Log Truck Safety Alert

The maintenance and inspection of truck and trailer rigging and hardware is an important component of safe and reliable log truck operations. In particular, bolster and scale pad bolts need to be to well maintained and replaced when necessary to avoid spilled loads.

This safety alert provides:

 

Thanks to Western Forest Products, Vulcan On-Board Scales and SI Onboard Weighing for their contributions to this alert.

INCIDENT: BROKEN BOLTS CAUSE LOAD TO SHIFT

Date: 7-Aug-12

Description:

While negotiating a turn on Stewart Main a loaded logging truck rolled onto its passenger side. Once the scale pad bolts pulled loose, and the load spilled, the tractor up righted itself and the vehicle came to a stop. As the truck up righted, the driver was thrown against the driver’s door injuring upper body & head.

Initial on-site investigation identified broken bolster bolts on the road approximately 200 meters behind the incident scene. The shearing off of the bolts in combination with the force & direction of travel may have caused the truck’s load to shift forcing the logging truck to roll onto its side.

Upon investigation of the bolts, it was identified that the threads on the upper portion of the bolt hole were completely worn off. The right side scale pad bolts were cracked 70% through.

The previous driver had experienced problems with the bolster & scale pad bolts loosening; the issue was dealt with by having a local maintenance shop tighten the bolts.

Learnings & Suggestions:

 

Load Cells Maintenance Tips

BEAM LOAD CELL

DRIVER’S DAILY INSPECTION

  1. Brush off any buildup of mud, ice or other debris that may obstruct the load cell’s deflection under load, and will impair your ability to see and feel your rigging. It’s best to do scale pad checks taking advantage of daylight during your circle check.
  2. Visually check load cells, mounting brackets, and fasteners for cracks, or other external damage. Check mounting bolts to confirm they are tight. Use a small hammer to tap the head of each bolt and confirm it is tight (a rattle will occur if the bolt is broken in the hole). The easiest way to check that bolts are secure is by using torque striping (see below)
  3. If torque stripes have been applied, confirm they are properly aligned. To apply a torque stripe: Use a durable, brightly colored paint. Paint a stripe crossing the head of the fastener, continuing down the fastened structure, as shown.
  4. Another method to check bolts is the hands-on method. Confirm the head of the mounting bolt is there. Grab hold of the head of each mounting bolt; twist it left and right. Give it a wiggle. If it has recently snapped or is coming loose, you should be able to feel a little play. If you do, get your mechanic to check / fix things before you leave the shop.
  5. Watch your rigging during loading and unloading.
    • If the loader operator is rocking the unit, you might see extra play at the bolster or trunion (depending on your system) if you have broken or loose mounting bolts. You should have caught this before now, but nonetheless, check it out before heading down the road.
    • When the Letourneau is lifting the load off the unit, look for slop or play at the bolster or trunion. If you see daylight under the scale pads, or your trailer frame looks to be lifting away from the suspension / axle assembly – you’ve got big problems to fix. Again, you should have caught the problem long before this, but if you see this don’t push your luck with another load.

Torque Tip - Scale pad bolts are more likely to fail as a result of a severe torque or twist (rather than an accumulation of the day to day ordinary stresses). If the D8 has towed you through a mudhole with a nasty lean, or the loader operator gives your rig a severe push or if you have hit the weeds, double-check your rigging, and your scale pad bolts.

MONTHLY INSPECTION - MECHANIC

Check the torque on load cell cap screws monthly. For new installations, check them at least weekly for first 2 weeks. See the Vulcan On-Board Scales recommended torque values below.

Torque Specifications:

Bolt Diameter 3/4" 7/8" 1" 1-1/8" 1-1/4"
Lb-ft 400-500 400-590 650-890 1000-1400 1450-1780

Torque Tip - A lot of shops won’t have a torque wrench that goes up to 1400 lb-ft. Using a 1" impact gun won’t necessarily give you the torque you need - some 1" guns are rated up to 3200 lb-ft and others top out at 1300 lb-ft. The condition of the tool and the shop air system has a big influence on torque output. You really can’t use an impact driver to estimate torque.

A cost effective solution you can use to reliably apply the correct torque is a torque multiplier.

Check welds on load cell brackets. IMPORTANT: If a weld repair is required, remove the load cell. CAUTION! Do not exceed 140 degrees Fahrenheit (60 C) on the load cell. Arcing on the body of the load cell voids the manufacturer’s warranty and may seriously damage the load cell’s structural integrity. The load cell must NOT be installed if this occurs.

Check load cell connectors; make sure they are finger tight plus an additional 1/8 of a turn with channel lock pliers (helps avoid scale errors due to moisture entering connector).

Do not grease or lubricate inside the load cell connector or VSL Vulcoder connector. They are highly sensitive to foreign substances and inaccurate readings will occur if components are contaminated.

If a connector is opened, clean the load cell connector and cable connector with cotton swabs and isopropyl alcohol, dry with a hair dryer (DO NOT OVERHEAT), and replace the O-ring before reconnecting.

In areas where salt is used on the roads, wrap the threads of the load cell connector with plumber tape, (Teflon tape). This will prevent salt from penetrating the threaded connection.

Vulcan load cells are plated for increased rust protection, but maintenance is necessary to claim warranty of load cells. Annually, apply high quality paint to the load cells, bearing pads, and mounting brackets.

For environments where high concentrations of salts are used on road surfaces, undercoating is recommended (3M, Universal Rubberized Undercoating, 3M P/N: 8883). Spray undercoating when load cells are connected to electronics and fully assembled with bearing pads and brackets.

Fill unused holes in load cells with grease, to protect against rust.

 

Vulcan V200 Owner’s Manual - http://www.vulcanscales.com/images/stories/library/manuals/v200.pdf
Vulcan V300 Owner’s Manual - http://www.vulcanscales.com/images/stories/library/manuals/v300.pdf

If you need additional information call:
Vulcan Customer Service at 1-800-237-0022 or
SI Onboard / VPG On-Board Weighing at 1-800- 989-1499

File attachments
Safety_alert_scale_pad.pdf
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