FI67881C - JAERNVAEGSBROMSSKO AV GJUTJAERN - Google Patents

Description

ΓΒ1 m ADVERTISEMENT £ 7 o Q 4 • IIbHP ^ (11) UTLÄGGNINGSSKRIFT O / öö C (45) Patent nyonnctty 10 C6 1935 Patent oeddelat (51) Kv.lk. '/ Lnt.ci.4 C 22 C 37/00 ENGLISH —FINLAND (21) Patent application - Pitentansökning 773871 (22) Filing date - Ansökningsdag 20.12.77 (F ») (23) Starting date - Giltighetsdag 20.12.77 (41) Published public - Blivit offentlig 19-07.78

National Board of Patents and Registration Date of publication and publication 7

Patent and Registration Publications Ansökan utlagd och utl.skrifcen publicerad ^ o.uz.05 (32) (33) (31) Privilege claimed — Begärd priority 18.01.77 USA (US) 759231 (71) Abex Corporation, 530 Fifth Avenue , New York, New York 10036, USA (72) Chandi P. B iswas, Ramsey, New Jersey, Hugo R. Larson, Ridgewood,

This invention relates to the metallurgy of cast iron brake shoes for use on railways.

In terms of predictable performance and reliability, cast iron is a superior friction material used on a railway car wheel, especially where operating requirements are stringent, such as when using the brakes for a long time on a steep descent under heavy load.

For many years, the standard composition of a cast iron brake shoe was considered to be approximately the following: 3% carbon, 1.5% silicon, up to about 0.15% sulfur, and up to about 1.5% phosphorus, the rest being iron, excluding impurities; manganese would be involved if scrap iron or steel were used as a raw material, as has often been the case. Sulfur and phosphorus were, however, classified as undesirable residues contained in the coke or metal charge used in the manufacture of iron.

An improvement in the metallurgy of cast iron brake shoes is disclosed in U.S. Patent 3,620,334 (see also British Patent 2,638,646). These show a powerful effect of increasing the amount of phosphorus, which unexpectedly results in a reduction in sparking and flame, which has the considerable merit of reducing the risk of fires that may occur as a result of sparking at the brake shoe-wheel interface. Equally important is the fact that a high amount of phosphorus results in a reduction in wear, which prolongs service life.

The threshold for improved performance appears to be 2% by weight phosphorus, with no major advantage above the upper limit of 6%. The concentrations of carbon and silicon may in fact be the same as in previous metallurgy: carbon and silicon may be present in a total amount of up to 6%, most preferably about 2.5 / 3.5% carbon and 1.6 / 2.2% silicon.

A gray cast iron brake shoe with more than 2% phosphorus consists mainly of granules of perlite and / or ferrite and graphite as a continuous network of tertiary eutectic rubber (steadite); wherein the steadite surrounds the perlite and / or ferritic granules as shown in the photomicrograph. Steadite in a typical ingot (e.g. 2.8% carbon, 3.0% phosphorus) solidifies at about 950 ° C compared to material outside the network which solidifies at about 1150 ° C. Steadite consists of Fe 2 C, Fe 2 P and Fe. It is believed that the steadite network, continuous, caused by a large amount of phosphorus, is the cause of the unexpected advantages of a high-phosphorus brake shoe. Iron in eutectic rubber may take various forms depending on the casting technique, which is not important for understanding or applying this invention. For example, the brittleness of iron can be varied by heat treatment without varying its continuity within the scope of this invention.

It has now been found in the context of the present invention that a railway shoe containing 2-5% phosphorus can be further improved by using sulfur in amounts that further reduce the wear rate, i.e. the service life of the brake shoe is further improved while affecting the suppressive effect of phosphorus sparking and flame retardation. only to a small extent.

The special features of the railway brake shoe according to the invention appear from the claims.

The invention will now be described in more detail by means of an exemplary embodiment with reference to the drawing, in which Fig. 1 shows a curve (indicated by a straight line) illustrating the wear rate of a railway brake shoe in relation to the amount of sulfur present and Fig. 2 is a photomicrograph (2G0x).

It is believed that the improved wear resistance of this invention is due to the eutectic rubber reinforced by FeS (ferrous sulfide). Whatever the theory is, the mere fact remains that the wear resistance is improved by using sulfur in excess of that required to form MnS (manganese sulfide). The reason for equalizing the amount of sulfur to form MnS is that the iron used contains some manganese, which preferably combines with sulfur. This MnS is undoubtedly associated with perlite and / or ferrite granules located outside the network of eutectic material.

The atomic weight of manganese is 55, sulfur 32, so for every weight percent of sulfur present, manganese is consumed in a ratio of 55/32, i.e. about 1.72. While allowing a small amount of unbound sulfur in a solid solution and with similar minor effects, the amount of sulfur (% by weight) that is not consumed and thus available for eutectic rubber can be written as S- (Mn / 1.8), which means sulfur present in weight percent minus manganese present in weight percent (each by analysis) divided by 1.8.

The curve shown in the drawing was obtained from the figures in Table 1 obtained from a dynamometer comparing test brake shoes to standard brake shoes to determine the wear rate. The standard brake shoe had the following (nominal) composition: carbon 2.8%, silicon 2.1% and phosphorus 3%. By first measuring the wear of the standard brake shoe and then successively measuring the wear of each test brake shoe, all under the same dynamometer conditions, it is possible to calculate the relative wear rates, i.e. the test brake shoe / standard brake shoe.

4 67881 TABLE 1 (% by weight; nominal value P = 3%)

Test brake% S% Mn S- (Mn / 1,8) Wear shoe_ speed 1 0,45 0,30 0,233 0,41 2 0,33 0,36 0,13 0,67 3 0,43 0,27 0.28 0.34 4 0.41 0.40 0.188 0.30 5 0.41 0.42 0.177 0.64 6 0.38 0.30 0.213 0.47 7 0.33 0.30 0.163 0.57 8 0.215 0.36 0.015 0.87 9 0.335 0.53 0.041 0.82 10 0.27 0.42 0.037 0.87 11 0.375 0.49 0.103 0.64 The curve confirms that as the excess sulfur increases, the wear rate decreases (WR), it means that when the sulfur content increases above the amount that can combine with manganese, the wear rate decreases. In practical terms, this means that railway brake shoes can be expected to withstand more emergency braking or more intense braking depending on the increase in excess sulfur, which can also play a significant role where train brakes are used for a long time in downhill mountainous areas of the world.

The carbon and silicon range has already been given; phosphorus is in the range of more than 2-10% by weight, but 2.4-5% is preferred.

It is noted from the above that if the brake shoe contains at least 2% phosphorus, mainly to reduce the tendency to flame, it is possible to allow at least and considerably more than 0.15% sulfur in the brake shoe without adverse effect; the jar-rye shoe is indeed being further improved, as the curve proves, which already benefits in that it allows the use of more sulfur-containing iron than previously assumed. Such iron is usually cheaper.

A photomicrograph (200x) is typical of a standard brake shoe as well as a test brake shoe used in dynamometer testing ti 5 67881 and showing the (gray) perlite grains surrounding the steadite as a continuous network (white).

The assembly of the railway brake shoe of the present invention is thus essentially as follows (wt%): carbon 2.5 to 3.5 silicon 1.6 to 2.2 phosphorus more than 2 to 10 sulfur and manganese are both present in a weight w / w weight ratio Mn / 1,8 Remaining iron excluding impurities and adventitious parts.

Steadite is formed as a natural result of the thermodynamics of light cooling, and is not required to form any special treatment.