Sialon Ceramics in Low-Pressure Diecasting: A Technical Guide for Foundry Engineers

Why sialon ceramics outlast aluminium titanate by 12x in LPDC riser tubes and temperature sensor protection tubes — with ROI analysis showing payback within 2–4 weeks.

July 27, 2026 · 12 min read

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TL;DR

In low-pressure diecasting, picking the right material for riser tubes and heat sensor protection tubes directly drives cycle cost and cast-part quality. Sialon ceramics — silicon aluminium oxynitride — outlast aluminium titanate (Al₂TiO₅), the most common budget pick, by 12x in service life, while standing up to chemical attack from molten aluminium for 12+ months under warranty. Aluminium titanate tubes are cheap to buy ($60–120 each) but fail through chemical breakdown and tiny holes within 3–6 months, pushing total yearly replacement costs far above sialon’s higher per-unit price. Compared with silicon nitride and coated steel too, sialon pairs strength, a non-stick surface, and true-to-size stability in one material, cutting how often you replace parts and how much downtime you face. For foundry teams, the switch from aluminium titanate to sialon ULTRA™ products pays for itself within 2–4 weeks through fewer replacements and better casting quality.

What is low-pressure diecasting and why material selection matters

Low-pressure diecasting (LPDC) is a metal-casting process used to make aluminium, magnesium, and brass parts with high accuracy and a smooth surface finish. During the process, molten metal (usually 650–1,100°C) is pushed through a riser tube into a mold under low pressure (typically 0.5–0.7 MPa). The metal then cools and hardens inside the closed mold before the finished part is removed.

LPDC is widely used to produce high-quality metal parts for the aerospace, automotive, and medical industries. A single LPDC machine can complete 30–80 casting cycles every hour. During each cycle, the mold and metal delivery system heat up to operating temperature and then cool quickly before the next part is removed. As a result, ceramic parts are exposed to hundreds of thousands of heating and cooling cycles every year.

Why material choice is critical

Cycle rate and heat stress – Most standard diecasting materials are designed for normal or moderate temperatures. However, riser tubes must withstand direct contact with molten metal at temperatures above 1,100°C while also cooling rapidly after every casting cycle. If the material cracks because of heat stress, production stops until the tube is replaced. As a result, a single unplanned replacement can cost $2,000–5,000 in lost production during a 24-hour operation.

Metal contamination and casting defects – heat sensor protection tubes remain submerged in molten aluminium to measure temperature and control the casting process. However, if the tube corrodes or molten metal sticks to its surface, contaminants enter the melt and create defects in finished parts. Consequently, a single faulty part may need to be scrapped or repaired, costing anywhere from $500 to more than $5,000 for aerospace components. Therefore, ceramic protection tubes should last at least 12 months to maintain product quality and reduce waste.

Dimensional stability and casting accuracy – Riser tube size directly affects metal flow, cooling speed, and pressure during mold filling. However, as the tube wears or corrodes, its inner diameter changes. As a result, metal flow changes, making it harder to keep part dimensions within specification. Therefore, operators must measure the tube regularly and adjust the process. In contrast, a material that keeps its ±0.02 mm tolerance throughout its service life removes the need for these adjustments and helps produce consistent parts.

Cost per casting – The purchase price of a component is important. However, downtime has a much greater effect on total production cost. For example, an LPDC line producing 100 parts per hour can make around 2,400 parts each day. Therefore, a riser tube failure that stops production for 2–4 hours can result in 200–400 lost parts. At the same time, if each part is worth $50–200, the lost revenue reaches $10,000–80,000 from a single incident. Ultimately, choosing a material that increases the mean time between failures (MTBF) by 30% reduces downtime, improves production efficiency, and lowers the cost of every casting.

