The Finished Part

July 4th BBQ

2008-07-03T07:49:00.003-04:00

Take a look at your wood deck or concrete or stone patio while you are grilling over the weekend. Does the surface need some attention? A few tips to begin the cleaning and restoration process:

Wood Decks -- Dry abrasive blasting with Corn Cob Grit can strip dirt, soils, stains and coatings without damaging the wood or raising the grain. Avoid harder media such as sand (don't ever blast with silica sand anyway) or glass or coal slag as these will definately etch the wood and can cause damage. The main benefit of dry abrasive blasting versus high pressure water is that the dry surface can be re-sealed immediately - a one weekend project instead of two or three.

Concrete or Stone Patios -- Stripping paint off concrete surfaces requires a more aggressive abrasive such as Crushed Glass Grit. Stone which can be softer than concrete might demand Crushed Glass Grit but Walnut Shell Grit may be a better option since it is not as aggressive and stone is easier to clean (typically no paint or coatings to remove).

Final tip -- Enjoy the BBQ first, then start the work!

Aluminum Oxide - Stabilized?

2008-06-23T16:18:00.003-04:00

A couple of months ago I put a post explaining some of the basics of Aluminum Oxide Grit. What I did not mention was that the ore that is used as the source for Aluminum Oxide is sourced from around the world. While a lot of the crude material is actually refined and processed in the US, it still needs to be shipped around the world.

Increasing crude costs mostly due to increased demand from developing countries (read: China) have combined perfectly with increasing shipping costs and the decreasing US dollar to produce price increases like we have never seen. In some cases, the cost to source, ship, refine and package Aluminum Oxide has doubled in the past couple of years.

Fortunately, it seems that some of the cost pressures are stabilizing so that pricing for Aluminum Oxide may soon fall back into the historical pricing pattern. I only hope that is sooner rather than later.

Soda Blasting

2008-06-09T09:36:00.003-04:00

Soda blasting is a specialty process that is used for applications where surface 'sensitivity' is critical. Soda (actually sodium bicarbonate or baking soda) blast media is a very soft media that can be used for stripping on a variety of surfaces including thin metals, aluminum, fiberglass, wood and glass without causing warping, etching or pitting. Many abrasive blasting media can also be used for these applications but different types may be needed for different applications.

The major reasons that soda blasting is not more popular include the cost of the media itself, the non-recyclability of the media (it can only be used once) and the requirement for specialty blasting equipment.

Baking soda (and anyone with a box in their refrigerator know this) absorbs all kinds of things including moisture very quickly. Super dry air is a necessity for soda blasting. Air driers and chillers also add to the difficulty and cost of soda blasting.

Abrasive Blast Polishing?

2008-05-28T09:24:00.004-04:00

I wish there was a way to polish metal, plastic and wood surfaces using abrasive blasting. Unfortunately, using abrasive media (no matter how soft or round) just doesn't produce a polished finish. Glass Bead will result in a uniform, satin-like finish on some metals and Steel Shot can 'almost polish' hardened steel surfaces.

So far, we have not identified a media and process to consistently create a high polish using a blasting process - especially on plastics and wood.

Have you had any success in this area?

All-Time High for Steel

2008-05-01T10:49:00.003-04:00

In a February post I explained the origins of the steel scrap surcharge. Basically, the base price of steel shot and steel grit is fixed but a surcharge is added (and changed each month) to bring the price of steel to current market value.

Well, the demand for steel in both Asia and Eastern Europe continues to grow and much of the scrap is being sent overseas to satisfy this demand. Obviously, increasing demand leads to increased pricing and even product shortages.

The current scrap surcharge is up about 500% in the past 5 years and has nearly doubled in the past six months. In addition, the lead times are continuing to extend for certain sizes and grades. Unfortunately, it does not look like this is going to be a short term problem unless steel manufacturers can figure out a way to make a lot more steel.

We're at an all-time high for steel prices but I fear we will continue to say the same thing many times in the near future.

Matching Nozzle Size and Grit Size

2008-04-25T08:28:00.004-04:00

Question: I would like to know if there is a standard for matching Nozzle opening size to media size. I am just starting out and I am not sure what size media I can use with my sand blaster. The literature on the blaster doesn't say. Can you help?

Response: Generally, the nozzle size you use should be at least 3-4 times the diameter of the grit size.

