Glass-ceramic for sealing high temperature heating elements

This product is used for sealing the end of heating element. High coefficient of expansion, low softening temperature, high insulation, lead-free

Technical information of FKBL013

Basic properties of sealing glass before sealing
Glass softening temperature	Glass transition temperature	Average coefficient of thermal expansion ( RT-300 °C)	End operating temperature	Resistivity (25 °C )
430~440 °C	400~410 °C	9.3±0.5×10-6 /°C	≤350 °C	109 Ω·m
Leakage current detection (detection voltage 1000 V)		Insulation resistance detection (detection voltage 1000 V)
Temperature(°C)	Leakage current (mA)	Temperature(°C)	Insulation resistance( MΩ )	Remark
100	0	100	2×106	Testing is performed on the insulating material itself，after packing according to the company's internal standards, which may affect the results.
250	0.007	250	1.5×103
300	0.016	300	55
350	0.043	350	6
RoHS Testing
substance	Detection value	substance	Detection value	Remark
Pb	not detected	Hg	not detected	Testing agency SGS, other macromolecular substances are not detected。
Cr6+	not detected	Cd	not detected

How to use glass products for sealing

Appropriate sizes of prefabricated glass parts are put into the end of the heating element, and then heated to a certain temperature by heating equipment (flame spray robbery, high-frequency heating machine, box furnace). When the glass begins to soften and flow to fill the gap, left it to cool to room temperature so that the glass solidifies, then the sealing process is complete.

Notes before sealing:

If you are using a heater such as box-type electric furnace, oven or toaster, be sure to calibrate the temperature zone, otherwise the sealing glass may not be melted or the temperature may be too high because the actual temperature is lower than the displayed temperature.
Before sealing, please make sure that your heating elements has been dried and the inner mgo powder is tightly filled.

The figure is a recommended temperature for box-type electric furnace sealing. Please pay attention to the cooling process after the sealing is completed.

Cautions:

Please remove moisture before sealing;
Do not use silicon sealant , silicone oil etc before sealing;
If the sealing temperature is too high, the metal materials may enter into the sealing glass and affect the insulation performance.

If you are using a high-frequency heating machine or a flame spray gun etc., please heat until it melts and then cool down slowly (quick cooling is not suitable).
How to choose Good heating equipment for glass sealing?

High frequency heating (Recommended)	Pros: Heat is applied to only part of the electric heating element to protect the rest of the tube from heat damage under high temperatures. Easy to use, can be moved. (Temperature rise curve can be set for certain models)
	Cons: Heating can only be done with a single individually.
Chamber Heating	Pros: Heating temperature can be adjusted so that there is a cooling process after the glass is melted to avoid the phenomenon of sudden cooling, which leads to cracks in the glass.
	Cons: The whole electric heating element is heated, causing high energy consumption, a long time is needed (but considering the mass volume versus time, it is not considered time-consuming), and may cause damage to the tube and the magnesium oxide powder on the electric heating element. For odd shape tubes, they cannot be put into the box furnace.
Flame Gun	Pros: cheap and easy to use
	Cons: Unsafe to use a flame, and it is not easy to control the temperature. In addition, it is forbidden to heat the glass directly. Only the location below the glass ring (slightly below the wall of the electric heating element) can be heated. The gas of the flame gun may also react with the glass, thus changing the nature of the glass.

The Operating temperature for our Company’s glass sealing

Normal operating temperature of up to 650 degrees. If used for electric heat tube sealing, the temperature of the electric heat tube port should be stable at 400 degrees and below. At this temperature, the insulation performance will be excellent. The electrical resistance begins to decline once the temperature exceeds 450 degrees. At this time, the wall temperature of the electric heat tube may have reached 600-800 degrees.

Glass sealing effect

After the electric heating element has been glass sealed, it can be magnified under a microscope for observation. Around the mouth of the tube, there will be a uniform distribution of substances with glass luster, indicating that the sealing effect is good, with high surface gloss, and no obvious cracks found.

What should be avoided before and during the operation of glass sealing

Moisture is not removed completely before sealing
Add silicone before sealing
Using the furnace for heating when the temperature zone is uncalibrated
The material of the lead rod is nickel-plated or using other materials that affect the sealing effect
The interval between dehumidification and sealing is too long, and the electric heating element is cooled too fast, which may cause the magnesium oxide powder to absorb moisture.

Causes of cracks in glass after sealing

The dehumidification of the electric heating element are not well done and a large amount of moisture remains inside.
The expansion coefficient of the glass does not match the electric heating element.
Sudden frosting of glass after sealing.

The following methods can be used to solve a burst tube.

Use tubes of better quality. Tubes of different quality can withstand different pressure. It is easy for steel of poor quality to break.
Electric heating elements are sealed when the temperature is still about 120 degrees after drying. At high temperature, there is less water vapor and gas in the electric heating element.
Use good quality magnesium oxide powder and fill it as densely as possible (magnesium oxide powder particle size ratio optimization). Reduce the air between the gaps of each magnesium oxide powder particulate.

Content

Glass-ceramic for sealing high temperature heating elements

Technical information of FKBL013