Sialon material properties: why it’s engineered for LPDC

What is sialon? Sialon is silicon aluminium oxynitride (Si₆Al₂O₂N₈), a ceramic compound engineered to combine the thermal shock resistance of silicon nitride with the chemical inertness and toughness of aluminium oxide. The crystal structure bonds silicon, aluminium, oxygen, and nitrogen atoms in a lattice that resists both thermal cycling and chemical attack.

Thermal shock resistance – Thermal shock occurs when a material experiences a rapid temperature change and the outer surface contracts or expands faster than the interior, creating internal stress. The risk of cracking increases with:

• Temperature range (ΔT): LPDC cycles from 1,100°C to room temperature, a 1,000°C+ swing per cycle
• Thermal conductivity: high conductivity (fast heat transfer) creates steep internal gradients
• Thermal expansion rate: materials with high expansion rate crack under thermal cycling

Sialon is engineered with a low thermal expansion rate (5.0–5.2 × 10⁻⁶ /K). Aluminium titanate actually has an even lower expansion (0.5–1.5 × 10⁻⁶ /K), which sounds like an advantage-until you account for its very low flexural strength (20–30 MPa, versus sialon’s ~700 MPa). That brittleness means aluminium titanate fractures under mechanical pressure and vibration even when it handles the thermal cycling. The result: sialon survives thousands of thermal cycles and pressure pulses without visible microcracking, while aluminium titanate fails through mechanical fracture, porosity-driven metal infiltration, and chemical attack within 3–6 months.

Non-wettability by molten aluminium – Wettability is a materials science term for whether a liquid sticks to a solid surface. Molten aluminium “wets” steel and some ceramics, meaning it bonds to their surface and sinks into small surface flaws. When the metal cools, it pulls away and tears at the material’s surface, leaving behind bits of metal.

Sialon’s silicon-nitride bond repels water and won’t react with molten aluminium. The metal doesn’t stick to the surface — it beads up and rolls across the ceramic like water on waxed glass. This non-stick trait stops surface build-up, contamination, and bonding, so sialon surfaces come out of molten metal contact clean and true to size.

Staying inert in molten metal – Most ceramics hold up fine in air but break down when exposed to molten metals. Aluminium titanate (Al₂TiO₅) is especially prone to this: at foundry heat, molten aluminium attacks the titanium oxide part of its structure, weakening the grain edges and opening up more tiny holes. Once full of holes, the tube wall lets metal seep in, causing fast shape change and faster breakdown from the inside out. The usual result: a tube that looks fine on the outside has already failed on the inside.

Sialon’s silicon-nitride structure resists attack from molten metal, backed by a 12-month warranty against chemical breakdown. Field data from facilities shows sialon parts keeping their surface and strength after 36–72 months (3–6 years) of nonstop molten-metal contact — 12x the service life of aluminium titanate parts, which show clear wear within 3–5 months.

Staying true to size – Heat cycling and chemical exposure both cause shape drift. Heat cycling causes lasting changes in the material’s structure (tiny cracks, widening at the grain edges). Chemical exposure wears away surface material, thinning the wall and widening the bore.

Sialon ULTRA™ heat sensor protection tubes are made to ±0.02 mm precision and hold that precision for their whole service life. This matters a lot for heat sensor tubes, where bore width drift loosens the fit on the heat sensor lead, throwing off heat transfer and temperature-reading accuracy.

Riser tubes: geometry, function, and sialon’s advantage

A riser tube is a ceramic pipe that conducts molten metal from the holding furnace into the mold cavity under controlled pressure. It’s one of the most thermally stressed components in an LPDC machine because it:

1. 1. Is immersed in molten metal at 1,100°C
   2. Then, experiences rapid cooling as the casting solidifies and the mold is opened
   3. Meanwhile, is subject to pressure cycling (0 to 0.7 MPa per shot)
   4. In total, cycles 30–80 times per hour, 24 hours per day

   Riser tube geometry and function – A typical LPDC riser is a cylindrical ceramic tube, 10–30 mm in outer diameter, 100–300 mm in length, with a precisely machined internal bore (typically 6–12 mm) for metal flow. Specifically, the tube connects the holding furnace to the mold cavity via a pressurized chamber. During each shot:

