US2771358A

US2771358A - Machine elements for crushers

Info

Publication number: US2771358A
Application number: US443905A
Authority: US
Inventors: Spear Warren Mclellan
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1954-07-16
Filing date: 1954-07-16
Publication date: 1956-11-20
Anticipated expiration: 1973-11-20

Description

Nov. 20, 1956 w. MOL. SPEAR MACHINE ELEMENTS FOR CRUSHERS Filed July 16, 1954 BYQ ATTORNEY United States Patent MACHINE ELEMENTS FOR CRUSHERS Warren McLellan Spear, Cranford, N. J., assignor to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware Application July 16, 1954, Serial No. 443,905

6 Claims. (Cl. 75--128) The present invention relates to crushing machines and, more particularly, to chilled crushing elements for use in such machines which elements are made of a special nickel-chromium martensitic cast iron and have a tough,

ductile backing or core with a wearing or crushing surface of very high hardness.

It has been recognized heretofore that in the comminution of solid materials such as minerals, the comminution process may be divided roughly into mechanical operations characterized as crushing and grinding. Generally speaking, the mechanical equipment employed for In crushing, the crushed rock must be discharged from the crushing zone of the crushing machines in order to avoid the undesirable production of fines. In grinding, on the other hand, the desired pulverizing is accomplished by pressure and abrasion.

There are many types of machines which are employed for crushing, for example, jaw crushers, gyratory crushers, cone-type crushers, hammer mills, rolls of various types, etc. Since crushers are designed to load the material being crushed as beams or short columns, relatively high stresses are applied to the material in order to effect crushing. Necessarily, the crushing elements, i. e., the mechanical elements in the crusher which apply the crushing forces to the material being crushed, must withstand the stresses applied if the crusher is to be commercially acceptable.

Because of the manner in whichthe crushing stresses are applied, the crushing elements must have high impact resistance as well as high strength. Furthermore, since the material being crushed is almost invariably of a highly refractory nature, the crushing elements must also be able to withstand conditions of severe wear for a substantial length of time if the crusher is to be commercially acceptable.

- Because of the severe demands placed upon crushing elements when in service, the art has continually been searching for materials having an improved'combination of impact, strength and wear-resistant properties in order to lengthen the life of crushing equipment, to reduce costs, to provide improved crushing action, etc. It has now been discovered that when crushing elements or crushing surfaces are made of chilled nickel-chromium alloy cast iron of special composition, improved service life of th crushing elements is attained. It is an object of the present invention to provide chilled crushing elements having a high hardness in the chill and having a strong, tough backing or core.

Another object of the invention is to provide a crushing roll of special composition having a hard chill face and a strong, tough core.

The invention also contemplates providing chilled castings of special composition having a hard surface and having high strength and toughness in the core.

It is a further object of the invention to provide a method for producing chilled castings having a hard, practically unmachinable. face and having a strong, tough machinable core.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the drawings in which:

Figure 1 is a reproduction of a photograph of a chillcast' roll head for a pulverizing mill of the roller type after the roll head had been withdrawn from service in a mill, said roll head being made in accordance with the present invention;

Figure 2 is a reproduction of a photomicrograph taken at 250 diameters showing the etched structure in the chill surface of a roll head casting such as that shown in Figure 1 and made in accordance with the present invention; and

Figure 3 is a reproduction of a photomicrograph taken at 250 diameters showing the etched structure in the backing ofa roll head casting such as that shown in Figure l and made in accordance with the present invention.

Generally speaking, the present invention contemplates special chilled nickel-chromium alloy cast iron castings particularly adaptable foruse as crushing elements in crushers and containing about 3.4% to 4.2% carbon, about 1.1% to 0.6% silicon, about 3.5 to 5% nickel,

. about 0.4% to 1% chromium, about 0.1% to 0.6%

manganese, a small amount of magnesium up to about 0.1% effective to control graphite present in the cast iron to a spheroidal form, and the balance essentially iron and with the iron content being between about 88% and about 92%.

