Ejector Sleeves for Die Casting Dies — SKD61 (H13), Nitrided to HV900
An ejector sleeve in a die casting die does the same mechanical job as in a plastic mold — it pushes the casting off a core pin — but it fails for completely different reasons. Aluminum at 650–700 °C, a thermal cycle every shot, and molten metal that wants to solder to steel will destroy a sleeve that was specified for injection molding. This page covers what changes, which steel to use, and how to set clearance so the sleeve survives. GUNRI produces these sleeves in SKD61 with a nitrided case above HV900, up to 1,000 mm long.
First, a naming check: ejector sleeve is not shot sleeve
These two parts are frequently confused in die casting enquiries, and ordering the wrong one is an expensive mistake. Our standard ejector sleeves are the ejection parts covered on this page.
| Ejector sleeve | Shot sleeve | |
| Where it sits | Ejector half, around a core pin | Behind the plunger tip, at the shot end |
| What it does | Pushes the casting off the core | Contains the molten metal charge before injection |
| What flows through it | Nothing — the pin slides inside | Liquid aluminum at 650–700 °C, at pressure |
| Typical material | SKD61 nitrided, SKH51 | H13 / SKD61 with a hardened bore, often bimetal |
| Size | Millimeters to tens of millimeters | Tens to hundreds of millimeters |
If you are looking for the part the molten metal is poured into, you want a shot sleeve, not an ejector sleeve. This page covers the ejection part only.
What makes die casting harder on a sleeve
Four loads act on the sleeve in a die casting die that do not exist, or are far milder, in an injection mold.
1. Melt temperature and heat soak.
Aluminum is poured at roughly 650–700 °C; zinc around 380–420 °C; magnesium around 620–680 °C. Even though the sleeve is not in the melt path, the die block around it heat-soaks to several hundred degrees and the sleeve runs far above the 200–300 °C of a plastic mold. Nitriding is what carries the surface at those temperatures — core hardness alone does not.
2. Thermal cycling, every single shot.
The sleeve heats and cools with each cycle while the pin inside it responds at a different rate and to a different temperature. The running clearance therefore changes during the cycle. A sleeve bored to give 0.015 mm clearance cold can be tighter — or looser — at operating temperature, and both directions cause problems: too tight and it galls, too loose and flash migrates into the gap.
3. Molten metal adhesion (soldering).
Aluminum and zinc wet steel. Once a film of aluminum sticks to the bore or the outside diameter, it acts as an abrasive and the wear rate climbs sharply. A ground and polished bore with a nitrided case is the standard defense; a rough bore is an invitation.
4. Wash and erosion at the gate side.
If the sleeve sits near the gate or in the path of the melt front, it sees erosion that a plastic mold never produces. Geometry and position matter as much as the steel grade here.
Material: SKD61 is the default, and why
SKD61 is the JIS designation for the 5% chromium hot-work tool steel family; AISI H13 is the same family under a different standard. It is the default for die casting ejection parts for three reasons:
- Hot hardness. It retains hardness at die casting temperatures, where a cold-work steel starts to soften.
- Thermal fatigue resistance. Repeated heating and cooling is what cracks ejection tooling in die casting. H13/SKD61 is designed around that cycle.
- A tough core under a hard case. We specify 38–42 HRC through the core with a nitrided surface above HV900. The softer core absorbs impact and the hard case resists wear and adhesion — the combination that survives a die casting die.
What we do not recommend for die casting: SKH51 at 59–61 HRC. It is harder and it is excellent in abrasive-filled plastic molds, but its tolerance of thermal shock and impact is lower, and thermal cracking — not abrasive wear — is usually what kills a die casting sleeve.
How to set the clearance
There is no single catalog clearance number that is correct for die casting, because the answer depends on your die temperature, your alloy and the pin tolerance. What can be stated is the method:
- Start from the pin’s measured diameter at room temperature, not its nominal size.
- Calculate the sleeve ID at operating temperature using the expansion of both parts — the sleeve runs hotter than the pin in most dies.
- Leave a positive running clearance at temperature, small enough that flash cannot enter the gap.
- Check the cold clearance is still enough to assemble without pressing the sleeve onto the pin.
- Re-check after the first production run — measured wear in the first thousand shots tells you more than any calculation.
