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Paddle Arm Bolt Set
Grade 10.9 high-tensile bolt kits securing paddle arms and tips to the mixer shaft under continuous impact loading.
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At a glance
| Bolt grade | ISO 898-1 Grade 10.9 |
|---|---|
| Material | 42CrMo4 alloy steel, quenched and tempered |
| Tensile strength | 1,040–1,220 MPa |
| Thread sizes | M16, M20, or M24 (model-specific), coarse pitch |
| Surface finish | Zinc phosphate + oil (grey-zinc) |
| Washer hardness | HRC 38–45 |
| Kit quantity (twin-shaft) | 32–64 bolts + washers + nuts |
| Torque values | 180–450 N·m (size-specific); data card included |
Overview
The paddle arm bolt set comprises all high-tensile fasteners required to mount the paddle arms to the shaft hubs and to secure the replaceable paddle tips to the arm tip holders on one mixer shaft. Because the paddle assembly rotates through a dense aggregate charge at 35–55 RPM and absorbs significant cyclic impact energy at each revolution, the bolts must combine high tensile pre-load with resistance to fatigue loosening — a requirement that standard commercial hardware cannot reliably satisfy over extended WMM campaigns.
Avelta supplies the bolt set as a complete kit for one shaft or one full twin-shaft assembly, including hex-head cap screws, hardened washers, and where the design requires it, prevailing-torque locknuts. All fasteners are supplied in matched sets to allow simultaneous replacement as recommended in the WMM maintenance schedule.
Function
Correct bolt pre-load keeps paddle arms rigid relative to the shaft hub, preventing the micro-movement that leads to fretting corrosion on the shaft key and eventual arm loosening at operating speed. Paddle-tip bolts must similarly resist the cyclic tensile load imposed each time a tip strikes aggregate; under-torqued or fatigue-cracked tip bolts allow tip rotation or ejection, which can damage the trough liner severely in a single mixing cycle. Avelta bolt sets include a torque specification data card with each shipment to ensure correct installation pre-load.
Construction & quality
Manufactured to ISO 898-1 Grade 10.9, material 42CrMo4 alloy steel quenched and tempered to achieve tensile strength of 1,040–1,220 MPa and proof stress ≥940 MPa. Thread form: ISO metric coarse, M16 to M24 range depending on mixer model. Surface treatment: zinc phosphate plus oil for controlled coefficient of friction during torquing and corrosion protection in outdoor storage. Hardened steel washers (HRC 38–45) are included. Locknuts where used are all-metal prevailing-torque type, Grade 10, to ISO 7042. Bolts are 100% proof-load tested per batch.
When to replace
- Any bolt showing visible thread stretch, elongation, or necking at the shank
- Loose paddle arm detectable by hand movement at the shaft hub
- Fretting corrosion powder (red-brown oxide) at the arm-to-hub contact face
- Damaged or rounded hex socket drive preventing correct torque application
- Piecemeal bolt replacements at previous service (replace the full set at overhaul)
Compatibility & fitment
Kits available for all AVL-WMM mixer arm and shaft hub configurations; Avelta specifies metric thread size, length, and shank diameter to the customer's mixer serial number, with UNC inch-thread variants available on request.
Why buy from Avelta
Avelta fasteners are batch-tested to ISO grade before despatch and kitted as complete sets so that nothing is left unchecked at reassembly; mechanical test certification is available on request for quality-assured project records.
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