Metal mold working temperature and each part of the temperature
difference of ductile casting cooling temperature field has an
important role. To metal type local overheating area forced
water and air cooling is to ensure that the area to keep the
normal operating temperature, improve the production efficiency,
and at the same time, eliminate overheat, ensure the normal
cooling temperature field. Metal mold working temperature
control is advanced and effective means is to control the
cooling water outlet temperature and outlet temperature of
cooling water circulation speed regulation. In addition, to
local large and thick hot day parts can also be set high thermal
conductivity or heat storage capacity big metal insert or adjust
coating layer thickness and coating types are in place to ensure
that cast a form a reasonable cooling temperature gradient,
eliminate local shrinkage.
Nodular casting heat treatment is to point to by a heat
treatment standard, control the heating temperature, holding
time and cooling speed degrees, change alloy organization, its
main purpose is: to improve mechanical properties, enhance the
corrosion resistance, improve the processing performance, get
size stability.
In order to improve the actual effect of stress relieving,
heating temperature can reach the best ductile casting last
complete discharge temperature. In less than the last complete
discharge temperature, heating temperature, higher the stress
relief is more sufficient. However, the heating temperature is
too high, can cause nodular casting organization change, thus
affecting the performance of the ductile casting. For gray cast
iron parts, the heating temperature is too high, can make the
eutectoid cementite graphitization, nodular casting strength and
hardness of the lower. For white cast iron parts, the heating
temperature is too high, also can make eutectoid cementite
decomposition, nodular casting hardness and wear resistance
greatly reduced.
Nodular casting stress relieving heating temperature of 550℃.
When cast iron containing stable base structure of alloy
elements, can be appropriately increase to stress annealing
temperature. Low alloy castings for 600℃, high alloy gray cast
iron can be increased to 650℃. Heating rate is generally sixty
to 100℃. Heat preservation time according to the following
empirical formula calculation: H "2 ~ 8 range selection, type of
ductile casting thickness of the unit is mm, heat preservation
time unit is hours, H" in 2 ~ 8 range selection. Complicated
shape and requirements fully eliminate stress ductile casting
should take great H "value. With the furnace cooling rate should
be controlled in 30℃ / H the following, general ductile casting
cold to 150 ~ 200℃, a complex shape of ductile casting cold to
100℃ are.
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