Designation:B368–97(Reapproved2003)e1
Standard Test Method for
Copper-Accelerated Acetic Acid-Salt Spray(Fog)Testing
(CASS Test)1
This standard is issued under thefixed designation B368;the number immediately following the designation indicates the year of
original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A
superscript epsilon(e)indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
e N OTE—Sections8.1and10.1.12were editorially updated in July2003.
1.Scope
1.1This method prescribes the conditions required in copper-accelerated acetic acid-salt spray(CASS)t
esting for specification purposes.The standard does not specify the type of test specimen or exposure periods to be used for a specific product,nor the interpretation to be given to the results.
1.2This method is applicable to evaluating the corrosive performance of decorative copper/nickel/chromium or nickel/ chromium coatings on steel,zinc alloys,aluminum alloys,and plastics designed for severe service.It is also applicable to the testing of anodized aluminum.The suitability of this test and correlation of results with service experience should be determined before it is specified for coating systems or materials other than those mentioned in this paragraph.
N OTE1—The following standards are not requirements.They are referenced for information only:Practices B537and E50,Specifications B456and B604,and Test Method B602.
1.3This standard does not purport to address all of the safety concerns,if any,associated with its use.It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.For more specific safety precautionary information see8.1.1.8.1.
2.Referenced Documents
2.1ASTM Standards:
B117Practice for Operating Salt Spray(Fog)Apparatus2
1This method is under the jurisdiction of ASTM Committee B-8B08on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10on General Test Methods.
Current edition approved Oct.May10,1997.2003.Published March1998.July2003.Originally published as B368–61T.approved in1961.Last previous edition B368–85(1997).approved in1997as B368–97.
The CASS test was developed by the initiative of the Research Board of the American Electroplaters Society under AES Project15.
1
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version.Because it may not be technically possible to adequately depict all changes accurately,ASTM recommends that users consult prior editions as appropriate.In all cases only the current version of the standard as published by ASTM is to be considered the official document.
Copyright©ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA19428-29
59,United States.
B162Specification for Nickel Plate,Sheet,and Strip3
B456Specification for Electrodeposited Coatings of Copper Plus Nickel Plus Chromium and Nickel Plus Chromium4
B537Practice for Rating of Electroplated Panels Subjected to Atmospheric Exposure4
B602Test Method for Attribute Sampling of Metallic and Inorganic Coatings4
B604Specification for Decorative Electroplated Coatings of Copper/Plus Nickel/Plus Chromium on Plastics4
D1193Specification for Reagent Water5
E50Practices for Apparatus,Reagents,and Safety Precautions Considerations for Chemical Analysis of Metals,Ores,and
Related Materials6
3.Significance and Use
3.1The CASS test is widely employed and is useful for specification acceptance,simulated service evaluation,manufacturing control,and research and development.It was developed specifically for use with decorative,electrodeposited nickel/chromium and copper/nickel/chromium coatings.Use of the test has improved the quality of electroplated parts and led to the development of new and superior electroplating processes.
4.Apparatus
4.1The apparatus required for the CASS test consists of a fog chamber,a salt-solution reservoir,a supply of compressed air, one or more atomizing nozzles,specimen supports,provision for heating the chamber,and necessary means of control.
4.2The size and detailed construction of the apparatus are optional,provided the conditions meet the requirements of this method.The construction of the apparatus is described in the appendix of Test Method B117.For the CASS test,however,the requirements for air pressure and temperature are typically0.08to0.12MPa and60to65°C,respectively.The actual air pressure will be that required to produce the proper collection rate(see8.3.1).
4.3The apparatus shall be constructed so that drops of solution that accumulate on the ceiling or cover of the chamber do not fall on the specimens being tested.Drops of solution that fall from the specimens shall not be returned to the solution reservoir for respraying.
4.4Materials of construction shall not affect the corrosiveness of the fog,nor be themselves corroded by the fog.
5.Test Solution
5.1Prepare the salt solution by dissolving5parts by weight of salt in95parts of water conforming to Specification D1193, Type IV.The salt shall be sodium chloride(NaCl),ACS reagent grade,or equivalent.The pH of this solution shall be between
6.0 and
7.0.Impurities or contam-ination of either the salt or the water,or both,should be suspected if the pH is outside of this range (Note2).
5.2Add0.25g of reagent grade copper chloride(CuCl2·2H2O)to each litre of the salt solution;dissolve and mix thoroughly.
