US2828954A - Muffle furnace for heating billets to be forged or extruded - Google Patents

Description

April 1, 1958 w. M. DICKSON 2,828,954

MUFFLE FURNACE FOR HEATING BILLETS TO BE FORGED OR EXTRUDED 2 Sheets-Sheet 1 Filed March 8, 1955 INVENTOR William M. Dickson M Apnl 1, 1958 w. M. DICKSON 2,823,954 MUFFLE FURNACE FOR HEATING BILLETS TO BE FORGED 0R EXTRUDED Filed March 8, 1955 2 Sheets-Sheet 2 PIC-3.3 22

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A ORNEY3 United States Patent MUFFLE FURNACE FOR HEATING BILLETS .TO BE FORGED OR EXTRUDED William M. Dickson, Houston, Tex.

Application March 8, 1955, Serial No. 492,887

3 Claims. (Cl. 263-6) My invention relates to improvements in methods of heating billets of various shapes and sizes, which are to be subjected to hot forging or extruding operations in dies, and to an improved apparatus including an improved muflle furnace for use in carrying out the improvements in the method of heating. More particularly the invention relates to the heating of steel billets in such a manner as to improve the forging or extruding operations, the shapes produced, and extend the life of .the dies used therefor.

Present methods of heating billets .or bars for forging result in the formation of a very hard tenacious oxide scale on the surfaces of the bars or billets heated so that they either must be descaled before they are sent to :the forming dies or the operator must contend with a relatively short die life, resulting from the erosion of the dies by the metal oxide. Furthermore, the forging of billets or bars covered with oxide results in :the production of defective shapes, or shapes in which oxide scale is embedded and are not commercially acceptable for most purposes.

One method of descaling highly heated slugs cut from metal bars prior to sending the slugs .to the forming dies is disclosed in the recently issued United States Patent No. 2,698,951. However, regardless of the effectiveness of scale removal prior to forming the billets orslugs cut therefrom into shapes in the dies, there is a loss of approximately 3% in steel because of the scale formation during the heating of the billets or bars to the forging temperature. Since the steels and other metals used in forging operations are relatively expensive, the loss involved is considerable. I

The furnaces used for heating billets and bars ,tobe forge have also caused trouble because it has been necessary to move the billets or bars through the furnace, which at the temperatures involved, has caused erosion o h u na h a h, 0 that frequent long shut downs have been necessary in order to rebuil parts of the furna e, part cu ar y the hearth.

The primary object of my invention is to provide an improved method of heating billets to be forged or extruded in such a manner as to avoid the difiiculties referred to above Another object of my invention is to provide an improved apparatus including an improved furnace for effectively heating billets to be forged which will avoid the foregoing difficulties. v

In accordance with the invention theimproved method comprises the heating of metal billets to be forged in a closed muflle of a mufile furnace in the presence of a neutral atmosphere, which will prevent the formation of scale, vPreventing contact of the heated billets ith each other, and removing the billets from the mufile and subjecting them-to a forging or extruding operation. The billets are heated on a hearth in the muflie of a furnace, the'hearth comprising a relatively thin layer of refractory brick which .are merely laid loosely on a vsuhhearth and,

2,828,954 Patented Apr. 1, 1958 therefore, readily removable for quick repairs or replacement of a part or all of the brick.

The improved billet heating furnace of my invention comprises a motile surrounded by a heating chamber or other heating means, the :mufile preferably being formed of relatively thin refractory material and including a subhearth covered by a layer of loosely laid refractory brick which are arranged to prevent contact of one billet with another. Means is provided for generating and delivering a neutral, inert, non-oxidizing gas to the interior of the mufile for preventing oxide formation on the billets being heated stherein.

Where the muffle furnace is to be used for heating steel bars to 'be cut into slugs which are formed into the desired shapes in dies, the readily removable hearth in the mutile is built up of longitudinally-extending spacers, which extend above the removable hearth brick to preventcngagernent of adjacent bars with each other during the heating operation.

It was discovered that where steel billets, particularly long steel bars, are heated in the muffle in a neutral non oxidizing atmosphere, the bars will we'ld together at the forging temperature it they are allowed to contact each ot er. The upwardly projecting separators of refraetory brick solve this problem and avoid any difficulty which would prevent removal of the heated *bars from the mufiie ;as desired.

