DE2401245A1 - Centrifugal casting process - Google Patents

Description

January 10, 1974 Gzk / pn

Cabot Corporation, 125 High Street, Boston, Massachusetts,

UNITED STATES.

Centrifugal casting process

The invention relates to a centrifugal casting process and has the object of a centrifugal casting process in which during solidification Shattering slag is introduced into the centrifugal mold immediately after the molten metal is introduced to form a inner lining of the cast metal. The term "slag that cracks when solidifying" becomes a slag which undergoes a change in volume on transition to the solid state, which leads to cracking or tearing the slag leads.

The centrifugal casting of metal to different, essentially concentric hollow objects such as pipes have long been known. Gray cast iron is used to cast pipes or different types of steel or high-alloy castings, depending on the intended use of the object to be cast. at Pipes or other hollow objects made of steel or high-alloy materials by centrifugal casting there has long been a difficulty caused by the

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409833/0286

Causes shrinkage or contraction on the inside diameter of the pipe which leads to porosity and poor internal surface. A high percentage occurs with these pipes on rejects as a result of leaks and because of the poor surface. So far, there hasn't been a better one for this problem Solution than to pour the pipe with a thicker wall and a smaller inner diameter than what was called for, and then work off the damaged inner wall surface down to the solid metal in order to close the porous areas on the inner diameter remove and achieve a good surface quality on the inside surface. This is both in terms of processing time, the work and the reject losses are very expensive.

The present invention provides a method of solving this problem and spin casting articles that are largely free of one have internal porosity and a good internal surface. The process can be started / ended with any centrifugal casting process will.

A centrifugal casting process is provided which does the following Process steps comprises: pouring molten metal into a rotating centrifugal casting mold, immediately thereafter Pouring a molten slag that bursts upon solidification into the rotating centrifugal casting mold after the molten one Metal to form an internal slag lining in the centrifugally cast metal, cool to solidify the metal and slag that cracks as it solidifies and removing the slag from the centrifugally cast Object. Preferably, the slag is in the form immediately

409833/0286

bar after the metal casting has been completed, preferably within five seconds after the metal casting has been completed. The slag is preferably at a temperature of about 1650 ° C (300 ° F) and the weight ratio of slag to metal is about 0.3 or greater. A slag of calcium orthosilicate (Ca ₂ SiO ₄ ) is preferably used, which is diluted with calcium fluoride in order to lower the melting point. This slag bursts when it cools and can be completely removed, for example by pouring it out of the finished cast pipes. Another slag which bursts when solidifying can also be used, if so desired; however, it has been found that dicalcium orthosilicate is preferred.

'.' Other features, advantages and possible uses of the In the following, the invention is described using exemplary embodiments.

The accompanying drawings serve to explain the invention.

■ Example I

A batch of 675 kg (1500 lbs.) Of the alloy HAYNES * HL-40 (Trademark of Cabot Corporation) was potted into ten tubes, each 4 3/4 inches (120.6 mm) in outer diameter and 9.5 mm (3/8 in) wall thickness and 2.43 m (8 feet) long. This alloy contains about 30% chromium, about 20% nickel,

about 0.40% carbon, up to 2% manganese and each

- / up to 0.50% molybdenum
Siliciumj der Resx is iron, other elements and impurities

409833/0286 - 4 -

worked. Seven tubes were cast using the centrifugal slag casting process according to the invention poured, with liquid slag added immediately after pouring the molten metal became.

