Grinding Media — Balls, Cylpebs, Slugoids and Helipebs

Grinding media are the loose balls, cylinders and coils that do the actual work inside a ball mill or rod mill. This page covers what each type is, the sizes they are made in, and how to work out a charge. Every size is quoted on request — tell us your port and specification and we will quote it delivered.

Dimensions are given in millimetres, with the imperial equivalent in brackets where the trade still names one.

The four types

Type	Shape	Material	Hardness	Best at
Forged & rolled steel balls	Sphere, 12–152 mm (1/2–6 in)	Carbon / low-alloy steel	350–600 BHN	General duty, coarse to medium grind
High chromium cast balls	Sphere, 17–125 mm (5/8–5 in)	Chromium alloy white cast iron, 12%+ Cr	HRC 60–63, approx. 650/700 BHN	Abrasive ore where wear life pays for itself
Cylpebs & slugoids	Cylinder, 12–32 mm (1/2–1-1/4 in)	Carbon / manganese steel	approx. 500 BHN	Fine grinding, finishing duties
Helipebs	Coiled wire, hollow centre	Hardened steel wire	Hardened for abrasion	Fine cement production

Balls or cylpebs?

For the same nominal dimension a cylinder and a ball stand in a ratio of 3 to 2 in both surface and volume. The consequence is easy to miss: the exposed surface per tonne of charge is the same for the two. Cylpebs do not give you more grinding surface for your money.

What changes is the nature of the contact. A ball touches the charge at a point; a cylinder touches along a line and across a face. That is why cylpebs are chosen for fine grinding and finishing, where a ball charge leaves the product coarser than wanted — and why slugoids exist at all. Slugoids are cylinders whose length equals their diameter, so they tumble with the action of a ball while keeping a cylinder's contact area.

Charge tables

These two tables are not interchangeable, and the difference is not a rounding error. Steel media are calculated at a density of 7.85 g/cm³; high chromium cast media at 7.6. A 125 mm cast ball weighs 7.77 kg where a 127 mm steel ball weighs 8.42 kg. Using the wrong table puts roughly an 8% error into a mill charge calculation, which at a few hundred tonnes of media is not a small number.

Steel balls — forged and rolled, 7.85 g/cm³

Diameter	Weight each	Weight each	Pieces per tonne	Surface area, cm² each
12 mm	7 g	0.016 lb	140,795	4.5
15 mm	14 g	0.031 lb	72,087	7.1
17 mm	20 g	0.045 lb	49,520	9.1
20 mm	33 g	0.073 lb	30,412	12.6
25 mm (1 in)	64 g	0.142 lb	15,571	19.6
30 mm	111 g	0.245 lb	9,011	28.3
35 mm	176 g	0.388 lb	5,674	38.5
40 mm	263 g	0.58 lb	3,801	50.3
45 mm	375 g	0.826 lb	2,670	63.6
50 mm (2 in)	514 g	1.13 lb	1,946	78.5
63.5 mm (2-1/2 in)	1.05 kg	2.32 lb	950	126.7
76.2 mm (3 in)	1.82 kg	4.01 lb	550	182.4
88.9 mm (3-1/2 in)	2.89 kg	6.37 lb	346	248.3
101.6 mm (4 in)	4.31 kg	9.5 lb	232	324.3
114.3 mm (4-1/2 in)	6.14 kg	13.53 lb	163	410.4
127 mm (5 in)	8.42 kg	18.56 lb	119	506.7
139.7 mm (5-1/2 in)	11.21 kg	24.71 lb	89	613.1
152.4 mm (6 in)	14.55 kg	32.07 lb	69	729.7

Rolled up to 50 mm (2 in); forged from 63.5 mm (2-1/2 in) upward.

High chromium cast balls — 7.6 g/cm³

Diameter	Weight each	Weight each	Pieces per tonne	Surface area, cm² each
17 mm (5/8 in)	20 g	0.043 lb	51,149	9.1
20 mm (3/4 in)	32 g	0.07 lb	31,412	12.6
23 mm (7/8 in)	48 g	0.107 lb	20,654	16.6
25 mm (1 in)	62 g	0.137 lb	16,083	19.6
30 mm (1-1/4 in)	107 g	0.237 lb	9,307	28.3
40 mm (1-1/2 in)	255 g	0.562 lb	3,927	50.3
50 mm (2 in)	497 g	1.097 lb	2,010	78.5
60 mm (2-1/2 in)	860 g	1.89 lb	1,163	113.1
70 mm (2-3/4 in)	1.36 kg	3.01 lb	733	153.9
80 mm (3-1/8 in)	2.04 kg	4.49 lb	491	201.1
90 mm (3-1/2 in)	2.9 kg	6.4 lb	345	254.5
100 mm (4 in)	3.98 kg	8.77 lb	251	314.2
110 mm (4-1/2 in)	5.3 kg	11.68 lb	189	380.1
125 mm (5 in)	7.77 kg	17.13 lb	129	490.9

