Environmental Stress Cracking in Machine Guarding

Estimated reading time: 5 minutes

Environmental Stress Cracking (ESC) of Polycarbonate

Polycarbonate is a versatile material celebrated for its exceptional strength, impact resistance, and optical clarity. As a preferred choice for machine safety guards and shields, it provides unmatched protection in industrial settings. However, polycarbonate is not immune to challenges like any material, including environmental stress cracking (ESC). This article delves into the phenomenon of polycarbonate ESC, its causes, and practical strategies to prevent it, focusing on safeguarding machine safety shields.

Many of our safety guards utilize polycarbonate shields, a highly impact-resistant material ideal for safety systems. However, certain chemicals, including esters and ketones, can compromise polycarbonate. Synthetic oils and some cutting fluids may also react with it over time.

Let’s find out if there is anything that we can do to prevent ESC and prolong the life of polycarbonate shields.

What is Polycarbonate Environmental Cracking?

Although our polycarbonate shields are coated with a protective layer, manufacturing can create surface tension, leading to micro-fractures. These fractures, though minor, allow oils to interact with the polycarbonate material, weakening its chemical structure.

ASTM D883 states stress cracking is “an external or internal crack in a plastic caused by tensile stresses less than its short-term mechanical strength.” This behavior is especially prevalent in glassy, amorphous thermoplastics like polycarbonate.

ESC in polycarbonate refers to the degradation and failure of the material due to exposure to certain environmental factors, particularly chemicals, stress, and environmental conditions. This issue manifests as small cracks or crazing, which may eventually compromise the integrity and functionality of the material.

Characteristics of Polycarbonate

Polycarbonate stands out as an excellent material for machine safety applications due to its unique properties:

Impact Resistance: With up to 250 times the impact strength of glass, polycarbonate can withstand high-energy impacts.
Lightweight: It’s easy to handle and install at half the weight of glass.
Optical Clarity: Ideal for transparent safety shields, offering clear visibility.
Thermal Resistance: Performs well in various temperatures, making it suitable for diverse industrial environments.

Despite these advantages, polycarbonate is sensitive to specific environmental and mechanical factors that can lead to ESC.

Causes of Environmental Cracking

ESC occurs when polycarbonate is exposed to the combined effects of mechanical stress and chemical agents.

Key causes include:

Chemical Exposure: Contact with certain oils, cleaning solvents, and industrial chemicals can degrade the polymer structure.
Mechanical Stress: Internal or external stress, such as bending, fastening, or load-bearing, increases susceptibility to cracking.
UV Radiation: Prolonged exposure to sunlight can lead to surface degradation. This can be observed in
Temperature Extremes: Repeated cycles of heating and cooling may weaken the material. In fact, when the polycarbonate reaches temperatures higher than the glass transition temperature (Tg), it is more susceptible to ESC. Unfortunately, the glass transition temperature is relatively low, at around 293°F / 145°C. Hot coolant, cutting fluids, and radiating heat from the machinery can cause the polycarbonate to heat past its glass transition temperature point, degrading it.

Key factors influencing ESC in polycarbonate include internal stress and external agents. Internal stress, often a byproduct of manufacturing processes such as extrusion or molding, creates vulnerabilities within the material that make it more prone to cracking. Meanwhile, external agents like oils, coolants, and cleaning chemicals can act as catalysts, further weakening the polycarbonate’s structure and accelerating the formation of cracks and crazing. These factors can significantly compromise the durability and safety of polycarbonate safety guards and shields.

Preventing Environmental Cracking

To enhance the longevity of polycarbonate safety shields:

Minimize Stress: Use proper installation techniques, avoiding over-tightening fasteners and over-bending the polycarbonate.

Avoid Harsh Chemicals: Opt for polycarbonate-safe cleaning agents such as glass cleaner. Check with your coolant and cutting oils manufacturer to determine if they are polycarbonate-friendly.

Check the MSDS sheets for the lubricants and cutting oils used in the shop. Avoid using anything that mentions “esters.”

Avoid products containing esters. Additionally, never use ketones (such as acetone), thinners, mineral spirits, strong bases, or solvents to clean polycarbonate surfaces. Steer clear of benzene, lacquer thinners, mineral spirits, or fuels, and avoid exposing polycarbonate to high humidity at elevated temperatures (such as steam).

Minimize Temperature: Prevent the polycarbonate from getting too hot. Don’t place polycarbonate shields too close to hot surfaces, including radiant heat from processes or machinery. Hot coolant or cutting fluid can accelerate ESC, and it is important to verify if polycarbonate is used as a splash shield.

Maintenance Tips for Machine Safety Guards

Maintenance of machine safety guards is essential to ensure their longevity and continued effectiveness. Regular inspections play a crucial role in identifying potential issues early on. By routinely checking for signs of cracks, crazing, or discoloration, you can address problems before they escalate into safety hazards.

Gentle cleaning is equally important, as harsh chemicals or abrasive materials can degrade the surface of polycarbonate. We recommend using mild detergents paired with soft cloths to clean the shields, ensuring they remain clear and damage-free.

Additionally, installing protective barriers can further enhance the durability of safety guards. These barriers help limit direct exposure to potentially harmful chemicals, oils, or coolants, reducing the likelihood of environmental cracking. Together, these maintenance practices prolong the lifespan of polycarbonate safety guards and ensure the safety and efficiency of the machinery they protect.

Future of Polycarbonate in Safety Applications

Emerging technologies are enhancing the durability of polycarbonate through innovative formulations and smarter coatings. These advancements promise to make safety shields more resilient and cost-effective.

The Ferndale Safety Advantage

We design all our guards and shields that use polycarbonate with easy replacement in mind. Some of our products have easy-to-remove clips, while others use screw fasteners which make it a breeze to replace worn-out polycarbonate.

What causes environmental stress cracking in polycarbonate?

Environmental cracking occurs due to stress and exposure to chemicals or UV radiation.

Can environmental stress cracking be repaired?

No, once cracking occurs, replacement is recommended to ensure safety.

What are the best cleaning practices for polycarbonate?

Use mild, non-abrasive cleaners and avoid harsh solvents.

4. How can I protect polycarbonate safety shields from UV radiation?

Apply UV-resistant coatings or choose UV-stabilized grades.

Is there a way to reduce environmental stress cracking in polycarbonate?

The best solution is to reduce or remove environmental factors that cause stress cracking in polycarbonate. These factors include high temperatures, chemical exposure, UV radiation exposure, and mechanical stresses.

Which industries are most at risk of environmental stress cracking?

Industries with processes that generate high heat and use harsh chemicals frequently encounter issues around stress cracking.