TECHNICAL GUIDE · HIGH TEMPERATURE · HYDRAULIC LIFT CYLINDERS
Lift Cylinders in
High-Temperature Environments
Foundry · Casting · Metallurgy
Hydraulic lift cylinders operating in foundries, die-casting plants, heat treatment furnaces, and steel mill environments face a temperature challenge that is the mirror image of the cold-weather problem — instead of seals that become too rigid, they face seals that soften and extrude; instead of oil that is too viscous, they must contend with oil that thins to the point of losing film strength. Above 80°C continuous operating temperature, standard mineral hydraulic oil begins to oxidise and lose its viscosity characteristics; above 100°C, standard elastomeric seals begin to harden from heat aging; above 150°C ambient, fire-resistant hydraulic fluid becomes mandatory. This guide covers specification elements for hydraulic lift cylinders in high-temperature foundry, metallurgical, and heat-treatment applications.
Fire-Resistant Fluid
Thermal Shielding
LIFT CYLINDERS · HIGH TEMPERATURE ENGINEERING · JULY 2026
REFERENCE · HIGH-TEMPERATURE LIFT CYLINDER CRITICAL THRESHOLDS
OIL DEGRADATION
80°C continuous
Standard mineral oil oxidation rate doubles for every 10°C above 60°C — above 80°C continuous, change interval must be halved
FIRE-RESISTANT FLUID
Above 150°C ambient
HFA, HFB, HFC or HFDU fire-resistant hydraulic fluid mandatory when ambient exceeds 150°C near the lift cylinder
FKM SEAL LIMIT
+200°C
FKM (Viton) seals rated to +200°C continuous — the highest temperature elastomeric seal available for hydraulic lift cylinders
RADIATION SHIELDING
Mandatory foundry
Radiant heat from molten metal pouring can exceed 800°C at close range — all exposed lift cylinder components need shielding
SECTIE 01
Heat Sources and Temperature Zones in Foundry Applications
The thermal challenge is not a single elevated temperature but a combination of heat sources acting on different parts of the lift cylinder:
RADIANT HEAT
From open melt surfaces, pouring spouts, and red-hot castings during removal. Intensity: 500–1 500°C source temperature at 0.5–3 m from the lift cylinder. Radiant intensity falls with the square of distance but can still heat an unshielded rod surface to 200–400°C within seconds of a pour event. Shielding is the only countermeasure.
CONDUCTIVE HEAT
From hot workpieces placed directly on a machine table or carried by a fixture attached to the lift cylinder rod tip. A steel casting at 300°C placed on a table supported by the lift cylinder transmits heat directly into the cylinder structure — particularly the rod tip and rod end clevis. Thermal breaks (non-conductive material between the casting and the lift cylinder mounting) are required.
CONVECTIVE / AMBIENT
The general workshop ambient temperature in a foundry bay is typically 40–70°C even away from the immediate pour zone. This elevated ambient drives up the temperature of the hydraulic oil in the reservoir, the hoses, and the lift cylinder bore — all increasing the rate of seal and oil degradation. Oil cooling is required whenever the reservoir temperature consistently exceeds 60°C.
METAL SPLASH
Molten metal droplets ejected during pouring or casting removal can land on unprotected rod surfaces and instantly adhere, creating raised surface protrusions that will cut through any wiper or seal on the next extension stroke. Metal splash guards over the gland area of the lift cylinder are standard in aluminium die-casting and iron foundry environments.
SECTIE 02
Seal Material Selection for High-Temperature Lift Cylinders
The seal for a high-temperature lift cylinder is selected by the maximum sustained temperature at the rod gland — the hottest point in the hydraulic circuit because it is closest to the hot environment and exposed on each extension stroke. The following materials cover the temperature range encountered in foundry and metallurgical applications:
UP TO
100°C
PU (polyurethane) or NBR. Standard seal materials function correctly up to 90–100°C. Suitable for heat treatment ovens, warm forge shop general environment, and applications where the lift cylinder is not in the direct radiant zone. Above 90°C continuous, NBR begins to harden and crack from oxidative aging — PU maintains performance slightly longer. Neither material is suitable for foundry direct-zone applications.
100°C
TO 150°C
High-temperature NBR or HNBR (hydrogenated NBR). HNBR has significantly better heat aging resistance than standard NBR — it is used in automotive engine seals that operate at up to 150°C and is the appropriate upgrade for lift cylinders in elevated-ambient industrial environments where the gland temperature stays below 150°C. HNBR seal kits are available as a standard option for lift cylinders in general-purpose foundry and steel plant applications.
