US3861659A

US3861659A - Sinter pallet apparatus

Info

Publication number: US3861659A
Application number: US301303A
Authority: US
Inventors: Sydney T Evenstad
Original assignee: Certified Alloy Products Inc
Current assignee: Certified Alloy Products Inc
Priority date: 1972-10-27
Filing date: 1972-10-27
Publication date: 1975-01-21
Anticipated expiration: 1992-01-21

Abstract

Sinter pallet apparatus including a frame supporting a plurality of coextensive grate bars formed with relatively thick structural support bodies which are spaced apart to define air passages therebetween. Relatively thin heat shields are arranged over the respective bars and spacers are provided for spacing such shields from such bars to form a heat insulator space between such bodies and shields. Insulating air is disposed in the insulator space and retainer means is included for retaining the shields on the bars.

Description

United States Patent [191 [111 3,861,659

Evenstad Jan. 21, 1975 SINTER PALLET APPARATUS 3,548,763 12/1970 Farber 266/21 x [75] Inventor: Sydney T. Evenstad El Monte 3,617,040 11/1971 Relnfield et al. 266/21 C lif FOREIGN PATENTS OR APPLICATIONS [73] Assigneez Certified Auoy Products, Inc. g 347,461 4/1931 Great Britain 266/21 UX B h, l'f. eac Primary Examiner-Gerald A. Dost [22] Filed: Oct 27, 1972 Assistant Examiner-Paul A. Bell Attorney, Agent, or Firm-Fulwider, Patton, Rieber, [21] Appl. No.. 301,303 Lee & Utecht [52] US. Cl 266/21, 110/40 R, 432/241, 57 ABSTRACT 432/245 432/239 Sinter pallet apparatus including a frame supporting a y 53 plurality of coextensive grate bars formed with rela- 0 tively thick structural support bodies which are spaced apart to define air passages therebetween. Relatively [56] R f n Ct d thin heat shields are arranged over the respective bars e are ces l e and spacers are provided for spacing such shields from UNITED STATES PATENTS such bars to form a heat insulator space between such 311,633 2/1885 bodies and shields. Insulating air is disposed in the in- 1,889,052 11/1932 sulator space and retainer means is included for re- ?322682 13323 aining the shields on the bars, 3:420:512 1/1969 9 Claims, 15 Drawing Figures Patented Jan. 21, 1975 3 Sheets-Sheet 2 FIG.

Patented Jan. 21, 1975 3 Sheets-Sheet :5

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FIGJI SINTER PALLET APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The sinter pallet apparatus of the present invention relates to a pallet for conveying metallic pellets through a heat zone for heating thereof to relatively high temperatures.

2. Description of the Prior Art Numerous sinter pallets have been proposed which include coextensive grate bars spaced apart to define air passages therebetween. Further, covers have been proposed for such grate bars in attempt to protect such grate bars against wear. However, such prior art devices suffer the shortcomings that the grate bars are necessarily relatively thick and are exposed to the heat of the pellets carried thereon thus resulting in a high temperature differential throughout the thickness of such grate bars which results in excessive thermal growth on one side thereof thus causing warpage and thermal fatigue.

SUMMARY OF THE INVENTION The sinter pallet of the present invention is characterized by a plurality of relatively thick coextensive grate bars having relatively thin heat shields disposed thereover and spaced therefrom to form an insulator space having insulation disposed therein to insulate the thick bars from the high temperature of the relatively thin heat shields. Consequently, the heat shields are heated relatively rapidly to a substantially uniform temperature thus avoiding excessive temperature differential throughout the thickness thereof and the consequence warping due to non-uniform thermal growth.

The objects and advantages of the present invention will become apparent from a consideration of the following detailed description when taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagramatic view of a pallet conveyor employing a sinter pallet apparatus embodying the present invention;

FIG. 2 is a top view, in enlarged scale, of a sinter pallet apparatus included in the conveyor shown in FIG.

