A: A high-quality blast room is a large capital expense. Failure to give it basic care will severely shorten the life of this major investment. The company from which you purchased your blast room will most likely provide you with a full maintenance schedule broken into what needs to be done each day, week, month, and year. And while those instructions should serve as your guide for blast room care, here are seven items that should go right to the top of the list.

1. Filters: replace, don’t clean

Cartridge dust collector filters are self-cleaning; therefore, you should not send them out to be cleaned. Dust collectors are designed to blow air on filters, which knocks off caked-on dust from the filters while in operation.

Of course, at some point, the filters get sufficiently clogged that they no longer function properly. Plenty of companies will clean them, but the process degrades and weakens the filter material — just like clothes in a washing machine. At this point, you should get new filters, not clean the dirty ones. New filters are relatively inexpensive and will obviously be in better condition than ones that have been subject to the wear and tear of the cleaning process.

Because the filter material has been degraded, the vacuum from the reclaim system may punch a hole in it, causing the collector to suck dust straight into the mechanism. So while you may save a few dollars cleaning your filters, you’ll pay on the other end when you need to buy a new blower.

2. Don’t skimp on filter quality

Blast room owners often will shop around for the lowest price on filters but, as the saying goes, you get what you pay for. Not only are the cheaper filters made of a lower-quality material that wears quickly, they will generally have a lower MERV Rating (Minimum Efficiency Reporting Values).

MERV ratings signify an air filter’s effectiveness at reducing airborne particles and contaminants. The higher the ratings, the more effective a filter is at capturing smaller airborne particulates. So a filter with a lower rating will allow small-micron items to pass through undeterred.

3. Protect your blasting equipment

You’ve seen what abrasive blasting can do to the parts you process. Now, consider: That same media is running through your blasting equipment —what do you think it’s doing? Everywhere your media travels, every piece of material that it touches in your blasting operation is subject to the same abrasive effects as the items you’re blasting. The hose and the nozzle are especially susceptible to this wear and tear, but there really is no part of the equipment that doesn’t feel the wrath.

Because the dust from the abrasive media is traveling through the ductwork at an incredibly high velocity, it should be thicker than regular HVAC ductwork. (We recommend lining the ductwork with rubber to minimize erosion.)

4. Practice good housekeeping

Blast rooms are often viewed as filthy beasts that ultimately spread dirt and dust throughout a facility. They are dirty, but usually just on the inside. The real mess is caused by people who don’t practice good housekeeping.

• Often, workers will open the doors to the blast room while the dust is still floating around. A good rule of thumb is to wait 30 seconds to a minute after blasting to allow the dust to settle before opening the doors.
• Sometimes, forklifts are required to move parts or blasting media into the room. The forklift ends up accumulating grease on its tires, driving back into the shop, then repeating the process.
• Blast workers sometimes drag the hose out of the room, bringing the media with them.
•  Depending on the blast room configuration, workers might be loading media into a hopper that’s situated outside the room. It’s inevitable that some of that media can end up scattered on the facility floor.

Here are two pieces of simple advice that can go a long way toward keeping the area surrounding the blast room spotless (almost): 1: Ask those workers doing the blasting to be aware of these muck-producing activities and minimize their occurrence through constant vigilance. 2: Be sure workers keep a broom handy so they can sweep any stray media or particulate back into the room when they open the door.

5. Avoid the grind

The augers used in vacuum reclaim systems sit in a kind of trough but don’t actually touch bottom; rather, there’s a hanger bearing that keeps the auger suspended an inch or two in the air. As the media is pushed into the trough, it doesn’t come out until the space between the bottom of the trough and the bottom of the auger is filled. It’s designed this way so that when the auger begins to run, it’s basically working in a bed of media, not sitting flat on the bottom; if it were, the auger would grind right through the trough.

However, if the hanger bearing wears thin and that auger drops down, it will grind into the trough and eat right through the metal at the bottom. Now you’ve gone right through your floor, and all your media will start leaking out. This doesn’t take place overnight; however, if the hanger bearing isn’t checked regularly, it will happen before you know it.  

6. Beware of system overload

Speaking of the vacuum reclaim system, be careful not to dump too much spent media into the trough. These systems are equipped to regulate how much media falls through the trough down to the auger because it’s got to suck it into the cycle, spin it, then suck out the dust and debris. That can only happen at a certain speed.

Unfortunately, workers will sometimes drop a day’s worth of media on top of that auger all at once, after which they try turning it on. Now it won’t work because it’s blocked off; the auger has an incredible amount of steel grit sitting on it, and when you try starting it up with that volume of material, the spring is inevitably going to break at the weakest point.

Besides not overloading the reclaim system, don’t shut the system off while it still has media inside. A few types of blast rooms have their control panels set so they can only perform certain functions after others have been completed, thus avoiding the problem of starting them prematurely.

7. Conduct visual inspections

Make sure there’s no cracked glass in the windows. Also, when checking the windows, examine the seals around the frame, both inside and out, to ensure there are no gaps or crevices. Blast rooms are kept under negative pressure. So if you were to punch a hole in the room, it’s not going to blow material out of the room; it’s going to suck it into that hole, contaminating the blasting process.

Ensure that the glass shields on all the lights are in good shape. (Every now and then you should clean the light lenses so that the room is adequately illuminated.)

Inspect your Personal Protective Equipment (PPE) regularly to ensure everything is working properly: helmets, CO monitors, air supply, etc. It’s a good idea to train your blast room operators to check the equipment themselves since they’re the ones using it. Create a checklist to make inspection simpler and quicker.

About the Author

Photo Credit: Titan Abrasive Systems

Brandon Acker

Brandon Acker is president of Titan Abrasive Systems. Visit titanabrasive.com.

Photo Credit: Swarco Indusferica

In surface engineering, SwarcoBlast glass blasting beads are commonly used for the treatment of materials in injection- and pressure-fed blasting systems. The glass blasting beads are made of lead-free, hardened soda-lime silica glass. The beads are available in different variations and applicable for a variety of tasks. SwarcoBlast also notes that the beads are constantly subject to quality controls. The variations of SwarcoBlast’s glass blasting beads are used for cleaning, deburring, smoothening, the reduction of surface roughness, matting, polishing and shot peening of all sorts of materials.

