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Lesson 5 - Overall cost performance

The wear part and repair costs

The overall costs of a bucket can be split up as follows:
  • Purchase price
  • Wear part and repair costs
  • Downtime cost
High-quality steels cost more, but give longer life and thus usually a lower total cost. The following examples are based on calculated maintenance costs for buckets for machines in the 32 tons (70,000 lb) size class (as Volvo L220E). The total cost for bucket maintenance is compared for some buckets with different degrees of wear protections and different steel grades of the wear parts. We have studied the wear part cost and repair cost during 10,000 service hours. Three different loading situations are included: round gravel, limestone and granite loading.  
  • We compare various bucket alternatives with a reference bucket.
  • The reference bucket is a new, equipped bucket with HARDOX 500 base edge and HARDOX 500 bolt-on-edge or segments (marked with red text).
  • The total wear part cost and repair cost is related to the purchase price of the reference bucket. The purchase price is set to Cost Index = 100%.
  • By multiplying the resulting Cost Index with the purchase price of the reference bucket, you get an indication of the total wear part and repair cost in real money.

Costs and service life are based on field tests conducted by Volvo Wheel Loaders AB. Comparisons with other materials have been performed using the software WearCalc by SSAB Oxelösund. Cost index = Total wear part and repair cost divided with the purchase price of the reference bucket, as percentage. Relative cost = The Cost index of one alternative, divided with the Cost index of the reference bucket. 


Results for round gravel

For round gravel, a bucket without (grey area) or with bolt-on edge (yellow area) was tested with three steel grades (T1, HARDOX 400 and HARDOX 500):

 
BucketAbrasive
material		Base edge
steel		Bolt-on edge
steel		Cost IndexRelative costRepair days
G-3-0GravelT1 (320 HBW)No345%2.9716
G-4-0GravelHARDOX 400No270%2.3312
G-5-0GravelHARDOX 500No158%1.366
G-3-4GravelT1 (320 HBW)HARDOX 400199%1.722
G-4-4GravelHARDOX 400HARDOX 400185%1.591
G-5-5GravelHARDOX 500HARDOX 500116%1.000

The G-5-5 bucket (with HARDOX 500 base edge and HARDOX 500 bolt-on edge, and market with red text) has the lowest total wear part and repair cost. By "saving" the use of the bolt-on edge, the total wear parts and repair cost would be 36% higher!  Furthermore, the number of repair days are considerably lower. Costs during the down time (as loss of income, secondary costs etc) is not included in the Cost Index. To take down time costs into account, multiply the down time costs per day with the number of repair days.


Results for limestone


For limestone, a bucket with teeth (grey area) or with teeth and segments (yellow area) was tested with three steel grades (T1, HARDOX 400 and HARDOX 500):

 


BucketAbrasive
material		Base edge
steel		Segments
steel		Cost IndexRelative costRepair days
L-3-0LimestoneT1 (320 HBW)No408%1.4420
L-4-0LimestoneHARDOX 400No362%1.2814
L-5-0LimestoneHARDOX 500No301%1.068
L-3-4LimestoneT1 (320 HBW)HARDOX 400387%1.378
L-4-4LimestoneHARDOX 400HARDOX 400374%1.326
L-5-5LimestoneHARDOX 500HARDOX 500283%1.002

 
The L-5-5 bucket (with HARDOX 500 base edge and HARDOX 500 segments, and market with red text) has the lowest wear part and repair cost. For limestone, the dominant costs are the costs for wear parts and repair (almost 3 times the purchase price). Furthermore, the number of repair days are considerably lower for the reference alternative with HARDOX 500 cutting edge and HARDOX 500 segments.



Results for granite

For granite, a bucket with teeth (grey area) or with teeth and segments (yellow area) was tested with three steel grades (T1, HARDOX 400 and HARDOX 500):


BucketAbrasive
material		Base edge
steel		Segments
steel		Cost IndexRelative costRepair days
R-3-0GraniteT1 (320 HBW)No1232%2.0866
R-4-0GraniteHARDOX 400No1012%1.7148
R-5-0GraniteHARDOX 500No717%1.2126
R-3-4GraniteT1 (320 HBW)HARDOX 400877%1.4822
R-4-4GraniteHARDOX 400HARDOX 400801%1.3616
R-5-5GraniteHARDOX 500HARDOX 500591%1.0010



The R-5-5 bucket (with HARDOX 500 base edge and HARDOX 500 segments, and market with red text) has the lowest life-cycle cost. For granite, the dominant costs are the costs for wear parts and repair (about 6 times the purchase price). Furthermore, the number of repair days are estimated to 10 days. This is considerably lower than the 26 days for the bucket alternative without segments. A total cost difference of 21% is also found.

Comparison between limestone and granite

Wear of different rock types varies on the same bucket type. For the bucket with HARDOX 500 in the base edge,  with or without segments of HARDOX 500, for the limestone (L) and granite (R), we get a large difference: 


 
BucketCost indexRelative costDown time days
L-5-0301%1.068
R-5-0717%2.5326

BucketCost indexRelative costDown time days
L-5-5283%1.002
R-5-5591%2.0910

Granite loading costs about twice as much as limestone loading.
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