1、Designation: D7868 13Standard Practice forDetermining the Dry Fall (Fog) Properties of ProtectiveCoatings1This standard is issued under the fixed designation D7868; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers a procedure for qualitatively evalu-ating the dry fall properties of coatings. The establishment ofthe
3、test environment and the evaluation procedures are de-scribed.1.2 This practice uses panels containing an automotivefinish since these types of surfaces are often the primaryconcern relating to overspray damage. Panels coated with othersystems may be used as collection surfaces when they aredeemed t
4、o be more representative.1.3 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.4 This standard does not purport to address all of thesafe
5、ty concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D610 Practice for Evaluating Deg
6、ree of Rusting on PaintedSteel SurfacesD5402 Practice for Assessing the Solvent Resistance ofOrganic Coatings Using Solvent Rubs3. Terminology3.1 Definitions:3.1.1 dry/fall/fog coating, nan interior or exterior coatingspecially formulated so that the fine particles of overspray dryto a dust or powde
7、r during a free fall of a certain distance atspecific temperature and humidity ranges, and will not adhereto surfaces on which the overspray is subsequently deposited.4. Summary of Practice4.1 A structural frame is erected and enclosed. Spray targetsare placed inside the enclosure. Four steel panels
8、 coated withan automotive basecoat/clear coat system are placed on theenclosure floor to collect the dry fall. (Panels coated with othersystems or uncoated panels, or both, can be used when they aredeemed to be more representative.) A duplicate panel set ismaintained at the prevailing air temperatur
9、e, while the otherduplicate panel set is heated in oven and placed inside theenclosure immediately prior to atomizing the coating. Thecoating is atomized against the targets at each of two distancesand the panels are removed for evaluation. Two of the coatedsteel panels remain at laboratory ambient
10、conditions, while the“pre-heated” panels are returned to a laboratory oven. Theheated and ambient coated panels are cleaned and evaluatedafter 24-h for dry fall attachment.5. Significance and Use5.1 Attachment of overspray particles to vehicles and othersurfaces not intended to be coated can result
11、in propertydamage and insurance claims. Dry fall coatings are formulatedsuch that overspray particles dry as they move through the air,and before they land on horizontal surfaces. These particles canthen be brushed off, vacuumed or washed from the surfaceswith no damage. This practice can be used to
12、 evaluate the dryfall properties of coatings prior to large scale use. The practicecan also be used to evaluate whether the coating(s) possess thesame dry fall properties when the fallout collects on surfaceswith an elevated temperature.6. Reagents6.1 Commercially available Car Washing Concentrate.6
13、.2 Mineral Spirits.7. Procedure7.1 Construct a frame (enclosure) using steel conduit andcouplings or other materials of construction. The interior of theenclosure measures approximately 3 ft wide by 4 ft deep and is1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Co
14、atings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.46 on Industrial Protective Coatings.Current edition approved June 1, 2013. Published July 2013. DOI:10.1520D7868-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer S
15、ervice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States119 ft high in order to permit a dry fall t
16、est distance of 18 ft.3Enclose the frame with plastic sheeting or tarpaulins andsecure, making sure there is access at the base of the enclosureto add and remove the collection surfaces (coated panels). Abase constructed of plywood and protected with paper orplastic sheeting (that can be pushed in/p
17、ulled out to load/unload the panels) may be used. This requires the frame to beheightened approximately 2 in. from the floor surface usingwooden blocks or other methods (see Fig. 1).7.2 Fabricate and suspend (vertically) a spray target con-structed of18 in. by 3 by 3 ft wood or other rigid material
18、ontotwo hanging rods inside the enclosure. Mount troughs alongthe bottom edge of the target (optional) or position thecollection surfaces to prevent dripping coating on the dry fallcollection surfaces at the base of the enclosure. The spraytargets are positioned at the top of the enclosure to allow
19、a dryfall distance of 18 ft, and are positioned 48 ft and 24 ft from thespray gun tip (see 7.7 and 7.9). The spray targets shall bereplaced for each test to prevent build-up of wet coating on thetargets and potential dripping onto the dry fall collectionsurfaces at the base of the enclosure (See Fig
20、. 2).7.3 Mix and reduce (thin) the coating material according tothe manufacturers instructions, by the maximum amountpermitted. Record the material temperature. Atomize the coat-ing by airless spray (unless another spray method is mutuallyselected), using the pump pressure, hose diameter and tip siz
21、erecommended by the manufacturer. If the coating manufacturerrecommends a range of pump pressures and tip sizes, use thelowest pump pressure and the largest tip size (of the rangesrecommended) to create a worse case scenario. Record theactual pressure and tip size used, and the type, batch numberand
22、 amount of reducer used.7.4 Record the date and time of day. Measure and record theair temperature, relative humidity and dew point temperatureinside the enclosure. Testing should be performed when the airtemperature is between 60 and 80F (16 and 27C) and therelative humidity is between 40 and 85 %.
