Painted metals provide an attractive touch to everything from vehicles to furniture, fixtures and machinery. But, there are times when the job requires you to remove the paint from its surface.

Here are some advantages to paint removal and how you can facilitate the paint removal process on metals.

Advantages to Paint Removal

There are some pros to removing paint from metals, mainly to restore the fixture to its natural shine and texture. You might also decide to re-paint it with a different color.

If the paint has already begun deteriorating, removal will help prevent the chances of further corrosion or succumbing to rust formation. This will extend the metal’s lifespan and provide a more robust sheen.

Removing paint becomes more and more increasingly difficult with the number of layers that are applied. Think of this like layers on an onion, removing paint on items such as fixtures often can/will prolong its lifespan and eliminate any potential paint flakes making it into back onto the next time you need to paint.

Benefits of Getting a Clean Metal Surface

Opting for a clean, bare metal surface coincides with several key bonuses:

Visibility

Removing old paint can show off the true craftsmanship of the metal or fixture. This can be beneficial whether it’s a classic gem or a modern structure.

Adhesiveness

There’s nothing like a clean, bare metal surface when applying a new coat of paint. This will ensure your object survives a long-term workload, or even harsh weather conditions if it is primarily outdoors.

Creativity

Getting rid of old paint from metal surfaces helps contribute to a more industrial, bare bones look. Alternatively, it allows for a new paint job which can give the object a new aesthetic.

Preparations for Paint Removal

Preparing for paint removal is key to a seamless and effective process.

Cleaning

Eliminate any residue of dust, dirt, grease, gasket material or grime from the metal using a safe detergent and water combination. You will want to rinse the surface thoroughly to make sure it is 100% dry prior to commencing on the paint removal. Pay close attention to difficult to get areas like crevices or corners as well.

By cleaning the metal surface entirely, you’ll be able to establish a better foundation for the paint removal process.

Top Methods of Removing Paint from Metal Parts and Fixtures

There are several methods of removing paint from rejected parts and fixtures. Here are the most prevalent…

Chemical or Caustic Paint Stripping

Chemical or Caustic Paint Stripping breaks down old paint without scratching the surface or creating flying paint chips or dust. The chemical process can be caustic and creates a lot of hazards and expensive disposal of waste. Chemical strippers can be quite slow.

Solvent & Green Strippers

Solvent & Green Strippers are good for delicate surfaces but they can be quite slow. Thicker coatings may take several applications to remove all of the coatings. The set-up, waste containment, clean up, and drying can be time consuming. Many metal parts can rust after being subjected to the strippers.

Power Washing

Power washing with pressurized water. Containment of the contaminated water can be difficult to capture. Drying can take time and will cause ferrous parts to rust.

Burn Off Ovens

Burn off ovens can break the paint bond but usually need another step like blasting or pressure washing to remove the ash. A burn off oven can be expensive to purchase and operate. The process can take several hours to complete. Parts have to be immune to high temperatures.

Blast Cleaning

Blast Cleaning can operate at room temperature. Parts go into and out of the blast booth and machine dry so there is no need to dry. There are many types of blast media available to suit the type of paint or the substrate.

Tips for Effective Paint Removal

Effective paint removal begins with having the right tools in your toolkit. Here are some tools that can help your paint removal process.

Drop Cloths

Create a safe and protective barrier between the work area and surrounding surfaces. Drop cloths keep dangerous chemicals, dust, and paint chips from damaging nearby objects.

Heat-Resistant Gloves

Anyone operating heat guns or blowtorches during the paint removal process should adorn some heat-resistant gloves. Burns and excessive heat exposure can happen easily.

Safety Goggles

Eye safety also must be taken seriously. Safety goggles keep your eyes safe from unwanted dust, chemical splashes, and other dangers.

Dust Mask

Filter out dust particles during the paint removal process to avoid skin irritation and potential exposure risks.

Putty Knife

The more flexible blade provides a more controlled and precise paint removal effort. It avoids risking damage to the underlying metal.

Tongs

Another measure in the hand protection department, tongs are essential for handling small metal objects during the paint removal process.

Hard-bristled Brush

There’s likely to be some stubborn paint residue that doesn’t want to leave the scene. For this, you can utilize a hard-bristled brush to help finish the job.

Clean Rags

Once the job’s complete, you want to wipe away any excess paint and safely clean your tools.

Remove Paint Safety and Hassle-Free

By following a step-by-step approach and using items that are proven to be safe and effective, you will mitigate any potential danger and maintain the integrity of your surfaces.

