Gasket Materials for Transformers, Switchgear and Data Centre Power Equipment
In short: most sealing on transformers, switchgear and data centre power plant is done by four material families. Rubberised cork (cork-elastomer, such as Nebar) seals transformer lids, tanks and switchgear covers, because it conforms to large, out-of-parallel flanges at low bolt load. Compressed non-asbestos fibre (Klingersil, Novus) handles bolted joints at higher pressure and temperature. Tanged graphite takes the high-temperature and steam duties. Elastomer and foam sheet covers enclosure, ingress and vibration duties. The single decision that governs all of them is the fluid: nitrile-based materials for mineral oil, EPDM never in mineral oil, and ester fluids validated by test rather than by chart.
What actually needs sealing
| Equipment | Joint | Duty | Material family that usually wins |
|---|---|---|---|
| Oil-filled power and distribution transformers | Tank lid, inspection covers, radiator and conservator flanges, bushing mountings | Mineral or ester fluid, large flanges, modest bolt load, long service life | Rubberised cork (cork-nitrile), nitrile sheet |
| Switchgear | Enclosure covers, busbar chamber joints, cable box lids | Oil or gas retention, ingress protection, arc containment | Rubberised cork, nitrile, EPDM (non-oil duties) |
| LV panels, UPS and battery storage cabinets | Door and panel seals, cable entries | IP rating, dust, condensation, flame performance | Closed-cell sponge, solid elastomer, foam |
| Electronics enclosures and shielded cabinets | Lid and door seals | Ingress protection plus EMC compliance | Conductive and shielding materials |
| CRAC/CRAH units, chillers, heat exchangers | Panel joints, header and plate flanges | Water-glycol, condensation, thermal cycling | EPDM, compressed fibre |
| Liquid cooling — CDUs, manifolds, coolant distribution | Flanged and bolted coolant joints | Water-glycol or dielectric fluid, leak-critical, high duty cycle | EPDM, compressed fibre, elastomer sheet |
A point worth making to anyone specifying across a whole installation: the fluid flips the answer. EPDM is an excellent choice on the water-glycol side of a cooling system and the wrong choice on the oil side of a transformer. Nitrile is the reverse. Specifying one house elastomer across a site is how leaks get designed in.
Rubberised cork (cork-elastomer) — the transformer workhorse
Rubberised cork is cork granule bound in an elastomer. It does something solid rubber and fibre sheet cannot: it compresses substantially and recovers, so it seals long, relatively flexible flanges that are not perfectly parallel, without needing high bolt load. That is exactly the condition on a transformer lid or a switchgear cover.
Neolangite NL53 is a general rubberised cork gasket material manufactured for RAM Gaskets. Neolangite NL is a RAM trademark. It is a ramge of Nitrile-bonded cork gasket material which has many general uses.
Nebar is a range of rubber-bonded cork gasket materials manufactured in the UK by Tiflex Ltd of Liskeard, Cornwall, part of the James Walker Group. It is specified by grade colour, and several grades are designed specifically for transformer and switchgear duty. RAM cuts Nebar, and has held direct material accounts with the major sheet manufacturers for over forty years.
Where it goes wrong: rubberised cork is not a high-pressure material and it does not like prolonged dry heat. If your joint sees steam, high bolt stress or temperatures above the figures above, you are in compressed fibre or graphite territory instead.
Related: Cork Gasket Material · Transformer Gaskets
Compressed non-asbestos fibre — Klingersil, Novus
Compressed fibre sheet is the standard answer for bolted flange joints that are beyond cork and below graphite. The common high-performance grades — KLINGERSIL C-4400 and C-4430, and the Novus range — are aramid fibre bonded with a nitrile (NBR) binder, which is why they suit oils, water, steam, fuels, refrigerants, salt solutions and moderate acids.
One thing to know before you quote a number at a supplier: the serious manufacturers do not publish a single maximum temperature or pressure for these materials. Klinger specifies them by pressure–temperature diagram, because the safe limit for temperature depends on the pressure at that moment, on the gas or liquid being sealed, and on the sheet thickness. Anyone who gives you one number for a compressed fibre sheet is simplifying something that matters. Work from the current datasheet’s pT diagram for the exact grade and thickness.
RAM buys these grades directly from Klinger and Novus and cuts to drawing, so the material certification that arrives is directly traceable to the manufacturer.
Related: Gasket Materials Guide · Understanding Gasket Pressure
Tanged graphite and metal-reinforced sheet
Tanged graphite is flexible graphite laminated onto a thin stainless steel core — typically 0.1mm 316 stainless — whose punched teeth grip the graphite mechanically, with no adhesive to degrade. The tang adds the mechanical strength and blow-out resistance that unreinforced graphite lacks.
