Some industrial sectors are characterised by the so-called “harsh” environments, having excessively high or low temperatures.
In such contexts, which have an exceptional microclimate, it is necessary to pay a special attention to the “thermal stress”.
We will refer only to materials and, specifically, to industrial wheels, in particular high temperature wheels, and their resistance in harsh environments.
Microclimatic conditions in the industrial sector
The microclimatic conditions of work environments vary according to different factors:
- Production cycle (productions carried out at particular temperatures);
- Environmental characteristics (underground works, works at a height, etc.);
- Structural characteristics of work places (constructive materials, thermal properties, etc.);
- Plants with control functions of climatic conditions (fans, air conditioners, etc.).
Effects of thermal shock on materials
A sudden temperature variation can cause high temperature gradients to which various degrees of deformation, and consequently of stress, are linked. If such stresses exceed the limit values, materials can break.
The Thermal Shock Resistance capacity (TSR) is given by the formula
TSR= σ κ/ E α (10.33)
Thermal shock resistance is directly proportional to break strength and thermal conductivity. This means that the higher the thermal conductivity, the higher the material’s capacity to dissipate heat, thus reducing the temperature gradient.
Thermal shock resistance is inversely proportional to the Young’s modulus, whose increase leads to higher stresses with the same level of deformation, and to the expansion coefficient, whose increase leads to the increase of deformations due to the temperature variation.
Metal materials and glass have high values of thermal shock resistance: the first ones because of their high values of thermal conductivity, whereas the second one has a low expansion coefficient. Technology has allowed creating many resins having specific resistance capacities, also and above all in relation to high temperature wheels.
Materials for high temperature wheels
The materials that compose industrial wheels and relevant brackets are usually suitable to be used at “ambient” temperature (from 0°C to +40 °C).
In the case they are used at lower or higher temperatures, it is necessary to pay special attention to the materials of wheels and brackets.
The materials most suitable to be used in harsh environments are the following:
- silicone rubber,
- thermosetting resin,
- mechanical engineering cast iron,
- polyamide 6 charged with glass fibre.
For an effective resistance to thermal shock it is therefore recommended to correctly choose the manufacturing material of the tools used in harsh environments (with extremely hot or cold temperatures) such as industrial wheels.