In addition to the glass beads, SwarcoBlast also has a portfolio of other blasting media. SwarcoBlast glass granulates are mainly used for derusting, descaling and the deburring of metallic materials and woodworking; and are well suited for tasks with high ratios of blasting agent loss. Normal-, high-grade- and blasting corundums, crushed grinding wheels, plastic granulates, corn cob shots and walnut shell granulates complete the SwarcoBlast assortment.

Kennametal Inc. (Pittsburgh, Pa.) recently announced an addition to its portfolio of abrasive blast nozzles for advanced surface preparation: the Blast Ninja. Designed by Oceanit, a Honolulu-based innovation company, the Blast Ninja is said to be a premium nozzle delivering improved productivity and enhanced hearing protection in a military-grade product that is compliant with OSHA guidelines. 

The Blast Ninja reduces air exit velocity while maintaining particle velocity, resulting in a significant reduction in noise production at the source while maintaining blasting production. This proven technology remains Kennametal-manufactured and is now available directly through authorized Kennametal distributors.

The Blast Ninja proprietary technology leverages years of research conducted on jet engine noise reduction and was developed along with the U.S. Air Force Research Laboratory (AFRL) and the U.S. Navy’s Office of Naval Research (ONR). Its patented design also offers enhanced hearing protection. 

• Compared to conventional venturi nozzles (outputting 115dB), the Blast Ninja has up to 17dB quieter noise output. This allows operators for more productive usage time per OSHA guidelines.

• In proper conditions, Blast Ninja can meet OSHA’s noise standard compliance 29 CFR 1910.95 of four hours of exposure.

Kennametal | kennametal.com 

Editor’s Note: This paper is a peer-reviewed and edited version of a presentation delivered at NASF SUR/FIN 2016 in Las Vegas, Nevada on June 6, 2016.  A printable PDF version is available by clicking HERE.

ABSTRACT

Despite conscientious attempts to equilibrate vibratory variables such as bowl amplitude, roll angle, media species, media volume, part loading, process liquid concentration and flow rate, what appear to be identically set-up vibratory bowls will nonetheless finish identical loads of parts in varying time cycles.  Why is this so?   This paper will explore this phenomenon.  Techniques will be introduced that will allow operators to capture operational characteristics that aren't typically apparent.  A formula will then be introduced that will allow operators to apply this new data to calculate the amount of force that the media is actually applying to the parts.  It is the efficiency of the force applied to the parts during vibratory finishing that controls the efficiency and speed of the refinement cycle.

What is vibratory force?

During vibratory bowl processing, the bowl operating channel is converted into a fluidized bed of deburring media.  Vibratory media is the tool that is used to either deburr or polish the parts placed into the machine.

The applied force this media can generate on the parts can be partially predicted using Newton's Second Law, F = ma, where the variable m equates to mass.¹  In this paper m will be considered to be the weight of the media above the part at mid-channel.

The variable a equates to the acceleration of the mass.¹  In other words, an accelerating media mass will apply a greater finishing force to the part surface as compared to a slower moving equivalent weight of media.  The formula F = ma will be incorporated into a new formula that will be introduced later in this paper.  When measurable process variables are inserted into the new formula, a better understanding of efficiency differences between apparently, identically operating vibratory bowls can be calculated.

How is mass m determined?

Figure 1 -  Mass is the weight of the media column above a part at the bottom of the bowl at mid-channel.

Mass is the easiest variable to determine and in this paper, it is considered to be the weight, in pounds, of the media column, above the part at mid-channel, as shown in Fig. 1.

The poundage of mass is affected by:

1. Available depth of the vibe bowl channel
2. Attrition induced media depth reduction
3. Weight density of the media being used

All types of vibratory media are affected by media attrition.  With each passing hour a certain weight percentage of media is lost to frictional abrasion.  It exits the bowl as swarf in the effluent flow stream.^4,5,6  Therefore, microscopically, each individual piece of media decreases in volume every hour.^5,6  Media attrition is most noticeable as a decrease in the height of media in the vibe bowl channel over time.

As the volume of media decreases, so too does the weight in pounds of media above the part at bowl mid-channel, as shown in Fig. 2.

Figure 2 - Image of a vibratory bowl (a) with the proper depth of media present in the bowl channel and (b) where the media depth is too low, caused by attrition.⁶

Figure 2(a) shows a properly loaded vibratory bowl channel.⁶  The channel has an available depth of 10 in. and it contains 10 in. of media at proper loading.  This will allow optimal machine performance relative to media volume. Figure 2(b) shows the same vibe bowl after a prolonged period of running without adding media.  The depth of media now measures just 6 in.  With 4 in. of media lost to attrition, approximately 40% of the media volume is now missing.  As a result, the weight in pounds of media in the column above the part is reduced comparably.  If the reduced poundage of media in Fig. 2(b) is entered into the formula F = ma, then the amount of force F that the column of media above the part can apply is also reduced.  Less applied force means more required time to accomplish the same amount of work.

Table 1 - Media comparison table.

In vibratory finishing the species of media utilized is dependent upon the desired finish requirement for the parts and the speed with which the operation is to be performed (Table 1).^5,6

A high-density, non-abrasive media is typically used for chemically accelerated finishing of hardened steel parts.^5,6  Abrasive ceramic media is generally used for generic part deburring.  Lighter-density, plastic media is used to minimize media impingement damage on metallurgically softer metals such as aluminum, brass, copper and zinc.

Vibratory bowls are sold by their volumetric displacement.  Typically, larger volume machines have deeper channels and will hold more pounds of media.  If we examine a small area at the bottom of the vibe bowl operating channel, a machine with a deep channel will hold a taller column of media mass above that same area.  More media mass means more pounds of media and more mass m.  The larger the mass the more force is applied to a part surface.  As an example, consider a submarine (Fig. 3). The deeper the submarine dives, the more water pressure is applied to its hull, because there are more pounds of water above it.

Figure 3 - (a) A submarine near the surface has little water mass above its hull because the column of water above the submarine is virtually nonexistent; (b) a submarine at depth has significant water mass on its hull because the column of water above it is vast.

