CCT Chambers - Salt Spray Mode - how it works

Vent - see text for details Salt fall-out collecting funnel - see Catchpots text for details Salt fall-out collecting funnel - see text for details Heating panels - see text for details Chamber canopy - see text for details Air inlet to the chamber - see text for details Air saturator - see text for details Salt spray atomizer - see text for details Test samples - see text for details Test samples - see text for details Salt solution reservoir - see text for details Control panel - see text for details Test samples - see text for details sensors - see text for details Condensate drain - see text for details Salt solution pump and flow controller - see text for details
CCT Chamber - Salt Spray Mode
This mode of operation is provided as standard on all models of Ascott CCT chamber. It is designed to enable the widest possible range of international salt spray/fog test standards to be met. The control system fitted to Ascott CCT chambers enables the user to program whether salt spray testing is conducted alone, for tests such as ASTM B117, or in sequence with other climates, to form a cyclic corrosion test, for automatic execution by the chamber.

Compressed air inlet                        
Compressed air from a separate compressed air supply is required for the chamber. The primary use of this is to atomise salt water into spray at the salt spray atomiser, located inside the chamber, during salt spray testing. The compressed air supply should be clean, dry and oil free, pressurised to within the limits 1.4 to 6.0 bar (20 to 87 P.S.I.). Between these pressures the air supply should be capable of delivering a flow rate of at least 75 Litres (2.6 cubic feet) per minute, which equates to a free flow at atmospheric pressure of approximately 102 standard litres (3.6 standard cubic feet) per minute. Where a local supply is either unavailable or unsuitable Ascott offer an independent oil free air compressor as an optional accessory (ref.: ACC04). This requires connection to its own single phase electrical supply.

Air saturator                        
During salt spray testing, the compressed air utilised to generate the salt spray is bubbled through the air saturator (also referred to as a bubble tower or humidifier) in order to raise its humidity to c.100%RH at the point that it leaves the salt spray atomiser. This ensures a 'wet' and 'dense' salt spray is created. The temperature of the air saturator is user adjustable up to +63°C/145°F and is usually set several degrees above the chamber test temperature, in order to compensate for the cooling effect as the compressed air expands to atmospheric pressure on leaving the atomiser. Ascott air saturators are configured to top themselves up with water (distilled or deionised) automatically, but where a suitably pressurised supply of such water is unavailable, an optional accessory (ACC66) is offered to enable topping up of the air saturator by hand.

Salt solution reservoir                        
A separate salt solution reservoir is provided for ease of filling and cleaning. For floor standing chambers, it is mounted on castors for mobility. All reservoirs incorporate a transparent graduated sight glass for ease of monitoring the solution level inside. During salt spray testing, the salt solution (brine) is drawn from this reservoir by the chamber peristaltic pump, via a primary filter unit which removes any large undissolved salt crystals or other debris. In addition, Ascott offer an air agitating device which attaches to the salt solution reservoir as an optional accessory (ref; ACC96) to keep the salt solution stirred and homogeneous, by continuously bubbling compressed air through it. A single reservoir is supplied as standard with each new Ascott chamber (see chamber data sheets for capacity) - additional/larger reservoirs are available as optional accessories (ref; ACC02).

Salt solution pump and flow meter           
During salt spray testing, the salt solution pump positively draws salt water into the chamber from the separate salt solution reservoir, by peristaltic action, so avoiding the need for a gravity fed system and the consequent difficulties in maintaining a constant 'head' of salt solution to be sprayed. This salt water is delivered, via a graduated flowmeter, to the salt spray atomiser inside the chamber. The speed of the pump is fully adjustable by the user, to allow the quantity of salt solution atomised and hence the fall-out rate, to be precisely controlled. Two pumps and flowmeters are fitted to 2000L size chambers.

Salt spray atomiser                        
This is a specially designed salt spray atomiser, made from thermally stable, high performance polymer, to guarantee a uniform salt spray and featuring an integral filter to minimise blockages. During salt spray testing, it is here that the compressed air, delivered via the air saturator, meets the salt water, delivered via the salt solution pump and flowmeter, to create a finely divided salt spray (also referred to as 'salt mist' or 'salt fog'). This oxygen rich and highly corrosive salt spray rises from the atomiser, into the chamber atmosphere, where it then 'falls-out' on to the test samples beneath. The fall-out rate can be adjusted and precisely controlled, according to international standards, by adjusting the speed of the peristaltic pump and the compressed air pressure. Two atomisers are fitted to 2000L size chambers.

