Mechanical thermometer panel how to choice?

Thermometer panel is to show the effect of scale, general mechanical the panel of the thermometer has two kinds, one is the bottom of the aluminum, the other is a white ( Is actually coated aluminum bottom panel with a layer of white paint) 。 From the buyer's point of view, the role of the panel is according to temperature, so choosing white and aluminum background difference, basically see personal likes. From mechanical thermometer manufacturers point of view is different, there is a process problem, generally choose the bottom of the aluminum when temperature range is less than 250 c and white can be, but after more than 250 c temperature, the paint of the white panel may melt, so it's best to choose the bottom of the aluminum. Mechanical also belongs to the bimetallic thermometer thermometer, its working principle is to use different expansion coefficient of two kinds of metals ( Or alloy) Piece together form a thermal components, generally made spiral wound, its end ( The free end) Equipped with a pointer. When the temperature changes, the thermal component of curvature change, free end rotation, drive the pointer indicates the temperature value on the dial.