A proper paint removal process will ensure the long-term integrity and durability of your metal surfaces, while also providing endless possibilities.

Adapt the above methods of paint removal in a way that makes sense for your organization, while always prioritizing safety and necessary waste disposal techniques.

Sticking to a regular maintenance and cleaning schedule is key when using a blasting cabinet. Here are some factors that determine how often maintenance will need to be done:

Volume of parts

Just like putting miles on your car. Your equipment can only get you so far without revitalizing it with performance maintenance or cleaning.

Type of media used

Steel shot will eventually work its way through the walls of a blasting cabinet unlike cast zinc shot which cannot.  Durability, dust generation & mechanical wear are all factors.

Age of blaster

Below is a general list of tips you can use to help keep your basting equipment running like new.

Wheel Blast

Inspect the exterior of the machine to ensure that there are no leaks—these can happen in hoses or around the door.

Replace worn hoses and gasketing around doors as needed.

Check the amp gauge to ensure the machine is full. If full and amps are still low, check for clogs or obstructions between the hopper and blast wheel.

Do a pattern test of the wheel using a scrap steel panel painted to determine the blast pattern. Adjust the control cage accordingly.

Take a picture of the blast wheel blades using a cell phone camera. Look for wear on the blades.

Make sure grease points on all bearings are being hit based on the manufacturer’s recommendation.

From the outside of the machine look at all of the tumble blast roller shafts, elevator pulley shafts, or table blast motor shafts to make sure all are operating correctly.

Keep your dust collector clean. A dirty dust collector can result in dark dingy coated parts.

Air Blast

Check air hoses for leaks and inspect all connections. Listen for air leaks. We recommend double grip locking couplings, also known as Thor Couplings, in order to get a more secure hold on larger hoses.

Look at the nozzle bore to make sure it is not worn, and replace when the nozzle expands to the next size. For example, when your # 5 nozzle expands to a number #7 nozzle, it means you’re using too much abrasive and taking too long to blast.

Listen and look for clogs in the media pickup.

If you’re blasting large paint chips off parts, install a screen to remove paint chips from the media. This will prevent clogging of the media.

Keep an eye out for any cracks in the observation safety glass. Replace the glass window if it is frosted from media impacts (Cast zinc and cast aluminum will not frost glass windows).

Keep your dust collector clean. A dirty dust collector can result in dirty parts after blasting.

Over time surfaces become blemished due to a number of environmental contaminants, such as rust, or applied finishes such as paint. Removing rust or paint and other stuck-on materials is a job too tough for scrubbing or power washing and too intricate for sanding, so another method was developed, called media blasting. 

While everything from glass to walnut shells has been used for blasting, the original media of choice was silica sand. But blasting needs to be safe for the blasting operators because all blast media creates dust and inhaled dust of any type is a common carcinogen.

Safety equipment and particular materials are thereby favored so that jobs can be completed without harming both the blasting specialist and the work surface beneath the corrosion, grime, or other build-up that must be preserved.

Surface restoration is just one use of media blasting. Other application purposes include creating compressive stresses on workpiece surfaces, deflashing, deburring, edge rounding, descaling, roughening and simply smoothing a rough surface.

Various industries rely on media blasting to prepare products for additional stages in the manufacturing process, including trimming metal parts and blanks and preparing, for example, dental restorations for bonding (their minimal surface area makes it essential that optimal bonding conditions are achieved, often through sandblasting).

Various Blast Media Types 

The word “media” refers to the type of material launched at the surface via a spinning wheel or compressed air. Various media types exist to optimize the different goals of the blasting in question, with certain characteristics prized for unique applications, among them: hardness, friability (the ability of grains to break down into sharp edges), shape, surface profile, speed, pressure, and recyclability. These characteristics determine how well a particular type of media strips target material.

Earlier walnut shell was mentioned as a media type, and while most people would never think of nut shells being repurposed, walnut shells do an excellent job cleaning and stripping without causing damage to the substrate. Steel shot smooths and polishes, while steel grit removes paint quickly and ground glass is best for removing paint before repainting or recoating. These are just a few examples of the types of media, with blasting specialists getting creative to produce the best outcome for the goal of the project at hand.

Reusing Blast Media

When media is blasted at a surface—for example a rusty tow hook—using compressed air and a sprayer, the media is lost to the environment. Single-use applications are not environmentally friendly or cost-effective, but they are versatile in that they can handle any sized object, such as a large metal fuel tank (although for large applications, blast rooms are available, even complete with recovery floors which allow blast material to not be lost to the surrounding environment, reducing cost and contamination). 

