Powder-actuated tool
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A Powder-actuated tool (often called "Hilti guns" or "Ramset guns" after two of the companies who manufacture the tools) is a nail gun used in the construction and manufacturing industries to join materials to hard substrates like steel and concrete. Also known as "direct fastening," this technology relies on a controlled explosion created by igniting a small chemical propellent charge, similar to the process that activates a firearm.
Unlike firearms, powder-actuated tools come in either high-velocity or low-velocity types. In high-velocity tools, which are now illegal to manufacture and/or sell in the United States, the propellant acts directly on the fastener. This process is very similar to how a firearm works. Low-velocity tools introduce a piston into the chamber. The propellant acts on the piston, which then drives the fastener into the substrate. (The piston is analogous to the bolt of a captive bolt pistol.) A powder-actuated tool is considered to be low-velocity if the average test velocity of the fastener does not exceed 492 feet per second. Although high-velocity tools are now illegal to manufacture and sell, there are some (made decades ago) that are still in use in the shipbuilding and steel industries.
Powder-actuated fasteners are usually nails made of high-quality, hardened steel, although there are many specialized fasteners designed for specific applications in the construction and manufacturing industries.
Powder-actuated technology was developed for commercial use during the Second World War, when high-velocity fastening systems were used to temporarily repair damage to ships. In the case of hull breach, these tools would be used to fasten a plate of steel over the damaged area.
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[edit] Usage
The photograph on the right shows a powder actuated fastener and the box that it is kept in. A small box of charges can be seen, (with C22 on the top) that are .22 caliber explosives, referred to as "charges" or "boosters" that are loaded singly each time this particular gun is used. The colored straws in the tray also contain cartridges that are loaded singly with the manual action of the breech. The cartridges are color coded for the various strengths. The strength of the charge determines the power of the particular charge.
In the tray can also be seen 75 mm hardened steel nails. The heads are 8 mm and the points of the fasteners have plastic spacers (also 8 mm) to hold the fastener central in the bore, at the point.
Fasteners take various forms, for example with threaded ends to use as an embedded bolt, with washers at the tips that grip softer material etc.
[edit] Operation
The motive force for powder-actuated tools comes from the pressure built up by the cartridge. These cartridges function similarly to blank firearm cartridges. In fact, in many cases, the charges are firearm cartridges with modified casings. The .22 Short, developed by Smith & Wesson is a popular choice. Thus, the powder in the name is actually cordite. These charges may be hand-fed, or manufactured and distributed on a plastic strip.
The charges are activated when a firing pin strikes the primer, which is a small explosive charge in the base of cartridge. The primer then ignites the cordite, which burns rapidly. The gases released by the burning of the propellant build up pressure within the cartridge, which acts either on the head of the nail, or on the piston, accelerating the nail towards the muzzle.
Powder actuated tools can be classified a number of ways:
- Direct acting (the charge acts directly on the head of the nail or high velocity), or indirect (using an intermediate piston or low velocity)
- Single-shot, or magazine-fed
- Automatic or manual piston cycling
- Automatic or manual feed of the charges
[edit] Safety
As with their air-actuated cousins, powder-actuated guns have a safety interlock built into the muzzle. If the muzzle is not pressed against a work surface with sufficient force, the firing pin is blocked or cannot reach the load to fire it. This ensures that the gun does not discharge in an unsafe manner, causing the nail to become a projectile. Nonetheless, good judgment should always be used when using a powder-actuated nail gun, since the nail is driven with far more force than an air-actuated gun. The user should always make sure the surface being nailed into is capable of stopping and holding the nail.
Most manufacturers of powder-actuated nail guns offer training and certification for operators. Many projects and employers require this certification before an employee is permitted to use the tool.
In Australia, these tools are classed as firearms, since they fire a projectile with potentially lethal force. As such their ownership and use is regulated in Australia. The owner has to register the tool, and an operator of one of these tools is required to have a license and to have undergone training in their use. These laws are in keeping with Australia's extremely strict firearm laws, which are intended to dissuade any citizens from owning firearms of any kind.
In the US, failure to properly dispose of charges is a common OSHA safety violation. Proper training is required by OSHA before someone can use it on a jobsite.
[edit] Typical manufacturers
Manufacturers of powder-actuated tools and fasteners include Hilti, ITW, Powers, Ramset, Simpson Strong-Tie Anchor Systems, and Remington.
