polysius® Ball MillThe proven classical option for cement grinding.

Highest availability rates and the lowest maintenance requirement in grinding: that is what mills used for finish grinding and homogenization of brittle raw materials must deliver. Proven robustness and stable operation over decades are only achieved if what is inside the mill is right. This page is about the three things that decide that: the diapol 2.0 lifting diaphragm, polalloy slotted and backwall plates, and the mobile polgrind® slide ring grinding service.

Plate material utilisation: 84 % with polalloy, versus 60 % with conventional systems
polalloy hardness: 58 HRC, completely through-hardened
Wear comparison: polalloy plate at 14,100 operating hours; cast plate compared at 7,450 operating hours
diapol 2.0 types: Four: JND, DCD, CDD, DRD
polgrind® availability: Worldwide mobile machining service

The proven classical option for cement grinding. Whether employed as a two-compartment separator mill in an independent grinding system, or in combination with a high pressure grinding roll, the Ball Mill is a robust and reliable alternative for cement and granulated blast furnace slag grinding.

Used in combination with the sepol® high-efficiency separator, ball mills can reliably grind high-grade and very fine cements. Ball Mills achieve the highest availability rates and have the lowest maintenance requirement.

Why the ball mill still wins on availability

Highest availability rates among grinding systems
The lowest maintenance requirement — provided the internals are specified for the material
Proven for cement and granulated blast furnace slag grinding
Reliably reaches high-grade and very fine cements in combination with the sepol® separator
Works standalone or downstream of a polycom® high pressure grinding roll
Wear parts and internals serviceable — diaphragm segments and plate rings replaced individually, not as a whole

Configurations

	Two-compartment separator mill	In combination with a polycom®
Principle	Independent grinding system: coarse grinding in compartment 1, fine grinding in compartment 2, separated by the lifting diaphragm, with the sepol® closing the circuit	The high pressure grinding roll takes the coarse comminution upstream; the Ball Mill finishes the product
Diaphragm type	Intermediate diaphragm (JND) between the compartments; discharge diaphragm (DCD) at the mill outlet	Central discharge diaphragm (CDD) for double rotators; pre-drying compartment diaphragm (DRD) where the feed requires it
Typical benefit	The classical, self-contained cement grinding solution; full effective grinding length used	Higher throughput at the same mill size; same wear-part and service concept applies

Mill Internals – “Tuning for your ball mill”

The further improved diapol 2.0 lifting diaphragm, with types intermediate diaphragm (JND), discharge diaphragm (DCD), central discharge diaphragm (CDD) for double rotators and pre-drying compartment diaphragm (DRD), is the universal solution for your grinding. The air stream and the mill feed material are now separated from each other more effectively. The mill feed material falls directly behind the diaphragm, preventing onward pneumatic conveyance, meaning that the entire effective grinding length is used for grinding.

Installation and segmental construction

The diapol 2.0 is first and foremost easy to install. Workshop-fabricated segments can be joined on site with the need for only minimal welding. The special segmental construction, which allows the segments to slide up against each other, prevents the formation of stress cracks during operation. In addition, as installation is so easy, the time savings are significant, which means that the slightly higher capital costs quickly break even. Due to the simple segmental construction, wear parts such as lifter scoops and their correspondent heads can be replaced quickly and effectively.

Plate material and fastening

Fully hardened rolled-steel plates (polalloy) are used as the wear material for the slotted and backwall plates, or high-chromium cast iron if the application so requires. When using fully hardened rolled-steel plates, the geometry of the slots and the free area can be selected as required for the application. The slotted and backwall plates are fastened using shear bolts and expansion sleeves; as these plates are easily accessible and because they are fastened with expansion sleeves, it is very easy to replace them — the expansion sleeves are simply removed by flame cutting without damaging the framework.

Central opening and material flow

The greatest possible central opening ensures low air velocity and a low pressure drop. Access to compartment 2 from compartment 1 is also facilitated on opening the grate. The size of the opening is determined by the maximum grinding-media filling ratio. The mill feed material flow can be regulated by adjustable lifter scoops, which makes it possible to control the filling level in the grinding compartment.

SERVICE ADVANTAGES — DIAPOL 2.0

Easy to install due to workshop-fabricated segments
Flexible segmental construction to prevent stress cracks
Controlled material flow thanks to fixed and adjustable lifter scoops
Slot geometry can be freely designed
High operational reliability

The four diaphragm types

JND — intermediate diaphragm	Between compartment 1 and compartment 2 of the two-compartment mill
DCD — discharge diaphragm	At the discharge end of the mill
CDD — central discharge diaphragm	For double rotators
DRD — pre-drying compartment diaphragm	Where the feed material requires pre-drying

Wear Material – polalloy, “Extremely resistant to breakage and wear”

polalloy is an extremely wear-resistant material used for manufacturing slotted plates and backwall plates. Plates made of this material have significant advantages compared to products made of cast metals and rolled steel, because polalloy offers a high level of hardness and excellent toughness — this minimises the risk of breakage.

