Heating rate refers to the heating rate of the metal surface, which is the temperature rise of the metal surface temperature per unit time, and its unit is ℃/hour. The heating speed is closely related to the heating time. The faster the heating speed, the shorter the heating time, and the higher the productivity of the furnace. When increasing the heating speed, it will be limited by the following factors: firstly, the internal temperature difference allowed by the metal itself; The other is the heating capacity of the furnace. We know that the temperature distribution along the cross section of the tube blank is uneven when heating the solar photovoltaic support blank, and the surface temperature is higher than the temperature of the inner layer (or central layer), so there is a certain temperature difference. The poorer the heterothermal properties of steel, the larger the diameter of the solar photovoltaic support billet, and the faster the heating speed, the greater the temperature difference during the heating of the tube billet. This temperature difference will cause different thermal expansion between the inner and outer layers of the tube blank, resulting in temperature stress (also known as thermal stress) between the layers. When the internal stress exceeds the allowable fracture strength of the metal itself, the inner metal will be pulled apart and form circular cracks.

Therefore, the following factors should be considered when selecting the heating speed of solar photovoltaic support tube blanks reasonably:

1. The chemical composition and thermal conductivity of steel. Steel with low thermal conductivity should have a slower heating speed. As the carbon content and alloying element content in the steel increase, the thermal conductivity of the steel decreases. High alloy steel and some alloy steels have poor thermal conductivity at low temperatures, but they actually increase at high temperatures. Therefore, they should adopt low-temperature slow and high-temperature fast heating processes.

2. The plasticity of steel. The vast majority of steel grades have poor plasticity below 600 ℃, so slow heating should be used in the low-temperature preheating section. Steels with high carbon content and high alloy steels generally have poor plasticity and should be heated slowly at low temperatures.

3. The cross-sectional size of the solar photovoltaic support blank. When the diameter of the tube blank is large, the heating speed should be slower.

4. The structural state of steel. The plasticity of the cast structure is worse than that of the deformed structure. The casting structure has a large accumulation of impurities at the grain boundaries, resulting in low thermal conductivity. The rolled tube blank has better plasticity and stronger thermal conductivity than the continuous casting tube blank. Therefore, the heating speed of continuous casting billets is lower than that of rolling billets.