FEATURE. In this article we would like to discuss the different types of feed chains commonly used on small diameter

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1 FEATURE The Safety Aspects of Anchor Drill Rigs with Particular Focus on Feed Chains By Martin Bonzel, Area Sales Director North America, Klemm Bohrtechnik The Anchor Rig Feed Chain Safety Task Force was a joint task force created in the Associates and Safety Committees several years ago. Their purpose was to address specific safety threats from detached/falling drill heads mainly due to failure of the feed chain on small diameter anchor, micropile, and soil nailing rigs. The task force found that there was no single or magic solution to the safety issue, but they reported and stressed the importance of the feed chains to safe operation. The following article was written to address this issue by task force member, Martin Bonzel of ADSC Member Company KLEMM Bohrtechnik GmbH. (Roy Kern, ECA, Associates Committee Chairman) In this article we would like to discuss the different types of feed chains commonly used on small diameter drill rigs and the reasons why this particular Martin Bonzel chain type is usually chosen. We would also like to focus on the correct maintenance of the feed chain system to ensure that chain failure does not occur. The machine feed chain system is designed around the forces which occur during the drilling operation and calculated according to the European standards EN16228, with a safety factor of 3,5. The calculated safety factor ensures against failure of the feed chain system, when inspection intervals and maintenance is adhered to. The purpose of the feed chain is the lateral movement of the drill heads up and down the drill mast and to carry the load of upward and downward push and pull forces. In general on anchor and micropile drill rigs the feed and retraction forces range from 60kN to 130kN. Chains and chain parts are made of high quality case-hardened and heat treated steel. The choice of mast drive system is generally defined by design and purpose of the specific drill rig. The two standard drive systems are cylinder drive or motor and gear Pic. No. 1 Flyer Chain Layout of a flyer chain: Outer plate, inner plate and bolt. (continued on page 34) Pic. No. 2 Cylinder and roller carriage. Side view, Plan view and Schematic. FOUNDATION DRILLING July 2016 Page 33

2 Pic. No.3 Motor and gear drive. Sprocket wheel and roller chain. Pic. No. 4 Roller Chain Layout of roller chain Outer plate, Inner plate, Pin, Bushing and Roller. drive. This leads to the use of flyer chains in cylinder drive masts and roller chains in motor and gear drive mast. Whilst a drill mast with cylinder drive system works on the principle of a pulley. The motor and gear drive system uses a sprocket wheel to transfer the lateral movement. Examining the different drive systems i.e. cylinder drive or motor and gear drive. With the cylinder drive system flyer chains are used (see Pic. No.1). The piston rod of the cylinder is connected to a guide roller carriage that travels with the stroke of the cylinder up and down the inside of the mast profile (see Pic. No.2). This guide roller carriage or pulley system subsequently moves the drill head unit up and down the mast. The design of the guide roller carriage defines that the mechanical forces in the feed chain are 50% of the cylinder forces. Inversely, this also means that the distance and speed the sledge travels is twice the stroke and speed of the cylinder. The retraction force and feed force are in direct correlation to the piston area and the piston rod area, meaning that the ratio of area will define the different push and pull values when operated at the same hydraulic pressure. Flyer chains are built out of bolt and link plates and cannot transfer torque, so the movement of the drill head unit operates with the help of deflector rollers. The advantages of the cylinder drive system is its very compact mast design, excellent weight distribution and precise speed controllability in applications such as e.g. High Pressure Injection drilling. Lattice mast extensions used for example in High Pressure Injection drilling operations are easily attached to such masts. Drill masts with motor and transmission gear systems (see pic.no.3) use a sprocket wheel to transfer the torque of the motor into a lateral movement of (continued on page 37) Page 34 FOUNDATION DRILLING July 2016

