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Outrigger Jack Pads Nylon: MC Cast Nylon (PA6G) Pad Selection & Ground-Pressure Sizing Guide
2026-02-12
Most pad problems on site happen for two practical reasons:
- The contact area is too small → ground pressure is too high → settlement/sinking.
- Traction isn’t addressed (wet/muddy/oily/sloped ground) → sliding or pad movement.
This article covers: how to size the pad, how to choose materials, and what mistakes to avoid.
1) Why timber blocks and steel plates often cause trouble
Timber blocks (wood cribbing)
- Moisture can reduce predictability: hidden cracks and internal damage are common.
- Larger blocks become heavy, leading to inconsistent use and improvised setups.
Steel plates
- Strong, but very heavy to handle repeatedly.
- On wet, muddy, or oily surfaces, low friction can increase the risk of shifting.
- Rust and contamination can further reduce stability.
Why MC cast nylon (PA6G) pads are widely used
MC cast nylon (PA6G)—often referenced in the industry under grades like MC901/MC907—fits “reusable, standardized pad” use cases:
- Easier handling and repeated reuse
- Wear resistance and corrosion resistance
- Machinable features: carry handles/holes, chamfers, locating recess for the outrigger foot/float, anti-slip texture
Key point: “Will it sink?” is mainly determined by contact area vs. allowable ground bearing pressure. Material choice mainly affects pad deformation and slip resistance.
2) Quick pad sizing (two lines)
Use these two lines on site:
① Minimum contact area
A (m²) = R (kN) ÷ Allowable Ground Bearing Pressure (kPa)
② If using a square pad
L (m) = √A
In millimeters: L (mm) = 1000 × √A
Unit note: 1 kPa = 1 kN/m²
Example (method demonstration only)
R = 200 kN; allowable ground bearing pressure = 100 kPa
→ A = 2 m²
→ L ≈ 1.41 m (≈ 1410 mm)
3) How to get R (maximum load on one outrigger)
Avoid “total machine weight ÷ 4.” Outrigger reactions change with boom direction, working radius, lifted load, and swing position.
Recommended sources (best to worst):
- Manufacturer manual / load charts / published outrigger reactions
- Manufacturer pad-load tools (for example, Manitowoc provides pad load calculators for planning and documentation)
- If you must estimate: assume weaker ground (lower allowable pressure), use a larger pad area, and document the assumptions
4) How to determine “allowable ground bearing pressure”
Best source: geotechnical/site data or contractor-provided allowable pressure.
If site data is unavailable, use a conservative approach based on ground type and recognized reference tables (for example from DICA) as a communication baseline.
Regulatory framing: OSHA discusses ground conditions and supporting materials (blocking/mats/cribbing), emphasizing that ground must be adequate and supporting materials may be required in some conditions.
Practical rules (good for fleet SOPs):
- If ground condition is uncertain: assume a lower allowable pressure → increase pad area
- Backfill, trenches, voids, rain-softened soil, and poor drainage → be more conservative
- Ground condition isn’t only “hard vs. soft”: slope, drainage, compaction, and overall stability matter
5) Material choice: MC cast nylon vs. UHMWPE vs. rubber (by jobsite risk)
Start with one question: what’s your main risk?
- Settlement / pad deformation under heavy concentrated load
→ focus on enough area + pad stiffness/thickness/structure
→ often favors MC cast nylon (PA6G) for heavy-duty reuse scenarios - Slipping on wet/muddy/oily/sloped ground
→ focus on traction + features (anti-slip texture, rubber underside, anti-slip mats, locating recess)
Quick comparison
Option | Best at solving first | Typical site keywords |
MC cast nylon (PA6G) | stable support, reusable wear resistance, machinable features (locating recess/handles) | heavy duty, frequent dispatch, fleet/rental |
UHMWPE | balanced wear/impact properties; performance depends heavily on design + conditions | dry, relatively even ground, balanced choice |
Rubber / rubber underside | grip and slip resistance | rain, mud, oil, slopes, low-friction surfaces |
A note on “compression performance” (for explaining stability)
A commonly used test framework for plastic compression behavior is ISO 604 from ISO. Public material databases like MatWeb often show that nylon grades can exhibit higher compressive stress at the same nominal strain than UHMWPE—useful for explaining why nylon pads may feel more stable under concentrated loads (while UHMWPE may be chosen for other balanced properties).
Wet ground: features often matter more than base material
Anti-slip textures, rubber underside, and a locating recess for the outrigger foot/float are common approaches in the market (examples are discussed by suppliers such as Securatek).
6) Four common on-site mistakes
6.1 The outrigger foot/float is not centered
All calculations assume effective contact area. Off-center loading reduces effective area and increases local pressure.
Fix: use a locating recess/ring + visually confirm centering after setting.
6.2 Ground condition is ignored
Even with a calculated area, unstable ground (backfill, trenches, rain-softened soil, voids) can fail. Use more conservative allowable pressure and add supporting layers if needed.
6.3 Wet/oily/slope: “harder material” alone won’t prevent slipping
Low friction is the core issue. Use anti-slip texture, rubber underside, anti-slip mats, and locating recess.
6.4 Area is sized, but thickness/structure is not
Area addresses ground pressure; thickness/stiffness/structure address pad bending and local indentation under the outrigger foot/float. Heavy-duty jobs should treat thickness as the second sizing step.
7) Common questions
Q1: What does “allowable ground bearing pressure” mean?
It is the allowable pressure per unit area (kPa) that the ground can support. It directly determines how large the pad’s contact area must be to distribute the outrigger load.
Q2: What if I can’t find R (max load per outrigger)?
Check the manual/load chart first; then use manufacturer calculation tools. If you must estimate, be conservative: lower allowable pressure, larger pad.
Q3: Will MC cast nylon pads always slip in rain or mud?
Not necessarily. In wet conditions, features (anti-slip texture, rubber underside, locating recess) often determine stability more than base material alone.
Contact
For sizing support or custom machining (handles, locating recess, anti-slip texture), prepare:
- equipment type / capacity / model
- maximum load per outrigger R (unknown is acceptable)
- ground type (concrete/asphalt/soil/backfill/mud/oily/slope)
- conditions (dry/rain/mud/oil)
- quantity and delivery city
Hebei Hongrui Environmental Protection Technology Co., Ltd.
Tel: +86 191 3191 4795
Email: hebeimcnylon@gmail.com
Website: hbhrhbkj.com
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