US2763583A - Process for manufacturing porous cast iron - Google Patents

Description

United States Patent PROCESS FOR MANUFACTURING POROUS CAST IRON 8020 Kawasaki, Minatoku, Tokyo, Japan No Drawing. Application March 26, .1953, Serial No. 344,891

6 Claims. (Cl. 148-417) This invention relates to a method for easily producing cast iron which is excellently permeable by oil and is suitable for use in oilless bearings or the like.

This invention has for its object to increase the porosity of oil permeable cast iron so that it may contain the maximum possible amount of oil, without sacrificing its mechanical strength.

Where it is desired to make a bearing of an oil perme able metallic material made by sintering finely divided material in a forming mold therefor, the porosity of the surface of the product thus obtained tends to be im paired by the subsequent machining operations. This difficulty manifests itself particularly when such metals as copper, tin, etc., are used as the raw material.

it is well known that if a cast iron is repeatedly subjected to annealing, the phenomenon of the expansion of the volume of the cast iron i. e. the phenomenon of the so-called growth of the cast iron takes place. Numerous investigations have been made to prevent such a growth. This applicant noticed that this expansion Percent Carbon (in total) u 3.20 Combined carbon 0.50 Silicon 2.00 Sulphur 0.07 Phosphorus 0.70 Manganese 0.80

was heated to 700 C. and maintained at this temperature for about three hours, and thereafter it was cooled slowly to room temperature. This heat treatment procedure was repeated thirty times. The resulting product.

was a porous material having a specific gravity of 5.7. It was then immersed into a lubricating oil bath heated to 120 (3.. whereby a raw cast iron containing 26% of lubricating oil by volume was obtained. The bearing made from this final product by machining proved to be a very satisfactory one as a main bearing of a grinding machine with a main shaft revolving at a speed of 1500 R. P. M., the porosity of the machined bearing surface thereof being seemingly not impaired at all. Indeed, oilless bearings made of this oil permeable cast iron ob tained from grey cast iron as set forth previously have been used in practice with a favourable comment.

Since it seems that the formation of iron oxides around graphite-flakes distributed in the mass of a cast iron subjected to repeated annealing is one of causes of the growth of cast iron, this applicant arrived at the conclusion that the porosity of cast iron might be increased,

Copper 2,763,583 Patented Sept. 18, 1956 if such iron oxides were removed therefrom. Thus, the same raw grey cast iron as used in the previous experiments was heated to 700 C., maintained at that temperature for about three hours and thereafter cooled slowly to ordinary temperature. fifty times. The porous cast iron thus obtained, which had a specific gravity of 5.506, was immersed in a bath of 0.25% sulphuric acid. solution at room temperature for about 24 hours, and then thoroughly washed with water and completely dried. Itsspecific gravity then was 5.439. When a circulardisc made of this product 30.2 mm. in. diameter and 10.2 mm. in thickness was immersed in. a bath. of lubricant, the quantity of lubricant impregnated in it was 1.666 gr., whereas the quantity of lubricant impregnatedin a disc having: the same size, but not subjected to said acid pickling treatment proved to be only 1.00 gr. It is thus ascertained that the pickling treatment does increase the porosity of cast iron which confirms the truth of the applicants aforementioned conclusion. The results of this investigation have already been published.

Through a series of investigations just mentioned, this applicant hasrecently succeeded in obtaining excellent results in that an oil permeable cast iron having a. still much. greater mechanical strength can be obtained, and the experimental investigation in the direction of definitely increasing the porosity of the material without appreciably decreasing its mechanical strength has been advanced.

The latest investigations of the oilless bearing, the most importantintended field of use of oil permeable cast iron, tends to be directed. towards the enhancement ofthe mechanicalstrength of the latter, in order to meet the requirements of: large type or heavy duty bearings. Consequently, this applicant has further carried out a similar experimental investigation with ferrous materials other than grey cast iron for the purpose of the enhancement of their mechanical strengths. He has found out that when a white pig iron is annealed so as to produce a black heart malleablecasting, the structure of the latter will become such that its free carbon is: distributed in the. matrix of. the iron, and that when such a malleable casting is repeatedly heated and cooled, there will be obtained a porous material which is more homogenous than grey cast iron and its mechanical strength is surprisingly, increased. Thus a white pig iron (tensile strength 29.8 kg./mm.. Brinell hardness 315 and specificgravity 7.69), having the composition of:

Per cent Carbon c 2.48 Silicon. 0.92- Manganese 0.34 Phosphorus 0.11 Sulphur M..- 0.09 Chromium 0.03

i and, having been annealed atabout 850 Crfor twentysix hours, was heated to a temperature somewhat above or below the A1 transformation point, that is, 800 C., and then cooled to atmospheric temperature repeatedly, the number of repetitions being fifty times, whereby its mechanical properties became such that its tensile strength wa 27.2 kg/mmfi, Brinell hardness 80, and specific gravity 7.1. Upon impregnating the material thus obtained with lubricant, it was found that it could contain 4% by volume of the lubricant. Since with grey cast iron after the growth the mechanical strength is at most 13-15 kg./mm. it is apparent from these results that with white pig iron having a mechanical strength of the order of 27 kg./mm. a mechanical strength of at least twice that of grey cast iron is readily obtained.