' The special chilled cast iron crushing elements contemplated in accordance with the invention possess the particular property that the chilled portion thereof has a high hardness of at least about 600 BHN and the castings are of the definite-chill type, i. e., the castings are characterized by an abrupt transition from the hard chilled faceto a substantially carbide-free core which itself has'a martensitic structure. The martensitic core, which is characterized by the presence of graphite in a spheroidal form, has a high combination of strength and toughness, including a tensile strength of at least about 70,000 p. s. i. Accordingly, chilled crushing elements produced in accordance with the invention possess a highly advantageous combination of properties in that said castings have a very hard, wear-resistant chilled face united with a tough, strong, load-resistant, shock-resistant core. Chilled castings having the foregoing special combination of properties have included sections of from about 3 inches to about 10 inches or about 12 inches in thickness.

With reference to the drawing, it will be noted that the structure depicted in Figure 2, which is from the chilled face of a roll head made in accordance with and typifying the present invention, comprises columnar carhides in a matrix which is almost completely martensitic.

A few small spheroids are scattered through the structure. Figure 3, taken from the backing of a roll head such as shown in Figure 1, depicts the structure in the backing or core portion of chilled castings made in accordance with the present invention. It will be noted that this structure comprises a matrix of martensite and bainite with some well-scattered carbide. Spheroidal graphite is also present.-

In carrying the invention into practice, it is preferred to employ compositions containing about 3.5% to 3.8% carbon, about 0.9% to 1.1% silicon, about 4.5% to 4.8% nickel, about 0.5% to 0.7% chromium, about 0.2% to 0.6% manganese, and a small amount up to about 0.09% magnesium effective to control the occurrence of graphite in a spheroidal form in castings made from such compositions, with the balance essentially iron and with the iron content being about 88% to about 91%. These preferred compositions, when produced as chilled castings, are characterized by a high hardness on the chilled face of at least about 650 Brinell and by a high tensile strength in the backing or core of at least about 80,000

In addition to the elements in the amounts set forth hereinbefore, the special chilled cast iron crushing elements contemplated by the present invention may contain small amounts of incidental elements and impurities generally found in cast iron and which do not adversely affect the basic and novel characteristics of the castings. For example, the aforedescribed compositions may contain up to about 2% copper, e. g., about 0.2% to 1%; up to about 0.5% molybdenum, e. g., about 0.1% to 0.4%; up to about 0.2% phosphorus, e. g., about 0.01% to 0.1%; etc., Because of the powerful desulfurizing effect of magnesium, castings produced in accordance with the invention are usually very low in sulfur, e. g., the sulfur will usually be less than about 0.02%. 7

