480 hr comparison before and after damage
KEMP R&D report KPRD-20191209-02 compares mechanically damaged coatings under 5% NaCl salt spray at 35 °C.
Fasteners · Bolts · Threaded Rods
Plating for corrosion protection
Plating for corrosion protection
and precision assembly.
Fastener performance depends on both corrosion resistance and the integrity of surfaces subjected to tightening. Innozinc Ceramic Galvanizing combines over 500 hr corrosion resistance after mechanical damage in the cited comparison (zinc electroplating: 90 hr) with a thin approximately 8 μm deposit. Target thickness, pre-plating thread tolerances and gauge inspection work together to deliver reliable assembly quality.
500hr+
Corrosion resistance after damage
Zinc electroplating: 90 hr
Zinc electroplating: 90 hr
8μm
Plating thickness
Controlled thread dimensions
Controlled thread dimensions
80Cycle
Cyclic corrosion test (CCT)
Zinc electroplating: 5 cycles
Zinc electroplating: 5 cycles
25℃
Ambient-temperature plating
No thermal coating cure
No thermal coating cure
Innozinc representative SST 720–1,000 hr 26 analyzed substances not detected · Hexavalent-chromium-free options Plating at 25 °C · Reduced thermal distortion Barrel plating capacity: 7 t/day
Fasteners plated and supplied by KEMP. Approximately 8 μm plating at 25 °C supports thread-tolerance control and reduces thermal distortion.
Post-Damage Corrosion Resistance
Corrosion resistance
after tightening and fabrication
Alongside intact-specimen SST performance, fasteners benefit from corrosion assessment after mechanical damage. Tightening applies friction and contact pressure to thread flanks and bearing surfaces, making coating adhesion and damaged-area protection important quality characteristics.
Zinc electroplating · 8 μm
90hr
Corrosion resistance after mechanical damage
Intact reference specimen: 190 hr
Intact reference specimen: 190 hr
Hot-dip galvanizing · 50–77 μm
240hr
The thicker coating requires appropriate thread allowances
Mating-nut specifications and gauges control assembly fit
Mating-nut specifications and gauges control assembly fit
Innozinc 8 μm
500hr+
Corrosion protection after damage with controlled thread dimensions
Thin plating matched to gauge requirements
Thin plating matched to gauge requirements
Source: KEMP R&D comparative data and KTR test documentation. Post-damage corrosion resistance is assessed by salt spray exposure after impact or mechanical damage. KEMP supports sample assessment against your fabrication conditions and inspection specifications.
TOOLING TEST · ACTUAL SPECIMENS
Corrosion comparison
before and after mechanical damage
In KEMP's 2019 comparative study, intact specimens and specimens mechanically damaged by tool tightening were exposed to the same salt spray conditions for 480 hr. The study observed corrosion of the plated layer and fastening contact areas.
Intact specimens · 480 hr salt spray
No tooling test
Zinc ElectroplatingElectrolytic zinc depositHot-dip GalvanizingHDGInnozincCeramic Galvanizing · 8 μmGeometZinc flake coating · ZFCKEMPZIN ZF2KEMP high-corrosion-resistance specification
Tool-damaged specimens · 480 hr salt spray
After tooling test
Zinc ElectroplatingElectrolytic zinc depositHot-dip GalvanizingHDGInnozincCeramic Galvanizing · 8 μmGeometZinc flake coating · ZFCKEMPZIN ZF2KEMP high-corrosion-resistance specification
Test conditions: neutral salt spray (NSS), ASTM B117 / KS D 9502, 5% NaCl, 35 °C, 480 hr (20 Nov – 9 Dec 2019). KEMP R&D report KPRD-20191209-02. Specimens are shown in this order: zinc electroplating, hot-dip galvanizing, Innozinc, Geomet and KEMPZIN ZF2. This in-house study compares coating corrosion at mechanically damaged areas. Substrate materials and strength grades differ between specimens. Five of the original report's six specifications are shown. Geomet is a registered trademark of NOF METAL COATINGS.
