used in evaporator weld crack repairing and protecting
Evaporator is the key equipment in the process of bayer process alumina production,due to the acid and alkali corrosion and liquid flow scour abrasion,
the head,tube plate,cone,evaporation chamber and circulating tube of the evaporator often need to be changed.Need dismounting the head when
replacing the heating tube,and all of these components need be welding connection.The problems of welding connection is that weld joint life is too short,
it's usually half a year,even shorter than one or two months,the weld joint began to crack.
1.The crack reason analysis:
The reasons of causing crack generally are impurity segregation,welding internal stress and high concentration of alkali corrosion under high temperature.
Weld touches with high temperature alkaline medium to produce the crack,if makes the weld joint isolate from the high temperature alkaline medium.
Can prevent from appearing weld cracks,so use the corrosion resistant coatings as the isolation.
2. The measures of pre-coating anti corrosion coatings:
(1) Choosing adhesives: Choose the BD428 high temperature flakes anti chemical corrosion resistant coatings of Xiangyang City Hundred Shield
Coating Material Co.,Ltd as the main adhesive,choose the BD427 high temperature anti corrosion chemical resistant coatings of Xiangyang City
Hundred Shield Coating Material Co.,Ltd as the outside protective layers.
(2)Do the cleaning and activating treatment on the protection part.Clean up the surface heavy dirty with the grinder,until to reveal the metal substrates,
then do the sand blasting treatment.Using the coarse sand to do the sand blasting,it can further clean up the surface scale layer first,the second,
it can activate the metal surface,increase the effective contact area of metal and rubber,the third,it can eliminate the partial welding stress,
increase the fatigue strength and resistance to stress corrosion strength of the metal.The angle of the sand blasting and sand grains thickness have a
larger effect on the adhesive bonding strength,the angle is greater,the metal surface is easier to appear the pitting.The pitting has a good effect on
the improvement of the adhesive bonding force.But the angle is too large,it's easy to produce the sand grains mosaic phenomenon,if you can't
wash away the sand grains in the process of cleaning,it will bring down the bonding strength.Because the mosaic sand grains are harder to clean up,
the spray angle should not be too large.Finish the Sand blasting and do the cleaning,remove the surface dirt and other contaminants interfere with
bonding.After cleaning the surface should be coating operations as soon as possible.Glue to keep the environment clean and dry, otherwise,
because of the large surface activity is very easy to absorb dust and water vapor, resulting in a binding force.
(3)Spot welding tortoiseshell protective screening.To increase the adhesion of the coatings,spot welding a layer of tortoise shell protective screening,
need to prevent the detached things from blocking the pipeline during spot welding.
(4)Using the main adhesive.Because the viscosity of the adhesives is very big,using adhesive directly is not easy to make the adhesives touch with
the metal substrates fully,can use a layer of primer coat in advance,make the metal touch with the coatings closely.Use the BD427 high temperature
anti chemical impact corrosion resistant coatings as the primer coat,brush coating on the metal wall thinly.Due to the primer coat solution is thin,
can brush coating uniformly very easily.It can normally brush coating the BD428 flakes anti corrosion impact chemical resistant coatings after
brush coating the primer coat for 20 mins,after finishing the brush coating, generally it should be natural assimilation for 4 hours under 25
degree temperature.
(5)Using outer layer protection adhesive.Choose the BD427 high temperature chemical wearing corrosion resistant coatings,the coatings should be
smeared thin and uniform.Put forth your strength slightly during blade coating,repeatedly applying,to ensure that the interlayer bonding is compact,
and no gap,prevent the coatings appearing cavity.The whole coatings should be smeared uniformly,the adhesive and steel are smooth transition,
the surface of the coatings is smooth and clean.It can be put into using after finishing smearing and assimilation for 24 hours.
3.The application situation
Later period equipment overhaul,make a complete inspection for the evaporator of carrying out pre-coating the corrosion resistant coatings measures,
the overall anti corrosive coating is in good condition,bonding closely with the metal matrix,and without appearing uncoating,delamination,cracks,pitting
and corrosion phenomena etc.So you should use the adhesive isolation method to make the crack protection,the construction is easy,the method is simple,
the protecting effect is good,and the applicable scope is wide,especially suitable for on-site protective treatment.
Construction case photos show for evaporator weld crack anti corrosion abrasion wearing resistant repairing
