Tumble Blasting Paint Hooks

Continuously painting parts using an automated process often involves hanging the parts from a moving track using paint hooks. These hooks invariably will get a build-up of paint and need to be stripped. Abrasive blasting with the proper media will strip the paint and allow the maximum usage lifetime of the hooks. Using a tumble blaster will allow for automated blasting of many parts in a batch and minimal downtime for the hooks.

The two pictures below show the part both before blasting (painted black) and the hooks after blasting with either 60 Mesh Aluminum Oxide Grit or 12-16 Mesh Melamine Plastic Abrasive Blast Media. A batch of these parts were tumble blasted for only 6 minutes at 60 psi.

Aluminum Oxide Blasted (right)

Melamine Blasted (right)

Both media types removed the excess paint and left the parts ready for re-use. An initial review seems to appear that the Aluminum Oxide Grit did a better job of removing the paint.

Upon a closer analysis, the Melamine actually provided an overall better result as can be more clearly seen in the comparison picture below. The Melamine Plastic part on the left does have a small amount of paint left on the surface but enough exposed metal to allow for the hook to perform properly and even could be used in a  electro-coating process, if necessary.

The Aluminum Oxide blasted part is also clean but this media tended to etch the metal and will ultimately result in fewer usable cycles and/or failure of the hook.

Investment Casting

Investment casting is process where parts are produced inside a mold (a.k.a., investment) which is then removed from the part to expose the molded piece. As the investment casting process typically requires high temperatures to liquefy and pour the metal alloy into the mold, discoloration of the final part is common. In addition, the investment material can often get stuck inside slots and grooves of the part. Both the discoloration and stuck investment can be seen in the part on the bottom of the picture.

The clean part seen in the top of the picture was a result of abrasive blasting. In this case, the hard metal alloy part was tumble blasted with White Aluminum Oxide for only a few minutes. The end result is a clean, uniform surface finish ready for the next steps in the part production process.

A good explanation of the investment casting process can be found on Wikipedia at http://en.wikipedia.org/wiki/Investment_casting.

Cleaning Paint Plugs

When painting large quantities of parts - especially on a production line - it is common to use plugs and masking materials to prevent paint from being coating on unwanted areas. These materials are often made of flexible materials such as silicone, urethane and rubber in order to make it easier to plug the holes or slots or whatever area needs to be protected. Often, these plugs are discarded after a few uses as the coating builds up on the surface.

Removing the paint off the plugs allows for a longer lifetime of the plugs and significant cost reductions. Many companies will simply roll the plugs on a hard surface to remove the paint or knock them with hammer or similar. Since the plugs are typically flexible, it is difficult (but not impossible) to use a mass finishing process such as vibratory tumbling to get the uneven forces (i.e., rolling on a surface) necessary to knock the coating off. In addition, vibratory tumbling is often done wet so the plugs would need to be dried prior to re-use. Of course, this type of process eliminates the hand cleaning one part at a time.

Abrasive blasting is another process that can be used to strip the paint. On hard rubber plugs and similar, this process works very well especially in a tumble blast system. On more flexible parts, the results vary widely as the media can simply 'bounce' off the surface. The success pictured above was a simple blast cleaning with Walnut Shell Grit to completely strip the paint.

The type and thickness of the coating and the flexibility of the part are important factors when trying to determine whether blasting or tumbling will properly remove the coating. Testing of the parts is typically needed to determine the viability of cleaning re-using the plugs.

Titanium Medical Screws

Titanium metal is used for medical and dental implants due to its strength, non-corrosive properties and bonding ability with soft tissue and bone. In order to encourage this bonding process and to give the tissue a good surface to adhere to, the metal needs to have an anchor profile. This very similar to preparing a surface for paint or coating. A rougher surface will provide more surface for bonding.

The titanium bone screws in the picture show a before and after blasting. These screws have a very smooth surface (before on left) after the machining process. Since the size of the screw is very small, it is difficult to blast the screws one at a time. A Tumble Blast system was used to create the lightly etched profile (blasted part on right) on the surface. The tumble blasting batch process allows for a large number of parts to be blasted at one time in a short period.

The surface finish shown was accomplished in about 10 minutes using 60 Mesh White Aluminum Oxide. This grade of media (99.5% pure aluminum oxide) was used to prevent contamination of the metal surface and provide a consistent and uniform finish from part to part.

Etching Stainless Steel

Stainless steel can be polished to mirror surface finishes. Sometimes, the surface needs to be etched in order accept a coating or prepare the part for a process that requires a little 'grab'. While tumbling in a vibratory system or a barrel tumbler will create a matte finish, the surface is generally not rough enough for many coatings. Also, when the parts are small, it can be difficult to separate the media from the parts in a tumbler.

Stainless Steel Etching

When an etch is required and the parts are small, a tumble blasting process is often an ideal solution. The stainless steel parts above (before and after) are less than 1/2" in any dimension. These parts were tumble blasted with 60 mesh Aluminum Oxide Grit for only 20 minutes. Depending on the size of the blasting basket, batch sizes as large as 3 cubic feet can be processed at one time.

Tumble Blasting Steel Parts

Tumble blasting is a process that allows for a batch or load of parts to be abrasive blasted automatically. Tumble blasting is beneficial when a large quantity of 'smaller' parts make it difficult or labor intensive to blast one at a time. This process also removes the inconsistency of manual blasting as each part in every batch will result with the same finish on the entire surface area of the part.

The most successful part sizes are generally less than 4 inches and batch weights are generally less than 150 pounds. The tumble blaster specifications and basket size will determine what combination works optimally.

The stainless steel parts pictured above (before on left) are about 3" in size and weigh less than 2 pounds each. The parts were tumble blasted for less than 10 minutes with Coarse (#6) Glass Bead to remove the heat treat discoloration and achieve the finished surface on the right. The geometry of these parts are ideally suited for this process since they will tumble over each in 3 dimensions allowing all areas of the part to be exposed to the blast stream.

Glass Bead Tumble Blasting

Large batches of relatively small parts that need to be blasted can be extremely labor intensive when blasting each part by hand. Batching a load of parts together in an automated tumble blasting process will allow for quantities of parts to be blasted all together without the need for an operator's 'hands-on' blasting. Tumble blasting also provides coverage on all areas (3-D, 360 degrees) of the part as the load tumbles under the blast stream.

Before Tumble Blasting

After Tumble Blasting

This is one piece of an old ratchet set with parts ranging in size up to 1" diameter and 3" long. The rusty load was tumbled blasted for 10 minutes with Medium-Fine Glass Bead at 80 PSI. The result is a like-new, smooth, satin finish.

Tumble Blasting Electrical Parts

Cleaning small or delicate parts by hand can be a difficult and time consuming process. This customer manufactures a variety of electrical parts and components and often needs to remove brazing, heat scale and flux. The large quantity of parts makes it costly to abrasive blast clean the parts by hand.

The parts were cleaned in a tumble blast system using Glass Bead. The process involved loading a open-ended, rotating basket with a batch of parts. The blast gun was pointed at the parts while they tumbled under the blast stream. The cycle time was about 30 minutes to clean a 5 gallon load of parts.