Iggesund Forest’s Iain Lawrence on what you need to know about chain shot

IAIN Lawrence, export sales manager for Swedish harvester bar manufacturer Iggesund Forest, is leading the charge against chain shot, the high-speed ejection of chain parts during a breakage. Here, Iain outlines the steps operators can take to reduce the risk of chain shot and what good practice looks like.

WHAT IS YOUR BACKGROUND?

My career in forestry began with Sandvik Windsor in 1993. I moved to Oregon Cutting Systems in June 2001, then to Iggesund Forest in August 2018.

WHAT IS THE BACKGROUND OF IGGESUND FOREST?

Iggesund began manufacturing saw bars in 1986, The production is in the town of Strömsbruk, Sweden, 300 kilometres north of Stockholm.

The company was purchased in 2010 by P Wikstrom J:r AB. This company also owns Olofsfors AB, the world-leading producer of forestry tracks. They are manufacturing in the town of Nordmaling, which is near to Umeå, in eastern Sweden.

Iain Lawrence.

WHAT IS CHAIN SHOT?

Chain shot is the high-speed (309 m/s) ejection of chain parts during a chain breakage. This only happens on the second break. However, the second break can occur during the initial breakage.

WHAT CAN CAUSE CHAIN SHOT?

There are many factors that need to be considered. Chain can break due to:

• excessive saw chain speed

• excessive guide bar feed force

• poor or no lubrication

• improper saw chain tension

• incorrect sharpening and maintenance.

The saw chain breaks.

After a saw chain break, the ‘free’ end of the saw chain begins to whip away from the break.

If the saw chain is not contained by the saw box or a chain shot guard, the broken saw chain’s free end can speed up rapidly, carrying immense dynamic energy. At the peak of the whip, saw chain pieces may break loose and be ejected at high speed.

WHAT CAN BE DONE TO REDUCE THE RISK OF CHAIN SHOT?

Primarily, make sure all of the above are observed and corrected.

General good work practice: every four hours, remove chain and fit sharpened or new saw chain, then turn the saw bar over, clean the rails and oil holes.

Every week: remove sharp edges from saw bar with a file or grinder.

Check drive sprocket for wear: the guideline for sprockets is replace after using 10 saw chains or 0.6 mm of wear are observed. A worn sprocket damages the side links of a saw chain: this makes the parts weaker and therefore, if not replaced, will result in a broken saw chain, and greater risk of a chain shot.

Maintenance of saw chain in workshop:

• Clean.

• Inspect for missing or loose parts, damage or excess wear to saw chain.

• Repair if possible, otherwise discard the saw chain.

• Sharpen.

• Clean and lubricate.

• Again, if the chain has broken twice it should be discarded.

• At this stage, chain should be inspected for stretch. If this is the case, the chain should be discarded. A stretched chain will create a chain shot on breakage.

• Stretch gauges are available.

The ejected piece or pieces usually travel in the cutting plane of the guide bar but can deviate to either side.

WHEN IS CHAIN SHOT MOST LIKELY TO HAPPEN?

It can happen any time.

WHAT ADVICE DO YOU HAVE FOR MACHINE OPERATORS WHEN IT COMES TO CHAIN SHOT?

The above advice will reduce the incidence of a chain shot. The other critical point is to make sure the saw bar is not cutting towards the cab of the machine. In most cases, ejected parts follow the line of the saw bar. Make sure shot guards are in place and in good condition, and make sure the chain catcher is in good condition and not missing or broken.

Chain shot typically originates near the drive sprocket area of a cutting system, but it can also originate from the bar tip area of the guide bar.

ARE THERE ANY COMMON MISCONCEPTIONS ABOUT
CHAIN SHOT?

I don’t think it is so much a misconception, just more of a complacency – operators thinking, ‘It will never happen to me’.

Chain shot from a .404” pitch saw chain penetrated a 13 mm polycarbonate door window, striking and killing the operator (Washington, USA).

HOW SERIOUSLY DO YOU THINK CHAIN SHOT IS TAKEN BY THE INDUSTRY?

The OEMs do take this pretty seriously, as do many machine operators, but there is definitely a complacency which I believe is misguided. This can be a real problem; chain shot is nothing to laugh and joke about. When we say that a chain should be discarded if broken twice, or you should change the sprocket after 10 chains, this is normally greeted by a few words, and many comments like, “I never change mine until it breaks”, or “It’s been on the machine since I got it”.

The damage a worn sprocket can cause to saw chain.

WHAT WORK IS BEING DONE TO EDUCATE MACHINE OPERATORS AND MAKE THE JOB SAFER?

During my time at Oregon, we developed a training programme to present to OEMs and user groups. I have continued to develop this programme at Iggesund. Even though we do not manufacture saw chain, we do sell it, so it is important to keep this developing and make sure the information gets to where it needs to be. This training has been presented to many OEMs at head office level and some subsidiaries. It is something we are keen to develop and we are more than happy to make this presentation to any OEM or end user group.

iain.lawrence@iggesundforest.se

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