The alloy was rotated at 1566 ° C (2850 ° F) at 50 revolutions cast per minute (rpm) rotating mold. At the end of the metal casting process, the molding speed was up 1150 rpm. increased and then to 900 rpm. decreased. 63.5 kg (140 lbs) alloy was used per tube. For those with Slag addition to cast pipes was 15.9 kg (35 lbs) molten Used slag. The results of the test including the time between pouring the metal and pouring the slag, the slag temperature in the furnace, the wall thicknesses and those determined metallographically Shrinkage depths are shown in Table 1. The pipes no. 1, 4 and 9 were made without slag and should be considered conventional tubes of this size. The timing of the Slag addition was measured from the end of metal pouring. The tube temperature was measured in the oven with an optical Measured by pyrometer. The wall thickness measurements were made with gauges

/ (3 inches)

Run about 7.5 cm 'from the end of the pipe. The depth of shrinkage was measured metallographically by making a cross section of the tube has been polished and examined under the microscope. The numbers indicate the maximum depth of the shrinkage phenomena found at.

5 -

409833/0286

Panel I.

Results for alloy "HAYNES" HL-40, lot 2351 Centrifugal slag casting - Example 1

O
CD
OO
CO
CO

Slag pipe addition no. Time in seconds (1)

IrI

1-2
1-3
1-4

1-5
1-6
1-7
1-8.
1-9

1-10

no

slag

admitted

4.0 5.0

no

slag

admitted

4.5 6.5 8.0 8.0

no

slag

admitted

4.5

Slag furnace temper. (op) ⁰ C

(2)

Wall thickness hot end cold end

(Inch) mm (inch) mm

see table II

(2950) 1621 (3/8) 9.5 (1/4) 6.4 (3050) 1677 see table II

(3/8) 9.5 (3/8) 9.5

(3050) 1677 (3/8) 9.5 (3050) 1677 (3/8) 9.5 (3100) 1705 (3/8) 9.5 (3100) 1705 see table II

(3/8) 9.5 (3/8) 9.5

(9/32) 7.2 (5/16) 8.0 (3/8) 9.5

(3150) 1761 (3/8) 9.5 (9/32) 7.2

(1) at the end of metal casting t-0

(2) measured optically in the oven

Metallographic Depth of Shrinkage. Hot End. Cold End

(Inch) mm

(0.080) 2.03
(0.040) 1.02

(0.075) 1.90

(Inch) mm

(0.070) 1.78 (0.055) 1.40

(0.085) 2.16

After a sample was cut for an air test, tubes No. 1, 3 and 8 became lengthwise slotted and then the wall thickness was measured in micrometers, at intervals of about 30 cm along the pipe. The measurement results are given in Table II. The permissible range of wall thickness for pipes of this size is at 9.5 mm -O + 1.6 mm (3/8 inch -0 + 1/16) or 9.5 to 11.1 mm (0.375 to 0.4375 inch).

409833/0286

Plate II

Wall thickness measurements of a pipe with an outer diameter of 120.6 mm, cast from alloy "HAYNES" HL-40 using the centrifugal method

CD
CO
GO

Distance from cold end (feet) cm

(0) - (cold end)

(1) 30.5

(2) 60.9

(3) 91.4

(4) 121.9

(5) 152.4

(6) 182.9

(7) 213.4

* Cast without slag Wall thickness (inch) mm Pipe No. 1-1 * Pipe No. 1-3 Pipe No. 1-8

(0.365) 9.27

(0.370) 9.40

(0.375) 9.53

(0.373) 9.47

(0.376) 9.55

(0.380) 9.65

(0.382) 9.70

(0.377) 9.58

(0.377) 9.58

(0.402) 10.21

(0.405) 10.29

(0.403) 10.24

(0.400) 10.16

(0.388) 9.86

(0.375) 9.53

(0.360) 9.14

(0.389) 9.88 ro
J **
O (0.393) 9.98 MM (0.397) 10.08 Cn (0.396) 10.06 (0.385) 9.78 (0.377) 9.58 (0.353) 8.97 (0.343) 8.71

Example II

Two batches of 675 kg (1500 lbs) of the alloy HAYNES HL-40 were cast into 21 tubes each 4 3/4 "(120.6 mm) outside diameter, 3/8" (9.5 mm) wall thickness and 8 feet in length. Sixteen pipes were cast using the slag spinner casting process, being liquid Slag was added after metal casting, and 5 pipes were cast without adding slag as usual.