Table 1
480 hr exposure: intact versus mechanically damaged
Assessment of the specimens shown above| Surface Treatment | Intact · 480 hr | Mechanically Damaged · 480 hr | Observed Performance |
|---|---|---|---|
| Zinc electroplating · 8 μm | Extensive red rust | Widespread red rust and staining | Red rust on the intact specimen |
| Hot-dip galvanizing · 50–77 μm | Extensive white rust + 30% red rust | Extensive white rust and progressing red rust | Surface corrosion despite the thicker coating |
| GeometZinc flake coating (ZFC) | No defects observed | Red rust observed | Performance changes after mechanical damage |
| Innozinc 8 μm | No defects observed | No defects observed | Protection retained after damage |
A key Innozinc benefit is corrosion protection after mechanical damage. Assessment covers both intact specimens and tool-damaged coating areas to establish the surface-treatment quality of assembled fasteners.
Mechanically damaged specimens in comparison
The two specimens received the same tool-damage conditions. The Innozinc specimen on the left shows surface discoloration; the Geomet specimen on the right shows red rust on the head and corrosion-product staining. Innozinc combines sacrificial protection from electrodeposited zinc with an inorganic composite barrier to improve corrosion resistance at damaged fastening surfaces.
ASSEMBLY TEST
Coating condition immediately after tightening
M24 · Two tightening cycles with a 700 N·m air tool (Aug 2023)Geomet (zinc flake coating) After tightening
Innozinc (Ceramic Galvanizing) After tightening
Coating integrity after tightening: tightening tests on M16 (120 N·m, 4 cycles) and M24 (700 N·m, 2 cycles) observed damage at contact surfaces. Fastener specifications link tightening torque, thread tolerances and damaged-area corrosion resistance.
Tightening test: Aug 2023. Separate from the 2019 study with 480 hr salt spray exposure.
Tightening test conditions: impact and pneumatic tools applied the specified torque and number of tightening cycles. Test documentation records plating deformation and damage at tool-contact areas.
Manufacturing Requirements
Four Priorities in Fastener Surface Treatment
Manufacturing and assembly quality affect total cost alongside corrosion performance.
PROBLEM 01
Plating integrity during thread engagement
Thread flanks and bearing surfaces experience contact pressure and friction during tightening. Managing plating adhesion, deformation capability and damaged-area corrosion resistance improves fastener protection after assembly.
Post-damage corrosion resistance: 500 hr+ (zinc electroplating: 90 hr)PROBLEM 02
Thread tolerances and plating thickness
Plating thickness affects thread pitch diameter and assembly clearances. Innozinc's approximately 8 μm thin deposit limits dimensional change, with processing conditions set against thread gauges and post-plating tolerance requirements.
Approximately 8 μm plating · Gauge-controlled fitPROBLEM 03
Environmental specifications and optimized post-treatment
Innozinc achieves corrosion resistance through a zinc layer and inorganic ceramic film. Chromium-free process specifications help optimize post-treatment operations and substance-control requirements.
26 analyzed substances not detected · Streamlined post-treatmentPROBLEM 04
Galvanic corrosion control at dissimilar-metal joints
Potential difference, contact-area ratio and electrolyte exposure affect galvanic corrosion between galvanized steel and stainless steel. Innozinc-h offers a high-corrosion-resistance composite coating for dissimilar-metal connections, specified around mating materials and fastening conditions.
Galvanic current density: 65% lower with a carbon-steel counterface vs. the tested HDG referenceAfter tightening Before exposure
After salt spray exposure Same area
KEMP R&D's in-house ASTM B117 salt spray records show corrosion at tool-contact areas. The right-hand specimen uses a ceramic zinc electroplating specification other than Innozinc and illustrates the relationship between mechanical damage and corrosion location.
Thread Tolerances
Plating thickness designed
around thread pitch diameter
For 60° threads, plating on the flanks increases the effective pitch diameter. A uniform thickness t gives an approximate geometric increase of 4t. Pre-plating tolerances and target thickness are coordinated to meet post-plating gauge requirements.
Hot-dip galvanizing Thread allowance required
A 50–77 μm coating produces an approximate geometric pitch-diameter increase of 200–300 μm. Pre-plating thread tolerances and mating-nut specifications must accommodate the coating, with post-plating gauges confirming assembly fit.
