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A pellet mill that forms nothing on the first batch is one of the most common complaints in the first days of a new machine or a new die, and it is rarely a defective mill. The first batch is the hardest batch the machine will ever run, because the die is cold and unpolished, the roller gap has not been bedded in, the moisture has not been tuned to the new die, and the operator has not yet learned how the machine behaves. A mill that forms nothing on the first batch often forms well after the die is broken in and the settings are corrected, and the operator who changes the die or the machine before the break-in is finished usually makes the problem worse.

This page is about a first batch that forms nothing at all. The page on the low formation rate is about a batch that forms pellets at a low proportion, and the two are diagnosed differently. It is written for the operator and the commissioning engineer who are starting a new machine or a new die.

The short answer

A first batch that does not form comes from one of five causes: the die is not run in, the moisture at the die is outside the workable range for the new die, the roller gap is not set correctly, the feedstock is not prepared to the specification the die was selected for, or the die temperature has not reached the operating range.

The practical rule: run the die in with a prepared material before the production material, set the roller gap on every roller, hold the moisture at the die, and bring the die temperature into the range before the output is judged. A first batch that does not form is a normal break-in symptom if the die is new, and it is a fault if the die has been run in and the five checks below have been run and the batch still does not form.

Why a new die does not form on the first batch

A new die is not the same as a run-in die, and the difference is in the hole surface and in the compression.

A new die has hole surfaces that are rougher and entry edges that are less polished than a run-in die, and the material does not slide through them as easily. The result is a higher resistance, a lower throughput, and a pellet that does not form until the die is polished by the material passing through it.

The die temperature also takes time to reach the operating range, because the die body has to heat up through the friction of the material, and a cold die does not soften the lignin enough to bind the pellet. A new die that is fed production material at full rate before it is warm produces dust and unformed material, and the operator often reads this as a machine fault.

The first batch is therefore the batch on which the die is broken in, and it should be run with a prepared loading material rather than with the production material.

Nothing forming versus a low formation rate

When nothing forms at all, the material is not reaching the die, or it is reaching the die without being pressed, and the feeder, the roller gap, and the die blockage are checked first. When the formation rate is low, the material is reaching the die but not binding well, and the moisture, the temperature, and the compression ratio are checked first. The two symptoms look similar at the discharge, but they point to different causes, and the diagnosis should start from the symptom rather than from the die.

Causes of a first batch that does not form

The die is not run in. The most common cause is a die that has not been broken in. The die should be loaded with a prepared material before the production material, at a low feed rate, until the die is warm and the pellets form steadily. Feeding production material at full rate into a cold, new die is the most common reason a new die blinds in the first hours.

The moisture at the die is outside the range. A new die has a different workable moisture range from a run-in die, and the moisture that worked on the old die may be wrong for the new one. A moisture that is too high makes the material slip and the pellet soft, and a moisture that is too low makes the pellet brittle and dusty. The moisture should be measured at the die inlet, not at the dryer outlet, and the target should be established in the break-in rather than taken from the old die’s setting.

The roller gap is not set correctly. A roller gap that is too wide leaves the material unpressed and the pellet does not form, and a gap that is too tight overloads the motor and blinds the die. The gap should be set on every roller to the manufacturer’s specification for the new die, and it should be checked again after the first hours of running, because the new parts settle under the initial load.

The feedstock is not prepared to the specification. A new die is selected for a specific feedstock, moisture, and particle size, and a feedstock that is coarser, wetter, or more abrasive than the specification does not form on the first batch. The particle size should be matched to the die hole diameter, and the contamination should be removed before the die.

The die temperature has not reached the range. A new die takes longer to reach the operating temperature than a run-in die, and a die that is below the range does not form a durable pellet. The die temperature should be monitored, and the feed rate should be adjusted to bring the temperature into the range before the output is judged.

How to tell a break-in problem from a real fault

The break-in problem improves as the die is polished and the settings are corrected, and a real fault does not improve with time.

The formation should climb within the first hours of running, and a formation that rises from nothing to a steady pellet is the normal pattern. A die that still forms nothing after several hours of proper loading is a fault rather than a break-in symptom, and the feeder, the roller gap, the die, and the drive should be checked in that order, because the feeder and the roller gap are the most common causes and the die and the drive are the less common.

What to check before changing any part

The five checks below are the minimum, and the fault is confirmed when they have been run and the batch still does not form. The checks should be recorded, so that the next shift can see what was done.

The die has been run in, not just started. The loading material has been used at a low feed rate until the die is warm, and the production material has been introduced only after that.

The moisture at the die has been measured and set, and the target has been established in the break-in rather than taken from the old die.

The roller gap has been set on every roller to the manufacturer’s specification, and it has been re-checked after the first hours of running.

The feedstock has been matched to the die specification, including the particle size, the moisture, and the contamination.

The die temperature has reached the operating range, and the feed rate has been adjusted to bring it into the range rather than to force the output.

How to correct a first batch that does not form

Run the die in properly. Load the die with a prepared material at a low feed rate, bring the die up to temperature, and only then change to the production material and bring the feed up in steps. The loading material is normally a dry material of the same family as the production material, prepared so that it slides through the die holes, and the loading continues until the die is producing pellets steadily at the operating temperature and the current has stabilized.

Set the moisture at the die. Measure the moisture at the die inlet and adjust it in the conditioning stage rather than in the hopper, and record the target as the baseline for the new die.

Set the roller gap on every roller. Set the gap to the manufacturer’s specification, check it on every roller rather than one, and re-check it after the first hours of running.

Match the feedstock to the die specification. Confirm the particle size, the moisture, and the contamination against the specification the die was selected for, grind the material if it is too coarse, and remove the stones and the metal before the die.

Bring the die temperature into the range. Adjust the feed rate to bring the die temperature into the operating range before the output is judged, and monitor the temperature against the record from the break-in.

What to specify before buying a line

Before the line is specified, the break-in procedure should be addressed in the commissioning plan and in the quotation. The quotation should state the die specification matched to the feedstock, the roller gap setting, the loading material recommendation, and the acceptance test on the actual material. A line that is specified without the break-in procedure is a line that can fail on the first batch and be judged on that batch rather than on the steady state.

If you are commissioning a new pellet mill and the first batch does not form, send the die specification, the feedstock, the moisture at the die, the roller gap setting, the loading procedure, and the first-batch record, and the Shandong Changsheng Machinery team can review the break-in and the settings and propose the correction and the acceptance test.

Bottom line

A first batch that does not form is usually a break-in problem, not a defective machine, and the diagnosis depends on whether nothing forms at all or the formation rate is merely low. The die has to be run in with a prepared material, the moisture at the die has to be set for the new die, the roller gap has to be set on every roller, the feedstock has to be matched to the die specification, and the die temperature has to reach the operating range before the output is judged. A formation that climbs from nothing to a steady pellet within the first hours is the normal break-in pattern, and a die that still forms nothing after several hours of proper loading is a real fault, with the feeder, the roller gap, the die, and the drive checked in that order. Confirm the five checks before changing any part, record them so that the next shift can see what was done, keep the first-batch record so that the break-in can be compared with the steady state, and specify the break-in procedure and the acceptance test in the quotation so that a new line is judged on the material and the settings rather than on the first batch.