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Operation & Maintenance Manual: PCL Ceramics RotoBowl Pressure Casting System.

3.0

Process description

3.0.1

Simplified casting process diagram

Operation & Maintenance Manual: PCL Ceramics RotoBowl Pressure Casting System.

3.0.2

Simplified layflat control and wash system diagram

Operation & Maintenance Manual: PCL Ceramics RotoBowl Pressure Casting System. 3.0.3

Simplified slip system diagram

Operation & Maintenance Manual: PCL Ceramics RotoBowl Pressure Casting System. 3.0

Description of processes The diagrams on the preceding pages generically depict the key elements of the RotoBowl pressure casting process. The following text should be read with reference to these diagrams and also with reference to the specific Process and Instrument Diagram (P&ID) for the supplied system (see section 6).

3.1

Preparation of moulds for casting: If PCL Ceramics moulds are used, the processes whereby moulds are prepared for service is fully described in section 5. Failure to rigorously adhere to the prescribed procedures for the care and maintenance of moulds will impair the efficiency of the casting process and may cause premature mould failure. In order to prevent bacterial growth within the porous structure of PCL Ceramics pressure casting moulds, periodic impregnation with a bactericide is necessary. The mould washing system, an integral part of the RotoBowl, is the means by which this impregnation is performed. The water tank together with the water pump (an air driven diaphragm pump) and associated pipe work and valves comprise the means by which a chlorinating agent is mixed with a predetermined volume of water and then pumped through the moulds. Preparatory to mould washing, water tank fill valve is energised and water is admitted to the water tank via the float operated level control valve. When the vessel is full the appropriate amount of a suitable chlorinating agent is now manually added to the vessel contents. The table at the end of section 5 prescribes the amount of chlorinating agent to be added. Configuration and operation of the mould washing process is carried out from the HMI full details of which are given in section 6.

3.2

Preparation of machine for casting: Before the commencement of a series of automatic casting cycles the following actions should be taken – • Check that all machine guards are secured and all safety devices operational. • Ensure that all fluid and air filters are in good working order and with the appropriate filter elements installed. • Ensure the availability and correct condition of all necessary utilities. Typically these are – Mains compressed air at 6-bar pressure. Water at 4 to 6-bar pressure. Electrical supply to suit machine requirements. Supply of correctly formulated slip to slip tank at the correct temperature. •

Set the appropriate process parameters. Typically these are – Mould filling pressure 2 - 4 bar Casting pressure 10 - 15 bar Mains air pressure 6 bar Consolidation pressure 3 - 6 bar Release air pressure 3 - 6 bar

Ensure the process parameters are set correctly. The process parameters tabulated below, are approximate only and will vary dependent upon local condition, the mix of products being simultaneously cast, and the number and size of moulds installed. They are also a simplification of the machine control as up to 18 separate process steps can be programmed. For information on the procedure for setting process steps see section 6 As a general guide, a bowl casting machine will have the following programmed operating steps: Mould purge Manifold circulation LP mould filling HP casting Pre-consolidation

3 seconds 15 seconds 100-150 seconds 360-1000 seconds 60 seconds

Operation & Maintenance Manual: PCL Ceramics RotoBowl Pressure Casting System. Consolidation Post consolidation Drain Vent moulds

