Hammer Drill Research Articles

Concrete building blocks made with recycled demolition aggregate

A study undertaken at the University of Liverpool has investigated the potential for using recycled demolition aggregate in the manufacture of precast concrete building blocks. Recycled aggregates derived from construction and demolition waste (C&DW) can be used to replace quarried limestone aggregate, usually used in coarse (6 mm) and fine (4 mm-to-dust) gradings. The manufacturing process used in factories, for large-scale production, involves a “vibro-compaction” casting procedure, using a relatively dry concrete mix with low cement content (≈100 kg/m 3). Trials in the laboratory successfully replicated the manufacturing process using a specially modified electric hammer drill to compact the concrete mix into oversize steel moulds to produce blocks of the same physical and mechanical properties as the commercial blocks. This enabled investigations of the effect of partially replacing newly quarried with recycled demolition aggregate on the compressive strength of building blocks to be carried out in the laboratory. Levels of replacement of newly quarried with recycled demolition aggregate have been determined that will not have significant detrimental effect on the mechanical properties. Factory trials showed that there were no practical problems with the use of recycled demolition aggregate in the manufacture of building blocks. The factory strengths obtained confirmed that the replacement levels selected, based on the laboratory work, did not cause any significant strength reduction, i.e. there was no requirement to increase the cement content to maintain the required strength, and therefore there would be no additional cost to the manufacturers if they were to use recycled demolition aggregate for their routine concrete building block production.

Acoustic assessment of pneumatic and electric jackleg drills used in the mining industry.

Hearing loss is the most prevalent disease among miners. A study of U.S. western hard-rock mines revealed that 96% of machine operators were overexposed to noise, with jackleg drill operators having the most rapid noise dose accumulation. Traditionally, jackleg drills have been driven by pneumatic power. However, there are currently available rotary hammer drills powered by electricity. This paper presents an acoustic assessment of pneumatic and electric jackleg drills that involved noise source identification (NSID), penetration rate and operator’s cumulative noise dose measurements, and determination of sound power levels. NSID using microphone phased array technology revealed two dominant noise sources for the electric drill, one located at the drill and one located at the drill steel-rock interaction place. In contrast, NSID for the pneumatic drill showed only one dominant noise source located at the drill. Penetration rate and noise dose measurements were combined to estimate the accumulated dose and time required to drill a reference depth hole. Sound power level measurements yielded overall 115 and 125 dB(A) for the electric and pneumatic drills, respectively. The results show that the acoustic performance of the electric drill, despite its slower penetration rates, overcomes the benefits of traditional pneumatic drills.

Field Evaluation of a Modified Intervention for Overhead Drilling

Drilling holes into concrete or metal ceilings is one of the most physically demanding tasks performed in construction. The work is done overhead with rotary impact hammer drills that weigh up to 40 N. The task is associated with pain and musculoskeletal disorders at the wrist, forearm, shoulder, and back. The mechanism of injury is thought to be the high forces and non-neutral shoulder and wrist postures applied during drilling. Previously, we described a field study of a foot lever and inverted drill press intervention devices that received poor usability ratings compared with the usual method for overhead drilling based on problems with mobility and productivity. Using a participatory intervention model, feedback from construction workers (N = 13) was used to develop a new intervention design that incorporated a wheeled tripod base and a unique method of aligning the drilling column to vertical. A different group of construction workers (N = 23) evaluated usability and fatigue of the new device during their regular overhead drilling in comparison with the usual method. Four of 12 usability ratings were significantly better with the intervention device compared with the usual method. Subjective shoulder fatigue was less with the new intervention (1.1 vs. 3.3; scale 0 to 5; p < 0.001). This difference was supported by objective outcome measures; the mean hand forces during drilling were 26 N with the intervention compared with 245 N with the usual method. The percentage of time with the shoulder flexed or abducted to more than 60 degrees was less with the intervention compared with the usual method (21 vs. 40%; p = 0.007). There was significantly less head extension with the intervention compared with the usual method. There were no significant differences in overall productivity between the two methods. This study demonstrates that a new intervention device for overhead drilling has improved usability and subjective fatigue ratings compared with the usual method. These improvements are most likely due to the reduced hand forces, reduced shoulder abduction and flexion, and reduced drilling time.