When centrifugal casting, it is common to pour the metal at 1566 ° C (2850 ⁰ F) in a steel mold which is at 50 rpm. turns. After the metal was poured, the molding speed became 1100 rpm. increased and then to 900 rpm. reduced to the point of solidification. The first pipe cast in this series of tests was cast in a conventional manner, but with the molding speed at 900 rpm. was held. It has been found that 900 rpm. is too slow because the metal stops in the middle of the pipe. The remaining tubes were cast in a conventional manner, but with the molding speed at 1100 rpm. was held until solidification occurred.

The slag centrifugal casting process for this series of experiments was carried out as follows:

1. During solidification zerspringende slag was melted and maintained at a higher temperature or 1761 ° C (3200 F ^0).

2. Two tubes were poured from each batch, 120.6 mm

(4 3/4 ") outside diameter, 1 cm (0.0400") wall thickness, 2.43 m (8 feet) long with no slag in conventional manner.

- 9 409833/0286

3. Sixteen tubes were cast, 120.6 mm each (4 3/4 ") outside diameter, 1 cm (0.400") wall thickness, 2.43 m (8 feet) long, the invention Slag centrifugal casting method was used.

All tubes were 30.5 cm (12 in.) From the cold end (opposite the pouring spout) cut up; these parts were cut in half, with the one facing away from the cold end Half was used to perform an air test. At the cold end of each tube there was a 2.5 cm (1 inch) thicker Cut off the ring at the end remote from the cold end. These rings were divided into four equal segments and one Metallographic examination to determine the shrinkage porosity.

After all the tubes for the air test and the metallographic Examination were cut, several tubes were cut lengthwise to make wall thickness measurements. Tubes # 2-1, 2-2, 2-4, 2-6, 2-7 and 2-1O of Lot # 2551 were slit lengthways and wall thickness was measured with micrometers at the ends and in 30.5 cm increments along the tube. Table III shows the measurement results in the distribution along the pipe.

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409833/0286

Plate III

Wall thickness measurements of a pipe
process cast from alloy 30.5 (cold end) (0.239)
6.07 Wan of 120.6 mm outer diameter in
"HAYNES" HL-40 from Lot 2551 k e (inch) mm Slingshot Distance from the cold end _D »," ™ "
(Feet) cm * J * ^No. 60.9 (0.405)
12.34 Pipe no.
2-2 ** d d i c Pipe no.
2-6 Pipe no.
2-7 (D 91.4 (0.565)
14.35 (0.406)
10.31 Pipe no.
2-4 (0.389)
9.88 (0.365)
9.27 Pipe no.
2-10 (2) 121.9 (0.572)
14.53 (0.405)
10.29 (0.398)
10.11 (0.394)
10.00 (0.388)
9.86 (0.380)
9.65 σ
co (3) 152.4 (0.563)
14.30 (0.407)
10.34 (0.392)
9.96 (0.402)
10.21 (0.390)
9.91 (0.387)
9.83 co
co
CaJ (4) 182.9 (0.348)
8.84 (0.418)
10.62 (0.397)
10.08 (0.409)
10.39 (0.406)
10.31 (0.391)
9.93 µ CD
ro (5) 213.4 (0.253)
6.43 (0.412)
10.47 (0.409)
10.39 (0.409)
10.39 (0.415)
10.54 (0.405)
10.29 ι 03
Φ (6) 244.0 (hot end) (0.224)
5.69 (0.402)
10.21 (0.404)
10.26 (0.411)
10.44 (0.425)
10.80 (0.410)
10.41 (7) (0.402)
10.21 (0.409)
.10.39 (0.405)
10.29 (0.434)
11.02 (0.416)
10.57 (8th) (0.386)
9.80 (0.410)
10.41 (0.391)
9.93 (0.434)
ll _? 02 (0.415)
10.54 (0.409)
10.39 (0.415)
10.54

Acceptable wall thickness range from 9.5 to 11.1 mm (0.375 to 0.4375 in). * poured without slag, 900 rpm.
** Cast without slag, 1100 rpm.

