Grinding Balls
Forged steel grinding balls for ball mills, heat treated right through for slow, even wear and resistance to breakage Get In ContactLooking for grinding balls that wear slowly and keep their shape? William Boulton supplies forged steel grinding balls for ball mills in mining, cement, power generation and mineral processing. Each ball is drop forged or rolled from wear-resistant steel, then quenched and tempered so it is hardened right through, not just at the surface, and keeps grinding efficiently as it wears down.
Our standard range covers diameters from 20 mm to 90 mm, in hard, medium and soft hardness classes for wet or dry grinding. We’ll help you match the ball size, grade and charge make-up to your mill, your material and your target grind, and our breakage guarantee gives you extra peace of mind with every order.
Not sure which size or grade you need? Call our team on 01782 816158 or send us your mill details.
Hardened right through
Controlled quenching and tempering give consistent volume hardness, so balls keep grinding efficiently as they wear.
20–90 mm as standard
Ten standard diameters for ball mill and regrind duties, with other sizes and grades available subject to review.
Breakage guarantee
If breakage goes above 3%, we replace the broken balls free of charge.
Expert support
Our engineers help you choose ball sizes, grades and charge make-up, and support you once the media is in your mill.
What are grinding balls?
Grinding balls are the steel media that do the work inside a ball mill. A ball mill is a rotating cylinder, partly filled with balls, that reduces crushed ore, clinker, coal and other materials to a fine powder or slurry. As the shell turns, the ball charge is carried up the side of the mill and then cascades and tumbles back down, breaking particles by impact and grinding them by attrition as the balls roll and rub against each other.
The ball charge usually fills around 30–40% of the mill’s internal volume, and keeping it topped up is a major operating cost: balls wear away steadily, so new media has to be added to keep the charge and the grind consistent. A ball that wears slowly and evenly, and doesn’t break, lowers your steel consumption per tonne and keeps your mill performing predictably.
We also supply ball mills for batch and continuous grinding, so we understand grinding media from the mill side as well as the media side.
Forged steel, high chrome or ceramic?
The right grinding media depends on how much impact your mill delivers, how abrasive your material is, whether you grind wet or dry, and whether your product can tolerate iron. Here’s how the three main types compare.
| Compare | Forged steel grinding balls | Cast high chrome balls | Ceramic balls |
|---|---|---|---|
| How they’re made | Drop forged or rolled from steel, then quenched and tempered | Cast from high chromium iron, then heat treated | Formed from ceramic powders such as alumina or zirconia, then sintered |
| Main strength | Toughness and impact resistance, with high, consistent hardness | Very high abrasion resistance from hard chromium carbides | Iron-free grinding with very low wear and contamination |
| Bear in mind | Wears faster than high chrome in highly abrasive, dry duties | More brittle, so less suited to high-impact grinding | Lower density gives less impact energy, so not for coarse feeds |
| Typical uses | Wet ball mills and regrind mills in mining, and coarse grinding chambers | Cement finish and raw mills, coal mills and abrasive regrind duties | Fine and ultra-fine grinding of ceramics, pigments, pharmaceuticals and food |
Find out more about our cast high chrome balls and ceramic grinding balls, or see our SAG balls for semi-autogenous mills.
How our forged grinding balls are made
- Steel selection – wear-resistant, high-carbon steel grades are chosen for the right balance of hardness, toughness and low wear.
- Controlled heating – the steel is heated to a carefully controlled forming temperature.
- Forging or rolling – each ball is drop forged or rolled into a dense, consistent sphere.
- Quenching and tempering – a controlled thermal cycle hardens every ball uniformly and sets the hardness profile your mill needs.
- Inspection – checks can include hardness testing, dimensional verification, visual inspection and material certificates.
What makes a good grinding ball?
- Volume hardness, not just surface hardness – a ball that is hard all the way through keeps wearing slowly as it gets smaller, instead of wearing faster once a hard outer layer has gone.
- Toughness – the ball has to survive repeated impacts without cracking, spalling or breaking.
- Roundness – balls that keep their shape grind more efficiently than worn, flattened or misshapen media.
- Consistent chemistry and size – tight control from batch to batch gives predictable wear rates and makes consumption easier to track.
Grinding ball sizes and technical data
Our standard range covers nominal diameters of 20, 25, 30, 35, 40, 50, 60, 70, 80 and 90 mm. Hardness steps down slightly as the diameter increases, balancing wear resistance against the toughness that larger balls need to withstand heavier impacts.
