Tannery Machine Cases: Transport Protection for Shaving & Embossing Units

Whether the fibre surface of a hide leaving a drum or horizontal shaving machine looks clean depends on a fraction of a millimetre: the clearance between each blade edge on the helical knife shaft and the fixed mesh knife. Whether an embossing pattern plate still holds a crisp relief after three hundred compression cycles at 80 °C depends on whether anything hard ever touched the roller face. Neither component is expensive in itself — a knife shaft plus holder assembly runs to little more than a hundred thousand yuan — yet in a tannery, replacing a chipped shaft means idling an entire wet-processing line while spare parts are sourced. So the real question for a machine being relocated is not whether it will survive a drop. It is whether it can be installed and test-run the moment it arrives on site. Tannery transport damage is rarely caused by violent impact; it accumulates slowly. Humidity inside the case climbs during the first fortnight, chrome liquor residue gradually attacks the passivation film, the anti-rust oil on the blades is neutralised by sulphide remnants, and an unsupported roller face picks up an acrylic press mark from road vibration.

JUNZHIJIA builds tannery machine cases on one principle: isolate chemical media from precision edges and roller faces in physically separate compartments, and specify humidity, temperature and residue parameters as verifiable numbers rather than experience, so that arrival acceptance becomes a documented inspection instead of a subjective glance.

Table of Contents

• Vibration Sources and Dynamic Balance of the Helical Knife Shaft
• Chipping Rejection Criteria and When to Change Blades
• Passivation and Isolation of Chrome Tanning Liquor Residues
• Preventing Pressure Marks and Thermal Shrinkage on Embossing Roller Ends
• Rust Prevention for Blades in High-Humidity Wet Shops
• Sulfide Tanning Agents: Odour Control and Sealing Requirements
• Alignment Accuracy When Changing Pattern Plates
• Removing and Storing Hydraulic Cylinders and Seals
• Preserving the Gap Between Mesh Knife and Pressure Knife
• Packaging Prohibitions for Chrome-Contaminated Wastewater
• Compartmented Rust Protection for Blades, Holders and Residual-Forming Parts
• Arrival Inspection and Documenting Chipping Claims
• Frequently Asked Questions FAQ
• Conclusion and Related Reading

Vibration Sources and Dynamic Balance of the Helical Knife Shaft

The heart of a shaving machine is a transverse helical knife shaft carrying blades arranged in a spiral. The blades rotate with the shaft, and a shearing plane forms between each edge and the fixed mesh knife, cutting and pushing outward the collagen fibre bundles released by liming and unhairing. The shaft sits in bearing housings at both ends, driven at one end by a sprocket or gear train. This assembly is extremely sensitive to vibration: once dynamic balance is disturbed, vibration travels along the shaft into the bearing housings, then into the frame and into the floor, and the shaft-to-bearing clearance is cyclically amplified across a band from a few tens of hertz to several hundred.

Transport is not the only source. If the owner lifts the bare shaft with wire rope, the dents pressed into the journal become a periodic excitation once it spins. If balance weights were shifted during removal and not refitted to their marked angle, the result is textbook dynamic imbalance. If blade stacking sits on a flange face with residual rust scale, a 0.05 mm face step accumulates across several dozen blades into an overall offset. Each of these may still sit inside factory tolerance, yet after 500 km of road transport under continuous random vibration, the symptom seen at commissioning is a doubled vibration reading at the holder and a sharp rise in chipping rate.

For a slender precision part such as a knife shaft, a single uniform foam wrap is never adequate. Support must be applied at two or more points positioned close to where the bearing housings actually sit, shortening the unsupported overhang to what the case can tolerate. The mechanics are identical to the multi-point support logic described for Spindle Protection Cases, except that a spindle is controlled for coaxiality while a knife shaft is controlled for radial runout.

Chipping Rejection Criteria and When to Change Blades

Blade failure is not gradual; it is sudden. Once a chip appears, the notch is enlarged by every subsequent hide, fibres are pulled into filaments at the gap, and a comb-like defect appears on the finished surface. The judgement is therefore not about whether chipping occurred, but about where it must stop the line.

