US3474576A - Process of conditioning metal - Google Patents

Description

United States Patent 3,474,576 PROCESS OF CONDITIONING METAL John A. Mueller, Buffalo, and Stanley D. Mark, Jr., Grand Island, N.Y., assignors to The Carborundum Company, Niagara Falls, N.Y., a corporation of Delaware No Drawing. Filed June 25, 1965, Ser. No. 467,098 Int. Cl. B24b 1/00 U.S. Cl. 51-322 2 Claims ABSTRACT OF THE DISCLOSURE A method of conditioning metal billets by applying a grinding wheel to a billet heated to elevated temperatures and rotating said grinding wheel at a surface speed substantially greater than the conventional rate. A high metal removal rate is obtained without corresponding increases in wheel wear and power consumption.

This invention relates to conditioning metal and, more particularly, to a process for removing the surface layer from nickel or iron alloy billets, slabs or blooms prior to rolling. Hereafter, the term billet is used generically and includes slabs, blooms and other shapes.

When a billet is formed, there are defects in the billet, such as cracks, snakes and slivers. Also an oxide scale forms on the surface. If these defects are not removed, they will persist when the billet is worked into shape and evidence of the defects will appear on the surface of the finished product. Conditioning is the process of removing scale and surface defects from billets. This process may be carried out using a rotary grinding wheel mounted in a grinding machine so that the surface speed, load, and rate of metal removal can be controlled accurately. Conditioning by grinding is preferred particularly when the billet is made of an expensive metal alloy, since it produces a better surface finish and removes less metal than flame scarfing and other methods.

Conditioning takes place just before the billets are formed into bar stock and other shapes. Often conditioning occurs in a production line manner and in order to carry out the process efficiently, it is necessary to remove metal at the optimum rate. The metal removal rate generally depends on the type of grinding wheel used, the load imposed on the grinding wheel and the surface speed of the grinding wheel. Improved grinding rates may be achieved by increasing the surface speed and increasing the load on the wheel. When this is attempted, however, the power required to turn the wheel and the rate of wear of the grinding wheel increase, and at high surface speeds and high loads, there is the danger of breaking the wheel. Therefore, it is customary to operate the grinding wheel at a sufficiently low speed and low load to avoid rapid wheel wear, while at the same time obtaining a reasonable metal removal rate.

In view of the limitations of the present conditioning methods, it is an object of this invention to provide a method for efliciently removing a surface layer from nickel or iron alloy billets.

It is a further object of this invention to provide a method for increasing the rate of metal removal in conditioning nickel or iron alloys.

It is a still further object of this invention to provide a method for improving the surface finish of nickel or iron alloy billets obtained by conditioning.

We have discovered that conditioning of billets of iron or nickel alloys can be carried out in a substantially more efiicient manner at elevated temperatures and by using a resin bonded wheel rotating at a surface speed greater than 12,500 surface feet per minute. The optimum temperature for carrying out the grinding operation depends 3,474,576 Patented Oct. 28, 1969 on the composition of the billet, but generally the process should be carried out at a temperature in the range extending from the lowest visible heat temperature to soaking pit temperature. or nickel and iron alloy billets, the process should be carried out between 1100 F. and 2200" F.

The rate of metal removal of resin bonded Wheels increases in a straight line relationship with surface speed of the grinding wheel. The upper limit of surface speed for resinoid grinding wheels for metal conditioning until recently has been about 12,500 surface feet per minute (s.f.p.m.), but improved formulations and structural improvements now permit this type of grinding wheel to be operated safely at even higher speeds. It would appear that the straight line relationship of surface speed to metal removal rate would continue at higher surface speeds.

In seeking an improvement in the efiiciency of conditioning operations, we have discovered that the straight line relationship of metal removal rate to wheel speed does not prevail at elevated temperatures. A remarkable improvement in the rate of metal removal occurs at high temperatures and high wheel surface speeds, without corresponding increases in wheel wear and power rate. Generally, the benefits of the method of this invention are obtained by grinding at surface speeds greater than 12,500 s.f.p.m. and at temperatures between 1100 F. and 2200" F. Preferably the surface speed should be approximately 16,000 s.f.p.m.

To illustrate the remarkable improvement in metal removal rate obtained by the method of this invention, a series of tests were conducted utilizing a slab grinder with a resin bonded wheel 24 inches in diameter and having a thickness of 3 inches. The material used during the test was a No. 304 stainless steel. The speed of the wheel head was feet per minute and the wheel head indexed /2 inch on each stroke. The grinding continued for 15 minutes during each test and the grinding pressure was 900 pounds. The grinding wheel grading was the same for each test, WA 16-W3-BZ1.