Mass rolling velocity

Figure 4 - This is a 45 ft³ vibratory bowl capable of holding 36 ft³ of media.  It has a 25” wide channel.  The vertical roll is 78.5” or the circumference of the 25” diameter circle formed by the media mass in the bowl channel, when properly filled with media.^3,6

Mass rolling velocity can be measured as the distance a part travels per minute of time.  The further the distance traveled per minute of time, the more work that is done in that minute of time because the part is contacted by the media more often.³  Mass movement in the vibratory bowl undergoes two, simultaneous planes of motion; vertical roll and horizontal slide.^3,6  Vertical roll is shown in Fig. 4. 

Vertical roll is the circumference of the circle formed where the width of the channel is the circle diameter.^3,6  A vibratory bowl channel properly loaded with media will generate maximum circumference.  When the media level is low due to attrition, the circle diameter is smaller, its resulting circumference is shorter and so too is the mass rolling distance.  Horizontal slide is the distance required to lap the bowl channel one time (Fig. 5).

Calculation of mass velocity

Using the circumference information just described for vertical roll and horizontal slide, it is possible to calculate mass velocity as the distance parts travel per minute of processing time.  Being able to complete this calculation is important to being able to later calculate the applied media force.

As an example, let us assume that a part placed in the 45 ft³ vibratory bowl makes four vertical rolls per one horizontal lap and that this action is completed in 60 seconds.  This motion is shown in Fig. 7. 

It is possible to calculate the part’s velocity or distance traveled per minute as follows:

Figure 5 - An overhead view of the 45 ft³ vibratory bowl shown in Fig. 4, illustrating the concept of horizontal slide.

Figure 5 shows an imaginary circle bisecting the vibe bowl operating channel.  This circle is the average horizontal distance traveled because half the time parts are on the outside of this line and half the time they are on the inside.  The horizontal distance traveled is calculated to be 157 in.  Combining vertical roll and horizontal slide results in the helical, spiral, mass-motion pattern shown in Fig. 6.

Figure 6 -  The mass helical motion pattern when vertical roll and horizontal slide are combined.⁶

Figure 7 - The helical motion pattern of four vertical rolls per horizontal lap in 60 seconds time.

Projecting Part Contact Area

Figure 8 - Orthographic representation shows the sphere of volume within which the red cylinder rotates along its x, y and z axes.⁶

During vibratory processing, parts will move through and be contacted by the media mass orthographically.⁶  During an orthographic roll, a part, regardless of size and shape, will rotate about its x, y and z axes within a sphere of volume inscribed by its longest, or length, dimension (Fig. 8).  At any one moment in time during vibratory processing, the orthographic rotational alignment of the part relative to its x, y or z axes is random and indiscriminate.  We can assume however, that for the overall duration of the process cycle, its alignment to the media mass will be uniformly distributed relative to its x, y and z axes.

Since media force is applied to an area of the part, the question arises; “What one area of the part is being contacted at any one particular moment in time?”  This is an unknown entity, as we can’t see the momentary alignment of the part within the media mass at any one moment and therefore the area contacted is an indeterminable variable.

It is possible however, to calculate a “part’s average area.”  In orthographic rotation for the entire processing cycle, the average area is what will be forcefully contacted by the media at any moment in time.

Illustrative example: Average part area:

Let us assume that the red cylinder in Fig. 8 is a part 8 in. in length, 1 in. in width and 2 in. in height.  Its average area can be determined by volumetric dimensions from the smallest box which envelops it, if it is placed flat on a table as follows:

Average part area calculation

1.  Area length 1:           (2 sides)(2 in.)(8 in.) = 32 in.²

2.  Area length 2:           (2 sides)(1 in.)(8 in.) = 16 in.²

3.  Area of ends: (2 sides)(1 in.)(2 in.) =  4 in.²

4.  Total Part O.D. area =  52 in.²

Therefore, the average contact area at any one time is:

5.  52 in.² ÷ 6 sides = 8.67 in.²

Accordingly, we can say that on average, 8.67 in.² of the part is being forcefully contacted by media at any one moment in time.  This same model for calculating the average surface area of any shaped part can be used.  Simply take the dimensions of the smallest rectangular box that will envelop the part.   

Average surface area assumptions

Note that we must make two assumptions for the average area calculation above.  They are:

1. An ornately configured part will have an exact area that may be somewhat larger or smaller than the area of the box within which it can be contained.  Even though this may be true, using the average area and not the exact area will be sufficient for comparing the efficiencies of identical machines in the vibratory processing room.
2. The volume of the box enveloping the part has four-each, x-axis or length sides.  By taking the average length area of the sum of the two narrow and two wide sides we can determine the average length area exposed to the media when the part is in the x-axis-orientation at the bowl’s mid-channel base.

Effect of centrifugal force

Centrifugal force via centrifugal barrel and centrifugal disc units reduce processing time,⁴ and this equipment is commonly found in finishing departments (Fig. 9).

 Figure 9 - (a) A centrifugal barrel finisher; (b) a centrifugal disc finisher.

In a traditional vibratory bowl, a very slight centrifugal force is generated in the axial portion of the mass (Fig. 10).⁶

Figure 10 - Mass rolling action and location of the axial centrifugal force.⁶

The traditional formula for centrifugal force is given as F = mv²/r.  By taking into consideration the force of gravity on the average surface area of the part by the column of media above it and combining the traditional mechanical engineering force formula of F = ma with the formula for centrifugal force we can generate a new formula that can be used to determine the force being applied to the average surface area of a part during vibratory processing.  The new media contact force formula so created is shown as:

MCF = (m/g)(v²/r),        

where formula variables are:

m = lb. of media column above the average area

g   = gravity, a constant of 32 ft/sec²

v   = part velocity in feet per second

r    = radius of the media mass present

This formula is useful because it allows the vibratory operator to understand more fully how the following variables affect vibratory bowl performance:

1.  Different media having different densities

2.  Varying velocity; fast bowl vs. slow bowl

3.  Different bowls with different channel radii

4.  Attrition induced varying media radii

Determining the MCF variables

There are four variables which must be substituted into the MCF formula to determine media contact force.  They are determined as follows:

m = Mass of media variable

To calculate the pounds of applied media mass above the part, we will use as an example:

1.  The density of HDNA media found in Table 1.

2.  The average part area of the part calculated previously (p. 5).

3.  The 45 ft³ vibratory bowl containing, when properly loaded, 36 ft³ of media (Figs. 4 & 5). 

Figure 11 - The column of media above part average surface area.

