US3150224A

US3150224A - Apparatus for making steel shot

Info

Publication number: US3150224A
Application number: US53426A
Authority: US
Inventors: Nelson A Libman
Original assignee: Metal Blast Inc
Current assignee: Metal Blast Inc
Priority date: 1960-06-22
Filing date: 1960-09-01
Publication date: 1964-09-22
Anticipated expiration: 1981-09-22
Also published as: GB951812A

Description

* fiv' 22, 19 L N APPARATUS FOR MAKING STEEL SHOT 3 Sheets-Sheet 2 Filed Sept. 1, 1960 INVENTOR.

NELSON A. LIBMAN BY Sept. 22, 1964 N. A. LIBMAN APPARATUS FOR MAKING STEEL snow 3 Sheets-Sheet 5 Filed Sept. 1, 1960 INVENTOR.

NELSON A. LIBMAN United States Patent 3,159,224 APEPARATUS Fill? MAKTNG STEEL El -HUT Nelson lib-man, Univers ty Heights, Ulric, assignor to gdheital lllast inc, Cleveland, tlthio, a corporation of Filed Sept. l, 196%, her. No. 53,42. l Claims. {t1 2645- This invention pertains to blast cleaning and more particularly to a novel and improved method and apparatus for making steel shot for blast cleaning.

This application is a continuation-impart of United States patent application Serial No. 37,885, tiled lune 22, 1960, by Nelson A. Libman, for Abrasive Material and Method of Making Same, now abandoned in favor of continuation-in-part Serial No. 80,505, iiled January 3, 1961, under the same title. in that application a disclosure is made of a novel and improved steel shot for abrasive cleaning and a method of making such shot. Here an apparatus for the manufacture of shot of the type taught in that application and a process for making the shot are disclosed.

As is set out in the parent application, in many manufacturing processes metal bodies, such as steel castings, are treated by impinging metal shot against the surfaces of the body. In blast cleaning the body being treated is placed in a suitable container and metal pellets known as shot are impinged against the surfaces of the body. The impingement is usually obtained either by entraining the shot in a blast of air to project the shot, or by mechanical means projecting the shot, against the body. This art is known generally as metal blasting, or shot blasting, and will be referred to here by these terms.

The types of shot used in metal blasting usually are classified as iron, malleable or steel. The malleable shot is superior to chilled iron in terms of life characteristics and steel is, of course, superior to malleable. At the same time the cost of chilled iron shot is quite low, the malleable more expensive than the chilled iron, and the steel, heretofore, has been quite expensive.

Generally speaking, most manufacturing techniques can be satisfactorily performed with any one of the three classes of shot. Accordingly, the shot is usually selected for a given job on a basis of cost of sufhcient shot of the selected type to do the job.

The present invention provides a simplified apparatus for use in producing steel shot of very high and uniform quality at a cost comparable to the cost of producing malleable shot. The invention includes a novel process by which these advantages are obtained and novel and improved controls for the obtainment of a continuous process.

With this invention gray iron is first melted in a cupola. The gray iron is then formed into a stream which is dispersed as by a blast of air to separate the stream into a plurality of drops. The drops are then caught in a quenching tank to produce, as a result, chilled iron pellets. These chilled iron pellets are then sorted or graded into groups, each of which includes pellets of substantially uniform size.

The pellets of one group are then placed in a feed bin. They are continuously gravity fed from the feed bin into a first tube. The tube is an elongated cylindrical tube which is open at its ends. The shot pellets are annealed in the tube as they are passed through the tube. The pellets then pass from the first tube outlet through a gravity conveyor to an inlet of a second tube. The second tube is formed of a material which has less aflinity for oxygen at the temperatures under consideration than does the carbon in the pellets. As the pellets are passed through the second tube they are heated to a temperature in eX- cess of 1650 F. and less than the fusing point of the till ice

pellets. They are maintained in the second tube until the carbon content is less than 1.7%. Thereafter, the pellets are gravity fed to a water-cooled tube for air cooling or water quenching depending on the hardness desired.

Accordingly, one of the principal objects of this invention is to provide a novel and improved apparatus for the manufacture of steel pellets and to a process of using such apparatus.

