A die-casting shot sleeve is condemned to scrap or repair on the same five signals every shift, and the inspection sequence matters: measure first, look second, then decide. Standard HPDC sleeves run an inner diameter of 80–150 mm against a length of 400–1400 mm, so an acceptable ID reading is meaningless unless it is taken at the exact stations called out on the original drawing [S5].
Visual cues catch only the gross failures (deep scoring, through-wall cracks, biscuit-stuck pour land), so a defensible checklist mixes a bore scope, an internal micrometer or bore gauge, and a crack-detection method sized to the sleeve material [S2]. For shops that also run surface prep, a separate shot blasting machine routine sits beside the sleeve checklist and should not be folded into it.
Five failure modes that drive a sleeve off the line
Inner-diameter wear, scratches and scoring, erosion around the pour area, deformation/ovality, and thermal cracking are the canonical reasons a shot sleeve comes out for service [S2]. Of these, ID wear is the most expensive to misjudge, because each 0.05–0.10 mm of bore growth lets more metal escape behind the plunger tip, destabilising injection and raising flash.
Scoring is a symptom, not a diagnosis. Per the OEM repair guidance, long scratches trace back to one of five root causes: poor lubrication, foreign particles, incorrect plunger-tip clearance, plunger-tip damage, or abnormal thermal conditions [S2]. Fixing the sleeve without fixing the root cause puts the same scoring pattern back inside 200–500 shots.
Quantitative checks: ID, ovality, straightness, wall
Measure internal diameter at multiple positions along the bore; the readings expose local wear, taper, ovality, and diameter change that visual inspection cannot resolve [S2]. A sleeve that "looks round" at the ends can still be 0.3 mm tight in the mid-band, which is enough to wipe a plunger tip.
Straightness, not just roundness, has to be checked because a sleeve can bow internally while looking straight from outside, and the plunger must travel through it without binding [S2]. Wall-thickness verification is the gate before any machining decision: if the minimum wall would drop below the drawing value after re-boring, the sleeve goes to scrap, not to the lathe.
Cracks, pour-zone erosion, and the replaceable-insert option
Visible cracks must never be left in service. Before any weld or repair is attempted, the depth, location, and root cause (thermal cycling, water-pocket blockage, alloy chemistry) should be confirmed with a non-destructive method appropriate to the sleeve material, and severe cases are replaced rather than repaired [S2].
The pour area takes the worst thermal-mechanical punishment, with local erosion and surface damage from repeated molten-metal contact. Some OEM designs counter this with a replaceable pour-area insert, gun-drilled underside cooling, and a cooling ring at the shot end, options that change the inspection points a checklist must cover [S5]. For sleeve geometry that links to the machine frame via the industrial valve-style lubricant ports, the thread spec (1/4 NPT, 3/8 NPT, 5/8 NPT, or G1/2) and its position relative to the distributor become inspection items too [S5].
Repair vs replace: the decision matrix
Three criteria separate a repairable sleeve from a scrap sleeve: minimum wall thickness remaining after re-boring, crack depth relative to wall, and dimensional drift beyond drawing tolerance [S2]. A sleeve that fails any one of the three is uneconomical to repair, regardless of how clean the bore looks.
Surface damage routes to one of three paths: small scoring takes polish or light machining, mid-depth erosion takes weld-rebuild plus post-weld heat treatment, and through-wall cracks or heavy ovality go to scrap [S2]. Shops running a refurbishing programme report that a structured diagnosis before any turning work is the single biggest factor in keeping sleeves inside OEM dimensional spec, which is why total refurbishing services begin with a written inspection report rather than a quote [S1].
Maintenance rhythm: per-shift, weekly, and between-campaign
Per-shift, the operator checks the shot system: sleeve for visible wear, shot pressure setpoint against the process card, and lubrication flow at the LUB DROP, COMBI LUB, TUBE LUBE, or GROOVE LUBE port the cell is configured for [S5][S8]. Anything more than a visual light-up goes to the metrology bench.
Weekly or per-campaign, the sleeve comes out for a full ID/ovality/straightness survey, a borescope pass along the full length, and a crack check on the pour land and the cooling-channel gun-drilled underside [S2][S5]. Plants that bundle this with the shot sleeve cleaning station and the surrounding shot blasting machine PM tend to catch the slow-growth defects before they show up as flash or cold-shut on the casting.
When NOT to repair a shot sleeve
A sleeve is not repaired when minimum wall would fall below the drawing value after re-boring, when a visible crack has any measurable depth, when ovality or taper exceeds the OEM tolerance band, or when straightness has drifted beyond the plunger-tip clearance budget [S2]. In all four cases, replacement is safer and cheaper than weld-rebuild.
A second "do not repair" condition applies to surface-alloyed or nitrided sleeves (NITOP, WX, MULTIX grades): machining through the nitrided case to chase a score will strip the wear-resistant layer, and weld-repair on these grades is rarely approved by the OEM, so any damage that breaches the case routes straight to scrap [S5]. For context on how a sleeve decision fits into the wider HPDC tool-room economics, the Shot Sleeve Lifespan: Replacement and Reconditioning Guide for Die Casting walk-through lines up the same wall-thickness and crack gates against expected shot counts.