The Science Behind Media Blasting and Its Effect on Different Surfaces

You can think of each piece of blasting media material as the head of a tiny hammer, hitting and chipping a piece of surface corrosion, paint or other coating from an object. But the shape of different types of media is not all the same due to unique friability; the way a material breaks when made small enough to become blasting media determines the shape of its edge, making it more or less corrosive as it is projected against the surface in question, although this is only one characteristic of blasting media.

Characteristics of Abrasives

Hardness (Mohs)

The ability of materials to scratch one another, developed by Friedrich Mohs. Plastic is less hard than silicon carbide, for example. 

Anchor pattern

Peaks and valleys form when an abrasive media is shot at a work surface, and the roughness degree of these characteristics determines how well a coating adheres. 

Friability

How a material breaks down, what its edges look like once this occurs, largely determines the characteristic of shape. 

Shape

Different shapes contact work surfaces to different degrees. For example, rounded abrasives contact the surface more but cut less aggressively due to having soft edges; angular shapes have less contact but more aggressive cutting. 

Recyclability

Not every type of blast media can be recycled, or sent through gravity-fed or centrifugal airwash reclaimers that separate the dust created by blasting from the abrasive media that is suitable for continued use.

Different Surfaces

The surface being blasted is a critical consideration when choosing the type of blast media to apply. If you use the wrong blast media, or apply it with the improper amount of pressure, you can cause damage to the surface. Damaging an expensive aircraft component could result in major losses for a blasting business. 

Iron fixtures

Iron fixtures such as fences and artwork are often blasted in order to restore them to their original luster. 

Mechanical parts

These components become caked with grease and dirt which is nearly impossible to clean without the aid of blasting media that penetrates every small crevice, often without requiring disassembly, blown clear from the components via the power of compressed air. 

Plastics

Plastic is much more malleable than metal, so when it’s blasted with media there’s a greater risk of warping, melting, scratching and other forms of damage.

Blasting Machine Types

Siphon Blast Cabinets

For smaller applications, blast cabinets are helpful; they contain handheld blasting nozzles and arm-entry holes whereby the operator can apply blasting media in a closed environment, ensuring that media is reused. Suction guns pull blast media through a hose to a blast nozzle which directs the media to the target, such as an engine block needing corrosion cleaning. Blasting is so effective that even the blast hose nozzles are subject to wear as the abrasive material passes through and onto the surface of the target object, ready to be replaced once the amount of wear expands the nozzle opening 1/16” of its original size. 

Direct Pressure Blast Cabinets

As its name implies, direct pressure works at a higher speed than siphon blast cabinets, appropriate for heavy-use industrial blasting applications. Productivity is increased and heavier media is an option, usually doubling the stripping time of caked-on residue.

Tumbler Machines

Small industrial components are tumbled while a rotary wheel blaster runs overhead, spraying the components with media. Often uses include shot peen, cleaning, deburring, and descaling castings. 

Rotary Table Machines

Alloys, forgings and castings are treated within these machines which feature a rotary pedestal and turning table. Centrifugal blast equipment if for high volume production. Each blast wheel can throw hundreds of lbs of shot per minute 

Blast rooms

These enclosed rooms prevent blasting media from leaving the area and may include systems for reclaiming and reusing media by separating the dust from the media. These rooms can be mobile, weatherproofed, and customized to accommodate certain components like wind turbine blades.

Advantages of Abrasive Media Blasting Over Other Surface Preparation Methods

Safety

Blasting operators need to stay safe as inhalation of virtually anything risks an otherwise safe substance turning into a carcinogen once it becomes imbedded into lung tissue (silicosis is caused by inhaling large amount of silica dust, a condition that plagued earlier sand blasting operators who had no respirators to protect themselves.) Chemicals pose their own risks when used to strip materials, as anyone who has used powerful household cleaners such as degreasers knows first-hand. Without exposure to chemicals, and while wearing proper personal protective equipment, blasting operators remain free from risk.

Environmentally friendly

Not only is blasting machinery reusable—along with many blasting materials themselves—naturally-occuring blasting materials like corn cob and walnut shell are harmless to the environment and those who operate blasting equipment (as long as these materials are not inhaled). 

Cost effective

Sand was first used as a blasting material due to its extremely low cost, but great pressure has largely discouraged the use of sand as a blast media due to safety concerns. Blast media specialists look instead to increase value, such as superior greater durability and less scrap, in exchange for the use of blast media that cost more. 

Controlled environment

While working within a blast cabinet or blast room, blast media operators keep the media contained and in many cases suitable for reuse.