The media applies a force equal to the weight in pounds of the column of media above the average surface area of the part.  For this and all subsequent calculations using the MCF formula, it will be assumed that the part is centered at the base of the channel, congruent with the channel bisecting circle (Fig. 11).

Determine the weight in pounds of the media column above the average part surface area:

1.   Weight of mass (lb.)

2.   From Table 1: 1 ft³ HDNA = 125 lb./ft³

3.   Average area of part = 8.67 in.²

4.   Volume of column of media above average part area:

      a. (8.67 in.²)(25 in.)             =  216.75 in.³

      b. 216.75 in.³ ÷ 1,728 in.³/ft³ = 0.125 ft³

5.   Mass = (0.125 ft³)(125 lb./ft³) = 15.63 lb.

V = Velocity of part variable

The part velocity of 471 in./min., as discussed with Fig. 7.  Converting to ft/sec:

1.         471 in/min ÷ [(12 in/ft)(60 sec/min)] = 0.654 ft/sec

Establishing a standard control model for the media contact force calculation

The standard control model for this example or any vibratory room, is the ideally set-up vibratory bowl.  That is, the vibratory bowl that has the optimum velocity, media density and media level for the processing cycles being used.  Substituting the variables just determined into the MCF formula, we will establish a standard control model for this paper.  This model then becomes the standard against which other bowls are compared or the standard against which the bowl itself is compared in the future as operating conditions change.  The MCF formula will be utilized to determine the pounds of media force applied to the average part surface area during finishing.

MCF variables for standard control

1.  45 ft³ bowl: channel diameter of 25 in. = 2.08 ft

2.  Channel radius = 2.08 ft ÷ 2 = 1.04 ft

3.  Gravity = 32 ft/sec²

3.  Mass of applied media = 15.63 lb.

4.  Mass velocity = 0.654 ft/sec

MCF calculations for standard control:

MCF     = (m/g)(v²/r)

            = [15.63 lb. ÷ 32ft/sec²][(0.654 ft/sec)² ÷ 1.04ft]

            = [0.488 lb./ft/sec²][0.428 ft²/sec² ÷ 1.04ft]

            = (0.488 lb./ft/sec²)(0.412 ft/sec²)

MCF     = 0.201 lb. of media contact force

To understand how this is relevant to the performance of similar vibratory bowls in the same vibratory department, let’s now use the MCF to calculate the pounds of applied media force in three comparative examples that are relevant to normal vibratory room operating conditions. 

MCF Example 1: The effect of media attrition

In this example, we assume that the standard control vibratory bowl has changed only in that the volume of media is 2 in. lower due to media attrition.  Vibratory bowls having low media volumes are a typical inefficiency found in most vibratory departments.  All other variables as determined for the standard control bowl situation will remain the same in this example.

The immediate effect of media attrition is that the column of media above the part average surface area is shorter.  In this example, the column is 23 in. tall as compared to 25 in. tall for the standard control situation.

A secondary effect is that the circumference of the vertical rolling circle is shorter because the diameter of the media in the channel is now only 23 in.  How does the loss of just two inches of media depth affect the applied media force on the part?

A media mass diameter of 23 in. means the circumference of the vertical roll has decreased from 78.5 in. to (π)(23 in.) = 72.22 in.  If we assume the same four rolls per lap in 60 seconds noted earlier, the total distance traveled per minute or velocity is reduced from 471 in./min as follows:

1.  Radius of media mass  = 23 in. ÷ 2 = 11.5 in.  = 0.96 ft.

2.  Vertical distance (4)(72.22 in.)                        = 289 in.

3.  Horizontal distance traveled                           = 157 in.

4.  V = Distance per minute                                 = 446 in./min = 37.17 ft/min = 0.62 ft/sec

The shorter column of media above the average surface area of the part decreases the weight in pounds of media above the part, calculated as follows:

1.  Volume = (8.67 in.²)(23 in.) = 199.41 in.³ = 0.115 ft³ media

2.  Weight = (0.115 ft³)(125 lb./ft³) = 14.38 lb.

Example No. 1 MCF calculation: 2 in. media loss by attrition

MCF     = (m/g)(v²/r)

            = [14.38 lb. ÷ 32 ft/sec²][(0.62 ft/sec)² ÷ 0.96 ft]

            = [0.449 lb./ft/sec²][0.38 ft²/sec² ÷ 0.96 ft]

            = (0.449 lb./ft/sec²)(0.40 ft/sec²)

MCF     = 0.180 lb. of media contact force

MCF Example 2: The effect of the density of the media used

In this example, we will assume all variables are equivalent to the standard control vibratory bowl situation, except that, instead of filling the bowl with HDNA media from Table 1, the vibratory bowl has been filled with polyester plastic media at 65 lb./ft³.  How will this change in media density affect the pounds of media contact force on the average surface area of the part? 

The diameter of the media mass remains constant at 25 in.   Therefore, the vertical roll distance remains the same at 78.5 in.  However, the lighter density of the plastic media significantly changes the mass weight in pounds, in the media column above the average surface area of the part:

1.  Volume = (8.67 in.²)(25 in.) = 216.75 in.³ = 0.125 ft³ media

2.  Weight = (0.125 ft³)(65 lb./ft³) = 8.13 lb.

Example No. 2 MCF calculation: lighter density media

MCF     = (m/g)(v²/r)

            = [8.13 lb. ÷ 32 ft/sec²][(0.654 ft/sec)² ÷ 1.04 ft]

            = [0.254 lb./ft/sec²][0.428 ft²/sec² ÷ 1.04 ft]

            = (0.254 lb./ft/sec²)(0.412 ft/sec²)

MCF     = 0.105 lb. of media contact force

MCF Example 3: The effect of a change in mass velocity

In this example, we return to the standard control operating conditions and make one variable change, assuming the four rolls per lap now requires 75 seconds instead of 60 seconds.  This is a typical operational change in a vibratory department that can occur when a new processing run of parts is added to the bowl and the new load of parts weighs more than the original load of parts.  In such instances the vibratory bowl is now moving more weight and as a result the rolling rate of the mass decreases.  How will this change affect the media contact efficiency and therefore the process efficiency of the cycle?

