Silicon carbide (SiC) heating elements provide high-temperature resistance, low thermal expansion coefficient, and excellent chemical stability. They are widely used in high-temperature processes of body sintering and glaze melting, meeting the requirements of various kilns and furnaces.
In production, the failure of SiC heating elements is a big challenge for many ceramic manufacturers. To help address it, this article analyzes the causes of SiC heating element failure. Through practical production cases, provide measures for extending the service life of SiC heating elements and reducing production costs.
3 Major Causes of SiC Heating Element Damage
The causes of SiC heating element damage can be categorized into 3 types: physical damage, improper operation, and environmental factors.
Physical Damage
Silicon carbide heating elements are hard and brittle. They possess relatively weak compressive and impact resistance. Improper handling in transportation, storage, or installation can result in latent damage, causing the elements to break during use.
Transportation Collisions
SiC heating elements are usually transported in batches. If the elements are not wrapped in layers using cushioning materials or if they are subjected to jolting and stacking pressure during transit, micro-cracks can easily form. These cracks expand rapidly under high temperatures due to thermal stress, finally leading to the fracture.
Silicon Carbide Heating Elements Breakage Due to Packaging & Transportation IssuesImproper Storage
Storing SiC heating elements in a damp warehouse can cause the aluminum layer at the cold end to decompose and peel off. It often leads to cracking after the power is turned on.
In addition, debris falling and striking the elements can directly cause damage or breakage. When SiC heating elements are stacked for long-term storage, the products at the bottom may deform, affecting installation and increasing the risk of damage.
Incorrect Installation
If the furnace holes are too small, or the furnace packing is stuffed too tightly, the elements will be unable to rotate freely, which triggers fractures. Excessive force also causes damage.
Moreover, when the length of the heating zone does not match the furnace width, parts of the heating zone extending into the furnace wall will burn the wall. This will cause localized overheating, leading to damage to the heating element. If the cold end extends beyond the furnace wall ＜50-150mm, it results in insufficient cooling of the connecting clamps and damages the SiC heating element.
Improper Operation
Lack of sufficient understanding of SiC heating elements or not following kiln operating procedures results in damage. Standardized operations can effectively avoid these problems.
Improper Resistance Matching / Wiring
The resistance value of SiC heating elements increases as temperature rises and service time lengthens. When using multiple elements, not measuring and matching resistance values results in uneven load distribution within the same kiln. Elements with higher resistance will bear more power, leading to early failure.
Connecting multiple SiC heating elements in series causes the resistance of individual elements to rise rapidly, shortening their service life. Ceramic kilns should utilize parallel wiring.
Improper Temperature Control
Applying the rated voltage during the power-on phase causes the SiC heating elements to heat up too rapidly. This excessive speed of thermal expansion and contraction generates internal stress, triggering fractures.
Frequent Shutdowns
During continuous use, SiC elements will form a SiO2 protective film to slow down oxidation. Intermittent shutdowns cause the film to rupture repeatedly, significantly accelerating the oxidation.
Excessive Surface Load
The surface load of a SiC heating element is the ratio of heating power to the surface area of the heating zone. The higher the load, the faster the oxidation and the shorter the lifespan. Increasing the power of the elements to pursue efficiency leads to excessive surface loads, accelerates aging and breakage.
Maximum Temperature & Surface Load of SiC Heating Elements in Different AtmospheresUnable to Dissipate Heat
As a result of close packing of the green bodies in the furnace or insufficient ventilation of the system, the heat generated by the SiC heating elements cannot escape effectively.
When the distance between the SiC heating elements and the green bodies or the inner wall of the furnace becomes less than three times the size of the heating zone diameter, heat accumulation takes place. Localized overheating will exacerbate aging and damage.
Environmental Factors
The atmosphere and humidity within the ceramic kiln significantly affect the service life of SiC heating elements.
Atmospheric Corrosion
Alkali metals in glazes will volatilize at high temperatures to form alkali vapors. They can combine with the SiO2 film and produce low-melting-point sodium silicate glass, dripping to damage the film and thus accelerating oxidation.