Send us the alloy, the die temperature and the pin diameter and we will propose an ID band with the reasoning shown, so you can check it against your own die trials.
Failure modes and what each one tells you
| What you see | Most likely cause | What to change |
| Bore galls, pin seizes | Clearance too tight at temperature, or bore finish too rough | Open the ID band, polish the bore, confirm nitriding |
| Aluminum film builds up on the OD | Adhesion — surface not nitrided or case worn through | Restore nitriding, polish, check case depth |
| Sleeve cracks along its length | Thermal fatigue, or brittle case on a soft substrate | Verify core hardness 38–42 HRC, review case depth |
| Flash ring on the casting | Clearance opened up by wear, or ID oversized from the start | Measure wear trend, tighten ID band |
| Head sheared off | Ejection load too high for the wall thickness, or misalignment in the ejector plate | Increase wall, check shoulder form and plate fit |
| Pin bends inside the sleeve | Sleeve not supporting the pin over full stroke | Lengthen the sleeve to cover the stroke |
Detailed failure analysis with fixes
Specifications
| Parameter | SKD61 (standard for die casting) | SKH51 (on request) |
| Material standard | JIS SKD61 / AISI H13 equivalent | JIS SKH51 / AISI M2 equivalent |
| Core hardness | 38–42 HRC | 59–61 HRC |
| Surface | Nitrided, HV900 and above | Through-hardened |
| Max length | 1,000 mm | 300 mm |
| Coaxiality | 0.06 mm | 0.01 mm |
| Achievable precision | 0.01 mm | 0.005 mm |
| Bore | Ground and polished | Ground |
| Customization | ID, OD, length, shoulder and head form to drawing | Same |
Sizes and coatings beyond this table are quoted per drawing — contact us with your diameter range and we will confirm what is available.
Ordering: what to send
The fastest route to a correct sleeve is four numbers and two facts:
- Pin diameter (measured)
- Boss / core diameter
- Ejection stroke
- Overall length available in the ejector plate
- Alloy being cast (Al / Zn / Mg)
- Die temperature in production
With those, we return an ID/OD/length proposal, the shoulder form, and the grade recommendation.
Manufacture and quality
GUNRI (Dongguan Gunri Precision Hardware Co., Ltd.) has manufactured precision die and mold components since 2006 from a 10,000 m² base, certified to ISO 9001:2015 and IATF 16949:2016, exporting to more than 30 countries and producing OEM parts for foreign brands. Sleeves are hardened, ground, nitrided and then the bore is finished; coaxiality is inspected on the finished part.
FAQ
Can a standard injection mold ejector sleeve be used in a die casting die?
Mechanically it fits, but it usually fails early. Die casting adds melt temperatures around 650–700 °C for aluminum, thermal cycling every shot, and molten metal adhesion. A sleeve specified for injection molding has the wrong surface treatment and clearance for that environment.
Why SKD61 instead of SKH51 for die casting?
SKD61 is a 5% chromium hot-work steel, equivalent to AISI H13. It keeps a tough core at 38–42 HRC while the nitrided case above HV900 resists wash and adhesion. SKH51 at 59–61 HRC is harder but less tolerant of thermal shock and impact, which is the dominant failure mode in a die casting die.
What clearance should I run between sleeve and ejector pin?
It depends on the die temperature and the pin tolerance, not on a single catalog number. The sleeve ID must be sized so that at operating temperature the running clearance stays positive without allowing flash into the gap. Tell us your die temperature and alloy and we will quote the ID band.
Do you make sleeves to AISI H13 or only JIS SKD61?
SKD61 is the JIS designation of the same 5% Cr hot-work family as AISI H13. We produce to SKD61 as standard and can work to an H13 drawing or a customer material specification on request.
How do you reduce aluminum sticking to the sleeve?
Surface finish and the nitrided case do most of the work: a polished bore and an HV900 case reduce adhesion and wear. Correct clearance and adequate draft on the ejected boss matter as much as the steel.
What sizes and lengths can you produce?
SKD61 sleeves: precision to 0.01 mm, coaxiality 0.06 mm, length up to 1,000 mm. SKH51 sleeves: precision to 0.005 mm, coaxiality 0.01 mm, length 300 mm. Custom ID, OD and shoulder geometry are made to drawing.
Send pin diameter, alloy and die temperature
You get a sleeve specification with the clearance reasoning shown — not just a part number.