Solution Summary: Cordless Electric Adhesive Dispenser
Adhesive dispensers (i.e., caulking guns) are tools to hold and apply a cartridge of substance (i.e. caulk) that can be used in sealing gaps and cracks and filling holes in a broad range of materials. Cordless electric adhesive dispensers (Figure 1) are battery-powered tools that can eliminate workers’ manual squeezing efforts while enhancing their control over the dispensing volume and flow rate.
(Photo courtesy of Milwaukee Tool)
Adhesives such as epoxies are used throughout various stages in construction: hard-wearing coatings for floors, sealing bridges, and etc. One specific application of epoxies is to anchor rebar in a concrete slab. The process includes the following steps:
• Drill a hole slightly larger (usually sixteenth to quarter of an inch) than the diameter of the rebar.
• Blow out the dust from the hole using compressed air (some drills have a vacuum system inside them that can finish these two steps simultaneously), and clean the hole further using a nylon brush (if necessary).
• Fill the hole approximately two-thirds full with epoxy using a caulk gun.
• Insert the rod in the hole and adjust it accordingly.
Epoxy makes a strong bond between the concrete and the rebar, so they can perform as an integrated structural element. A common way to apply epoxy in this situation is to use a manual caulk gun. However, manual guns require a significant amount of force to dispense epoxy through the nozzle into holes in the concrete. This process also includes repetitive pressing of the trigger. Excessive force and repetition are two well-known factors that can contribute to musculoskeletal disorders (MSDs). Cordless electric adhesive dispensers (CEAD) could provide an alternate solution and reduce MSDs by minimizing both the workers’ force and repetition.
While the details may vary based on manufacturers’ guidelines, a general method to use the tool is as follows:
• Insert the cartridge (or foil pack) by pressing the release button, pull back the parallel piston rods, fit the cartridge, and screw the rear lug.
• Adjust the selector switch, squeeze the trigger, and fill the mixing nozzle.
• Discard a small amount of the mixture to ensure that the epoxy is consistent.
• Adjust the selection switch based on the hole’s depth and the amount of mixture needed (this amount can vary from 5 ml to 75 ml in some models).
• Press the trigger and fill the hole.
• Remove the cartridge by turning the selector switch to off, press the release button, pull the rods back and take out the cartridge.
Various models of electric dispensers are available on the market. Other than weight, which can play a big role in choosing the right model, one can select a dispenser based on its voltage and battery capacity. The availability of different cartridge sizes and the ability to adjust the amount of material dispensed could be other factors in selecting the tool.
The M18™ Cordless 20-oz Aluminum Barrel Caulk and Adhesive Gun (Photo courtesy of Milwaukee Tool)
Table 1 provides more information on some available models.
Any injury to the soft tissues (muscles, tendons, ligaments, joints, and cartilage) and nervous system could be classified as a musculoskeletal disorder or MSD (OSHA, 2000). These injuries often damage upper limbs/extremities (i.e., arms, from fingers to shoulder, and neck), lower limbs/extremities (i.e., legs from hips to toes) and back (http://www.hse.gov.uk/msd/index.htm) and could cause numbness, stiff joints, muscle loss, and etc. Ignoring ergonomics principles could expose workers to physical stressors, including vibration, awkward postures, repetitive motions, etc. that could lead to serious MSDs like carpal tunnel syndrome (CTS).
