What is a Piston Rock Splitter?

 A Wedge Splitter has been known as A hydraulic Rock Splitter for some time.

There has been quite a time of hydraulic rock splitters of wedge type for concrete wall demolition. Some companies modified the concepts and made bigger size wedge splitters  for excavator mounted use. This type of wedge splitter has been used for demolition of concrete structures or rock mountain demolition all over the world.

There is one country this wedge type is not popular , i.e  Korea. This does not mean that any wedge type splitter is not used at all in Korea.  The wedge splitters are used limitedly in very narrow space  such as shaft sinking of less than 2 meters of diameter . They did use them very widely until 1990's.
                       

A wedge type splitter mounted on excavator cracks the rock with more powers than manual ones.

A Piston Spliter Appeared disregarding Wedge's Splitting Force.

  HRD-tech started manufacturing piston-cylinder type rock splitters since late 1980 with a concept from a Japanese company. In Japan, some rubber tube splitters were used. One importer visited Korean machining company to find out the steel made splitters.
The concept is simple and clear to understand. The hydraulic power from the pressed oil is transmitted to to the piston's bottom , of which top is expanding and adding stress to the holes' wall of rock. Then rock wall  made by pre-drilled hole  is cracked to the frontal side of the piston.

When one rod of 10 pistons  within a rod of 85mm  is pressed by the stress of pressed oil 1,000 kp/cm2 ,the 10 pistons of 46mm diameter provides surface of 166cm2.
This means 166 tons are produced by a cylinder when the powerpack pressure remains
as 1,000kp/cm2. With oil pressure of 1,300 kp/cm2, one cylinder can produce 215 tons of pressing power.

A cylinder  of   85mm diameter with 11 pistons.

Analysed  Splitter in detail

When the piston rod bottom(Q3) is pushed up by the pressed oil, the piston rises with the power. This power pushes the rock wall in the holes. When the surface Q3 is big, the rod's pushing power is big. But if  Q is too big, the cylinder wall is too weak. We must find the safe but powerful size of the piston by trial and error. In case of 85mm cylinder, this rod power was calculated as 16.6 ton when power pack pressure is 1,200 kp/cm2.

When we use 95mm cylinder, the piston size is increased too. The splitting force is increased too. But the cylinder weighs too heavy for manual handling with 9 pistons.  95mm cylinder is now adopting 6~7 pistons system . 95mm cylinder has been used only for the hard rock breaking. Most popular size has been 80mm or 85mm cy;linder with 10 pistons now.

 Splitters have been tried in various sizes

As the need for more sophisticated application arises, customers look for varying  size splitters.  150mm cylinders and 185mm cylinders are those required.  These sizes are used for the drills made by either core drills or DTH hammers.

150mm Cylinder with 8 pistons

                           

185mm Cylinder with  1 piston 

 With piston type cylinders, the drilling time matters. Splitting can be performed very efficiently.  Ordinary manual rock demolition, the small size ( 80, 85, 95mm ) cylinders are used. The drilling time is not too long. One hole drlling in a rock with 1000mm deep takes 30seconds to 45 seconds per each.  And the normal spacing requires 40cm ~50cm distance for efficient splitting.

However there is very hard rock which must be removed. Then larger size drilling is attempted. 165mm holes or 200mm holes are made. Our 150mm splitter or 185mm splitter is used.

Here we find an interesting fact about the splitting force generated by one or multiple piston splitters.  

When we calculate the piston pushing force which is used for breaking rock, the 80mm cylinder produces the least power. 85mm cylinder produces a bit higher power. 95mm produces higher than the previous one. Naturally  150mm produces the more power. 185mm cylinder produces the biggest power.

But the large size cylinder is limited in its number of piston because of manual lifting.

So 185mm cylinder has only one piston. 150mm cylinder has 2 pistons for manual handling.

Refer to the following table which HRD-tech is used ( hand held types only)

Above table shows only the hand-held splitters which are limited by its weight. Hrd-tech  has limited it under 30kgs.
As we can assume, hard rock may require more powerful breaking stress from the splitter.
 This stress is a combination of power pack pressure, splitter's piston size, number of pistons .
 When the number is more, the weight is increased more.

Of course, we can think about the machine held splitters of larger diameter and longer
but heavier splitters. These areas have been our keen interest for the future development.

 Special Characteristics of a Piston Rock Splitter.

You will find that small size cylinder has less piston strength than large cylinders.

 Considering the total splitting force of a cylinder , we find that SR150 has 58.8 tons  and SR 185 has 114 tons while the 80mm or 85mm cylinder has 182 tons and 229 tons.

Does it mean that 85mm cylinder performs the best? No, not at all. As far as the splitting is concerned,  185mm cylinder does the best splitting job. Why?

