off any residual oils, prior to glass bead blasting.
This block has been degreased, but surface rust and some contaminants remain.
The same block has now been shot blasted and tumbled. The block is now ready for machining.
There are instances where washing/scrubbing and rinsing by hand are applicable, such as performing a final wash and rinse of an already-machined engine block prior to assembly. Using very hot water (as hot as your hands can tolerate) and Dawn dishwashing liquid can produce excellent results. With the block on a stand that allows you to rotate the block, shoot hot water into all oil and coolant passages, and then pour Dawn into the same passages. Using dedicated (and clean) bristle brushes that are designed for block cleaning, scrub passages as access permits; follow with multiple hot water rinses until all traces of soap are eliminated.
This Chevy big-block has been stripped down and placed into a cleaning oven. The block is secured within a tubular cage. With the cage mounted in the oven, the machine rotates the block during the thermal cleaning process to distribute heat evenly, cooking off all grease, paint, rust, and sludge.
Here, the airless shot blasting process has been completed, resulting in a clean, down-to-bare-metal block that’s ready for tumbling. After the block has cooled down in the oven, the block, still mounted in its cage, is moved to an airless steel shot blasting cabinet, which cleans off the ash created by the oven.
An enclosed blast cabinet can be ideal for cleaning certain parts, such as pistons, connecting rods, mounting brackets, valvecovers, etc., but the media must be selected carefully. A variety of blasting media is available, including but not limited to “glass bead,” crushed walnut shells, crushed corncobs, crushed pecan shells, plastic bead, and soda. Depending on the media, you can accomplish not only cleaning to bare metal, but also lightly deburring razor-sharp edges where desired. Never use a high-abrasive media such as sand, which is simply far too aggressive. If an abrasive media is used, such as glass bead, the component must be thoroughly and carefully washed and rinsed afterward to remove all bead particles. For that reason, it is not wise to glass bead blast an item such as an intake manifold, because the possibility of particles being trapped inside runners is too great.
The cage is then disassembled and removed from the block. Using the shop’s overhead crane, the caged block is removed from the shot blaster.
Finally, the block is placed into a rubber-lined tumbler drum. The drum rotates, allowing the block to tumble randomly. As the block tumbles, any remaining steel shot is knocked loose and removed from the block.
Block Cleaning Brushes
Regardless of the method of degreasing used, always clean oil and water passages with appropriate-sized bristle brushes. A long-bristle rifle brush can be used to clean oil galley passages from the front to rear of a block. Small-diameter rifle brushes can be used to clean oil passages in crankshaft main and rod journals. A dedicated-diameter, long-handled rifle brush can be used to clean camshaft bores. Very small-diameter specialty rifle brushes are also available specifically for cleaning the inside of oil-through pushrods. After brushes have been run through any passage, the passage must then be rinsed with pressurized hot water followed by blowing dry with compressed air. After you’re finished with brush work, and before you store the brushes, wash all brushes with hot water and detergent and rinse with hot water to remove any contaminants from the bristles.
Cabinet Tips
Blasting cabinets are wonderful pieces of equipment to have in any shop for cleaning, deburring, and/or achieving a soft “footprint” for planned coatings. However, long-term use creates some wear issues. The viewing window (usually glass) can eventually become etched, even if you’re not blasting directly into the window. Although this doesn’t affect function, it makes viewing more difficult. Consider installing peel-off clear window film on the inside surface of the glass. Just like peel-off clear film that’s used on many race helmet visors, as the exposed layer of film becomes etched/foggy, you simply peel off to expose the next layer, or peel off the existing layer and install a fresh layer. As an example, Goodson Tools & Shop Supplies offers these films (you can cut to fit your window) under P/N GB-FILM. The use of this protective film saves the expense and time of replacing the viewing glass.
Keep an eye on the cabinet door gasket. Especially if the cabinet is designed to open from the top (with the weight of the door continually compressing the gasket), the seal can eventually become compressed, leading to a loss of cabinet vacuum (assuming your cabinet features a vacuum pump) and external media leakage. With the cabinet door closed and matched, when you turn on the cabinet’s vacuum pump, your glove arms should quickly be drawn into an extended position (as though they were being inflated). If not, you have a vacuum leak.
Blasting cabinet gloves are always an issue, especially when you’re blasting smaller handheld items, where you end up blasting into the glove fingertips. Buy the highest quality gloves available to extend fingertip life (avoid the bargain imported stuff). A variety of glove styles is available, some made as one-piece (glove and arm) and some with replaceable gloves (attaching to the arm sleeve with a clamp). If you’re replacing the arm sleeves (whether the arms feature integrated gloves or separate gloves), you need to order them with the appropriate port hole size so that the entry of the sleeves fits your cabinet’s ports. Also, make sure that the sleeves are long enough to enable you to reach all the way to the rear of the cabinet. Short arms are annoying, forcing you to stop work and open the cabinet to retrieve an item that’s out of reach.
Pay close attention to the cabinet’s interior lights. Use only the type of bulb recommended by the cabinet manufacturer. The bulbs must be heavy duty, with outdoor-grade glass that’s thick and withstands accidental blasting.
If you expect to rely on your blasting cabinet, keep spare consumables at the ready to avoid downtime. This includes spare light bulbs, gloves, a viewing glass, blast gun nozzle (ceramic or carbide), feed hose, hose clamps, and door seals. Preplanning avoids the need to place an emergency order from an out-of-town supplier while the cabinet sits idle.
Depending on the location of your blasting cabinet, you might consider a freestanding welding curtain that surrounds the cabinet area. Unless the cabinet is located in a separate “dirty” room, this minimizes airborne media dust that can easily scatter throughout the shop.
Prior to glass beading any part, the part should already be thoroughly degreased, removing all grease, oil, and soft sludge. Otherwise, bead sticks to these contaminants, potentially trapping bead in crevices and holes. If a cleaning oven is available, the part may be cooked for a few minutes to remove any oils prior to glass beading.