FIG. 3 is a vertical sectional view, in enlarged scale, taken along the line 3-3 of FIG. 2;

FIG. 4 is a vertical sectional view, in enlarged scale, taken along the line 4-4 of FIG. 2;

FIG. 5 is a vertical sectional view, in enlarged scale, taken along the line 5-5 of, FIG. 2;

FIG. 6 is a top view of a second embodiment of the sinter pallet apparatus of the present invention;

FIG. 7 is a vertical sectional view, in enlarged scale, taken along the line 7-7 of FIG. 6;

FIGS. 8 and 9 are vertical sectional views, in enlarged scale, taken along the respective lines 8-8 and 99 of FIG. 6;

FIG. 10 is a vertical sectional view taken through a third embodiment of the sinter pallet apparatus of the present invention;

FIG. 11 is a horizontal sectional view taken along the line 11-11 of FIG. 10;

FIG. 12 is a vertical sectional view, in enlarged scale, taken along the line 12-l2 of FIG. 11;

FIG. 13 is a vertical sectional view taken through a fourth embodiment of the sinter pallet apparatus of the present invention; and

FIGS. 14 and 15 are vertical sectional views, in enlarged scale, taken along the line 14l4 of FIG. 13 with FIG. 15 depicting a heat shield unlatched for removal thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 2, 3 and 4, the sinter pallet apparatus, generally designated 20, of the present invention includes a rectangularly shaped pallet frame 21 having a plurality of elongated grate bars disposed longitudinally therein in parallel arrangement. Referring to FIG. 3, the grate bars 23 include a relatively thick body 25 which has upwardly projecting bosses 27 formed therein, such bosses including longitudinally extending open ended dovetail grooves 29 (FIG. 4). Relatively thin slat-like heat shields 31 are spaced above the grate bar bodies 25 to form air spaces 33 between such bodies and the bodies of the grates 25. The heat shields 31 include downwardly projecting dovetail tongues 35 which slide longitudinally into the respective grooves 29 for securing the heat shields 31 in place. The grate bar bodies 25 are themselves spaced apart and the respective heat shields 31 are formed in their opposite longitudinal edges with cutbacks which are disposed in confrontation with one another to form vertically extending through flow passages 37. Thus, the slats 23 combine to form a permeable platform for receipt of pellets 41 to be sintered, and such pellets are passed beneath a high temperature inverted furnace 43 which rapidly raises the temperature of such pellets 41 thus resulting in rapidly raising the temperature of the heat shields 31. However, the relatively massive structural bodies 25 of the respective grate'bars 23 are insulated from the high temperature heat shield 31 by means of the insulative air in the air gaps 33 between the body of such grate bar bodies 25 and the heat shields 31 thus enabling the relatively massive grate bar bodies 25 to remain at a relatively uniform temperature to thus prevent excessive thermal growth on the top side thereof which may result in warpage and even thermal fatigue.

In the processing of certain ore, the ore is pulverized and subsequently formed into individual balls or pellets 41. The pellets are subsequently charged into gas furnace and cooperate together to form air passages therearound to facilitate heating thereof. In order to hold the pellets 41 in their pelletized configuration, it is necessary to heat them to a high temperature. Thus, after formation thereof, the pellets 41 are fed from a hopper 44 onto the bed formed by air permeable pallets 20 car ried on a conveyor, generally designated 51, to be passed beneath an inverted furnace 43 which heats such pellets to temperatures in the neighborhood of 2,400F. Consequently, the grate bars forming the air permeable pallets 20 are subjected to extremely high temperatures on their top sides thus frequently resulting in such bars becoming warped due to non-uniform thermal growth. Consequently, it is desirable to provide an air permeable pallet 20 which has an extremely tough abrasion resistant bed for receipt of the abrasive pellets 41 and which provides for long life of such bars without warpage or thermal fatigue. I

The pallets 20 include rectangular frames 21 which are carried on their opposite sides from

wheels

55 and 57 which travel in

respective conveyor tracks

59 and 61. The pallet frames 21 are formed at their front and rear extremities with

respective rails

63 and 65 which receive the opposite ends of the respective grate bars 23, the rail 65 being removable for selective removal of the grate bars 23. The opposite ends of the grate bar bodies 25 are bifurcated to form downwardly and outwardly projecting

fingers

69 and 71 for receipt under the

respective rails

65 and 63 to hold such grate bars in place.