The velocity calculation change is as follows:

1.  Time = 60 sec ÷ 75 sec = 0.80

2.  Velocity = (471 in./min)(0.80) = 377 in./min = 31.42 ft/min = 0.524 ft/sec

Example No. 3 MCF calculation: slower mass velocity

MCF     = (m/g)(v²/r)

            = [15.63 lb. ÷ 32 ft/sec²][(0.524 ft/sec)² ÷ 1.04 ft]

            = [0.488 lb./ft/sec²][0.275 ft²/sec² ÷ 1.04 ft]

            = (0.488 lb./ft/sec²)(0.264 ft/sec²)

MCF     = 0.129 lb. of media contact force

MCF efficiency comparisons: standard control to the three examples

For comparison purposes, you will find the applied media force values for the standard control situation and the three examples just calculated in Table 2. 

Table 2 - MCF efficiency differences.

Assuming that the standard control vibratory bowl scenario has been properly vetted and is the optimum operating condition for all similar-sized vibratory bowls in the vibratory room, performing an MCF calculation on each bowl will show how media contact force varies considerably from bowl-to-bowl.  What were once often-ignored variables can now be utilized to understand performance inefficiencies and assist in increasing room performance.

Discussion of results

When setting up the vibratory department, it is critical to establish the most efficient and therefore optimum operational conditions.  Obviously, this is necessary to ensure that the room is operating at peak efficiency and production throughput can be maximized for consumable cost efficiency.

Within each family of vibratory bowls, as determined by volumetric displacement, will be a set of operational characteristics related to velocity of the mass, depth of media in the channel and density of media used.  When the standard control situation has been established, other bowls having the same volume can be compared to the standard control bowl using the MCF to determine why processing times vary from bowl-to-bowl.

Previously, vibratory bowl operational conditions were noted using an amplitude gauge.  Although useful in capturing the most elemental basics of machine set-up, an amplitude gauge can’t be utilized to determine the performance differences between adjacent machines having varying processing cycle times.  This is an aggravatingly maddening conundrum in situations where the operator is trying to match production cycles and part quality run-after-run in multiple side-by-side machines.  By taking just a few measurements to determine mass velocity and the depth of missing media, MCF calculations can now be applied to adjacent machines of identical volumes to understand their performance differences.

As mentioned previously, loss of media volume due to attrition is the single most commonly found performance degradation characteristic in vibratory bowl finishing.  The MCF in Example 1 showed how significant the loss of just 2 in. of media depth can be in machine performance.  Such a loss is hardly noticed in most vibratory rooms, let alone is it addressed with the timely addition of new media to maintain media level.  Yet the degradation of the machine performance would proceed unchecked, run-after-run, until significantly longer times were noticed.  The use of the MCF can now be used to calculate answers to previous suppositions reflective of efficiency loss.

Likewise, in Example 2, the MCF calculation can be used to see how a change in media density will affect processing efficiency.  There are situations that require the use of lighter or heavier density media.  By using the MCF, it is now possible to predict the lengthening or shortening of the vibratory processing cycle as a consequence. 

If we consider the bowl’s slower rolling speed, as in Example 3, the result of a heavier load of parts being placed into the bowl, in the past the only way to measure the bowl’s operation characteristics was by the use of an amplitude gauge.  But by using MCF it is now possible to understand how the processing time will be lengthened, the result of the slower speed. 

Table 3 - Projected cycle time differences resulting from the three previous examples correlated to 1 hour.

Table 3 allows us to view the projected changes in processing time as a result of the three comparison examples.

Conclusions

Vibratory finishing efficiency is dependent upon several variables that are most definitely synergistically interrelated.  This paper has identified the most critical variables, has described procedures to measure them and has introduced a formula into which the quantitatively measured variables can be substituted to generate qualitatively important performance information. 

This paper has additionally shown how the change of one variable such as media depth is synergistically related to distance travelled and then mass velocity.  Previously, operators may have supposed an interrelationship between the two but were impotent in capturing and quantifying their suppositions.  The introduction of the MCF has given them that tool. 

Optimizing performance in the vibratory room is critical for time and consumable efficiency.  Attention to operational details is important in maintaining this efficiency.  It is now possible to not only understand that these variables exist but to also use them to generate a performance advantage or correct inadequacies where and when possible.  

References

1.  J. Lucas, Live Science Website, Force, Mass & Acceleration: Newton's Second Law of Motion, June, 2014; www.livescience.com/46560-newton-second-law.html .

2.  Naval-Technology.com; Image of U.K. Astute Class, SSN Nuclear Submarine; 2002

3.  W.P. Nebiolo, "An Easily Understood Technique for Measuring Vibratory Bowl Speed and Optimizing Vibratory Bowl Processing Efficiency," Proc. SUR/FIN '07, Cleveland, OH, 2007.

4.  W.P. Nebiolo, "A Comparison of the Advantages and Disadvantage of Assorted Mass Finishing Techniques," Proc. SUR/FIN '09, Louisville, KY, 2009.

5.  W.P. Nebiolo, "Estimating the Total Solids Burden during the Waste Water Treatment of Vibratory Finishing Effluents," Proc. SUR/FIN '11; Rosemont, IL, 2011.

6.  W.P. Nebiolo, REM Training Manual Edition No. 9; REM Chemical, Inc.; Southington, CT; Dec. 30, 2014.

7.  www.subsim.com; website; radio room forum; silent hunter, periscope and antennas fix images.