Another feature of .my invention involves the use of means in .the dis-charge end of the furnace for guiding the bars inisnccess-ion to a common relatively small outlet opening. 111 the heating of steel bars -to be cut into slugs for forming metal articles, 'it is necessary to heat a nuns-her of steel bars .in a furnace 'in order to have sufficient hot bar stock to maintain a continuous forging operation. Therefore, as soon as one bar is removed from the furnace, a cold that is inserted in its place. The hottest bar is always used first and there is a definite sequence of removal and replacement of the bars in the furnace. Mysimproved'funnace, therefore, includes means located directly above the hearth for guiding the highly heated bars to .a single .zrelatiuely small outlet where they are picked top by :the feeding means :of the forging machine, for example a machine of the type disclosed in the above-mentioned rpatent.

IIlhe improved method and heating apparatus of the present invention includes other features and advantages, which are described more in detail hereinafter in connection with an'illustrative embodiment, the heating apparatus .of which is shown in the accompanying drawings 1B i ,pattof this application.

In the drawings:

Fig. l is a broken horizontal sectional view showing a furnace, particularly arranged for heating metal bars;

Fig. 2 is a broken vertical sectional view taken on the line 2--I2.of Fig. 1;

Fig. 3 is a fragmentary vertical sectional view taken on the line 3--3 of Fig. .1, and

fig. 4 is a diagrammatic view, partly in section and with parts broken :away, illustrating means for supplying a neutral non-oxidizing gas to the mufile of the furnace iflustra-tedin Figs. 1 to "5..

'Ihe improved apparatus of the present invention is illustrated in connection with the heating of long steel bars to be cut into slugs for formation into the desired shapes in dies. Referring to Figs. 1 to 3 of the drawlngs, the heating apparatus comprises a furnace 10 supported in any desirable manner, for example, above the floor on steel supports and across *beams, not shown. The furnace proper includes an outer steel casing '12 lined at the top, bottom, ends and sides with high temperature fire bgiok .14 held together by m lllidllp with fire clay mortar in the usual manner. The finance illustmed is particularly adapted for heating long bars of from about to 1 inches in diameter or larger and 20 feet long, for example. The furnace includes a muifle 16 extending lengthwise from end to end of the furnace for receiving and heating the bars. The muffle 16 is made up of relatively thin high temperature refractory walls, for example of carborundum, and is spaced from the inside fire brick walls of the furnace proper. The mufi lc includes a fixed hearth 18, sides 20 and a cover 22 cemented together with refractory cement to form a hermetically closed chamber, except for portions of the ends which include openings extending through the fire brick and steel end walls of the furnace 10. Throughout the length of the furnace, the muffle 16 is supported on transverselyextending, substantially-spaced apart walls 24 of fire brick, which are illustrated as resting on the bottom wall of the furnace and extending to the inside of the fire brick side walls of the furnace 10, but they need not extend entirely to the side walls but merely under the fixed hearth 18 of the mutile 16.

The mume is advantageously heated by rows of burners 26. While only single burners are shown in Figs. 1 and 2, burners 26 are provided on opposite sides of the furnace projecting into the space between the walls 24 supporting the muffle. Each burner 26 may include a gas or oil delivery pipe 28, an air admission control 30 and a refractory metal 'sleeve 32 extending through the tire brick side wall into the spaces on opposite sides of the supporting walls 24. It is to be understood, of course, that a fan may be used for delivering air under pressure to the burners through the control members 30.

The flames from the burners 26 project under and around the mufile so that it is heated on all sides and as uniformly as possible from end to end. The furnace gases are discharged from the furnace chamber surrounding the muffie through openings, not shown, provided in the roof of the furnace.