   1. First, pressure is applied (0.5–0.7 MPa), pushing molten metal up the riser into the cavity
   2. Next, metal solidifies inside the closed mold (typically 5–15 seconds)
   3. Then, pressure is released and the mold opens
   4. Subsequently, the solidified casting is ejected and the mold resets
   5. Finally, the riser and mold are heated again for the next cycle

The riser must survive this cycle without cracking, dimensional change, or metal contamination. Thermal stress is extreme because the tube is simultaneously exposed to molten metal (heating from inside) and cool mold surfaces or ambient air (cooling from outside), creating steep temperature gradients.

Why aluminium titanate falls short in LPDC – Aluminium titanate riser tubes are common in diecasting because they’re inexpensive ($60–120 per tube) and have low thermal expansion. In LPDC’s specific conditions, however, they fail on three fronts:

• Flexural strength of ~20–30 MPa cannot withstand 0.5–0.7 MPa pressure pulses over thousands of cycles – microfractures propagate quickly
• High natural porosity (10–15%) allows molten aluminium infiltration, causing internal corrosion and sudden dimensional change
• Chemical attack from molten Al on the TiO₂ phase degrades grain boundaries, accelerating failure
• Mean time between failures: 3–6 months under continuous LPDC

Why silicon nitride is better, but sialon is better still – Silicon nitride (Si₃N₄) is superior to aluminium titanate for mechanical strength (flexural ~600–700 MPa) and chemical resistance. Facilities that switched to silicon nitride risers report 2–3x longer life than aluminium titanate.

However, silicon nitride has a weakness in LPDC: it is more brittle than sialon and tolerates microcracks less gracefully. Sialon’s aluminium oxynitride lattice provides higher fracture toughness (K₁c ~6–7 MPa·m^0.5 vs silicon nitride’s ~4–5 MPa·m^0.5), meaning it absorbs the mechanical shocks of pressure cycling without propagating microcracks into catastrophic fracture.

Sialon ULTRA™ riser tubes deliver 30% longer service life than standard ceramic alternatives by:

• Lower heat expansion (5.0–5.2 × 10⁻⁶ /K) – less internal stress while cooling
• Balanced heat flow – steeper swings than silicon nitride alone, but still within safe limits
• Higher crack resistance – tiny cracks don’t grow into full breaks
• Non-stick surface – no molten-metal sticking or surface wear

Real-world riser tube performance:

Material	Service Life (months)	Cycles to Failure	Failure Mode	Cost per Tube
Aluminium Titanate	3–6	5,000–12,000	Porosity infiltration, chemical corrosion, pressure fracture	$60–120
Silicon Nitride	10–15	20,000–30,000	Stress fracture, delayed failure	$300–500
Sialon ULTRA™	36–72 (3–6 yrs)	60,000–144,000+	Rare failure; mostly scheduled replacement	$400–600

At 50 cycles per hour, 8,000 hours per year of operation:

• Aluminium Titanate: Fails after 1–3 months, requiring frequent replacement.
• By comparison, Silicon Nitride: Lasts 4–8 months, offering a longer service life but still needing regular replacement.
• In contrast, Sialon ULTRA™: Lasts 36–72 months (3–6 years), greatly reducing replacement frequency, downtime, and maintenance costs.

For a foundry running 5 LPDC machines with 10 riser tubes each (50 tubes total):

• Aluminium Titanate strategy: ~150–200 replacements per year
• Sialon strategy: ~8–15 replacements per year

Installation and specification – Sialon offers custom riser tubes for any geometry, including non-standard bore diameters, threading for pressure-vessel connections, and custom lengths. Specification requires:

• Outer diameter and bore diameter (precision to 0.1 mm)
• Length and any features (threads, steps, grooves)
• Pressure rating and temperature range
• Lead time (typically 2–3 weeks for standard sizes)

Thermocouple protection tubes: accuracy, contamination risk, and service life

heat sensorare the temperature sensors inside LPDC machines, reading metal temperature in real-time to control heating power and shot timing. A heat sensor measures temperature via the Seebeck effect-a small voltage generated at the junction of two dissimilar metals when heated. That voltage is proportional to temperature.