Footnotes

*Corresponding author:

William P. Nebiolo

REM Surface Engineering

325 West Queen Street

Southington, CT 06489

Phone:   (860) 621-6755

Cell:        (860) 985-3758

E-mail:   wnebiolo@aol.com

About the author

William P. Nebiolo received a B.A. degree from The University of Connecticut and an M.S. degree from Long Island University.  Bill began his metal finishing career at Union Hardware Div. Brunswick Sporting Goods as a plating lab technician.  After 2-years at Eyelet Specialty Co. as a plating foreman, 5-years at Nutmeg Chemical as the laboratory director and 3-years at The Stanley Works Corporate Laboratory as chief electrochemist, Bill accepted a position at REM Chemicals, Inc. in Southington, CT as a sales engineer in 1989.  He remains at REM to this day, currently serving as Sales Engineer for REM's Midwestern Sales Territory and as REM’s Product Manager.

He joined the NASF as a member of the Waterbury Branch of AES in 1978.  Working his way through the branch officers’ chairs, Bill served as Waterbury Branch President 1984-85 and was appointed Branch Secretary in 1991.  Bill spearheaded the merger of the Waterbury, Bridgeport and Hartford Branches into the Connecticut Branch in 2004, then petitioned and was awarded branch certification through AESF National.  Bill was immediately appointed Connecticut Branch Secretary and remains in the role to this day.  He has represented the Connecticut Branch as a NASF National Delegate, has served as a technical chair at several NASF SUR/FIN technical sessions was awarded an NASF National Award of Merit in 2010 and in 2012 was elevated to the position of Connecticut Branch Honorary member.   

To date, Bill has published a dozen papers in assorted technical journals and presented more than 20 papers at technical conferences and seminars.  From 1996-2000 Bill served as one of SME’s Mass Finishing Technical Training Program instructors at more than two dozen training sessions.   Bill is the author of the SME Mass Finishing Training Book and the REM Training Manual, which is now in its 9th edition. 

Norton RazorStar belts are well suited for challenging off-hand and automated grinding applications. Photo Credit: All images Norton | Saint Gobain Abrasives

While creating a shaped grain may be nothing new in the world of abrasives, the optimum shape for that grain has been elusive until recently. A new three-pointed curved grain approach has shown impressive advantages including in tough grinding applications. This grain technology was unveiled by Norton | Saint-Gobain Abrasives as part of its RazorStar coated abrasive line that includes belts, fiber discs and quick-change discs.

Combining razor-sharp grains along with a supersized grinding aid can help significantly reduce heat generation for cooler cuts and longer life on a range of materials such as carbon steel, aluminum, stainless steel, nickel alloys and other hard-to-grind metals.

RazorStar fiber discs, quick-change discs and belts feature engineered shaped ceramic grain to increase grinding performance.

Enabling exceptionally high cut rates and material removal, the engineered shaped grain in Norton RazorStar belts and discs features a consistent shape from grain-to-grain along with razor-sharp cutting points. For long, abrasives life, the patented geometry and tough micro-structure enable the grain to stay sharp, as new cutting points are exposed when the grain fractures. These abrasive products also feature a high concentration of grains that are oriented in an upright position, so the abrasives are ready to cut and aggressively perform at their sharpest point.

This ceramic-based star-shaped grain is designed to improve grinding with coated abrasives across a range of industries. In several instances of tough foundry applications, RazorStar products are able to compete with bonded abrasive wheels for material removal rate (MRR) and overall value. Tests conducted by the Norton Abrasive Process Solutions (APS) team in robotics labs have shown the products to consistently outperform other abrasives because of the combination of several abrasive disciplines such as grain shape, grain application, tough backing and grinding aid.

The APS Program draws upon the experience of the Norton team along with access to 30 different machines, and an APS Robotic Automation Cell located at the Higgins Grinding Technology Center in Northborough, Massachusetts. The APS team provides abrasive process development, optimization, automation and in-house testing. Services encompass the testing and optimization of new abrasives, improving quality and/ or throughput, and exploring new and customized processes.

Application testing

In the Norton APS Robotics Lab, all types of abrasives can be tested head-to-head on the same part. When testing various bonded abrasive wheels against RazorStar belts, even with belt change time considered, part production with the belt performed better, provided additional value because of the improved cut rate, and  in many cases, produced a better final finish.

These height maps show a traditional shaped grain belt (left) vs. RazorStar belt (right). There are more standing grains in the RazorStar belt due to the highly upright orientation.

Steel casting material removal

A foundry customer approached the Norton APS team seeking a more productive solution for removing four pounds of cast steel from a part gate area that they were manually using bonded wheels to accomplish. While the team pursued the use of various high cut bonded wheels, a RazorStar belt was also applied to the test, removing more material in a shorter time frame.

Using a firm serrated rubber contact wheel and running the R990S RazorStar 36+ grit coated abrasive belt at a higher horsepower rate produced a high MRR. While the MRR was enhanced via the additional horsepower, significant MRR was achieved even when the RazorStar belt was run at half of the final selected horsepower. It is significant to note that when running at horsepower ranges near 100, the backing on the belt was able to withstand the pressure and force.

The improved process results from the lab tests resulted in a newly designed automated system incorporating the RazorStar belt. The result for the customer was improved operator safety by removing manual grinding operations from the application, while receiving substantial ROI.

RazorStar belts in an automated setup at the Norton APS Lab.

Cobalt nickel chrome alloy

Another example of grinding performance that can be achieved with RazorStar is demonstrated when grinding cobalt nickel chrome alloy on a robotic backstand grinding machine. The foundry customer had been using a traditional 36+ grit belt for this application. The APS team recommended that the foundry cast part be ground with a 36+ grit ceramic based RazorStar belt at an approximately 50 pounds of pressure setting. In doing so, a substantial cycle time improvement was achieved, leading to a 44% total cost savings per part and an improvement of 30% more parts per belt.

Stainless steel casting gate removal

Heat is the enemy in most grinding operations, and the star-shaped engineered ceramic grain of RazorStar belts produces high MRR on tough metal with less pressure, resulting in less heat. The grain shape in addition to the high percentage of grains that remain upright when cutting provides an advantage, particularly for aerospace, defense and gas turbine manufacturing applications. In a stainless steel (15-5 PM [powder metallurgy]) casting gate removal example, thesebelts removed over 38 grams of material where in the same amount of time other 36+ coated conventional ceramic abrasive belts only removed 18.6 and 15 grams. In addition, the RazorStar belt temperature remained low during the grinding process while high temperatures were observed with the conventional ceramic abrasive products.