{If the grit is still getting stuck in the nozzle, try reducing the blasting pressure (psi) and making sure there is no moisture in the system.}

Mass Finishing Basics (Part 4)

2008-04-10T11:56:00.003-04:00

The art of mass finishing really shows itself when trying to select a tumbling media. Media is the material ('stones') that parts are tumbled with in either a vibe or barrel tumbler. The types of media available are as varied as the parts that can be tumbled in a mass finishing process.

Ceramic Media is available in bonds or formulations that range from super aggressive, cutting to non-abrasive polishing. The most popular preformed shapes are triangles, cylinders and variations of these shapes. Ceramic media is typically used with hard metals such as steel. Softer metals such as aluminum can be tumbled with ceramic media but care should be taken so the process is not too aggressive. Precision Media is a high density version for specialty applications.

Plastic Media and Synthetic Media have a lower density and are thus less aggressive than ceramic media. These media are typically used with aluminum, copper, brass and other soft metals. Popular preformed shapes include cones, pyramids and wedges.

Steel Media is used primarily for polishing and burnishing operations in barrel tumblers. Some vibes can be set-up to handle the weight of the steel media which is 3-5 times as heavy as the other preformed shapes.

Other types of tumbling media include Hardwood Media (dry tumbling of wood and some plastic parts), Aluminum Oxide (surface finishing and etching), Walnut Shell (burnishing) and Corn Cob (burnishing) as well as many other specialty media.

Choosing the proper type, size, shape and bond is critical to making sure that the required finishing is achieved. Common problems include excessive media wear, poor and/or inconsistent surface finish, too much (or too little) edge rounding and media 'jamming'.

Wood Stripping

2008-03-28T12:14:00.002-04:00

Question: I’m renovating a house built in 1917 and I would like to remove the years of built up paint off the 6 panel doors and trim that was used in the house. There are 15 doors and probably a 1000 lineal feet of various finish boards. Which Machine and Media should I purchase? Approximately how much media will I need?

Response: Either the KF110DM or the KF65DM will work with the Corn Cob Grit or Walnut Shell Grit. The Walnut Shell Grit will offer a more aggressive stripping action but the surface may require some sanding depending on the surface finish you require. Corn Cob Grit will be more ‘sensitive’ to the wood surface but will not strip as quickly.

The quantity of media required will depend on how aggressive the blasting that is required. Multiple layers of durable paint will demand more media; however, both Corn Cob and Walnut Shell are re-usable. If you are blasting in a clean area you can pick up the media and re-blast it a few times – just be careful to not pick up anything that could be blasted and damage the wood surface.

Motorcyle Parts

2008-03-25T08:59:00.002-04:00

Question: I want to clean /polish an aluminum motorcycle engine. Would walnut shell be the best media for the job? I want a clean, lightly polished look typical of stock bikes.

Response: Walnut Shell Grit will clean the surfaces relatively well but will not have an impact on the surface finish. A Medium-Fine or Fine Glass Bead will clean the metal and leave a satin-like finish on the surface.

Aluminum Oxide

2008-03-17T13:19:00.003-04:00

Aluminum Oxide (a.ka. aluminium oxide, alumina, aloxite, corundum) is generally sourced from bauxite ore. While bauxite is the primary ore for aluminum metal, Aluminum Oxide is extracted using the Bayer Process to remove unwanted impurities.

Aluminum Oxide is a very hard, versatile blasting media that can be used in a variety of applications for removing oxidation and scale off metals to etching stone and glass surfaces. The pure (>99%) White Aluminum Oxide is used when surface non-contamination is critical like when blast cleaning medical parts.

The hardness and large grit sizes available also make Aluminum Oxide an excellent choice for non-skid flooring. Aluminum Oxide is commonly used as an abrasive for sandpaper.

I'll bet you didn't know that precious stones like rubies and sapphires are simply Aluminum Oxide (corundum) crystals contaminated with other metals like chromium, titanium and iron.

Mass Finishing Basics (Part 3)

2008-03-03T13:32:00.004-05:00

Vibratory tumblers come in all different shapes and sizes. Bowl style vibes include both round bowl and oval-bowl shapes. Tub style systems look kind of like bathtubs. In general, vibes are produced in sizes as small as 1-2 gallons up to 150 gallons (and much larger). Both systems force the tumbling media and parts to vibrate and rotate around the vibe.

Tub style vibes force the parts (and media) to vibrate and rotate around the center axis of the tub. This creates a similar sliding and rolling action to a barrel tumbler but adds the additional vibratory energy working against the parts resulting in shorter cycle times. Since tub style vibes can be very long in length and diameter extremely large large parts can be tumbled.

