How to Make Furnace Heating Elements Last Longer

Simple checks and habits that help silicon carbide and MoSi2 heating elements last longer and fail less often.

Heating elements are the heart of an electric furnace. When one fails, production stops, and replacing a full set costs real money. The good news: most early failures have simple causes, and a few habits can add a lot of life to your elements.

This article covers both common types: silicon carbide (SiC) and molybdenum disilicide (MoSi2).

1. Fit them carefully

Ceramic elements are brittle. Many break before they are ever switched on.

Carry elements in their box, and hold long ones in the middle and at both ends.
Check that the holes in the furnace wall line up and are large enough. An element must never be forced in.
Leave room for the element to expand when hot. Do not clamp it tight.
Make clean, tight electrical connections. A loose clamp heats up, and that heat can crack the end of the element.

2. Heat up and cool down gently

Fast temperature changes put stress on the element and on the furnace lining.

Follow the heating rate the element maker gives, especially from cold.
Avoid opening the furnace wide at full temperature.
After a long stop, heat up slowly so any moisture in the lining can escape.

3. Know the weak temperature ranges

MoSi2 elements can slowly turn to powder if they are held for a long time between about 400 and 700 °C. Pass through this range quickly and do not idle there.
SiC elements age faster when they run near their highest temperature, or in steam, hydrogen or some other gases. Running a little cooler can add a lot of life.

4. Keep the furnace clean

Dust, glaze, salts and metal splashes can attack the surface of an element. Keep the load from touching the elements and clean the chamber regularly. Some materials (such as glazes with lead, or some alkali vapours) are especially harmful; ask your supplier if you work with them.

5. Watch the electrical side

SiC elements slowly increase in resistance as they age. This is normal. Check the voltage and current from time to time, and raise the voltage step by step to keep the power steady.
MoSi2 elements change very little with age, but they have low resistance when cold, so the power control must limit the starting current.
Keep a simple log: date, hours, voltage, current, temperature. It tells you when elements are ageing and helps you plan changes before a breakdown.

6. Replace them the right way

With SiC, replace elements in matched sets, or choose new ones with a resistance close to the elements still in use. Mixing new and old elements of very different resistance overloads some and underloads others.
With MoSi2, single elements can usually be replaced on their own.
Always check the holders, terminals and cables at the same time.

A quick checklist

How often	What to check
Every day	Temperature reached in normal time, no unusual smell or noise
Every week	Connections are tight and not discoloured
Every month	Voltage and current; look inside for cracks, deposits or sagging
Each stop	Clean the chamber, check supports and the lining near the elements

When to call us

If elements fail early again and again, the cause is often the furnace setup, the power control or the atmosphere, not the element itself. Send us details of your furnace and a photo of the failed element, and we will help you find the cause. Contact us.