Failure Analysis of a Hammer Drill Shaft under Complex Loading Paths and Severe Environmental Conditions

This paper describes the failure investigation of a tubular shaft that is part of a hammer drill assembly. The failure investigation was particularly challenging as the fracture surfaces were completely damaged during and subsequent to the failure process. However, careful examination of the component and its assembly revealed many clues that pointed to the root causes of failure. It was determined that the shaft was subjected to impact, fatigue, bending and torsional loads simultaneously at elevated temperatures. The basic failure mode was identified as a combination of torsional fatigue and rotating bending fatigue failure that originated on the inside diameter of the shaft. The root causes were determined to be operational overload in combination with rough machining marks on the bore surface and higher than necessary operating torque required to overcome the dry adhesive friction in the system. The preventative measures recommended were many-fold including improving surface finish on the bore diameter, reducing dry sliding friction, decreasing the overall level of dynamic loads by appropriate design changes and adding a surface strengthening heat treatment

Optimization of drilling and blasting operations in an open pit mine—the SOMAIR experience

Drilling and blasting play vital roles in opencast mining. These operations not only affect the cost of production directly but as well and significantly, the overall operational costs. This research was carried out to find a possible way of optimizing the drilling and blasting operations in an open pit mine of Somair (Société des Mines de l'Air), in the Niger Republic. In order to optimize the drilling operation, the time taken by two drilling machines to accomplish the same task was analyzed statistically. The result indicates that the Down the Hole Hammer Drilling Rig (DMNo406) is more efficient than the Drill Master (DM405). The relative unit consumption of two explosives (Explus and Nitram 9), when used under the same operating conditions, were also considered and the results indicate Explus to be more economical per unit consumption with a range of 0.15 g/t–0.183 g/t, when compared with Nitram 9 with a unit consumption range of 0.19 g/t–0.24 g/t in the study area.

Numerical simulation of impact on pneumatic DTH hammer percussive drilling

The process of DTH (down-the-hole) hammer drilling has been characterized as a very complex phenomenon due to its high nonlinearity, large deformation and damage behaviors. Taking brittle materials (concrete, granite and sandstone) as impact specimens, the explicit time integration nonlinear finite element code LS-DYNA was employed to analyze the impact process and the penetration boundary conditions of DTH hammer percussive drilling system. Compared with previous studies, the present model contains several new features. One is that the 3D effects of DTH hammer drilling system were considered. Another important feature is that it took the coupling effects of brittle materials into account to the bit-specimen boundary of the drilling system. This distinguishes it from the traditional approaches to the bit-rock intersection, in which nonlinear spring models are usually imposed. The impact forces, bit insert penetrations and force-penetration curves of concrete, granite and sandstone under DTH hammer impact have been recorded; the formation of craters and fractures has been also investigated. The impact loads of piston-bit interaction appear to be relatively sensitive to piston impact velocity. The impact between piston-bit interaction occurs at two times larger forces, whereas the duration of the first impact doesn’t change with respect to the piston velocity. The material properties of impact specimen do not affect the first impact process between the piston and bit. However, the period between the two impacts and the magnitudes of the second impact forces greatly depend on the specimen material properties. It is found that the penetration depth of specimen is dependent on the impact force magnitude and the macro-mechanical properties of the brittle materials.

