A common mistake that many blasters make is to consider the cost of abrasive media only in calculating the cost of blasting. There are a number of cost factors to consider – including some that are not as obvious in calculating the true cost. Even when some blasters do consider all the relevant factors, they sometimes consider each cost independently. What may be ignored is the interplay of the various cost factors.
Abrasive Media cost:
This is the most visible cost and many blasters focus mainly on reducing this cost. However, a cheaper abrasive can result into an increase in other costs such as follows:
a. A softer abrasive may result in longer time to blast and increased labour and equipment running cost
b. A dustier abrasive may result in poor visibility and a poor finish requiring remediation. If a coating is applied on a poorly prepared surface, it would result in an even higher cost.
c. Use of more abrasive media even if it is cheaper also results in more disposal costs.
d. A cheaper media may not be as clean and the dustier environment may result in compromised operator vision, accidents and workplace safety and environmental fines.
e. Many blasters make the error of using coarse abrasive when a finer abrasive can provide better results. A finer abrasive will have more impact per unit of volume. The more particles in the stream, the more of the surface can be blasted at the same time. For instance, instead of using a hard, expensive abrasive, or a coarse particle, crushed glass can be a good choice for work on relatively soft surfaces such as concrete or wood. Refer to the article on How to Choose the Right Abrasive Blast Media for more details.
f. The cost of abrasive media should be the purchase cost inclusive of all freight, warehousing and delivery to the job site.
The key to achieving a lasting coating for any application is to choose the right abrasive depending on the surface being blasted and the surface profile desired. With the right abrasive, one can get the job done faster, minimise the volume of abrasive used and maximise the profits.
Abrasive Flow Rate:
- Use the optimal amount of abrasive flow required to achieve the desired surface profile on the substrate. An excessive flow results in waste of media and a lower flow fails to achieve the desired profile and wastes labour and equipment time.
- Use the right equipment that allows you to vary and fine tune the flow precisely to the required level.
- Calculate the flow rate as the amount of media used per hour of continuous blasting.
Cost of disposal of used abrasive:
An often ignored cost component is the cost of disposal of used blast media.
Calculate the cost of disposal to include the disposal costs including dumping fees, taxes, labour to pack, freight and packing.
The labour cost is the hourly rate of the blaster+ a proportion of wage overheads (meal breaks, leave, training and non-productive time) + direct supervision time.
Equipment Running Cost:
Factor the cost of owning and running the equipment – (blast equipment, compressor, vehicle), rental, maintenance depreciation and running costs including consumables such as fuel, rust inhibitor.
Square Metres Blasted Per Hour:
The number of square metres blasted per hour depends on a number of different factors such as the thickness and type of coating, the substrate being blasted, surface profile required, operator experience. In general, a thicker coating or corrosion will take longer to remove and a substrate with multiple levels, grooves (eg – a car) will take longer than a flat surface (eg. Industrial steel). Base the flow rate on a physical inspection of the substrate, the thickness of the coating, surface profile required and past experience of flow rates using the same equipment on similar surfaces to remove similar level of coating/corrosion.
Use the following formula for calculating the TOTAL cost of blasting.
Quantum Total Cost of Blasting Per Square Metre =
Stated as = (D+E)/F + (B+C) x (A/F)
This is your direct cost of blasting. Add an appropriate level of mark-up to cover the administrative and selling and marketing overheads. Include additional travel costs required to be incurred for the job.
Finally, add an appropriate level of margin to your cost to calculate the charge out rate per square metre to quote to the customer. Compare it with charge out rates offered by the competition to ensure that you are competitive and arrive at the optimal charge out rate.