As employed herein the term grate bar" refers to a rather heavy bodied bar which is conventionally mounted on a pallet to receive the pellets 41 directly thereon for heating thereof. The grate bars 23 are formed on their opposite sides with spacers 67 which project from the grate bar bodies 25 approximately one-eighth of an inch for abutting against one another to cooperate in forming air passages 68 (FIG. between such spacers 67 that are approximately onefourth of an inch in width. The grate bar body is approximately 1 inch in width and approximately 1% inches in vertical thickness thereby providing a relatively massive structure. In contrast, the heat shield 31 is approximately 0.20 inches thick and 1 inch wide.

The bosses 27 project upwardly from the top surface of the grate bar bodies 25 approximately one-fourth of an inch and are themselves approximately threefourths of an inch long in the longitudinal direction of the grate bar 23 and are spaced apart approximately 2 inches thus providing air spaces 33 having a dimension of approximately one-fourth inch thick by 2 inches in length.

The heat shields 31 may be made of various exotic or treated metals that will withstand high temperatures and those shown in the preferred embodiment are made of an alloy designated 2512 which includes 25 percent chrome and 12 percent nickel. Further, in applications where sulphur fumes are present, it has been found that such shields 31 perform particularly well when constructed of 2512 alloy to provide a tough core and then plating such cores with 98 chrome to a thickness of approximately 5 mills.

Referring to FIG. 4, the heat shields 31 are formed from a generally flat elongated slat 73 with the respective tongues 35 projecting downwardly therefrom, such tongues being slightly longer in vertical length than the depth of the grooves 29 whereby such tongues will act to support theheat shields 31 from the bottom of the respective grooves 29. It will be appreciated that each tongue 35 is approximately three-fourths of an inch in horizontal length with such tongues being spaced apart approximately 2 inches thus aligning each tongue in its respective groove 29.

Referring to FIGS. 2 and 5, the heat shield slats 73 are formed in their opposite sides with spaced apart cutbacks 45 which align together to form the respective vertical air passages 37, such air passages being approximately 2 inches in length and one-fourth of an inch in width. Referring particularly to FIG. 5, the cutbacks 45 are formed with a downwardly and inwardly slanted vertical surface thus causing the cutbacks 45 of adjacent slats 73 to cooperate together in forming a vertically extending through air passage 37 which tapers downwardly and outwardly on its opposite sides thus providing a configuration whereby any pellets 41 passing into the top end of such passage falling downwardly through such passage to pass freely from the bottom thereof.

Referring to FIG. 1, when it is desirable to heat the pellets 41, the individual pallets 20 are placed in the

tracks

59 and 61 forming the conveyor 51, and such conveyor started to commence travel of such pallets horizontally from left to right as viewed in FIG. 1. The inverted furnace 43 is started to develop a high temperature gas to be drawn downwardly through the pellets 41 and permeable pallets 20 by means of a wind box 79.

A rapper may be provided for rapping each pallet 20 as it passes thereby to thus knock any pellets 41 remaining thereon loose before recommencing travel to the inverted furnace 43. In certain instances it is desirable to provide a hopper 87 of sintered pellets 89 ahead of the raw pellet hopper 44 for distribution of such pellets 89 onto the pallets 20 to form a hearth layer of protective pellets thereover to protect the heat shields 31 from the excessively high temperature to which the unsintered pellets 41 are to be heated. However, for most present day applications, with the pallet apparatus of the present invention, there is no necessity of providing a hearth layer of protective pellets 89. However, for the purpose of this description, it will be assumed that such hearth layer is distributed on the pallets 20.