It is critical that the composition of the special chilled cast iron crushing elements contemplated in accordance with the present invention be maintained within the limits set forth hereinbefore. Thus, when the carbon content is less than about 3.4%, the hardness of the chilled face is unsatisfactorily low and the chill tends to be indefinite, While the strength of the backing or core is unsatisfactorily low. In addition, a carbide network tends to persist in the structure of the backing or core, i. e., the area which is remote from the chilled face. On the other hand, when the carbon content exceeds about 4.2%, the chill tends to be shallow. The silicon content of the special cast irons, taken in conjunction with the carbon content, is likewise critical. Thus, when the silicon content is lower than about 0.6%, a semi-continuous carbide network persists in the backing or core behind the chilled surface with the result that the strength thereof is low as compared to that of castings within the invention. When the silicon content exceeds about 1.1%, there is an undesirable tendency for secondary graphitization to occur in the chilled portion of the casting with resultant lowered hardness in the chill. The chromium content of the special cast irons of the invention is also critical and must be closely controlled so that at least one-half inch to an inch of chill will be provided in chilled castings and so that the backing or core will be tough. Thus, the chromium content should not be lower than about 0.4% as otherwise the desired thickness of chill cannot be maintained and there is an undesirable tendency for acicular ferrite to form in the core rather than the desired martensitic structure. The chromium content should not exceed about 1% as otherwise a carbide network structure is produced in the core with the result that the tensile strength of the core is substantially reduced. As an example, castings produced in accordance with the invention containing about 1% chromium have tensile strengths in the core of about 70,000 p. s. i. or more, but otherwise comparable castings containing 1.5% chromium have tensile strengths in the core under 50,000 p. s. i. The nickel content of the special cast irons likewise critically affects the properties of the compositions. Thus, when the nickel content is below about 3.5%, pearlite tends to form in the core rather than the desired martensitic structure but when the nickel exceeds about the chill hardness is lowered. It is generally preferable to employ the higher nickel contents in producing castings having the heavier included sections, e. g., sections which are 10" or 12" or more in thickness. Magnesium present in the compositions has a very important effect upon the strength of the core and upon carbide stability. Thus, the presence of magnesium in an amount which will cause the occurrence of spheroidal graphite in the core likewise enables the formation of martensite in the core in the presence of the amounts of chromium, nickel, carbon and silicon set forth hereinbefore. In the manufacture of the special compositions contemplated by the present invention from ordinary foundry cast iron raw materials and using the ordinary foundry melting equipment, it is generally necessary to retain about 0.04% magnesium. With highly specialized melting techniques and/or highly pure raw materials, e. g., raw materials very low in sulfur, lower amounts of retained magnesium may be used. If amounts of magnesium higher than about 0.1% are retained, there is a tendency to produce dirty castrngs.

In producing the special chilled cast iron castings contemplated in accordance with the present invention, it is important to employ a graphitizing inoculation, e. g., a late addition of a graphitizer such as ferrosilicon, silicon metal, etc. This procedure is unusual in the production of ordinary martensitic cast irons (such as cast irons containing about 4.5% nickel and about 1.5% chromium which are sold commercially under the trademark Ni-Hard), but is necessary in the production of castings contemplated by the present invention in order to prevent formation of an undesirable carbide network structure in the core of the castings. For example, about 0.2% to 0.6% of silicon as a late ladle addition operates as a satisfactory graphitizing inoculation. It has been found that proper inoculation either eliminates the occurrenc of carbides in the core or causes them to occur as isolated islands, thereby minimizing harmful effects on strength and ductility of the core. Accordingly, the process for producing the special chilled cast iron crushing elements comprises establishing a bath of molten cast iron containing about 3.4% to 4.2% carbon, about 0.1% to 0.8% silicon, about 0.4% to 1% chromium, and about 3.5% to about 5% nickel, incorporating into said bath magnesium sufiicient to provide a small but effective amount up to about 0.1% retained magnesium in final castings, inoculating the bath with about 0.3% to about 0.6% silicon as a silicon-containing agent and thereafter casting metal from the bath in an inoculated condition. Generally, the metal is poured into sand molds having metal chills disposed at one or more places about the mold cavity to hasten freezing and cause occurrence of a hard chilled surface in the castings at said places. Since nickel is present in the special cast irons contemplated by the present invention, it is convenient to add magnesium to the bath in the form of a binary or more complex nickel alloy. When this is done, the initial nickel content of the bath is lowered and the nickel added with the magnesium is employed to raise the final nickel content of the castings to the required value.

