In 1947 entirely new equipment was conceived and developed in the form of horizontally faced other article sorting machines, which reduced the fatigue of the sorting staff by providing more comfortable and improved working conditions, reduced noise levels and enabled better supervision of staff. The first horizontal faced OA machine was installed in Melbourne Mail Exchange on a trial basis in 1947 at a cost of £2,000 and was still in service in 1979. Because of the success of the Melbourne trial the machine became a Commonwealth standard and a number of machines were installed in the Melbourne and Sydney Mail Exchange equipment refurbishment programmes that occurred in the early 1950s.

Like the vertical faced sorting machine the horizontal faced OA sorting machine is essentially a multiple of sorting fields each composed of the appropriate number of receptacles with an input feed of unsorted articles and a cyclical delivery arrangement to take the sorted articles to the next processing area. A general view of a horizontal faced OA sorting machine is shown above.

The machine has a 24 bin sorting field with the bins in four longitudinal rows each of six bins. Each bin is 8 inches wide x 13 inches long x 14 inches deep. In the front of the sorting field is a shallow storage conveyor used to bring unsorted mail to the sorting staff. Beneath each machine are four clearing conveyors, one for each row of bins. The machine has a head and tail unit; these units accommodate the drives and the tensioning devices as well as the input chutes to the shallow storage conveyor. Each sorting bin has a hinged bottom and an operating rod runs the full length of the sorting fields. Each bin door or bottom has a small piece at the free end, hinged on spring loaded hinges to ensure articles caught by closing doors are not damaged.

The bin sizes were chosen to handle the majority of OAs that arrive at Mail Exchanges and the capacity of the bin is matched with the clearing cycle of the machine. The mail is discharged from the bins in rows of four across the field at the one time through the hinged doors in the bottom of the bins, the OAs falling onto each of the four separate belts beneath the bins. At the same time each of the other multiples of that row, also discharge the OAs onto the belt beneath the machine. This means that all mail sorted for the four locations is discharged onto the belts at the one time.

The opening of the bins is arranged by energising the latch magnets, lifting the latches and withdrawing the operating rods at the side of the machine allowing the bin doors to fall open and the contents to drop onto the clearing conveyors which are running at a speed of 380 feet per minute. After 4.5 seconds the operating rod is restored closing the bin doors. The other bin doors open at 18 second intervals, each of the rows of bins discharging in turn. Thus the clearing cycle for the machine is 108 seconds (6 rows x 18 seconds). Mail on the clearing belts was fed to floors below by means of spiral fibre glass chutes and then onto sloping conveyors (37° to the horizontal). The OAs discharged from the sloping belt conveyor into hoppers appropriate to their destination.

Approximately 15 of these machines were in operation in Australia during the early to mid 1970s. With the establishment of the decentralised mail network with new mail centres being built on a single floor operation, this type of sorting machine was not suited for that type of operation. There were several problems with this type of equipment. First while sorting staff were instructed not to place large articles in the bins, such articles found their way into the bins causing jams and missorts. Sometimes a Mail Officer bent a large letter to ensure it fell through the bottom of the bin onto the conveyor below, that large letter often fell at an angle across the conveyor and caused jams or temporary delays on the clearing belt resulting in missorts. Second the conveyor runs to the discharge hoppers on the floors below the equipment were often long and any slippage on the belt often causing articles to miss the correct drop panel when it was operated, again resulting in missorts.

The sorting or throughput capacity of the OA machine installed at Redfern Mail Exchange in 1966 was 25,000 OAs per hour with the machine staffed with 36 sorters.

Extracted from “A History of the Development of Mechanisation in Australia Post” by T R Pickering, Retired Manager Engineering, AP HQ