Why heat sensor need protection – Without protection, a bare heat sensor lead immersed in molten metal would:

• Oxidize instantly (lose its junction properties)
• In addition, dissolve into the molten metal (chemical attack)
• Furthermore, embed molten metal into its surface (wettability), contaminating the casting

Therefore, manufacturers place the lead inside a ceramic protection tube, which typically measures 6–10 mm in outer diameter and 1,200–1,600 mm in length. The tube has a 1–2 mm wall thickness and a precisely machined internal bore that holds the heat sensor securely In this way, the tube acts as a barrier between the heat sensor and molten metal.

Accuracy and temperature measurement – The heat sensor measures temperature via the voltage difference between its junction (inside the ceramic tube, near the molten metal) and the reference point (outside the machine). Specifically, heat must transfer from molten metal → ceramic tube wall → heat sensor lead.

If the ceramic tube wall has deposits, RUSTING, or dimensional changes:

• Heat transfer slows → temperature reading lags reality
• Bore diameter drifts → interference fit loosens → air gap increases → temperature reading accuracy drops by 10–50°C
• Contamination embeds in the tube wall → thermal conductivity changes → reading errors

Sialon ULTRA™ thermocouple protection tubes are manufactured to ±0.02 mm precision bore tolerance, ensuring consistent fit on the heat sensor lead and stable thermal contact. The non-wettable surface prevents metal embedding, and the chemical inertness prevents wall RUSTING or deposit buildup over the 12+ month service life.

Failure modes and contamination risk:

Failure Mode	Symptom	Consequence	Timeline
Steel tube corrosion	Bore narrows; tube weakens	Thermocouple binding; inaccurate readings; rare sudden failure	2–4 weeks
Aluminium Titanate chemical attack & porosity	Grain-boundary corrosion; metal infiltrates through pores	Temperature reading error (±15–60°C); bore dimensional drift; sudden failure	2–4 months
Silicon nitride thermal stress	Microcracking; bore diameter drift	Erratic readings; difficult diagnosis	4–8 months
Sialon ULTRA™ (rare)	Eventual wear after 12+ months	Graceful degradation; predictable replacement cycle	12–18 months

In precision casting, a temperature error of ±20°C causes:

• Slower metal fill → dimensional shrinkage or misalignment
• Premature solidification → porosity and voids
• Casting defects that may not be visible until machining or assembly
• Scrap rate increases by 5–15%

For a foundry casting 1,000 parts per month at $100–500 cost per part, a 5% scrap increase = $5,000–25,000 per month in lost revenue. Upgrading from aluminium titanate HEAT SENSOR to sialon protection tubes prevents this loss while extending service life from 2–4 months to 12+ months – reducing replacements from 3–6 per year to one.

Installation and specification – Sialon ULTRA™ thermocouple protection tubes are available in lengths up to 1,600 mm, with precision bore tolerances and optional external surface machining (grooves, steps, or specific finishes for mold integration). Specification requires:

• Bore diameter (±0.05 mm tolerance to fit HEAT SENSOR lead)
• Outer diameter (typically 6–10 mm)
• Length (typically 600–1,600 mm)
• Material grade (sialon for standard applications; silicon carbide for ultra-high-temperature furnaces)

Lead time: 2–3 weeks for standard sizes; 3–4 weeks for custom bores or large diameters.

Total cost of ownership: replacement frequency, downtime, and ROI

Aluminium titanate tubes look inexpensive on the purchase order – $60–120 per tube versus $400–600 for sialon. But with a service life of 3–6 months, the total annual material spend converges quickly, and the replacement labour and downtime costs tip the calculation firmly toward sialon.