Common shop practice grades chipping by notch length combined with depth. The working rule is straightforward: any single notch longer than 3 mm, or deeper than one third of the edge thickness, is scrap and the blade must be changed. Notches between 1 mm and 3 mm located behind the cutting edge can be dressed out, but symmetry must be re-checked afterwards. Any visible notch on the leading edge falls straight into the change sequence, because a leading-edge defect can only grow. Beyond geometry, a furrow deeper than 0.15 mm running along the cutting direction, step-like collapse on the back of the edge, and a blue temper band across the blade belly caused by overheating all redistribute hardness, and such blades belong in the change queue rather than in service.

Replacement timing can also be driven by accumulated work rather than by visible defects. In conventional vegetable-tanned leather shaving, a single blade typically reaches the end of its stable working window somewhere between 15,000 and 30,000 standard hides of 0.6 to 0.9 square metres, depending on hide thickness, shaving thickness and line speed. Past that point the edge dulls even with no visible defect, and dulling raises both cutting force and heat generation. Good practice is to log hide counts per blade and swap to a spare at the upper limit rather than waiting for a chip. The documentation shipped inside the case therefore includes a blade service ledger; the format for such records is covered in Case Repair and Spare Parts Documentation.

Passivation and Isolation of Chrome Tanning Liquor Residues

Chrome tanning is the defining process of the industry, and the hexavalent chromium in the liquor is both strongly oxidising and toxic. After equipment has run in chrome pits, spray booths or wet finishing stations, metal surfaces carry a chrome-bearing wet film and crystalline deposit. That residue must be treated before transport, otherwise three problems arise at once: corrosion, loss of protection, and exposure risk for anyone handling the case.

The purpose of passivation is to reduce the reactive chrome to a stable trivalent form and, at the same time, to produce a continuous inhibiting film. Two routes are common in practice. The first is reduction, using sodium bisulphite solution at low temperature, followed by thorough rinsing of the reaction products. The second is passivation combined with sealing, using phosphate or chromate solutions that form a conversion film on the surface. Both routes share one mandatory requirement: rinsing and drying must follow, because leftover passivation solution is itself a fresh corrosion medium.

The most frequently missed prohibition here is aluminium compatibility with chrome residue. Acidic chrome liquor dissolves aluminium rapidly, so chrome-bearing parts must never be wrapped in aluminium foil and must not share a case with aluminium liners, aluminium tools or aluminium tape. This rule is often buried beneath a generic moisture-first instinct, yet the two requirements collide: aluminium foil performs superbly against moisture, and that is precisely why it gets misused. Shell material and coating selection is discussed in Corrosion-Resistant Enclosure Selection, but note that article addresses the enclosure body while this one addresses how the inner cavity isolates chrome media; the two are complementary rather than interchangeable.

Preventing Pressure Marks and Thermal Shrinkage on Embossing Roller Ends

The working elements of an embossing press are a clamping pair: an embossing roller and a smooth roller, with leather fed between them into the heated zone. The pattern plate carried on the embossing roller presses grain into the hide under combined pressure and temperature. Embossing rollers are commonly steel or bronze based with a hard chrome plating. The surface is hard, but the plating is brittle, and any hard point contact leaves a permanent mark.

Marks come from three mechanisms. The first is point loading in transit: when a pattern plate is stored touching the roller face with only partial contact and no overall support, the weight of the internal parts concentrates onto a few support points and burns a mirror-flat mark or a matte patch into the plating. The second is foam compression: EPE foam under sustained high load takes a permanent set, and once the load is released it does not recover, leaving a texture on the roller face that mirrors the foam surface. The third is frictional micro-slip: vibration lets the roller face and the plate shift slightly during transit, and the hard plating rubs itself into furrows.

Thermal shrink is frequently misdiagnosed as a manufacturing defect on site. An embossing roller runs at 60 to 90 °C, and steel expands at roughly 11 to 13 × 10⁻⁶ per kelvin, so a 1.2 m barrel lengthens by about 0.9 mm between ambient and 80 °C before contracting on cooling. If a pattern plate has been hard-clamped against the roller offline, thermal expansion is restrained and the plate is left in residual stress, which can print the plate edge onto the very first hide after start-up. The correct stored attitude is a 1 to 2 mm gap between plate and roller face with no axial constraint, leaving the thermal cycle free to move.

Rust Prevention for Blades in High-Humidity Wet Shops

Wet-processing halls typically sit between 70% and 90% relative humidity year-round, and coastal tanning bases hold above 90% reliably through the monsoon season. When a knife shaft, holder or embossing roller is sealed with residual moisture still on it, a high-humidity micro-environment forms inside the case within days.

