JPS6035799B2 - Sea heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sheathed heater having an improved structure at the end of a sheathed tube.

In a sheathed heater that uses a sheathed tube made of quartz or crystallized glass (product name: Gyroceram, etc.), if magnesia is filled to fix the electric heating element inside the tube, thermal expansion of the sheathed tube and magnesia Due to the large rate difference, the sheath tube could be damaged due to expansion of magnesia when energized.

In order to prevent this damage, attempts have been made to adjust the packing density of magnesia, but if the packing density is reduced, gaps will be created in the magnesia layer in the sheath tube during use of the sheathed heater, resulting in insufficient fixation of the electric heating element. However, there were drawbacks such as uneven heat generation of the heating element and early disconnection. The present invention has been made to eliminate such conventional drawbacks, and provides a presser that forms a gap at the end of the sheath tube and presses the electrically insulating powder contained in the tube into the gap. The present invention provides a sheathed heater in which the electrically insulating powder does not loosen even during use, and there is no risk of damage to the sheathed tube made of quartz or crystallized glass.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In the figure, 1 is a sheathed tube made of quartz with a diameter of about 6 sides, 2 is an electric heating element made of nichrome wire disposed inside this sheathed tube 1, and 3 is a high melting point electric insulator made of magnesia with a mesh size of 40 to 200. 4 is a lead-out terminal conductor made of iron and nickel alloy, and 6 is a closure made of a glass composite made of magnesia. Reference numeral 6 denotes a gap formed at the end of the sheath tube 1, and in this gap 6, a pressurizer 7 made of a bell made of mild steel or copper is formed to have a smaller diameter (than the inner diameter of the sheath tube 1). It is provided so that it can pass through the lead terminal conductor 4 and move up and down. This sheathed heater is used, for example, in an infrared furnace, with the end where the pressurizer 7 is provided facing upward. When the electrically insulating powder 3 in the sheath tube 1 expands due to heating by electricity, the pressurizer 7 is placed in the gap 6. The inside of the sheath tube 1 is pushed up to prevent expansion and damage to the sheath tube 1. Then, when the electricity is turned off and the electrically insulating powder 3 cools and contracts, the presser element 7 is lowered and acts to pressurize the electrically insulating powder 3, so that the electrical heating element 2 is fixed and prevented from deforming.
In the above embodiments of the present invention, the pressurizer is pressurized with a weight, but it is not limited to a weight, and a spring may be inserted to apply constant pressure at all times. In that case, the sheathed heater may be placed in a horizontal position It works effectively even when used.

Further, these pressurizers are not limited to one end of the sheath tube, but may be provided at both ends in the case of a double terminal type. Furthermore, the material of the sheath tube may be quartz, or ceramics such as crystallized glass, alumina, or magnesia porcelain, and is extremely effective for sheath tubes in which swaging cannot be performed after filling the sheath tube with electrically insulating powder. As explained above, in the sheathed heater of the present invention, a gap is provided at the end of the sheath tube, and a presser is provided in this gap to press the electrically insulating powder. This has the advantage that even a sheathed tube can be prevented from being damaged, and the electric heating element can be securely fixed.

[Brief explanation of drawings]

The drawing is a partially sectional plan view showing an embodiment of the present invention.

Claims (1)

[Claims] 1. In a sheathed pipe with an end closed, in which an electric heating element is disposed and electrically insulating powder is contained to bury the heating element, a gap is formed at the end of the sheathed tube, and a gap is formed in this gap. A sheathed heater characterized by being provided with a pressurizer that presses the electrically insulating powder.