5.3The pH of the salt-copper solution shall be adjusted to the range of3.1to3.3,as measured on a sample of the collected spray,by the addition of glacial acetic acid,ACS reagent grade,or equivalent(Note3).The pH measurement shall be made electrometrically at25°C.Before the solution is atomized,it shall be free of suspended solids(Note4).
N OTE2—A solution having a specific gravity of1.030to1.040,when measured at a temperature of25°C,will meet the concentration requirement. It is suggested that a daily check be made.
N OTE3—The initial solution may be adjusted to a pH of3.0to3.1,with the exception that the pH of the collected fog will be within the specified limits.Adjustment of the initial pH for makeup solution is based upon the requirements to maintain the required pH of the collected samples.If less than 1.3or more than1.6mL of the glacial acetic acid are required per litre of sodium chloride and copper solution to attain the specified pH,some discrepancy in the system may be suspected(the purity of the water or sa
lt,or both;the accuracy of the pH meter;the general cleanliness of the system;etc.).
N OTE4—The freshly prepared salt solution may befiltered or decanted before it is placed in the reservoir,or the end of the tube leading from the solution to the atomizer may be covered with a double layer of cheese cloth to prevent plugging of the nozzle.
6.Air Supply
6.1The compressed air supply to the nozzle or nozzles for atomizing the test solution shall be free of oil and dirt(Note5). Pressure shall be adequate to provide a specified condensate rate.Pressure of0.1060.02MPa has been found satisfactory(Note 6).
N OTE5—The air supply can be freed of oil and dirt by passing it through a water scrubber or at least60cm of suitable cleaning material,such as sheep’s wool,excelsior,slag wool,or activated alumina.Commercialfilters for compressed air may be used.
N OTE6—Atomizing nozzles may have a critical pressure,at which an abnormal increase in the corrosiveness of the salt fog occurs.If the critical pressure of a nozzle has not been determined with certainty,control offluctuation in the air pressure within60.0007MPa by installing a pressure regulator valve minimizes the possibility that the nozzle will be operated at its critical pressure.
2Annual Book of ASTM Standards,V ol03.02.
3Annual Book of ASTM Standards,V ol02.04.
4Annual Book of ASTM Standards,V ol02.05.
5Annual Book of ASTM Standards,V ol11.01.
6Annual Book of ASTM Standards,V ol03.05.
7.Test Specimens
7.1The type and number of test specimens to be used,as well as the criteria for the evaluation of the test results,shall be defined in the specifications covering the material or product being tested or shall be mutually agreed upon between the purchaser and the supplier.
8.Procedure
8.1Preparation of Test Specimens—Clean metallic and metallic coated specimens.Unless otherwise agreed upon,clean decorative copper/nickel/chromium or nickel/chromium coatings immediately before testing by wiping significant surfaces with a cotton pad saturated with a slurry containing10g of pure magnesium oxide powder(ACS reagent grade)in100mL of distilled water.Upon rinsing in warm running water,be sure that the clean surface is free of water break.Anodized aluminum parts may be cleaned with inhibited1,1,1-trichloroethane or other suitable organic solvent(see8.1.1).Warning).Do not clean organic and
other nonmetallic coated specimens.Other methods of cleaning,such as the use of a nitric-acid solution for the chemical cleaning or passivation of stainless steel specimens,are permissible when agreed upon between the purchaser and the supplier.Take care that the specimens after cleaning are not recontaminated by excessive or careless handling.Protect the cut edges of plated,coated, or multilayered materials and areas containing identification marks or in contact with the racks or supports with a coating that is stable under the conditions of the test,such as wax,stop-off lacquer,or pressure-sensitive tape.
8.1.1Caution—1,1,1-Trichloroethane tape.(Warning—1,1,1-Trichloroethane should be used in a well-ventilated area away from openflames.)
8.2Positioning of Specimens—Position the specimens in the CASS test chamber during the test so that the following conditions are met:
8.2.1Support or suspend the specimens1562°from the vertical and preferably parallel to the principal direction of horizontal flow of fog through the chamber,based upon the dominant surface being tested.Support or suspend automobile parts,however, so as to expose all significant surfaces at the general level of the condensate collectors.If the position on the automobile is vertical, place the part in an incline position15°from vertical to allow surface wetting by the condensate.If the position on the automobile is facing down,rotate the part approximately180°to test the significant surface.If there are several significant surfaces at different angles,expose each surface of one or more specimens.
8.2.2Make sure the specimens do not come in contact with each other or any other metallic material or any material capable of acting as a wick.