The corrosion physics has clear thresholds. Carbon steel begins to corrode in the presence of a water film at around 60% relative humidity, but the effective threshold drops sharply when residues are present: chloride, sulphate residue and exhausted hydrophilic inhibitors can push the onset down below 40%. Tannery metal surfaces are enriched in exactly those species — sulphates from tanning agents, chloride from process water, phosphate from cleaning chemicals. This is why standard anti-rust packaging that works for ordinary steel often fails in a tannery.

Distinguish protection in transit from protection in storage. Transit relies on materials: vapour-phase corrosion inhibitor paper and coatings, an aluminium-plastic barrier, silicone or molecular-sieve desiccant. Storage relies on management: never stack directly on the floor, leave ventilation gaps, and prevent condensation. A case pulled straight from a cold store into a 30 °C summer evening will condense water on its inner walls; this in-case condensation is a more common cause of corrosion than transit vibration. Humidity and stacking detail is covered in Warehouse Stacking and Moisture Control. One more point: humidity indicator cards belong inside the case. Readings taken outside the case have no relationship to the internal micro-environment, and that mistake is made routinely on site.

Sulfide Tanning Agents: Odour Control and Sealing Requirements

Unhairing and liming rely heavily on sodium sulphide and compounded sulphide systems. These materials are volatile, alkaline and carry a strong rotten-egg odour. Sodium sulphide meeting acid residue on a machine surface generates hydrogen sulphide.

That produces three requirements with no counterpart in ordinary machinery packaging. The first is sealing: if a sulphide-contaminated part is packed in a conventional breathable structure, gas escapes and odour contaminates both the case interior and the surroundings. Odour complaints during transport usually originate here. The second is material compatibility: sodium sulphide attacks aluminium, zinc and galvanised fittings aggressively, so sulphide-bearing parts must not be bagged with aluminium liners or galvanised fasteners. The third is gas volume headroom: if residual liquor keeps volatilising inside a sealed case and absorbs environmental water, internal pressure rises, so the case needs breathing capacity or a designed void.

For sulphide-contaminated parts, the recommended packing is a double barrier bag with an adsorbent layer: the inner bag in direct contact with the metal is a barrier bag applied after inhibition, and an outer diffusion-barrier bag is sealed over it, typically by heat sealing the neck. Even if the inner bag has a pinhole, the outer layer retains the gas. The cushioning in this scenario must be closed-cell, meaning polyethylene, expanded polypropylene or cross-linked polyethylene foam, because open-cell EPE and EVA absorb sodium sulphide liquor and become a lasting source of odour and corrosion after unloading. The trade-off between those foams is examined in EPE and EVA Foam Comparison.

Alignment Accuracy When Changing Pattern Plates

Pattern plates on an embossing press are consumables. Depending on leather type and pattern life, a set lasts anywhere from a few months to a year. Both new machine delivery and plate replacement on an older press are therefore high-frequency transport scenarios. The plate itself is usually a thin sheet of brass, zinc alloy or stainless steel, fixed to the roller face by screws or dowel pins.

The transport difficulty is not strength; it is holding positional accuracy. Once screw-hole and dowel-hole position tolerance is destroyed in transit, the plate mounts out of position and the pressed grain shows uneven depth and registration error. This is a small-looking damage: a 0.5 mm shift at one hole is invisible by eye, yet accumulated across the plate it produces 1 to 2 mm of pattern misregistration.

Complementing this is the requirement that alignment accuracy arrives with the case documents: plate changeover records, the pattern identifier of each plate matched to its roller position, and screw torque specifications. Without those three items, a plate goes on with the wrong pattern depth and the shop ends up tracing the problem back to the wrong part. Packing logic for finished leather goods is comparable to Leather Goods Cases, but a pattern plate is a precision metal part, so both the cushioning grade and the rust protection requirement are one class higher.

Removing and Storing Hydraulic Cylinders and Seals

The compression action of an embossing press is normally driven by a hydraulic cylinder. When the machine is stripped for shipment, the cylinder is usually detached from the frame and packed separately, and detached hydraulic parts are the category most often handled on assumption. Once an oil seal or O-ring is released from compression it remains under strain; packed with no positional restraint at all, it develops a permanent set within weeks, and reassembly is guaranteed to leak.

