Blast Cleaning 101

In our Beyond the Blast series, we explored “What is Shot Peening?” and “What is Shot Blasting?” answering the most frequently asked questions our Bronco team receives on each topic. We now dig deeper into blast cleaning, providing an introductory technical tutorial. Understanding blast machine fundamentals allows you to troubleshoot and efficiently improve your shot blasting operation.

Wheel blast equipment has five key components:

Each component plays a critical role in the blast machine’s operation. If one component is not working properly, machine efficiency and performance are affected. 

Blast Wheel

The blast wheel is the heart of any blast machine. Originally patented in 1932, the blast wheel has seen countless changes and improvements since its inception. 

The impeller moves abrasive through an opening in the control cage.  The control cage ensures the abrasive is evenly distributed onto the blades at precisely the right time. The abrasive picked up on the leading edge of the blades rapidly accelerates and leaves the end of the blades in the form of a blast pattern with a relatively narrow width and variable length. Once released, the abrasive must be properly focused on the work surface to be cleaned. 

The impeller, control cage, and blades are directly responsible for a blast cleaning machine’s efficiency, cleaning, and equipment lifespan. Wear affects blast wheel efficiency. Worn blast wheel components like the blades, control cage, or impeller are the primary cause of changes in the blast pattern. This wear slows down the abrasive flow and creates erratic patterns, increased wear, and less efficient cleaning. The key to ideal performance is to inspect these parts regularly and replace worn parts before excessive wear is detected.

Separator

Without clean abrasive material in the machine, the blast wheel will not clean efficiently. A good separation system is required to clean the abrasive material.

A separator removes contaminants from the abrasive operating mix so that only clean, properly sized abrasive is returned to the blast wheel for reuse.

There are a few different separation methods, all of which aim to maintain a proper operating mix and produce a consistent, repeatable result. A good operating mix includes a wide range of abrasive sizes, which play an important role in creating the desired finish. A good operating mix also means less wear on the internal wheel components. Excessive contaminants, such as sand, abrasive fines, and dust, are sometimes more damaging to the equipment than the abrasive material used to clean your products.

Two common separation methods are:

The abrasive curtain must be evenly distributed over the air orifice and flow at a uniform rate to maintain efficient air washing. If the curtain has a void or opening, the air will follow the path of least resistance and enter the void opening at an increased velocity. The increased velocity at the void removes usable large abrasive particles that should remain in the operating mix. A spreader bar and adjustable swinging baffle are required to ensure a full width of material is presented to the air currents This uniform, low-velocity curtain permits a more thorough air washing of the abrasive.

Separator efficiency is affected by the flow of the abrasive through the air stream, the size of the orifice, air velocity, and the distance from the abrasive curtain to the expansion chamber.

The degree of success of the separator performing this operation helps determine machine wear, abrasive consumption, and the speed and quality of cleaning.

2. Mechanical Separation

While most applications can use simple air wash separation, other methods, such as mechanical separation, are sometimes required based on application parameters or to improve separation due to heavy sand loads. Mechanical separation is typically achieved using a vibratory screener, magnetic drum, or rotary screen.

For example, shot peening applications require a very specific shot size to produce the desired result. In this case, a vibratory screener is used to ensure only properly sized abrasive material is returned to the hopper for reuse.

A magnetic drum separator may be used in sand foundry applications to more efficiently separate sand from the rest of the metallic abrasive being used.

Rotary screen separators efficiently remove flashing, gating, chunks of sand, and other large debris. In this design, abrasive travels through a perforated rotary drum to remove large contaminants and foreign objects from the abrasive stream. Usable abrasive falls through the drum’s perforated holes, and large contaminants fall down a discharge hose.

While mechanical separation can be incorporated into the abrasive handling system, air wash separation is still necessary to remove residual fines and dust from the abrasive stream.

Ventilation

Proper ventilation is a critical part of the blast cleaning process. Dust collectors provide three important functions related to the clean and efficient operation of a blast cleaning machine. 

The functions of a dust collector are:

• Maintain a consistent airflow through the separator to efficiently separate abrasive materials.
• Provide negative pressure inside the blast cabinet. By creating negative pressure in the cabinet, outside air is drawn in and travels to the dust collector with the residual dust created by the blast cleaning process.
• Retain the fine particulates created by the shot blasting process that would otherwise be exhausted into the atmosphere.

The dust collector must provide the required amount of air at a constant rate for all three of these elements to function properly.

While it is frequently overlooked, dust collection is crucial to the performance and safety of any blast machine.

Abrasive Handling

Work Handling

The work handling system conveys the parts or material to be cleaned into the abrasive stream. Choosing the proper work handling system ensures the parts will be cleaned efficiently.

There are four general types of work handling designs:

Regardless of the work handling design, all equipment requires proper maintenance to ensure efficient and safe cleaning.

Understanding your blast machine is key to efficient cleaning. For more in-depth knowledge on blast cleaning, our Bronco team of experts is ready to help. We can answer your questions, recommend the perfect equipment for your needs, and provide ongoing support to ensure your blast cleaning success.