Vacuum Heat Treatment Furnace Cases: Protection for Hot Zones & Pump Sets

A vacuum heat treatment furnace hot zone is a textbook "light but brittle" assembly. Graphite heating elements, graphite felt and rigid carbon-felt insulation, molybdenum or tantalum radiation shields and a water-jacketed vessel wall all cooperate to create the thermal envelope. The pump set that serves it is normally a cascade of rotary-vane, Roots, dry screw or diffusion stages, with rotor-to-stator clearances that live permanently in the 0.05 to 0.15 mm band. Both families share one trait: individual pieces are rarely heavy, but their geometry retention and their fracture behaviour are unforgiving. A single 30 g shock can snap a graphite heating rod in two or drag a Roots rotor against its end plate.

JUNZHIJIA's protection principle for vacuum furnace components is that packing is not "wrapping things up" — it starts by quantifying the allowable acceleration and allowable distortion of every fragile class, then decouples each class dynamically from heavy and rigid neighbours using compartmented supports. In other words, the case has to be promoted from container to isolation system, and the foam from filler to calculable damping element. This article works through the hot zone, the shields, the pump set, seals, clean liners, port protection, moisture control, test validation and arrival acceptance in sequence, giving an executable structure at each step.

Table of Contents

• Fragility Limits of Graphite Heating Elements: Deriving Support Layout from Allowable Acceleration
• Buckling Risk in Thin Heat Shields: Clamping and Interlayer Gap Preservation for Molybdenum and Tantalum
• Matching Lifting Lugs and Stacking Load Paths on the Hot-Zone Frame
• Preserving Pump Rotor Clearances: Isolated Pump Compartments and Axial Stops
• Oil Drain-Down and Oil-Mist Isolation for Roots and Rotary-Vane Pumps
• Light-Shielded Sub-Packing and Compression Limits for FKM and FFKM Seals
• Cleanroom-Compatible Liner Selection: Low-Outgassing Foam and Silicon-Free Barrier Film
• Fragile-Part Compartments for Vacuum Gauges and Thermocouples
• Port Protection for CF/KF Flange Knife Edges and Quick-Connect Fittings
• Moisture Control and Desiccant Sizing for Long Ocean Voyages
• Transport Test Matrix: Combined Vibration, Drop and Stacking Validation
• Unpacking, Cleanroom Transition and Acceptance Criteria on Arrival
• Frequently Asked Questions FAQ
• Conclusion and Related Reading

Fragility Limits of Graphite Heating Elements: Deriving Support Layout from Allowable Acceleration

Graphite heating rods, graphite cloth heating bands and CFC (carbon-fibre-reinforced carbon) heating beams typically show flexural strengths between 30 and 60 MPa with a failure strain below 1 percent. There is no plastic plateau. Once stress crosses the elastic limit, the part fractures; structural steel would yield and deform first, graphite simply cracks.

Translating that into packaging language takes two conversions. The first is stress. For a 20 mm diameter, 2000 mm long graphite rod treated as a simply supported beam in three-point bending, stress follows 3FL/(2bh²). At a 400 mm support pitch carrying a 50 N concentrated load, peak bending stress is roughly 7.5 MPa. Widen the pitch to 800 mm and the same load doubles the stress to about 15 MPa, consuming the safety factor almost entirely. The second conversion is acceleration. In ISTA 3A, a 1 m drop can produce peak accelerations of 40 to 60 g. If the cushion attenuates that to 15 g, a 1.2 kg graphite rod momentarily carries an inertial force near 180 N, far above what its ends can tolerate as a point load.

So the support logic reduces to a single rule: spread point loads into distributed loads, and shorten unsupported spans until they can no longer generate dangerous bending moments. In practice this means a continuous cradle along the full length, support pitch held at 300 to 400 mm, EVA or PE pads on the cradle faces compressed by only 15 to 25 percent, and absolutely no unsupported ends. Strapping must never be cinched across the middle of a graphite rod, because a strap is a textbook concentrated load.

