Concrete Canoes

While it seems a bit counter-intuitive, a concrete canoe can float. Using materials like Glass Beads and Pumice to create a more bouyant material, these student groups have worked with us over the years to great success (and failure).

Out of Concrete and Drudgery Come Canoes That Float - NY Times; June 23, 2013

Polishing Stainless Steel

After heat treating and laser cutting stainless steel parts, the edges generally need to be deburred and the surface needs to be cleaned from scale and discoloration prior to polishing. A two-step vibratory tumbling process is normally used to achieve a uniform surface finish.

The part on the far left in the picture shows the burrs and slight discoloration on the edges. The first step was to tumble the parts with a Ceramic Media to get a the uniform, tumbled, matte finish shown on the part in the center of the picture. For this particular part a 2 hour cycle time with a general purpose tumbling compound resulted in the finish seen.

The second step (far right in picture) was also a 2 hour vibratory tumble with a Precision Ceramic polishing (porcelain-type) media and a high lubricity tumbling compound. The surface is improved to a more uniform and brighter finish and the part is ready for a clear coat or further polishing as needed.

3D Printed Parts

An interesting thread about deflashing and surface finishing 3D printed parts has been started on the ShopTalk Forum. As this 3D manufacturing process becomes more popular and mainstream, surface finishing using both barrel tumbling and vibratory tumbling will continue to be an issue. Please provide any comments and experience you have either on The Finished Part Blog here or on the Forum.

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.

Stainless Steel Finishes

There are four major types of surface finishes that are designated for stainless steel. While many of these finishes are somewhat subjective, below is a guideline for the most common finishes:

#3 Coarse Finish -- Usually a preliminary, coarse surface finish. Also referred to as rough grinding. Used for removing gates from cast parts, heavy burrs, weld splatter. Often accomplished with a disc or belt grinder but parts can be tumbled part-on-part with an abrasive grit to achieve a #3 finish.

#4 Brushed Finish -- Defined as a directional or uniform surface finish. Removes surface defects in the surface but accepts fine polishing lines. A #4 Sanitary Finish is a slightly smoother, polished finish commonly designated in the food, dairy and medical industries. Tumble polishing can be used to accomplish a close approximation to a #4 Finish.

#6 Fine Finish -- A polished, softer version of a #4 Finish. Often less reflective than a #4 Finish. No polishing lines or surface defects visible.

#8 Polished Finish -- All surface defect are removed. Mirror-like finish depending on the quality of the metal. Highly buffed surface.