Reducing Silica and Dust Exposures in Construction During Use of Powered Concrete-Cutting Hand Tools: Efficacy of Local Exhaust Ventilation on Hammer Drills

Concrete cutting in construction is a major source of exposure to respirable crystalline silica. To reduce exposures, local exhaust ventilation (LEV) may be integrated into the hand tools used in concrete cutting. Volunteers from the New England Laborers Training Center participated in a field study focused on the use of LEV on concrete-cutting hammer drills. A randomized block design field experiment employing four workers measured the efficacy of four hood-vacuum source combinations compared with no LEV in reducing dust and silica exposures. Using four-stage personal cascade impactors (Marple 294) to measure dust exposure, a total of 18 personal samples were collected. Reductions of over 80% in all three biologically relevant size fractions of dust (inhalable, thoracic, and respirable) were obtained by using any combination of hood and vacuum source. This study found that respirable dust concentrations were reduced from 3.77 mg/m3 to a range of 0.242 to 0.370 mg/m3; thoracic dust concentrations from 12.5 mg/m3 to a range of 0.774 to 1.23 mg/m3; and inhalable dust concentration from 47.2 mg/m3 to a range of 2.13 to 6.09 mg/m3. Silica concentrations were reduced from 0.308 mg/m3 to a range of 0.006 to 0.028 mg/m3 in the respirable size fraction, from 0.821 mg/m3 to a range of 0.043 to 0.090 mg/m3 in the thoracic size fraction, and from 2.71 mg/m3 to a range of 0.124 to 0.403 mg/m3 in the inhalable size fraction. Reductions in dust concentrations while using the four LEV systems were not statistically significantly different from each other.

초고강도콘크리트와 보강 구조물을 사용한 금고 충전부의 초고열과 극한충격파괴에 대한 거동

It is a trend to increase safekeeping properties in financial company as the world economy situation has been globalized and advanced. The development of a securable vault door resisting to malicious trespass is needed. Therefore, this study focuses on developing high performance concrete placed at the inside of the vault door, and all materials used in this study is easy to obtain in domestic considering economic competitiveness. The compressive strength over 170 MPa was targeted, and structurally strengthening was also planned in order to resist to over heating by torch and extreme impact loading by hammer drilling machine. Several types of fibers and reinforcing structures were used in order to resist those external heating and loading. This purpose was required to satisfy UL 608 standard of a vault door. Consequently, the result from this study is expected to be applied to construction field of major facilities, which should guarantee the safety from an external attack such as terror.

An experimental investigation of jack hammer drill noise with special emphasis on drilling in rocks of different compressive strengths

An attempt has been made in this paper to investigate the influence on sound level due to drilling in rocks of varying physical properties i.e. compressive strength and abrasivity using jackhammer drill. For this purpose, a jackhammer drill setup was fabricated wherein the thrust applied can be varied while drilling vertical holes. The compressive strength and the abrasivity of various rock samples collected from the field were determined in the laboratory. A set of test conditions were defined for measurement of sound level of the jackhammer drill.Also, with the help of the experimental setup, vertical drilling was carried out on the rock samples for varying thrust and air pressure values and the corresponding A-weighted equivalent continuous sound levels were measured.The results of this study indicate that, increase in thrust increases the sound level at higher midband frequencies in the noise spectrum. The study indicated the sound level near the drill rod to be 0.5 to 1.5 dB, 2.0 to 3.0 dB and 4.0 to 6.0 dB higher relative to that at the drill bit, the exhaust and the operator’s position respectively at an air pressure of 5 kg/cm 2 and 160 N thrust for all the rock samples tested. Both the thrust and air pressure were found to have a significant effect on the sound level produced by jackhammer drill at all the measurement locations. The study further shows that an increase in sound level of the order of 1.5 to 2.5 dB at the operator’s position can occur with an increase in air pressure by 2 kg/cm 2 at 160 N thrust and with an increase in compressive strength and decrease in abrasivity of rocks. Also, the increase in sound level at the operator’s position with increase in compressive strength and decrease in abrasivity of rock is of the order of 1.0 to 2.0 dB. In order to maintain a constant penetration rate in the rocks, both the thrust and air pressure need to be increased with an increase in compressive strength and decrease in rock abrasivity.Therefore,increased compressive strength and lower abrasivity of rocks will require higher air pressure and thrusts to be applied to achieve an optimum penetration rate and therefore will result in higher sound level at the operator’s position and at other measurement locations. © 2007 Institute of Noise Control Engineering.