Bowl vibes add circular movement around the bowl in addition to the typical tumbling and vibrating. Since the entire load is moving around the bowl, this system allows the option for a separating screen (either above or below the load) to automatically remove the parts from the media. Unlike tub style systems, bowl vibes can only process parts smaller than the bowl channel width.

Polishing Eyes

2008-02-26T09:41:00.004-05:00

An interesting thread (edited slightly) on the ShopTalk Forum:

Question: We are looking to for a way to polish parts made from a clear urethane casting resin, shore hardness 85D. We currently do all hand polishing and the result is a high glass type polish and looks good.

Response: Urethane is designed to be very resistent to abrasion and does not polish the way most plastics do. Most of the work must be processed in a wet operation with a ceramic or porcelain polishing {Precision Ceramic} media in order to provide enough pressure to abrade the urethane. If the starting finish is rough, the {first step using general purpose} ceramic and abrasive (i.e., pumice) will smoothe out the surface. The "pre-polish" would be done in the porcelain media using a fine Aluminum Oxide powder - 100 to 150 grit. Start the water level very low (30% ) and then after 6hrs, raise the water level to even with the top of the load. Run overnight. The final high polish would be achieved using a dry process with wood pegs and {Microlyte} polishing cream . It may take 6-12 hrs to achieve the final polish.

Why a Steel Scrap Surcharge?

2008-02-20T09:07:00.004-05:00

Steel Grit and Steel Shot primarily use scrap steel as the source raw material. The scrap is melted, the chemistry is modified and then solidified into small particles using a high pressure stream of water. Back in the early 1970's (as well as today) the scrap steel market was very volatile with significant monthly swings in prices. This made long term purchasing difficult for large shot and grit users.

A pricing scheme for steel shot and grit was developed that fixed the base price and added a surcharge to that base based on the ups and downs of the market. The Iron Age Scrap Price Bulletin has been used as the standard for setting the monthly steel scrap surcharge.

In the last 30+ years the pricing scheme has become the accepted standard. As such, the base price of Steel Grit and Steel Shot remains consistent and the applicable steel scrap surcharge is applied at the time of shipment. It's a strange but fair system that gives everyone - suppliers and purchasers - an opportunity to get the best value.

Mass Finishing Basics (Part 2)

2008-02-15T15:00:00.003-05:00

The two types of barrel finishing systems are rotary barrel tumbling and centrifugal barrel tumbling. Both mass finishing techniques use tumbling media, water (usually) and compounds to tumble parts inside a closed barrel. The similarities end there.

Rotary barrel finishing is an abrasive process that involves a sliding and rolling motion of the media/parts load. Filling the barrel 50-60% full allows the upper layer of the load to slide down (due to gravity) as the load is turned-over. Changing the load size as well as the ratio of media to parts to water to compound will create more or less aggressive operations. This ancient mass finishing technique is a highly economical, time-tested technique.

Centrifugal barrel finishing creates more sliding action at higher rates as the individual barrels spin independently of the turret rotation (think of the carnival ride with individual cars that spin while the entire carousel of cars are spinning) . The high centrifugal force created inside the barrel compacts the media/parts load and results in low part to part interaction. These high forces also lead to lower cycle times and very smooth, consistent surfaces finishes.

Getting Aggressive with Tumbling

2008-02-12T15:40:00.000-05:00

Barrel tumbling is a time tested method to deburr, polish and create a desired surface finish. Vibratory tumbling is a new (well...newer) technology that also works great and has replaced barrel tumbling for deburring and surface finishing for lots of reasons. The aggressiveness of a vibe is largely limited by the tumbling media being used.

Welcome back - barrel tumbling. Extremely aggressive processes can be achieved in barrel tumblers. Rough cut, laser cut, parts with lots of slag and scale, heavily rusted parts can be tumbled successfully part-on-part in a barrel tumbler. The weight of each part acting on the others creates an environment in the barrel that will clean these parts in a way that a vibe never could. Adding a grit to the process will add to the cutting action.

Sure, it's a loud process. It can even be a little dirty. But the results speak for themselves.

It's the Economy!

2008-02-08T14:03:00.000-05:00

The economy has been getting a lot of attention as the presidential candidates and Congress argue about the best way to 'fix' it. While all these macro-economics discussions are interesting on a "micro" level we continue to see inflationary pressure on our raw materials.

It seems that every new year brings a new round of price increases from our suppliers (along with a cheery 'Happy New Year'). We are analyzing everything we are doing to minimize the effect for our customers. So far, for most products we have been able to keep any increases to a selective few products.

