GB2413107A

GB2413107A - Method and apparatus for controlling the drying of a clay body on a former

Info

Publication number: GB2413107A
Application number: GB0408385A
Authority: GB
Inventors: Peter David Hurley
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-04-14
Filing date: 2004-04-14
Publication date: 2005-10-19
Also published as: GB0408385D0

Abstract

A method and apparatus for controlling the environmental factors involved with drying a clay body on a pre-shaped former comprises a sealed enclosure for holding the pre-shaped former which is covered with a wet clay or ceramic coating. The method includes the steps of inducing evaporation of the water content by heat and air flow, removing the water laden air by condensing means, controlling the contraction of the clay body by controlling the rate of evaporation, whereby the whole process is computer controlled. Electrical resistance moisture meters may be used to monitor the drying clay. The clay body may be a bust which once the former is removed has its internal gas pressure maintained for final drying.

Description

Former Remover Controls This invention relates to a method and apparatus

for the controlling of the environmental conditions during the process former remover.

More parhcularly the controlling of the temperature, humidity, air flow and air or gaseous pressures also cycle time together with the controlling of the contraction rate of the clay body in the process former remover.

It is known from GB 2387569 the use of pre-shaped former removal from wet ceramic material also from GB 645998 that the electrical resistance change in wet concrete becomes more or less lineahaving removed the air bubbles. This invention address the problem of the time required to allow for the evaporation of the water content from within the clay body together with the controlling of the stages of loss of water content, also the prevention of movement of the clay body bust during the removal of the former whilst giving additional internal support to the clay body bust having removed the former.

According to the present invention there is provided a method and apparatus, of controlling the internal and external environmental factors during the process former remover, the pre-shaped former with it's coated wet ceramic material is placed within a heat and air flow controlled enclosure, the temperature inside the enclosure is elevated to induce evaporation of the water content in the clay body, the enclosure air circulating fan which assist the evaporation by removing the water laden air from within the enclosure, this air will pass through a condensing unit where excess water in the air will be removed prior to returning to the enclosure, thus controlling the evaporation rate and therefore the contraction rate of the clay body and the internal gaseous pressure of the bust is maintained above external atmospheric pressure with the process being computer controlled.

The enclosure is a sealed container and could be fabricated from plastic, wood or steel, the heating of the enclosure could be by electric or gas, the air circulating fan could be either force draught or exhaust draught by axial flow or centrifugal flow, the condenser could take the form of an orifice tube where the air velocity is increased and then allowed to slow and expand, on expansion the air could come in contact with a cold surface and this action would remove the water from the air, or the air could be passed over a artificially cooled surface which would have the same effect in removing the water content from the air.

The velocity of the air circulating through the container is controlled inversely proportionally to the electrical resistance given by the clay body bust up to the leather stage of the clay body bust, that is to say from the initial resistance reading being low the air flow will be high and as the resistance increases the air flow will reduce and stop until the former has been removed when the air flow will be reinstated to finally dry the bust.

The clay body is formulated to minimise the amount of water content which will reduce the time required for the removal of the water from the body, this body could be a clay slip body or alternatively a clay engobe body, this can be achieved with the use of deflocculates which control the minerals magnetic charge, the clay has a natural magnetic charge which is formed from the motion of the earth's inner molten metal core and the clay particulate having a inner and outer layer, the inner layer being negatively charged and the outer layer positively charged, if the positive magnetic charge of the particulate is increased then the particulate repel each other which make the mixture more fluid, the alkali cation type deflocculant, with an alternative method being the polyanion type which increases both the negative and positive charge of the particulate, or a combination ratio of the two methods could be employed, a further alternative being non-electrolyte deflocculant could be used, this embodiment is not restricted to a water clay body and could be clay in powder form mixed with a polymer, then applied to the pre- shaped former and when fired the former and polymer would be burnt off, also the ceramic polymer mix could be used in injection moulding or centrifugal moulding to form the bust prior to firing.

