This literally is, in many cases, the illusive $64,000 question! But in reality, it’s not all that difficult to generally estimate the operating costs of a typical machine. You just have to know how, and MetFin wants to be your source for this kind of important knowledge.
The overarching principle of this exercise is to keep the calculation simple and also to think in the long term versus any brief time period. The second basic principle is to establish an “operating savings account” for blast machine costs, where funds are accrued on an hourly basis but may not be spent for several months or years. If you have a personal Health Savings Account, then it’s very similar and uses the same principle.
Nearly all shot blast machines have the following Operating Cost Components:
- Blast Wheel(s)
- Abrasive Handling and Recirculation Systems
- Dust Collection Systems
- Work Conveyor/ Material Handling Systems
- Blasting Media (Abrasive)
- Compressed Air
To keep this exercise simple, assign a “cost value” to each of the components as follows (again, keep in mind this is a long term cost model, not a pinpoint or snapshot calculation):
Blast Wheel(s) – Use a value of $1.50 per blast wheel, per blast hour, for the average process. Why “per blast hour” you ask? Because the blast wheel is not a significant cost item if it’s not throwing abrasive. Most machines have an hour meter that shows total blast hours (i.e. when abrasive is being fed to the blast wheel or wheels). If your operation is a foundry or other process where high concentrations of debris can be mixed in with the abrasive, then you may elect to increase this average amount to $1.75 or even $2.00 per blast wheel per blast hour. Again, this is a long term averaging calculation, so it can be adjusted a few years from now if you see your “savings account” is either too full of accrued monies or starving for money.
Abrasive Handling and Recirculation Systems -These components sometimes are running even though no abrasive is being thrown, so for estimating purposes, assign a cost value of $1.00 for each hour the machine is available for production. If you want to get a bit more precise on this then install a time meter that runs when the abrasive reclaim elevator runs. If your machine is equipped with 3 or more blast wheels, then consider increasing this accrual amount to $2.00 per available operating hour.
Dust Collection Systems – Commonly referred to as the “lungs of the system”, the dust collector often runs all day long whether the blast machine is running or not. To keep your operating costs in check and conserve energy, we recommend that the dust collection system be tied into the abrasive handling system so they both come on and go off at the same time. If your collector uses standard filters, accrue $1.25 per operating hour to cover the maintenance expense. If you have a more unique collection system, then consider increasing the amount to $1.50 or $1.75 per operating hour.
Work Conveyor/Material Handling Systems – This is a difficult component to estimate costs for since there are a multitude of different material handling methods employed on shot blast machines. In our quest to keep the calculations simple, consider using the following broad categories or types of machines:
- Tumbling Work Conveyor
- Mesh Belt Conveyor
- Rotating Table
- Roll Conveyor
- Hook Type Machine
- Pass Through Monorail
For handling types 1, 2, or 3 use an average hourly accrual amount of $2.00 and for types 4, 5, or 6 use $1.50.
Blasting Media (Abrasive) – The range of blasting medias used in airless shot blast machines is very broad, and the cost range is also broad. For illustration purposes, we’ll consider an application where standard steel shot is used and the machine is equipped with two blast wheels, each driven by a 15 HP motor. Assume the steel shot has a cost value of $.60 per pound, including inbound shipping cost.
For general estimating purposes, the typical blast cleaning process will consume 0.4 pounds of abrasive per wheel drive motor horsepower, per blast hour (through natural degradation, carry-out, leaks or other). Some machines or processes consume more abrasive and some less. To get a handle on the estimating process, start here and adjust as needed to arrive at an estimate value that mirrors actual results over time.
To generate the calculation, multiply the three values noted above (30 HP x 0.4 lbs. x $.60 per lb.) to get to the cost per operating hour. In our example, the cost component representing blast media is $7.20 per blast hour (12 pounds consumed x $.60 per pound).
Electricity – Probably the easiest cost component to calculate. Total up the horsepower of all the motors on the equipment, multiply by 0.7355, and the result is Kilowatts. Look at an electric bill to get the average cost per kWh (Kilowatt Hour), and then multiply the two components to get the electricity cost per blast hour. For the time period when blasting is not in process (the machine is powered up but abrasive is not being fed to the wheels), use a factor of 25% of the calculated rate. Chart your Blast Hours per Production Day for a few weeks to get an average, and don’t be surprised if the actual Blast Hours rate is less than 50% of the available production time per day.
Compressed Air – Airless shot blast machines consume such a minimal amount of compressed air that it rarely is practical or necessary to develop a cost component for this utility. However, if your machine has a dedicated compressor, then you’ll have to treat it as a part of the machine and assign an hourly cost value. Best bet would be to work with your compressor supplier to come up with this value.
The MetFin team wants to be YOUR SOURCE for helpful information, new equipment, repair parts, service and technical expertise when it comes to blast cleaning equipment! Find us on the web at www.metfin.com or call us at 1-800-537-8966.