Innozinc Ceramic Galvanizing Controlled thread fit
An 8 μm deposit produces an approximate geometric pitch-diameter increase of 32 μm. Thin Innozinc plating reduces thread-profile change and additional machining, with fastening quality controlled through pre-plating tolerances, mating nuts and gauge criteria.
Thickness control matched to thread tolerances
Current distribution and thread geometry affect local deposit thickness. KEMP's cited thread-plating record is 6–8 μm. Processing conditions reflect thread specifications, tolerance classes such as 6g/6H and thread-rolling conditions. Sample assessment combines gauge inspection with corrosion requirements.
Current distribution and thread geometry affect local deposit thickness. KEMP's cited thread-plating record is 6–8 μm. Processing conditions reflect thread specifications, tolerance classes such as 6g/6H and thread-rolling conditions. Sample assessment combines gauge inspection with corrosion requirements.
Performance & Cost
More corrosion protection
at the same coating thickness
The table presents recorded red-rust comparison results. Current representative SST specifications are 720–1,000 hr for Innozinc and 1,500–2,000 hr for Innozinc-h. Application specifications pair coating thickness with test conditions and acceptance criteria.
| Characteristic | Zinc electroplating | Zinc electroplating + sealer | Hot-dip galvanizing | Innozinc | Innozinc-h |
|---|---|---|---|---|---|
| Corrosion resistance (SST, red-rust criterion) | 190 hr | 240 hr | 480 hr | 1,000 hr | 1,500 hr+ |
| Corrosion resistance after mechanical damage | 90 hr | — | 240 hr | ≥500 hr | ≥500 hr |
| Cyclic corrosion test (CCT) | 5 Cycle | — | 40 Cycle | 80 Cycle | 80 Cycle↑ |
| Coating thickness | 8 μm | 8 μm + sealer | 50~77 μm | 8 μm | 8~15 μm |
| Oversize tapping of mating nuts | Not required | Not required | Specified to accommodate coating | Gauge-controlled fit | Gauge-controlled fit |
| Dissimilar-metal / galvanic corrosion | Poor | Poor | Poor | Good | Very Good |
| Reference post-treatment | Trivalent / hexavalent chromium | Chromium-based post-treatment | Hexavalent-chromium post-treatment | Chromium-free options | Chromium-free options |
| Process temperature | Ambient temperature | Ambient temperature | Immersion at approximately 450 °C | Ambient plating at 25 °C | Ambient plating at 25 °C |
Source: KEMP R&D comparative data and KTR test results. SST values use a red-rust criterion; white-rust specifications use different acceptance criteria. Quotations reflect geometry, specific surface area and monthly volume. Send drawings and production quantities for product-specific pricing.
Table 2
Process Characteristics in Comparison
Deposition, curing and downstream fabrication| Characteristic | Zinc electroplating | Zinc flake coating (ZFC) | Hot-dip galvanizing (HDG) | Innozinc |
|---|---|---|---|---|
| Process temperature | Ambient temperature | Thermal cure at 180–300 °C | Immersion at approximately 450 °C | Ambient plating at 25 °C |
| Thermal coating cure | Not required | Required | Not applicable | Not required for deposition |
| Thermal distortion / tempering exposure | No high-temperature deposition step | Exposure to the curing temperature | High-temperature exposure | Ambient-temperature deposition |
| Oversize tapping of mating nuts | Not required | Not required | Specified coating allowance | Gauge-controlled fit |
| Sacrificial protection at cut edges | Available | System-dependent | Available | Available from zinc layer |
| Grounding / electrical continuity | Assembly assessment | Assembly assessment | Assembly assessment | Assembly assessment |
| Bend performance | Cracking | Limited | Delamination | 140° |
| Hydrogen-embrittlement process considerations | Hydrogen charging during electroplatingElectrolytic process | No electrolytic chargingNon-electrolytic deposition | Lower retained hydrogenHigh-temperature immersion; pretreatment remains relevant | Process controls requiredElectrolytic process — see application specifications below |
| Reference post-treatment | Trivalent / hexavalent chromate | Specification-dependent | Hexavalent-chromium post-treatment | Chromium-free options |
High-strength fastener process control: for property class 10.9 and above, pretreatment, plating and post-treatment are qualified against the customer's hydrogen-embrittlement control requirements. Fastener application specifications
Cyclic corrosion: in the 2025 production assessment (KS D ISO 14993, 40 cycles), both ceramic-zinc-plated and hot-dip galvanized U-bolt specimens showed no red rust. The table's 80-cycle and 40-cycle figures are product-reference values; that direct U-bolt comparison used 40 cycles.