One further caution: graphite felt and CFC parts are extremely sensitive to oil contamination. Where a consignment mixes oil-lubricated items, follow the compartment logic described in carbon fibre production line component cases to isolate carbon parts from oil-bearing ones. If the raw material ships as powder rather than solid, the sealing and inerting approach in metal powder storage protective cases is the better reference.

Buckling Risk in Thin Heat Shields: Clamping and Interlayer Gap Preservation for Molybdenum and Tantalum

Metal heat shields act as the reflector of the thermal field. Common materials are molybdenum, tantalum, tungsten and stainless steel, with individual sheet thickness between 0.2 and 1.0 mm. Interlayer spacing normally sits at 8 to 15 mm across 10 to 30 layers. This stack is acutely sensitive to compression: once one layer takes a plastic crease, local emissivity and reflection angle shift together, thermal uniformity wanders by more than plus or minus 5 percent, and workpiece hardness scatter after quenching widens measurably.

The most common packaging mistake is assuming that wrapping the whole shield stack in soft foam is safe. The opposite is true. Foam wrapping creates a uniform external pressure, and a thin-walled cylinder's critical buckling load under external pressure is far below what it can carry in-plane. The correct approach is a shaping ring: a rigid PET or PP ring sized to the stack outside diameter, with 3 to 5 mm of soft padding bonded to its inner face, so the stack is braced radially rather than gripped. Axially, two carrier plates with locating steps clamp the stack; step depth is 2 to 3 mm less than stack height to leave room for thermal expansion and assembly tolerance.

Interlayer spacing survives only if the three equispaced distance pillars stay in place. Keep the original pillars during transport. If the stack ships disassembled, temporary distance blocks must be added inside the packing, together with a disassembly note telling the site to remove them before loading the furnace. Field data shows that shield stacks shipped without temporary blocks typically show more than 2 mm of spacing scatter after an 800 km road leg.

Brazing and sintering furnaces use shield stacks of very similar construction, so the shaping-ring practice described in brazing furnace component cases transfers directly. For coastal projects, set the external metal hardware's corrosion class using the mapping in salt spray corrosion testing and protective cases.

Matching Lifting Lugs and Stacking Load Paths on the Hot-Zone Frame

A hot-zone frame complete with retort, water jacket and flanges usually weighs between 200 and 2000 kg. The mass itself is not extreme, but if the lifting lugs and the case's load-bearing beams do not share the same force line, the entire load transfers into in-plane shear of the case wall — precisely the weakest mode for an injection-moulded shell.

Design to a three-point alignment: lug, beam, foot. The base carries two full-length beams whose projection coincides with the lifting lugs, each beam at least one twelfth of case height. Local ribs are added on the inside of the wall behind every lug, at no less than 1.6 times the nominal wall thickness. Anti-slip feet sit at the four base corners with 70 to 85 Shore A hardness, balancing friction against vibration attenuation.

On stacking, a hot-zone assembly should generally travel as the bottom tier. If a second tier is unavoidable, only rigid frame parts or empty cases may go above, and the top load must stay under 500 kg. Tier count is verified against residual deflection after 48 hours of static load, with case-top sag limited to 1/200 of the span.

A frequently overlooked detail is the centre-of-gravity mark. The centre of gravity of a hot-zone assembly rarely sits at the geometric centre of the water jacket; it usually shifts toward the flange and door side. Mark the CG projection line and the lifting direction arrows on two adjacent faces and state the maximum permitted tilt angle in the shipping documents, normally no more than 15 degrees. Forklift tines must penetrate at least two thirds of the case length, and single-side lifting is prohibited. In practice, a meaningful share of vacuum furnace transport incidents trace back to single-side forklift lifts that twisted the frame — and once a frame twists, the door sealing face flatness never returns to design value.