For the purpos of giving those skilled in the art a better understanding of the invention, the following illustrative examples are given:

EXAMPLE I A bath of molten cast iron containing about 3.5% carbon, about 0.5% silicon, about 0.35% manganese, about 3.7% nickel, about 0.06% phosphorus and about 0.02% sulfur was established. A portion of the bath was treated with chromium to contain about 0.5% chromium, was then treated with magnesium as a nickelmagnesium alloy to contain about 4.2% nickel and about 0.07% magnesium, was divided into separate portions which were respectively inoculated with about 0.3%

and about 0.45% silicon as ferrosilicon containing about silicon and cast to provide castings including 2 x 6" x 6" chill blocks chilled on the 2" x 6" face and sand cast 1.2-inch diameter arbitration bars. Another portion of said bath was treated to contain about 1% chromium, treated with magnesium as a nickel- Inagnesium alloy to contain about 4.3% nickel and about 0.08% magnesium, was then divided into two portions which were respectively inoculated with about 0.25% and about 0.6% silicon as a ferrosilicon containing 85% silicon and cast to provide similar castings. The chill blocks were subjected to a hardness survey and the arbitration bars were subjected to a transverse test over 12- inch centers with the following results:

Brinell Hardness b Chill Blocks Arbitration Bars Transverse Properties Hardness, BHN

Deflection, Load, lbs. Inches 0.13 5,800 i 495 0. 15 6, 770 512 V 0. 4, 300 546 L 0.13 6,350 555 EXAMPLE II A bath of molten cast iron containing about 3.6% carbon, about 0.5% silicon, about 3.7% .nickel, about 0.6% manganese, and about 0.07% phosphorus was established. A portion of said bath was treated with about 1% of a nickel-magnesium alloy containing about 14% magnesium. This portion was then divided into two portions, each of which was inoculated with about 0.25% and about 0.5 silicon, respectively, as ferrosilicon containing about 85% silicon and each of said inoculated portions was then cast to produce castings including 3-inch thick keel blocks. Another portion of said bath was treated with chromium to contain about 0.48% chromium, was treated with magnesium in the same manner as the aforedescribed portion, was divided into two portions which were then inoculated with 0.25% and 0.5 silicon, respectively, as ferrosilicon containing about 85% silicon and cast to produce castings including 3-inch thick keel blocks. Still another portion of said bath was treated to contain 0.91% chromium, and was then treated with magnesium, divided into two portions, inoculated and cast in a similar manner to the aforesaid portions. Tensile specimens were machined from the aforedescribed castings and were subjected to tensile A bath of molten cast iron containing about 3.5% carbon, about 0.4% silicon, about 0.3% manganese, about 0.08% phosphorus, and about 3.7% nickel was established. A portion of this bath was treated with 1% of a nickel-magnesium alloy containing about 14% magnesium and was then inoculated with about 0.5% silicon as ferrosilicon containing about 85% silicon and cast without further treatment. Other portions of the bath were treated to contain about 0.47% and about 0.96% chromium, respectively, and were cast after similar magnesium treatment and inoculation. These castings contained about 4.5% nickel. Castings including 3-inch thick keel blocks were prepared from each said portion. A 1.2-inch diameter impact specimen machined from a keel block containing 0.47% chromium tested in the unnotched condition broke at 70 foot-pounds, while a similar specimen machined from a keel block containing 0.96% chromium broke at 40 foot-pounds. A similar specimen machined from the iron which was not treated to contain chromium did not break in the impact test. These specimens were stress relieved at 400 F.

The foregoing results show that chilled castings within the critical compositional ranges required by the present invention have a high hardness in the chill and have high strength and toughness in the backing or core. In contrast thereto, a chilled casting having a composition outside the present invention and containing about 3.1% carbon, about 4.5% nickel, about 0.5 chromium, about 0.22% phosphorus, about 0.6% manganese, about 1% silicon (including about 0.5% silicon added as an inoculant) and about 0.08% magnesium was produced in the form of a 4" x 6" x 6" block chilled against a 4" x 6" face. The hardness of the chill was 627 Brinell but the chill was very shallow with the hardness falling to 484 Brinell at a point fii-inch below the chilled face. Such a casting is unsatisfactory for use as a crushing element. In addition, an undesirable carbide network persisted in the core and the tensile strength of the core metal was only about 42,500 p'. s. i., even though spheroidal graphite was present in the core'structure. The matrix structure of the core comprised pearlite and bainite.

