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| Model | Cylinder Diameter (mm) | Cylinder Length (mm) | Effective Volume (m³) | Rod Loading (t) | Speed (r/min) | Power (kW) | Capacity (t/h) | Weight (t) |
|---|---|---|---|---|---|---|---|---|
| ZKBM2130 | 2,100 | 3,000 | 8.8 | 18 | 21.4 | 220 | 14-50 | 48 |
| ZKBM2430 | 2,400 | 3,000 | 12 | 25 | 19 | 250 | 25-75 | 60 |
| ZKBM2745 | 2,700 | 4,500 | 18 | 38 | 18.4 | 500 | 100-200 | 90 |
| ZKBM3245 | 3,200 | 4,500 | 32 | 67 | 16.4 | 800 | 200-500 | 145 |
| ZKBM3660 | 3,600 | 6,000 | 54 | 100 | 15.8 | 1,250 | 320-800 | 190 |
Notes: capacity depends on ore hardness, feed size, product size requirement and rod charge; figures assume wet open-circuit grinding of medium-hard ore. All models use steel rods as grinding media with wet overflow discharge. Drive is by motor through a reducer and girth gear, or by a low-speed synchronous motor on larger units. Contact Ormaise with your ore test data and target product size for a model and rod charge recommendation.
Stock-listed crushing and screening equipment manufacturer, serving 2,000+ operations since 2003.
A rod mill does coarse grinding where a uniform product and low over-grinding matter. Its classic duties are primary open-circuit grinding ahead of finer stages, feed preparation for gravity separation circuits, and artificial sand production from rock. The ZKBM series is widely used in artificial stone sand, ore dressing plants, water conservancy and glass building materials, taking crusher-product feed and delivering an even, coarse-ground product.
The mill is a horizontal cylinder charged with steel rods. Driven through a reducer and girth gear, the cylinder lifts the rod charge by friction and centrifugal action until it cascades down. The rods lie parallel and grind in line contact: coarse particles wedge between the rods and are broken first, while fine material slips through the gaps. Ground product leaves continuously by wet overflow through the discharge hollow shaft as new feed enters.
The media and the product differ. A rod mill uses steel rods in line contact, takes a coarser feed, and delivers a uniform product of roughly nought point eight to three millimetres with few slimes, normally in open circuit. A ball mill uses steel balls in point contact, grinds much finer, and usually runs in closed circuit with classification. Rod mills run at a lower share of critical speed with a thirty-five to forty percent rod charge, while ball mills run faster with a heavier ball charge. Many plants use both: the rod mill prepares the feed, the ball mill finishes it.
Three designs are recognized. Overflow discharge, the ZKBM configuration, is the most common: product leaves over the rim of a large hollow shaft, and it suits wet primary grinding. End peripheral discharge passes product through ports around the shell at the far end, giving a shorter residence time. Center peripheral discharge feeds at both ends and discharges around the middle of the shell, giving the shortest residence time and the coarsest product, which made it the classic manufactured-sand machine.
Tungsten and tin ores are brittle, and their valuable minerals are recovered by gravity separation, which fails on over-ground slimes. The rod mill breaks coarse particles selectively and lets liberated fines leave quickly, so the valuable mineral stays in the size range where jigs and shaking tables work. That is why these plants grind in stages with rod mills and regrind middlings the same way.
Yes, and it is one of the main duties of the ZKBM series. The mill takes screened crusher product and grinds it into a well-graded sand with few ultra-fines and a favourable particle shape. Because the product band is narrow and even, the downstream washing and classification circuit is easy to balance. Rod mill sand lines are a standard choice where the feed rock is suitable and water is available.
Rods are high-carbon steel, hard enough to break cleanly at the end of their life, never bending or tangling. Make-up rods are added at the largest size on a regular schedule, and worn rods are removed once they approach the bending range. Rod consumption typically runs between a tenth and one kilogram per tonne of ore depending on abrasiveness. Keeping the charge level and rod sizes in balance is the core of rod mill operation, and Ormaise supplies original-specification rods and liners as consumables.
Ormaise supplies grinding rods, liners, gears and bearings matched to the build record of each mill, together with commissioning support, operator training and remote diagnostics. Every ZKBM mill ships with its factory test report, so service and parts questions are answered against the actual data of your unit throughout its working life.
A rod mill looks like a ball mill, but it grinds differently. The cylinder is charged with steel rods running nearly its full length, and as the shell rotates at roughly sixty to seventy percent of critical speed the rods cascade and roll over each other. Contact between rods is along lines, not points. A coarse particle caught in the charge wedges the rods apart and is pinched and broken first, while particles already fine enough slip through the gaps untouched. The rod bed works like a series of roll crushers with a built-in screen effect. The practical results are a steep, narrow size distribution, very little slime, and a product whose coarsest and finest ends are both controlled.
The two mills share a shell, a drive and a lining, but they serve different steps of the circuit:
| Item | Rod Mill | Ball Mill |
|---|---|---|
| Grinding media | Steel rods, line contact | Steel balls, point contact |
| Typical feed | Up to about 20-30 mm, crusher product | Finer feed, often rod mill or SAG product |
| Typical product | About 0.8-3 mm, uniform gradation | Fine to very fine, for flotation and leaching |
| Circuit | Usually open circuit as primary grinding | Usually closed circuit with classification |
| Over-grinding | Low; few slimes, selective on coarse particles | Higher; more fines in the product |
| Classic duties | Gravity-circuit feed, artificial sand, coarse primary grinding | Fine grinding for flotation, regrind |
The classic arrangement is a rod mill ahead of a ball mill: the rod mill converts crusher product into a uniform coarse feed, and the ball mill finishes the liberation work. Rod mills run with a thirty-five to forty percent charge and a cylinder length about one and a half times the diameter; the length keeps the long rods parallel and prevents tangling.
Large new concentrators increasingly favour SAG mills and high pressure grinding rolls, and the rod mill has become a specialist. It remains the right answer in three situations. First, gravity circuits on brittle ores such as tungsten and tin, where over-ground slimes are unrecoverable and selective grinding protects recovery. Second, artificial sand production, where the rod mill turns screened crusher product into a well-graded sand with few ultra-fines and a favourable shape, as an alternative or complement to a vertical shaft impactor. Third, coal-water slurry, quartz sand and similar industrial duties where an even, controlled coarse grind is the product itself. Upstream, the crushing plant built around a jaw crusher and cone crusher prepares the feed that the mill expects.
Overflow discharge is the commonest arrangement and the one used by the ZKBM series: ground product leaves over the rim of a large discharge hollow shaft, the slurry level in the mill stays low, and the product moves out quickly. End peripheral and center peripheral designs shorten the residence time further for coarser products, and center peripheral discharge was the classic manufactured-sand layout. In most duties a rod mill runs in open circuit because its product is already narrow in gradation; classification equipment is added where the next stage or the product specification demands it.
Rod mill operation centres on the charge. Make-up rods are added at the largest size on a regular schedule, worn rods come out before they shrink into the bending range, and the charge level is held steady because both capacity and gradation follow it. Rods are made from high-carbon steel so they break cleanly at the end of life, never bending or tangling in the mill. The ZKBM design supports this routine: conical end caps with a small curvature keep the rod charge in regular motion, the large discharge hollow shaft gives real access for maintenance, and liners and rods are supplied as original-specification consumables matched to each machine.
