Page 257 - Centrifugal Pumps Design and Application

230 Centrifugal Pumps: Design and Application

Austenitic manganese steel, which work-hardens under impact, is used
in very slow-speed, dredge-type pumps when handling large dense sol-
ids.
Hard metal materials are used to resist erosion abrasion (caused by the
combined effects of cutting wear parallel to the surface and to a lesser
extent deformation wear). Depending on the nature of the slurry, a wide
selection of materials are available. (Note: Values listed in Table 13-1 are
average.) A tabulation of alloys for abrasion resistance is given in Table
13-2.
It is the ability of elastomeric materials to deform elastically under im-
pact that makes them ideally suited to resist erosion wear. Natural rubber
will far outlast metal provided it is compatible with the liquid being

^ Table 13-1
Average
Material ASTM No. Brinnell Characteristics and
Name_ Casting Hardness Typical Applications
Ni-Hard 1 A-532 550 2.5% chrome, 4% nickel, 3,3%
Class 1 carbon. Good resistance to cut-
ting-type erosion, it is not rec-
ommended for acids but can be
used for mildly alkaline slurries.
Ni-Hard 4 A-532 575 8% chrome, 6% nickel, 3.3%
Class 1 carbon. Compared to Ni-Hard 1,
it has a higher tensile strength
and is more resistant to both cor-
rosion and erosion.
High chrome alloy A-532 650 26% chrome, 2.8% carbon. Su-
Class B perior erosion resistance and bet-
ter corrosion resistance down to
5 pH. This material can be ma-
chined by conventional means in
its annealed state then hardened
and tempered with minimum dis-
tortion.
*PACE™ 400 27% chrome, 2% nickel, 2%
moly, 1.6% carbon.
The most suitable alloy for ero-
sive, corrosive slurries in the
range 1 to 11 pH. However its
erosion resistance is inferior to
high chrome iron.
* Registered trademark ofAbex Corporation