2008 should end up being an exciting year and we will continue to work hard to do things Right From The Start!

Tumbling with Steel Media

2008-02-05T12:17:00.000-05:00

Polishing all types of metal with steel media is an established procedure for many industries. As the price of steel increases (especially stainless grades), many companies are looking at barrel and vibratory tumbling with carbon steel instead of stainless. The BIG disadvantage of carbon steel is rust. Of course, the big ADVANTAGE is cost.

Keeping carbon steel clean and corrossion-free is critical to getting an acceptable surface finish on the parts. Using the proper chemical compounds is the answer to this problem. Even though acid compounds will return the rusted steel to near original condition, this should be avoided as this can actually make rusting problems worse.

Steel media should first be restored with a cleaner (like Kramco 750) containing sequestrants, detergents and be pH buffered to remove the corrossion and prevent flash rusting. The second step is to treat the shot with a rust inhibitor that will both prevent rust formation and not contaminate the parts {like oil based rust inhibitors}. Simply tumbling the steel media with a non-durable rust inhibitor (like Kramco 510) for a few minutes, draining the solution and then letting it air dry will keep the shot clean and bright even during longer term storage.

Corn Cob Grit for Everything!

2008-02-01T07:44:00.000-05:00

Just a few applications and advantages of Corn Cob Grit:

Log home blasting - won't damage logs or etch wood
Spill clean-up - absorbs more than 100% of it's weight in oil and water
Burnishing - used in barrel and vibratory tumblers to brighten metal and plastic parts
Degreasing - absorbs cutting oils, grease and soils for cleaning parts
Biodegradable - 100% organic, natural, no health hazards
Abrasive - it's soft, but can be used in abrasive hand soaps
Playing field absorbent
Reusable in blasting applications - lowers operating costs and can even extend life of other more expensive media
Parts drying - vibe and barrel tumbling to dry parts after deburring and/or polishing steps

Four Times is Twice as Big

2008-01-28T16:50:00.000-05:00

Just one more quick comment on CFM, nozzle size and blasting...

I discussed a little about the differences and relationship between CFM and PSI in a previous post. PSI is basically the amount of force you blast with. CFM is the volume of air being used during blasting.

It is sometimes suprising to realize how much air (CFM) is required during blasting. At a given PSI setting, the amount of air needed is directly related to the nozzle size being used. The larger the nozzle, the more air that is required. This also means that if you want to use a large nozzle, you will need a large compressor.

For example, at 80 psi, a 1/8" nozzle will require 20 CFM. At the same pressure a 1/4" nozzle will require 85 CFM and a 1/2" nozzle will demand 340 CFM. A basic chart that shows the air requirements for different nozzles at different pressures is on the PPB Series page.

Rule of thumb: double the nozzle size, quadruple the CFM required.

Blasting - CFM vs PSI

2008-01-24T13:14:00.000-05:00

There are a few variables that need to be addressed when determining the blasting system that will work best for your application. Two critical issues are the blasting pressure (PSI) and the air requirement (CFM).

PSI {pounds per square inch} indicates the force that the blasting media is being discharged from the nozzle. The PSI measurement is independent of the nozzle size being used and is directly related to the pressure setting on the air compressor and/or the blasting pot. The most common abrasive blasting pressure used is 80 psi.

CFM {cubic feet per minute} is the volume (cubic feet) of air that is being sent threw an opening per unit time (the minute part). The CFM required during blasting is based mostly on the nozzle size being used. A larger nozzle will require more air just like a larger hose will need more water. Abrasive blasting is using air continuously so the compressor used must be able to supply enough CFM to 'keep up with' the blaster. For comparison, pneumatic (air powered) tools only use air in small increments so much less CFM is required.

Side note: For a given nozzle size, the CFM requirement will go down with lower blasting pressures (PSI). Using the garden hose comparison, more water will come out of the hose if the spigot is turned to a higher pressure, less if the spigot is turned down.

Dust Control

2008-01-22T08:33:00.000-05:00

We recently had a post on our ShopTalk Forum about how to control dust during vibratory tumbling. Either Walnut Shell Grit or Corn Cob Grit can be used quite successfully to burnish parts with a dry tumbling operation.

As these organic media break down (or if a fine grit is used initially) the vibrating action can send dust all over the place. Adding water to reduce the dust is not really an option (muddy Walnut Shell doesn't burnish very well).

Something as simple as draping a rubber mat over the tub or fitting a similar mat over a bowl vibe will keep the dust to a minimum. Using a thick, heavy-duty sheet of rubber of foam and bracing it to the machine will give good dust control and keep the mat from vibrating off.