Where the furnace is used for heating 20 foot metal bars, it is made considerably longer, as for example, from 6 to 8 feet longer, so that the discharge end of the muffle is provided with means for guiding the bars to a central, relatively small outlet from the muffle. Referringparticularly to Figs. 1 and 2, the structure inside the mufile shell toward the charging end comprises a longitudinal row of fire brick 34 in each of the lower corners of the mufile which extend considerably above a readily removable hearth therebetween comprising rows 36 of thin flat refractory brick laid flatwise on the hearth 18 and alternating with rows 38 of refractory brick placed edgewise sothat they serve as spacers to prevent engagement of adjacent metal bars 40 with each other. The alternating rows of loosely placed refractory brick 36 and 38, as shown in Fig. 1, terminate toward the forward end of the furnace somewhat short of the forward ends of the bars 40 and from that point on, the hearth of the muffie is comprised of loosely placed refractory brick 42 of the same thickness as the rows of refractory brick 36, all of which are merely laid on the fixed hearth 18.

Forward of the termination point of the rows of refractory brick 36 and 38, the bars 40 extend into the mouth of a V-shaped guiding means comprised of converging rows 44 of fire brick cemented together and re spectively forming continuations of the side fire brick 34 inside the muflle. At the forward end of the furnace, as shown in Fig. l, the rows 44 comprising the guiding means, extend sulficiently .above the refractory brick 42 to guide the billets or bars 40 through an opening 50 into a narrow outlet passageway 46 of refractory material extending outside the furnace. This passageway is a rectangular-shaped tube through which the bars are moved readily to a pair of feed rollers 48 for feeding the bars to a forging machine, for example of the type disclosed in the abovementioned United States patent.

While the guiding means 44 is shown as a converging row of tire brick placed over the loosely laid refractory brick 42, the respective sides may be composed of readily removable angular-shaped units with their backs extending respectively against the side walls 20 of the mufile.

Fig. 3 of the drawings shows the structure at an intermediate point along the guiding means 44 and the rectangular shaped opening 50 at the outlet of the muffle. In other respects, the forward or outlet end of the muffle is closed off by a fire brick end wall 52 in the end of the mulile as shown in Fig. l. The end of the muffle 16 may abut the fire brick at the end of the furnace 10 if the end of the muffie extends only to that point. At the opposite end of the mulfle, the billets or bars are introduced through a narrow horizontal opening, the floor of which is shown at 54 in Fig. 1, which is even with and may be comprised of the thin refractory brick loosely laid in the bottom of the mufile. The opening may have a height equal to that of the fire brick 34 so that fire brick 56 may be loosely placed in the opening to exclude the admission of air, one brick being removed during the insertion of a cold billet or bar and when a push bar is inserted to push a hot bar forward to the rolls 48.

The arrangement for supplying the neutral or nonoxidizing gas to the rnufile is shown diagrammatically in Fig. 4. In this view, the rnuflle 16 is shown in section but only diagrammatically without any of the interior structure. The inert non-oxidizing gas may be made in any desired known manner, as for example by an apparatus comprising a generator 58 having a furnace chamber 60 surrounding a reaction chamber 62 filled with catalytic or contact material 64. The reaction chamber 62 and its contents are heated by means of a plurality of burners 66, which discharge into the chamber 60, the spent combustion gases being discharged through outlets 68 at the top of the combustion chamber. Natural gas is supplied under pressure to the reaction chamber 62 through a valved pipe 70 along with air under pressure supplied through a pipe 72. These gases are introduced in the proportion of 1 part natural gas to 3 parts air by volume and reacted or burned in the chamber 62 at a temperature of 1850 F. to produce an inert, neutral non-oxidizing gas containing little or no free oxygen for use in the muffle 16.- The hot gas as it leaves the reaction chamber 62 through the pipe 74 is conducted through a cooler 76, in which the gas is cooled to room temperature or below and then conducted through a pipe 78 into a separator 80 for the separation of any condensable materials, such as water, which is withdrawn through a valved drip line. The separated gas leaving the separator 80 is conducted through a pipe 84 and introduced into the top of the mufile 16 through one or more inlet connections preferably located toward the longitudinal center portion of the mufi'le.

Suflicient neutral gas is produced in the generator 58 and introduced into the muflle to provide a neutral nonoxidizing atmosphere for billets in the muflie and to insure a constant low pressure flow of gas through the opening 50 and between the fire brick 56 at the rear of the muflle to prevent the entrance of air.