Preserving Pump Rotor Clearances: Isolated Pump Compartments and Axial Stops

Rotary-vane rotor-to-end-plate clearance, Roots impeller-to-housing clearance and dry screw meshing clearance all sit between 0.05 and 0.15 mm. At that scale, any axial shock displacing the rotor by more than 0.1 mm leaves a score on the end face. Once scored, ultimate vacuum degrades from the 10⁻² Pa class to the 10⁻¹ Pa class and keeps deteriorating under hot operating conditions.

Three rules govern pump packing. First, each pump body gets its own compartment and never shares one with flanges, steel plates or wear liners. Second, the pump is hard-stopped both axially and radially, with 5 to 10 mm of EVA separating the stop from the body; stops are fixed to the case base with countersunk bolts and must not rely on foam compression alone. Third, inlet and outlet ports are plugged and the plugs mechanically secured so they cannot work loose and drop into the pump cavity during handling.

Relative placement inside the case matters as much. A hot-zone frame is a rigid heavy part; a pump is a precision light part. If both sit on the same horizontal layer, high-frequency frame vibration travels through the base plate into the pump on a road leg. The engineering answer is to put the pump set on a dedicated deck above or below the frame, separated by a 20 mm IXPE isolation mat that breaks the transmission path.

Oil Drain-Down and Oil-Mist Isolation for Roots and Rotary-Vane Pumps

Oil-sealed vacuum pumps must be drained before shipment. This is not optional. Residual lubricant sloshes with vehicle motion and seeps from sight glasses, exhaust ports and shaft seals, contaminating foam, corroding flange faces and forming oil mist under hot conditions that migrates into nearby graphite felt. Once graphite felt absorbs oil, it outgasses for hours during the heat-up ramp and holds the vacuum level down.

Drain-down has three parts. First, drain until dripping stops, with zero residual level in the sight glass. Second, fit an absorbent pad over the exhaust port and secure it with a tie; use non-woven polypropylene absorbent rather than loose fibre wadding so nothing sheds. Third, immediately seal the drained pump in its own barrier bag with a 5 g silica sachet to stop the shaft seal from taking up ambient moisture.

Structurally, leave a 3 to 5 mm gap between the absorbent pad and the pump body. Pressing the pad against the body wicks away the protective rust-preventive film and creates corrosion spots right at the shaft seal.

It also pays to distinguish transport attitude from operating attitude. Some Roots and diffusion pump oil reservoirs only avoid overflowing into the pumping chamber in one specific attitude. Mark the transport orientation on the packing and, where necessary, wedge the body into its design attitude rather than laying it flat. Diffusion pumps deserve particular care: the jet tower and baffle stack are cantilever structures, and a long voyage on its side lets internals creep under their own weight, showing up as lost pumping speed and oil back-migration on arrival. Standard practice is an "arrow up" mark plus attitude locking inside the case, and a note in the shipping documents requiring a 4 hour settling period before power-up.

Light-Shielded Sub-Packing and Compression Limits for FKM and FFKM Seals

Vacuum furnace seals are mostly fluoroelastomer (FKM), with perfluoroelastomer (FFKM) for high-temperature or aggressive service and silicone for some low-temperature flanges. Two degradation mechanisms dominate in storage: ozone and ultraviolet ageing, and compression set. The first comes from light and air, the second from stacking pressure.

Two countermeasures follow. For light, seals go into opaque aluminium-foil laminate bags or black PE bags, with no sulphur- or chlorine-bearing materials inside and never in the same bag as an oiled pump body. For compression, the packaging box must keep per-piece pressure below 0.05 MPa when stacked, and continuous stacking beyond five tiers is not acceptable. Large-diameter O-rings above 500 mm are best hung or folded in a figure-eight, with a soft sleeve supporting the fold so no permanent crease forms.

Batch control is equally important. Label every bag with material, hardness, inside diameter, cord diameter, cure date and recommended service window. FKM normally stores for 5 to 8 years, but in a package that is not light-shielded and an environment that stays above 30 degrees Celsius, the practical window can shorten to under 3 years.

