Basic Process Descriptions
All systems comprise of two tanks – Process tank and Boil Tank. In mono solvent systems the boil tank is off set and reduced in size to the minimum requirement to reduce the amount of first fill solvent required. Parts do not immerse in the boil tank in this configuration. In Co-Solvent systems the boil tank is sized to allow parts to be immersed.
Solvent is boiled in the boil tank to create a vapour blanket which is maintained around the mid point if the condensing coils. The vapour rises and fills the vapour zone where it condenses on the coils and falls into a collection trough. The condensed solvent is directed back into the process tank via a water separation device. The process tank fills and solvent runs over a weir to return to the boil tank to complete the solvent cycle. This provides a constant distillation of the solvent material.
In mono solvent systems components are placed in a suitable basket, which is then placed into the immersion zone of the process tank. The ultrasonic agitation (if fitted) is switched on. Following a period in immersion the ultrasonics are switched off and the parts are lifted to dwell in the vapour zone. After the vapour dwell the parts are then lifted into the freeboard zone above the cooling coils. The cool freeboard atmosphere causes any residual solvent on the parts or basket to vaporise and collect on the cold plates in this area.
In Co-Solvent systems parts can also be placed in to the immersion zone of the boil tank.
The fluid in the process tank is heated and may be ultrasonically agitated to help the removal of contaminants. The ultrasonic energycauses cavitational implosions at the surface of the parts causing any small particulate matter to be dislodged and removed. The fluid in the process tank may be constantly filtered to ensure all particles greater than the filter’s nominal bore size are removed.
In addition to the above the Bluestone F is integrated with a remotely mounted vapour detection system. The system is purpose designed and calibrated for use with the flammable solvent of choice. Throughout the main machine are detector heads strategically positioned to detect a build up of flammable vapour. The control system is interconnected with a mains contactor supplied. The mains electrical supply to the machine is wired through this contactor. The control system will switch off the contactor should vapours reach 20% of the lower explosive limit (LEL) of the vapour / air mixture thus removing the mains supply from the system.
The system is integrated with an internally mounted fire detection and suppression system. The system is purpose designed and calibrated for use with suitable flame detectors and CO2 discharge suppression. Upon detection of a flame the control system will energise the CO2 cylinder and discharge extinguishing CO2 into both the mail process tank and the air space between the tank and frame. The control system is interconnected to the PLC and safety circuits. All detectors, sensors, switches and activators are fully protected from both open and short circuits. The mains electrical supply to the unit is interconnected to the main machine supply. The system is battery backed and will operate in a powered down situation. However, as with all cell-powered circuits the power is time limited and must not be left powered down for a continuous period. Upon flame detection the mains supply to the machine will be removed.
Intrinsic Safety Circuits. All control and operating systems are designed to be intrinsically safe. All signalling devices are routed through approved barriers designed to operate as an interface between hazardous and safe areas. All valves, cylinders and motors are air operated and / or ATEX approved.
The work carrier is loaded into the process tank and the run time set on the operator interface panel. The process commences when the start button is pressed and continues as follows:-.
The process tank lid closes and initiates the caustic solution fill. The pump will start and transfer the pre-heated process fluid from the caustic storage vessel to the process tank. When the solution is at the correct level in the process tank the pump will switch off automatically and the ultrasonic agitation starts and continues for the set process time. The heaters are also activated.
The etch process cycle commences. During the process, the heating in the tank is closely monitored to maintain a consistent temperature of 90–95 degrees Celsius. If the thermal conditions in the tank raise the temperature above 95 degrees C, the plate cooling will activate to reduce the temperature to within process parameters.
At the end of the etch process cycle, the caustic solution is pumped back to the storage tank. Once drained the process tank and work carrier are sprayed with fresh water to reduce cross contamination of the storage tanks. This spray rinse water is pumped to the caustic storage tank.
The rinse cycle then commences. The pump will start and transfer pre-heated fluid from the rinse water storage tank. When the rinse water is at the correct level in the process tank the pump will switch off automatically. The ultrasonic agitation starts and continues for the set process time. The heaters are also activated. The rinse cycle operates for a fixed time period, nominally 20 minutes.
At the end of the rinse cycle, the rinse water is pumped back to the storage tank. Once drained the process tank and work carrier are again sprayed with fresh water to reduce cross contamination. This spray rinse water is pumped to the rinse water storage tank.
At the end of the spray rinse cycle hydrogen levels are monitored. If hydrogen is not detected, an alarm notifies the operator that the cycle is complete. The lid may be opened from the operator control panel to allow removal of the work carrier.
During the complete process cycle the levels of both the storage and process tanks are monitored and topped up as necessary. The addition of the rinse water to the caustic storage tank will compensate for evaporation thus reducing wastage.
The rinse water is recycled and used to top up the caustic tank, the rinse water is not sent to waste.
The fresh caustic may be purchased at maximum strength, 47%, the system will automatically dilute the concentration to the operating strength, typically 25 – 30% by using the rinse water.
This optimises the system and reduces the transportation costs, less to deliver and no rinse water to dispose of.
The process consists of four separate and distinct phases of operation. These are all fully programmable and selectable in recipe format. The end user can program up to fifty separate recipes for pre-selection by operators.
The components are placed in the work basket (optional) that is then placed in to the work carrier situated at the front of the machine. The sliding lid is closed and sealed and remains sealed for the entire process. Once sealed the carrier can then rotate through 360degrees, oscillate through at a selectable angle or remain stationary dependant on the program required.
During this cycle parts can be sprayed with distillate and / or the process chamber can be filled with solvent for immersion with or without ultrasonics.
During this cycle solvent vapours are directed into the process chamber for first or final clean. The vapours introduced here condense on the parts to produce very clean solvent for final rinsing or precision cleaning.
The pressure inside the process chamber is reduced by use of a vacuum pump. The air evacuated from the chamber is passed through the cooling system and active carbon filter. Once this cycle is complete atmospheric pressure is restored and final drying occurs by recirculating air in a closed loop.
Prior to opening the door the air inside the process chamber is recirculated through the active carbon filter to remove all traces of solvent from the parts, basket and carrier.