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Trust In God, But Keep Your Powder Dry As published in the July 7, 2011 issue of
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Trust In God,But Keep Your Powder Dry
As published in the July 7, 2011 issue of
8/6/2019 TrustInGod-AssemblyMag-July2011
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Dispensing: Sweating Bullets by John Sprovieri, Editor in Chief Assembly Magazine
“Trust in God, but keep your powder dry.” That was goodadvice to riflemen in the 1800s, and it still applies today.These days, however, gunpowder is protected from theelements inside a cartridge that’s been sealed with a high-tech adhesive.
A modern cartridge consists of the bullet itself; the case; the propellant; the rim,which aids in loading; and the primer, which is located at the bottom of the caseand ignites the propellant. The primer consists of small metal cup, a small amountof an explosive compound, and a triangular piece of metal called the anvil. Whenstruck by the firing pin, the center of the cup collapses, pressing the explosiveagainst the anvil. The explosive ignites and shoots a flame into the case, ignitingthe propellant and expelling the bullet.
During assembly, the primer is pressed into a hole at the base of the case. Theprimer must be flush, or the cartridge will not feed correctly in the magazine. Afterthe case is filled with propellant, the bullet is pressed into the case and crimped inplace.
To keep moisture from spoiling the propellant, a sealant must be applied betweenthe bullet and the case. In the past, this sealant was applied inside the case beforethe bullet was inserted. The sealant “was an emulsion, like a black tar,” explainsLarry Henderson, president of L-Tech Enterprises Inc., an ammunition assembler inEubank, KY.
This material presented three problems for L-Tech. First, because the sealant wasapplied before the bullet was inserted, the company could not assemble cartridgesif a problem arose with the material or the dispensing process. “With the[emulsion], you had to insert the bullet within a short period of time after it wasapplied,” says Henderson.
Another issue was that the quality of the seal depended on how accurately thebullet was pressed into the case. If the bullet scraped against the inside wall of thecase, a leak path could be created. Finally, dispensing the material accurately wasdifficult with small caliber ammunition. “With the smaller cartridges, we justcouldn’t get it to seal,” says Henderson.
As between the bullet and the case, a sealant also has to be applied between thecase and primer to prevent moisture from compromising the explosive. For thistask, L-Tech had been using a solvent-based material, which could be put on afterthe primer was inserted. The problem with that material, however, was its curespeed. L-Tech wanted a sealant that cured instantly and did not contain volatileorganic compounds. As lethal as its products may be, L-Tech wanted an eco-friendly assembly process.
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A Good Seal
For help, L-Tech turned to Hernon Manufacturing Inc., asupplier of adhesives, sealants, dispensing machines andcuring equipment. Based in Sanford, FL, the company hasbeen working with ammunition manufacturers for years,including ATK, General Dynamics, Remington, Winchester, IMIand the Chemring Group.
For the junction between the bullet and the case, Hernonprovided its External Bullet Sealant 59541, a single-component, solvent-free, dual-curing anaerobic adhesive.Applied after assembly, this toughened material wicks downbetween the bullet and the cartridge case in less than 5seconds. Once inside the joint, it reaches fixture strength inless than three minutes. Any adhesive that remains outside the
joint cures in seconds when exposed to ultraviolet (UV) light.Full strength is reached in 24 hours.
The material has good gap-filling properties and maintains aseal even under full vacuum. When fully cured, the adhesive isa thermoset plastic that resists most solvents and withstandstemperatures ranging from -65 F to 400 F.
“That material just wicks right around the cartridge,” saysHenderson. “It’s been working really well.”
For the junction between the primer and the case, Hernonprovided its Ammunition Primer Sealant 59621. Like the bulletsealant, the primer sealant is a low-viscosity, single-component, dual-curinganaerobic adhesive. It, too, is applied after assembly, penetrating the joint bycapillary action and curing quickly in the absence of oxygen. Adhesive that is notdrawn into the joint is cured via UV light.
The material cures quickly at room temperature without the need for surfaceactivators or heat. Fixturing strength develops in two to three minutes, or within 10seconds by exposing the joint to high-intensity, long-wavelength UV light (365nanometers). To ensure full curing, the UV light irradiance should exceed 60milliwatts per square centimeter. Full strength is reached in 24 hours.