This question needs to be solved in terms of the splitting force. The  powerful splitting force does not necessarily mean the total maximum power. It does mean individual piston's force and some part from the splitting force.

Let's look at the following diagram.

Shearing Force & the Fracturing Force

When the piston expands, it makes fractures along the line of cylinder length. The rock is split  from top to bottom in parallel to the cylinders' length. But still the cracking or the shearing is not finished.  Left side rock part must be broken by shearing force .

The important force required to remove the left side rock is from shearing force from the splitter.  This shearing force depends on the pistons' strength plus bottom piston's

pushing force to the frontal direction.

If a narrow area is pushed by a piston rod( hydraulic stress) and cracked like the picture above, this will make cracks ( fracturing), which initiates the shearing simultaneously. This shearing action will require backing force supported by the other pistons.

Fig. Sheared Bottom

 Above figure shows that sheared bottom area  calculated . When we use spacing of 50cm between holes, this area will be roughly 7,500 cm2 (= 50 x 150 ).

 Required shearing strength is  15,000 tons.(= 2,000 kp/cm2  x 7,500 cm2 )

  If we assume that 3 cylinders of 85mm dia.  are used at the power pack pressure of 1,200 kp/cm2, total expanding force will be maximum 520 tons.  This  expanding stress is roughly 1/30 of the required shearing strength. ( =520ton/15,000ton)

    Something must be considered other than shearing strength from above calculation.

The writer has been suspicious about this queer phenomenon. The splitting force of 182~229 tons covers the required shearing strength( 15,000tons ) in reality.

 What happened? How does a splitter of 182tons shear the area ( abb4a4 ) which requies  shearing strength of  15,000tos?

The blogger has a hypothesis that  a hydraulic stress from the piston splitter might act on a very narrow point in frontal direction.   This narrow stressed line is stressed  prior to neighboring line and begins to be cracked.  Immediately after this point is yielded, the neighboring lines are continuously yielded eventually resulting to breakage.

The writer has no proof for this hypothesis yet. However the writer has been experiencing this "queer' breakage in daily work sites.

This is the very special characteristic in piston rock splitting in comparison with the wedge splitting. With the wedge splitters, the wedge indeed has very high splitting force. With the small darda, the splitting force is 2~5 times of piston splitters. With the large size mechanized splitters, the wedge splitting force is 10~15 times higher than that of piston splitter.   In actual demolition site, the wedge  cracks the rock very slowly and less efficiently comparing to a piston splitter.

For example, 12 inch darda splitter has splitting force of 385 tons. This cylinder is inserted into 45mm dia hole.  Then it can split the rock( granite of 200MPa CP) with 25~30cm spacing. With the piston splitter of 85mm dia cylinder, you can break the rock with the spacing of 50cm  easily. A  85mm  piston cylinder has splitting force of 199 tons.  This piston splitter breaks the rock much easier than 12 inch wedge splitter of 385 tons force. But it sounds something wrong. A smaller force splitter splits the rock better and faster?  I am talking about the occurring facts daily.

Applications of the piston splitters.

The piston splitter has been applied to many similar demolition sites to wedge has been applied. So far most of piston spliters are used for rock removal for such places;
 ground rock for building foundation,  underground tunnel rocks, rocks on the mountain , rocks near historical building , rock near residential area. shaft sinking, trench making ,
etc.  

Even the manual piston spliter can perform breaking job very efficiently. It works faster than any wedge splitter of similar size. Manual piston spliters have been popular in many places. Our piston rock spliter has been used in N.Y for breaking Manhattan rock since 2007. Recently our piston spliters are used in African continents. India, Chile, Phillippines, Russia, and China has been using our splitters from time to time.

Following video will show you some tips on how to use a piston rock splitter.

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Before cracking

 The following photo shows how a splitter cracks the rock in inserted hole.

After cracking 

Each cylinder produces more than 166
tons of expanding stress.




 

  When more than a cylinder is used
  in a line to push the rock wall inside the drilled holes, it produces enormous
 power. See below.

3 splitters in line  before cracking.
       

 For a full video, visit Https://Youtu.be/1rfZIfRNtcU.

3 splitters in line after cracking

It is usual to use 4 splitters in line for removing the rocks in foundation site of buildings.
Sometimes they add 2 more splitters in order to increase this power and expedite the demolition work.

A conventional rock spliter done with wedge type is not comparable in its power.( see video http:// Youtu.be/-H1dt5osMJs " breaking Bedrock with a mechanical splitter"

 The piston type splitter is now used on many demolition sites.

 For eg, construction field ( see Youtu.be/1rfZIfRNtcU )

This technology summarized as "Drill & Split" is very useful and efficient in any mechanical demolition.

This system must be optimized based on experiences.  . One drill  with 2 splitters  and an excavator etc must be from  experienced professionals.

If you need  see  details, visit web site, www.hrd-tech.com  for further details.