USE OF BALL-BEARING STEEL WASTE FOR CENTRIFUGAL CASTING OF BEARING RINGS

E. P. FILIMONOVA, B. S. KARASYUK

(Presented by the scientific seminar of the departments of physical metallurgy, metal technology, and welding production)

The bearing industry is a major consumer of steel. Losses of metal in chips and in unused waste amount in the bearing industry to 60–70% [1].

Our metallurgy has large production capacities. Under the adjusted plan, production of pig iron in our country in 1965 will rise to 72–73 million tons, and steel to 95–97 million tons. Along with a further increase in metal production, great attention is being paid to the use of scrap metal. At present, 46% of all steel is smelted from scrap metal [2]. With the expansion of metallurgical and metalworking production, the waste of ferrous metals will also increase accordingly. According to preliminary estimates, in 1965 ferrous-metal waste will amount to more than 40 million tons.

The role of scrap metal in the development of the national economy is exceptionally great. Rational consumption of scrap metal makes it possible to reduce unnecessary transportation and to use it for its direct purpose with the least losses. The sooner remelting is carried out, the smaller the losses from corrosion (it should not be forgotten that approximately one quarter of the iron mined in a year is lost to corrosion).

In the bearing industry it is possible to use scrap metal for manufacturing bearing rings by the method of centrifugal casting. At the First State Bearing Plant, such a method is used in manufacturing rings for large-size bearings; the coefficient of metal utilization is thereby increased almost twofold [3].

To verify the expediency of introducing into the bearing industry the production of bearing-ring blanks by the method of centrifugal casting, let us compare two methods of manufacturing bearing rings of types 208, 306, and 408.

1. The generally accepted method currently in use for producing bearing-ring blanks from rolled stock by subsequent forging.

2. The method of obtaining bearing-ring blanks by centrifugal casting.

To trace the production of bearing rings by the first method, one must begin with the smelting of steel at metallurgical plants. This technology consists of the following operations [4]:

1. Smelting steel in a basic electric-arc furnace or an acid open-hearth furnace.
2. Siphon casting of the steel.
3. Removing ingots from the molds.
4. Annealing the ingots at 800–830°C.
5. Removing surface defects from the ingot.
6. Heating the ingots before rolling on blooming mills.
7. Rolling the ingots.
8. Rolling the billets on section mills.
9. High-temperature tempering at 700°.
10. Inspection and transport of the rolled product to the plant warehouse.
11. Transport of the rolled product to bearing plants.
12. Heating the metal before forging at the bearing plants.
13. Forging the bearing rings.
14. Annealing the forged rings.
15. Machining.

The technology for obtaining bearing-ring blanks by the method of centrifugal casting consists of the following operations:

1. Remelting waste ball-bearing steel.
2. Casting the steel into individual or tubular blanks in the molds of centrifugal machines.
3. Removing the castings from the molds.
4. Annealing the blanks.
5. Cutting the tubular blanks.
6. Machining.

From a comparison of these two technological processes it is clear that the production cycle for ring blanks by centrifugal casting is considerably simpler and shorter, and saves a large amount of metal and time. It is enough to point to the elimination of such operations as rolling ingots on blooming mills and section-rolling mills, transporting the section rolled product to bearing plants, and forging it. All this relieves rolling mills, forging equipment, and railway transport, and saves funds, fuel, and time.

From a comparison of the two technological processes for manufacturing bearing rings considered above, it is possible to calculate the consumption of metal for the manufacture of forged rings and rings obtained by centrifugal casting.

Let us determine the metal consumption per 1 ton of bearing-ring forgings of types 408, 306, and 208.

To determine the consumption of steel ShKh15 for the manufacture of 1 ton of bearing-ring forgings, it is necessary to take into account the metal consumption norms for all metallurgical operations, beginning with steel smelting [5]. Metal losses during smelting amount to 12% per 1 ton of ingots. Losses due to metal burn-off, both when casting ingots and in centrifugal casting, are the same and amount to about 5%. In both cases we exclude them from the calculation. Then \(12 - 5 = 7\%\), and the metal consumption per 1 ton of ingots will be

\[ \frac{1}{0.93} = 1.075 \text{ tons}. \]

The consumption of ingots for producing 1 ton of blanks is 1.274 tons [5].