- ii. - ■

The results of the air test can best be seen from Table IV. The samples were processed to a certain wall thickness and after each reduction in wall thickness, the air test is carried out. The test consisted of sealing both ends of the tube and immersing the tube in water. Compressed air was inserted at one end of the tube and held for a period of time. The air test was carried out according to Union Carbide regulation CFTM-IOO carried out, with exception the tested surface. The regulation requires that a groove at least 25.4 mm (1 inch) wide, flat at the bottom, be made up to the Wall thickness is worked out to perform the test. A 76 mm (3 inch) wide, flat-bottomed groove was made for the present Trials worked out to the wall thickness for the test because it was assumed that the 76 mm (3 inch) groove Width represents a tougher test condition than the 25.4 mm (1 inch) width groove because of the larger test surface area.

The taper of the tubes that were not cut lengthways was determined by five measurements (with micrometers) around the circumference of both at the hot as well as at the cold end of the pipe. Averages and the difference were formed from these measurements between the two mean values was taken as a measure of the tapering of the pipe and is shown in Table V as Wall thickness taper specified.

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409833/0286

T a f e 1 IV

Results of the air test at the cold end of the centrifugal slag casting process cast pipes 4 3/4 in. (120.6 mm) in diameter

JtS O CD

Batch pipe No. No. 2551 2-1 * 2-2 * 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 2552 2-11 * 2-12 * 2-13 2-14 2-15 2-16 2-17 2-18 * 2-19 2-20

W _a nddickenbereich and error (inch) mm

(0.090 (0.090 (0.015 (0.015 (0.015 (0.015 (0.030 (0.015 (0.015 (0.030 -

(0.090 -

(0.130 ***

(0.015 -

(0.015 -

(0.015 -

(0.130 -

(0.015 -

(0.015 -

0.095 **)

0.095)

0.020)

0.020)

0, 020)

0.020)

0.035)

0.020)

0.020)

0.035)

0.095) 0.140)

0.020) 0.020) 0.020) 0.140) 0.020) 0.020)

2.28 2.28 o. 38 0.38 0.38 0.38 0.76 0.38 0.38 0.76

2.28 3.30

0.38 0.38 0.38 3.30 0.38 0.38

2.41 2.41 0.51 0.51 0.51 0.51 0.89 0.51 0.51 0.89

2.41 3.56

0.51 0.51 0.51 3.56 0.51 0.51

M CO

* poured without slag; corresponds to conventionally manufactured pipe of this size

** Committee

*** more than 0.5 mm (0.020 inch) wall thickness; cannot be edited any further

The tube samples subjected to the metallographic test were polished onto disks with fine alumina and then electropolished in a solution of 85% methanol and 15% sulfuric acid. The results were through Measurement of a magnification of 100 times obtained using a micrometer stage. The numbers give the greatest Depth of porosity for each sample. The results of the metallographic examination by measuring the depth of porosity, The results of the measurements on the polished pipe sections are shown in Table V.