The pallets 20 are caused to move along the conveyor tracks 59 and 61 by means of a prime mover, such as a motor driven oversized sprocket which sequentially engages the respective pallets 20 and urges them along such tracks. As the pallets 20 pass under the hearth hopper 87, the sintered pellets 89 will be distributed over the bed formed by the composite heat shields 31 to form a hearth layer approximately 3 to 5 inches thick.

The pallets 20 having the hearth layer of pellets 89 are then passed beneath the hopper 44 of raw pellets 41 to have such raw pellets distributed over the hearth layer. The pellets 41 are then conveyed beneath the inverted furnace 43 and the wind box 79 will create a partial vacuum beneath such pallets 20 to cause the heated gases from such furnace to flow downwardly through the passages formed between the pellets 41 and 89 to flow through the passages 37 formed between the heat shields 31 and then downwardly through the passages 68 formed between the respective grate bar bodies 25, it being appreciated that a substantial amount of the heat of the gases from the furnace 43 is removed by the pellets 41 and 89 and the heat shields 31 before such gases contact the grate bar bodies 25. As the pallets 20 progress under the furnace 43, the pellets 41 and 89 will become heated and the heat shields 31 may become heated to temperatures in the order of 2,000F.

However the relatively, stagnant air which is isolated within the insulator spaces 33 (FIG. 3) formed between the heat shield slats 73 and the grate bodies 25 provides a relatively low rate of heat transfer between the slats 73 and grate bars 23 thus forming an excellent heat insulator which results in the temperature of such grate bar bodies 25 being approximately 500F. to 700F. lower than the temperature of the heat shields 31. Consequently, the grate bars 23 are subjected to relatively constant temperatures throughout their 2 inch vertical thicknesses thus avoiding excessive differential thermal growth and consequent warpage and thermal fatigue from repeated heating. In contrast, the relatively thin heat shields 31 will be heated relatively rapidly and uniformly thus preventing warpage thereof, it being appreciated that the tongues 35 (FIG. 4) are free to 'slide longitudinally within the grooves 29 thus accommodating longitudinal thermal growth of such heat shields 31 relative to the grate bars 23. It should be noted that the relatively rapid heating of the heat shields 31 to high temperatures greatly facilitates heating of the pellets 41 since the heat from such shields is reflected back toward such pellets.

As the respective pallets pass from beneath the furnace 43, such pallets will be tipped to an inverted position as they pass thus exposing the pellets 41 and 89 to cooling air and dumping such pellets onto the delivery conveyor 83. As the pallets 20 are conveyed back to the starting point in their inverted positions, such pallets will cool substantially before they again reach the furnace 43. As the pallets 20 pass in front of the rapper 85, each pallet will be rapped one or more times to jar the respective heat shields 31 to free any pellets 89 or 41 that may be stuck thereto or which may have wedged therebetween. It has been found that the bosses 27 carrying the shield tongues 35 provide adequate support for such shields against the force of the rapper 85.

If at any time the heat shields 73 become excessively worn or warped, such heat shields may conveniently be replaced by sliding such shields longitudinally with respect to the grate bars to move the respective tongues 35 clear of the grooves 29 (FIG. 4) to free such heat shield 31 from its grate bar 23. Such heat shield 31 may then be replaced by a repaired or new heat shield 31 by merely sliding such heat shield into position. It will be appreciated that the grate bars 23 may weigh between 5 and 9 pounds while the heat shields 31 weigh approximately only 1% pounds thus resulting in substantial metal saving each time replacement is required and rendering the taskof replacement much easier. In practice, the sintered pallet apparatus of the present invention has proven to provide a cost savings of between 75 percent and 400 percent per ton of sintered ore.

Referring to FIG. 6, the sintered pallets, generally designated 91,shown therein are generally similar to the pallets 20 shown in FIG. 2 except that the opposite ends of the grate bars, generally designated 93, are formed with vertically facing upwardly and outwardly opening cavities 94 (FIG. 7) which receive downwardly projecting fingers 95 formed integrally with respective heat shields, generally designated 97. Further, the heat shields 97 are formed with downwardly projecting supports 99 which are disposed intermediate the respective tongues 101 (FIG. 8). It will be noted that the heat shields 97 span only approximately one-half the total length of the respective grate bars 93, the proximate free ends of such grate bars 97 being free floating and formed with downwardly and inwardly inclined ends 103 which cause any pellets 41 lodged therebetween to be urged upwardly thereout of as the respective shields 97 are heated and grow in length resulting in the proximate ends thereof being driven closer together.