150°C
TO 200°C
FKM (Viton / fluoroelastomer). FKM is the correct seal material for lift cylinder glands up to 200°C continuous. It has excellent resistance to both heat aging and chemical attack from the release agents, lubricants, and cleaning chemicals used in aluminium die-casting and iron foundry operations. FKM seals are 3–5× the cost of NBR equivalents but are the only elastomeric option for sustained operation above 150°C. For fire-resistant fluid systems, verify compatibility — some water-glycol fire-resistant fluids are not recommended with FKM; use EPDM instead.
ABOVE
200°C
PTFE-based composite seals. Above 200°C, no standard elastomeric material maintains adequate dynamic sealing performance. PTFE composite seals (PTFE filled with glass fibre, carbon, or bronze) remain functional up to 260°C but have higher static friction and less ability to recover from gland surface imperfections. Above 200°C, the lift cylinder application should also be reviewed for whether hydraulic actuation is the correct technology — electromechanical or pneumatic actuators may be more appropriate above the hydraulic fluid’s thermal stability limit.
FKM and HNBR seal kits for high-temperature industrial lift cylinder applications are available as options from the hefcilinder product range. Specify the maximum continuous gland temperature and the hydraulic fluid type at enquiry to receive the correct seal specification.
SECTIE 03
Fire-Resistant Hydraulic Fluid — Types and Selection
ISO 12922 classifies fire-resistant hydraulic fluids into four types. The correct type for a foundry lift cylinder depends on the ambient temperature, the available infrastructure, and the specific heat resistance requirement:
| FLUID TYPE | COMPOSITION | TEMP LIMIT | SEAL COMPATIBILITY |
|---|---|---|---|
| HFA — oil-in-water emulsion | 95–98% water + concentrate | +50°C max | EPDM preferred; NBR generally acceptable. Not for FKM. |
| HFC — water-glycol | 35–50% glycol + water | +60°C max | EPDM or NBR; FKM not recommended. Zinc must be removed from circuit — water-glycol corrodes zinc. |
| HFDU — anhydrous polyol ester | Synthetic ester, water-free | +80°C, flash pt 300°C | EPDM or FKM; NBR swells in ester. Best performance for foundry applications. |
| HFDR — phosphate ester | Synthetic phosphate ester | +70°C, flash pt 270°C | Only EPDM and PTFE compatible — FKM, NBR, PU all degrade in phosphate ester. Used in steel mill hydraulic systems. |
System conversion warning: Converting a lift cylinder system from mineral oil to fire-resistant fluid requires complete draining and flushing of the circuit, replacement of all seals with fire-resistant fluid-compatible grades, removal of any zinc-plated components if converting to HFC water-glycol, and a check of all painted surfaces in the reservoir (many paints are attacked by water-based fluids). The lift cylinder must be rebuilt with the new seal kit before filling with fire-resistant fluid — do not mix the old seals with the new fluid and expect compatibility.
SECTIE 04
Thermal Shielding and Cylinder Positioning
Before upgrading seals and fluid, the first engineering decision for a foundry lift cylinder application is to minimise heat exposure through positioning and shielding. A well-shielded unit with standard seals will outlast a poorly positioned lift cylinder with premium seals — thermal engineering is always more effective than material substitution:
POSITIONING
Mount each lift cylinder as far from the radiant heat source as the mechanical configuration allows. For each additional metre of distance from a molten metal pour, the radiant heat intensity drops to one quarter — moving the installation from 0.5 m to 1.0 m from a typical pouring spout reduces the radiant heat load by 75%. If the cylinder must be close to the heat source, orient the rod-gland away from the radiant zone — it is acceptable for the barrel end to be exposed to elevated temperature more than the gland end.
RADIATION SHIELD
A polished stainless steel sheet positioned between the molten metal source and the cylinder reflects the majority of the radiant heat and is the single most cost-effective protection measure available. A 304 stainless steel shield 1.5 mm thick at 200 mm from the cylinder surface will reflect 60–70% of the radiant heat that would otherwise be absorbed by the rod and barrel. Cool-touch temperature on the cylinder side of the shield should be verified with a surface pyrometer during production to confirm the shield is positioned correctly.