On-Line Monitoring to Detect Third-Party Damage on Underground Natural Gas Pipelines Using Accelerometer

Even though an excavation is not under the direct control of the utility operators, it is the main cause of third-party damage on the underground natural gas pipelines. Since the damage due to third-party excavation may lead to horrible consequences, preventative techniques that can reduce the third-party damage are needed. The purpose of this paper is to introduce an on-line monitoring system using accelerometer to detect a propagating acoustic pressure pulse that is produced from the third-party damage. Also, in order to verify this system, the corresponding field tests were performed considering many third-party damage sources(breaker, hammer drilling, etc.) and signal transmission ratio of each source. From the tests, signals developed by the third-party damage sources were successfully detected with the digital filter, which can distinguish external noises at the distance of 13km. Therefore, it is expected that the system can be used as a useful tool for the third-party damage monitoring of underground natural gas pipelines

Determination of Lime in Hot-Mix Asphalt

Lime is added to hot-mix asphalt to mitigate stripping and other modes of moisture damage. No standard forensic test exists for the measurement of the lime content after it has been incorporated in the asphalt. This paper evaluates several methods to quantify the amount of hydrated lime (calcium hydroxide) in asphalt. A rapid analytical technique, Fourier transform infrared spectroscopy, was identified for determining the quality and quantity of lime. It yields qualitative or semiquantitative results from samples as small as 10 mg. No sample preparation is involved, and the binder can be scraped directly from large stones in the hot mix. The analysis can be completed in 30 s and offers the possibility of timely adjustment to the mix. For more accurate quantitative measurement, a second procedure is recommended. Samples are taken from cores with a hammer drill. The lime is separated from the resulting dust by acid extraction, and the calcium level is determined by atomic absorption spectroscopy or ion exchange chromatography. Different methods for removing the binder are discussed.

Determination of Lime in Hot-Mix Asphalt

Lime is added to hot-mix asphalt to mitigate stripping and other modes of moisture damage. No standard forensic test exists for the measurement of the lime content after it has been incorporated in the asphalt. This paper evaluates several methods to quantify the amount of hydrated lime (calcium hydroxide) in asphalt. A rapid analytical technique, Fourier transform infrared spectroscopy, was identified for determining the quality and quantity of lime. It yields qualitative or semiquantitative results from samples as small as 10 mg. No sample preparation is involved, and the binder can be scraped directly from large stones in the hot mix. The analysis can be completed in 30 s and offers the possibility of timely adjustment to the mix. For more accurate quantitative measurement, a second procedure is recommended. Samples are taken from cores with a hammer drill. The lime is separated from the resulting dust by acid extraction, and the calcium level is determined by atomic absorption spectroscopy or ion exchange chromatography. Different methods for removing the binder are discussed.

Sound power measurement techniques for powered hand tools

As part of a project to reduce noise induced hearing loss in the construction industry, NIOSH developed a database of sound power level measurements of electric powered hand tools typically used in the construction industry. The tool testing jigs and setups specified and illustrated in ANSI S12.15 were modified to accommodate the higher precision ten‐microphone arrangement used in ISO 3744. ANSI S12.15 is sometimes vague regarding the tool testing jig design, so test jigs were designed to supplement existing specifications in the standard. In the course of the project, test jigs were designed, techniques were devised to improve repeatability of measurements, to reduce waste materials, to reduce measurement setup time, and to reduce data acquisition time. Several types of tools were tested including circular saws, grinders, screw drivers, drills, jig saws, reciprocating saws, miter saws, hammer drills, belt sanders, and impact wrenches. The test jig designs and measurement techniques may help others to save time, reduce waste material, and improve measurement repeatability. Additionally, a microphone was placed in the nominal hearing zone of the tool operator to acquire a time series to assess other sound metrics.

충격 햄머 드릴의 성능향상을 위한 연구

This paper Presents the performance test of an impact hammer drill in conjunction with the parameter consideration of coefficient of restitution, lubrication and friction, pressure leakage, vibration damper and production quality. Novel measurement setups are innovated in order to get the Parameter data. The measured data are compared with the computational results, and this comparison gives a confidence on the computational model, which can be used for a optimal design of impact hammer drills.