Cleanroom-Compatible Liner Selection: Low-Outgassing Foam and Silicon-Free Barrier Film

Hot zones are usually wiped down and nitrogen-purged before loading, and in some cases assembled inside a cleanroom. That makes the outgassing behaviour of the liner a selection criterion. Low-molecular-weight plasticisers, silicone mould-release agents and flame-retardant dust all release under vacuum, contaminating the chamber and stretching pump-down time.

EPE pearl foam outgasses little and recovers well, which suits cradle padding. EVA foam has low compression set and high load capacity, which suits load-bearing layers under heavy parts. IXPE cross-linked polyethylene foam has a high closed-cell ratio and good moisture-vapour resistance, making it the right choice for combined isolation and moisture-barrier layers. What to avoid is foam produced with silicone mould release and foam formulated with halogenated flame retardants.

For barrier film, prefer silicon-free PET/aluminium-foil laminate or PE barrier film. Surfaces that touch graphite parts and molybdenum shields never use siliconised release paper. Before loading, every liner should be wiped with alcohol and dried at 60 degrees Celsius for 2 hours to drive off adsorbed water and surface additives.

The full clean-packing routine, including wipe agents, heat-seal parameters for barrier bags and cleanroom airlock staging, is covered in cleanroom equipment protective cases. Where pump vibration is the dominant risk rather than cleanliness, the isolation-mat selection table in shockproof protective case structures is a useful companion.

Fragile-Part Compartments for Vacuum Gauges and Thermocouples

Vacuum gauges, whether Pirani or ionisation type, are glass-to-metal sealed assemblies with low mechanical strength and high shock sensitivity. Tungsten-rhenium and type K thermocouples commonly use 0.2 to 0.5 mm wire, and their ceramic insulating beads crack when bent. Failures in this class are often invisible: the part looks intact but the vacuum seal already carries a micro-crack.

The compartment design principle is one gauge per cell, with 2 mm EPE on the cell walls and a 5 mm recessed step in the cell floor so the gauge neither rolls nor presses against its flange. Thermocouples are fixed straight, lying in grooves on a one-piece carrier, with the groove radius slightly larger than the wire diameter and low-tack tape spanning the groove. Never coil a sheathed thermocouple into a loop; a coil radius under 40 mm puts micro-cracks into tungsten-rhenium wire.

Thermocouples with ceramic insulators benefit from retaining bosses on both sides of the groove to stop axial migration. Place all small-part compartments in the upper-middle region of the case, away from the base load path and the top stacking zone.

Ionisation and Pirani gauges have one further requirement. The glass-to-metal seal is the most fragile location: a shock first produces a hairline crack that is difficult to see, and in service the symptom is a chamber that will not pump down or a reading that drifts. In packing, hold the gauge in a flange-bearing, bulb-free attitude, with the flange rim seated on an EPE ring support and the glass bulb touching no hard surface at all. If a protective cage ships with the gauge, keep at least 3 mm clearance between cage and bulb. At incoming inspection, look past the exterior and examine the seal ring under magnification for fine cracks, then run a hold test to confirm leak-tightness.

Port Protection for CF/KF Flange Knife Edges and Quick-Connect Fittings

System leak rate is acutely sensitive to flange knife-edge condition. CF (ConFlat) flanges seal through a copper gasket against a 15 to 30 degree knife edge; a 0.1 mm deep indentation on that edge can degrade leak rate from the 1×10⁻¹⁰ Pa·m³/s class to the 1×10⁻⁸ Pa·m³/s class. KF (NW) flanges seal on an O-ring against a flat face, and a scored face is equally fatal.

Protection proceeds in three steps. First, cap the ports. CF flanges get dedicated blank plates with rubber backing, clamped by four bolts torqued evenly between 5 and 15 N·m depending on flange size; single-point over-torque is forbidden. KF flanges get a clamp and blank with 3 mm of soft padding on the inner face. Second, protect threaded ports with plastic plugs screwed in no deeper than the thread length, so load transfer cannot damage the threads. Third, protect pneumatic and water quick-connects with caps rated to resist a 20 N side load without coming off.