Cylpebs and slugoids — 7.85 g/cm³

Size	Weight each	Weight each	Pieces per tonne	Surface area, cm² each
12 × 12 mm (1/2 in)	11 g	0.024 lb	93,863	6.8
13 × 13 mm	14 g	0.03 lb	73,826	8
15 × 15 mm	21 g	0.046 lb	48,058	10.6
16 × 16 mm (5/8 in)	25 g	0.056 lb	39,599	12.1
17 × 17 mm	30 g	0.067 lb	33,014	13.6
19 × 19 mm (3/4 in)	42 g	0.093 lb	23,647	17
20 × 20 mm	49 g	0.109 lb	20,275	18.8
22 × 22 mm (7/8 in)	66 g	0.145 lb	15,233	22.8
25 × 25 mm (1 in)	96 g	0.212 lb	10,381	29.5
30 × 30 mm	167 g	0.367 lb	6,007	42.4
32 × 32 mm (1-1/4 in)	202 g	0.445 lb	4,950	48.3

Cylpebs are made to any required length between 12 mm and 30 mm (1/2 in and 1-1/4 in) diameter. The equal-length sizes above are the standard ladder; specify your own length and we will quote it.

Selecting a size

• Large media grind by impact. Coarse feed and hard ore need the kinetic energy a big ball carries.
• Small media grind by abrasion. A 12 mm ball gives roughly 160 times the pieces per tonne of a 152 mm ball, and the surface goes up with it. Fine product comes from surface, not impact.
• Most mills run a graded charge, not one size, and top up with the largest size as the charge wears down.

Tell us the mill diameter, the feed size and the product you want, and we will recommend the ladder rather than leave you to guess it.

Hardness, and why the test matters

Hardness is the property that governs how fast media wear away, so it is the number worth checking. There are two tests and they are not interchangeable.

The Brinell test presses a hard steel ball into the metal under a set load and measures the diameter of the dent. The Rockwell C test presses a 120° diamond cone and measures how far it sinks under a 150 kg load against a light initial load.

The difference decides which one you can trust. Brinell uses a steel indenter, and above roughly 650 BHN the indenter itself deforms against the workpiece — so the dent is partly the ball collapsing, not the metal yielding, and the reading is false. Above that hardness only the Rockwell C test is valid, and any Brinell figure quoted alongside it is an estimate converted from Rockwell, not a measurement. This is exactly the range high chromium media sit in, which is why they are specified HRC 60 / HRC 63 and only approximately 650/700 BHN.

One further caution: converting hardness to tensile strength in kg/mm² is unreliable. It only holds for ordinary annealed steel below about 0.5% carbon — a Brinell hardness under about 175. It does not hold for grinding media.

Standards

There is no ISO or DIN standard for grinding media itself. The product was never internationalised; what governs it is a mix of national specifications and material standards, plus the international standards for the hardness tests. The ones worth naming in an enquiry:

Standard	Covers
ISO 6508	Rockwell hardness test — the valid test for high chromium media
ISO 6506	Brinell hardness test — valid below approx. 650 BHN
ASTM A532	Abrasion-resistant cast irons, 12–28% Cr — the material behind "high chrome"
GB/T 17445	Cast grinding balls (Cr-alloy white iron, ductile iron), China
IS 6079	Grinding media specification, India
ASTM A128	Austenitic manganese (Hadfield) castings, 11–14% Mn
ASTM A297	Heat-resistant Cr-Ni castings — the austenitic special compositions

ASTM E10 and E18 are the American equivalents of ISO 6506 and ISO 6508 and are accepted interchangeably by most mills.

Special compositions

Where the charge must stay non-magnetic, or resist corrosion as well as wear, media can be cast in austenitic grades:

Composition	Family
12/14% Mn and 16/18% Mn	Austenitic manganese (Hadfield)
26% Cr / 9% Ni	Austenitic chromium-nickel
25% Cr / 12% Ni
25% Cr / 20% Ni
15% Cr / 35% Ni

Send us the duty and the specification you are working to and we will confirm the grade before quoting.

Quoting

Grinding media price moves with the steel market and with freight to your port, so there is no useful list price — which is why every size here is quoted rather than listed. Send us your enquiry with the mill, the duty, the size ladder and the port, and we will quote it delivered.