Being able to achieve efficient, cost-effective, and repeatable airless blast-cleaning results has long been a source of frustration and difficulty for many companies. The process, consumables, and equipment are not overly complex, so why is it that cleaning results and costs are so difficult to successfully manage?
This article will address some of the most commonly seen problems, and how a new and different abrasive, Frohn Rapid-Blast shot and the Sinto WE series air-wash separator will reduce process variation and help to lower blast-cleaning costs.
How to Reduce Process Variation and Lower Blast-Cleaning Costs
1. Keeping the hopper full - with automatic shot adders, this is typically not an issue. Without them, it can be a problem.
A low hopper level will increase the temperature of abrasive causing faster breakdown by increase of the rate of fatigue of particles. Shot fatigues with use as it absorbs energy as well as transmits energy to clean.
A low hopper will cause the blast pattern to move due to size distribution issues caused by low hopper level.
A low hopper will increase maintenance costs due to #2 and resulting leaks associated with hot-spot movement.
2. Keeping the operating mix clean and dust-free
TThe tool used in airless blast-cleaning is typically high- or low-carbon cast carbon steel shot and/or high-carbon grit. Depending on the application, cut-wire shot and stainless-steel shot/grit are also appropriate for use. The important thing to keep in mind regarding the tool is that it must be kept free of abrasive fines and dust, and the particle size distribution (coarse, medium and fine size particles) must be maintained to work properly.
The ventilation system includes the air-wash separator and dust collector, which are the primary components that ventilate the blast cabinet. They clean dust and fines out of the operating mix and control the particle size distribution in the machine. Clean means dust-free in our case and is important in terms of keeping parts and the plant clean, but also keeps maintenance costs low and reduces variation.
Abrasive dust is not spherical; a percentage of abrasive dust is angular and sharp. This shape scraping along component surfaces is a major source of wear and size classification and is also critically important.
3. Keeping the particle size distribution consistent
Keeping steel shot operating mix in the proper size distribution is critical for cost control and consistent results. For blast-cleaning, the mix of sizes should be kept in large/coarse, medium, and fine sizes in proportions recommended by your provider. A good rule of thumb is 60% large, 30% medium, and 10% fine. This will provide the energy to clean difficult areas and provide the best coverage to reduce cycle times. Notice zero (0%) dust in the pan. Experts in the industry recommend that 2% of dust in the operating mix will increase maintenance costs by 50%, a large factor when considering costs and profits.
A consistent size distribution will also keep the hot-spot and blast pattern in the same place. A correctly calibrated blast-pattern is critical to efficient cleaning, and maintaining the operating mix size distribution will keep the blast pattern from moving.
Why it is Difficult
The entire shot-blast system is dynamic. Multiple parameters that change performance are ever-changing depending on air-flow velocities, operating mix size distribution, component wear, abrasive leaking from cabinet, and amount of shot in the hopper. These parameters are the most critical for control of process variation.
High wheel wear
Parts not getting cleaned
Longer cycle times
Excessive abrasive consumption
Dust on parts
Leaks in cabinet
Dust in operating mix
Hot-spot setting, operating mix too fine
Hot-spot setting, operating mix too fine or coarse
Leaks, abrasive carry-out
Air-wash efficiency, air-flow volume
Hot-spot has moved, operating mix not optimal
It is always recommended to contact your abrasive supplier if you see problems of this nature. They should be able to check the machine and provide a detailed explanation and corrective action to solve these issues.
Ideas to Help
One of the main variables is abrasive consumption. Depending on the breakdown rate of the product(s), this can contribute to process variation. Higher consumption products such as HG grit or hard shot will exacerbate issues.
For this reason, Frohn has developed Rapid-Blast. A cast shot/cut-wire shot blend in ratios specifically designed to reduce consumption and reduce cycle times. This product can help in most situations and provide the most efficient tool for cleaning parts. It is available in sizes to fit any application.
Using the Ervin test machine, we have data showing improvement in two important cost-determining factors. Customer trials validate these lab results and in some cases are even better in terms of abrasive consumption.
Not only can the abrasive media make a difference, but keeping control of the abrasive media’s size distribution is of critical importance. The WE-3 air-wash separator performs this function. Proper control of the tool or operating mix in our case affects everything from the hot spot of the blast wheel(s) to cleaning rates and operational costs.
The WE air-wash separator by Sinto is the most accurate, hands-off air-wash separator on the market. It is so efficient that 99.7% of dust, sand, and fines can be separated on the first pass eliminating the need for magnetic separation. Magnetic separators work great but they are expensive and are mechanical, which requires maintenance and can contribute to variation.
Issues with process variation and inefficient blast-cleaning are seen more frequently now vs. just a few years ago. Multiple reasons contribute to this, but the primary cause is lack of maintenance resources and loss of tribal knowledge in the workforce.
No time or resources available for PM
“We lost our expert/s”
“We have more important problems to solve”
Whatever your situation, it is possible to improve blast-cleaning results and reduce costs by following some simple guidelines.
Perform sieve analyses to verify operating mix is correct. Check and maintain proper air-flow in the air-wash separator.
Check and maintain full spread of the abrasive curtain.
Maintain the correct abrasive level in the blast machine.
Replace abrasive that has leaked or has been carried out.
Make small incremental improvements in process, products, and people (training) every day.
Sinto USA and Frohn North America are continuously working to develop new products that bring value to our customers and move the industry forward. If you have interest or are having issues related to process variation, call Sinto/Frohn for assistance.
ROBERTS SINTO CORPORATION
A SINTO AMERICA, INC. COMPANY
150 Orchard Street
Grand Ledge, MI 48837, USA