Pack all port protectors in a separate bag and include a port-protection checklist listing quantities and position numbers. That makes reconciliation at site straightforward and prevents a forgotten cap from ending up inside a gas line.

Another port class gets overlooked: viewports and electrode feedthroughs. A quartz viewport slides along its sealing face under side load, so support the window rim on an annular soft pad and leave 2 mm of expansion clearance on each side. Ceramic insulators on electrode feedthroughs crack under bending, so slip a PP protective tube over the feed rod and locate both ends with soft plugs. For feedthroughs that ship with cable attached, never wind the cable around the rod; coil it separately in a dedicated cable channel with a bend radius of at least eight times the cable outside diameter.

Moisture Control and Desiccant Sizing for Long Ocean Voyages

Vacuum furnace components ship by sea to Southeast Asia, the Middle East and Europe, with voyages of 20 to 45 days crossing several climate bands. Container temperature swings more than 20 degrees Celsius between day and night, and when internal air drops below dew point, moisture condenses on graphite felt and molybdenum shields. Graphite that has absorbed water outgasses for tens of hours, and damp molybdenum can pit.

Control uses three barriers plus a calculated desiccant load. The part-level barrier puts graphite parts, shields and seals into individual barrier bags. The case-level barrier requires an O-ring-sealed shell rated IP65 or better to IEC 60529, fitted with a pressure equalisation valve so the differential from temperature swings cannot push the seal open. The shipment-level barrier adds an aluminium-foil vacuum film over the whole case or desiccant blankets inside the container.

Size the desiccant against free internal volume: silica gel at 200 to 300 g/m³, or calcium chloride composite at 100 to 150 g/m³. For voyages beyond 30 days or routes crossing the equator, take the upper figure and add 20 percent margin. Place one or two humidity indicator cards inside, positioned near a viewing window so the reading can be checked without opening the case.

Transport Test Matrix: Combined Vibration, Drop and Stacking Validation

Passing a single test does not mean the pack survives real logistics. Random vibration on the road, drop impact during handling and long-term static pressure in the warehouse all act on the same consignment, and failures tend to be cumulative rather than isolated.

Use ISTA 3A for parcel distribution or ISTA 3E for unitised loads as the primary protocol, supported by the GB/T 4857 series and ASTM D4169. Random vibration runs a PSD profile at 1.0 g rms vertical and 0.5 g rms horizontal for 60 minutes each. Drop height follows gross weight bands: 760 mm up to 20 kg, 610 mm from 20 to 40 kg, 460 mm above 40 kg. Stacking applies 1.5 times the actual stacking load for 48 hours.

Failure criteria must be fixed before testing, never adjusted afterwards. Three hard criteria suit vacuum furnace parts: no visible cracking in graphite, shield out-of-plane distortion of 1.5 mm or less, and no scraping felt when the pump rotor is turned by hand. Failing any one of them sends the design back to the support layout rather than to a thicker foam slab.

Unpacking, Cleanroom Transition and Acceptance Criteria on Arrival

Unpacking follows a fixed sequence: outside first, then inside, then cleanliness. Only after confirming no through-wall damage, no severe bulging and an unchanged humidity indicator may the case be opened. Open in a dust-free, oil-free area, ideally peeling the outer packaging in the cleanroom anteroom so road dust is not carried into the assembly zone.

At the cleanroom boundary, open the part-level barrier bags inside the airlock, wipe surfaces first, then transfer to the assembly station. For graphite parts and shields, inspection focuses on ends and edges: chipped rod ends and creased shield rims are the first places to reveal a problem. Pump sets are turned by hand immediately on unpacking to feel for scraping, and axial end float is measured and compared with the factory record.