Room Temperature Temperature 1,700 F.

Wheel Speed, s.f.p.m.

Although a wheel speed of 16,000 s.f.p.m. requires a different wheel grading for optimum results, the same wheel grading was used throughout the series of tests so that the effects of changes in wheel speed and temperature could be observed. All conditions other than Wheel speed and temperature remained the same during the tests.

As indicated by the above table, the metal removed during each fifteen minute test varied from 43 pounds at room temperature and 12,500 s.f.p.m. to 279 pounds at 1700 F. and 16,000 s.f.p.m. If 43 pounds is considered the base performance, the data shows that the improvement due to increasing the speed of the grinding wheel at room temperature is the difference between lbs. and 43 lbs., or 12 lbs. difference. The improvement which can be attributed to increasing the temperature of the metal at a speed of 12,500 s.f.p.m. is the difference between 132 lbs. and 43 lbs., or 89 lbs. difference. If the improvement in metal removal due to increasing the speed is added to the improvement due to increasing the temperature, the result indicates that the total improvement expected by increasing both speed and temperature should be 101 lbs. From the above table, however, it can be seen that the total improvement is the difference between 279 lbs. and 43 lbs., or an improvement of 236 lbs. These results are tabulated as follows:

Improvement due to speed change only=5543=l2 lbs.

Improvement due to temperature change only:

13243=89 lbs.

Total improvement expected=l2+89=l0l lbs.

Actual improvement due to temperature and speed changes=27943'=236 lbs.

It is apparent that there is a synergistic effect that causes a far greater improvement in metal removal than would be expected. In the example given above the results are 2.34 times greater than expected. At the same time that the metal removal rate is increasing dramatically, the grinding ratio is improved over that at room temperature and the power required per unit volume per unit time is reduced substantially. The method of this invention thus achieves remarkably high metal removal rates Without sacrificing efliciency.

The method of this invention is preferably carried out on a grinder in which the billets are supported on a table. The grinding wheel traverses over the surface of the billet which remains stationary. The table surface supporting the billet insulates one side of the billet and by suitable shielding, the temperature of the billet may be controlled.

One important application of the method of this invention is in the removal of scale from ingots, billets and slabs which have been heated in soaking pits at temperatures of the order of 2200 F. to 2400 F. The scale becomes embedded in the billets and surface defects cause serious problems in the subsequent processing of the steel, such as hot rolling. The billets may be cooled below the transformation temperature and then subjected to the conditioning method of this invention. The grinding wheel preferably operates at a surface speed greater than 12,500 s.f.p.m. and preferably at speeds as high as 16,000 s.f.p.m. Since the conditioning operation can be carried out on the billets almost immediately after they leave the soaking pits, and since the rate of metal removal is substantially increased, surface grinding of the billets at high speed and high temperature in accordance with this invention significantly decreases the time required in preparing the billets for further processing to form bar stock or other shapes. Instead of requiring an increase in power consumption rate and a decrease in grinding ratio, as might be expected, the significant improvement in these factors at elevated temperatures improves the overall efiicieney of the conditioning operation.

Another advantage of utilizing high speed, high temperature grinding with a resinoid bond grinding wheel is that the surface finish is superior to that produced at lower temperatures and lower speeds. This superior finish in the conditioning operation improves the quality of the finished article.

While this invention has been described in one embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims.

We claim:

1. A method of conditioning nickel and iron alloy billets comprising maintaining a billet at a temperature of about 1700 F., applying a rotary resinoid bond grinding wheel to the billet While rotating the wheel at a surface speed of about 16,000 surface feet per minute.

2. A method of conditioning nickel and iron alloy billets comprising maintaining a billet at a temperature of about 1700 F., applying a rotary resinoid bond grinding wheel to the billet, traversing said wheel relative to said billet While rotating the wheel at a surface speed of about 16,000 surface feet per minute.

References Cited UNITED STATES PATENTS 1,689,512 10/1928 Worton 51-322 1,689,544 10/1928 Worton 5l322 2,704,912 3/ 1955 Soderlund 5 l35 3,118,254 l/1964 Di Lella 5l92 X FOREIGN PATENTS 529,541 8/1956 Canada.

OTHER REFERENCES Grinding Wheels and Their Uses by Johnson Heywood, second edition published by The Penton Publishing Co., 1942, pp. 369 and 37.

LESTER M. SWINGLE, Primary Examiner