Another object of this invention is to provide a novel and improved continuous process of converting pellets of iron shot into high quality steel abrasive shot.

Another object of the invention is to provide a novel and improved apparatus for the manufacture of steel abrasives which apparatus includes an open-ended, elongated tube rotatable about a horizontal axis and having an internal sleeve formed of a material capable of Withstanding temperatures up to the fusing temperature of the ferrous pellets and having a lower atfinity for oxygen than the carbon in the pellets in a temperature range of from d F. to the fusing temperature of the pellets.

A related and more specialized object of the invention is to provide a mechanism having a tube with a sleeve liner formed of carbon-free stainless steel. As used herein, the term carbon-free is intended to mean a steel that is carbon-free relative to the minimum carbon content of the steel shot which is produced.

A further object of the invention is to provide a novel and improved apparatus for the manufacture of steel shot which apparatus includes first and second rotatable openended tubes positioned one above the other for rotation about horizontal axes, and at least one burner nozzle positioned at the inlet end of each such tube to direct a stream of hot gas through the tube to heat and transport steel shot through each tube, a plurality of batfies in each such tube to agitate the shot as the tubes are rotated, and control valves to control the volume and temperature of gas directed through each of the tubes with the control valve for the lower tube including means to control thequantity or" oxygen in the flow of hot gas.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a side elevational view, the parts broken away and removed for clarity of detail, of an apparatus for manufacturing steel shot;

FIGURE 2 is a sectional view of the device as seen from the plane indicated by the line 22 of FIGURE 1;

FIGURE 3 is a sectional view of the lower one of the tubes as seen from the plane indicated by the line 3-3 of FIGURE 2 and on an enlarged scale with respect to FIGURE 2;

FIGURE 4 is a sectional View of the tube of FIGURE 3, on the scale of FEGURE 3 and as seen from the plane indicated by the line 4=-4 of FIGURE 3; and,

Fl'GURE 5 is a diagrammatic View of the device and the controls.

Since this invention includes both an apparatus and a process, the description portion of the specification will be divided into separately identified parts. The first part is directed to the apparatus, the second to the process.

The Apparatus Referring now to the drawings, and FIGURE 1 in particular, a feed bin iii is provided. Chilled iron pellets are continuously fed to the bin lit by a conveyor 11. A supply of pellets, indicated at 12, are continuously gravity fed from the bin through a pellet nozzle 13.. The pellet nozzle 13 delivers, continuously, a supply of these chilled iron pellets to inlet end 14 of an annealing tube 15.

A pair of burner nozzles 17 are positioned adjacent the inlet end 14 of an anealing tube 15. A suitable fuel such as natural gas mixed with an appropriate quantity of air is directed from each of the nozzles 17 to provide a continuous flow of hot gas through the tube 15. The flow of hot gas both heats the pellets and propels them through the tube 15.

As the pellets are propelled from the tube through outlet end 13, they are trapped by a combination deflection baffle and hood 19. A hood outlet Ztl is provided to conduct a gravity fed flow of pellets through an inlet end 21 of a second and lower tube 22. The lower tube 22 is a carbon removal tube.

The carbon removal tube 22 has another pair of nozzles 23 positioned adjacent its inlet end 21. These nozzles 23 provide a continuous blast of air and fuel which is burned in a manner similar to fuel projected by the annealing tube burners 17. The pellets are projected through the carbon removal tube 22 until they come out in outlet end 24 into another combination hood and deflection battle 25.

The pellets coming out of the outlet end 24 or" the carbon removal tube 22 are steel pellets. These steel pellets, or shot, are gravity fed through a conduit 26 into a cooling tube 27. The steel pellets are air cooled within the cooling tube 27 which, in turn, is continuously cooled by a water bath provided by an elongated spray nozzle 28. The pellets may also be quenched in a tank 79 or subjected to a water spray for quick cooling.

