Degreasing , also known as oil, grease metal surface materials are all aspects of the process from the process until the completion of the parts brought in during the storage and transportation of oil to rust . Metallic materials and parts in further surface treatment ( such as plating, coating , anodizing, passivation , etc. ) must be put before the oil surface clean, otherwise it will affect the rust, in addition to the quality of the oxide scale , but also affect the surface plating , painting quality layers . As the source of oil in a wide variety, the degree of contamination vary widely, so the problem is very complex degreasing . Another object is also a lot of oil , a variety of metal materials from a variety of different sizes made of metal , different levels of complex shape parts , but also the overall plant and equipment ( such as machine cleaning and maintenance , cleaning and disinfection of food equipment ) , etc. this shows the complexity of the work of oil , affecting a wide range, and in many cases the strict quality requirements of cleaning , or even to meet the state standards or industry regulations. Therefore, we must be given adequate attention.
First, skim factors
The quality of skim skim depends on temperature , skim time , mechanical and degreaser four factors .
1 degreasing temperature
Generally , the higher the temperature , the more thoroughly degreased . This is because of three reasons First, the oil temperature to a change in the physical properties , such as high dropping point rust grease , petrolatum, solid paraffin and the like , at a lower temperature even with a high concentration of alkali is also difficult wash. However, when the temperature of the oil to improve their viscosity will reduce or even remove favor the formation of droplets . Second, to promote a chemical reaction , the general said , the temperature rose to 10 degrees , doubling the speed of a chemical reaction . Third , accelerating the movement of the surfactant molecules , thereby promoting infiltration , emulsion , dispersion and other effects . With increasing temperature , the solution is also increased ability to dissolve the dirt . However, not all applications are the higher the temperature the better, with its various degreasing agents suitable temperature range , the use of certain types of surfactant in the degreasing solution , the high temperature can cause precipitation of the surfactant aggregates as oil beads attached to the surface , causing uneven phosphate film blur .
2 degreasing time
Degreasing operations must ensure sufficient degreasing time , the injection pressure of the degreasing time is generally 1.5 to 3 minutes , dipping degreasing of 3 to 5 minutes ( depending on the type and number of the fixed oil ) . Increase the degreasing time , i.e. extend the contact time of the degreasing liquid and oil , to improve degreasing effect . The more oil , skim the longer time required . In pipeline operations , often do not allow the use of long time , it is generally first degreased by spraying to 1 minute , 3 minutes and then dipping degreasing .
Degreasing , the mixture was stirred by means of a pressure jet or mechanical action is very effective because the injection force and fresh degreasing solution has a good contact surface parts , the degreasing liquid and uniform content , help to improve the degreasing effect ; the injection degreasing agents rely on mechanical forces to promote infiltration and sabotage the film , thus effectively forcing the oil from the surface of the part ; procure parts from the injection of oil emulsified and dispersed in the degreasing solution to prevent the oil and then adsorbed onto the cleaned surface of the part . In defatted , the mechanical effect is particularly important. Generally speaking , the injection pressure is more than a dipping degreasing times faster . The injection pressure is usually (0.1 ~ 0.2) Mpa ( degreasing agent for pressure injection of foam must be low to avoid excessive foaming and to affect the normal operation of degreasing liquid loss ) , dipping degreasing can not be considered static immersion, the circulation pump must be equipped the solution was kept stirring , the cycle is about 5 times per hour, the volume of the bath .
4 . Impact degreasing agent for degreasing effect
Degreaser composition and method of use has a great influence on the degreasing effect . For example , a surfactant -containing alkaline degreasing better than the individual effect of the alkaline degreasing solution . For high dropping point of the solid or semi-solid oils , other than an effective degreasing solvent cleaning effect . To improve the ability of emulsifying and dispersing the oil , and an appropriate increase in the content of the surfactant in the degreasing agent is effective , and different species and different surfactants alkaline degreasing effect of an object are some differences , is through good degreasing agent a large number of trials , the proportion of its components with each other repeatedly screened and determined. For alkaline degreasing agent containing a surface active agent , the most effective cleaning action to play the critical micelle concentration is in the upper surface active agent . Use, the degreasing agent will continue to be consumed so that the concentration decreases, and therefore must be supplemented with periodic degreasing agent , in order to maintain the required concentration . Degreasing effect of the concentration is not linear relationship between the rise in the degreasing agent , so for high quality requirements skim case should not be taken to greatly increase the concentration of the method , and should be degreased quadratic approach , both a degreasing solution may be the same and need not increase the concentration of the additional .
In actual use , we must consider all the factors that control the various factors that are in the best condition , so skim achieve satisfactory results .
Second, the matter should be noted that the choice of degreaser
Before skim , you should consider the following aspects selection and degreasing agents :
1 . The material to be processed parts
Different metals have different corrosion boundaries lye , therefore, must choose the right PH value degreaser according to the material of the part. The following table:
Corrosion of various metals critical PH value : 2 type and quantity of oil
To consider the chemical nature of the oil on the part of ( the time saved can react with the surrounding medium affect skimmed , and skimmed liquid can occur saponification ) , oil of state (solid or liquid , oil and dust particles in the solid content ) , oil the adsorption of the substrate ( molecular polarity ) , etc., and then choose the appropriate degreaser . For example animal and vegetable oils are saponified and thus at a higher temperature is effective degreasing with sodium hydroxide . Mineral oil does not occur saponification reaction with sodium hydroxide skim on the inappropriate application of good emulsifying properties degreaser to work. With the general water-based degreasing agent at low temperature or the semi-solid is difficult to clean rust grease , then degreased with a solvent is effective . Wash adsorption strong anti-rust oil than washing machine oil difficult , therefore, should choose a better degreaser to clean the rust oil .
3 degreasing agent right choice
Degreasing methods, different requirements for degreasing agent . The injection pressure due to mechanical forces degreasing , good degreasing effect , it is a state in the highly foaming , low foam degreasing agent thus selected is necessary , dipping degreasing mechanical action is weak, and therefore better performance to choose skim good degreasing agent , an appropriate increase in the content of a degreasing agent and a degreasing time extension .
4 Note that the next process with
The next process is acid or phosphate, phosphate has no surface before adjustment processes are concerned with the selection of degreasing agent . Because different pre-treatment with phosphate supporting different quality of the resulting phosphate coating , the quality is also different. Alkali degreasing and pickling phosphide crystal is large and osteoporosis. For degreasing, if the next process is thin phosphate treatment , you should use the table with low alkalinity adjustment process degreasing agent ; If there is a separate table adjustment process , only considering degreasing effect , alkalinity little impact , do not worry ; If the next process is pickling rust , you do not have to tune the selection table with degreaser, and adjust a table in front of phosphate treatment alone ; such processes longer intervals , the selection of a smaller tendency to rust after washing degreaser ( degreasing agent such as phosphate type ) or to increase wet the process . For heavy oil in place , or not easy to clean surface , to pre- scrubbed by hand , he is not only skim requirements, but also can significantly improve the quality of phosphate , phosphate coating by pre- crystallization of small scrub , dense, and without pre- crystallization of the thick scrub and more.