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2015FallShotcreteEMag

Dry-Process Nozzle Setups Dry-Process Machines Fig. 5: Rotary guns have over 50 years in the Fig. 4: These dry-process nozzles are designed field use. This dry gun barrel-type gun is an air to handle the high material velocity and produce over/hydraulic unit for more consistent material adequate spray patterns; also shown are flow and has an external air exhaust to keep it different hose coupling sets. Six of the nozzle from bubbling up through the hopper during setups have water rings with 8 to 16 small material discharge. This gun type can push 1/16 in. (1.6 mm) holes that create a cone when macro- and micro-steel and synthetic fibers the water is turned on; as the material passes through the gun. These guns have pushed through the water, the material is partially material over 400 ft (120 m) vertically and over mixed as the nozzleman builds up the layers. 2500 ft (760 m) horizontally The 2 in. (50 mm) setup water ring has 16 straight holes in it and requires more water pressure and air volume to properly mix and compact the material 500 ft (150 m) horizontally and 100 ft (30 m) vertically, even though a few contractors have pushed past the manufacturer’s rated distances. Bowl guns have a short life cycle due to the wear items and the light-duty gear boxes that need constant upkeep. The missing external exhaust chamber in some bowl guns results in air being discharged back through the hopper, causing bub- bling of the material and excess dusting. This type of machine was also designed for a less skilled worker, who just has to feed the hopper of the machine (gun) during operation. Fig. 6: Bowl guns have been used over 50 years Remember, it requires more volume of air to in the field use. It has no external exhaust, successfully convey the material through the allowing the excess air to bubble up through rotary dry guns. The higher air volume is also the hopper. The U-shaped bowl makes it needed to run the air motors of the machines difficult to push macro-synthetic and steel fiber without causing blow by (bubbling up in the open mixtures up and through the material outlet and hoppers) when gunning horizontal and vertical limits the horizontal distance the material can runs, which is commonly not experienced when be pushed operating a pressure vessel type of gun. Remember to consult your manufacturer when attempting to (15 m) of 1-1/2 in. (38 mm) material hose while push material horizontally and vertically long gunning horizontal surfaces. When the nozzle is distances if you experience bubbling material up above the hopper of the open vessel guns, the air through the hopper. ACI 506R-054 lists the com- requirement will always be higher due to the extra pressor capacities and material hose diameter air volume needed to convey the material out and (refer to Table 3-1 in the document). All open up through the mixing nozzle. The air motor on vessels need a minimum of 600 CFM (17 m3/min). the rotary guns takes as much as 185 ft3/min Some manufacturers say you can use a 365 ft3/ (5.25 m3/min) of air to run it properly. min (10 m3/min) compressor provided the unit is One of the biggest issues that is faced by the hydraulically driven and you only have 50 ft shotcrete contractor since the early 1970s is that 12 Shotcrete • Fall 2015


2015FallShotcreteEMag
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