3D-printed parts

When asked by an automation integrator to help find the best method to grind rough 3D-printed Inconel parts, Norton determined that using a PushCorp RBS unit for driving a RazorStar belt could minimize heat and achieve an accurate and consistent MRR. With the belt, 0.250 inch to 0.333 inch of the stacked 3D printed material was removed in one to two passes and held to a surface level tolerance of  ±0.065 inch. Ideal for robotic setups, the parts were processed and returned to the customer and their automation integrator, demonstrating that they could successfully build a robot system using a RazorStar belt. 

Steel frame weld elimination with discs 

High-quality results were also achieved when using RazorStar discs for weld removal. In an application driven by the PushCorp spindle motor, a 36+ grit disc left a mid-30 Ra (min) surface finish which was then final finished to 9 Ra using a Norton Vortex Non-Woven Flap disc. This final finish was four times smoother than the customer’s previous two-step method and was completed approximately twice as fast on the thick sheet steel component compared to their previous method.       

Demands for more efficiency and consistency in quality in surface grinding only continue to increase. Engineered shaped ceramic grain abrasive products such as the ones described can provide an edge with fast cutting, smoother finishing and provide many advantages for grinding operations.

David Keller. Photo Credit: Hubbard-Hall

Hubbard-Hall welcomes David Keller as a senior chemist. In this role, Keller will be responsible for product development, evaluating formulations and working with customers on cost savings initiatives.

Keller brings 28 years’ experience in product development, specializing in cleaners used in the aerospace OEM and MRO, and industrial and institutional markets. Most recently, he worked Brulin & Company Inc. as an industrial/process line chemist.

“Hubbard-Hall’s philosophy is that they ‘adopt’ their employees, not just hire them. Well, I was abducted! The way the technical team works side by side with their customers and future customers, coincides with my passion for understanding how things work and finding process improvements,” Keller states.

He earned a bachelor’s degree in chemistry from Lawrence Technological University, and completed coursework and research toward a master’s degree in chemistry from Indiana University. He has been a member of the American Chemical Society since 1995. Keller has also been published in Inorganic Chemistry and contributed to the Handbook for Critical Cleaning and the Handbook for Critical Cleaning — Cleaning Agents and Systems.

Keller will report to Mike Valenti, director of technology, and be based in the Inman, South Carolina facility. “David brings a proven track record in product innovation, manufacturing improvements and customer success. He will be a valuable asset to our customers in our mission to reduce chemistry usage and process complexity,” Valenti says.

Photo Credit: Titan Tool Supply

The Dia-Strip and Dia-Sheet lapping and polishing film from Titan Tool Supply Inc., a supplier of industrial-grade optical instrumentation and precision micro finishing tools, is designed to provide cost-effective, reliable, microfinishing support for a variety of challenging lapping and deburring tasks. Applications include the precision polishing of plastic molds, die cast dies, carbide and ceramics. Dia-Strip and Dia-Sheet film incorporate pure virgin diamond powders in their highest concentrated forms, which the company says enables maximum material strength, durability and performance.

The powders are first graded for uniformity and then held into place by a thin nickel. With this approach, 90% of the grains are left exposed for cutting, yet are unable to escape the film because of the strength of the bonding agent. This construction is said to make Dia-Sheets and Dia-Strips highly durable, yet also flexible, bendable and formable. As a result, Titan Tool Supply says the film can cut virtually any material, including steel, stainless steel, carbide, ceramics, glass, plastics and wood. It is also compatible with EDM surface finishes, which are typically too hard to be touched by most abrasives.

Film is offered with a choice of either 2" × 4" Dia-Sheets or 0.5" × 2" Dia-Strips in thicknesses ranging from 0.003" to 0.019". It is further offered with a choice of six distinctive grits, ranging from coarse 80/100 (0.012" thickness), to superfine 1100 (0.003" thickness). Overall film flexibility and thickness is directly proportional to customer choice of coarseness or grain size.

Titan Tool Supply’s Dia-Strip and Dia-Sheet lapping and polishing film is also said to be highly adaptable to a variety of specialty precision microfinishing applications. The film can be cut to size via the use of scissors or tin snips and is supplied with 3M double-sided industrial tape. As the film backing is completely flat, it can bond onto any material and form the shape needed to create specialty tooling, lapping and deburring wheels. This also makes the film particularly useful within plastic mold and cast die manufacturing applications. These applications typically have precision polishing of thin slots and slits as a finishing requirement, yet the use of traditional polishing stones would be otherwise precluded because they are prone to breakage.

The film is also well suited for precision microfinishing lapping and polishing requirements within space-constrained environments, as well as the lapping of curves, contours or other complex geometries. Additional applications for Dia-Strip and Dia-Sheet film include specialty deburring tools, diamond wheels, specially shaped diamond dressers for aluminum oxide or silicon carbide grinding wheels and stones, specialty hones and sanding discs.

A photo of the entrance to the second facility.
Photo Credit: Miles Chemical

Miles Chemical, a full-line chemical services company, opened a 16,000-square-foot building adjacent to its existing 16,000-square-foot facility in Anaheim, California.

“As a result of the pandemic and supply chain challenges, our customers and suppliers were looking for local supply and finished goods blending,” says Anthony Miles, Miles Chemical president. “With the increase in demand, it made sense to expand our Anaheim operations. It was a bonus to have a building become available right next door. We will now dedicate one building for blending/packaging liquids/dry materials and the other building for distribution warehousing.”

Regardless of the supply chain, many customers have storage limitations. “With transportation costs and lead times increasing, local blending eliminates those variables,” says Mike Miles, CEO. “We will continue to look to enhance our capabilities.” 

For high-efficiency precision metal grinding, the IG 282 SD rotary surface grinder has numerous new features to bring precision, efficiency, and technology to industrial grinding processes. Photo Credits: All photos by DCM Tech

In manufacturing, it is often necessary to grind metals and alloys to certain specifications (i.e., thickness, parallelism, surface condition). However, the process of bringing a stock sheet or plate to precise dimensions has traditionally been time-consuming and labor-intensive. Although today’s automated advanced rotary surface grinders have resolved these issues to speed production dramatically, loading and unloading the workpiece typically still requires an operator.

