| The purpose of bisk firing is (1) to
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| | during sintering or vitrification.Slump
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| completely vitrify or densify a ceramic
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| | is due to the weight of the part on
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| body in the case of bone china, fine
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| | itself.Drag is due to the friction
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| china, and industrial ceramics or (2) to
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| | between the part and its setter or the
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| partially vitrify a body in the case of
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| | kiln car deck.A shrinkage block of a body
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| porcelain.Taking porcelain first, Case
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| | can be formed into a two-diameter
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| (2), the body is taken to a temperature
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| | cylinder about 3 inches high with a top
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| to which enough strength is developed to
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| | half diameter of perhaps 1-3/4 inches and
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| be automatically handled in glazing
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| | a bottom diameter of 2 inches. The drag
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| operations (in modern factories) but
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| | shrinkage is determined by the diameter
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| porous enough to be easily glazed by
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| | of the block touching the kiln car deck
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| dipping methods.Porcelain wear does not
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| | or setter, the slump is determined by
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| have to be supported during bisk firing
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| | measuring the total and shoulder height
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| and defects generated are usually chips
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| | of the block, and the normal shrinkage is
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| or breakage from handling.Kiln dirt can
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| | determined by measuring diameters not
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| cause defects here, but rarely. If they
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| | affected by drag or slump.An example of
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| are formed, they often be removed by
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| | how large cylindrical shapes are fired
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| grinding methods.Sometimes sand, perhaps
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| | will illustrate what sometimes must be
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| alumina, is placed between dinner plates
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| | done.A setter is machined from the same
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| so they can be stacked without any chance
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| | material as the cylinder. This base
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| of sticking. This sand is easily removed
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| | setter is coated with a solution of PVA
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| by subsequent operations. If a speck of
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| | (polyvinyl alcohol) and sprinkled with
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| sand is left on the wear during glazing,
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| | sand (alumina). For smaller cylinders
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| it will cause a glost ware defect as
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| | this step can be omitted.On top of this
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| described in the next article.In the
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| | is placed a step setter. The step is
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| first case, Case (1), the body is heated
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| | about 3/8 inch.The ceramic cylinder has
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| on a temperature / time cycle where full
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| | its ends coated with a solution of PVA
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| strength is developed (usually through
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| | (polyvinyl alcohol), dipped in setting
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| sintering) in non-glazed industrial
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| | sand (perhaps alumina), and is placed on
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| ceramics.For fine china and bone china,
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| | the step setter.The upper step is the
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| the body develops maximum translucency
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| | diameter of the ceramic cylinder. (Well
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| through vitrification.The wear often has
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| | leave a few thousandths.)The step setter
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| to be supported during firing.Three major
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| | maintains the lower diameter of the part.
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| problems relate to the high-temperature
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| | As the base setter shrinks, the base
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| firings of Case (2). The first problem is
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| | setter (and step setter) will shrink,
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| shrinkage. The second problem is slump.
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| | pulling the cylinder in with it.But we
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| The third problem is drag. These factors
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| | are not firing yet.A hollow cylinder
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| play a major part in the distortion of
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| | (perhaps 2 inches in diameter) made of
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| large parts during firing.For fine china
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| | the same material as the part is placed
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| and bone china, the dinner plates and
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| | on the step setter dead center.A top step
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| similar items are fired in refractory
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| | setter, treated as above, is placed on
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| saggers. The ware settles into the shape
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| | top of the ceramic part, its minor
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| of the sagger as it softens during
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| | diameter fitting into the cylinder and
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| firing. Therefore, the ware is fully
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| | resting on top of the inner support
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| supported. The saggers are covered so
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| | cylinder.The support cylinder will
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| there is no kiln contamination.
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| | decrease slump caused by the weight of
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| Operations may be required to remove any
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| | the top step setter.The top step setter
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| particles from the ware before
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| | maintains the diameter of the part.After
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| glazing.Small parts are not a problem for
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| | firing, the cylinder will not be perfect,
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| industrial ceramics. Larger parts are a
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| | but if there is enough grind stock and
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| different matter.The shrinkage and slump
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| | the upper and lower diameter have been
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| and drag factors must be known.Shrinkage
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| | maintained during firing, the part can be
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| is caused as the particles move together
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| | machined to the specified dimensions.
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