Evaluation of Workers' Exposure to Total, Respirable and Silica Dust and the Related Health Symptoms in Senjedak Stone Quarry, Iran

The present research was conducted in a stone quarry of marble located in northeast of Iran. Time weighted average of total dust, respirable dust, and crystalline silica (alpha-quartz) concentration in workers' breathing zone were monitored by using both gravimetric and XRD methods. The results showed that the employees working in hammer drill process had the highest exposure to the total and respirable dust: 107.9 +/- 8.0 mg/m3, 11.2 +/- 0.77 mg/m3 respectively, while the cutting machine workers had the lowest exposure (9.3 +/- 3.0 mg/m3, 1.8 +/- 0.82 mg/m3). The maximum concentration of a-quartz in total and respirable dust were detected equal to 0.670 +/- 8.49 x 10(-2) and 5.7 x 10(-2) +/- 1.6 x 10(-2) mg/m3 respectively, which belonged to the exposure of the workers of hammer drill process. The prevalence of skin and respiratory symptoms were higher in hammer drill workers, however, respiratory symptoms showed no significant prevalence. Regarding the average age of workers (31.6 +/- 1.9 yr) and average of their work history (3.8 +/- 1.0 yr), these results were predictable.

Effective use of water in a system for water driven hammer drilling

Drilling with water driven down-the-hole (DTH) hammers is a recently developed method for competitive production of boreholes. In order to prevent large amounts of water being used during operation, the drilling fluid is here directly processed into a quality acceptable for reuse. The effectiveness is evaluated in well drilling with a mobile prototype water cleaning and pressurising unit. Especially the presence of abrasive particles in the fluid can drastically reduce tool life and make the method inefficient. The vital significance of this relation has called for detailed studies and a process simulation model for determining particle concentration and size distribution has been developed. This paper describes the model and how it is applied. Simulation results of different system configurations are also presented.

Influence of 3D effects on the efficiency of percussive rock drilling

The aim is to investigate the influence of 3D effects on the efficiency of three processes for percussive rock drilling, viz., hammer drilling, down-the-hole drilling and churn drilling, each based on the use of tube-shaped members. A 3D axisymmetric finite element study is carried out for systems with idealised geometries. The efficiencies obtained are compared with formulae obtained from 1D analyses. It is found that the efficiencies based on 3D analyses are generally slightly lower than those based on 1D analyses. The difference is typically about 4% for hammer drilling, of the order of a percent or less for down-the-hole drilling, and practically non-existent for churn drilling. In the case of hammer drilling, the reduction of efficiency due to 3D effects is found to be slightly larger for tubes with relatively thin walls than for tubes with massive cross-sections. The lower efficiency in 3D is partially due to contributions to the kinetic and potential energies from components of velocity and stress which do not promote the performance of work on the rock. It is concluded that from a practical point of view, there is no need of 3D corrections of the 1D results for efficiency except possibly in the case of hammer drilling.

Prevalence and pattern of occupational exposure to hand transmitted vibration in Great Britain: findings from a national survey

OBJECTIVESTo estimate the number of workers in Great Britain with significant occupational exposure to hand transmitted vibration (HTV). Also, to identify the occupations and industries where such exposures arise, and...

Validity of self reported occupational exposures to hand transmitted and whole body vibration

OBJECTIVESTo assess the accuracy with which workers report their exposure to occupational sources of hand transmitted (HTV) and whole body vibration (WBV).METHODS179 Workers from various jobs involving exposure to HTV...

Analysis of Impact Hammer Rebound to Estimate Rock Drillability

¶In this paper, the piston rebound common to both the Schmidt Impact Hammer and down-hole hammer drills has been analyzed and calculated by means of stress wave theory and the energy conservation law. A quantitative relationship between the amount of rebound of the piston and the impact resistance index, or hardness of the rock, has been established. Those analytical results will not only be of benefit in acquiring a deep understanding of the usable range and condition of the Schmidt Impact Hammer, but also provide a definite answer to the feasibility of using the hammer rebound in drills with down-hole hammer tool to carry out a real time measurement of the nature of the formation under the bit.