SPLASH GUARD
A metal splash guard covering the rod gland area — typically a curved steel plate at the gland end of the lift cylinder — prevents molten metal droplets from adhering to the rod surface. The splash guard must be designed to allow the rod to extend and retract freely while covering the gland entry. Clean the splash guard weekly to remove accumulated solidified metal droplets before they build up to a thickness that contacts the rod.
THERMAL BREAK
Where the lift cylinder rod tip or mounting bracket contacts hot workpieces or a heated machine structure, insert a thermal break — a ring or plate of low-conductivity material (phenolic resin, ceramic, or stainless steel with a reduced cross-section) between the hot component and the lift cylinder mounting. A well-designed thermal break can reduce the temperature transmitted into the cylinder end from 300°C to under 80°C, allowing standard seals and fluid to remain in specification.
SECTIE 05
Rod and Barrel Specification for Elevated Temperatures
The rod and barrel materials of a high-temperature lift cylinder must be selected for both their mechanical performance and their thermal behaviour at sustained elevated temperatures:
ROD MATERIAL
Standard 42CrMo4 alloy steel retains adequate strength to 200°C. Above 200°C, the rod’s heat treatment may begin to temper — the rod hardness decreases, increasing susceptibility to rod bending under side load. For sustained operation above 150°C rod temperature, stainless steel rod (316 or duplex 2205) eliminates the tempering risk and provides inherent corrosion resistance against the water-based fire-resistant fluids used in high-temperature systems.
STANGCOATING
Hard chrome softens above 250°C (microhardness reduction begins at approximately 200°C) and must not be relied upon for wear resistance at sustained elevated temperatures. HVOF tungsten carbide maintains hardness to 450°C and is the correct rod coating choice for lift cylinders in foundry applications where the rod surface may be intermittently exposed to radiant heat peaks. Ceramic coatings (aluminium oxide, chromium oxide) extend the thermal tolerance further and provide additional thermal insulation for the underlying steel.
BARREL COATING
The outer barrel of any high-temperature lift cylinder should be painted with a high-temperature coating rated to at least 250°C — standard epoxy or polyurethane industrial coatings blister and peel at above 120°C. Silicone-based high-temperature paints rated to 600°C are available for direct application to the barrel surface and provide thermal insulation as well as corrosion protection in the foundry environment. The barrel internal surface requires no special treatment beyond the standard honing — internal temperature is governed by the oil temperature, which must be controlled by the cooling system.
For high-temperature foundry and die-casting lift cylinder applications, and heat treatment environments, the industriële machinebouw hydraulische cilinder range provides configurations with FKM or HNBR seals, HVOF rod coating, high-temperature barrel coating, and fire-resistant fluid compatibility documentation.
SECTIE 06
Maintenance Programme for High-Temperature Lift Cylinders
Thermal acceleration of seal aging means that high-temperature lift cylinders require a significantly compressed maintenance schedule compared to equivalent industrial units in a standard thermal environment:
WEEKLY
Inspect all lift cylinder rod surfaces for oil weeping at the gland, any molten metal splash on the rod, and condition of the splash guard and radiation shield. Clean any solidified metal from the splash guard and shield before it accumulates to a thickness that could contact the rod. Check hydraulic oil temperature in the reservoir — if consistently above 70°C, increase oil cooler capacity before the temperature accelerates seal and oil degradation further.
QUARTERLY
Oil sample analysis for viscosity, acid number (TAN), water content, and ISO cleanliness. High-temperature mineral oil or HFDU ester degrades primarily through oxidation — TAN increase above 2.0 mg KOH/g indicates the oil must be changed regardless of hours or volume pumped. Replace hydraulic filter elements. Inspect lift cylinder rod chrome for any discolouration or cracking that indicates localised overheating.
6 MONTHS
Replace hydraulic oil regardless of TAN if the reservoir temperature consistently exceeds 70°C. Inspect all lift cylinder gland seals during the oil change — a seal that has been operating in a high-temperature environment shows characteristic surface hardening, reduced elasticity, and often slight swelling from oxidation products. Replace any seal showing visual signs of heat aging rather than running it to failure.
ANNUALLY
Full lift cylinder seal kit replacement as a preventive measure on all units operating in the high-temperature zone. Rod chrome thickness measurement — HVOF coating in a foundry should show minimal wear but check for any areas where molten metal impact has eroded the coating surface. Pressure test all lift cylinders at 1.5× working pressure after rebuild. Inspect and clean all radiation shields and thermal breaks — replace any that are warped, cracked, or have lost their reflective surface condition.