The tubes each have a plurality of annular support collars. These annular support collars are designated by the numerals 3t), 31, 32 on the

tubes

15, 22, 27 respectively. A plurality of

support wheels

33, 34, 35 are provided for the

tubes

15, 22, 27 respectively. The

support wheels

33, 34, 35 are respectively journaled at 36, 37, 38 on a frame 40. As is best seen in FTGURE 2, the

support wheels

33, 34, 35 are provided in pairs such that each one of the

collars

30, 31, 32 rides on an associated horizontally spaced pair of the

support Wheels

33, 34, 35 respectively. In this manner the

tubes

15, 22, 27 are rotatably supported on the frame 40.

Motors

41, 42, 43 are mounted on the frame at and suitably connected to the

tubes

15, 22, 27 to cause relative rotation of the frame and tubes. In the embodiment shown all of the motors drive the tubes with chains and sprockets shown at 44, 45, 46 respectively.

In the case of the annealing tube 15, a very satisfactory member can be made with a single, one-piece, cast steel, tubular cylinder. The plurality of inlet guide baffles 49 are provided in the interior of the tube adjacent the inlet end 14 to assist in directing the pellets into the interior of the annealing tube 15. A series of elongated agitation baflies 50 are in the tube and they extend from near the inlet end 14 to the outlet end 18 to agitate pellets in the tube as the device is used.

One of the outstanding advantages of the invention is obtained through the difierence in construction between the carbon removal tube 22 and the annealing tube 15. The carbon removal tube 22 includes an inner sleeve liner 51. This sleeve liner is preferably formed of a carbon-free stainless steel; that is, a stainless steel having less carbon than the minimum carbon content of the steel shot which is produced. The liner may, however, be formed of a stainless steel material which has an excess of carbon above the desired minimum content of the steel shot, and the mechanism operated for a time, with or without the pellets passing through it, in a manner corresponding to the process which will be described below to decarburize the liner 51.

The material or" the liner 51 must, as indicated, he carbon free relative to the steel shot produced. It must also be capable of withstanding up to the fusing temperature of the pellets. This fusing temperature will be in the neighborhood of 2250 F., depending upon the size and chemical content of the particular pellets. It is also essential that the sleeve liner 51 be formed of a material which has less ailinity for oxygen than does carbon in the temperature ranges to which the liner will be subjected, namely from about 1650" F. to the fusing point of the pellets. The tube must also have good abrasion resistance to withstand eroding action or" the pellets passing through the tube. Other materials which have these described characteristics may be substituted for the carbon-free stainless steel.

The carbon removal tube 22 has a plurality of inlet battles 53 adjacent the inlet end 21. The inlet baffles 53 correspond in function to the inlet baffles 49 of the anhealing tube 15. Agitation baflles 54 which correspond in function and general construction to the agitation baffles 50 are also provided in the carbon removal tube 22. The

baffles

53, 54 of the carbon removal tube must, like the sleeve liner 51, be carbon free and be formed of a material capable of withstanding the temperature found in the tube and have less afiinity for oxygen at those temperatures than does carbon. These baliies, like the sleeve liner 51, need not be completely carbon free at the time of installation, but will be made so when the apparatus is operated according to the process described below.

The burners 17 are supplied by suitable conduits 60. The conduits 6?? may be supplied by suitable mixing valves 61, or in the alternative connected directly to suitable fuel and air supplies. In the arrangement shown a supply of air under pressure 62 is connected to the mixing valves 61 by conduit es. Valves 64 are provided to control the pressure and volume of the air supplied to the mixing valves 61. Fuel under pressure, preferably natural gas, is supplied by a source 65. The gas or other fuel is conducted by conduits 66 to the mixing valves 61. The pressure and volume control valves 67 are in the conduits 66 and control the quantity and pressure of the gas supplied to the mixing valves.

To control the temperature in the carbon removal tube and the rate of flow of shot through the tube, controls for the nozzles are provided which are similar to the controls for the nozzle 17. Thus, conduits 49 conduct mixed gas and air from mixing valves 71. Mixing valves 71 are supplied air under pressure from the suitable source 72 by conduits 73. Volume and pressure control valves 74 control the air supplied to the mixing valve 71. Fuel under pressure is supplied by a source 75 to the mixing valves by conduit 76. Volume and pressure control valves 77 are provided to control the quantity and pressure of the fuel.