120-220 seconds 1 second 10 seconds 10 seconds

For the purpose of the following process descriptions, unless otherwise stated, all process valves and pumps are deemed to be “closed” and “off” respectively. Additionally, the moulds are assumed to be closed by the influence of the hydraulic cylinders. 3.3 Automatic casting cycle sequence description. Close moulds If the “Auto start pre conditions” are correct the auto cycle will commence; the moulds close (if not already closed) by use of pneumatic cylinders. Hydraulic Compress The mould pack is compressed by the two hydraulic cylinders to a pre-set pressure. Compress rim and foot moulds The layflat tubing is filled at low pressure and then the high pressure pump is energised that then compresses the rim and foot tubing with water to a pre-set pressure. Mould purge Water, expressed from the mould during the removal of the cast ware, may accumulate in the low points of the moulds. To avoid detracting from the quality of cast ware this water is purged from the moulds at the beginning of each casting cycle. This is achieved by introducing compressed air via the consolidation valves. The slip dump valves are opened and any residual slip and water is expelled out of them. Mould purging takes approximately 3-10 seconds. The consolidation valves close on expiry of the set mould purge period. Manifold circulation This ensures that the properties of the slip entering the mould are consistent with that of the contents of the slip supply. Manifold circulation takes approximately 15 seconds. The air operated slip pump is energised causing it to start pumping slip and a fixed pressure. The slip manifold valve and run off valve are open at the start of the cycle allowing slip to circulate through the manifold and back to the slip tank. Low pressure mould filling Mould filling is initiated by the opening the mould valves. Slip enters the mould cavity under the influence of the low pressure slip pump. The total time for filling the moulds is usually set to be equal to the time required to reach the set pressure, plus a dwell period of some 30 seconds. Medium pressure filling is completed using the same pump at a higher pressure. High pressure casting The mould fill valves are closed and the 15 bar air feed valve is opened, applying 15 bar air to the slip contained within the stainless steel mould pressure vessel. During “casting”, the mould acts as a filter. Clay filtered from the slip is deposited on the mould cavity surfaces and the filtrate (water) passes through the porous structure of the mould and into the internal air distribution system. Excess water is drained from the mould via the drain ports on the quick exhaust valves fitted to the release air system of each mould part. The time required for “casting” will vary considerably depending upon a number of factors. Among the factors that influence “casting” time are – • The thickness of the drain cast section of the ware being produced.

Operation & Maintenance Manual: PCL Ceramics RotoBowl Pressure Casting System. • •

The properties of the casting slip. The “casting” pressure.

Pre-consolidation drain Having deposited solid clay on the mould cavity walls to the required thickness it is necessary to expel from the mould that slip which remains fluid. The slip run-off valve and mould drain valves open; the slip manifold valve remains closed, thereby establishing a route for slip to pass from the mould back to the slip tank. Consolidation air valves open and air is introduced into that part of the cast ware item containing slip. Under the influence of this pressure, slip is expelled from the hollow parts of the clay ware item. Typically, this part of the process cycle is around 60 seconds but will vary depending upon a number of factors. Among these factors are – • The volume of slip to be drained. • The fluidity of the slip. • The consolidation air pressure. It is generally undesirable to extend the pre-consolidation drain period by more than a few seconds beyond the point where the mould is fully drained. Consolidation Consolidation air pressure is set on the HMI by means of a proportional pressure regulator mounted to the back of the main service stand. Each mould (body and rim) has 2 separate and individually controlled consolidation feeds, each having its own proportional pressure regulator. On completion of the pre consolidation phase the mould drain and run off valves close. The air pressure within each of the drained cavities will increase to the highest value set by the adjustment of proportional pressure regulator. Consolidation of the cast ware continues to a point where it is firm enough to handle during de-moulding and normally takes between 150 and 300 seconds. The hydraulics and rim and foot layflat tubing pressure is generally reduced at this point to a pre-set intermediate level. Post consolidation On expiry of the consolidation period, the mould drain and run off valves will open, the consolidation valve remains open. This allows any remaining liquid slip in the moulds to go into the slip manifold. Drain At this point the consolidation valves close, removing the air pressure supply in the mould cavities. The mould drain and run off valves remain open, effectively connecting the mould cavities to atmospheric pressure Vent The mould drain valve and manifold drain valves open, effectively connecting the mould cavities to atmospheric pressure, in preparation for de-moulding. The casting process cycle is now complete. Layflat Decompress The layflat vent and return valves opens for a pre-set time. This lowers the pressure in the layflat system. After this time has elapsed the layflat vacuum supply and vacuum valves open. This removes the rest of the water from the layflat tubing. Hydraulic Decompress The hydraulic cylinders are decompressed fully. Mould opening and clay ware removal The automatic demoulding sequence now takes place.

Operation & Maintenance Manual: PCL Ceramics RotoBowl Pressure Casting System.


The body mould opens automatically and the rim mould is raised to the upper position. The robot will run its cycle to demould the piece from the body mould. After the piece has been removed from the mould it is placed onto a demoulding table. The robot will then return to its home position.

Both manual and automatic operations of the demoulding process are more fully described in section 6. For further information about the machine operation refer to section 2