Thus, operation of the sinter pallet apparatus shown in FIGS. 6 through 9 is substantially the same as that described hereinabove, and air trapped in the insulator space 105 formed between the underside of the heat shields 97 and the top of the body of the grate bars 93 will serve to thermally insulate the grate bars 93 from the heat of the respective heat shields. Further, the supports 99 will provide additional support to the shields 97 to resist the shock introduced by the rapper as such shields 97 are rapped.

The sinter pallet apparatus, generally designated 109, shown in FIGS. 10 through 12, is similar to that described hereinbove except that the grate bar, generally designated 111, is formed at its opposite ends with upwardly projecting ears 113 and 115 which are formed with inwardly opening

grooves

117 and 119, respectively. The grate bar 111 is further formed centrally with an upward projection which is formed in its opposite sides with

horizontal grooves

121 and 123 aligned horizontally with the

respective grooves

117 and 119 for receipt of the opposite ends of respective slat like heat shields 127. The grate bars 111 are further formed in their opposite halves with intermediately located upwardly opening

dovetail grooves

131 and 133 which receive downwardly projecting

dovetail tongues

132 and 134 which provide support against the rapper 85.

Referring to FIGS. 11 and 12, the

heat shields

127 and 129 are formed in their opposite sides with longitudinal cut-outs which cooperate to form vertically through air passages 135 which extend substantially the full length of

such heat shields

127 and 129, the edges of such cut-outs being slanted downwardly and inwardly as shown in FIG. 12 to form such passages 135 with bottom openings that are larger in cross section than the top openings thereof. Again, this arrangement facilitates release of any pellets 41 or 89 which might pass downwardly into the respective passages 135. Consequently, operation of the pallet 109 is substantially the same as that set forth hereinabove with the grate bar 111 being thermally insulated from the

respective heat shields

127 and 129 during sintering of pellets located thereon.

The sinter pallet, generally designated 139 shown in FIG. 13, provides a relatively convenient means for securing heat shields, generally designated 141 and 143, to grate bars 145. The grate bars 145 are formed in their opposite extremities with upwardly projecting bosses 147 and 149, an intermediate boss 151 being formed therebetween. The bosses 147, 149 and 151 are all formed with longitudinally extending cylindrical keyway cavities 153 (FIGS. 14 and 15) which have a reduced-in-cross-section chordal opening in the tops thereof defining relatively narrow keyway necks 155. The heat shields 141 are formed with slats 157 having downwardly projecting key elements projecting therefrom and formed in their bottom extremities with cylindrically shaped stops 159 which are cut off along chordal lines at their upper and lower extremities to form an upper cut-back 161 and a lower chordal side 163. Thus, the bosses 147, 149 and 151 support the slats 157 elevated from the body of the grate bar 145 to form insulator spaces 167 which trap air to insulate the grate bars 145 from the heat shields 141.

The opposite edges of the slats 157 are cut on complementary slants 142 to enable such slats to be nested together as shown in FIG. 14.

Operation of the sinter pallet apparatus 139 shown in FIGS. 13 through 15 is substantially the same as set forth hereinabove except that the respective heat shields 141 and 143'may conveniently be removed by merely lifting the free edges thereof to essentially unbutton the stops 159 from the retainer cavities 153 as shown in FIG. 15 to enable such shields to be lifted freeof the grate bars 145 for convenient replacement thereof.

From the foregoing, it will be apparent that the sinter pallet apparatus of the present invention provides a convenient and economical means for conveying pellets through a high temperature zone for sintering thereof. The pallet apparatus provides for a long and trouble-free service life and substantially reduces the cost of replacing worn or warped elements.