Improved carbon removal characteristics are obtained if the air is enriched with extra oxygen. Oxygen is supplied from a source 35 which is controlled by valve 86 and connected to the air supply conduit 73.

The Process size. Pellets of excessive size are comminuted to reduce their size. The comminuted pellets are then graded by size. Other methods may be used to atomize the iron to produce the chilled iron pellets.

The process, after the chilled iron shot is formed, can best be understood by reference to FIGURE 5. Chilled iron shot pellets are continuously fed from the bin 10 through the tube 13 into the annealing tube 15. The pellets are blown through the annealing tube by the blast of burned natural gas or other fuel emitted by the nozzles 17. As they pass through the tube 15 they are agitated by the battles 50 as the tube 15 continuously rotates. This agitation exposes all the pellets to the hot gases emitted by the nozzle 17 to assure uniform heat treatment of each of the pellets.

It should be noted that while the tube is identified as an annealing tube and while the process which occurs in that tube is an annealing process, one of its principal purposes in the present environment is the preheating of the pellets prior to their conduction into the carbon removal tube 22. The pellets, as they are emitted from the annealing tube 15, will be chilled iron pellets that are partially, if not completely, transformed into malleabie iron shot.

The valves 64, 67 are adjusted so that the gases emitted by the nozzle 17 maintain the temperature of the pellets in the annealing tube 15 at from about 900 F. to about 1200 F. The pellets are conveyed through the tube 15 by this flowing consumed fuel and air mixture in from about 9 to about 22 minutes.

The pellets are conveyed from the outlet end 18 of the annealing tube 15, immediately and while still hot, to the inlet end 21 of the carbon removal tube. The pellets are conveyed through the carbon removal tube 22 in from about 9 to about 22 minutes at a temperature of from about 1650 F. to the fusing point of the pellets which, as previously noted, will be about 2250 F.

When the pellets are conveyed through the carbon removal tube 22 at the speed and temperatures described, the carbon in the pellets tends to migrate to the surface of the pellets. As the hot oxygen-laden air passes over the pellets, the carbon is oxidized or burned off, thus converting the annealed shot to steel. With the pellets maintained in the tube for this period of time and under the described conditions, the carbon is lowered to less than 1.7% by Weight in each of the pellets and preferably is lowered below 1%. Adjustment of the valves 74, 77, and therefore the volume of air and fuel supplied, is used to control the temperature and rate of flow of the pellets and thus to obtain this desired end.

Since the apparatus and process described are continuous, periodic samplings of the finished product may be made to provide an excellent, practical application of statistical quality control. Samples periodically taken can be immediately subjected to suitable testing such as a centrifugal impact test to determine the physical properties of the product. If the product in any given sample is slightly varied from the desired product, adjustment may be made in the air and fuel supplies to improve the characteristics of the finished product.

Example As a specific example, the shot used will be capable of passing through a screen with a 0.078 inch opening. With shot of, for example, approximately .033 size the shot will be passed through an annealing tube of 2 feet in diameter and 18 feet in length at about 2 tons to about 3 tons per hour and preferably at about 3 tons per hour. To propel shot through the annealing tube at this rate, air at from about 150 to about 300 cubic feet per minute and preferably about 300 will be fed to the burners 17. Natural gas is mixed with the air to provide an adequate supply of consumed gases at the temperatures described. There are from about 8 to 11 parts of air to one of gas and preferably about 11. The pressure of the natural gas will be from about 6 ounces to about 8 ounces and preferably about 8 ounces, While the pressure of the air will be from 15 ounces to ounces and preferably about 20 ounces.

After the shot has passed through the annealing tube of this example, it will be conveyed to a carbon removal tube of about 2 feet in diameter and about 18 feet in length at about 2 tons to about 3 tons per hour and preferably at about 3. To propel shot through the carbon removal tube at this rate, air at from about 150 toabout 300 cubic feet per minute and preferably about 300 cubic feet per minute is fed to the burners 23. This air is mixed with natural gas in the same ratios as in the burners 17 to provide an adequate supply of oxygenladen, consumed gases at the temperatures described.

id The pressure of the natural gas Will be from about 6 ounces to about 8 ounces and preferably about 8 ounces, While the pressure of the air will be from 15 ounces to 20 ounces and preferably about 20 ounces.