Chamber heating mats                        
Silicone rubber encapsulated electrical heating mats are strategically bonded to the outside surfaces of the bottom and sides of the inner working chamber. Here they radiate heat uniformly into the chamber, under the control of the chamber temperature controller. In the salt spray mode of operation, these heaters give the chamber a user adjustable temperature range from ambient to +50°C/122°F.

Control panel                        
Forming the centre-piece of the ergonomically designed control panel is a state of the art, touch-screen, Human Machine Interface (HMI). It is here that the user controls and monitors the various chamber functions. The HMI incorporates alpha-numeric text messaging and digital displays of chamber variables such as temperature, humidity and time . Also included is a useful trend logging facility. This generates a graphical display of set values for temperature & humidity, over a 72 hour time period, and compares this to the actual temperature and humidity achieved inside the chamber, over the same period. All chamber control panels incorporate an emergency stop and other safety facilities.

Chamber canopy                        
The chamber canopy is effortlessly opened/closed using pneumatic cylinders, which are activated at the touch of a button on the control panel. An automatic purge facility is incorporated to minimise the risk of corrosive salt spray escaping into the laboratory when the chamber is opened.

Strategically located sensors, mounted inside the chamber and air saturator, monitor the climate continuously and convey this information to the Human Machine Interface (HMI), where it is displayed digitally at the control panel. Temperatures are monitored by PT100 precision temperature sensors and displayed to a resolution of 0.1°C. CCT chambers are also equipped with a special design of corrosion resistant humidity sensor. This measures the relative humidity electronically inside the chamber and displays this at the HMI as %RH to a resolution of 1%RH.

Test samples                        
Test samples are accommodated within the chamber generally by placing on, or by suspending beneath, sample racks. A full set of sample racks are provided as standard with each new chamber (see chamber data sheets for quantity) in a choice of styles. Additional sample racks are available as optional accessories, if required, as is a reinforced false floor (ref; ACC19) for supporting large/heavy test samples directly on the chambers internal base.

Exhaust vent                        
This vents spent salt spray from inside the chamber to atmosphere. The chamber should therefore ideally be located adjacent to an outside wall, and a hole made through the wall to accommodate the exhaust pipe. The end of this pipe should be directed away from persons and property, and be shielded from wind to prevent any disturbance to the conditions inside the chamber. If access to an outside wall is not possible or inconvenient, Ascott offer an optional accessory called an Exhaust Salt Scrubber Unit (ref; ACC92). This comprises of a free standing enclosure, which should be located near to the chamber, and connected to the chamber exhaust vent outlet, a floor level drain and a continuous pressurised mains water supply. The unit works by directing the chamber exhaust towards its internal base, where a significant surface area of relatively cool liquid condensate/water is retained. The relatively warm salt laden exhaust passes over this and is simultaneously sprayed with a fine mist of cool water from a mains water sprayer located in the top of the unit. The combined effect of this is to condense and wash out the salt water droplets present in the exhaust, so that they combine with the retained liquid in the base of the unit. Surplus liquid is drained to waste from the base of the unit and the remaining 'scrubbed' compressed air from the chamber exhaust is allowed to vent from a port in the top of the unit. ACC92 is not suitable for chambers fitted with the SO2 gas dosing optional accessory (ref; ACC46) due to the toxic nature of the SO2 which may exist in the exhaust.

Condensate drain                        
A floor level drain is required to remove to waste the excess salt fog condensate etc. which accumulates over the internal base of the chamber interior during testing. If access to a floor level drain is not possible or inconvenient, Ascott offer an optional accessory (ref; ACC20) comprising of a waste water trough and pump, which locates on the floor behind the chamber. Condensate from the chamber drain outlet is directed into this. When the holding tank becomes full, the condensate will automatically be pumped out by a marine specification pump. This will discharge waste water to a remote drain or effluent tank located up to 10M/30ft away horizontally and up to 3M/10ft vertically. ACC20 is not suitable for chambers fitted with the SO2 gas dosing optional accessory (ref; ACC46) due to the possible existence of H2SO4 in the condensate.

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