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409833/0288

Plate V

Batch pipe Results at Alloy "HAYNES" HL-40; Slag centrifugal casting example II Pan temperature (3000) - (3000) slag Slag- Wall rejuvenation mm 0 Metallographic 2.03 No. No. ture of (2920) (3000) (2) Metal - ** Depth of Time of (Λ \ ( ⁰ F) ⁰ C (2800) _ (2900) relationship (inch) 0.53 Shrinking on 3.05 Slag addition t (2820) (2800) 0.76 cold end 0.51 2551 2-1 * Seconds (2820) (3000) 0.46 (inch) mm 1.02 - (2820) - (0) 0.18 0.76 ' 2-2 no slag TO- (3000) 0.56 (0.080) 1.02 given - (3000) (3000) 1649 - (0.021) 1.75 £ 0.64 2-3 no slag TO- (2820) 1604 0.2 (0.030) 0.13 (0.120) 0.64 2-4 given 1538 0.2 (0.018) 0.28 (0.020) 0.89 ι CD 2-5 8.0 1548 0.2 (0.007) 0.91 (0.040) 0.89 CX) 2-6 8.0 1548 0.2 (0.022) (0.030) CO 2-7 4.0 1548 0.3 (0.069) 0 (0.040) 3.05 co 2-8 4.0 1649 0.3 (0.005) (0.025) 2-9 8.0 1649 0.3 (0.011) 0.20 (0.025) 3.30 CD
hi ^ 2-10 8.0 0.3 (0.036) 2.92 (0.035) 1.02 [SJ
03 2552 2-11 4.0 2.49 (0.035) 0.76 CD 4.5 - (0) 2.23 1.02 2-12 no slag TO-* 0.51 (0.120) ° » ⁷⁶ ro given 1649 - (0.008) 0.76 2-13 no slag TO- 1649 0.3 (0.115) (0.130) 2-14 given 1593 0.3 (0.098) 0.30 (0.040) 2.54 II 2-15 8.0 1538 0.2 (0.088) 1.07 (0.030) 0.76 _Μ 2-16 8.0 1649 0.2 (0.020) 0.69 (0.040) 1 02 £ 2-17 8.5 0.2 (0.030) (0.030) 2-18 8.5 (0.025) I. 5.0 1649 .. (0.012) H 2-19 no slag TO- 1548 0.2 (0.042) (0.100) Cl 2-20 given 0.3 (0.027) (0.030) 4.5 (0.040) 4.5

Footnotes panel V:

* cast at 900 rpm, all others at 1100 rpm.

** Difference in thickness at the cold and warm end a pipe of 2.43 m

(1) Slag time starts with the end of metal casting

(2) Temperature was measured with an immersion thermocouple in the ladle prior to casting

Further metallographic examinations revealed a dark Tape around the inner diameter of the cast pipe with the addition of liquid slag. Fig. 1 shows a photograph of the polished and etched cross section of the cast pipe, the state being as shown at A in the figure. Figure 4 is a photomacrograph at eight times magnification and shows the carbon build-up on the inside Diameter of the pipe poured with liquid slag as shown at B in the figure. Figure 3 is a photomacrographic one Representation in eight times magnification and shows the shrinkage on the inner diameter of the pipe without liquid slag, such as shown at C in the figure. The amount of shrinkage or shrinkage in the pipe cast without liquid slag is noticeably greater than in the pipe cast with slag is.

Hardness tests were carried out on the cross-section of several cast pipes and showed a difference in hardness values of about ten points on the Rockwell A scale between the inner one and the outer diameter. Because of the differences in hardness

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409833/0286

were samples of a chemical analysis of carbon on subject to inner and outer diameter. Chips were from both places (inner diameter and outer diameter) des Itohres removed and led to the following results: carbon on the inner diameter 1.20%; Carbon on the outside diameter O, 41%. Another examination of chips from the inner diameter and outer diameter of one other pipe gave essentially dissimilar results: carbon on the inside diameter 1.10%, carbon on the outside diameter 0.44%. The carbon range for the used Alloy HAYJiES HL-40 is 0.35-0.45; consequently, there is a carbon build-up on the inner diameter of the Rohres took place. Chemical analysis of the batch showed that all of the elements, including carbon, were inside the ranges prescribed for the alloy HAYNES HL-40; this shows that the increased carbon content is presumed was absorbed from the slag. It is believed that due to the high temperature and the length of time during that the molten slag was held in the graphite lining of the furnace, the slag was carbon from the lining has absorbed and a carbon exchange between the liquid slag and metal took place on the inner diameter of the pipe.

