solidification sllrinkage) being mistaken for cracks. It was, therefore, necessary to section the specimens for examina-tion in the pkane indicated by X - X in Figure 1, The results of the examina tion of specimens brazed with three of the alloys tested are given in Table 1 From the results given in this Table it will be seen .. , ... .. F"

~ 7~39 ~hat nei~her of the alloys referred ~o as Nos. 1 and 2 produced crack-free ~ointæ under the experimental conditions used in this investigation. Similar results were obtsiDed with all the other alloys tested apart from alloys accordlng to aspects of this lnvention. These latter are exemplified by alloys 1O.3 and gave very satlsfactory results. The nominal compositions of alloy 3 as given in the table was:
38Cu-33Zn-25~g-2Mn (Melting range 710-810C.) Kilogram quantities of these alloys were made as 3 mm diameter wire and 1 mm and 3 mm thick sheet. The materials were fabricated without any difficulties by conventional methods (hot rolling followed by cold rollir and annealing) and further evidence has shown them to be satisfactory brazing alloys.

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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1 A silver-containing brazing alloy comprising an alloy of copper zinc, silver, manganese and nickel;
wherein the proportion of zinc is 15-40 wt.%;
wherein the proportion of silver is 15-45 wt.%;
wherein the proportion of manganese is 0.2-15 wt %;
wherein the proportion of nickel is 0.2-10 wt.%;
and wherein the balance is substantially copper.

2. A brazing alloy according to claim 1 and, apart from impurities, consisting essentially of: 33 wt.% zinc; 25 wt.% silver; 2 wt.% manganese;
2 wt.% nickel; and 38 wt.% copper.

3. A cutting tool having at least one cutting tip or at least one cutting insert secured to a shank of the tool by a brazing alloy as claimed in claims 1 or 2.

4. A rock drill comprising: a steel shank; a groove in one end of said shank; a carbide cutting tip inserted in said groove; the dimensions of said groove providing a joint gap between said tip and the walls of said groove; and a brazing alloy as claimed in claim 1 disposed in said joint gap and brazing the tip to the shank.

5. A rock drill according to claim 4 including two or more cutting tips.

6. A rock drill according to claims 4 or 5, wherein the joint gap is not less than 0.004 inch.