Three actions follow removal. First, seal the ports: fit a dust cap plus a blank plate on the extended rod end so that knocks in transit cannot scar the sealing surface, and fit blank plugs in both cylinder ports, because debris entering a port goes straight into the system and can jam a spool. Second, restrain the rod: the rod must carry no radial load whatsoever. Lay the cylinder horizontally or suspend it vertically; never let the rod end take weight. If floor space forces a horizontal position, raise the rod end so the end cap carries the entire mass. Third, store seals separately: O-rings, U-cups and scrapers removed from the barrel go into a dedicated seal bag in a separate compartment so the body cannot press them out of shape.

Packaging detail for hydraulic and pneumatic items is set out more fully in Hydraulic and Pneumatic Component Cases; this section concentrates on the attitude and sealing requirements tied directly to embossing press assembly. Pressure equalisation valves are covered separately in Case Pressure Equalisation Valves, but note what that part does: it balances the pressure difference across the case so the shell does not deform. That is a different objective from retaining sulphide gas, and tannery machine cases are normally specified as sealed type rather than high-flow breathable type.

Preserving the Gap Between Mesh Knife and Pressure Knife

The shearing pair of a shaving machine has a moving half and a fixed half. The moving half is the set of blades on the helical knife shaft; the fixed half is the mesh knife, also called the pressure knife, bolted to the frame. The mesh knife is built from a number of parallel tooth bars stacked together, with the gaps between teeth forming the discharge channel. The clearance between pressure knife and shaft determines shaving thickness and how completely the fibre bundle is severed.

Failure of this clearance has nothing to do with machine vibration; it is caused by movement of parts inside the case. Two lift operations, one on loading and one on unloading, are enough to shift the whole set of pressure knife bars, and transit vibration can open the gaps between stacked bars. On site the machine is then assembled at the original 0.2 to 0.6 mm clearance. Too small and the blades strike the teeth, chipping instantly. Too large and the fibre is not fully severed, producing an uneven shave.

The governing principle for the pressure knife assembly is pack it in the assembled datum state: assemble it once at the works at the process clearance, mark the position, and restore to that mark after transit rather than re-setting the clearance on site. This logic travels well beyond rolling cutters, and the edge-protection reasoning in Abrasive and Consumable Parts Cases is worth reading alongside it, but the pressure knife pair adds one extra requirement: the assembly relationship between the two halves must be preserved, not merely the condition of each part.

Packaging Prohibitions for Chrome-Contaminated Wastewater

Machine sites always hold a little chrome-bearing wastewater and wash liquid: overflow residue from wet-processing pits, floor washings, and what is left in spray lines after draining. None of it may travel inside the machine case. The packaging stage owns two responsibilities: preventing residual liquid from being packed, and preventing already-contaminated packing material from being reused.

A container that has held chrome liquor is itself contaminated waste and should not return to other duties. A pattern common on tannery sites is to pour the liquid into a temporary drum and empty it back into the machine, and that loop carries residue into internal dead corners, which becomes a hidden source of corrosion later. For full-case packing, the media type, protection class, stacking layer count and post-opening handling instruction must be marked conspicuously on the outside; marking practice and stacking discipline are covered in Warehouse Stacking and Moisture Control.

Compartmented Rust Protection for Blades, Holders and Residual-Forming Parts

Everything so far has dealt with two families of risk, chemical and mechanical, and both land on the case structure through the same device: compartmentation. A typical tannery machine case is not built as large parts on one layer with small parts stuffed into the gaps. It is divided into independent cells organised by medium and by function.

Three structural points deserve emphasis. First, cells must be genuinely independent, achieved with an interleaved layer or a separate inner liner, not merely by placing different parts in different positions; parts migrate in transit, so isolation has to come from structure rather than from packing habits. Second, lining closure matters more than softness: in sulphide and chrome scenarios an open-cell foam absorbs residual liquor and becomes a persistent source of contamination, so closed-cell foam is preferable to a softer open-cell grade. Third, support stiffness and cushioning must be designed as separate layers: an outer cushion handles shock while an inner support restrains displacement, and separating them lets the support cavity fit closely without sacrificing impact resistance. The material differences between the foams themselves are covered in EPE and EVA Foam Comparison.