Damp green bodies will release large amounts of water vapor when entering the kiln. They react with the silicon carbide to produce SiO2 and hydrogen, weakening the heating elements’ mechanical strength.
Humid Environments
Excessive humidity in the production workshop or poor kiln sealing makes SiC heating elements absorb moisture. When energized, the internal moisture evaporates rapidly, generating internal pressure that easily causes bursting or cracking.
A humid environment also accelerates oxidation at the cold ends of the heating elements, leading to increased contact resistance and severe localized heating.
Case Study of SiC Heating Element Damage
A ceramic manufacturer specializing in daily-use ceramics utilizes a roller kiln with U-shaped silicon carbide heating elements for body sintering. The enterprise experienced frequent fracturing of elements.
Some elements broke within 1-2 weeks of being energized, while others were damaged after about 1 month of use. It caused fluctuations in kiln temperature, resulting in product defects like glaze cracking and deformation, severely impacted production.
Upon investigation, the reasons for the damage to the heating element were identified in 3 main areas.
Oversights in Transportation and Inspection
This batch of SiC heating elements was packaged in wooden crates with only simple foam filling. Vibrations during transport caused latent cracks in several ones.
Moreover, the enterprise didn’t conduct surface inspections or resistance tests. After receiving the materials, they installed them directly for use.
Non-standardized Operations
To increase efficiency, operators applied the rated voltage directly during the power-on stage, causing the elements to fracture due to rapid heating. And the kiln was shut down intermittently 2-3 times daily, causing the protective film to rupture repeatedly.
Material Corrosion
During the feeding process, the glaze was not mixed evenly. It led to molten glaze splashing onto the surfaces of the SiC elements, causing long-term corrosion.
Incompletely dried green bodies also released huge amounts of water vapor, further aggravating the damage.
Improvement Measures
To solve these problems, the enterprise implemented the measures below.
The packaging method was changed to a double-buffer system using layered EPE foam and traditional foam. It added surface inspection and resistance testing procedures during receiving to eliminate damaged, damp, or out-of-tolerance elements.
Improved Silicon Carbide Heating Elements PackagingOperators were required to apply only half of the rated voltage during the power-on phase, gradually increasing it when the furnace temperature stabilized. It also reduced frequent intermittent shutdowns. During inactive periods, the furnace maintained a constant 400℃ for heat preservation.
They regulated the glaze mixing process and feeding operations, extending mixing times to ensure uniformity and prevent glaze splashing. Besides, they also extended the drying time for green bodies, adding a testing phase to ensure bodies are completely dry before entering the kiln.
Following these improvements, the service life of the heating elements was extended to over 3 months. The stability of the kiln temperature improved significantly. The product defect rate dropped markedly, effectively securing the production efficiency.
FAQs
- What is a silicon carbide heating element?
Silicon carbide (SiC) heating element is a non-metallic electric part. It is made from high-purity green silicon carbide. These elements provide excellent high-temperature resistance and stable performance for harsh industrial thermal processes.
- How to recognize a bad heating element?
The appearance of uneven temperature or cold spots in the furnace.
A rapid rise in the electrical resistance of the elements.
A physical breakage, or arcing, is an indication of the problem.
Conducting regular testing can help find any aged heating elements.
- What are the signs of a bad silicon carbide heating element?
The signs of a damaged SiC element mainly include cracked or fractured components. Other signs are:
Aluminum layer is peeling off.
Dark spots on the component.
Glaze splashes on the surface of the heating component.
- How long is the lifespan of a SiC heating element?
Standard industrial use typically lasts several months.
Proper voltage control and dry environments extend service life. Frequent shutdowns and chemical corrosion significantly shorten it.
Conclusion
Silicon carbide heating elements are often damaged by wrong transportation, installation, operation, as well as environmental influences. By identifying the causes of damage and standardizing operations, you can reduce element loss while ensuring stable operation, improving product qualification rates.
Do you need professional services for SiC heating elements from design to installation? Please feel free to contact Newthink New Materials. We provide high-quality silicon carbide heating elements to support the steady progress of your industrial production.
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