This work also requires frequent annealing, for otherwise the wires or tubes would rupture.
The second system is especially used for annealing large and heavy objects.
Types of muffle furnaces are figured in the article Annealing, Hardening And Tempering.
Further, all the subsequent processes of cutting, moulding and annealing become increasingly difficult, owing to the greatly increased risk of breakage arising from either external injury or internal strain, as the dimensions of the individual piece of glass increase.
The heat passes from the melting furnace into the annealing kiln.
The bowl is severed from the blowing iron, and the wine-glass is sent to the annealing oven with a bowl, longer than that of the finished glass, and with a rough fractured edge.
The finished bottle is taken by the " taker in " to the annealing furnace.
It is, however, equally important that the glass as a whole should be flat and remains flat during the process of gradual cooling (annealing), otherwise great thicknesses of glass would have to be ground away at the projecting parts of the sheet.
The annealing process is therefore carried out in a manner differing essentially from that in use for any other variety of flat glass and nearly resembling that used for optical glass.
The rolled sheet is left on the castingtable until it has set sufficiently to be pushed over a flat iron plate without risk of distortion; meanwhile the table has been placed in front of the opening of one of the large annealing kilns and the slab of glass is carefully pushed into the kiln.
Before the glass is introduced, the annealing kiln is heated to dull red by means of coal fires in grates which are provided at the ends or sides of the kiln for that purpose.
The sheet thus rolled is roughly trimmed while hot and soft, so as to remove those portions of glass which have been spoilt by immediate contact with the ladle, and the sheet, still soft, is pushed into the open mouth of an annealing tunnel or " lear," down which it is carried by a system of moving grids.
Their original softness can be restored to them by "annealing," i.e.
The specific gravity of cast gold varies from 18.29 to 19.37, and by compression between dies the specific gravity may be raised from 19.37 to 19.41; by annealing, however, the previous density is to some extent recovered, as it is then found to be 19.40.
(6) Annealing the blanks and (in some mints) cleaning them in acid.
By repeated passages through the rolls the bars are hardened, and to facilitate further reduction they are usually softened by annealing before being passed to the finishing rolls.
The blanks are next softened by annealing, and are then thoroughly cleaned before being passed to the coining presses.
Thermal Treatment.-The hardening, tempering and annealing of steel, the chilling and annealing of cast iron, and the annealing of malleable cast iron are explained readily by the facts just set forth.
The Tempering and Annealing of Steel.-But this sudden cooling goes too far, preserving so much 0-iron as to make the steel too brittle for most purposes.
The annealing of such iron may occur in either of two degrees - a small one, as in making common chilled cast iron objects, such as railway car wheels, or a great one, as in making malleable cast iron.
The joint effect of such chilling and such annealing is to make the metal much harder than if slowly cooled, because for each 1% of graphite which the chilling suppresses, 15% of the glass-hard cementite is substituted.
But in most such cases, in spite of the annealing, this hardness is accompanied by a degree of brittleness too great for most purposes.
In making malleable castings the annealing, i.e.
The reason is that the particles of temper graphite which are thus formed within the solid casting in its long annealing are so finely divided that they do not break up the continuity of the mass in a very harmful way; whereas in grey cast iron both the eutectic graphite formed in solidifying, and also the primary graphite which, in case the metal is hypereutectic, forms in cooling through region 3 of fig.
With repeated hammering, drawing out and annealing, it gains much in strength and toughness, and the addition of a very minute quantity of carbon converts it into steel, less tough, but of the keenest hardness.
Sheet metals can be made to assume almost any shape under the hammer, or by pressure, provided they are subjected to annealing to restore the property of malleability.
Objects that do not require annealing are produced by dozens per minute, and all the movements of feeding and stamping and removal are often automatic. The ductility of metals and alloys is utilized in wire and tube-drawing through dies on long benches.
But the severity of the treatment would tear the material asunder if rearrangement of the particles were not obtained by frequent annealing (q.v.).
The process of casting and annealing, in the case of the specula of the great Melbourne telescope, was admirably described by Dr Robinson in Phil.
Our bakers' ovens, hot-air ovens or stoves, annealing ovens for glass or metal, &c., would all be called fours in, French and Olen in German, in common with furnaces of all kinds.
In the construction of this soft-iron instrument it is essential that the fragment of iron should be as small and as well annealed as possible and not touched with tools after annealing; also it should be preferably not too elongated in shape so that it may not acquire permanent magnetization but that its magnetic condition may follow the changes of the current in the coil.
Among other things, it was found that the behaviour of cast cobalt was entirely changed by annealing; the sinuous curve shown in Fig.
Some preliminary experiments showed the striking difference in the effects of annealing at a red heat (840° C.) and at a low white heat (1'50° C.).
Further, it was shown that the thermo-electric curves were modified both by tensile stress and by annealing in the same manner as were the change-of-length curves, the modification being sometimes of a complex nature.
In all branches of glass manufacture the process of " annealing," i.e.
Processes of annealing, or very gradual cooling, are intended to relieve these strains, but such processes are only completely effective when the cooling, particularly through those ranges of temperature where the glass is just losing the last traces of plasticity, is extremely gradual, a rate measured in hours per degree Centigrade being required.
From the annealing kiln the slabs of glass are transported to the cutting room, where they are cut square, defective slabs being rejected or cut down to smaller sizes.
The process will probably be abandoned as soon as the tarnishing of the metal during rolling and annealing can be avoided.
This was passed again and again between gradually approximated rollers, with occasional annealing, until the desired thickness had been attained.
The after-treatment of castings by annealing exercises great influence on results in malleable cast iron and steel.