| 摘要 |
<p>A hot air welding gun for use in welding thermoplastic articles is equipped with a triac in the supply circuit of the heating element spiral, and with a potentiometer for manual setting. The firing of the triac is controlled by a resistor with a positive temp. coefft. which responds to temp. rise and increases its resistance when the temp. should rise because of a reduction in the rate of the cold air supply. The changed resistance acts on a integrated circuit on a printed circuit board and reduces the firing pulses for the triac. This keeps the heating element spiral at the lowest temp., compatible with the air supply rate, and results in a longer life of the heating element. Damage due to fusion of the ceramic element holder at temp. exceeding 1000 degrees C is reliably eliminated.</p> |