On shell sealing class and latch type, two different goals must be separated. Waterproofing and dust ingress call for a higher IP rating and a pressure equalisation valve, described in Case Pressure Equalisation Valves. Retention of escaping gas calls for continuous welds and a gasket running uninterrupted around the whole lid. Tannery machine cases usually need both, and in cells holding sulphide residue sealing takes priority over breathability.

Arrival Inspection and Documenting Chipping Claims

No matter how well the transport protection is executed, arrival re-inspection cannot be removed from the contract. The point of re-inspecting tannery machine parts is to establish whether they can be installed directly, so the procedure is defined per component type rather than left as a general look at the exterior.

Record the sealed state before opening: seal number, any water staining or impact deformation on the case, and the humidity indicator reading taken outside. These are the raw records that settle a later dispute. After opening, work through the cells in reverse assembly order — accessories and tooling first, then pattern plates and roller parts, then the shaft and blades last — so that a large part never blocks a small one and no secondary handling is needed.

The purpose of the evidence trail is to separate damage on arrival from damage in service. If those records are made on the day the case is opened, they form a complete baseline; without them, responsibility cannot be assigned later whether the fault is the supplier's or the operator's. Documenting a claim does not imply the equipment is faulty, it gives both parties a common starting point. The procedural detail pairs well with the documentation system described in Case Repair and Spare Parts Documentation — the paperwork should be prepared before shipment and checked against the physical contents at the moment of opening.

Frequently Asked Questions FAQ

Q: Can the knife shaft and the blades of a shaving machine travel in the same case?

A: Technically yes, but it is not recommended. The shaft is a large precision rotating part that needs multi-point support and radial location, while the blades are thin edges that need soft isolation with no mutual contact. If one case is used, a separate inner liner must divide the two, and that liner needs enough stiffness to resist relative movement in transit. Otherwise the blades slide axially inside the case and end up jammed between the mesh knife and the pressure bars, and the first thing you see on opening the case is a set of scoring marks across the edges. The sounder arrangement is a shaft cell and a blade cell in two separate cases, numbered individually and secured to the same pallet at loading. Where loading efficiency matters, an integrated case with an internal divider works, but the divider strength must be calculated separately as a load-bearing member; a foam panel is not a structural member and cannot be treated as one on site.

Q: How far must a chipped edge go before the blade is scrapped, and can it be run in the meantime?

A: The hard rule combines position and size, and both must hold. On position: a chip on the cutting leading edge, the zone that actually performs the cut, means any visible notch requires immediate replacement, because subsequent shaving draws fibres into the notch and deepens it, producing the comb-like defect. On size: a notch anywhere on the blade that exceeds 3 mm in length, or one third of the edge thickness in depth, must also be replaced even if it sits behind the cutting edge. Beyond geometry, two indirect criteria apply. A furrow deeper than 0.15 mm running along the cutting direction changes the effective edge geometry, and a blue temper band across the blade belly shows that local hardness has been redistributed by overheating. Track hide counts per blade as well: in conventional vegetable-tanned work a single blade reaches its stable limit somewhere between 15,000 and 30,000 standard hides, and the swap should happen at that upper limit rather than after a chip appears on the surface.

Q: Can equipment carrying chrome liquor residue be packed without passivation?

A: No. A hexavalent chrome wet film sealed inside a case creates a sustained high-humidity micro-environment and progressively destroys the anti-rust film on steel parts. The purpose of passivation is to reduce and seal the residue; alternatives exist but carry far higher demands. Relying on drying alone to prevent corrosion is impractical, because the film is itself hygroscopic. The workable sequence has three steps: reduce first with sodium bisulphite solution at low temperature and rinse thoroughly, then passivate with a phosphate or chromate solution to form a conversion film, then dry and seal immediately. Two quick checks confirm the result on the inspection bench. Visually, the surface should read as an even passivation grey rather than a bright white bloom. Mechanically, wipe with a clean white cloth and confirm no chrome colour transfers to it. Parts that fail either check must not be packed in the same cell as parts that passed, since the untreated surface will still outgas and attack the neighbouring steel for the whole journey.

Q: Can an embossing pattern plate be stored pressed directly against the roller face?