In contrast to the high impact values produced in chilled crushing elements contemplated by the present invention, it may be pointed out that the impact value in a 1.2-inch diameter sand casting made of prior art magnesium-free martensitic nickel-chromium white cast iron rarely exceeds about 25 foot-pounds. The improvement in impact properties which characterizes chilled crushing elements produced according to the present invention greatly contributes. toward longer service life. Thus, it has been found that when the present invention is applied to roll heads for a roller mill, breakage of the roll heads is practically eliminated. Figure 1 depicts a roll head made in accordance with the invention after service in a roller mill. It will be noted that the worn surface of the roll head is free from spelling, chipping, cracking, etc.

As previously indicated, the castings produced in accordance with the present invention may be made by a process comprising establishing amolten cast iron bath containing amounts of carbon, nickel, chromium and manganese set forth hereinbefore, adding to said bath a small amount of magnesium effective in the final casting to cause the occurrence of spheroidal graphite in the backing or core, adding about 0.3% to about 0.6% silicon as a late ladle addition to provide an inoculating effect and to provide in the final casting silicon contents set forth hereinbefore and then casting the magnesium treated inoculated melt into molds. The molds may be provided with metal chills to cause the occurrence of hard chilled portions on the surface of the casting at the desired locations. Magnesium convenient-1y may be added as a nickel-magnesium alloy containing from about 4% to about 20% of magnesium. In this manner, a portion of the required nickel content of the final cast iron may also be introduced at the same time. Of course, other magnesium-containing alloys, for example, binary or more complex alloys of magnesium with other elements such as silicon, copper, manganese, etc., may be employed. Inoculation may conveniently be effected using ferrosilicon, e. g., alloys of silicon and iron containing 50% or more of silicon. Silicon metal or proprietary inoculating materials sold commercially for the purpose 7 of reducing dendriticism and reducing chill in foundry gray cast irons may be employed.

The special chilled cast iron castings provided in accordance with the present invention may be melted in the usual melting equipment available in the foundry, e. g., the cupola furnace, the electric furnace, the induction furnace, etc. Because close control of the composition is essential, it may be convenient to employ the electric furnace or the induction furnace in the production of castings contemplated by the present invention.

Chilled castings produced in accordance with the pres ent invention are useful in crushing machinery and other applications wherever mechanical components are required which have a hard, wear-resistant chilled face and a tough, strong core. Examples of mechanical elements which satisfactorily may be produced in accordance with the present invention include roll heads for roller pulverizing mills, metal working rolls, drop balls, skull crackers, large grinding balls, jaw crusher plates, roll shells, gyratory crusher cones and mantles, swing hammers, etc.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. In a machine for crushing solid materials, a crushing element made of chilled martensitic cast iron of the definite chill type having a hard, wear-resistant outer portion and a tough, ductile inner portion containing spheroidal graphite, said cast iron containing about 3.5% to 3.8% carbon, about 0.9% to 1.1% silicon, about 4.5% to 4.8% nickel, about 0.5% to 0.7% chromium, about 0.2% to 0.6% manganese and a small amount up to about 0.09% magnesium effective to contorl the occurrence of graphite in said crushing element in a spheroidal form, and the balance essentially iron.

2. In a machine for crushing solid materials, a crushing element made of chilled martensitic cast iron of the definite chill type having a hard, wear-resistant outer portion and a tough, ductile inner portion containing spheroidal graphite, said cast iron containing about 3.4% to 4.2% carbon, about 1.1% to 0.6% silicon, about 3.5% to nickel, about 0.4% to 1% chromium, about 0.1% to 0.6% manganese, and a small amount up to about 0.1% magnesium elfective to control the occurrence of graphite in said crushing element in a spheroidal form, and the balance essentially iron.