Direct cost of ownership (50 riser tubes across 5 LPDC machines):

Cost Factor	Aluminium Titanate (Annual)	Sialon ULTRA™ (Annual)	Savings
Material cost (~175 replacements vs ~12)	$10,500–21,000	$4,800–7,200	$5,700–13,800
Replacement labour (4 hrs × $100/hr)	$70,000	$4,800	$65,200
Subtotal (material + labour)	$80,500–91,000	$9,600–12,000	$68,500–79,000

Even on direct costs alone – before counting downtime – sialon is cheaper to run than aluminium titanate, because the labour cost of constant replacements wipes out AT’s per-unit price advantage entirely.

Indirect cost of ownership (production loss):

Indirect cost of ownership (production loss)

An unexpected riser-tube failure on an active LPDC line usually leads to:

• 1–4 hours of downtime for fault finding, mold removal, tube replacement, reassembly, and system setup.
• As a result, production drops by about 300 parts during a typical 3-hour stop (100 parts per hour). At $100–500 per part, this equals $30,000–150,000 in lost revenue.

Because aluminium titanate fails much more often than sialon (2–4 unexpected failures per month on a 5-machine line versus 1–2 per year), foundries can avoid most costly downtime by switching to sialon.

• Aluminium titanate: 24–48 unexpected failures per year × $50,000 average loss per failure = $1,200,000–2,400,000 in yearly downtime costs.
• By comparison, Sialon: 1–2 unexpected failures per year × $50,000 average loss per failure = $50,000–100,000 in yearly downtime costs.
• Therefore, yearly downtime savings are about $1,100,000–2,300,000.

Quality and scrap costs

In addition to reducing downtime, sialon also lowers the number of faulty castings. Because it keeps its shape and prevents molten aluminium from sticking to the surface, it helps maintain steady production quality over time.

For example, a foundry operating 10 LPDC machines and making 50,000 parts each month can expect:

• Aluminium titanate: 3–7% scrap rate because of pores, temperature errors, and size changes, resulting in 18,000–42,000 faulty parts each year.
• By contrast, Sialon: 0.5–1.5% scrap rate because there are fewer material-related defects, resulting in 3,000–9,000 faulty parts each year.

As a result, with an average scrap cost of $200 per part (materials and labour), sialon reduces yearly scrap losses by about $1,500,000–6,600,000.

Total ROI on sialon ULTRA™ adoption:

In summary, switching from aluminium titanate to sialon delivers:

• First, direct savings on materials and labour total $68,500–79,000 per year.
• In addition, reduced downtime saves $1,100,000–2,300,000 per year.
• Furthermore, lower scrap rates save another $1,500,000–6,600,000 per year, although the exact amount depends on the facility.
• Overall, total yearly savings range from $2,668,500–9,079,000.

Payback timeline: The extra cost of sialon over aluminium titanate (roughly $280–480 per tube × 35 tubes = $10,000–17,000 upfront) pays for itself in less than two weeks through downtime savings alone. Furthermore, procurement teams see the long-term value when they track quarterly performance using key metrics such as::

• Mean time between failures (MTBF) – sialon is 12x longer than aluminium titanate
• Casting yield (%) – sialon improves yield by 3–7 points
• Unplanned downtime hours – sialon reduces unplanned downtime by 90–95%
• Cost per casting – sialon reduces cost per part by $20–80

All Sialon ULTRA™ products carry a 12-month warranty against chemical attack in molten aluminium, providing procurement teams with a guaranteed replacement window and predictable cost model.

Try Sialon Ceramics

Sialon Ceramics ApS manufactures the Sialon ULTRA™ product line-riser tubes, thermocouple protection tubes, and custom ceramics engineered for LPDC and extreme-temperature foundry operations. Founded in 1986 and headquartered in Copenhagen, the company brings 40 years of expertise in advanced technical ceramics to precision diecasting.