During the patented manufacturing process, the through-hardened plate material is heated only slightly in its initial state, so its structure remains unaffected. In contrast to surface-hardened plates, wear thus remains almost constant even after the first millimetres. Moreover, when wear has been detected, it is necessary to replace only the most affected plate rings. polalloy has a hardness of 58 HRC and also offers excellent toughness, so the risk of plate breakage can be minimised.

polalloy plates are supplied in thicknesses of 50 mm and can be efficiently used down to a remaining thickness of 8–10 mm. As opposed to conventional systems that are worn out once 60 % of the plate material has been lost, polalloy plates can be used until 84 % of the plate material has been lost.

Our experts adjust the slot geometry of slotted polalloy plates to the specific operating conditions. In this way, we ensure process-related optimisation. Clogging no longer occurs with these plates, hence little or no cleaning is necessary.

	Conventional systems	polalloy plates
Material utilisation	Worn out at 60 % material loss	Usable until 84 % material loss
Supplied thickness	—	50 mm, efficiently used down to 8–10 mm remaining
Hardening	Surface-hardened	Completely through-hardened; structure unaffected by the patented process
Wear behaviour	Changes after the first millimetres	Remains almost constant even after the first millimetres
Documented example	Cast plate after 7,450 operating hours	polalloy plate after 14,100 operating hours

Service Advantages – pollalloy

Completely through-hardened plate material increases wear resistance
Process-related optimisations due to a specific slot geometry contribute to an overall optimisation of the processes
Efficient use of the plates down to a remaining thickness of 8–10 mm
Verifiable characteristic values of the material
No slot deformation caused by grinding media
Maximum resistance to breakage thanks to excellent toughness

Service – polgrind®, “To true up slide rings”

Slide rings for shell-supported ball mills are exposed to extreme forces on an ongoing basis. Due to irregularities in mill operation, the surfaces of these components are damaged over the course of time. This leads to unevenness and damage to the machines. Our mobile polgrind® machining service ensures that the surfaces are returned to a pristine condition — this means that your mill can once again run smoothly.

The centrepiece of our service is the systematic grinding process: slide rings are carefully machined using grinding belts with different grit sizes. This allows us to eliminate all unevenness, damage and roughness, and the surfaces are returned to a first-class condition.

To ensure optimum quality, the roundness of the slide rings is measured, documented and evaluated before and after grinding. The slide ring lift values and the oil temperature are also documented. To avoid any unnecessary downtime when performing the grinding work, it is recommended to carry out a preliminary inspection before the work is carried out.

polgrind® is available to customers worldwide; universal electrical devices ensure compatibility around the globe.

1 — Preliminary inspection: Recommended before the work is carried out, to avoid any unnecessary downtime during the grinding work
2 — Measure and document: Roundness measured, documented and evaluated before grinding; slide ring lift values and oil temperature also documented
3 — Systematic grinding: Slide rings carefully machined using grinding belts with different grit sizes, eliminating all unevenness, damage and roughness
4 — Verify: Roundness measured, documented and evaluated again after grinding; surfaces returned to a first-class condition

Service Advantages – polgrind®

Effective elimination of defects and surface damage to slide rings
Documentation of the process by an electronic roundness measuring device
Can be used worldwide
Significantly increases the service life of slide rings and ball mill bearings

Upgrade & Modernization

Every one of these is an intervention inside an existing ball mill.

Upgrade	Effect	Condition
Replace the diaphragm with diapol 2.0	Air stream and mill feed material separated more effectively, so the entire effective grinding length is used for grinding; segmental construction prevents stress cracks	Workshop-fabricated segments, joined on site with minimal welding
Switch the plates to polalloy	Through-hardened material at 58 HRC used down to 8–10 mm remaining — 84 % of the plate material instead of 60 %	Supplied at 50 mm thickness; high-chromium cast iron available where the application requires it
Adjust the slot geometry	Process-related optimisation; clogging no longer occurs, so little or no cleaning is necessary	Adjusted to the specific operating conditions of your mill
Fit adjustable lifter scoops	Mill feed material flow regulated, filling level in the grinding compartment controllable	Lifter scoops and their heads are replaceable wear parts
True up the slide rings	Eliminates unevenness, damage and roughness; significantly increases the service life of slide rings and ball mill bearings	Shell-supported ball mills, available worldwide
Replace only what is worn	Only the most affected plate rings need replacing; expansion sleeves removed by flame cutting without damaging the framework	Plates fastened with shear bolts and expansion sleeves

Ball Mills achieve the highest availability rates and have the lowest maintenance requirement

The proven classical option

for cement grinding.