Product Lineup
Selecting Innozinc or Innozinc-h
Both grades use thin Ceramic Galvanizing. Selection is based on the required corrosion resistance and exposure environment.
Innozinc
Standard grade · SST 720–1,000 hr
- Approximately 8 μm plating — thread dimensions controlled against gauge requirements
- Post-damage corrosion resistance ≥500 hr — over five times the 90 hr zinc-electroplating reference
- Integrated corrosion protection supports a streamlined post-treatment sequence
- Chromium-free options · 26 analyzed substances not detected
Recommended applicationsGeneral bolts, nuts and screws; threaded rods; anchor bolts; indoor equipment fasteners — general atmospheric exposure
HIGH-CORROSION-RESISTANCE GRADE
Innozinc-h
Aggressive environments · Salt · Acids · Dissimilar metals
- Representative SST 1,500–2,000 hr · Coating thickness 8–15 μm
- Galvanic corrosion rated Very Good — connections to stainless steel members
- Acid resistance rated Good — acidic atmospheric exposure
- A candidate replacement for zinc-nickel plating in specification-matched applications
Recommended applicationsOutdoor, coastal and marine fasteners; bolts contacting stainless steel; equipment in acidic atmospheres — combined salt, acid and dissimilar-metal exposure
A single customer can specify Innozinc for indoor components and Innozinc-h for outdoor or aggressive-service components.
Total Cost
From plating to assembly,
improve total manufacturing cost
Compare plating cost together with thread rework, reinspection and localized touch-up labor. Innozinc's thin deposit and fabrication capability create opportunities to simplify the manufacturing sequence.
Table 3
Post-Treatment, Assembly and Rework Operations
Process requirements compared; costs calculated from customer production data| Cost Element | Zinc electroplating + sealer | Hot-dip galvanizing (HDG) | Innozinc |
|---|---|---|---|
| Secondary sealer operation | Required | — | Streamlined specification available |
| Oversize tapping of mating nuts | Not required | Required | Reduced through thickness/tolerance control |
| Reinspection / retapping after oversize tapping | — | Additional operation | Reduced rework requirement |
| Correction of thermal distortion after plating | — | May be required | No high-temperature deposition step |
| Heating and drying energy | Sealer drying | LNG-heated zinc bath | Ambient-temperature deposition |
| On-site cut-edge touch-up | Application-dependent | Touch-up material required | Sacrificial protection from adjacent zinc |
| Assembly-clearance management | Low | Control oversize-tap allowance | Precision through thin plating |
| Hexavalent-chromium requirements | Select compliant post-treatment | Select compliant post-treatment | Chromium-free options |
Product-specific manufacturing cost: compare before/after costs including plating, thread rework, reinspection, touch-up labor and round-trip transport. Drawings, surface area, monthly throughput and minimum batch size determine the plating specification and quotation.
Application
Product Applications and Plating Selection
Barrel plating (7 t/day) handles small parts in volume; rack and acid-zinc lines accommodate long and large components.
General bolts · Nuts · Small screws
Barrel-plated components such as hex bolts, washers and small screws, with protection focused on surfaces exposed to tightening damage.
Recommended · InnozincThreaded rods · All-thread · Round bars
Standard members for ceiling hangers and equipment supports. With threads along the full length, deposit thickness directly affects assembly fit. Applications include data-center and cleanroom support systems.
Recommended · InnozincAnchor bolts · Expansion anchors · Adhesive anchors
Embedded and exposed sections experience different environments. Corrosion resistance after installation damage protects exposed fastening areas.
Recommended · InnozincStuds · Double-ended studs · Special fasteners
Double-ended and nonstandard geometries require thickness-distribution control. Thin plating supports gauge-compliant threads at both ends.
Recommended · InnozincFasteners in contact with stainless steel
Dissimilar-metal joints require coordinated control of Galvanic corrosion and contact-interface protection. Innozinc-h specifications reflect mating materials, contact-area ratios and electrolyte exposure.Outdoor · Coastal · Marine fasteners
Applications combining salt exposure with repeated tightening. Container locking-rod experience includes a one-year marine demonstration and DEKRA testing.