The Sialon ULTRA™ advantage is built on three core capabilities:

1. Material science: Sialon’s silicon aluminium oxynitride composition combines thermal shock resistance with chemical inertness, delivering 30% longer service life than standard ceramics while maintaining dimensional stability under thermal cycling.

2. Precision manufacturing: Custom riser and temperature sensor tubes are manufactured to ±0.02 mm tolerances, with threading, grooves, and client-specific geometries available. In addition, lead times are typically 2–3 weeks for standard sizes.

3. Global support: With operations in Denmark (headquarters), Spain (regional hub), and North America (USA/Canada toll-free support), Sialon provides direct engineering expert advice, custom design services, and rapid replacement logistics.

Next steps: Contact Sialon Ceramics today for a free consultation about your LPDC application. Before your call, have your current riser and temperature sensor tube specifications ready (outer diameter, bore diameter, length, and current failure rate) so that the team can design a Sialon ULTRA™ solution and provide a cost-of-ownership comparison with your current material. As a result, most LPDC facilities see ROI within 2–4 weeks.

• USA/Canada toll-free: +1 (833) 709-1399
• Europe (Denmark): sialon.com
• Email: info@sialon.com

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Frequently Asked Questions

Why does sialon perform better than cheap ceramics in LPDC applications?

Aluminium titanate (Al₂TiO₅) has low thermal expansion, but it is weak (about 20–30 MPa bending strength) and contains many small pores. As a result, pressure pulses of 0.5–0.7 MPa can quickly create tiny cracks in LPDC. In addition, its porous structure allows molten aluminium to enter the material, leading to internal damage and RUSTING. By comparison, sialon combines low thermal expansion with a much higher bending strength of about 700 MPa. Therefore, it resists both heat and mechanical damage over thousands of casting cycles.

What is the service life difference between sialon and aluminium titanate riser tubes?

Aluminium titanate riser tubes usually last 3–6 months in continuous LPDC service. In contrast, Sialon ULTRA™ riser tubes typically last 36–72 months (3–6 years), which is about 12 times longer. At 50 cycles per hour, cheap ceramics usually fails after 5,000–12,000 cycles, whereas sialon can reach 60,000–144,000+ cycles. Furthermore, every Sialon ULTRA™ tube includes a 12-month warranty against chemical attack from molten aluminium. In practice, many customers continue using the tubes well beyond the warranty period.

How does sialon’s non-wettable surface reduce DIRT?

Sialon’s silicon nitride bond does not react with molten aluminium. As a result, the metal cannot stick to or soak into the ceramic surface. In contrast, cheap ceramics has a porous structure that allows molten aluminium to enter the material. Consequently, the tube wears from the inside and can release titanium oxide particles into the molten metal. Because of this, Sialon temperature sensor protection tubes keep their size and bore accuracy throughout their service life. This helps provide accurate temperature readings and clean, DIRT-free casting.

Can sialon temperature sensor protection tubes prevent IMPURITIES in harsh conditions?

Yes. Aluminium titanate tubes often fail within 2–4 months because of RUSTING and molten metal entering the pores. As a result, temperature readings can be off by ±15–60°C. By comparison, Sialon’s higher impact strength and non-wettable surface prevent these problems. Therefore, the bore stays clean and accurate for 12 months or longer, helping maintain reliable temperature control during LPDC production.

What is the total cost advantage of switching to sialon?

Although Sialon tubes cost more to buy ($400–600 compared with $60–120 for aluminium titanate), the total yearly cost is much lower. This is because cheap ceramics usually needs 150–200 replacements per year, while sialon requires only 30–40. In addition, labour costs alone are about $70,000 per year for cheap ceramics, compared with about $14,000 for sialon.

When you also account for downtime, the savings increase even more. Overall, a five-machine foundry can save more than $2.6 million per year and recover the extra cost of Sialon in less than two weeks.