3 Pic. No.5 Chain overstretching. the drill head unit. The motor and gear system operates with a roller chain. It offers identical feed and retraction forces and by means of switching gears, a fast travel function can be actuated. This has a time saving advantage when travelling up and down the drill mast without drill tools. The axis of the motor is connected to the sprocket wheel which interlocks with the roller chain. The motor and gear design is technically a more simple design than the cylinder with guide roller carriage. The external position of motor and gear has advantages in serviceability and accessibility of the drill mast components. The structure of a roller chain is a combination of external and internal side plates with pin and sleeve over which the roller rotates (see pic.no.4). Renewing sections, extending or reducing the length of the roller chain can be done easily by adding chain sections and securing them by means of a bolt and pin. components of the chain such as pins and links should be examined for wear marks, grooves or mechanical deformation. External wear must not exceed 5% of the original cross section of the link plates. If any signs of such wear or damage are detected, then the chain pieces or the complete chain must be replaced. The weekly inspection should be based on the daily inspection and extended to the surrounding machine elements, such as deflection rollers and sprocket wheels. A more elaborate inspection of the feed chain should be undertaken biannually or every 500 hours to verify that the chain has not been stretched beyond its permissible limits. The elongation is measured over a stretch of 17 chain links. The permitted elongation should not exceed 2% of the original length, otherwise the chain must be replaced. In the manufacturers maintenance manual there are references to the original length of pitch of a single link and the length of a 17 link stretch of chain (see Pic. No.7). These references can be used to gauge against the measurements taken from the feed chain system. The importance of these regular inspections to avoid the risk of chain failure cannot be over stated. Neglecting such maintenance can lead to severe machine damage, serious injuries or even fatalities. A comprehensive maintenance system must be in place to ensure that the above described procedures are undertaken. Chain Tensioning Systems Chain tensioning systems guarantee the correct tension of the feed chain. This is an important issue with respect to the longevity of the chain. The correct tension ensures an even wear and avoids a folding or overlapping of the chain links (continued on page 38) Maintenance and Safety Requirements In the life cycle of the feed chain, be it a flyer or roller chain, it is advised and stated within the manufactures maintenance manual to check the feed chain system at regular intervals. These maintenance cycles are built upon daily, weekly and biannual inspections. It is important to ensure that the feed chain is clean and lubricated in order to avoid a build-up of dirt deposits. An overstretching or possible tearing of the chain (see Pic. No.5) itself can occur when dirt deposits are carried over the deflector roller of the mast. This also applies to the use of a suitable lubricant. It is important that the chosen grease or lubricant does not thicken and contribute to the build-up of a so-called grease collar. The inspection of the chain begins with a simple daily visual check to look for cracks on the chain surface (see Pic. No.6) and to ensure the correct working tension. The Pic. No.6 Chain surface damage. FOUNDATION DRILLING July 2016 Page 37

4 Pic. No.7. Excerpt from the manufactures manual to gauge the elongation on the feed chain. which can cause the chain to damage the piston rod or mast housing or even lead to a failure of the chain itself. There are a number of common tensioning systems, manual bolt tensioning, manual grease tensioning cylinder or automatic hydraulic tensioning cylinder. The design of the manual bolt tensioning system is engineered around a slidable rear deflector roller which is moved by means of threaded bolts. This sliding movement increases the distance between the two deflection rollers on either end of the mast, thus so tensioning the feed chain. As a safety precaution to counteract any vibrations that occur during the drilling operation a fixed plate or locking sheet is installed to ensure that the threaded bolts remain in there set positions (see Pic. No.8). A second chain tensioning system, which is not so commonly installed but for the sake of a thorough description should not be omitted in this article, is the manual grease tensioning cylinder. This system is manually pre-tensioned by means of a grease gun. The basic principle is similar to the above described manual bolt tensioning system, the difference being that the slidable deflector roller is moved by means of a grease filled cylinder. The grease input valve is positioned toward the bottom of the mast and is more easily accessible. (see Pic. No.9). The hydraulic tensioning system operates on the same principal as the grease tensioning cylinder, by sliding the deflector rollers further apart and by doing so tensions the feed chain. This occurs automatically, by means of a hydraulic cylinder which is pressurized when a drilling function i.e. feed or rotation is operated. There are safety valves in place to ensure that the chain is not over tensioned. This system is the most advanced and user friendly as it automatically adjusts the chain tension as soon as a drilling operation is started (see Pic. No.10). (continued on page 41) Pic. No.8 Manual bolt tensioning system. Page 38 FOUNDATION DRILLING July 2016

5 Pic.No.9 Connection point for grease tension cylinder. All three tensioning systems, manual bolt tensioning, manual grease tensioning cylinder or automatic hydraulic tensioning cylinder are suitable for both flyer and roller chains. Feed chains have proven, over many decades, to be extremely reliable in the unquestionably difficult environment in which they perform. The guarantee for safe and efficient operation lies in the correct service and maintenance of these vitally important machine parts. The focus on machine safety takes a central role in the initial design and the daily operation of a modern-day drill rig. With the introduction of the new European Standard EN16228 the safety codes demand a number of far reaching changes to the functionality of the drill rigs. Changes that take the actual drilling method i.e. single pass drilling, rod handling systems, magazines or manually loaded rods and casing into consideration. These factors then determine the drilling parameters e.g. speed and force range. Discussions between drill rig manufactures and the board of European Standardization with respect to the final version of the EN16228 are still on-going. A number of issues relating to the practicality of this new norm, in particular the subject of cages, are still under discussion. As a conclusion it can be said that the operating safety of the drill rig is a focal point in our industry today. An operation where the installation of drill tooling is done mechanically which subsequently leaves the area of moving parts free of human contact is the desired outcome. Photography and illustrations Copyright Klemm Bohrtechnik. Pic. No.10 Automatic grease tensioning cylinder. FOUNDATION DRILLING July 2016 Page 41