TECHNICAL FAQ
High-Temperature Cylinder Questions
Vraag 01
Our die-casting machine lift cylinder rod seals need replacement every 3 months — is this a seal quality problem or a temperature problem?
Three-month seal life on a die-casting machine cylinder almost certainly indicates a temperature problem rather than a seal quality issue. Die-casting machines expose the rod to three concurrent thermal insults: the elevated ambient of the machine bay (typically 50–70°C), radiant heat from the die during opening when the casting is ejected, and occasional direct contact with release agent spray (which at die temperatures can be superheated steam rather than liquid). Before changing to a higher-grade seal, measure the actual rod surface temperature during a production cycle using a surface pyrometer or thermal imaging camera during die opening. If the rod surface temperature exceeds 100°C during any part of the cycle, the seal replacement interval will never reach 12 months with any standard elastomeric seal — the lift cylinder seal must be upgraded to FKM and a splash shield installed over the gland area. If the rod temperature stays below 80°C, the short seal life indicates contamination (release agent or cooling water reaching the gland) rather than thermal damage — inspect the gland wiper for condition and replace with a scraper-type wiper that better excludes the die-casting release agent spray.
Vraag 02
We are installing a new tilt table in our grey iron foundry and need to specify the hydraulic lift cylinders — what is the minimum specification package for this environment?
For a grey iron foundry tilt table, the minimum specification is: FKM rod seals rated to 200°C; HVOF tungsten carbide rod coating; stainless steel rod if the rod surface can be exposed to direct radiant heat from the molten iron; high-temperature silicone barrel coating to 600°C; fire-resistant hydraulic fluid (HFDU synthetic ester recommended — better lubricity than water-based options and compatible with FKM); polished stainless steel radiation shield between the ladle path and the cylinder rod axis; metal splash guard over the gland area; and thermal break inserts between the tilt table structure and the cylinder mounting clevis. For the hydraulic power unit, locate it outside the foundry bay if possible, or at minimum in a cabinet with a filtration package designed for the iron dust and carbon contamination present in foundry air. The oil cooler should be sized to maintain reservoir temperature below 60°C continuously.
Vraag 03
Our steel plant uses HFDR phosphate ester fluid in the lift cylinder circuit — which seal material is compatible?
Phosphate ester fire-resistant fluid (HFDR type) is one of the most chemically aggressive hydraulic fluids for elastomeric seals. Of the common seal materials, only EPDM and PTFE composites are reliably compatible with phosphate ester fluids across their full temperature range. NBR swells significantly in phosphate ester within hours — typical swell rates of 30–60% volume increase are reported with standard NBR in phosphate ester exposure, which immediately destroys the seal’s dimensional fit in the gland. PU similarly degrades rapidly. FKM (Viton) is problematic — some grades swell in phosphate ester and some are acceptable, but the variability between FKM compound grades makes it unreliable for specification without specific compatibility confirmation from the seal manufacturer with the actual fluid formulation in use. The standard specification for rod seals in a phosphate ester steel plant system is: EPDM rod seal, PTFE backup ring, PTFE-lined guide ring. Confirm the specific EPDM compound’s compatibility with the actual phosphate ester grade being used — there are different phosphate ester formulations with varying levels of additive packages that affect compatibility.
Vraag 04
What is the maximum hydraulic oil temperature before installing an oil cooler on a foundry hydraulic circuit?
The practical upper limit for sustained oil temperature in a foundry circuit is 60°C for mineral oil and HFDU ester, and 50°C for HFA and HFC water-based fire-resistant fluids. Above these limits, oil oxidation proceeds at a rate that makes annual oil changes necessary even with premium fluid grades — at 70°C continuous, a mineral oil that would last 2 000 hours at 60°C may only last 1 000 hours; at 80°C continuous, only 500 hours. Seals in the lift cylinder degrade faster when oil temperature exceeds 70°C — NBR and standard PU seal aging to the point where annual replacement is required even with premium seal grades. Installing an oil cooler whenever reservoir temperature consistently exceeds 60°C is the most cost-effective maintenance investment for any foundry lift cylinder system. The cooler typically pays for itself in reduced seal and oil replacement costs within 6–12 months of operation.
HIGH-TEMPERATURE LIFT CYLINDER SUPPLY
Specifying Lift Cylinders for Foundry or High-Heat Service?
Tell us the maximum ambient temperature, the radiant heat source distance, and the hydraulic fluid type — our engineers specify the correct hefcilinder seal, rod coating, and barrel coating for your high-temperature application.
Redacteur: Cxm