I claim:

1. Sinter pallet apparatus comprising:

a frame including a pair of coextensive rail means;

a plurality of elongated coextensive grate bars projecting between said rail means and formed with relatively thick structural support bodies spaced apart transversely to form flow passages therebetween, said grate bars having top and bottom sides and being formed on said respective top sides with respective first retaining elements spaced longitudinally therealong;

a plurality of elongated heat shields including relatively thin flat slats disposed above and projecting parallel with said respective grate bars and formed with respective second retaining elements projecting from the bottom sides thereof received in said respective first retaining elements to lock said respective heat shields on said respective grate bars, said second retaining elements having relatively small horizontal cross sections; and

spacer means projecting from said heat shields and spacing said respective heat shields from the respective bodies of said grate bars to form heat insulator spaces between the respective bodies of said grate bars and said heat shield slats, said spacer means and second retaining elements cooperating to form said spaces with relatively large horizontal dimensions in the longitudinal directions of said heat shields whereby sintered pellets may be received on said heat shields for conveyance under a furnace directing heat thereonto and heating of said pellets to a relatively high temperature will result in heating of said heat shields to a relatively high temperature while air trapped in said insulator spaces will act as an insulator to resist direct transfer of heat from said shields to said respective grate bars to thereby permit said respective grate bars to remain at a relatively low temperature.

2. Sinter pallet apparatus as set forth in claim 1 wherein:

said spacer means space said respective heat shields from said respective grate bodies at least oneeighth of an inch.

3. Sinter pallet apparatus as set forth in claim 1 wherein:

said heat shields are formed on their opposite sides with longitudinal cut-backs which form open bottom heat passages having sides which angle downwardly and inwardly whereby pellets wedged into the top of said heat passages will fall freely downwardly therethrough.

4. Sinter pallet apparatus as set forth in claim 1 wherein:

said grate bar bodies are at least three times as thick as said heat shields.

5. Sinter pallet apparatus as set forth in claim 1 wherein:

said heat shields are constructed of 25 l 2 alloy plated with substantially 5 mills of 98 percent chrome. 6. Sinter pallet apparatus as set forth in claim 1 wherein:

said grate bars are formed on their opposite ends with upwardly projecting ears including horizontally projecting groove means which open inwardly to confront one another to define said respective first retainer elements; and

said heat shields are of sufficient size to have their respective opposite extremities received in said respective groove means and be retained thereby.

7. Sinter pallet apparatus as set forth in claim 1 wherein:

said grate bars are formed with upwardly opening grooves defining said first retaining elements, said slats being formed with respective cavities having relatively large dimensions transverse to said grate bars and being necked down towards the top thereof to form reduced in cross section necks; and

said heat shields are formed with downwardly projecting tongues forming said second retaining elements and received in said respective grooves and being formed to closely fit said respective cross sections of said cavities and then necking down to project through said respective necks.

8. Sinter pallet apparatus as set forth in claim 1 wherein:

said grate bars are formed with respective keyway cavities projecting longitudinal of said respective bars and which are formed in their upper portions with circular cross sections transverse to said bars to form said first retaining elements, said cavities forming in excess of a semicylinder and opening along their top sides in chordal necks having a dimension transverse to said bars which is less than the diameter of said respective circular cross sections; and

said heat shields are formed with downwardly projecting keys received in said respective keyway cavities and said keys are formed with stops which are circular in cross section to compliment the upper portion of said keyways and are cut off horizontally below the horizontal diameters of said respective keyway cavities to form respective vertical thicknesses sufficiently small to, when the slats are rotated to project vertically, fit through said respective necks, said slats projecting transversely to the respective one sides of said respective keys and being cut back at their respective opposite sides to substantially the center of said keyway cavities to accommodate rotation of said keys in said respective keyway cavities to enable said thickness thereof to fit out through said respective necks.

9. Sinter pallet apparatus as set forth in claim 8 wherein:

said slats project sufficiently far in said one direction to have the free edges thereof received in the respective cutbacks of respective adjacent heat shields.

