1. Microwave generator(15 to 75kW),
2. Microwave Tunnel(designed to suit both 20kg and 30kg blocks),
3. Entry conveyor,
4. Weigh Conveyor,
5. Exit conveyor
6. User interface and controls.

Operation

Frozen blocks (20kg or 30kg) are loaded manually onto the entry conveyor, which can hold up to 20 blocks at any time. Each block is then indexed automatically to the weigh conveyor where the weight is used to determine the microwave heating time and power level.

After weighing, the block is then automatically moved into the tunnel and is heated to the required temperature. On completion of the heating cycle, the block is ejected from the tunnel onto the exit conveyor ready for further processing. Frozen block handling functions are controlled by the use of standard industrial photo electric sensors.

The microwave generator provides the electromagnetic energy and houses most of the control devices associated with the system. Microwaves produced inside the generator are propagated along the wave guide and then into the cavity. Energy entering the cavity is then absorbed deep into the frozen block causing an even increase in temperature.

Block temperature is determined by the level of microwave power(kW) and the heating time(sec). The maximum power is dependant on the system size and is easily controlled from the front panel by adjusting the knob labeled "POWER".

The heating time is a function of the block weight and can be scaled by adjusting the heating time multiplier (MUL).

Heating Time(sec) = block weight(kg)x(MUL)

Generator

The generator is a stand alone device containing the magnetron, power supply, circulator and all control functions associated with the system operation. The generator can be located up to 30m away from the tunnel and is linked to the tunnel by wave guide and multi-core cable.

Technical Data:

Microwave power 10 to 75kW
Motors/controls/fans 5kW
Sources 1 off @ 10 to 75kW
Frequency 915MHz +/- 10MHz
Circulator/dummy load YES
Supply voltage 380V
Cooling water required(distilled) up to 20 l/min
Cabinet Stainless steel(304L)
Wave guide linking cavity(7m) Stainless steel(304L)
Tempering tunnel(3m x 1.1m x 0.9m) Stainless steel(304L)

Controls

All system control functions such as heating time, cycle startup and meter readings are located on an easily accessible operator friendly control panel. The control panel includes;
- key switch
- start button
- stop button
- run light
- power control(5 - 75kW)
- heat time multiplier
- E/stop
- fault indication

The system will also include a remote panel from which machine operation can be controlled.

The system uses an Allen-Bradley PLC(SLC 500 series) with a RS Linx communication package allowing seamless connection to PLC's via direct or modem connection. RS Linx will also allow remote program modification or fault finding with a minimum of effort or disruption.

Safety

In order to ensure operator safety, each door frame is fitted with a microwave choke ensuring international occupational safety limits for leakage radiation are maintained. The system complies with Australian standard AS2772.1 -1998 "Maximum Exposure levels - 100kHz to 300GHz " and the European Committee for Electromechanical Standardisation(CENELEC) pre-standard ENV 50166-2

Machine safety is maintained by the following safety circuits and appear as fault indicators on the front panel;

- AIR monitors the flow of cooling air to the magnetron,
- WATER monitors the flow and temperature of cooling water to the magnetron
- DOORS microwaves disabled unless both doors are closed,
- E/STOP will illuminate if emergency stop is activated,
- ARC DETECT detects internal magnetron or inverter arcing,
- CONT FAULT indicates a problem within the inverters,
- P.S TEMP indicates an over temperature condition within the generator,
- AUX indicates smoke detected within the cavity,

Tunnel

The tunnel is capable of accommodating 2off 30kg blocks. The conveyor inside the cavity will oscillate the block during the tempering cycle to ensure heating is homogeneous throughout. Temperature uniformity is further improved by equally distributing the available power through up to four input ports.

Conveyors

The system comprises three external Polyethylene conveyors(entry, weigh and exit) individual motor gearbox drives per conveyor.