Crusher lubrication schedule and grease selection

Why a crusher lubrication schedule and grease selection deserve their own sheet

A crusher lubrication schedule and grease selection sit one level above the shift walk-around. The walk-around asks whether a point was served. The schedule states which product goes in, in what dose, at what spacing and inside which temperature window. In crushing plants a large share of bearing losses does not come from a missed point at all, but from the wrong product or the wrong volume reaching the right point. The document therefore reduces to three questions: what, how much, how often.

Grease is a package, not a single property

Although it carries one trade name, a grease is three components working together: the thickener that gives it body, the base oil that actually carries the load, and the additives chosen for the duty. Getting two of the three right does not rescue the third.

Consistency grade

Consistency is described on the NLGI scale. Grade 2 is the default across most general bearing work: it pumps through manual guns and centralised systems alike, and it stays in the housing well enough to act as a barrier against dust. Softer grades flow more readily at low temperature and higher speed; stiffer grades hold position better on slow, heavily loaded or vertical arrangements.

Thickener and dropping point

The dropping point is the temperature at which a grease loses its structure and begins to flow. It is a quality marker rather than a continuous service ceiling, and equipment always runs well below it. Lithium complex thickeners deliver a high dropping point and are widely used in crushing duty. Where water ingress dominates, as on washing lines, calcium sulfonate complex products come to the front. Mixing thickener families can collapse consistency, so a product change means emptying and cleaning the housing instead of topping up over the old charge.

Additives

Crusher bearings work under shock loading. Extreme pressure additives build a sacrificial film on the metal surface and keep asperities apart when the oil film thins. EP products are therefore the normal case in this service, not an upgrade.

Setting interval and dose

The interval comes from the bearing, not the calendar. The governing figure is the speed factor: shaft speed multiplied by the bearing mean diameter, that mean diameter being half the sum of bore and outside diameter. As the product rises, grease heats more readily, fill volumes come down and intervals shorten. Most crusher and feeder housings sit inside the band where grease lubrication is comfortably sufficient; faster arrangements call for softer consistency and smaller doses.

Dose is expressed as a share of the free space in the housing. Standard horizontal arrangements are filled to roughly a third or a half of that space, moving toward the lower end as speed climbs. The logic of the limit is plain: enough free volume must remain that the rolling elements are not permanently kneading surplus grease.

Over-greasing costs as much as starvation

Continuing to pump into a full housing produces three separate failures. The first is churning heat: rolling elements plough surplus grease, internal friction climbs and temperature climbs with it. The second is the ageing that heat accelerates, as base oil bleeds out early and the thickener hardens into deposits that block the very paths fresh grease must travel. The third is seal damage, because once the charge has nowhere to go the pressure a grease gun develops can push a seal out of its seat, and from that moment the housing stands open to dust. Reaching for the gun whenever a bearing runs warm therefore usually enlarges the problem it was meant to solve.

Proving the schedule with records

An unwritten schedule is not a schedule. One sheet per machine carries product name, dose, interval and last application for every point, together with a note whenever a product change required the housing to be emptied. On centralised systems, pump outlet pressure and blocked-line alarms belong on the same sheet. Plants that work this way find spare parts consumption becomes predictable, and predictability is the only thing that makes stock and downtime planning possible. The wider subject is collected under maintenance and wear.

Frequent questions

Can two brands be mixed?

The thickener family decides, not the label. Products built on the same thickener usually cross over without incident; different families can collapse the consistency of the mixture. When in doubt, purge and clean.

A bearing runs warm. Add grease?

Check fill level and seal condition first. Warmth points more often to too much grease, or to a failed seal, than to too little.

Do summer and winter need different products?

Where ambient temperature swings widely, review base oil viscosity and consistency grade seasonally, and take the decision against the temperature window printed in the machine manual.