Recommended · Innozinc-h
Industrial bolts
Studs · Double-ended studs
U-bolts · Bent components
Nuts (barrel plating)
Washers (barrel plating)
Marine and offshore bolts
Special and nonstandard fasteners
Rivets · Inserts
Products plated and supplied by KEMP. Photographs show the silver-white ceramic zinc finish. Colored or blue chromate post-treatments are handled as product-specific specifications.
Table 4
Product-Specific Plating Specifications
Product requirements and process qualification| Product | Exposure Environment | Recommended Specification | Technical Basis |
|---|---|---|---|
| Hex bolts and nuts | Indoor · General atmosphere | Innozinc | Post-damage corrosion protection · Thread-tolerance control |
| Small screws and machine screws | Indoor · General atmosphere | Innozinc (adjusted thickness) | Deposit thickness adjusted to the thread specification |
| Threaded rods · All-thread | Indoor equipment and ceiling supports | Innozinc 8 μm | Sacrificial cut-edge protection · Full-length threads |
| Threaded rods · Anchors | Outdoor · Coastal · De-icing salts | Innozinc-h | SST 1,500–2,000 hr · Galvanic corrosion rated Very Good |
| Expansion and wedge anchors | Indoor embedded installations | Innozinc 8 μm | Residual corrosion protection after impact and expansion |
| Embedded foundation anchors (J/L type) | Embedded in concrete | Project-specific finish | Embedded and exposed portions specified according to concrete and atmospheric exposure |
| U-bolts · Hook bolts · Square U-bolts | Outdoor · Pipe supports | Innozinc-h | Adhesion retained in the cited 140° bend test |
| Washers · Small screws | Indoor · General service | Innozinc (barrel plating) | High-mix, small-batch production · Barrel capacity 7 t/day |
| Bolts contacting stainless steel | Dissimilar-metal interface | Innozinc-h | Galvanic corrosion rated Very Good |
| Fasteners for grounding / electrical continuity | Electrical assemblies | Innozinc | Assembly contact-resistance assessment reflecting contact surfaces and fastening conditions |
| High-strength bolts, property class 10.9 and above | — | Process qualification required | Hydrogen-embrittlement controls and process qualification against customer specifications |
| F10T / S10T slip-resistant bolting assemblies | — | Process qualification required | Approved slip-factor and torque-coefficient requirements for the complete bolt assembly |
Advantages
Reduce Rework and Improve Manufacturing Cost
Streamlined Post-Treatment
Innozinc's representative SST specification is 720–1,000 hr. Its composite coating provides an opportunity to streamline additional sealer operations, with process and test conditions established on the actual component.
Plating at 25 °C · Reduced Thermal Distortion
Ambient-temperature electrodeposition reduces thermal-distortion exposure in long threaded rods and bars while maintaining dimensional precision. Eliminating the hot zinc bath reduces deposition-stage heating and operating requirements.
Chromium-Free Corrosion Protection
Chromium-free Innozinc specifications combine corrosion protection with substance-control requirements. The cited analysis reports 26 tested substances not detected; product-specific documentation identifies the methods and detection limits.
Coating Integrity in a 140° Bend Test
For formed and bent special fasteners, the cited test retained the coating without cracking through a 140° bend. This supports alternative plating and fabrication sequences.
Barrel Capacity: 7 t/day
KEMP operates three Ulsan lines: rack plating at 35 t/day, acid-zinc plating at 10 t/day and barrel plating at 7 t/day. Small fasteners use barrel processing; long rods and bars use rack processing.
Marine Demonstration Experience
Container locking rods provide experience under salt exposure and repeated fastening friction, including a one-year marine demonstration and DEKRA testing.
Performance Data
Fastener performance supported by
assembly conditions and test results
Product specifications link corrosion protection in the assembled or damaged state with thread tolerances and assembly quality.
Bolt-and-clip assembly assessment
In-house testing assessed an assembled specimen after 2,664 hr salt spray exposure. Assembly conditions and surface observations are available in the relevant test documentation.
