HEATING DEVICE

Abstract

A heating device includes a substantially cylindrical shaft joined to a joint surface of a plate-shaped ceramic substrate opposite to a heating surface, the ceramic substrate including a resistance heating element embedded in the ceramic substrate. The shaft includes a flange portion formed in the end joined to the ceramic substrate and a first cylindrical portion connecting to the flange portion, and a ratio D3/D1 of an inner diameter D3 of a joint area in the flange portion and an outer diameter D1 of the first cylindrical portion is not less than 92%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further objects, features and advantages of the invention will more fully appear in the detailed description of embodiments of the invention, when the same is read in conjoint area with the drawings, in which:

FIG. 1 is a cross-sectional view showing an embodiment of a heating device according to the present invention;

FIG. 2 is an enlarged cross-sectional view of the main portion of the heating device;

FIG. 3 is an enlarged cross-sectional view of the main portion of the heating device; and

FIG. 4 is an enlarged cross-sectional view of the main portion of the heating device.

Claims

1. A heating device, comprising: a plate-shaped ceramic substrate including a heating surface on which an object to be heated is placed;a resistance heating element disposed in the ceramic substrate; anda substantially cylindrical shaft an end of which is joined to a joint surface of the ceramic substrate opposite to the heating surface, the shaft supporting the ceramic substrate, whereinthe shaft includes a flange portion formed in the end joined to the ceramic substrate and a first cylindrical portion connecting to the flange portion, anda ratio D3/D1 of an inner diameter D3 of a joint area in the flange portion and an outer diameter D1 of the first cylindrical portion is not less than 92%.

2. The heating device according to claim 1, wherein the shaft includes a plane surface or a curved surface connecting an inner peripheral edge of the joint area of the flange portion and an end of an inner peripheral surface of the first cylindrical portion.

3. The heating device according to claim 2, wherein the plane surface or curved surface is a chamfered surface or a curved surface with a curvature radius of not more than 1.5 mm.

4. The heating device according to claim 1, wherein a main component of the shaft is the same as a main component of the ceramic substrate.

5. The heating device according to claim 1, wherein the shaft includes a second cylindrical portion connecting to the first cylindrical portion on a side further from the ceramic substrate, andthe outer diameter D1 of the first cylindrical portion is larger than an outer diameter D2 of the second cylindrical portion.

6. The heating device according to claim 5, wherein a ratio D2/D1 of the outer diameter D2 of the second cylindrical portion to the outer diameter D1 of the first cylindrical portion is not less than 40% and not more than 80%.

7. The heating device according to claim 5, wherein an outer peripheral surface of the first cylindrical portion and an outer peripheral surface of the second cylindrical portion are smoothly connected by a curved surface having a curvature radius of 1 to 5 mm.

8. The heating device according to claim 6, wherein length of the outer peripheral surface of the first cylindrical portion from the joint surface is 8 to 70 mm.