When using the heat method of degrading the former, the heating device ( 3) could take the shape of a square column or a circular column with similar cross sectional area or could take the form of a larger cross section area with less height, the emission of heat via convection can be positioned along the length of the device, heat emissions from the lower end of the device could induce the former to degrade from the bottom up or heat emitting from the upper end of the device could induce degrading from the top of the former to the bottom with the heating device following a Rayleigh-Benard convection current pattern, with the element cylindrical in shape and it's length extends into the bust at the centre of the neck for at least three quarters of the height of the bust, the heat produced being from the upper two thirds of the element this is achieved by the positioning of the heat generating windings, on activation the heat will degrade the former from the top to the bottom, there will be a build up of gaseous pressure inside the bust using this removal method which uncontrolled lifts the bust to equalise the internal and external gaseous pressures, this could be controlled by mechanical means that is the bust is supported on a plate attached to an inverted piston rod ( S) the piston is supported within a cylinder with a connecting pipe ( 8) from the inside of the bust to the bottom of the cylinder where the increase in gaseous pressure lifts the piston and plate with the bust until the piston passes an orifice ( 6) in the cylinder wall which allows the egress to atmosphere of the pressured gas, a spring ( 7) is positioned under the piston to remove oscillations, or this could be by the use of a low pressure switch ( 9) activating a two way pneumatic solenoid valve ( 10), when the switch ( 9) is activated this energises the solenoid pneumatic valve ( 10) to allow egress of the pressured gas to atmosphere, or this could be by a connecting balance pipe ( 8) from the inside of the bust placed in a water tank ( 11) when the internal gas pressure builds the increase in pressure forces the gas through the pipe into the water tank ( 11) through the water and then out to atmosphere, the depth of the pipe in the water tank ( 11) will determine the internal gaseous pressure of the bust together with allowing for the reduction in internal pressure of the bust when the bust has cooled having had the former removed achieved by the reversing of the air flow external to internal.

Alternatively when using the liquid chemical degradation method of former removal, a small diaphragm compressor or reciprocating compressor fitted with a pressure relief valve feeds compressed air inside the bust at low pressure, this pressure will alter depending on the mass of the bust being produced within the reign of approximately 25 millimetres and 50 millimetres water gauge, 250 Pa - 500 Pa or 2.5 - 5 Milbar, with the relief valve regulating the internal pressure of the bust through out the process, also with attention to the release of gaseous pressure from the foam if closed cell beads are used in the foam manufacture, with using the liquid chemical compound degradation method the release of the chemical through the dispenser is so arranged as to project the liquid chemical compound to the top of the fommer and then allow the liquid chemical compound to fall through the former due to gravity, a further alternative could be by gaseous chemical degradation where the chemical compound is introduced to the foam as a gas, this gas is supplied at a relative pressure above atmospheric air pressure through a pressure reducing valve.

During the stages of the clay body from leather firm to leather hard and then on to dry the internal gaseous relative pressure of the bust is maintained above the external relative atmospheric pressure equivalent to the pressure required to support 50% - 75% of the mass of the clay body, by the activation of a compressor initiated by the computer and its software from the resistance reading received from the clay body or by the pressure balance tube, this pressure is determined by averaging out the mass of a number of equal size busts when dry and adding an additional 25% of this mass for the water content of the clay body when wet, averaging out the cross sectional area of the busts at nose tip level, calculating the force required to support the mass from Force = Mass X Gravity also Force = Pressure X Area, dividing this force by the cross section area to determine the pressure then dividing this pressure by two to arrive at the 50% pressure required to support the wet clay body, this pressure being set by the relief valve or the depth of the balance tube in the water tank depending on the method of former degradation used.

Controls for this process are directed by a computer and computer software in the form of electrical and electronic signals which gathers information from the enclosure environment via sensors monitoring the temperature, humidity and gaseous pressures together with the electrical resistance readings of the bust in digital form, these sensors converting either electrical resistance generated from heat into a digital form or analogue information into digital form to produce binary code which the computer receives, the computer collates and monitors this information then initiates the actions in response to I/O events during the process time cycle, which could be via a programmable logic controller or PC and programming language system for example a SCSI architecture using PCI bus interface alternatively the use of Fieldbus technology with either ISP or WorldFIP protocols, the actions initiated by the computer being the stop start of the cycle, the onion of the enclosure heater, the on/off and circulating fan motor speed control, this could be controlling the voltage to a DC motor or through a phase inverter for a AC motor, the onion of the former heater or the initiation of the chemical compound to the former together with the safety interlocks initiations or acceptances.

