با هزینه ای اندکی شما میتونید فایل (Emulsifiers) را تهیه کنید.

قسمتی از متن :

‏1

Emulsifiers

When removal of the penetrant from the defect due to over-washing of the part is a concern, a post emulsifiable penetrant system can be used. Post emulsifiable penetrants require a separate emulsifier to break the penetrant down and make it water washable. Most penetrant inspection specifications classify penetrant systems into four methods of excess penetrant removal. These are listed below:

Method A: Water-Washable

Method B: Post Emulsifiable, Lipophilic

Method C: Solvent Removable

Method D: Post Emulsifiable, Hydrophilic

Method C relies on a solvent cleaner to remove the penetrant from the part being inspected. Method A has emulsifiers built into the penetrant liquid that makes it possible to remove the excess penetrant with a simple water wash. Method B and D penetrants require an additional processing step where a separate emulsification agent is applied to make the excess penetrant more removable with a water wash. Lipophilic emulsification systems are oil-based materials that are supplied in ready-to-use form. Hydrophilic systems are water-based and supplied as a concentrate that must be diluted with water prior to use .

Lipophilic emulsifiers (Method B) were introduced in the late 1950s and work with both a chemical and mechanical action. After the emulsifier has coated the surface of the object, mechanical action starts to remove some of the excess penetrant as the mixture drains from the part. During the emulsification time, the emulsifier diffuses into the remaining penetrant and the resulting mixture is easily removed with a water spray.

Hydrophilic emulsifiers (Method D) also remove the excess penetrant with mechanical and chemical action but the action is different because no diffusion takes place. Hydrophilic emulsifiers are basically detergents that contain solvents and surfactants. The hydrophilic emulsifier breaks up the penetrant into small quantities and prevents these pieces from recombining or reattaching to the surface of the part. The mechanical action of the rinse water removes the displaced penetrant from the part and causes fresh remover to contact and lift newly exposed penetrant from the surface.

‏3

The hydrophilic post emulsifiable method (Method D) was introduced in the mid 1970s and since it is more sensitive than the lipophilic post emulsifiable method it has made the later method virtually obsolete. The major advantage of hydrophilic emulsifiers is that they are less sensitive to variation in the contact and removal time. While emulsification time should be controlled as closely as possible, a variation of one minute or more in the contact time will have little effect on flaw detectability when a hydrophilic emulsifier is used. However, a variation of as little as 15 to 30 seconds can have a significant effect when a lipophilic system is used. Quality Control of Emulsifier Bath

Quality control of the emulsifier bath should be performed per the requirements of the applicable specification. The information provided here may not reflect the requirement of current specifications and is provided here for general education purposes only.

Lipophilic Emulsifiers

Lipophilic emulsifiers are miscible with penetrants in all concentrations. However, if the concentration of penetrant contamination in the emulsifier becomes too great, the mixture will not function affectively as a remover. AMS 2644 requires that lipophilic emulsifiers be capable of 20% penetrant contamination without a reduction in performance. AMS 2647A requires the emulsifier to be replaced when its cleaning action is less than that of new material.

Since lipophilic emulsifiers are oil-based, they have a limited tolerance for water. When the tolerance level is reached, the emulsifier starts to thicken and will eventually form a gel as more water is added. AMS 2644 requires that lipophilic emulsifiers be formulated to function adequately with at least 5% water contamination and AMS 2647A requires that lipophilic emulsifiers be replaced when the water concentration reaches 5%.

Hydrophilic Emulsifiers

Hydrophilic emulsifiers have less tolerance for penetrant contamination. The penetrant tolerance varies with emulsifier concentration and the type of contaminating penetrant. In some cases, as little as 1% by volume of penetrant contamination can seriously affect the performance of an emulsifier. One penetrant manufacture reports that 1 to 1.5% penetrant contamination will affect solution with a 10% concentration of emulsifier. As the emulsifier concentration increases in the solution, the penetrant contamination tolerance also increases and a solution with a 30% emulsifier concentration can tolerate from 5 to 8.5% penetrant contamination. The percentage of added penetrant required to destroy washability of the emulsifier can be measured and an oil tolerance index is commonly used to compare the tolerance of different emulsifiers to contamination by penetrants. AMS 2647A requires that the emulsification bath be discarded if penetrant is noted floating on the surface or adhering to the sides of the tank.

تصاویری از چند صفحه نخست فایل :

توجه فرمایید بدلیل تهیه ی تصویر با نرم افزار های خارجی متن نمایش داده شده در تصاویر ممکن است دارای اشکالاتی در نمایش برخی حروف باشد که در فایل اصلی بدون مشکل است