Designing Modular Machine Enclosures

Aug 26, 2022 | Blast Resistance, Shielding Solutions

At TotalShield, we are frequently asked by our customers to develop shielding enclosures for potentially dangerous operating machines. These machines have the potential to release fragments, explosive gases or pose other dangers to the operator or a bystander. That is why we frequently design machine enclosures for the following scenarios:

  • High-speed rotating equipment, including centrifuges, fans, turbochargers, or drills
  • Machines that pose a risk of explosion, including generators and autoclaves
  • Machines that pose a risk of pressure injury, including equipment that uses high-pressure liquids or gases, such as catalytic reactors or compressors

Keep reading to learn more about how we design our polycarbonate machine guards. 

Our Process for Designing a Machine Guard

We use a collaborative approach to design a machine guard that involves our customer and testing partners. Our typical process for designing a custom machine safety enclosure involves the following steps:

  1. A customer approaches us with a hazardous industrial process and a desire to protect their employees.
  2. We quantify the potential modes of failure and the associated forces and energies involved.
  3. We check our proprietary testing archive to appropriately size the machine guard protection level.
  4. If the forces or mode of failure fall outside our existing test data, we engage with a third-party testing partner to validate our estimates and calculations.
  5. TotalShield designs and manufactures custom shielding solutions to protect the customer’s staff from potential harm.

Designing a sodium hypochlorite generator enclosure

A good illustration of this process is our work to develop machine guard enclosures for a municipal water system’s sodium hypochlorite generators.

Water treatment facilities are increasingly utilizing onsite sodium hypochlorite generators as an alternative to chlorine gas-based treatments. While these generators have environmental and cost benefits, they can also result in explosive failure in rare cases. 

Sodium hypochlorite generators use common salt (sodium chloride) and electrolysis to produce chlorine, hydrogen, and sodium hydroxide. The hydrogen gas produced as a byproduct of the reaction is vented. However, if the venting of this gas is interrupted, if the gas is accidentally pressurized within the system, or if the gas is combusted, an explosion can occur.

TotalShield was approached by a water municipality that experienced such an explosion in one of their sodium hypochlorite generators. Hydrogen gas built up and exploded, sending dangerous fragments into the surrounding area. Fortunately, no one was nearby when the accident occurred. The following image shows the damaged generator unit.

Damaged sodium hypochlorite generator.
Model of a fluid-filled acrylic tube under explosive overpressure.

The municipality engaged TotalShield to provide custom polycarbonate blast rooms as primary containment for all of its generators to ensure the ongoing safety of its employees.

Because the explosive and ballistic forces involved in the explosion of a sodium hypochlorite pressure vessel fell outside the parameters of our existing testing archive, we first calculated the theoretical forces involved. Using force modeling software, our testing partner modeled a fluid-filled acrylic tube under explosive overpressure.

To validate the model and calculations, we worked with our research partner to conduct a series of tests that simulate the explosion that can occur in this generator. The image at the right shows the test fixture that our research partner fabricated.

Test fixture for an enclosure.

The video shows the results of the explosive test:

To give an idea of the forces involved in this test, an unconstrained test of the fluid-filled acrylic tank resulted in fragments being ejected up to 96 feet away!

Acrylic tank used on proof testing.

Having verified the explosive loads associated with a sodium hypochlorite generator failure, we next designed a series of machine guard enclosures for the various generators installed throughout the municipal water system. Because these generators were already installed, we had to design our enclosures to conform to existing room and equipment dimensions and configurations. In addition, our enclosures needed to allow access to the end caps of the generators for maintenance, and all polycarbonate panels had to be easily replaceable in case of damage.

The following images provide a sample of the various enclosures we manufactured for this customer.

Clear machine enclosure-blue framing
Room enclosure for sodium hypochlorite generator
Sodium clear hypochlorite generator enclosure
Machine guarding design

Custom Machine Guarding for Hard-to-Fit Areas

Many customers contact us for machine guarding after the plant and equipment are already installed. This can be for a variety of reasons. Perhaps the equipment experienced an unforeseen failure during the initial design, and shielding is needed to prevent injury if a similar failure occurs in the future. Or maybe the customer has conducted a safety review and determines that there is a need for a safety enclosure in an existing facility.

In either case, a custom shielding solution is needed that will:

  • conform to the existing machinery dimensions and clearances around the machine
  • allow for service and operation of the machine
  • provide a modular construction approach in which all parts of the enclosure can be brought into the factory and assembled with minimal interruption to existing equipment
  • ensure the safety of plant personnel 

We can design custom enclosures that can conform to hard-to-fit areas in an existing plant. Our modular design allows small panels to be brought into the work area and assembled around existing equipment. This eliminates the need for costly equipment downtime.

For example, we designed two secondary containment enclosures for large centrifuges in an existing plant used in an industrial refining process. As the CAD model shows, the polycarbonate machine guards were designed with a top half removable for easy assembly and machine servicing. In addition, the shielding was designed to accommodate existing pipes, allowing the enclosure to be assembled in place.

CAD model showing a centrifuge enclosure.

The image below shows the two machine guards being installed in the existing plant. Note that the white wraps on the enclosures are to prevent scratches during installation. After installation, these wraps are removed, allowing for complete visibility of the centrifuge operation with enhanced safety.

Installation of a machine guarding.

Primary vs. Secondary Containment

We are also asked to provide both primary and secondary containment enclosures. Primary containment is the “first line of defense” in case of failure. For example, we have designed a polycarbonate blast room for an industrial customer designing and testing rocket motors. In case of a failure, our blast room will contain any fragments or pressure released.

We also design secondary containment as an additional level of protection for a machine that already has primary containment included in its design. 

Most industrial centrifuges come equipped with a metal containment structure designed to stop objects that might be accidentally released while the centrifuge is in operation. However, when a large payload is used in the centrifuge or when a catastrophic failure occurs (such as the separation of the centrifuge arm itself), the primary containment can be breached. In this case, we can engineer a secondary containment system such as a benchtop enclosure or room enclosure around the centrifuge to act as a secondary level of protection. 

The image below shows the centrifuge primary containment (blue steel enclosure) and the TotalShield secondary containment in the form of a clear polycarbonate blast room.

Clear blast room as a secondary containment for a machine.

As you can see, we design a specific shielding solution for each of our customer’s business applications. 
If your company uses a potentially hazardous machine or machining process, and you would like to discuss a customized solution for machine guarding, give us a call! We are always ready to help our customers stay safe.

Want to talk more?

Let us know your business needs, and our engineering team will start designing your shielding solution.

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