A preferred embodiment of this invention will now be describe by way of example and with the accompanying drawings in which: Drawing 1/3 illustrates:- the mechanical means of equalising the internal pressure of the bust where, pre-shaped former 1, ceramic coating 2, heating device 3, electrical resistance leads 4, inverted piston and plate 5, cylinder orifice hole 6 and oscillation prevention spring 7.

Drawing 2/3 shows:- pneumatic means of pressure control where, ceramic coating 2, heating device 3, balance pipe 8, pressure switch 9 cab solenoid pneumatic control valve 10.

Drawing 3/3 illustrates:- the water tank method of pressure control where, ceramic coating 2, locating device 3, balance pipe and water tank 11.

The pre-shaped former ( 1) is coated with a wet clay body ( 2) the clay particles having a high zeta charge to minimise the water content on application and provide for minimum shrinkage during the wet to leather stages of the clay body.

The coated pre-shaped former is placed into an enclosure on top of the heating element ( 3) or conversely, the electrical resistance monitor leads ( 4) are attached to the clay body and the enclosure sealed, the devices computer is activated to start the process cycle by either keyboard input or via visual display input, on activation the computer and computer program gathers information of the electrical resistance from the clay body, the internal temperature of the enclosure also the external air temperature and the enclosure air circulating fan status together with the hygromtric state of the air inside the enclosure, when the resistance reading of the clay body is low and the internal air temperature of the enclosure is below 20 degrees Celsius above external ambient air temperature then the enclosure heater is activated also the enclosure air circulating fan.

The air that is circulated through the enclosure is passed into a air condensing unit which removes the water content of the air prior to reintroducing this air back into the enclosure where the air then picks up further water droplets evaporating from the clay body, the maximum circulating air velocity within the enclosure is below the velocity capable of deforming or distorting the wet clay body coating on the former but high enough to provide free space around the surface of the bust to allow water molecules to escape the clay body and can be controlled to prevent this escape of the water from the clay body by allowing the build up of saturated air inside the enclosure thus blocking the free space next to the surface of the bust by means of reducing or ceasing the enclosure air circulation flow rate.

With the electrical resistance readings from the clay body following a similar pattern as described in Patent Specification GB 645998 page 1 line 91 - page 2 line 6 the initial readings being measured in milk ohms and as the water is removed from flee clay body the readings rise more or less linearly with time, the rate of rise can be controlled by the amount of air flow over the bust, as the water is removed from the clay body the wet clay body turns to a leather soft like substance which is still not self supporting at this stage of the cycle, the enclosure air circulating fan starts to slow down and then stops triggered by the increase of the electrical resistance from the bust and allows the build up of water molecules in the air, until the air inside the enclosure is saturated with water and can not allow the escape of water molecules from the surface of the bust, thus reducing fewer contraction of the bust, at this time the leather form like clay body is self supporting and the former can be removed, the pressure balance internal to external of the bust is regulated by the balance pipe ( 8) and the water tank ( 11) having removed the fonder indicated by the internal air temperature of the bust, the enclosure air circulating fan is restarted and the evaporation of the remaining water in the clay body continues and talces the clay body from leather firm to leather hard and then dry, with the bust being free to contract through out these stages, when the clay body is dry indicated by the electrical resistance of the bust and the relative humidity within the enclosure the cycle is stopped the bust is removed and sent to the kiln for firing and then finishing.

Claims

Claims 1. A method and apparatus for the controlling of the environmental

factors in the process fonder remover comprising the steps of:- enclosing the per-shaped former with it's ceramic coating, inducing the evaporation of the water content of the clay body, removing the water laden air from the enclosure, controlling the contraction rate of the clay body, removing the pre-shaped former, maintaining an elevated pressure inside the bust with the process being computer controlled.
2. As claimed in Claim l wherein the induced evaporation is by heat and air flow means.
3. As claimed in Claim 1 wherein the removal of the water laden air from the enclosure is by condensing means.
4. As claimed in Claim I wherein the contraction rate of the clay body is controlled by controlling the evaporation rate.
5. As claimed in Claim 1 wherein means of controlling the internal gaseous pressure of the bust is provided.
6. As claimed in Claim 1 wherein means for computer control are provided.
7. As claimed in Claim 1 wherein the apparatus comprises, enclosure, air circulating fan, condenser, sensors, pressure control device, computer and computer software.
8. As claimed in Claim 1 and Claim 4 substantially as described herein with reference to Drawings 1/3, 2/3 & 3/3 inclusive of items 1 to 11.