To prevent them from toppling over during digging, transporting earth and raising or lowering the bucket, excavators need to be fitted with a counter weight at their back that balances out the forces.
Typically, these counter weights are made of cast iron. Cast iron offers a number of advantages over other materials, such as concrete: Higher density, less fragile than concrete, made by casting so that even complicated shapes are easy to produce.
Even though cast iron is a strong and very long-lasting material, high degrees of wear and tear common in the construction industry do take their toll over time.
A large provider or construction rental equipment contacted QuantiServ about repairing a cracked counter weight on a relatively large, USA-made excavator.
An inspection showed the presence of three individual cracks with a combined length of 750 mm. Why the counter weight was suffering from cracks is not entirely clear. One or more collisions with an object during tail swing, or latent stresses in the casting might be possible explanations.
It was in any case apparent, that unsuccessful attempts had been made to repair two of the cracks by arc welding. It is very hard to weld cast iron. Most attempts fail, especially if the repair is attempted under site working conditions.
At QuantiServ we always repair cast iron by metal stitching, which is a cold process and which results in a repair that is always as strong as the original part, and often stronger.
The failed welding meant that we had to spend more time and effort during the metal stitching than would normally be required. We estimate that it took about twenty additional working hours to deal with the damage caused by the arc welding.
We charged the customer a total of USD 15’000 for the repair, including traveling and accommodation costs. The retail sales price of a new counter weight was USD 36’850, meaning that the customer’s insurance company saved USD 21’850 by having it repaired rather than replaced.
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