To fill in this missing piece of the automation process, rotary surface grinders are now available in “robot-ready” versions for easy connection and integration with third party robotic arms. By adding robotics for the loading and unloading of workpieces, machine shops and OEMs with higher production demands can now substantially increase cycle times while improving precision on unattended machines.

“There are many scenarios in which a company can benefit from using robotics in the grinding process. A robotic arm can increase productivity and enable higher volume manufacturing as well as remove the operator from repetitive loading and unloading so they can move to more complex tasks. It can also minimize the handling of sharp, dangerous, or delicate parts,” says Erik Lawson, Engineering Manager at Winona, MN-based DCM Tech, a designer and builder of industrial rotary surface grinders.

DCM Tech IG 282 SD rotary surface grinder

To facilitate the automation of the loading and unloading of its rotary surface grinders, DCM Tech redesigned the IG 82 Series to include discrete digital I/O inputs and outputs for easy connection to virtually any third-party robotic arm. Industrial robotic arms emulate the movements of a human arm using multiple rotary joints that act as axis points. The end of the robotic arm is fitted with a fingerlike gripper, designed to safely manipulate and handle parts. These devices include a controller, actuators, sensors, software, and vision systems, if needed.

Once programmed by the integrator, the robotic arm will load and unload the part, as well as clear away any debris before repeating the process.

“The addition of robotics to our automated rotary surface grinders is a significant step that moves our industry toward providing solutions that are more fully automated,”Lawson says.

By adding robotics for the loading and unloading of workpieces, OEMs and machine shops with higher production demands can substantially increase cycle times while improving precision on unattended machines.

With vertical spindle, rotary table surface grinders, the table rotates with the workpiece held firmly in place underneath a vertical spindle. The grinding is not performed by the peripheral edge of the wheel, but by the entire diameter of the abrasive surface, which facilitates grinding performance and consistency. The surface grinders are designed with advanced sensors and controls that automatically maintain very tight tolerances, removing material down to within one ten-thousandth of an inch of the final thickness.

According to Lawson, the IG 82 series grinders already provide advanced features that minimize or eliminate operator intervention after set-up.

One example is the part detection system, which automates the initial contact between the abrasive wheel and the part. In the past, this typically had to be finessed by the operator. With this updated option, advanced sensor technology detects vibration and can automatically fine-tune not only the pressure of the spindle motor but also how quickly it moves the wheel down onto the part. When the machine senses the abrasive wheel has contacted the part, it automatically begins the grind cycle.

Automatic part detection eliminates the need for the operator to do time- consuming, error-prone ‘manual touch-offs,’ where they would manually feed the grinding machine until it just touches the surface of the part before backing off and restarting it.

To increase production, “the grinders offer three grinding modes: conventional, incremental, and grind to height, which starts aggressively and then becomes increasingly more precise when nearing the desired outcome,” Lawson says. “For greater automation, a continuous grind setting is also available, in which the machine automatically cycles through all three grind settings.”

For high-volume production, it is also necessary to periodically dress the grinding wheel. It is vital to remove grains, clogs, and excess bonding material so the wheel can return to its original surface finish and sharpness. Dressing is also used to help restore the wheel’s shape, which changes with wear. The IG 82 series comes with a programmable auto-dress capability with selectable dress frequency. “This eliminates the need for time-consuming manual dressing and improves production uptime,” Lawson says.

The advanced rotary surface grinders are already much faster than conventional reciprocating grinders because the units can get much closer to the required dimensions before any finishing steps. This capability can reduce or even eliminate some lapping and polishing steps.

With a conventional surface grinder, if stock with standard thickness needed to be ground down, an operator would stop short of the required removal and leave an unpolished surface. Using another machine was often required to remove the remaining material, but this could involve excessive time and labor.

According to Lawson, a rotary surface grinder will usually finish the work of a reciprocating grinder in a fraction of the time. For the manufacture of carbide blocks, one OEM was able to document a 14X improvement in cycle time by replacing a reciprocating grinder with a DCM rotary surface grinder.

Advanced surface grinders like those from DCM Tech are designed with sensors and controls that automatically maintain very tight tolerances, removing material down to within one ten-thousandth of an inch of the final thickness.

In addition, programmable human machine interface (HMI) controls allow operators to enter virtually any requirement into a touch screen at setup. This capability enhances processing flexibility, so it is easy to adjust any grinding factor to prevent an issue from reoccurring.

For routine processes, the use of a variety of grind “recipes” with sets of parameters for specific parts can further speed production, enhance quality, and aid in quick changeover. Different grind recipes can be set for different customers, material types, or even part numbers, so complex programming or data does not need to be entered at the start of each job. A new recipe can be created for job variations, such as a different finish or number of parts.

According to Lawson, the automation already provided by an advanced rotary grinder combined with a robotic arm will allow the operator to set up the machine and then attend to other tasks. The machine does not need to be constantly monitored because it has built-in load monitoring. “Load monitoring allows the user to set limits, so the machine does not overtax the part being ground or overload the spindle. If something a little unusual happens, it can continue without interruption or shutting down,” says Lawson.

As manufacturers and machine shops seek to become more productive and competitive, using robotic arms along with automated grinding systems will increasingly become a best practice technique for high-volume facilities.

Josh Gardner. Photo Credit: Wall Colmonoy

Wall Colmonoy (USA) welcomes Josh Gardner as business development manager for Surfacing Products as part of the Alloy Products Americas’ sales team. Gardner will be responsible for expanding product applications for new and existing surface coating customers. He will work alongside the sales team, performing technical inputs for surfacing and thermal spraying techniques, including laser cladding, plasma transferred arc (PTA), high-velocity oxygen fuel (HVOF) and spray and fuse.

Gardner has over 23 years of experience in thermal spraying, laser cladding, PTA welding, HVOF and sales applications for oil and gas, mining, agriculture and aerospace industries. He has additional experience in training personnel, and designing and installing thermal spray systems.

Gardner earned a bachelor’s degree in computer science from the University of Houston. He has completed additional studies in business and process engineering.