Short answer
The shank of a tool that has come out is the cheapest diagnostic instrument you have for what is happening inside the breaker. A narrow band polished on one side means side load, even polish all round means normal contact, deep longitudinal scores mean dust in the seat and insufficient lubrication, blue or straw colour means overheating, and a deformed pin bed means the retaining set has been running loose. These marks do not tell you why the tool finished; they tell you that the next tool will finish the same way. Where nobody reads them, the same bill repeats on every tool.
Look at the shank properly first
- Wipe the shank with a cloth as soon as the tool is out. Marks are invisible under grease and dust.
- Hold it to the light and turn it; polished areas only stand out as the angle changes.
- Note where the mark is: near the tip of the shank, near the pin bed, or along its whole length.
- Put the old and the new tool side by side if you can; the difference comes from comparison, not from memory.
What each mark means
- A narrow, bright band on one side: side load. The breaker is not bearing square on the material, or the tool has been used as a lever. Expect the bushing to be worn on the same side.
- Even, light polish all round: normal contact. This is what a shank that has run true in its bushing looks like.
- Deep longitudinal scores: abrasive dust has entered the seat, with insufficient or wrong grease. The same scores will be on the inner face of the bushing.
- Blue, purple or straw colour: overheating. Dry running, seizing or long uninterrupted blows.
- A deformed and spread pin bed: the retaining set has been running loose. Where this is not stopped, the seat deforms next.
- Mushrooming or burring at the shank tip: the tool has been left in the wrong place, from blank firing or from staying far too long on one spot.
From mark to cause: two typical cases
First case: one side of the shank polished, the opposite side matt. That says the tool has been leaning the same way inside the bushing throughout. The cause is almost always the working angle: the breaker is bearing at an angle rather than square, or the tool has been levered to lift rock. Fit a new tool and keep the same habit and the mark returns within three weeks.
Second case: fine, deep scores along the shank, with grease that has gone dark and carries rock dust. Here the cause is the lubrication routine: either the interval is too long, or the grease is wrong, or the greasing was done with the tool in the air so the grease went outwards rather than into the seat. Look for the same scores on the inner face of the bushing; where both appear, the decision is to deal with the bushing as well.
The greasing sequence decides the mark
Grease is applied with the tool PRESSED AGAINST THE GROUND. Greased with the tool in the air, the gap between shank and bushing is open and the grease leaves through the gap instead of reaching the contact face. This is the commonest cause of deep scores on site. We set out the correct sequence step by step in the greasing technique guide.
Do and don’t
Do
- Wipe and photograph every shank that comes out; the record pays off on the second tool.
- Note the direction and position of the mark, not just "worn".
- Where the shank is marked, look at the inner face of the bushing too; both tell the same story.
- Where you see discolouration, question the working routine rather than blaming the tool.
- Share what the mark showed with the operator; what needs correcting is usually a habit.
Don't
- Do not "true up" a shank by grinding; the dimension drops and the clearance grows.
- Do not refit a tool that has gone blue; its heat treatment has changed.
- Do not ignore a deformed pin bed; the next item on the bill is the seat.
- Do not decide from one tool; where two tools carry the same mark, the cause is in the system.
- Do not carry on with the same grease and the same interval once you have seen the mark.
What record keeping buys you
A single photograph of every shank that comes out builds into a series within six months. Three shanks from the same machine polished on the same side in a row are no longer coincidence but an operator habit, and the conversation to have is clear.
The same record helps on the buying side: without knowing how many hours tools last and how they finish, you cannot know which tool type suits that site. Tool selection only rests on data through this record.
What HKM uses
Taking the greasing interval out of human hands
On sites where shanks show deep scores and darkened grease, the problem is usually not the grease itself but the interval: in a busy shift manual greasing gets skipped. An automatic lubrication station feeds grease continuously while the breaker works and the tool is pressed down, which removes both causes of the mark at once.
SolidLube automatic lubrication station(solid-lube.com)