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Tamping-style capsule fillers
 
Q: How can we increase the efficiency of our tamping-style capsule fillers?
 
 
imageWhen operators set up tamping-style capsule fillers properly to tamp the powder, the equipment will create an evenly layered powder slug prior to filling a two-piece capsule with the slug. These fillers can also be set up to fill capsules with liquid, pellets, or tablets, but most capsules are filled with powder. The tamping process produces filled capsules with more accurate and consistent weights compared to dosator-style capsule fillers. You adjust the weight range by changing the depth of the tamping pins and the thickness of the dosing disc.
 
Tamping-style capsule fillers provide setup adjustments to allow for the filling of a range of products having different properties, such as fine, thick, sticky, abrasive, or viscous. A common mistake is to use settings for thick powders and not make any adjustments for fine powders.
 
If the capsule filler is set up for a fine powder and you introduce a thick powder, the machine will likely seize, jam, or crash. If the capsule filler is set up for a thick powder and you introduce a fine powder, the machine will likely produce capsules that are acceptable but at the expense of excessive powder loss, unplanned downtime for cleaning, and premature wear of spare parts. Failure to properly operate and maintain your capsule fillers can also result in poor performance.
 
To maximize the efficiency of your tamping-style capsule fillers, evaluate the following factors related to proper setup, operation, and maintenance.
 
Dosing disc thickness
Using a dosing disc with the correct thickness is critical to allowing the capsule filler to tamp the powder into an evenly layered slug. A dosing disc that's too thick won't allow for the amount of tamping pressure required to create a good powder slug. Powder loss will occur as the disc indexes from the last tamping station to the transfer station and as the powder transfers from the dosing disc to the capsule body. The powder that doesn't fall into the capsule body at the transfer station will disperse around the machine and eventually cause closing and separation issues and require frequent replacement of the seals, bearings, and shafts.
 
The most accurate way to determine the optimal dosing disc thickness is to set the tamping pins to the recommended depths, tamp and fill good slugs, and then weigh the filled capsules. You can use the simple algebraic equation below to solve for the required thickness X.
 
Filled capsule weight =     target weight    
thickness of dosing disc used       X    
 
A less accurate but much faster and more efficient method to determine an approximate thickness is to use a slug tester or a dosing disc determinator. These tools can simulate the tamping process and determine the required dosing disc thickness without requiring a capsule filler, eliminating the setup time, and using much less product.
 
A slug tester uses a measured dose of powder at the target weight, together with a punch and die that simulates the tamping pin and dosing disc bore for the required capsule size. You apply a set force—typically 40 newtons—to the powder inside the die and then measure the length of the slug to determine the required dosing disc thickness.
 
A dosing disc determinator is a stainless steel rectangular block that simulates a dosing disc with a row of holes for each capsule size and a consistent thickness, typically 15 millimeters. You fill the bore with powder for the required capsule size and then use a tamping pin with a rubber mallet to manually tamp a slug. You weigh the slug and use the algebraic equation above to determine the required disc thickness.
 
Tamping pin depth
A dosing disc has six pockets of bores that allow for five tamping stations and one pocket for the fixed transfer station. You should set the depths of the tamping pins so that the fifth tamping station allows the tamping pins to sit just above the top of the dosing disc bore. This station levels off the powder slug before the powder wiper cleans excess powder from the top of the slug.
 
You should set the fourth tamping station 2 millimeters into the bores and then set each of the remaining three stations 2 to 3 millimeters deeper than the previous station. This allows the tamping pins at the first station to go the deepest and the remaining four tamping stations to tamp even layers on top of the first tamp, creating a compact, smooth, and evenly layered powder slug.
 
Tamping ring height
The tamping ring height is adjustable so that you can set the gap between the ring's top surface and the dosing disc's bottom surface to suit the powder properties. Thicker powders require a wider gap; finer powders require a tighter gap.
 
If the gap is too tight, the machine will jam. If the gap is too wide, excess powder will spill out of the dosing station. A gap of .003 inch is recommended as a starting point. After you determine the correct gap for a specific product, add that information to the batch card, together with the dosing disc thickness and tamping pin depths to decrease the setup time for the next production run.
 
Transfer station alignment
The transfer station is where the dosing pins press the powder slug out of the dosing disc and into the lower capsule body. If the dosing disc bore and the lower segment bore are not aligned at the transfer station, the slug will hit the side of the lower segment bore and a portion of the powder won't enter the capsule body.
 
You should check this alignment during every setup because it's easy to check at this point and re-align if needed, before you assemble the tamping station. If you have to re-align the lower segment turret after you introduce powder, you then must remove the powder and disassemble the tamping station to properly re-align the lower segment turret to the dosing disc. You can adjust all of the other stations—faulty, closing, ejection, cleaning, and separation—to align to the lower segment turret. It's easy to overlook the fact that a turret is out of alignment because you can adjust everything else to work and make acceptable capsules at the expense of lower yields and inefficiency.
 
Dust extraction manifolds and dust collection cyclones
Dust extraction manifolds at the dosing, closing, and cleaning stations pull excess powder away from the machine. If the excess powder is not pulled away, it can enter the segment bores and cause closing and separation issues. Excess powder can also cause excessive wear to the seals, bearings, and shafts of the main table and segment carrier.
 
A dust collection cyclone can help the operator determine how much powder loss is occurring while a capsule filler is running and to make any required adjustments while the batch is in process. Cyclones can catch up to 99 percent of excess powder and can significantly extend the life of the vacuum system's filters.
 
Setup teams
Setup teams that include an experienced maintenance mechanic and operator can decrease changeover time and prevent operational issues by ensuring that the capsule filler is set up and running properly at the start of a production run.
 
Powder diverters
If the centripetal force isn't strong enough to distribute the powder from the dosing disc's center into the disc's bores along the outside, the result can be low capsule weights and high weight variations. You can install powder diverter fins and a powder diverter cone to force the powder to the outer edge of the powder bowl and into the disc bores.
 
Coated tooling
Coated segments, tamping pins, and dosing discs can prevent powder sticking and protect against wear. Tooling suppliers commonly use General Magnaplate's Nedox SF-2 [1] and HMF [2] coatings. These coatings are FDA- and USDA-compliant and offer increased lubricity and corrosion resistance compared to nickel and chrome plating. Tooling suppliers must custom-manufacture the coated tooling to allow for the thickness of these coatings.
 
Preventive maintenance
Following a preventive maintenance schedule and regularly changing the grease, bearings, springs, and seals can ensure that your capsule filler runs optimally. This maintenance can also prevent damage and wear to more expensive parts such as the segment carriers, shafts, cams, and guide plates.
 
Training
Investing in hands-on training can pay dividends in decreasing powder loss, unplanned downtime, and frequent replacement of common wear parts while increasing yields, production, efficiency, and profitability.
 
References
  1. General Magnaplate. Nedox SF-2 coating, accessed 6/25/19.
  2. General Magnaplate. HMF coating, accessed 6/25/19.
 

 
Brendan Kelly is general manager at Index Encapsulation Equipment and Compression Components and Service, both in Warrington, PA. The companies provide capsule fillers, tablet presses, and control systems to the pharmaceutical and nutraceutical industries.
 
Do you have a question for our experts? Send your questions to pwright@cscpub.com, and we'll have an expert answer them.
July 8, 2019
 
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