Need to Know: Potential Savings Seen

April 11, 2005
with Pass-through Blast Cleaning

A pass-through blast cleaning system offers the potential for reducing blaster operating and maintenance costs per cleaned part by 20 to 50% compared to batch-style blast cleaning. And, depending on material handling upstream and downstream from the blaster, pass-through blasting should reduce labor costs associated with cleaning by 50 to 90%.

Those are key selling points for Viking Blast and Wash Systems, which offers several pass-through blast cleaning systems for metalcasters. It has been developing the pass-through concept for most of the past 25 years, and also makes standard batch-type blasters, washers and vibratory shakers, and dust collectors.

According to Deron J. Lock, Viking general manager, pass-through cleaning is particularly advantageous with products too delicate to tumble, such as aluminum castings with protrusions or fins. It also is advantageous with some castings with a mass that makes tumbling impractical.

The pass-through concept is illustrated in the photo and the diagram. Castings are shown loaded onto an 18-in. wide manganese alloy mesh belt. The belt conveys them into the blasting chamber, where they pass through a pattern of abrasive thrown by multiple blast wheels. The diagram illustrates the blasting patterns generated by six blast wheels. In the photo, a reservoir for blast media, the media cleaning system, and a dust collector are mounted above the blast cabinet.

Conveyor openings and cabinet sizes are determined by the range of casting sizes to be processed. Castings are fed into the machine by robot, conveyor, or by hand.

Viking offers pass-through blasting systems in a series of standard designs, which may be customized to match a foundry’s particular requirements. Customization is easy to do and important for “right sizing” the machine to the casting size and configuration.

According to Lock, “Most people believe ‘changes’ to the standard design are expensive, but really they are not. The extra cost of customizing is small compared to the efficiency gained by having the right machine for the part.”

The Viking blast wheel generates a velocity of nearly 300 ft/second, making it one of the most cost-effective cleaning wheels on the market. Viking blast wheels are bi-directional, run at 3,600 rpm, and are said to be efficient, rugged, and easy to maintain.

Generally, four, six, or eight wheels will achieve good 360° coverage, and provide multiple impact angles on casting sides, tops, and bottoms, as well as leading- and trailing-edge impact angles. Sometimes a wheel can be mounted to point at a particular problem area, assuming that the casting can be placed on the belt with a consistent orientation.

In addition to adding blast wheels, the processing capability for any particular design can be customized by boosting blast wheel horsepower and adding abrasive conveyance capability. A machine can be set up with only one 10-hp blast wheel, or as many as eight 30-hp blast wheels.

Belt speed is always variable depending on the kind of casting or the desired processing speed. A variable speed drive, for example, may have a processing speed ranging from three up to 15 fpm, or even faster.

Most parts can be successfully blasted on a pass-through system, but there are limitations, Lock says. Some parts with deep holes or pockets tend to carry out abrasive. Abrasive can be removed from these cavities in some cases using high-velocity re-gen blowers, though he admits, some parts just will not clean out.

Some castings, with many interior angles, may not receive coverage as thorough as they would with a long cycle in a tumble blaster. Another limitation comes with heavy, flat parts. They may exit the system with a belt pattern on the bottom where they sit on the belt.

Lock points out that the pass-through blasting system has a higher initial capital cost, but that can be offset over time by lower operating and labor costs.