Fix the acceptance criteria into a form: case sealing class and pressure equalisation valve condition, desiccant and humidity indicator status, graphite part appearance and dimensions, shield interlayer spacing, pump rotor freedom, returned port-protector count and completeness of shipping documents. Any failed item is tagged and quarantined rather than released to assembly. For these three-piece deliveries, the cases, liners and document sets are produced and inspected to project drawings by Kexin New Materials (Guangdong) Co., Ltd.

Frequently Asked Questions FAQ

Q: Can graphite heating elements be wrapped directly in ordinary PE foam?

A: Direct wrapping is not advisable. Ordinary EPE pearl foam has a low compression modulus, so while it does convert a point load into a face load, it cannot restrain lateral movement; repeated vibration then lets a graphite rod knock against adjacent hardware until an end chips. The workable sequence is EPE as the face-contact cushion, then a cradle with locating grooves that constrains the rod, with support pitch held between 300 and 400 mm and no unsupported ends whatsoever. On slender parts, add lateral retaining plates so the rod cannot migrate along the case length. Cut cradle grooves slightly oversized and line them with 3 mm EVA so the rod rests on a compliant surface instead of a machined edge. Never cinch a strap across the middle of a rod, because a strap is a textbook concentrated load. Wrap-test the finished assembly and inspect both ends for chipping before releasing the batch, and record the cradle pitch on the packing drawing so repeat orders reuse the same geometry.

Q: How much heat-shield distortion justifies replacement?

A: Judge the nature of the distortion rather than a single number. Local out-of-plane depressions deeper than 1.5 mm inside the effective reflective zone normally require replacement, because the local change in emissivity disrupts thermal uniformity directly and shows up later as wider hardness scatter across the workload. Where distortion sits in the edge clamping zone and interlayer spacing is unaffected, reshaping followed by re-evaluation is acceptable. For measurement, stand the stack on a surface plate and check adjacent-layer gaps with a feeler gauge; scatter beyond 2 mm is out of tolerance. Also confirm the distance pillars are present and square, since a bent pillar silently changes several gaps at once. Replacement cost is far lower than the cost of reworking a batch ruined by an uneven thermal field, so whenever the reflective zone is involved, the decision rule should lean toward replacement rather than repair. Keep the pre-shipment inspection record with the shipment so the receiving site can compare distortion figures against the baseline taken before packing.

Q: Must vacuum pumps be drained of oil before shipment, and what about dry pumps?

A: Oil-sealed pumps must be drained completely, to the point where dripping stops and the sight glass shows no residual level. Leftover oil seeps from shaft seals, sight glasses and exhaust ports during handling, contaminates foam and flange faces, and forms a mist under hot conditions that graphite felt then absorbs, causing prolonged outgassing after loading. Dry screw and claw pumps have no oil sump but still need attention. Plug and mechanically secure the inlet and outlet ports so a loose cap cannot enter the pumping chamber. Clean residual dust and condensed process gas from rotor surfaces, then measure and record rotor end float against the factory figure. Dry pumps in fact carry a higher dust-control requirement than oil pumps, because ingested grit accelerates clearance loss. Never turn a dry rotor by hand until the ports are confirmed clear and the transport locks have been released. Photograph the oil sight glass and the sealed exhaust port before the case is closed, so any seepage found on arrival can be traced to a specific stage of the journey.

Q: What cleanliness class does vacuum furnace packing have to meet?

A: For hot zones and pump sets, ISO Class 8 is the practical floor for the packing environment; hot-zone parts destined for semiconductor or optical coating duty should move to ISO Class 7. The class is delivered by the part-level barrier bag and the environment in which it is sealed, not by the case itself. Parts are bagged in the clean environment, then vacuum-drawn or nitrogen-flushed and heat-sealed. The case only needs a dust-free inner wall with no mould-release residue, and its outward sealing class is a separate question governed by IP65 or better to IEC 60529. Liner materials must meet low-outgassing requirements, which rules out foam made with silicone release agents and formulations using halogenated flame retardants. Where possible, ask the foam supplier for a batch outgassing statement. Document the wipe agent, drying schedule and heat-seal parameters so the routine is reproducible from batch to batch, and train the packing operators against that document rather than against verbal guidance. A short video of the sealing step is often the cheapest quality control measure available.