The consumption of blanks per 1 ton of section rolled product will be taken, according to plant data [5], as 1.085 tons per ton of rolled product. This value is given for

rolled stock of Ø 130–160 mm. For the inner bearing rings of types 408, 306, and 208, rolled stock of 42–36 mm is used. For these diameters the consumption of blanks per 1 ton of commercial rolled stock will be greater, but since we have no data for rolled stock of this diameter, it will be possible to take the blank consumption per 1 ton of commercial rolled stock as equal to 1.085 tons.

The consumption of rolled stock per 1 ton of forgings for inner rings in the GPZ-5 forging shop is:

for type 208—1.05 tons per 1 ton of forgings,

for type 306—1.084 tons per 1 ton of forgings,

for type 408—1.105 tons per 1 ton of forgings,

or

\[ \frac{1.05+1.084+1.105}{3}=1.079 \text{ tons per 1 t of forgings.} \]

On the basis of the data given, we determine the metal consumption for producing 1 ton of bearing-ring forgings of types 208, 306, and 408:

\[ 1+0.075+0.274+0.085+0.079=1.513 \text{ tons per 1 ton of ring forgings.} \]

Let us determine the metal consumption per 1 ton of bearing rings cast by the centrifugal method. In this case, during casting, according to practical data, metal losses amount to 10 kg per ton [5]. If tubes are cast, the metal losses for cutting amount to 137 kg per 1 ton of cast rings [3]. The total metal consumption for one ton of cast ring blanks of a given type will be

\[ 1+0.010+0.137=1.147 \text{ tons.} \]

Thus, comparing the two processes in terms of metal consumption per one ton of bearing-ring blanks, the saving of metal with the centrifugal method of producing rings, as compared with forged ones, is

\[ 1.513-1.147=0.366 \text{ tons.} \]

If the plant produces 1 ton of cast blanks for bearing rings of types 208, 306, and 408 per day, then 300 tons of cast ring blanks will be obtained in a year.

In comparison with forged ring blanks, the metal saving will be

\[ 300=0.366 \times 110 \text{ tons per year.} \]

Let us calculate the metal saving in rubles when manufacturing inner bearing rings of type 208 by casting.

By forging methods these rings are obtained from a Ø 36 mm bar. The cost of 1 ton of such bar is 127 rubles. One ton of ShKh15 steel scrap costs 24 rubles. The difference in metal cost per 1 ton of cast blanks will be \(127-24=103\) rubles.

The annual saving in rubles for metal will be

\[ 300 \times 103=30900 \text{ rubles.} \]

According to GPZ-1 data, the cost of a cast bearing ring of type 3636/01 is lower than that of a forged one by 3 rubles 75 kopecks. By using cast blanks alone, the plant saves tens of thousands of rubles per year [5]. Other bearing plants may follow the same path.

Conclusions

The use of bearing-ring blanks manufactured by the centrifugal-casting method makes it possible:

1. To save hundreds of tons of ShKh15 steel per year.
2. To obtain large annual savings in rubles on metal.
3. To produce bearing rings at a lower cost than forged ones.

References

1. Economy of material resources at the 1st State Bearing Plant. Collected articles, published by the sector of the USSR Gossnab, 1952.
2. G. I. Grebov. Improving the use of scrap of ferrous metals. Moscow, 1960.
3. E. P. Filimonova. Heat treatment of cast steel of the ShKh15 type. Author’s abstract, Tomsk, 1955.
4. M. I. Kolosov, A. I. Stroganov, I. Ya. Aizenshtok. Production of ball-bearing steel. Moscow, 1960.
5. ENIIPT. Report on Topic No. 4 for 1953. Provision of technical assistance to plants in the centrifugal casting and hot rolling of ring blanks.