Automotive Machining. Mike Mavrigian
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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.
Glass bead blasting cabinets feature rubber gloves that allow the operator to handle and manipulate parts in the cabinet. These gloves are prone to wear and should be inspected on a routine basis. Gloves are available in various sleeve diameters and lengths to accommodate all blasting cabinet models. A blasting cabinet features a glass viewing window. The inside surface of the glass eventually becomes abraded, making it difficult to see through. Depending on how much use the cabinet sees, plan to replace the glass about once each year.
Blasting cabinet guns feature a ceramic nozzle that provides the appropriate media spray pattern. The ceramic nozzles, although very hard, eventually wear, lowering media blasting efficiency. Nozzles are easily replaced. It’s wise to keep a few new spares handy.
A view of a hopper in a glass bead cabinet. Depending on the cabinet’s hopper design, media may start to build up on the tapered walls. In conjunction with airborne moisture absorption, the media is less able to accumulate over the media feed tube. Keeping the hopper full with the required level of fresh media helps to avoid this.
Maintaining a blast cabinet’s clear viewing glass and adequate dust vacuum improves worker visibility.
If the part to be cleaned features hidden passages that cannot be positively cleaned, avoid blasting with an abrasive media. Also, avoid bead blasting into female threaded holes, since beads can be trapped, and the abrasive action can degrade the thread integrity. After bead blasting, use compressed air to flush all traces of the bead particles. Do not try to initially remove bead particles with a wet rinse, as this can easily cause beads to be stuck to surfaces, possibly in small clumps inside any passages. Also, never use an abrasive media on a part that is wet or features oil or grease. The part must be degreased, rinsed, and dried prior to blasting.
Concerns about potentially contaminating threaded holes with media can be avoided by plugging these holes with temporary bolts. After bead blasting, remove the bolts and manually clean female threaded holes with a chaser tap and solvent. I discuss the use of chaser taps later in this chapter.
Soda (sodium bicarbonate, essentially a form of baking soda) is a nice choice, since it’s water soluble and allows easier removal via rinsing. Soda’s benefits include being able to clean even surfaces that are still contaminated with oil or grease. Soda does a great job of cleaning, but it does not allow you to soften sharp edges because it’s not as aggressive as other media such as glass bead. Although soda might be usable in a conventional blast cabinet, it’s best to use a blast system that is designed for soda for highest efficiency and dust reclamation.
There are distinct advantages to the use of soda, instead of traditional methods