Claims

1. Sinter pallet apparatus comprising: a frame including a pair of coextensive rail means; a plurality of elongated coextensive grate bars projecting between said rail means and formed with relatively thick structural support bodies spaced apart transversely to form flow passages therebetween, said grate bars having top and bottom sides and being formed on said respective top sides with respective first retaining elements spaced longitudinally therealong; a plurality of elongated heat shields including relatively thin flat slats disposed above and projecting parallel with said respective grate bars and formed with respective second retaining elements projecting from the bottom sides thereof received in said respective first retaining elements to lock said respective heat shields on said respective grate bars, said second retaining elements having relatively small horizontal cross sections; and spacer means projecting from said heat shields and spacing said respective heat shields from the respective bodies of said grate bars to form heat insulator spaces between the respective bodies of said grate bars and said heat shield slats, said spacer means and second retaining elements cooperating to form said spaces with relatively large horizontal dimensions in the longitudinal directions of said heat shields whereby sintered pellets may be received on said heat shields for conveyance under a furnace directing heat thereonto and heating of said pellets to a relatively high temperature will result in heating of said heat shields to a relatively high temperature while air trapped in said insulator spaces will act as an insulator to resist direct transfer of heat from said shields to said respective grate bars to thereby permit said respective grate bars to remain at a relatively low temperature.

2. Sinter pAllet apparatus as set forth in claim 1 wherein: said spacer means space said respective heat shields from said respective grate bodies at least one-eighth of an inch.

3. Sinter pallet apparatus as set forth in claim 1 wherein: said heat shields are formed on their opposite sides with longitudinal cut-backs which form open bottom heat passages having sides which angle downwardly and inwardly whereby pellets wedged into the top of said heat passages will fall freely downwardly therethrough.

4. Sinter pallet apparatus as set forth in claim 1 wherein: said grate bar bodies are at least three times as thick as said heat shields.

5. Sinter pallet apparatus as set forth in claim 1 wherein: said heat shields are constructed of 2512 alloy plated with substantially 5 mills of 98 percent chrome.

6. Sinter pallet apparatus as set forth in claim 1 wherein: said grate bars are formed on their opposite ends with upwardly projecting ears including horizontally projecting groove means which open inwardly to confront one another to define said respective first retainer elements; and said heat shields are of sufficient size to have their respective opposite extremities received in said respective groove means and be retained thereby.

7. Sinter pallet apparatus as set forth in claim 1 wherein: said grate bars are formed with upwardly opening grooves defining said first retaining elements, said slats being formed with respective cavities having relatively large dimensions transverse to said grate bars and being necked down towards the top thereof to form reduced in cross section necks; and said heat shields are formed with downwardly projecting tongues forming said second retaining elements and received in said respective grooves and being formed to closely fit said respective cross sections of said cavities and then necking down to project through said respective necks.

8. Sinter pallet apparatus as set forth in claim 1 wherein: said grate bars are formed with respective keyway cavities projecting longitudinal of said respective bars and which are formed in their upper portions with circular cross sections transverse to said bars to form said first retaining elements, said cavities forming in excess of a semicylinder and opening along their top sides in chordal necks having a dimension transverse to said bars which is less than the diameter of said respective circular cross sections; and said heat shields are formed with downwardly projecting keys received in said respective keyway cavities and said keys are formed with stops which are circular in cross section to compliment the upper portion of said keyways and are cut off horizontally below the horizontal diameters of said respective keyway cavities to form respective vertical thicknesses sufficiently small to, when the slats are rotated to project vertically, fit through said respective necks, said slats projecting transversely to the respective one sides of said respective keys and being cut back at their respective opposite sides to substantially the center of said keyway cavities to accommodate rotation of said keys in said respective keyway cavities to enable said thickness thereof to fit out through said respective necks.

9. Sinter pallet apparatus as set forth in claim 8 wherein: said slats project sufficiently far in said one direction to have the free edges thereof received in the respective cutbacks of respective adjacent heat shields.