In operating the improved apparatus as described above to carry out the improved process, as for example the heating of long round steel bars for the production of nut blanks, the furnace is fired by the numerous burners 26 located along the sides thereof to provide a temperature of from about 2300 F. to about 2360" F. in the muflle. The muflle is loaded with a suflicient number of bars to provide for a continuous operation. In the present instance, the bars as illustrated in Figs. 1 to 3 are approximately 1% inches in diameter and 20 feet long. For bars of larger size, they should be heated to a temperature of approximately 2200" F. During the heating operation the generator 58 is operated to produce the neutral gas, so that a neutral non-oxidizing atmosphere is maintained in the muflle. v Whet i bars are at the desired temperature, the oporator at the rear end of the furnace pulls out one of the loose bricks 56 and pushes the first bar with a steel push rod 86 toward the front end of the furnace. As the bar moves forward from the initial position shown in Fig. 1, its forward end comes into engagement with one of the converging guides 44 so that the bar is directed toward the outlet opening 50. The bar is pushed until its forward end is engaged by the feed rollers 48, after which the push rod is withdrawn. In this operation the division or separator partitions 38 prevent the bars from engaging each other.

It has been discovered that as the bars 40 are pushed forward in the muiile of the furnace until they engage one of the guides 44, they will then bend slightly because of their high temperature so that they follow more or less closely along the guide until they enter the outlet opening 50. After the trailing end of the bar 40 being drawn out of the muflle by the guide rolls 48 is beyond the ends of the other bars in the rnuiiie, or nearly so, a cold bar, as for example the .bar 40', is inserted in its place. As the trailing end of the bar being withdrawn from the furnace reaches approximately the outlet 50, the next hot bar is pushed forward until it engages the trailing end and then is continued to be pushed until its forward end enters the rolls 48. After a cold bar, such as the bar 40' is inserted in place in the muflle, the adjacent brick to the left, or below in Fig. 1 is moved over in back of the bar 40' so that the operator will be ready to push out the adjacent hot bar with the push rod 86. Fig. 1 shows the push bar 86 in place for pushing the next bar 40, but it would not normally be inserted until the bar being fed is nearly out of the muffle.

The hot billets or bars 40 picked up in succession by the rollers 48 may be cut into slugs and the slugs formed into nut blanks in dies in the manner described in the above-mentioned United States patent, or in a similar manner.

If the billets or bars to be introduced into the mufiie 16 carry a small amount of scale, which they sometimes do after rolling, they may be preliminarily descaled in a conventional type acid pickling bath immediately before they are introduced into the mufile. The improved apparatus and method, therefore, produces billets at forging temperatures which are entirely free of scale and which may be sent directly to the forming dies, or cut into slugs which may be sent directly to forming dies, as for example, the nut blank-forming dies of the type disclosed in the above-mentioned United States patent. Consequently, any equipment usually employed for the descaling of slugs or billets after heating to a forging temperature and prior to being pressed in dies is entirely unnecessary.

The rows 38 of separating or dividing brick provide partitions which are particularly advantageous because they prevent engagement between the hot metal bars and consequent sticking or welding of these bars in the furnace. Rolled bars of 20 feet in length, for example, often include certain stresses or strains which are relieved when the bars are heated and would therefore cause the bars to roll over or bend to some extent. The separators or partitions are adapted to prevent any contact between bars either through their own action or through handling. The possible sticking of the bars together when heated to their forging temperature is particularly serious where they are heated, in accordance with the invention, in the presence of a neutral atmosphere so that they do not acquire a coating of metal oxide. The means for preventing contact between the bars and the use of the neutral atmosphere, therefore, cooperate in the heating operation to provide highly heated forgeable billets which are entirely or substantially free of scale. Furthermore, the heating of the billets to produce scale-free forgeable billets cures certain defects, such as cracks, which may have been caused in the rolling operations and which would otherwise be carried over into the forged or ex- 5 truded shapes. Some of these defects are ,mere surface cracks, but the improved process has the effect of welding these cracks so that they do not appear in the forged or extruded shapes.

The refractory brick used in the readily removable hearth and partitions in the muflie 16 are preferably so-called split" silicon carbide brick or Carborundum brick, about 1% inches thick. Silicon carbide refractories of this type have from 4 to 5 times the heat conductivity of ordinary high-temperature clay fire brick and are preferred, but other substantially equivalent high-temperature refractory brick may be used. The muffle is preferably made of silicon carbide refractory material or its equivalent. Furthermore, Carborundum" or equivalent refractory brick may be used to provide the guiding means 44.