Efficiency

While it seems like chemical cleaning would be quick, such as a dip of a metal part into a bath of stripping product, a second manual step often slows down the process when the residue created by the chemical stripping must be scrubbed clean. Most blasting media however don’t leave a residue; why replace one residue you’d like to remove with another? Disposal of used chemicals can also be a costly problem.

Prevents damage

When you use chemicals to strip materials the substrate can be damaged. This isn’t always so obvious at first as chemical damage can crop up long after the cleaning job is complete. Reversing this damage increases costs or, in the worst cases, changes the surface of the material rendering it unusable.

Transmet Corporation added a 2 Second Lean program to our Ownership Thinking program. In February all employees participated in training to learn to identify and eliminate waste. The training was lead by Shaox Li an Industrial Engineer.

Transmet’s Ownership Thinking program had already started employees in the Lean Culture. Now all employees have the authority, budget and time to eliminate waste daily. This will simplify all processes and provide better products and service to our customers.

Employees are sharing their weekly successes as we visit each person in their work area and learn about their waste elimination successes. Shown below are employees attending one of the four (4) introductory meetings.

Transmet employees learning how to be lean!

Transmet Corporation is a manufacturer and supplier of Cast Shot: Cast Aluminum Shot and Cast Zinc Shot.

Key Benefits of Cast Aluminum and Cast Zinc Shot:

• Does not damage substrates or wear blast equipment
• Leave smooth, shiny surface finish on parts
• No ferrous contamination on parts
• Increased durability (cycle life) of media
• Low dust

Shot Blasting Applications

Surface Finishing of Castings: Transmet Cast Shot products are used in surface finishing applications where ferrous contamination and/or damage to parts being shot blasted is a concern.

Learn more about surface finishing applications.

Paint and Coating Removal: Transmet Cast Shot products have proven to be cleaner and less costly than other paint and coating removal methods like chemical stripping, burn off, and even shot blasting with other media.

Learn more about paint and coating removal applications.

Corrosion Removal in Remanufacturing: Transmet Cast Shot products are similar in hardness to many substrates, making it easy to clean old paint, corrosion, and residue to refresh cores to “like new” OEM appearance.

Other Applications: Transmet Cast Shot products have also found successful applications outside of shot blasting. Adding Transmet’s pure aluminum shot to cast epoxy molds increases thermal conductivity by as much as 450% versus unfilled resins.

Durability Compared to Other Blast Media

The unique casting process used to produce both Cast Aluminum Shot and Cast Zinc Shot results in high durability, long-lasting products proven to outlast alternatives. Compare both Transmet Cast Shot products to Cast Stainless Steel, Zinc Cut Wire, and Cast Steel Shot.

Shot Blasting Machine Wear

Transmet Blast Media significantly reduces damage and wear on high-wear internal components like the impeller, control cage, wheel liners, blast wheel and blades. Cabinet wear as a whole is virtually eliminated.

This blast wheel has over 17000 hours of blasting with Transmet Cast Zinc Shot without damage:

Cast Zinc Shot

Transmet Cast Zinc Shot is a soft metallic blast media for deburring, deflashing, and surface finishing of light metal castings and other non ferrous products. Cast Zinc Shot has a density closer to stainless steel, giving it the mass to remove heavier flash. The 90 HK hardness of Transmet’s ZA4 Alloy is soft enough that it will not damage delicate castings. The resulting surface finish is very bright and evenly textured. If ZA4 Alloy Cast Zinc Shot is too hard, Transmet’s HG Alloy is softer (with a hardness of 60 HK) and suitable for applications requiring a very smooth surface finish.

Learn more about Transmet Cast Zinc Shot here.

Cast Aluminum Shot

Transmet Cast Aluminum Shot blast media is gentle enough to protect delicate gasket surfaces and critical date coding information; yet aggressive enough for deburring, deflashing, and general cleaning of light metal castings and other non ferrous products. The 319 alloy is the most popular for blast cleaning. The 100 Knoop hardness (HK) of the 319 alloy shot is similar in hardness to many die cast parts. For extra delicate blasting applications the 2N alloy can be used. The hardness is 25 HK.

Learn more about Transmet Cast Aluminum Shot here.

Stainless Steel Shot vs Cast Zinc Shot

Is your company using too much stainless steel shot in the shot blasting (abrasive blasting) process? It may be time to switch your blast machines over to Transmet Cast Zinc Shot.

Transmet ZA4 Cast Zinc Shot will last more than two times (2x) longer than cast stainless steel shot in blast cleaning operations.

