Assembly of counter-balance weight of hermetic reciprocating compressor for refrigeration

The assembling process can be divided into two main stages: In the first stage, the sub-assembly of the balancing weight. This involves joining the Crank Weight to the Crank Weight Base by resistance welding. The next stage is to assemble the counter-balance weight to the crankshaft eccentric. The details of the two assembly stages are as follows:

Stage One: Sub-Assembly Process
During the sub-assembly process, the required Crank Weight is welded onto the Crank Weight Base using a resistance-welding machine. Basically, it consists of a jig, a clamp, and two electrodes. Some safety features have also been built into the machine to ensure the safety of the operator.

During operation, the operator will place the required Crank Weight Base onto the jig with the dimples facing upward. The Crank Weight Base will be resting on top of the lower electrode. The correct Crank weight is then placed on top of the Crank Weight Base. By pressing the two “Start” buttons with both hands, the clamp will push the Crank Weight and Crank Weight Base against the jig to align the two parts together. This is followed by the upper electrode moving down to press on the two parts. At this point, high current of about 13kA will flow through the two electrodes, causing the contacts between the Crank Weight and the Crank Weight Base to melt and fuse together. The upper electrode will then retract back, followed by the clamp, and the counter-balance weight is then removed from the jig. The part is now ready for assembly onto the crankshaft.

The sub-assembly process is normally carried out in stand-alone stations to provide the parts required for the main assembly line.

Stage Two: Main Assembly Process
In the main assembly process, the counter-balance weight is assembled onto the crankshaft eccentric by shrink fitting. The equipment used for the shrink fitting process consists of a heater coil, a jig and a timer.

During operation, the operator will place the counter-balance weight onto the jig, which is just above the heater coil. By pressing the “Start’ button, the current will flow through the coil, causing the temperature to rise quickly. This will in turn heat up the counter-balance weight, causing it to expand. After about 3 seconds, the siren will be activated, and the current to the heater coil will be cut off. The operator will then transfer the heated counter-balance weight onto the crankshaft in the main assembly line using a plier and to align the notched portion of the counter-balance weight to the marking on the crankshaft. A punch will then be activated to press on the counter-balance weight against the crankshaft. This will provide good sitting of the balancing weight onto the crankshaft and at the same time helps to cool the counter-balance weight faster by heat transfer.