A: No. A hard pattern plate bearing directly on a chrome-plated roller face concentrates the assembly weight onto a small number of support points under sustained load, and the result is a permanent indentation or a matte patch that cannot be polished out, because the plating has a finite thickness. The correct arrangement leaves a 1 to 2 mm gap between plate and roller face so the roller can expand radially and axially when heated, with continuous distributed support along the entire length so no part of the barrel is left spanning open air. The lining must be a low compressive stress foam with good recovery, and the permanent compression set should be held within about 5%. Add a soft spacer between plate and roller face to stop relative sliding under vibration, and re-measure barrel diameter and concentricity before assembly. If the plate and roller are found hard-clamped together, do not force them onto the machine: the plate is carrying residual stress from an earlier thermal cycle, and the first hide off the press will show the plate edge printed on it.

Q: Is a higher case sealing class always better, and do sulphide-contaminated machines need a breathable case?

A: Not always; it depends on the medium. A tannery machine case faces two competing requirements. The first is water and dust ingress, which calls for a higher IP rating and a pressure equalisation valve. The second is containment of escaping gas, which matters mainly for residues such as sodium sulphide, a strong alkali with a severe odour. Cells holding sulphide residue should be sealed: continuous welds, a gasket running uninterrupted around the lid, and heat-sealed bag necks. The reason is that vapour from these residues is both pungent and an exposure risk to people, and it gains nothing from being able to breathe out. A pressure equalisation valve serves a different purpose entirely, relieving pressure differences caused by temperature change during transit so the lid does not deform and the seal does not fail. The usual specification for a tannery machine is a sealed main case, with equalisation valves fitted only in designated cells where they are genuinely justified by the route.

Q: Knife shafts show rust spots after two weeks in the case in a humid shop. Is that the case or the machine?

A: In most cases it is neither a leaking case nor a defective machine; it is one of two internal moisture sources that get overlooked. The first is residual humidity in the cavity. Metal surfaces carry a water film when a machine is stripped in a wet-processing hall, and if that film is still present at closing, a high-humidity micro-environment forms inside the case. On surfaces carrying residues, the relative humidity threshold at which corrosion begins can be pushed below 40%, so once started, rusting is only a matter of time. The second source is condensation inside the case. A case moved straight from a cold store into warm air will condense water on its cooler inner walls, and this happens frequently during the monsoon season and wherever winter temperature differences are large. Countermeasures are to dry the parts before packing and confirm the internal state with a humidity indicator card, to specify enough desiccant, and to avoid abrupt temperature changes and direct floor contact during storage. If rust appears only in the cells holding chrome or sulphide parts, check passivation and isolation first.

Q: Can a case that once held chrome-contaminated wastewater be recycled for other equipment?

A: It should not be recycled. Contamination left on packing material by hexavalent chrome liquor is an adherent type of contamination that keeps migrating through direct contact and through material reuse. Once a contaminated board, wooden pallet or foam liner goes to work with other goods, the spread goes far beyond what anyone anticipated. The correct sequence is: drain the residual liquor on site, rinse and wipe the machine, and hand the liquid to a licensed contractor through the chrome hazardous waste route. Liners that touched chrome parts are collected separately and not reused. The outer case is decontaminated or disposed of as hazardous waste depending on how visibly contaminated it is. Set the same expectation at purchase stage by telling the case supplier in writing that the chrome cell uses virgin material with a disposable liner and no recycled board, and record the condition of the packaging on arrival. One further point for the shop floor: a case used for both must be marked, otherwise the next person to open it has no idea what residue it may still contain.

Q: Blades arrive chipped and the supplier says it happened during installation. How should the evidence be recorded?

A: The evidence has two halves, and both matter. The first is the raw record made on the day of opening: the seal number, the exterior condition of the case including any impact damage or water staining, the humidity indicator reading, and the sealing state of every cell. Remember that a card read outside the case tells you nothing about the interior, so the internal card must be read after opening. When these details are already printed in the accompanying documents and the timestamp is confirmed jointly by the carrier and the consignee, their evidential weight is far higher than a description written afterwards. The second half is the per-blade ledger. Inspect every blade under at least 10× magnification and record, for each defect, which blade, which position along the edge, the notch length and depth, and whether it sits on the cutting leading edge or behind it, with a photograph of each finding. Critically, do not grind or install a chipped blade before the claim has been reviewed; grinding destroys the evidence that distinguishes transit damage from an in-service event, and once the edge is dressed the question can never be settled objectively.