AS 1627.4:2005 pdf – Metal finishing-Preparation and pretreatment of surfaces Part 4: Abrasive blast cleaning of steel

AS 1627.4:2005 pdf – Metal finishing-Preparation and pretreatment of surfaces Part 4: Abrasive blast cleaning of steel.
Type WA: This type consists of crystalline corundum which is whitish in colour and contains at least 99% aluminium oxide.
1.3.14 Grit
Particles that are predominantly angular, that have fractured faces and sharp edges and that are less than half-round in shape.
1.3.15 High-carbon cast-steel gilt
A metallic blast cleaning abrasive obtained by crushing high-carbon cast-steel shot into sharp-edged angular particles.
1.3.16 Ilmeijlte
Natural occurrmg mineral sand which is separated, dried and sieved and prepared for use as
a blast cleaning abrasive.
1.3.17 Preparation classes
Classification describing the quality of preparation achieved by a method of surface
cleaning.
1.3.18 Profile
See ‘Surface profile’.
1.3.19 Profile comparator
See ‘Surface profile comparator’.
1.3.20 Rust grades (Initial rust grades)
Classification describing the initial amount of mill scale and rust on a steel surface before any surface preparation has taken place.
1.3.21 Spot (Selective) blasting
The abrasive blast cleaning of a previously coated surface to produce areas of bare exposed metal and areas of brush-blasted surface.
1.3.22 Shot.
2.1 MATERIALS AND TYPES
A wide variety of natural and synthetic granular materials are used for abrasive blast-cleaning. A range of solid materials commonly in use for the preparation of steel surfacesbefore coating is given in Table 2.1.Each material provides a characteristic performanceand surface finish.
2.2 REQUIREMENTS
Abrasives shall be dry (except when added to pressurized liquid or slurry blast cleaningsystems) and shall be free-flowing to permit consistent metering into the blast stream.
The level of soluble salt contamination in the abrasive can be critical to the performance ofa coating system particularly when used to contain fresh water. An upper limit ofconductivity shall be 25 mS/m as assessed by ISO 11127-6.
The effect of salt contamination is more pronounced in hot，humid or fresh waterenvironments.
NOTE: For guidance on safety requirements see Appendix C.2.3 SELECTION CONSIDERATIONS
2.3.1 Abrasives and equipment
Selection of a suitable abrasive,together with an appropriate blast-cleaning method andoperating conditions, is necessary to achieve the required standard of surface preparation.The type of blast cleaning abrasive, i.e. its composition, particle size distribution, shape,hardness, density and impact behaviour (deformation or shatter characteristics), is importantin determining the standards of cleanliness,the cleaning rate and the resulting surfaceprofile of the blast cleaned surface.
2.3.2 Preliminary tests
Preliminary blast cleaning tests are recommended to determine the most effective abrasive,blasting parameters,the resulting surface preparation grade，(see Appendix B) and theresulting surface profile, see As 3894.5. If recycled abrasive is to be used for the surfacepreparation work,it is essential that a preliminary test be carried out with the samematerial, as new abrasive may give misleading results.
The size and shape of the particles may change during use and this may affect the resultantsurface profile of the blast-cleaned steel if the abrasive is reused.