Q: How should desiccant be sized for a shipment to Southeast Asia?

A: Start from free internal volume: silica gel at 200 to 300 g/m³, or calcium chloride composite at 100 to 150 g/m³. Southeast Asian routes typically run 15 to 30 days and cross subtropical and equatorial bands, so take the upper figure and add 20 percent margin. A pressure equalisation valve is mandatory; without it, day-night temperature differentials make the case breathe in damp air and the desiccant is exhausted long before arrival. Place two humidity indicator cards, one near the viewing window and one at the base, so you can tell whether condensate has pooled at the bottom. Keep at least 100 mm between barrier-bagged graphite and the desiccant packs so nothing presses on a bag seam. If the itinerary includes more than one transhipment, or the container may sit on a quay for several days, add a further 10 percent and specify desiccant blankets for the container itself. Whatever the calculation returns, record the figure on the packing list so the next shipment on the same route starts from a validated number rather than an estimate.

Q: Can a damaged CF flange knife edge really change the leak rate?

A: The effect is direct and substantial. CF flanges form a metal-to-metal line seal between the copper gasket and the knife edge, and an indentation deeper than 0.1 mm can degrade leak rate from the 1×10⁻¹⁰ Pa·m³/s class to the 1×10⁻⁸ Pa·m³/s class, with further deterioration under bakeout conditions. Packing must keep the knife edge out of the load path. Use a dedicated blank plate with rubber backing, torque the bolts evenly between 5 and 15 N·m in a diagonal sequence, and never tighten one bolt fully first. Flange faces must not be stacked directly; insert 3 to 5 mm of soft padding between layers and label the stack so the protective plates return with the hardware. If bright marks appear on a knife edge after transport, run a helium leak check before deciding whether to dress the edge or replace the flange outright. On high-value chambers, ship a spare gasket set with the hardware so a damaged flange does not stall commissioning for weeks.

Q: How do I decide lifting points and stacking tiers for very heavy hot-zone assemblies?

A: Lifting points belong at the frame's original lifting lugs, and the case base beams must project to coincide with those lugs so the force path runs lug, beam, foot in one line. Tier count is set by residual deflection after a 48 hour static load test, with case-top sag limited to 1/200 of the span. Practical values: hot zones up to 300 kg allow three tiers; 300 to 800 kg allows two; 800 to 1500 kg allows two with three base beams and a top load under 500 kg; anything above 1500 kg travels as a single tier on a steel base frame. Mark the centre of gravity on two adjacent faces, state the maximum tilt angle in the shipping documents, and require forklift tines to penetrate at least two thirds of the case length with no single-side lifting. Where the frame is close to a tier limit, reduce the load rather than relying on the case, because a twisted hot-zone frame will not return to its designed door-sealing flatness.

Q: What lead time and minimum order quantity apply to a custom vacuum furnace case?

A: Lead time depends on whether tooling is required. Using an existing standard mould, the run from drawing approval to first shipment is typically 15 to 25 days. A new injection mould adds 30 to 45 days for toolmaking and trials, including one or two rounds of trial-shot inspection. Minimum order quantity is banded by case type: standard sizes usually start at 50 to 100 units, while a newly tooled size generally starts at 200 to 300 units so the tooling cost can be amortised. If the project is still at prototype stage, bridge with a standard case plus a custom EVA liner, then start tooling once volumes are confirmed.

Conclusion and Related Reading

Vacuum furnace parts fail in transit when everything already looks packed. Quantify allowable acceleration and distortion first, then decouple each part class with compartments, cradles, stops and isolation. JUNZHIJIA builds liners, tooling and document sets to your drawings.

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