To aid in inspection, Hernon adds a fluorescent dye to the sealants. The dye glowsunder UV light, enabling a vision system to detect whether the adhesive haspenetrated the entire joint. “It makes inspection much simpler,” says Henderson.
“We also use a high-intensity black light to manually inspect any cartridges that arekicked out by the automatic inspection system.”
At the bullet sealing station,the cartridgesass beneath a
dispensing valveequipped with amedical-gradeneedle. The
needle isositioned at anangle to the
cartridges. Itsbeveled tip isust above theunction between
the bullet and case, but doesnot touch thecartridge. Photocourtesy Hernon
Manufacturing Inc.
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Formulating the sealants was a challenge. “The sealants must have enoughviscosity to stay where they are dispensed, but also be thin enough to wick into the
joints,” says Tom Bray, engineering manager at Hernon.
The materials also have to create a good seal without impairing the performance of the cartridge when fired. Hernon’s adhesives and sealants meet a number of military specifications, including MIL-A-46106A, MIL-A-46050C, MIL-I-17563C, MIL-R-46082B, MIL-S-22473E, and MIL-D-46163A.
High-Speed Dispensing
If developing a good bullet and primer sealant is akin toputting a round or two into the X ring from 50 yards, thendesigning a system to dispense that material at the speeds andaccuracies necessary for high-volume ammunition assembly islike going 10 for 10.
Hernon’s Auto Sealer 5000 is designed specifically fordispensing and curing sealants on pistol and rifle ammunition,including blanks. The system applies sealant to both theprojectile and the primer at speeds in excess of 200 rounds perminute.
Assembled cartridges are fed into the system from a largevibratory bowl. From the bowl exit, the cartridges slide onto acustom-made chain conveyor that resembles the treads for a
tank or bulldozer. Each link in the chain contains an open slotto hold one cartridge. The cartridges are placed on theconveyor perpendicular to the direction of travel, with the tipof the bullet facing the opening. As the conveyor moves, thecartridges roll in place like roller bearings.
At the bullet sealing station, the cartridges pass beneath Hernon’s Sure Shot 3200dispensing valve equipped with a medical-grade needle. The digitally controlledvalve is driven by a servomotor. The needle is positioned at an angle to thecartridges. Its beveled tip is just above the junction between the bullet and case,but does not touch the cartridge.
As a cartridge rolls beneath the needle, a single drop of sealant is applied to the
joint. The rolling action of the cartridge ensures that the sealant is evenlydistributed around the entire joint. The amount dispensed is accurate to within±0.5 microliter.
At the primer sealing station, a second Sure Shot 3200—equipped with a curvedneedle—dispenses a dot of sealant on the primer. Unlike the previous station, theneedle must contact the cartridge to apply the sealant.
At the primer sealing station, a second valve—equipped with acurved needle—dispenses a dot of sealant on therimer. The
needle must contact thecartridge to
apply the sealant. Photocourtesy HernonManufacturing Inc.
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That requirement was a challenge, says Bray. Given the lowviscosity of the sealant, moving the needle up and down at 200cycles per minute tended to send drops flying before theyreached the primer. Hernon’s engineers solved the problem bymoving the needle in an oscillating path, rather than straight upand down.
At the next station, the cartridges roll past two UV lamps.The lamps both cure the sealants and serve as a light sourcefor a pair of machine vision system, which check theintegrity of the seals.
The system can handle a range of different sizes, from .22-to .762-caliber. Tooling changeover can typically beaccomplished in 30 to 60 minutes. One feeder bowl canaccommodate three ammunition sizes.
To see the Auto Sealer 5000 in action, please visit thehernon ammunition sealing website at ammo.hernon.com.For more information on adhesives, sealants, dispensing
machines and curing equipment, call Hernon at 1-800-527-0004 or visitwww.hernon.com.
121 Tech Drive, Sanford, FL 32771 | T: (407) 322-4000 | E: [email protected]
The Auto Sealer 5000 applies sealant to boththe projectileand the primer at speeds in excessof 200 rounds
er minute. Photocourtesy Hernon
Manufacturing Inc.
