News

A pellet die that cracks has usually been through a condition that the die was not designed for, and the crack is the visible end of a chain that started earlier. A material defect or a manufacturing defect can also produce an early crack, and the die record and the supplier documentation separate the service crack from the defect crack. The crack can start at a die hole, at the die edge, or at the die body, and the location and the pattern point to the cause. The die is not simply a wear part that fails at the end of its life: a crack in a die that is still within its wear limit is a sign of an overload, a heat event, or a mechanical problem, and replacing the die without finding the cause produces a second cracked die.

This article is written for plant operators and maintenance teams who have to decide whether a cracked die can be used, how the crack should be inspected, and what to correct before the replacement die is installed. It covers the crack types, the causes, the safe inspection, the decision to replace or to stop, and what to confirm with the die supplier.

Crack Type and What It Points To

The crack location and the crack pattern point to the cause, and the corresponding relation is taken from the crack type table, the die record, and the supplier documentation.

Crack location and pattern	Likely cause	What to check
Radial crack from a die hole toward the die edge	Fatigue from a hole that was blocked, or a hole that was overloaded	The die hole condition, the feed, and the die hours
Crack along the die edge or the die flange	Mechanical overload, or a die that was dropped or hit	The die handling, the installation, and the foreign object record
Crack across the die body, between the holes	Heat crack from a die that ran dry or overheated	The die temperature record, the feeder, and the moisture
Multiple small cracks on the die surface	Heat fatigue from repeated temperature cycling	The startup and shutdown procedure, and the die temperature
Crack at the die hole entrance only	Impact from a foreign object	The die chamber, the magnet, and the material

A radial crack from a hole points to a hole condition or a feed problem. A crack along the edge or the flange points to a mechanical event. A crack across the body points to a heat event. Multiple small surface cracks point to temperature cycling. The crack at the hole entrance points to an impact.

How to Tell a Heat Crack from a Fatigue Crack

The two cracks are both service cracks, and the surface evidence separates them.

Evidence	Heat crack	Fatigue crack
Crack path	Across the die body, between the holes	From a hole toward the edge, following the hole pattern
Surface colour	Discoloured, oxidised, or heat-tinted around the crack	Original die colour, without a heat tint
Crack edge	Rounded or opened by the thermal cycle	Sharp, with a fine origin at the hole
Location	Often at the die surface and the body	Often at a hole that was blocked or overloaded
Die history	A dry run, a feed interruption, or an overheating event	A blocked hole, an excessive feed, or a hole that was run with a worn roller

The heat crack comes with a heat record, and the fatigue crack comes with a hole record. The two are confirmed by the surface inspection and the production record, and the repair decision should be made with the die supplier.

Causes of a Die Crack

Overload from a Blocked Hole or an Excessive Feed

Why it cracks: A die hole that is blocked has no material passing through it, and the local pressure around the hole rises because the material cannot pass. The die material around the hole is loaded beyond its limit, and a radial crack starts at the hole and runs toward the edge. An excessive feed produces the same effect across the die face.

What to check: The die hole condition, the feed rate, the motor current, and the die hours.

What to do: Clear the blocked hole using the die manufacturer procedure, correct the feed and the moisture, and replace the die if the crack has reached the edge or the crack is visible on the working surface.

Heat Crack from a Dry Die or an Overheating Event

Why it cracks: A die that runs dry has no material cushion between the roller and the die, and the friction heat rises. When the die surface temperature exceeds the thermal fatigue limit of the die material, a heat crack develops, and the surface expands and contracts until the crack opens. An overheating event from a blocked die or a cooling failure produces the same effect.

What to check: The die temperature record, the feeder delivery, the moisture, and the cooling.

What to do: Correct the feeder and the moisture, restore the cooling, and replace a die that shows a heat crack across the body or multiple surface cracks.

Mechanical Impact

Why it cracks: A die that is dropped during handling, hit during installation, or struck by a foreign object can crack at the edge or the flange. A foreign object inside the die chamber can also chip the hole entrance, and the chip can develop into a crack.

What to check: The die handling and the installation record, the die chamber contents, the magnet, and the material.

What to do: Replace a die with an edge crack or a flange crack, and inspect the die chamber and the magnet before the replacement is installed.

How to Inspect a Cracked Die Safely

The die should be inspected with the machine stopped and the power isolated.

1. Stop the feed, then the main motor, and lock out the power.
2. Allow the die to cool according to the machine manual before the inspection.
3. Clean the die surface with the method stated in the manual.
4. Inspect the die surface with a light and a magnifier, and record the crack location and the length.
5. Inspect the die hole entrance for a chip, a blockage, or a deformation.
6. Check the roller surface and the clearance at the same time.
7. Record the die hours, the material, the moisture, and the temperature at the time of the crack.