8.2.3Place each specimen so as to permit free settling of fog on all specimens.
8.2.4Make sure the salt solution from one specimen does not drip on any other specimen.
8.2.5Place the specimens in the chamber just prior to bringing the test chamber to the required temperature and turning on the air,since storage in an idle chamber overnight,or for other significant length of time,can affect test results.
N OTE7—Suitable materials for the construction or coating of racks and supports are glass,rubber,plastic,or suitably coated wood.Bare metal should not be used.Specimens are preferably supported from the bottom or the side.Slotted wooden strips are suitable for the support offlat panels.Suspension from glass hooks or waxed string may be used as long as the specified position of the specimens is obtained.If necessary,such suspension may be made by means of secondary support at the bottom of the specimens.
8.3Conditions in the Salt-Spray Chamber—Maintain the exposure zone of the CASS test chamber at a temperature of4961°C during the exposure period(Note8).After closing the test chamber,bring the temperature to49°C before the fog is turned on.The test duration shall commence when the temperature is4961°C and fog is present in the chamber.Heat the air supply by passing fine bubbles through heated distilled or deionized water(see Specification D1193,Type IV)so that the temperature of the air after expansion at the nozzle is4961°C.Record the temperature within the exposure zone of the closed cabinet(Note9)twice a day at least7h apart(except Saturdays,Sundays,and holidays,when the s
alt-spray test is not interrupted for exposing,rearranging, or removing test specimens or to check and replenish the solution in the reservoir).
N OTE8—This can be best accomplished by preheating the chamber to49°C before starting solution atomization.
N OTE9—A suitable method to record the temperature is by a thermometer that can be read from outside the closed cabinet.The recorded temperature must be obtained with the salt-spray chamber closed to avoid a false low reading,because of wet-bulb effect when the chamber is open.Automatic control of temperature in the chamber and a continuous record of temperature are desirable.
8.3.1Place at least two clean fog collectors within the exposure zone so that no drops of solution will be collected from the test specimens or any other source.Position the collectors in the proximity of the test specimens,one nearest to any nozzle and the other farthest from all nozzles.A preferred arrangement is shown in Fig.1.Make sure that the fog is such that for each80cm2 of horizontal collecting area each collector collects from1.0to2.0mL/h of solution,based on a typical run of at least22h(Note 10).Maintain the sodium chloride concentration of the collected solution between4.5and5.5mass%(Note11and Note12). Dilution and evaporation of condensate should be avoided(Note13).
N OTE10—Suitable collecting devices are glass funnels with the stems inserted through stoppers into graduated cylinders.Funnels with a diameter of 10cm(area of about80cm2)and50-mL cylinders are preferred.
N OTE11—A solution having a specific gravity of from1.030to1.040,when measured at25°C,will meet the concentration requirement.The concentration may also be determined as follows:Dilute5mL of the collected solution to100mL with distilled water and mix thoroughly;pipet a10-mL
aliquot into an evaporating dish or casserole;add40mL of distilled water and1mL of1%potassium chromate(K
2CrO
4
)(ACS reagent grade with less
than 0.005%chloride)and titrate with 0.1N silver nitrate (AgNO 3)(ACS reagent grade)solution to the first appearance of a persistent red coloration.A test solution that requires between 3.9and 4.9mL of 0.1N Ag NO 3solution will meet the concentration requirements.
N OTE 12—It has not been found necessary to check copper concentration of the collected solution.
N OTE 13—Factors that may contribute to dilution and evaporation of condensate and make it difficult to control the concentration are lower temperature,inadequate cover insulation,and prolonged storage of test solution at above room temperature.
8.3.2Direct or baffle the nozzle or nozzles so that none of the spray can impinge directly on the test specimens.
8.4Continuity of Test —Unless otherwise specified in the specification covering the material or product being tested,the test shall be continuous for the duration of the entire test period.Continuous operation implies that the chamber be closed and the spray operating continuously,except for the short daily interruptions necessary to inspect,rearrange,or remove test specimens,to check and replenish the solution in the reservoir,and to make necessary recordings as described in 8.3.Schedule operations so that these interruptions are held to a minimum.
8.5Period of Test —Designate the period of test by the specifications covering the material or product being tested or as mutually agreed upon between the purchaser and the supplier.
N OTE 14—Typical exposure periods are:6,16,22,48,96,192,240,504,and 720h.
