Top Six Pointers for Maintaining Your Shot Blast Machine
1) Safety first:
Shot leakage is often a nuisance item that does not really affect the immediate blasting capability of the unit. Shot build up on the floor however, is a slip and fall hazard, while abrasive escaping at velocity is an eye protection concern. This concern goes right into the overall shop cleanliness for safety objective. Leakage areas:
A) Vestibule seals are normally of a flexible urethane, Lexan or rubber and wear or break over time. Order these replacements in advance for shutdown opportunities. Cabinet seals are designed to be changed out regularly and do not require great skill.
B) Shaft seals are robust and effective, but over time can loosen up allowing a trickle of shot that adds up over time. These shaft seals should be replaced when the shaft or bearings are replaced. Accumulating shot can destroy a bearing as well as being a safety concern.
C) Monorail slot seals are not often considered as they leak on the top of the unit out of view by ground level visual inspection. Regular visual inspection is needed. If left untended, shot will exit at velocity and make it to the floor eventually. These seals are often made of rubber and/or brush, as well as internal shielding made of manganese or cast materials. It is wise to have these materials on hand as well for maintenance at shutdown times.
2) Blast Cabinet integrity:
While blast wheel maintenance is the primary ongoing, common service item of all wheel blast machines, it is not typically the factor that effects the long-term viability of the unit as blast wheels are a bolt on component. Neglected cabinet maintenance can compromise the structure, viability, and associated safety of the unit. Cabinet maintenance is another review consideration that is not easy to observe without intentional visual inspection at the appropriate intervals (100-300 hours depending on conditions). Cabinets are normally lined with replaceable cast plates, manganese, or AR plates. Viking blast cabinets have no welded liners and all liners are replaceable. Cabinets are designed to provide longer intervals between inspection and potential maintenance and are often overlooked due to personnel changeouts, maintenance personnel shortages or neglect. Significant disregard to blast cabinets and vestibules can lead to structural and wall compromises which requires longer down time to repair than just an internal liner replacement. These seemingly small areas grow quickly. Temporary covers and makeshift patches should be considered temporary until correct liner replacement or repairs are complete! That is tantamount to a decision to compromise a significant investment in production capability. Viking has a team of service personnel and service trucks available to help with these issues. Please consider consulting Viking for repair advice or field service.
3) Blast wheel maintenance:
Due to the maintenance friendly nature of the Viking blast wheel, this does not rank as #1 or #2, but it is the most maintenance intensive part of all blast units. Proper maintenance and targeting are at the very heart of blasting efficiency. After a Viking service tech performs a thorough visual inspection of the unit, he will prioritize maintenance and service issues, and blast wheels almost always get first attention. Upon consultation about cleaning results, a service tech will verify proper abrasive load on the wheels and perform visual inspection of all the wheel components. VMAX blast control cages will typically last two blade changeouts, but we frequently recommend changing them together, to maximize targeting efficiency. Viking engineers have located the wheel position and control cage position based on 3-D modeling. As wear in the control cage opening broadens the pattern, taking some of the abrasive out of the target zone, reducing efficiency and accelerating unnecessary cabinet wear. Depending on wear the impeller is often changed while the wheel is torn down. The blast wheel liners (some manufacturers don’t include these) are very robust so visual inspection at each blade change is sufficient and can last up to 3 blade changes with some variabilities. Viking will always have ample supply of blast wheel consumables, but one full changeout of wheel wear parts in your maintenance department is prudent. (blades, impeller, control cage, set of 3-wheel liners)
4) Dust collector performance:
Viking supplies a dust collector with most units, and our service techs are very capable of adjusting for proper airflow and maintenance. Viking dust collectors are engineered to have between 6 and 20 air changes in the cabinet per minute, depending on application and proper duct speed. Negative pressure should be visible in the seals and airwash separation system. Most collectors have a means to determine differential pressure between the clean and dirty air-chambers within the dust collector by use of a magnahelic or photohelic gauges. This pressure differential is the #1 indicator of filter condition. Filter cartridges typically have an operating life of 0-5” on the mag /photohelic gage and should be kept in stock to minimize down time and possible emergency expedited freight. Dirty cartridges compromise airflow for evacuating dust from the cabinet, cleaning the abrasive in the airwash, and reduction of velocity within the ducting. Reduced duct velocity is a serious safety concern, as dust could settle in the duct work prior to duct cleaning intervals. Duct cleaning should be done as required, but thoroughly inspected at least every 6 months, and cleaned if needed. Be mindful or your, unique conditions regarding the need for duct cleanout. Viking service techs are not equipped to do this, so make sure you hire a local, capable contractor to inspect and clean out ducting with accumulated dust. Develop your own in-house capability to inspect regularly as well. Make your company aware of all NFPA safety requirements regarding dust in your particular application whereby informed decisions can be made concerning potential dust hazards and disposal. Consult your local fire suppression service to get a dust hazard analysis if you don’t have one. They can help you with all fire suppression, explosion protection, and mitigation. Be sure and use a qualified installer and inspector for all your fire suppression, explosion protection and other mitigation requirements.
5) Airwash separator:
The airwash allows you to drop a thin even stream of abrasive into the storage hopper while drawing a forced airflow through the abrasive as a way of removing fines and dust. There is no benefit in throwing dust, or abrasive too small to impart significant kinetic energy. Furthermore, dust and sand are more abrasive to wheel wear parts than clean abrasive, so it is very important to maintain a properly tuned air wash and air flow. Your Viking technician can make all these adjustment with basic hand tools. Depending on your conditions it may be wise to do a sieve analysis of the abrasive returns to the storage hopper. Visual inspection of the abrasive is pretty telling, but sometimes actual data analysis can yield improvements.
6) Media selection:
This one is not as difficult as some new blast machine consumers may suppose. While important, it is relatively easy and inexpensive to change media if staying with the same base metal. This recommendation only addresses metallic abrasives. We recommend using the smallest carbon steel shot that provides the profile, and SSPC finish required in most cases. Carbon steel shot is the most cost effective if the application allows it. Smaller shot breaks down slower and causes less wear on the blaster. There are 11 basic shot sizes, and 10 basic grit sizes all with approximately the same cost per pound. In selecting abrasive, we prefer work from smaller media to larger in the media sizing process. Viking can make recommendations on media selection and sizing as well as perform in-house testing to verify the approximate abrasive requirements. For more information about carbon steel shot or grit, cut wire, stainless steel or zinc abrasives consult a Viking service tech.