Research On Optimal Processing Conditions Of Chemical Milling Fluid Based On Bayer Method

Chemical milling uses a well-formed chemical milling fluid to dissolve the workpiece to achieve the desired shape and size.When uses chemical milling technique to process aluminum alloy,the main component of the chemical milling fluid is sodium hydroxide.When the aluminum in the workpiece dissolves into the chemical milling fluid,the concentration of Al³⁺ keeps increasing,and the concentration of Al³⁺ is a key factor affecting the quality of the workpiece.When it reaches 70g/L,it produces The quality of the workpiece has not been able to meet the standard,and the milling fluid needs to be scrapped.Because the aluminum alloy chemical milling fluid is mainly sodium hydroxide,it can not be processed by the existing environmental protection technique,the company can only be delivered to the hazardous waste company,and the annual cost will bring a lot of pressure to the company.In the Bayer process,aluminum hydroxide is added to the sodium aluminate solution,and the sodium aluminate is decomposed into aluminum hydroxide.In this paper,the Bayer process is applied to the treatment of chemical milling fluid,and the concentration of Al³⁺ is decreased by adding hydrogenated alumina to the chemical milling fluid.Based on the predecessors,this paper finds the best process for processing chemical milling fluids: after diluting the chemical milling fluid,adding seed crystals and stirring,the sodium aluminate in the chemical milling fluid is decomposed into aluminum hydroxide,and then separated.Processing,chemical milling fluid can be reused.In order to find the best process parameters and conditions,the following experiments have been made in this paper to obtain the following conclusions:?1?The milling fluid contains a large amount of SS.This paper proves that SS will affect the decrease of Al³⁺ concentration.When using unfiltered chemical milling liquid for experiments,the Al³⁺ concentration only drops by 4% at 36 h.?2?The saturation of milling fluid,Al³⁺ concentration and total alkalinity are important factors affecting the removal rate of the milling fluid.Dilution can change these three conditions to improve the removal rate of the milling fluid.The optimal dilution ratio is 1:1?the volume of deionized water is equal to the volume of the milling fluid?,and the Al³⁺ concentration and total alkalinity are 33.27g/L,respectively,and 128g/L,under these conditions,the Al³⁺ concentration decreased by 21.42% at 36 h.?3?Appropriate agitation makes the aluminum hydroxide seed crystals evenly distributed in the chemical milling fluid,which provides better conditions for the decomposition of sodium aluminate in the chemical milling fluid.When the stirring speed is 125 rpm,the concentration of Al³⁺ in the 1:1 dilution can be reduced by 22.92%.Too fast agitation speed is not conducive to the reaction.?4?The temperature can accelerate the movement speed of each ion in the chemical milling liquid and shorten the reaction time.At 70 ° C,the Al³⁺ concentration decreased by 18.9% at 12 h,but the increase in temperature caused the solution to decrease in saturation and increase in water evaporation,which was not conducive to the reaction of the chemical milling fluid.When the reaction was carried out for 36 h,the concentration of Al³⁺ in the sample at a constant temperature of 70 ? decreased by 14.88%,which means that the concentration of Al³⁺ in chemical milling increased again.If it is necessary to speed up the reaction and increase the temperature is a good choice,too long a reaction time will be detrimental to the reaction.?5?The aluminum hydroxide produced by the reaction of the chemical milling liquid can be used as a seed crystal after being washed and dried.If the factory does not use deionized water,the use of tap water will cause white suspension in the milling fluid,covering the reaction of sodium aluminate and aluminum hydroxide seeds.?6?Find the optimum aluminum hydroxide seed crystal addition parameter Hs for the treatment of suitable chemical milling fluid.When Hs is 4.8,the reaction effect can be optimized.?7?Applying the experimental parameters to the actual milling fluid treatment project of aerospace enterprise in Shanghai,the effect is good,the milling fluid can be used stably,and the quality of the milling and milling workpiece also meets the qualified standard.