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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)
• Electricity
• 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:

1. Tumbling Work Conveyor
2. Mesh Belt Conveyor
3. Rotating Table
4. Roll Conveyor
5. Hook Type Machine
6. 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.

 

This question is one of the most frequently asked by operators of batch type cleaning machines, most commonly called a “tumble blast” or “barrel blast” machine, of which there are probably more in operation than any other style of blast cleaning machine in the market.

Tumble blast machines employ either an endless rubber belt or a metal slat and chain conveyor as the main carrier of the components being cleaned. If the sidewalls of the machine were see-through, the upper portion of the conveyor would appear in roughly the shape of the letter “J”, with the rounded area of the “J” serving as the cradle in which the materials being processed are contained during the cycle. The “J” is formed into a closed loop by a three point conveyor support arrangement, combined with the continuous belt or chain.

The two sides of this endless conveyor are closed off and supported by round plates, commonly referred to as barrel heads or drum end plates, which rotate along with the slow moving conveyor.

So, going back to the question, how does a machine operator know if this type of machine is “Full”, or being filled with parts to a correct level? To determine where the “Full Load” line is, the easiest and most reliable way is to form an imaginary line along the face of either barrel head, with the ends of the line located at the those points where the belt/chain conveyor first makes contact with the barrel head, and up to the point where the conveyor leaves contact with the barrel head to follow its return path. Note that this line will generally not exactly bisect the barrel head in half, but will split it approximately 60/40. This 40% side is the lower side and is the area which the parts being processed will nest when the conveyor is motionless. A “Full Load” approaches this imaginary line but does not cross it.

If the quantity of parts is too great, then when the conveyor is moving and the parts are tumbling, the parts will fall or climb outside of this line. Conversely, when there are not enough parts loaded in the machine, the tumbling action (if the parts are even tumbling) will not move the parts even close to the imaginary line.

A machine operated with excessive batch loads will have problems, and so too will a machine that is routinely operated with less than full loads. An overloaded machine will suffer from parts getting trapped or jammed in the “wedges” created where the conveyor engages the barrel head in the front portion of the machine, which can either cause a rubber belt to tear or cause a chain link to crack or worse– break. The machine operated with less than full loads will also suffer increased wear on the conveyor parts and barrel heads due to exposed surfaces, and it is also likely that insufficient tumbling of a small batch load will result in parts not being completely processed in one cycle, necessitating reblast and increasing process costs.

Keep in mind that most rubber belt conveyor tumble blast machines have a weight restriction, so a combination of quantity plus weight is required data to calculate what comprises a “Full Load”. Most machines equipped with a slat and chain conveyor are not weight restricted, or have a much higher density limit, so volume is usually the key determinant in the calculation.

Keep costs down and machine operation optimum by running “Full Loads” in your tumble blast machine!

 

If your operation is using a centrifugal blast machine for surface cleaning or shot peening, you owe it to yourself to consider using cut wire shot for surface prep applications. Based on the finish required from your shot blast operation, you can choose several different types of abrasive media to achieve your desired result.

The most common abrasive is cast steel shot due to its low initial cost. Alternatives to cast steel shot include cut wire shot and stainless steel cut wire shot.  Cut wire shot provides a longer cycle life and decreased breakdown rates which result in fewer replenishment orders, but the price is higher. Higher priced still is stainless steel cut wire shot, which provides an even longer cycle life and produces excellent results due to its strength and uniformity in cleaning. In applications where ferrous contamination is prohibited, stainless steel cut wire shot is your best choice.  Even though cast shot has a much lower price point than cut wire, cut wire will last significantly longer while providing additional benefits, and might be the best choice for your operation.

Advantages of Cut Wire for Blast Cleaning:

• Longer Life
  Two to six times longer cycle life than cast steel shot.
• Cleaner Environment
  Primarily dustless for cleaner blasting operations
• Better Results:
  Uniformity and strength yield excellent results
• Replace Less Often
  Longer lifespan means less inventory to truck in and maintain

Lifespan Gains

Cast steel shot, typically used as the abrasive media in pass through machines, tumble blast machines, spinner hanger machines, reduction descalers, and table blast machine lasts an average of 800 cycles before breaking down and having to be replenished. Cut wire shot, on the other hand, typically lasts 3,000 to 4,000 cycles – and stainless steel cut wire lasts even longer, up to 11,000 cycles – before needing to be replenished.

Productivity Gains

From the perspective of increasing productivity, cut wire shot flows through blast machines better and rounds off nicely over time. This efficiency of throughput can actually improve the operation of your machine over time. Extending the lifespan of capital equipment like tumble blast machines, spinner hanger machines, production descalers and table blast machines represents a real cost savings.

Replenishment Efficiencies

More cycles means less shot to order, ship and handle.  The final landed cost of your shot includes the man-hours spent ordering, shipping, off-loading, inventorying and refilling your blast equipment.  Abrasive cost per cycle combined with carry out loses is what ultimately allows you to determine if the switch from cast steel shot to cut wire is the right financial decision.

Maintenance Savings

There is also a gain to be realized in machine maintenance costs. Cut wire shot particles don’t fracture, producing less dust resulting in less filters to order, lowering your operations costs as well as a creating a cleaner work environment.

Explore the Options

More than just the initial cost should be considered when choosing your abrasive media.  While the initial cost per pound of cast steel shot is less than half the cost of cut wire, the increased volume needed to compensate for the shorter cycle life results in a leveling out effect of the total cost over time. Consider the extended cycle times, improved machine operation, decreased maintenance and lower shipping costs and you may realize that you could gain a lot by using shot with a higher initial cost.  Let us help you decide:  contact us online, or call 860-668-1050. We’ll give you a customized assessment of your operation’s unique needs.

 

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Cut Stainless Wire – The Right Solution

Recently MetFin was contacted by one of our customers to help them meet a new quality standard for cleanliness on their heat exchanger equipment. They had been using a S170 cast steel shot for years to achieve the desired surface profile but meeting the new quality standard was proving to be difficult.  MetFin recommended a stainless steel cut wire. Switching from the cast steel to stainless cut wire proved to be a relatively easy transition. Once the old shot was removed and the new stainless steel cut wire loaded, the machine was started up with no other adjustments.  While the customer’s motivation had been reducing dust and improving cleanliness to meet the new specification, other benefits quickly became apparent.