23、 The enclosureshould not be mechanically ventilated.7.5 Place duplicate 4 by 6 in. steel panels coated with anautomotive system (basecoat/clear coat) in the center of theenclosure base. The color of the coating on the panels shall beblack unless another panel color is mutually selected orrequired fo
24、r contrast to the color of the dry fall product beingevaluated. Record the coating system on the panels as well asthe color of the finish coat on the panels. The surfacetemperature of the panels shall be measured and recorded.Place a second set of duplicate steel panels (that have beenpre-heated in
25、an oven maintained at 50C until a surfacetemperature of 122F (50C) is attained).4Record the oventemperature. This set of pre-heated panels (designed to repli-cate a hot surface) shall be placed inside the enclosure within10 s of coating atomization to minimize heat loss. Identify theback sides of th
26、e panels with the replicate number; (forexample, 1, 2) and the condition (for example, normal and hot).Position the normal temperature and pre-heated (hot) panelsrandomly on the base of the enclosure.7.6 Position the spray target (described in 7.2) at the top ofthe enclosure against the back wall. O
27、rient the target vertically(the middle of the target should be approximately 18 ft fromthe dry fall collection platform at the base of the enclosure).Record the start time, then atomize the coating against thespray target (48 in. from the spray tip) for 45 6 3s.5Monitorthe atomization time using a s
28、topwatch.After the elapsed spraytime, immediately remove the panels from the base of theenclosure.Allow two of the steel panels to remain at laboratoryambient conditions (nominal 77F (25C) and 50 % relativehumidity) for approximately 24 h. Immediately place thepre-heated panels back into laboratory
29、oven (maintained at122F (50C) for 24 h. After the 24 h period, proceed to 7.8.3Other dry fall distances can be selected as agreed upon between purchaser andseller. The enclosure height may be adjusted to accommodate other dry falldistances.4The use of thicker steel panels (for example, 0.25 in.) wil
30、l retain heat longerthan thinner steel panels.5Shorter atomization time (for example, 15 s.) may be invoked when shorter dryfall distances (for example, 10 ft) are employed.FIG. 1 Dry Fall EvaluationEnclosure with Plastic Sheeting(NoteBase is heightened using 1.5 in. wooden blocks.)D7868 1327.7 Repe
31、at steps 7.2-7.6 with a new target positionedmidway in the enclosure so that it is 24 in. from the spray tip.To reduce any influence of residual solvent vapors inside theenclosure, allow a minimum of 30 min between spray trialswith the same product (for example, between 48 and 24 in.spray distances)
32、 and a minimum of 1 h between products.67.8 Allow the panels removed from the oven to equilibrateto room temperature, then evaluate the surface of the ambientand oven panels by attempting to remove the dry fall by drybrushing (using a clean, soft bristle dust pan brush). Rate andrecord the degree of
33、 attachment after dry brushing (DB) usingFig. 3 (4DB to 1DB).7.9 If dry brushing will not remove the overspray, usemoderate pressure7with a cellulose sponge and standard carwash concentrate, diluted per the manufacturers instructionsin warm (70 to 90F (21 to 32C) water to scrub the surface.Rate and
34、record the degree of attachment after scrubbing thesurface with the car wash (CW) solution using Fig. 3 (4CW to1CW).7.10 If moderate scrubbing with a cellulose sponge andstandard car wash concentrate in warm water will not removethe overspray, use moderate pressure with cotton cloths andmineral spir
35、its to scrub the surface. Rate and record the degreeof attachment after scrubbing the surface with mineral spirits(MS) using Fig. 3 (4MS to 1MS).7.11 Other methods of removal such as pressure washingmay be used.8. Report8.1 The following information shall be documented andreported.8.1.1 Product manu
36、facturer and product number.8.1.2 Batch number of product and reducer.8.1.3 Date and time of testing.8.1.4 Coating system used on dry fall collection panels.8.1.5 Prevailing temperature and relative humidity condi-tions.8.1.6 Type and amount of reducer added.8.1.7 Application method.8.1.8 Applicatio
37、n equipment (pressure, tip size, hose diam-eter).8.1.9 Pre-test oven temperature.8.1.10 Post-test oven temperature.8.1.11 Dry fall distance (if greater or less than 18 ft).8.1.12 Elapsed time of atomization.8.1.13 Elapsed time from collection to evaluation.8.1.14 Qualitative attachment rating on amb
38、ient coatedpanels.8.1.15 Qualitative attachment rating on post-heated coatedpanels.8.1.16 Procedure(s) used to remove the overspray from thepanels (dry brushing, car washing solution/sponge, mineral6Alternatively, one side of the enclosure may be opened for ventilation betweenspray trials or product
39、 trials, or both.7As defined by Section 6.1 of Practice D5402, the pressure exerted onto acellulose sponge or cotton cloth on a laboratory balance required to generate 1000to 2000 g of force shall be considered by this practice to be moderate pressure.FIG. 2 Illustration of Target Suspension Inside
40、Upper Area of Enclosure(NoteTop is enclosed with plastic or tarpaulins.)D7868 133spirits/cloth, etc.). If a car washing solution is used, report themanufacturer of the car washing solution and the concentrationused.9. Keywords9.1 dry fall; dry fog; oversprayASTM International takes no position respe
41、cting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This st
42、andard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM Internat
43、ional Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown belo
44、w.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).FIG. 3 Dry Fall (Fog) Attachment RatingsD7868 134
