Large‑scale SAG (Semi‑Autogenous Grinding) mills are critical equipment in mineral‑processing plants. Mill liners are fastened by numerous M48 heavy‑duty bolts. During operation, these bolts endure continuous impact load, severe vibration and corrosive slurry‑moisture environment, representing extremely demanding service conditions.
Existing on‑site pain points:
- Conventional metal‑filled anti‑seize pastes brought large dispersion of torque‑preload relationship. Under identical tightening torque, actual bolt preload varied widely. Some bolts suffered insufficient pre‑tension and loosened under long‑term vibration.
- Under‑tensioned bolts endured cyclic impact loads and tended to fatigue fracture, leading to liner displacement.
- Bolt failures triggered unplanned shutdowns. Each downtime for mining plants resulted in substantial production losses.
- Traditional metal‑based anti‑seize agents risk fastener brittleness caused by metal diffusion and environmental contamination.
- During maintenance shutdowns, some threads suffered galling‑seizure, making bolts hard to remove and extending man‑hours for repairDuPont
Solution
The project team selected MOLYKOTE P‑74 metal‑free assembly paste as dedicated assembly lubricant for mill liner bolts, following official application specifications:
- Thoroughly clean bolt threads and washer contact surfaces before assembly to remove mineral dust and old lubricant residues.
- Apply sufficient and uniform coating of P‑74 paste onto bolt threads and washer bearing faces.
- Tighten bolts with torque multiplier according to defined process torque. Leverage the product’s low and stable friction coefficient, converting applied torque into bolt elongation and clamping force as much as possible.
- Avoid mixing with other on‑site lubricants to maintain stable, calculable friction coefficient for torque‑preload control.
Key product matching advantages:
- ‑ Non‑metallic formulation eliminates fastener brittleness risk from metal ingredients and reduces environmental impact.
- ‑ High‑load‑carrying performance with 4 800 N four‑ball weld load, suitable for heavy impact‑loaded conditions.
- ‑ Consistent friction coefficient, stable even after repeated tightening‑loosening cycles, greatly narrowing pre‑load dispersion.
- ‑ Reliable corrosion protection against slurry and moisture corrosion. Paste service temperature ‑40～200 °C; dry separating film can withstand short‑term peak up to 1 500 °C for transient high‑temperature events.
- ‑ No intentional addition of PTFE or PFAS substances, complying with modern environmental‑protection requirementsDuPont.
Implementation Results
fter multi‑group bolt comparison tests and long‑term field validation versus conventional anti‑seize products used onsite:
- Under identical tightening procedures, bolt yield‑strength performance improved by minimum 10 %. Bolt pre‑load values became more concentrated. Higher portion of applied torque transferred into clamping force, reducing under‑tension incidents.
- Failure rates of liner‑bolt loosening and fatigue fracture decreased obviously. Unplanned mill shutdown incidents were reduced and plant operational availability improved.
- Thread galling‑seizure during maintenance dropped significantly. Bolts could be disassembled smoothly and maintenance man‑hours were shortened.
- Metal‑free formula removed brittleness risks from metal migration and eased on‑site environmental‑management pressure.
- Stable friction coefficient allowed maintenance engineers to reliably apply calculated tightening torque and realize standardized component assembly.
Note: Actual performance depends on bolt grade, surface finish, tightening procedure and maintenance interval. End‑user evaluation under real‑world conditions is recommended before large‑scale adoption.
Extended Application Scenarios
eyond mining mill liner bolts, MOLYKOTE P‑74 fits threaded joints and assembly points across multiple industries:
- Automotive: exhaust bolts, spark‑plug threads, brake‑mechanism assembly.
- General machinery: flanges & flange seals, valve bolts, splined shafts, press‑fit joints.
- Equipment manufacturing: linear sliding guides, sliding contact bearings, hinges.
- Chemical and pulp‑paper equipment: heavy‑load threaded connections requiring calculable torque and easy later‑stage disassembly
Key Reference Parameters
Appearance: Grayish‑black paste
‑ Continuous service temperature (paste): ‑40～200 °C; short‑term peak for dry‑film up to 1 500 °C
‑ Four‑ball weld load(DIN51350‑4): 4 800 N
‑ Thread / head friction coefficient(M12‑8.8 blackened bolt): 0.14 / 0.08
‑ Shelf life: 60 months from manufacturing date
‑ Composition: solid lubricants, synthetic oil, thickener and adhesion promoter; no intentional PTFE or PFAS addition.
Customer Take‑away
For critical threaded joints under vibration‑impact, corrosion and alternating temperature cycles, high‑strength bolts alone cannot guarantee long‑term reliability. Selecting a metal‑free assembly paste with stable friction coefficient and high load‑bearing capacity helps convert tightening torque into uniform clamping force, reduce bolt loosening and fracture, cut unplanned downtime and facilitate future maintenance disassembly.
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