Have you ever tried DJ type high-speed flame spraying system

       

Taking DJ type high-speed flame spraying
system as an example, the influence of process parameters on the coating
performance is introduced.

(1)   Powder properties. At present,
the powder suppliers provide a wide range of carbide powder, and the powder characteristics
often show great differences due to the different powder making process. The
powder characteristics include: particle size distribution, particle shape,
surface roughness, etc. For DJ2700 equipment, the appropriate powder size is:
15 μ m-40 μ m. Search wococarbide or sales-manager202 (@)wococarbide.com for
more tungsten carbide powder information.

(2) Oxygen gas flow and ratio. The flame
temperature and characteristics of high-speed flame spraying depend on the
oxygen gas flow and mixing ratio. When spraying high-speed flame, the flow of
oxygen and gas shall be determined according to the requirements of equipment
first to ensure that the flame flow of the spray gun reaches the designed power
level. There are many factors in the actual production process which can cause
the fluctuation of oxygen gas ratio, and oxygen gas ratio is very important to
determine the final coating structure. Theoretically, the ratio of oxygen to
propane is 5:1 (c3h8+5o2=4h2o+3co2) in theory. The combustion ratio produces a
neutral flame (that is, the oxygen and gas molecules are exhausted during
combustion). If the ratio of gas decreases, the oxygen molecules in the flame
flow will produce an "oxidation" atmosphere, which will lead to the
excessive oxidation of molten powder particles and the increase of oxide
content in the coating. The flame with low temperature and oxygen deficiency
will be produced when the gas is too much in the mixture. The molten particles
and holes in the coating increase, while the oxide content decreases. In fact,
the neutral flame does not exist. At high temperature, the combustion process is
not completely reversible. The reactants and the reaction products coexist in
the way of thermal and chemical equilibrium. The results show that the high
performance coating can be obtained when the oxygen gas ratio is between
4.2-5.6 for DJ high-speed flame spraying system.

(3) Distance of spraying. The results show
that: the DJ high-speed flame spraying system, when the powder particles reach
the maximum temperature within 100mm from the exit of the spray gun, the
particle temperature decreases gradually with the increase of spray distance.
In the range of 100-230mm, the particle temperature decreases by about 60 ℃,
and the reduction range is not large, and the particles can still maintain a
high temperature of about 1775 ℃; The particle velocity is a gradual
acceleration process within 190mm from the exit of the gun. The maximum
velocity is over 480m/s at 190-200mm from the exit of the gun. On the 170-230mm
spray distance, the particle velocity is basically maintained at more than 480m
/ s. Considering the adverse effect of high temperature flame flow on the heat
transfer of the substrate, the spray distance should be increased as much as
possible. Therefore, for DJ type high-speed flame spraying system, the suitable
spray distance should be 190-230mm. Compared with other spraying processes, the
adjustable range of spray distance of high-speed flame spraying is relatively
large, which is due to the high speed of particles. The larger adjustable range
of spray distance is very beneficial to the actual production, because the
suitable spray distance can be selected according to the shape, size and
coating thickness of the workpiece, so as to obtain the best coating with
comprehensive performance.

(4) Powder delivery. For any thermal
spraying process, powder feeding is an important parameter that affects the
coating performance. Under a specific spraying process, a certain powder has a
suitable range of powder delivery.

If the powder delivery is too small, the
possible adverse effects are:

1) It is too melted by spraying powder, and
the powder is burnt, and the smoke is large, which is easy to pollute the
coating.

2) Each spray can not completely cover the
path of the coating, which results in the increase of the porosity of the
coating.

3) The coating cracking and production cost
are increased easily after the spraying time is prolonged.

If the powder delivery is too large, the
possible adverse effects are:

1) The powder melting is not enough, the
bonding strength of the coating decreases and the porosity increases.

2) The coating stress increases, which
leads to the cracking of the coating.

3) The deposition rate of powder decreased
and the production cost increased.

The results show that when the powder
delivery rate changes from 38-60g/min, the porosity of the coating is between
1.12-2%, the microhardness is hv1000-1300, the deposition rate of powder is
40-50%, and the coating performance is excellent. When spraying CRC NiCr
coating, the satisfactory coating quality can be obtained when the powder
feeding quantity changes between 27-45g/min.

Search wococarbide or sales-manager202
(@)wococarbide.com for more metal powder information.