The high-temperature refractory brick 42 and those forming the rows 36 become worn and eroded through constant movement of the billets or bars 40 thereover. In fact, after use for a considerable length of time, they may have worn channels through half their thickness. Therefore, at some time when the furnace is down, such worn brick are readily removed and replaced by opening up the one or both ends of the muflle.

While the improved process and apparatus has been illustrated in connection with the particular embodiment shown in the drawings in which the billets are long round bars, it is to be understood that billets of other shapes may be heated in the furnace and the spacers or partitions 38 arranged accordingly so that no contact between billets is permitted. Furthermore, while the improved mulfle furnace of the present invention is particularly useful in connection with a controlled neutral atmosphere to prevent scale formation, it is also useful where a neutral atmosphere is not employed and where scale formation is permitted. If the furnace is continuously used for the latter purpose, the readily removable hearth need not include the partitions or separators 38, although they may be present, since billets coated with oxide have no tendency to stick or weld together in the furnace. In any case, the readily removable hearth has the advantage of preventing wear of the subhearth 18.

It is to be furthermore understood that while the furnace may be heated to advantage by burners using gas or oil, the furnace muffle may be heated by other sources of heat, as for example by providing suitable well-known types of electrical heaters associated with the mufiie walls, which are made up of high-temperature refractories, such as silicon carbide or its equivalent, having high heat conductivities.

I claim:

1. An apparatus for heating metal billets to be subjected to hot forging or extruding operations in dies, comprising a furnace including a heating chamber in which the billets are heated to a forging temperature, a hearth of refractory brick in said heating chamber, means for supporting said hearth, said refractory brick being laid loosely on said supporting means so that the brick of the hearth are readily replaceable, said hearth being adapted to receive and support a plurality of the billets side-byside, said heating chamber having inlet and outlet ends respectively having openings for inserting and discharging billets, the billet outlet opening being located at the level of the hearth intermediate the sides of the hearth, and means located in the outlet end portion of the heating chamber including a V-shaped wall structure mounted on the hearth and converging therealong toward and registering with the billet outlet opening for guiding heated billets on the hearth toward the billet outlet opening.

2. An apparatus as claimed in claim 1, in which said wall structure comprises separate readily removable walls of refractory material on the hearth and converging toward the billet outlet opening.

3. An apparatus for heating metal bars to be subjected to hot forging operations, comprising a furnace including a substantially closed elongated muffle of high temperature refractory material in which the metal bars are heated, means in the furnace for heating the muflle and metal bars, said mutfie having inlet and outlet ends for bars and being provided with a fixed hearth, a readily removable hearth in the muflle resting on and covering the fixed hearth on which the metal bars rest side-by-side, said readily removable hearth comprising a plurality of rows of relatively thin high temperature refractory brick of high heat conductivity extending lengthwise of the muffle from the inlet end to a point substantially spaced from the outlet end of the mufile, the brick of said rows being laid loosely for ready removal from the muflle, rows of refractory brick partitions alternating with the rows of brick of the readily removable hearth and extending above the brick of said hearth rows, thereby providing open-topped channels through which the metal bars heated in the muffie can be respectively moved without contacting the metal bar in one channel with the metal bars in adjacent channels, said inlet and outlet ends of the muffle being provided with openings for respectively inserting and discharging metal bars, the outlet opening being located intermediate the sides of the muttie, and a V-shaped wall structure extending above the readily removable hearth in the outlet end portion of the mufile and, converging therealong from said point toward and registering with the metal bar outlet opening for guiding heated metal bars on the hearth in said channels to the metal bar outlet opening.

References Cited in the tile of this patent UNITED STATES PATENTS 961,462 Ridd June 14, 1910 1,362,368 Talley Dec. 14, 1920 1,630,162, Boucek et a1 May 24, 1927 1,693,370 Colby Nov. 27, 1928 1,976,092 Quarnstrom Oct. 9, 1934 FOREIGN PATENTS 633,987 Germany July 30, 1936

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