In order to simultaneously achieve the lowest possible air test shrinkage and minimization of taper of the tube wall, the slag temperature, as the results must be (F 300O ⁰⁾ raised to 1649 ⁰ C or higher, the slag-metal ratio must be set to O, 3 or higher

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409833/0 286

and the slag time must be reduced to about 4 seconds or less; all of these factors must be in These areas are kept with the least possible changes during the procedure. In addition, the "main effect" of the heat differences in the alloy HL-4O is seen in the fact that it clearly exceeds the general area of the tube taper in the area reliably holds 95%.

What is amazing is that there are no major effects or interactions were found that are important for influencing the metallographic shrinkage, which is random in size over the entire range of possible factors is distributed. However, this result can be attributed to the test method used be. The pipes have been cut across so that you can get into a special area where. the porosity is problematic.

Example III

Ten tubes were cast, eight tubes according to the invention Process with liquid slag and two pipes without slag. The procedure was as follows:

1. Slag that cracked upon solidification was melted at 1705 to 1733 ° C (3100 to 315O ° F) or below.

(Although the previous example has shown that higher slag temperatures work best in terms of the degree of Tapering and shrinking are the temperature reduced to the carbon pickup from .the ladle to reduce).

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409833 / Ö28S

2. Two pipes were cast, 4 3/4 "outside diameter, 0.400" wall thick, 2.43 m long (8 feet), with no slag. The casting speed was 50 rpm, and was set to 1100 rpm. increased to the point of solidification.

3. Eight pipes were cast, 4 3/4 "outside diameter, 0.400" wall thick, 2.43 m long (8 feet), using the slag spinner of the present invention.

4. All ladles and containers were preheated as hot as possible.

The conditions and behavior of the pipe during casting are shown in Table VI.

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409833/0286

Plate VI

pipe
No. Results with alloy
Centrifugal casting example III HAYNES HL-40, (2820) 1548 - Batch] 1582 I. Air test; Wall thickness range,
failure
(inch) ram 3.05-3.53 3-1 * Time of
Slag addition
Seconds Ladle temperature slags
the slag metal
(OF) o _c ratio (2780) 1526 0.3 No. 2681, slag 1599 (0.120-0.139) 3.18-3.58 ■ rs
ο
CD
GO 3-2 * (2700) 1482 0.3 Metal-
temperature
( ⁰ F) ⁰ C 1566 (0.125-0.141) 0.66 - 0.97 or CO
t / 0 3-3 - - (2850) 1566 0.3 (2880) 1582 (0.026-0.038) 0.58-0.86 approx 3-4 5.1 (2800) 1538 0.3 (2910) 1593 (0.023-0.034) 0.64-0.89 3-5 3.2 (2775) 1523 0.3 (2850) 1593 (0.025-0.035) 0.76-0.97 3-6 12.6 (2790) 1531 0.3 (2880) 1571 (0.030-0.038) 0.74-0.94 3-7 5.9 (2910) 1599 0.3 (2900) 1571 (0.029-0.037) 2.16-2.46 3-8 5.5 0.3 (2900) 1576 (0.085-0.097) 0.76-0.84 3-9 4.7 (2860) 1566 (0.030-0.033) 1.70 - 2.46 3-10 6.2 (2860) (0.067 - 0.097) 6.5 (2870) (2850)

* poured without slag

—A

K) Oil

Panel VII shows the pipe wall thickness measured at the ends and spaced 30.5 cm (1 foot) apart along pipe No. 3-9. Measurements were taken on each side of the cut in the tube from the cold end to the hot end .