3. As a new article of manufacture, a chilled marten- Sitic iron casting of the definite chill type having a hard, wear-resistant outer portion and a tough, ductile inner portion containing spheroidal graphite, said cast iron containing about 3.5% to 3.8% carbon, about 0.9% to 1.1% silicon, about 4.5% to 4.8% nickel, about 0.5% to 0.7%

8 chromium, about 0.2% to 0.6% manganese and a small amount up to about 0.09% magnesium effective to control the occurrence of graphite in said crushing element in a spheroidal form, and the balance essentially iron.

4. As a new article of manufacture, a chilled martensitic iron casting of the definite chill type having a hard, wear-resistant outer portion and a tough, ductile inner portion containing spheroidal graphite, said cast iron containing about 3.4% to 4.2% carbon, about 1.1% to 0.6% silicon, about 3.5% to 5% nickel, about 0.4% to 1% chromium, about 0.1% to 0.6% manganese, and a small amount up to about 0.1% magnesium effective to control the occurrence of graphite in said crushing element in a spheroidal form, and the balance essentially iron.

5. The method for producing chilled martensitic iron castings of the definite chill type which comprises establishing a bath of molten :cast iron containing about 3.4% to 4.2% carbon, about 0.4% to 1% chromium, about 0.1% to 0.6% manganese and the balance essentially iron, incorporating in said bath a small amount of magnesium up to about 0.1%, adjusting the nickel content of said bath to about 3.5 to 5%, inoculating said bath with about 0.2% to 0.6% silicon and casting metal from the thus-treated bath into a mold having at least one chill disposed in the mold cavity to provide a chilled casting from the thus-treated metal containing about 3.4% to 4.2% carbon, about 1.1% to 0.6% silicon, about 3.5% to 5% nickel, about 0.4% to 1% chromium, 0.1% to 0.6% manganese and a small amount of magnesium up to about 0.1% effective to control graphite present in said casting to a spheroidal form.

6. The method for producing chilled martensitic iron castings of the definite chill type which comprises establishing a bath of molten cast iron containing about 3.5 to 3.8% carbon, about 0.5% to 0.7% chromium, about 0.2% to 0.3% manganese and the balance essentially iron, incorporating in said bath a small amount of magnesium up to about 0.09%, adjusting the nickel content of said bath to about 4.5% to 4.8%, inoculating said bath with about 0.3% to 0.6% silicon and casting metal from the thus-treated bath into a mold having at least one chill disposed in the mold cavity to provide a chilled casting from the thus-treated metal containing about 3.5% to 3.8% carbon, about 0.9% to 1.1% silicon, about 4.5 to 4.8% nickel, about 0.5% to 0.7% chromium, 0.2% to 0.6% manganese and a small amount of magnesium up to about 0.09% effective to control graphite present in said casting to a spheroidal form.

Alloy Cast Irons, 1939 edition, pages 141, 142, 143 and 144.

Claims

1. IN A MACHINE FOR CRUSHING SOLID MATERIALS, A CRUSHING ELEMENT MADE OF CHILLED MARTENISTIC CAST IRON OF THE DEFINITE CHILL TYPE HAVING A HARD, WEAR-RESISTANT OUTER PORTION AND A TOUGH, DUCTILE INNER PORTION CONTAINING SPHEROIDAL GRAPHITE, SAID CAST IRON CONTAINING ABOUT 3.5% TO 3.8% CARBON, ABOUT 0.9% TO 1.1% SILICON, ABOUT 4.5% TO 4.8% NICKEL, ABOUT 0.5% TO 0.7% CHRONIUM, ABOUT 0.2% TO 0.6% MAGNESIUM AND A SMALL AMOUNT UP TO ABOUT 0.09% MAGNESIUM EFFECTIVE TO CONTROL THE OCCURRENCE OF GRAPHITE IN SAID CRUSHING ELEMENT IN A SPHEROIDAL FORM, AND THE BALANCE ESSENTIALLY IRON.