Size, weight and hardness guide
| Nominal diameter | Inch equivalent | Approx. weight per ball | Approx. balls per tonne | Hardness (HV) | Approx. HRC |
|---|---|---|---|---|---|
| 20 mm | 0.79 in | 33 g | 30,400 | On request | – |
| 25 mm | 0.98 in | 64 g | 15,600 | 675–830 | 59–65 |
| 30 mm | 1.18 in | 111 g | 9,010 | 675–830 | 59–65 |
| 35 mm | 1.38 in | 176 g | 5,670 | 675–830 | 59–65 |
| 40 mm | 1.57 in | 263 g | 3,800 | 675–830 | 59–65 |
| 50 mm | 1.97 in | 514 g | 1,950 | 675–830 | 59–65 |
| 60 mm | 2.36 in | 888 g | 1,130 | 654–800 | 58–64 |
| 70 mm | 2.76 in | 1.41 kg | 709 | 634–771 | 57–63 |
| 80 mm | 3.15 in | 2.10 kg | 475 | 615–748 | 56–62 |
| 90 mm | 3.54 in | 3.00 kg | 334 | 596–720 | 55–61 |
Weights are calculated for a solid steel sphere at 7.85 g/cm³ and are a guide only. HRC values are approximate conversions from the Vickers (HV) figures. Hardness for 20 mm balls is confirmed when you order.
Typical chemical composition (% by mass)
| Diameter | C | Mn | Si | P | S | Cr |
|---|---|---|---|---|---|---|
| All standard sizes (20–90 mm) | 0.60–0.90 | 0.30–1.20 | 0.15–0.60 | max. 0.025 | max. 0.025 | 0.01–0.80 |
Breakage guarantee
| Breakage rate | What we do |
|---|---|
| 0–3% | No claim |
| 3–10% | Broken balls replaced free of charge |
| Above 10% | All ball sizes involved in the breakage replaced free of charge |
Technical values are typical catalogue data rather than a guaranteed contract specification. Final chemistry, hardness, tolerances, packing and test documentation are confirmed on the quotation and material certificate for each order.
Choosing the right ball size and charge
There’s no single right size for every ball mill. The best diameter depends on:
- Feed size – coarser feed needs larger balls with more impact energy to break the biggest particles.
- Target grind – smaller balls give more contact points and more grinding surface for a finer product.
- Material hardness – harder, more competent materials need more energetic impacts.
- Mill diameter and speed – these set how high the balls are lifted and how hard they land.
- Wet or dry grinding – wet grinding adds corrosion to abrasion, which affects the wear rate and the best media choice.
Most ball mills run a graded charge of several sizes. A new mill is usually loaded with a mix of sizes, and the charge is then maintained by adding the largest size, or the two largest sizes, as the balls wear, so it settles into a stable size distribution. Bond’s ball size equation is a common starting point for the top size, but the best results come from tracking mill power, throughput and product size, then adjusting one step at a time.
Tell us your mill diameter and speed, feed size, material and target product size, and we’ll recommend a starting ball size and charge make-up.
Have a question? Call us on 01782 816158 or:
Why choose William Boulton for grinding balls?
William Boulton is a British engineering company based in Stoke-on-Trent, founded in 1852. As well as designing and building our own process machinery, we supply grinding media to ball mill operators across many industries, with the practical advice to get the most from it.
- Application-matched media – we recommend the ball type, grade and size for your mill, material and grinding duty.
- Technical support – our experienced engineers help you optimise charge make-up, replenishment and media consumption.
- Quality checks – documentation and checks can include material certificates, hardness testing and dimensional verification.
- Breakage guarantee – our forged grinding balls are backed by a clear breakage guarantee.
- Global delivery – our network supports customers around the world with timely delivery.
- The full grinding media range – from SAG balls and cast high chrome balls to ceramic grinding media. View all grinding media.
Grinding ball FAQs
What are grinding balls made of?
Our forged grinding balls are made from wear-resistant high-carbon steel, with typically 0.60–0.90% carbon plus manganese, silicon and a little chromium. Other types of grinding ball are cast from high chromium iron, or made from ceramics such as alumina and zirconia for specialist duties.
What size grinding balls do I need?
It depends on your feed size, target grind, material hardness and mill dimensions. As a rough guide, coarse grinding uses larger balls of around 60–90 mm, while fine grinding and regrind duties use smaller balls of around 20–40 mm. Send us your mill details and we’ll recommend a size.
Are forged or cast grinding balls better?
Neither is better in every mill. Forged steel balls are tougher and more resistant to impact, so they suit wet mining mills and coarse grinding. Cast high chrome balls are harder and more abrasion resistant, so they often last longer in dry, abrasive duties such as cement grinding, but they are more brittle. We’ll help you compare the cost per tonne ground for your application.
How hard are forged grinding balls?
Our standard forged balls range from about 596 to 830 HV, roughly 55–65 HRC, depending on diameter. Smaller balls are the hardest, while the largest have a slightly lower hardness range, which gives them extra toughness.
Can forged grinding balls be used for wet and dry grinding?
Yes. Our forged steel grinding balls suit both wet and dry grinding, wherever impact toughness and consistent size matter.
What happens if grinding balls break?
Our breakage guarantee covers you. If breakage is between 3% and 10%, we replace the broken balls free of charge. Above 10%, we replace all the ball sizes involved in the breakage.
How much of a ball mill should be filled with balls?
Ball mills typically run with a ball charge of around 30–40% of the mill’s internal volume. The right level depends on your mill’s power, speed and duty, so check it against your mill manufacturer’s guidance.
Do you supply grinding balls outside the UK?
Yes. Our global network supports customers around the world with timely delivery and technical support. Contact us with your location and requirements.