Washing machines are used to automatically or semi-automatically clean trays, racks, utensils and in the case of dishwashers glasses, crockery and cutlery.
The washing machines must be managed with regular cleaning of the machine and filters, regular changing of wash solutions, inspection of wash and rinse nozzles and control / monitoring of detergent temperatures and strengths.
Washing Machines are either flight type machines or single tank machines.
Flight Machines
With tunnel machines items are placed on a conveyor which transports them through a number of stages of the washing process. Each stage occurs in a different section of the washer; pre-rinse, wash with detergent, rinse and disinfect by temperature.
Single Tank Machines
With single tank machines the item is placed in a cabinet and the wash process takes place in the cabinet by sequencing the cleaning stages (prerinse, wash, rinse, disinfect).
Cleaning Stages
The short contact time with detergent and the relatively low impact energies of the wash nozzles means that to clean effectively high chemical energies are required. In most situations a high alkaline low foam detergent at 0.25% to 1% v/v is used at 55 to 75ºC.
A detergent wash should be carried out from a separate tank using a low foaming detergent appropriate to the equipment being cleaned and nature of soiling. A neutral or inhibited detergent may be employed for cleaning of sensitive items, such as aluminium trays, pots and pans.
Because different detergents are more suited to different water conditions, a water hardness test needs to be carried out. This will ensure that the risk of scale drop out is reduced. It may also prove beneficial in hard water areas to soften the water supply by having an on-site water softening system.
Rinsing for final disinfection should be carried out with water fed either directly from a heat exchanger or a separate enclosed non-recirculating tank. The rinse water should be maintained at a minimum of 82(C. Attention must be paid in hard water areas, as there could be a significant problem of scale drop out so ensure that the machine is regularly de-scaled.