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#332 Know-how on automation: Pressurized heating technology - 4: Points to remember when designing mechanism of pneumatic pressurization method

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March16, 2018

A pressurization method using rubber expansion body requires some empirical design technique such as a method of fixing the expansion body in place in the mechanism design, although it is advantageous in uniformity of pressurization.This section describes points to remember when designing mechanism of pneumatic pressurization method.

(1)Points to remember when designing mechanism of pneumatic pressurization method using rubber expansion body
1)Countermeasure for pneumatic pressure fluctuations by heating

・When a pneumatic pressurization method much like rubber expansion body is used with heating treatment, the energy inside the heating furnace will be greater than the pneumatic pressure in the room temperature, since the pneumatic pressure rises because of the heating temperature.The pressure conditions, thus, must be selected in consideration of this effect.
・If pressure rise due to heating cannot be addressed just by changing the pressure conditions, use of a pressure switch (mechanical or electrical), which reduces pneumatic pressure during heating process, might be one solution for the situation.
・When a heating furnace is used, it is simple to adopt a mechanical pressure release handle (for example, ball valve, Misumi BRKT) and to reduce the pressure by mechanically opening an open valve with a pneumatic cylinder, etc. (Figs.1 and 2).

[Fig.1]Overview of mechanical pressure reduction method with pneumatic pressurization method [Fig.2] Example of pressure release inside the heating furnace

2)Fixing rubber expansion body of balloon type

・The rubber expansion body as shown in Fig.1 is fixed with the platy metal frame onto the pressurization plate. It has to be fastened in such a way that smooth curved surface is formed without making wrinkles on the surface of the rubber expansion body.
・The shape of the metal frame for holding the rubber expansion body is thus important.
・Fig.3-a shows a commonly-used angular holding frame, whereas Fig.3-b shows a holding frame with large round inner corners.
・Fig.4 shows the states of circle parts of those rubber expansion bodies in Fig.3. The rubber expansion bodies are fixed to the individual holding frames and expanded.
・In Fig.4-a, the corners of the rubber expansion body are deformed in a complex manner.In Fig.4-b, the rubber expansion body is expanded with smooth curved surface.
・It is required to select the proper shape of holding frame as shown in Fig.4-b and the optimal volume of expansion of the rubber expansion body, and also to adopt a fixing mechanism free from air leaks during expansion even after use for long hours.

[Fig.3]Example of holding frame of rubber expansion body

[Fig.4]Comparison of shapes of holding frames of rubber expansion body and expanded states of rubber expansion bodies

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