These 'covers' also have the added benefit of reducing the noise level of the process.

Mass Finishing Basics (Part 1)

2008-01-18T08:40:00.000-05:00

There are two basic types of mass finishing - barrel tumbling and vibratory tumbling. Each of these mass finishing methods have pros and cons. There are also a number of sub-varieties which we will discuss in future posts.

Barrel tumbling might be more familiar if described as rock tumbling. Inside the tumbler the parts and media are lifted by the corners of the barrel and allowed to bump, scrape and slide against each other. The media used will depend on whether you are trying to deburr or polish your parts. Barrel tumbling is also good for part-on-part tumbling (another future post - so many posts and so little time). While typically used wet, barrel tumbling can also be a dry tumbling process. The big down side to barrel tumbling is the loading and unloading of parts.

Vibratory tumbling is a little different. Similar to barrel tumbling the parts and media are sliding against each but in more of a 'filing' motion. The tumbling action is occuring in 100% of the load with a vibe versus only 20-30% of the load in a barrel tumbler. This allows a vibrator (you know what I mean) to typically offer shorter cycle times. Vibratory tumbling can abrade and smooth a surface with minimal affect on the edges while barrel tumbling loves to round the edges. Vibratory tumblers can offer very simple and even automatic separation of parts and media.

Generally, barrel tumbling is good for durable parts that require heavy deburring or high polishing and for processes that use a lot of weight (i.e., tumbling with steel media). Vibratory tumbling is great for general purpose deburring, surface finishing and for easy loading/un-loading of parts.

Corn Cob Grit hard as Iron!

2008-01-16T09:23:00.001-05:00

All solid materials can be measured for hardness on the Mohs scale. The scale was created in 1812 by Freidrich Mohs and is based how easily one substance can scratch another. Diamond is the hardest rated at a 10 while talc is a very soft 1.

Suprisingly, Corn Cob Grit and iron have the same hardness at about 4.5. Even more amazing is that Corn Cob Grit is harder than brass (3-4), copper (2.5-3) and aluminum (2-3).

The really cool thing is that blasting with Corn Cob Grit won't frost or pit glass and can be used to absorb grease, oils and water from metal surfaces. Corn Cob Grit is also great for blasting on wood surfaces (more to come on that). I wouldn't recommend using iron grit near glass or on wood!

Deburring Aluminum Tube

2008-01-14T21:44:00.001-05:00

A client asked us for a process that would remove the burrs from an aluminum part consisting of an assembled tube within a tube. The part was made by inserting one tube into another and then bonding the assembly together. The outer tube was 4 inches larger in diameter than the inner tube. Holes were then drilled through both tubes of the assembly. The holes could only be drilled after assembling the two tubes together due to the critical tolerances involved. There were a total of about one hundred holes in each part. The challenge was to remove the burrs from the inner as well as the outer surfaces of both tubes.

The problem was solved by attaching the part to the vibratory tub in a fixed position so that it would move along with the tub, but still be able to rotate on its axis. By clamping the part down and forcing it to vibrate with the tub, the amount of energy transmitted to the part was greatly increased.

A deburring, ball-shaped Precision Ceramic Media was used to minimize the chance of having media get stuck inside the part. The tub was slightly under-loaded with media to increase the flow rate through the holes and to aid in rotating the part. The compound flow rate was kept at eight gallons per hour. A mild acid cleaning compound (Kramco 1030) was used to speed up the cutting rate and maintain good color on the aluminum.

Due to the elevated cutting energy, the part was completely deburred with a 0.005 edge break in a cycle time of ten to fifteen minutes in a tub-type three cubic foot capacity vibratory machine. The inner tube was deburred thoroughly, exhibiting a 0.003 edge break. The parts were originally being deburred by hand, which took over three hours per part. The vibratory finishing system developed not only dramatically reduced the cost of finishing the parts, but also produced a more consistent part than when finished by hand.

Glass Beads for Auto Restoration

2008-01-11T20:47:00.000-05:00

We have been receiving lots of calls from auto restoration companies and hobbyists looking for recommendations for stripping engine parts. A major concern is removing old paint, dirt and grime from aluminum parts that need to be repainted.

While each customer has a preference for surface finish they want to achieve, we have found that Medium Glass Beads offer the best balance of strip and clean rate with surface finish. This mesh size of glass beads leaves a satin-matte finish (if that makes any sense) which is perfect for painting or powder coating.