Oxygen is added, if desired, at up to cubic feet a minute. Preferably about 10 parts oxygen are added to one of air. Thus, under the described preferred conditions 30 cubic feet per minute of oxygen are added to the mixture. This is especially important with larger size shot Where relatively large amounts of oxygen are needed.

While the invention has been described with a great deal of detail, it is believed that it essentially comprises a novel and improved steel shot manufacturing apparatus which includes a carbon-free tube formed of a material having less affinity for oxygen at from 1650 F. to the fusing point of steel pellets than does the carbon in the pellets, and means to direct shot to be converted from chilled iron to steel through the tube in from about 9 to 22 minutes While heating the shot in an oxygen laden atmosphere to from about 1650 F. to the fusing point of the shot. The invention also includes the process of making shot with such an apparatus.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to Without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. In a mechanism for manufacturing steel abrasives the combination of, a frame, an elongated tube rotatably supported on the frame and having inlet and outlet ends, drive means connected to the tube to rotate the tube relative to the frame, supply means positioned adjacent the inlet end to introduce shot to be treated into the tube, a nozzle at said inlet end for directing a continuous flow of hot gases into said tube for heating the shot and rapidly propelling it through said tube, said tube including a plurality of agitation bafiles therein, means connected to said nozzle to vary the temperature volume of air passing therethrough, said tube being a steel member capable of withstanding temperatures of at least 1650" F. Without deformation and having a carbon content less than 1.7%.

2. In combination, a frame, a first heat treatment tube rotatably mounted on the frame, the tube having an air inlet end and an outlet end, shot supply means adjacent the inlet end for directing a flow of iron shot into the first tube through the inlet end, at least one first tube burner nozzle positioned adjacent the inlet for directing a flow of hot gas into the first tube for heating and propelling the shot through said first tube, a second tube carried on the frame parallel to and below the first and having inlet and outlet ends, gravity transfer means for transferring the shot from the outlet of the first tube to the inlet of the second tube, said second tube including a stainless steel sleeve liner extending from one end to the other for supporting the shot during a steel shot forming operation, at least one second tube burner nozzle positioned adjacent the inlet of the second tube for directing a flow of hot oxygen-laden gas into the second tube to decarburize the shot and propel it through said second tube, power means coupled to each of the tubes for rotating the tubes, and baffle means secured to the interior of the tubes for agitating shot in the tubes when the tubes are rotated.

3. The device of claim 2 wherein the second tube battles are decarburized ferrous members secured to said sleeve.

4. The device of claim 2 wherein a first control means is connected to each such first tube burner to maintain the temperature of the shot in the tube between about 900 F. and about 1200 F. and, a second control means References Cited in the file of this patent UNITED STATES PATENTS Kalling May 21, 1940 Hardesty June 23, 1942 3 Blair et a1. Mar. 2, 1954 Franck et a1. July 16, 1957 Chen Dec. 9, 1958 Cline July 21, 1959 Greene Nov. 17, 1959 MacDonald Feb. 23, 1960 Johnson Mar. 29, 1960 Rusciano et a1. Apr. 26, 1960

Claims

1. IN A MECHANISM FOR MANUFACTURING STEEL ABRASIVES THE COMBINATION OF, A FRAME, AN ELONGATED TUBE ROTATABLY SUPPORTED ON THE FRAME AND HAVING INLET AND OUTLET ENDS, DRIVE MEANS CONNECTED TO THE TUBE TO ROTATE THE TUBE RELATIVE TO THE FRAME, SUPPLY MEANS POSITIONED ADJACENT THE INLET END TO INTRODUCE SHOT TO BE TREATED INTO THE TUBE, A NOZZLE AT SAID INLET END FOR DIRECTING A CONTINUOUS FLOW OF HOT GASES INTO SAID TUBE FOR HEATING THE SHOT AND RAPIDLY PROPELLING IT THROUGH SAID TUBE, SAID TUBE INCLUDING A PLURALITY OF AGIATION BAFFLES THEREIN, MEANS CONNECTED TO SAID NOZZLE TO VARY THE TEMPERATURE VOLUME OF