Switching to Cast Zinc Shot

Switching from cast stainless steel to Cast Zinc Shot lowers:

• Shot Usage
• Freight Expense
• Inventory Cost
• Amount of Dust

Brighter Castings After Shot Blasting

Switching a shot blasting process over to Transmet ZA4 Cast Zinc Shot can lead to these potential benefits:

• Clean, bright castings (see picture below)
• Lower freight expense for blast media
• Lower inventory cost
• Lower the amount of dust in your plant

Blasting magnesium die castings can be extra challenging. Steel, stainless steel, and mineral abrasive media can cause galvanic corrosion and discolor magnesium.

If you take a look at the chart of galvanic compatibility you will notice that magnesium and stainless steel are very far apart. This means that there is a high potential for corrosion.

You’ll also notice that Zinc and Magnesium are very close together. The galvanic difference is less than one, so the potential for Zinc and Magnesium to interact is very low.

Transmet will do the Test Blasting

If you are too busy to investigate ways to improve surface finish, let Transmet do the shot blasting tests for you. We know it’s difficult for even the most cost-effective companies to find time to look at improvements in their manufacturing processes.

That is why a great first step in discovering if Cast Zinc Shot or Cast Aluminum Shot will work for your shot blasting process is to have the testing done in our Media Support Lab.

Blast Media Support Lab

The shot blasting Media Support Lab is located at our plant in Columbus, Ohio. We have shot blasting equipment in-house to blast finish parts you send in at no cost.

Transmet Engineers will demonstrate the resulting surface finishes from various sizes of Cast Zinc Shot, Cast Aluminum Shot, and Stainless Steel Grit. Process development work can also be completed in order to optimize cycle times, belt speed, and other blast parameters.

Changing Blast Media

Examples of successful applications of Transmet Blast Media:

• Transmet blast media lasts longer than alternatives
• Improves surface finish (smoother, brighter) on parts
• Eliminates ferrous contamination
• Eliminates warping of blasted parts
• Less dust in your plant and to dispose of

Flash Rust on Castings

Shot blasting of aluminum castings with steel shot can leave parts looking dull and dirty. Steel shot residue trapped on parts can also cause flash rust on castings. This leaves your castings with freckles of rust on the surface and in casting crevices. In periods of high humidity these freckles can appear overnight as the casting moves through subsequent machining, painting, or assembly steps.

Transmet Blast Media

Customers that have switched to Transmet Cast Aluminum Shot or Cast Zinc Shot have reported lower show usage, lower freight expense, lower inventory cost, and less dust produced and recycled.

Shot blasting with Cast Aluminum Shot leaves a brighter finish than steel:

Before: Aluminum Casting Blasted With Steel Shot

After: Aluminum Casting Blasted With Cast Aluminum Shot

Cast Zinc Shot has the mass for flash removal and deburring, leaving a brighter surface finish:

Before: Rusty Cast Iron Wrench

After: Same Cast Iron Wrench Blasted With Cast Zinc Shot

Blasting cast iron or other ferrous materials with Cast Zinc Shot leaves a 1-micron thick coating to temporarily prevent flash rust.

Blast Media Consumption Costs

A lot more than price per pound impacts total shot blasting consumption costs. Once it is discovered that a type of blast media works well on your parts, you can begin to look at the durability of the media (how long will it last in your process), the cycle time required of the media (how long you have to blast each cycle of parts), and the many other costs involved in operating a shot blasting process (electricity, dust collection, wear on machine components, etc.).

This Company Saved $45,000/Year

Transmet started working with a company that was using zinc cut wire to remove flash and impart a smooth surface finish on die cast parts. The company had strict surface finish requirements from their end user and was having trouble meeting their specification.

The end user wanted surface finish to be improved. To improve the surface finish the company increased their blast cycle times. Longer cycles then led to bottleneck issues in the shot blasting step.

The company sent sample parts to Transmet for testing in the Media Support Lab. The parts were blasted with varying cycle times and different sizes of Cast Zinc Shot.

Our recommendation was replacing the 0.040” zinc cut wire with RSZ-500-ZA4 Cast Zinc Shot.

Replacing Zinc Cut Wire With Cast Zinc Shot

The 500-micron Cast Media is slightly smaller than the zinc cut wire, but was effective for flash removal on the castings. The smaller particles also left a much smoother surface that was well within the required specifications of the end user.

After receiving the RSZ-500-ZA4 Cast Zinc Shot, the company cleaned out their blast machine and replaced the zinc cut wire. They immediately saw an improved surface finish and reduced blast cycle times by 50%.

Shot Savings Over Time

Year 1: $47,910

Year 3: $143,730

Year 5: $239,500