How to Convert Zirconia Sintering Curves Between Different Sintering Furnaces (Using a 4-Step Program as an Example)

In practice, many dental laboratories encounter a common issue:

After switching to a new sintering furnace, the original sintering program cannot be used directly.

This is especially true for equipment like the MIHM-VOGT, which has a relatively simple program structure—
The entire program consists of only 4 steps, and for each step, you only need to set:

Target temperature

Holding time

Rate of heating or cooling

Compared to many common devices, it lacks multiple segment settings, so many customers find it unfamiliar at first.

This article addresses a practical issue:
How to convert existing sintering curves into this 4-step program so they function properly.

Let's take the SHT-C zirconium block as an example.

I. First, Understand a Key Point 

Sintering curves may seem complex, but they essentially boil down to three core elements:

What is the final temperature?

What the heating process looks like

How long to hold at high temperature

In other words,
regardless of how many steps the equipment has, the essence is controlling temperature changes.

As long as these three points are properly aligned, the program will generally run without issues.

II. A Common Sintering Curve

Let’s start with a relatively common example (many devices are similar):

1.Room temperature → 300°C (preheating)

2.300°C → 1000°C (heating)

3.1000°C → 1530°C (continued heating) ,1530°C (hold for 2 hours)

4.Cool down to 800°C

Cool naturally to room temperature.

In some equipment, this curve might be broken down into 6 steps or even more.

III. Approach for a 4-Step Program

If converted to a 4-step program, it can be handled as follows:

Step 1: Preheating stage

Temperature: 300°C

Rate: 4°C/min

Hold: 0 minutes

This stage is primarily to stabilize the material and prevent the subsequent temperature from rising too rapidly.

Step 2: Heat up to 1000°C

Temperature: 1000°C

Rate: 4°C/min

Hold: 0

This involves continuously heating from the preheating temperature.

Step 3: Heating to 1530°C

Temperature: 1530°C

Rate: 3°C/min

Hold: 120 min

This involves continuously heating from the preheating temperature to the sintering temperature and holding there. This step is critical, as it determines the density and strength.



Step 4: Cooling

Temperature: 800°C

Rate: 5°C/min

Hold time: 0

Note: For this type of equipment, the final step must always be cooling.

IV. A Simple Method for Conversion

If you don’t want to redesign the process every time, you can use a relatively simple logic:

1) First, identify the highest temperature
→ Place it in Step 2 or Step 3

2) Separate the holding phase
→ Treat it as Step 3

3) All preceding heating processes
→ Combine them into Step 1

This approach works well in most cases.

V. Several Common Issues

1. Initial heating is too fast

This can easily cause internal cracking, which is particularly noticeable when creating long bridges.

2. Insufficient time during the degassing stage

This can result in porosity or an unclean surface.

3. Too rapid cooling

This may induce internal stress, affecting subsequent use,
and sometimes also impacting light transmission.

VI. Appropriate Adjustments for Different Materials

Different zirconia materials have varying requirements for sintering curves.

For example, multilayer zirconia is more sensitive to control of both heating and cooling rates.

Our HONCHON zirconia blocks have undergone multiple tests before leaving the factory,
and can be adapted with simple adjustments in common sintering furnaces (including those with a 4-step program).

If customers are unsure how to set the parameters, we generally recommend using the corresponding reference curve first, then fine-tuning it based on actual conditions.

VII. Finally, a Practical Suggestion

If you encounter the following issues:

Post-sintering deformation

Unstable strength

Color deviations

We recommend not adjusting just a single parameter,
but rather reviewing the entire curve.

If you find it difficult to assess the situation, you can also provide:

The material used

The sintering furnace model

The current program

We can generally help you review these details.