A die with a crack that is visible on the working surface, or a crack that reaches the edge or the flange, should not be returned to service. A die with a small surface mark that is not a crack can be monitored, and the mark should be recorded and compared at the next inspection. Where a crack is suspected but not visible, a dye penetrant inspection or another non-destructive method can be used by a qualified person, and the method should be confirmed with the die supplier.

When to Stop and Replace

Stop the machine and replace the die when any of the following applies.

Condition	Action
Crack visible on the die working surface	Stop. Replace the die.
Crack at the die edge or the flange	Stop. Replace the die, and check the installation and the handling.
Crack across the die body	Stop. Replace the die, and check the heat record.
Multiple surface cracks	Stop. Replace the die, and check the temperature cycling.
Chip or deformation at the die hole entrance	Stop. Replace the die if the hole geometry has changed.
Die crack with a new noise, a vibration, or a temperature rise	Stop immediately, and inspect the rollers and the die chamber.

A cracked die that continues to run can break into pieces, and the pieces damage the rollers, the die chamber, and the drive. The replacement is the safe action, and the cause should be corrected before the new die is installed.

What to Confirm Before Ordering a Replacement Die

The replacement die is specified against the material and the machine.

Item to confirm	What to provide
Material	The type, the moisture, and the ash or silica content
Die specification	The hole diameter, the effective working length, and the compression ratio definition
Die material	The alloy and the heat treatment proposed for the material
Machine and roller	The machine model and the roller configuration
Crack record	The crack location, the length, the die hours, and the condition at the time
Heat record	The die temperature and the feeder condition before the crack

The die material affects the crack sensitivity. A harder die resists the abrasive wear and can be more sensitive to a thermal cycle and an impact, and the alloy and the heat treatment should be selected against the material and the operating condition. The die supplier documentation is the reference for the alloy, the hardness, and the recommended application.

A die life figure should state the material, the moisture, the compression ratio, and the operating conditions it assumes. Where the figure does not state those conditions, it is a reference rather than a commitment, and the actual die record is the basis for the next selection.

Verifying the Replacement Die

The replacement die should be verified after installation, and the verification should be recorded as the new baseline.

Check	What to record	Why it matters
Initial output	The output at the stated feed rate and material	Establishes the baseline for the wear trend
Initial motor current	The current at the initial output	Establishes the baseline for the load trend
Initial pellet quality	The density, durability, and fines	Confirms the die produces the expected pellet
Die installation date and die hours	The date and the starting hours	Starts the service life record for the new die
Material and moisture at installation	The material and the moisture	Records the conditions the baseline applies to

A replacement die that shows a lower output, a higher current, or a lower pellet quality than the previous die at the same conditions should be inspected before production continues.

Frequently Asked Questions

Can I keep running a die with a small crack?

A crack that is visible on the working surface or reaches the edge is a die that should be replaced, and the machine should not run with it. A small surface mark that is not a crack can be monitored, with the mark recorded and compared at the next inspection.

What should I confirm with the die supplier after a crack?

The crack location, the length, the die hours, the material, the moisture, and the temperature record should be sent to the supplier, together with the die specification and the roller configuration. The supplier can use the record to review the die selection and the operating condition.

Can a cracked die be repaired?

A die with a crack on the working surface, at the edge, or across the body is not repaired, and it is replaced. A small surface mark that is not a crack can be monitored, and the mark should be recorded and compared at the next inspection. The repair decision should come from the die supplier, not from the site.

Why did the die crack before the end of its expected life?

A crack before the expected life points to an overload, a heat event, a mechanical impact, or a material or manufacturing defect. The die hole condition, the temperature record, the handling record, the material contamination, and the supplier documentation separate the cases, and the cause should be corrected before the new die is installed.

How is the die inspected for cracks?

The die is inspected with the machine stopped and the power isolated, after the die has cooled. The surface is cleaned and inspected with a light and a magnifier, and the hole entrance, the roller, and the clearance are checked at the same time. Where a crack is suspected but not visible, a non-destructive method can be used by a qualified person.

Request Die and Roller Support

Send the material type and moisture, the die specification, the die hours, the crack location and length, the temperature record, the roller condition, and the machine model. A die and roller review can then be prepared against the material and the machine rather than against a general catalogue.

---

Die crack inspection, replacement criteria, die life, and acceptance criteria in this article must be confirmed against the die supplier documentation, the machine manual, and the production record for the same material. This article does not provide universal values for these items.