The Bureau of Labor Statistics has reported that in 2015 MSDs accounted for 31 percent of all cases of nonfatal occupational injuries and illnesses requiring days away from work. (https://www.bls.gov/news.release/osh2.nr0.htm). Data from National Safety Council (NSC) also show that MSDs are two times more likely than a combination of amputations, fractures, bruises, contusions, cuts, lacerations, burns, and chemical burns to occur in workers’ compensation claims. The National Institute for Occupational Safety and Health (NIOSH) has named construction tradespeople/construction industry among the highest-risk workers/industries for MSDs. While various risk factors could contribute to MSDs, this study has focused on two conditions: 1) exertion of excessive force and 2) performance of the same (or similar) tasks repetitively for an extended period of time. These conditions can put pressure on workers’ nerves and hurt their tendons. Using caulk guns to dispense epoxy and other adhesives involves many movements of the hand and wrist, mainly wrist flexion and extension, which could expose a worker’s hands to both of MSD risk factors. Holding the tool in a stable position and pressing the trigger repetitively would localize the stresses to fingers, wrist, and arm. In a study on hand injuries, Armstrong and Chaffin (1979) found that forceful exertion with flexed wrist is significantly associated with CTS. Hymovich and Lindholm (1966) also pointed out that grasping hand tools while performing repetitive tasks could cause MSDs in hands.
How Risks are Reduced:
Ergonomic tools are designed to fit a worker’s body to reduce physical stress and eliminate serious MSDs. CEADs can mitigate physical stress to workers’ hands and arms mainly by replacing muscular energy with electric power provided by batteries. These tools also incorporate features that let workers control the amount of dispensed material, so they can reduce the number of repetitions that are necessary with manual tools. The latter feature acts through dosage metering/adjustment dials/knobs and could significantly facilitate the task of filling holes in concrete. For instance, workers could dispense more materials per trigger pull for deeper holes by adjusting a setting on the tool. Ultimately, the ergonomic design of these tools can reduce wrist strain, especially when using high-viscosity materials.
Although CEADs can reduce the time and repetition of tasks, they may have one disadvantage over manual guns: they are generally heavier because they include batteries. So, caution must be exercised when buying these tools, as they are manufactured with a broad range of battery capacities which may vary in their weights. Therefore, lighter tools (with lower battery capacities) are suggested whenever possible. Companies can buy more lower capacity batteries for tasks that require longer operation time.
Effects on Productivity:
CEADs could increase productivity significantly. These tools can dispense material much faster than their manual counterparts and finish the job in much less time. They also include features such as pressure release triggers that can reduce material waste. Measuring the effect of CEADs on productivity could motivate contractor companies to buy them despite their higher sale prices.
Using the tool:
• Make sure the depth of the hole is adequate to avoid structural failure.
• Start filling the hole by placing the nozzle at the end of the hole to prevent formation of air bubbles at the end that could weaken the bond between rebar and concrete. Failure to do so also could cause the epoxy to splash into the worker’s face when the rebar is placed into the hole.
• Make sure the hole is clean by removing dirt by blowing air into it. Use a brush if necessary. Remaining dust and dirt could weaken the bond between structural materials significantly.
• Mark the nozzle beforehand to recognize when to stop dispensing material.
• Discard nozzles properly after the task is finished; they cannot be reused.
Maintenance of the tool:
• Always remove the battery before performing maintenance tasks.
• Remove dirt from the tool.
• Clean the air vents with a brush.
• Only use a slightly damp cloth to clean the casing.
• Keep the battery away from oil, grease, and moisture.
• Do not use a malfunctioning tool.
• Always remove the battery when transporting/storing the tool and don’t transport batteries in bulk.
• Store the tool and battery in cool and dry conditions.
Safety risks involved in using this tool include:
• Chemical hazards: Epoxy and other adhesives should be applied with care to avoid contact with skin and eyes. Never point the tool toward yourself or anyone else and make sure that the nozzle is in place before dispensing material.
• Trap hazards: Loading and unloading cartridges should be done with care. Hands can be trapped.
• The process of anchoring rebars require workers to clean bored holes by using compressed air to blow out the dust prior to adding rebar adhesive. These are high dust activities that in the absence of controls would place workers at risk of lung disease, cancer, chronic obstructive pulmonary disease (COPD), lung scarring and silicosis with prolonged exposure. It is recommended to use a dust extraction drill bit to eliminate this risk.
Behzad Esmaeili, PhD - George Mason University
Pouya Gholizadeh - George Mason University
- Masonry, Tile, Cement & Plaster
- Apply caulk, sealants and waterproofing materials