Thread tolerances and corrosion grades
Target deposit thickness and gauge requirements are established using the thread-tolerance framework of ISO 4042 and ISO 965-1, then paired with the required corrosion grade.
Fastener Specification
Plating specifications and quality controls
optimized for general fasteners
Core applications include general bolts and nuts up to property class 8.8, threaded rods, anchors, studs and nonstandard fasteners.
Material and strength grade
Process selection reflects material and heat-treatment condition. High-strength fasteners such as classes 10.9 and 12.9 require hydrogen-embrittlement controls and process qualification before production.
Thread and assembly quality
Target thickness is matched to thread tolerances, mating nuts and tightening conditions, with gauges verifying assembly fit.
Post-fabrication corrosion resistance
Sample assessment reflects damage from tightening and fabrication to establish corrosion performance under customer conditions.
Implementation Process
From Sample Assessment to Production
KEMP develops plating specifications and sample programs for your components. Corrosion resistance, thread tolerances and assembly quality are assessed against customer inspection criteria before production conditions are finalized.
Ulsan barrel line Bolts · Nuts · Washers
Ulsan rack line Long and large components
1
Technical documentation Same day to 1 business day
Product-specific test documentation and the technical catalog are supplied by email. Tell us the application and required specifications so we can provide relevant data.
2
Sample plating Quantity, cost and schedule agreed
Provide material, strength grade, dimensions and quantity for the bolts and nuts. Our team will confirm the plating specification and sample arrangements.
3
Inspection with your gauges After sample plating
Thread gauges, post-tightening coating integrity and corrosion resistance are assessed against customer inspection specifications. Results establish production plating and quality-control requirements.
4
Testing to your requirements Agreed test program
Select salt spray, cyclic corrosion, post-damage corrosion and coating-thickness assessments, with results documented in the agreed report format.
5
Pilot batch → Production Agreed implementation plan
Pilot products are selected against corrosion, thread-tolerance and assembly-quality objectives. Sample results guide progressive approval of production specifications and supply conditions.
Track Record
KEMP's Production and Supply Experience
Marine steel outfitting has been supplied for more than 60 vessels at two major shipbuilders. KEMP's cited supply record covers over 80% of the Korean grooved fire-protection fitting market, with customers in power generation, heavy industry, construction and process plants.
Company-wide supply record across KEMP's business areas. Request product-specific fastener application examples from our team.
FAQ
Frequently Asked Questions
Technical guidance on fastener processing, assembly quality and production implementation.
Which fasteners are the main applications?
Core products are general bolts and nuts up to property class 8.8, threaded rods, anchors, studs and nonstandard fasteners. High-strength components require process qualification against material, heat-treatment and hydrogen-embrittlement control requirements.
How are thread tolerances controlled?
Target thickness reflects thread specifications, tolerance class and rolling conditions. The cited production range on threads is 6–8 μm. Gauge inspection and corrosion assessment are performed on actual components.
What does post-damage corrosion testing assess?
Specimens damaged by tightening, impact or fabrication are exposed to salt spray to observe white rust, red rust and coating condition. The fabrication method and test conditions are documented to support application-relevant comparison.
How is a quotation calculated?
Quotations use product geometry, surface area, plating specification and production volume. The assessment can cover the full manufacturing sequence, including sealers, oversize tapping, reinspection and fastening rework.
Can I request a small batch with multiple products?
Provide dimensions, quantity and material for each product. Our team will advise the rack or barrel process, minimum processing quantity, cost and schedule suited to the geometry and process.
Can Innozinc be compared with our current process?
We use your current surface-treatment specification and quality-improvement objectives to design a comparison on identical components. Results determine product-specific plating and production conditions.
Sample Request · Quantity, Cost & Schedule
Request Innozinc samples
Request Innozinc samples
for your fasteners.
- Request KTR third-party test documentation and the technical catalog.
- Connect sample plating, gauge inspection and corrosion assessment on actual components.
- Check plated threads against your thread gauge requirements.
- Receive guidance on hydrogen-embrittlement controls and process qualification for the material and strength grade.
- Start with material, strength grade, dimensions and quantity; our team will help define the sample program.
Technical & sample inquiries — Sales Director Gyeong-dong Ko +82 52 289 1155
Ask our team for the relevant test documentation.
Ask our team for the relevant test documentation.
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