Promoting the investigation for the purpose of provid- This procedure was repeated ing a porous, oil permeable cast iron material having a still greater mechanical strength in this way, this applicant has found out that a cast iron which has been caused to have a spheroidal graphitic structure has a greater tensile strength than usual. In consequence thereof, this applicant has succeeded, by heating and cooling such cast iron above and below its A1 transformation point repeatedly to effect the growth thereof, to obtain a porous, oil permeable cast iron having a mechanical strength three to four times as great as that of an ordinary grey cast iron, and yet capable of absorbing substantially the same amount of lubricant as that absorbed by the latter. In this experiment, a nodular cast iron (tensile strength 60.4 kg./mm. Vickers hardness number 290, specific,

gravity 7.3) containing 0.3% magnesium which was added thereto by employing 80:20 nickel-magnesium alloy and 0.5 silicon added thereto as an inoculant, was repeatedly heated and cooled between a temperature somewhat above or below 800 C. and ordinary temperature, the number of repetition being fifty times, thereby producing a grown up material having a tensile strength of 54 kg./mm. Vickers hardness number of 180, and specific gravity of 6.6, which grown up material when subjected toan oil impregnating treatment was capable of absorbing 6% by volume (0.75% by weight) of lubricant. This material is found to be suitable for use in heavy duty oilless bearings.

. Based on the results of the aforementioned experiment, and having ascertained that the degree of porosity of a cast iron can be enhanced by repeatedly annealing it to produce a very porous cast iron and then immersing this porous cast iron into a bath of sulphuric acid solution so as to eliminate the iron oxides distributed in that cast iron, this applicant hit on the idea that it would be possible to increase the porosity of a cast iron without sacrificing its mechanical strength, if the cast iron could be converted into one having a small specific gravity by repeatedly subjecting it to annealing operations to produce, in the first place, a porous cast iron having a great amount of iron oxides formed therein, and then reducing said iron oxides to metallic iron. Thus, a porous grey cast iron material (a rod of 30 mm. diameter, 200 mm. long, specific gravity 5.7) obtained from the previous experimental investigation but not yet subjected to said oil impregnating treatment, was exposed to air at ordinary temperature for sixty days. As it was observed that reddish rust of iron oxides had been formed throughout the mass of this material, the latter was subjected to the reduction treatment in a reducing gas stream at a temperature of 700 C. to 800 C. made from cokes. Then it was found that .these iron oxides .had been definitely re duced and the porosity greatly increased. It thus became apparent from this experiment thatprior to the reduction treatment according to the procedure of this invention, the oil containing capacity of the cast iron material was 0.5% by weight, whereas that-of the same cast iron after said treatment was 2.5% by weight, that is, its oil containing capacity wa multiplied five times.

Furthermore, the results of tests of the porous cast iron I claim:

1. The method of manufacturing porous cast iron comprising repeatedly heating cast iron to the temperature of its A1 transformation point and cooling the cast iron to the ambient room temperature, exposing the porous product so obtained to the oxidizing action of air at the ambient room temperature for an extended period of time, and reducing the oxides of the product in a stream of reducing gas.

2. The method according to claim 1 in which the heating and cooling is repeated fifty times from the high temperature of substantially 800 C. to the low temperature of the ambient room atmosphere, the exposure is for a time of the order of sixty days, and the reduction is at a temperature in the range from 700 to 800 C.

3. The method of manufacturing oil impregnated grey cast iron comprising heating the grey cast iron to about 700 C., maintaining the heating for substantially three hours, cooling the grey cast iron slowly to room temperature, repeating said heating, maintaining and cooling at least thirty times, exposing the iron to the ambient atmosphere and temperature for a period of substantially sixty days, subjecting the iron to an oxide reducing gas stream at a temperature in the range of from 700 to 800 C., and immersing the iron in lubricating oil until substantially no further oil is absorbed by the iron.

4. The method according to claim 3 in which the repetition of the heating, maintaining and cooling steps is of the order of fifty times.

5. The method of manufacturing oil impregnated white pig iron comprising heating the white pig iron to a temperature substantially equal to that of its A1 transformation point, cooling the white pig iron to atmospheric temperature, repeating the said heating and cooling fifty times, exposing the iron to the ambient atmosphere and temperature for an extended period, subjecting the iron to an oxide reducing gas stream, and impregnating the iron with oil.

6. The method of manufacturing oil impregnated nodular cast iron containing 0.3% magnesium and 0.5 silicon comprising heating the nodular cast iron to a temperature of substantially 800 C., cooling the nodular cast iron to room temperature, repeating said heating and cooling substantially fifty times, exposing the nodular cast iron to the oxidizing action of the atmosphere at ordinary temperature for an extended period, subjecting the repeatedly heated and cooled, and exposed nodular cast iron to an oxide reducing gas stream, and then im pregnating the nodular cast iron with oil.

References Cited in the file of this patent UNITED STATES PATENTS 1,511,063 Pack Oct. 7, 19 24 Lenel Ian. 16, 1940 OTHER REFERENCES Steel and Its Heat Treatment by Bullens, vol. 2, 5th ed., 1948, page 255.

Claims (1)

1. THE METHOD OF MANUFACTURING POROUS CAST IRON COMPRISING REPEATEDLY HEATING CAST IRON TO THE TEMPERATURE OF ITS A1 TRANSFORMATION POINT AND COOLING THE CAST IRON TO THE AMBIENT ROOM TEMPERATURE, EXPOSING THE POROUS PRODUCT SO OBTAINED TO THE OXIDIZING ACTION OF AIR AT THE AMBIENT ROOM TEMPERATURE FOR AN EXTENDED PERIOD OF TIME, AND REDUCING THE OXIDES OF THE PRODUCT IN A STREAM OF REDUCING GAS.