8.6Cleaning Tested Specimens —Unless specified in the specifications covering the material or product being tested,carefully remove specimens at the end of the test,rinse gently in clean,running,warm water (38°C,max)to remove salt deposits from their surfaces,and then dry immediately.To dry the specimens use a stream of clean,compressed air at 0.25to 0.30MPa gage pressure.N OTE 15—If steel parts are rinsed immediately after removal from the test chamber,small rust spots or flakes of rust may lift off and be rinsed away.It is then difficult to tell where the spots had been.If,after removal from the test chamber,the part is allowed to dry 30to 60min before rinsing,all corrosion spots are easily visible.This not does not apply to zinc-die castings.
8.7Calibration of Corrosive Conditions —This procedure for calibration and standardization of the corrosive conditions within the cabinet involves exposure of nickel test panels and determination of their mass loss in a specified period of time.This may be done monthly or more frequently to make sure the cabinet is operating within the limits specified in 8.7.4.
8.7.1Use nickel panels that are 7.5by 10cm,approximately 0.09cm thick,and made from the higher carbon grade (0.15%max)given in Specification B 162.
8.7.2Place one weighed nickel test panel in each corner of the cabinet with the 10-cm length inclined 3
0°to the vertical using plastic supports that are about 1.5by 4by 7.5cm.The four test panels should be on the inboard side of the condensate collectors parallel to the cabinet length.Make sure the top of the panels are at the same level as the top of the condensate collectors.
8.7.3Expose the test panels to 22h of CASS testing,recording test operating conditions on the data sheet as usual.Remove the panels from the cabinet and rinse each in reagent grade water (see Specification D 1193,Type IV)to remove salt.Immerse each panel in 20%by volume hydrochloric acid prepared with distilled water for 2min at 20to 25°C using nickel-copper alloy 400(UNS N04400)tongs.The tongs may be nonmetallic or another material that will not affect the mass loss of the nickel by galvanic action.Rinse each panel in water at room temperature and then in warm (38°C)flowing water.Dry panels in an oven at 100°C for 10min.Allow the panels to reach room temperature and weigh immediately on an analytical balance.
8.7.4Determine the mass loss of each panel by subtracting its weight after exposure from its initial weight.Determine the corrosive loss by dividing the mass loss by the area of one face of the test panel (77.5cm 2).The corrosive rate shall be 0.45to 0.85mg/cm 2to satisfy the requirements of this method.
9.Evaluation of Results
9.1A careful and immediate examination shall be made for the extent of corrosion of the dry-test specimens;or for other failure,as required by the specifications covering the material or product being tested;or by agreement between the purchaser and the supplier.
10.Records and Reports
10.1The following information shall be recorded,unless otherwise prescribed in the specifications covering the material or product being tested:
10.1.1The title,designation and year of issue of this method.
10.1.2The salt,water,copper chloride,and acetic acid used in preparing the salt solution,
10.1.3All readings of temperature within the exposure zone of the
chamber,
FIG.1Arrangement of Fog
Collectors
10.1.4Daily records of data obtained from each fog collecting device,including the following:
10.1.4.1V olume of salt solution collected in(mL/h)/8cm2,
10.1.4.2Concentration or specific gravity at25°C of solution collected,and
10.1.4.3pH of solution collected,
10.1.5Nickel panel corrosion rate calibration,
10.1.6Type of specimen and its dimensions,or number,or description of part,
10.1.7Method of cleaning specimens,
10.1.8Method of supporting or suspending the article in the salt-spray chamber,
10.1.9Description of protection used as required in8.1,
10.1.10Exposure period,
10.1.11Interruptions in the test,cause and length of time,and
10.1.12Results of inspections.
N OTE16—If any of the atomized salt solution that has not come in contact with the test specimens is returned to the reservoir,it is advisable to record the concentration or specific gravity and the pH of this solution also.
N
OTE17—Round robin testing revealed the inability to exhibit repeatability of the mass loss requirements of8.7.4.Further testing is ongoing to clarify the root causes.
11.Precision and Bias
11.1The reliability,reproducibility,and accuracy of the CASS test depends on proper and consistent control of a number of factors,including:
11.1.1Cleaning of the test samples,
11.1.2Positioning of the specimens and samples in the test cabinet,
11.1.3Rate of condensation within the test cabinet,
11.1.4CASS solution makeup,editorially
11.1.5Cabinet maintenance,and
11.1.6Calibration of corrosive conditions.
11.2The precision and bias of the CASS test is being determined and will include study of the reproducibility of the calibration procedure described in8.7.
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