No single bag or item can weigh more than 32kg. If you have a checked-baggage allowance of 35kg or 40kg your baggage must be split over at least two bags, with no bag weighing more than 32kg.
If any single bag or item weighs more than 32kg it must be carried as freight. See Qantas freight for freight options. The 32kg limit does not apply to electric wheelchairs and scooters, which may be checked in regardless of weight and will not incur any additional baggage weight or handling fee.