Typical published performance for the type: −200°C to +450°C, reduced to around +400°C in steam, with pressures to around 120 bar depending on thickness and application. Ash content is usually specified at 1.0% maximum. These are representative figures for the material type rather than a guarantee for a specific grade, and temperature and pressure limits cannot all be applied simultaneously.
In this sector tanged graphite is less about the transformer itself and more about the surrounding plant: steam, hot oil, heat exchanger and high-temperature flange duties where a soft sheet will not survive.
Related: Graphite Gasket Material
The fluid decides it: mineral oil, ester fluids and coolants
This is the section that saves the most money, because the wrong elastomer does not fail on day one. It fails after eighteen months in service, in an energised asset.
Mineral transformer oil. Nitrile (NBR) is the default. Acrylonitrile content drives the behaviour: higher ACN gives better oil resistance and lower swell, lower ACN gives better low-temperature flexibility. A practical continuous ceiling for NBR is around 100–120°C.
EPDM must not be used in mineral oil. EPDM is formulated for non-oil service and swells badly in hydrocarbons. It is an excellent material — on the water, glycol and steam side.
Ester fluids, natural and synthetic. As UK transformer fleets move to ester fluids for fire performance and biodegradability, the gasket question is being reopened on assets that were specified decades ago. Nitrile remains the workhorse; HNBR where more heat and ageing margin is needed; FKM for elevated temperature duties; fluorosilicone where heat and chemical resistance are both required. EPDM stays in the verify-before-any-oil-contact column. The important caveat, and the one the fluid manufacturers themselves make: generic compatibility charts are not sufficient for ester fluids. Validate by immersion testing at representative temperature using ASTM methods before committing a production specification.
Cooling circuits. Water-glycol is EPDM’s home ground, and the exact opposite of the transformer answer. For liquid-cooled racks and CDUs, the duty cycle and the consequence of a leak both argue for specifying the gasket at the same level of rigour as the fittings.
Related: Chemical Compatibility & Resistance
Enclosure, ingress and EMC
Enclosure sealing is a different problem from flange sealing: low closing force, long perimeters, door seals that must recover after thousands of cycles, and an IP rating to hold.
Closed-cell sponge and solid elastomer profiles cover most of it. Where flame performance is specified, the grade has to be selected against the actual standard called up, not against a colour or a general claim.
Where an enclosure also has to meet EMC requirements, the seal has to carry electrical continuity across the joint as well as keep water out — which means conductive materials rather than standard elastomer. RAM cuts shielding and conductive sheet materials alongside the rest of the range. This is a smaller part of what we do than the cork, rubber and fibre work above, and it is worth a conversation about your specific specification rather than a material chosen from a page.
Related: Electrical Gaskets
Specifying for volume production
Getting the material right is half of it. For a production programme the questions that decide the supplier are different ones.
Certification and traceability. Every batch traceable to the manufacturer’s material certificate, for the grade and thickness actually supplied. This is standard on RAM work, not an extra.
First article and PPAP. RAM supports PPAP submission, so the part can be signed off before the programme runs rather than argued about after it.
Cutting method, and why it changes the part. RAM cuts by die cutting, CNC knife, and water jet, with hand finishing where a part needs it. The choice is not arbitrary. CNC knife cutting suits soft sheet and short-to-medium runs with no tooling cost and fast design iteration. Die cutting is the right answer once a design is fixed and the volumes are steady. Water jet handles the harder and metal-reinforced materials that a knife cannot take. We have continuous capacity to manufacture very high volume consistently. We are a chosen supplier for huge UK and Global companies requiring continuous quality supply. We do not publish our customers but there is a reason we have been cutting gaskets at volume for 50 years, we are a trusted volume supplier to industry.
Call-off and stock holding. Scheduled call-off against an agreed programme, so material is held for your order, reducing lead times and allowing maximum flexibilty for the components you need to be cut at the right time.
Material range. RAM stocks and manufactures from over 1,200 different grades of gasket material, and cuts to any named material a drawing calls up. If your specification names a grade, we will supply the correct material.
Quality system. BSI ISO 9001:2015, and ADS SC21 for aerospace and defence supply chain performance.
Related: Volume & OEM Gasket Supply
Ask us to quote your volume
RAM Gasket Solutions has been manufacturing custom gaskets and seals in the UK since 1973. If you are specifying gaskets for transformers, switchgear, enclosures or cooling plant — whether that is a fixed drawing, a sample, a .dxf, or a description of the joint and the fluid — our technical team will match the material and quote the volume. We are consistently cutting gaskets in 1’s, 100’s and 1000’s, for our customers weekly.
Send us your specification · Use the Material Selector — or send a drawing, sample, .dxf or .pdf and we will come back with a material recommendation and a price for your quantities.