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409833/0286

Plate VII

Wall thickness measurements on a # 3-9 pipe of 120.6 mm (4 3/4 in.) Outside diameter, batch number 2681

Distance from 30.5 right W. Side of the other the] 10.08 mm 9.91 I. cold end
(Feet) cm 60.9 (0.383) 9.73 Cut ze / (inch) 10.26 10.13 IO Cl) 91, 4 (0.395) 10.03 Left side of the cut 10.19 Average 10.06 O (2) 121.9 (0.391) 9.93 (0.397) 10.13 (0.390) 10.11 I. CD
OO (3) 152.4 (0.398) 10.11 (0.404) 10.13 (0.399). 10.08 OJ
IaJ (4) 182.9 (0.395) 10.03 (0.401) 10.06 (0.396) 3 0.16 (5) 213.4. (0.405) 10.29 (0.399) 9.73 (0.398) 9.98 Ν » (6) 244.0 (0.403) 10.24 (0.399) 9.60 (0.397) 9.86 it (7) (0.398) 10.11 (0.396) (0.400) (8th) (0.383) (0.393) (0.378) (0.388)

The prescribed wall thickness range is 9.5 to 11.11 mm (0.375 to 0.4375 inches).

ro CO

OK) cn

The metallographic examination of the electropolished ear cross-sections showed shrinkage depths of 0.39 mm to 2.54 mm (0.035 to 0.100 inches). These results were obtained by placing a 300X magnification on a table with a Micrometer has been measured; the results are shown in Table VIII. On none of the pipes, according to Example III were cast, there was a dark line on the inside diameter. FIG. 4 is a photomacromatic representation at 8x magnification and shows that there is no dark line as is present in FIG.

Plate VIII

Tube with a diameter of 120.6 mm produced using the centrifugal slag casting process; metallographic shrinkage depth measurements

Lot 2681 Pipe no. Shrink depth (inch) mm 3-1 * (0.100) 2.54 3-2 * (0.100) 2.54 3-3 (0.070) 1.78 3-4 (0.050) 1.27 3-5 (0.040) 1.02 3-6 (0.040) 1.02 3-7 (0.050) 1.27 3-8 (0.060) 1.52 3-9 (0.035) 0.89 3-10 (0.040) 1.02

Shrink depth is the greatest depth of continuous porosity.

poured without slag

- 23 -

3/0286

Hardness measurements were carried out on various pipe cross-sections from the inside diameter to the outside diameter and showed a hardness difference of one or two points from the inside diameter to the outer diameter, where the outer diameter was a little harder.

A chemical analysis was made for a carbon study executed on the inside diameter and outside diameter. The results of the carbon investigation on the inner diameter and Outside diameters showed little or no carbon differences; both areas were within the given limits.

From the preceding representations it can be seen that the use of liquid slag in the centrifugal casting of Tubing leads to a significant reduction in the depth of shrinkage on the inner diameter and that the inner surface of the tube is improved.

A method of centrifugal casting of hollow metal objects has been established described, wherein liquid slag, which shatters when solidifying, is added to the rotating mold immediately after the molten metal has been poured, with a change in volume when the slag changes to the solid state occurs which causes the slag to crack.

Deviations from the conditions of the examples described are possible without departing from the scope of the invention.

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409833/0 286

Claims (3)

Claims 1. Method of centrifugal casting of hollow metal bodies, characterized by the process steps: a) pouring the molten metal into a rotating centrifugal casting mold, b) adding a molten slag, which cracks on solidification, to the rotating centrifugal casting mold immediately after pouring the molten metal, c) cooling the mold to solidify the metal, the slag solidifying and cracking, and d) removing the cast metal body from the mold and the cracked slag from the cast Body. 2. The method according to claim 1, characterized in that the slag which shatters during solidification is essentially consists of calcium ortho-silicate. 3. The method according to claim 1, characterized in that the slag which shatters when solidifying is made of calcium ortho-silicate consists of a sufficient amount of calcium fluoride to achieve the desired slag melting point to obtain. ⁷ ^ The method according to claim 1, characterized in that the slag is added within five seconds after the end of the metal casting. - 25 - 409833/0288 A method according to claim l _{fi characterized:%} that of the inner diameter of the metal is hardened by the addition of carbon by the presence of dissolved carbon in the slag at the time of addition » Γ Method according to claim Jp _h, characterized in that the carbon is dissolved in the lacquer by keeping the slag in a carbon casting container at an elevated temperature " 409833V0286