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Photos 1 Solder Glass SO 2 Kovar Alloy Pyroceram SD 3 How to Use Glass Products for Sealing 4 How to Choose Heating Equipment? 5 Glass Sealing Effect 6 What should be Avoided during the Sealing process? 7 Causes of Cracks Customers who bought this product also bought
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  • Glass-ceramic for Sealing High Temperature Heating Elements

    This product is used for sealing high temperature heating element. High expansion coefficient, low softening temperature, high insulation, lead-free. We have extensive experience in the professional field of sealing glass materials. According to customer needs, we can provide sealing glass materials and sealing devices for different substrates, usage environments, and application scenarios to achieve airtight sealing and gaps between glass, Ceramics, and metals. Welding, flat bonding, electrical insulation sealing, etc., and will not cause thermal damage to the material, achieving matching or compressive stress sealing. Products are widely used in high-temperature heating element, semiconductor components, optical communications, electric light sources, sensors, integrated circuits, home appliances, construction and other fields.

    The compressive strength of glass material is greater than the tensile strength. Therefore, in the structural design, if the structure is sealed with glass, when the heating element is cooled, the unsealed metal at the mouth end of the element can shrink freely. At the interface between the glass and the metal A bending moment is generated. Since both sides are symmetrical, the moments cancel each other out and the sealing is reliable.

    Generally used are glass powder and glass beads (rings). Glass beads (rings) are pressed with proprietary glass powder and come in various shapes and sizes. After being sintered, they have a certain strength and are easy to assemble. The products provided by our company are all made of lead-free glass and comply with the ROHS directive.

    Solder Glass SO Series

    Achieve air-tight insulation between the metal core of heating element and the metal of outer tubes, and are widely used in household appliances (such as water Heaters, ovens), industrial equipment (such as hot blast stoves, chemical equipment), and fluid heating systems (such as oil heaters, boilers, etc. ) and other fields. It is high insulation and high reliability.

    Product Performance:

    GradeCoefficient of Expansion X10 -7 K -1 Softening Point ℃Sealing Temperature ℃Glass System
    SO-82689440650-700Bi 2 O 3 -B 2 O 3 -SiO 2
    SO-91693405600-650PbO-B 2 O 3 -SiO 2
    SO-92794428600-700Bi 2 O 3 -B 2 O 3 -ZnO
    SO-90896530780-870SiO 2 -Al 2 O 3 -B 2 O 3

    Kovar Alloy Pyroceram SD Series

    Pyroceram sealing material is a glass material with a crystalline structure. It is structurally different from traditional amorphous glass. The fine crystals make the sealing product have high strength and temperature resistance, while the residual glass phase then achieve good infiltration with the metal, thereby achieving sealing. Microcrystalline sealing glass is mainly used for device products in high temperature, high pressure, or highly chemically corrosive environments.

    It has a wide and adjustable expansion coefficient, high strength, excellent chemical stability, high air tightness and high temperature resistance.

    Product Performance:

    GradeCoefficient of Expansion ×10 -7 K -1 Softening Point ℃Sealing Temperature ℃Glass System
    SD-40741558700-750SiO 2 -B 2 O 3 -ZnO

    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:

    1. 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.
    2. 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.

    1. Please remove moisture before sealing;
    2. Do not use silicon Sealant , silicone oil etc before sealing;
    3. 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 HeatingPros: 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 GunPros: 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.

    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

    1. Moisture is not removed completely before sealing
    2. Add silicone before sealing
    3. Using the furnace for heating when the temperature zone is uncalibrated
    4. The material of the lead rod is nickel-plated or using other materials that affect the sealing effect
    5. 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

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

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

    1. Use tubes of better quality. Tubes of different quality can withstand different pressure. It is easy for steel of poor quality to break.
    2. 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.
    3. 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.

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