Tamping: Fine-Tuning Capsule Filling

 Tamping: Fine-Tuning Capsule Filling
By Jon Carlisle
Encapsulation Technical Sales Manager
Natoli Engineering Inc.


If you’re thinking about encapsulating high-volume, well- formulated products, a tamper-style encapsulator is your best bet (dosator-style encapsulators work with sticky products, while hand-filling-style machines handle coarse products and small volumes well) Tamper-style encapsulators use pins to push through a pile of powder, forcing an ambiguous amount into a dosing bore. This is repeated several times prior to transfer into the capsule body. 

The capsule’s contents is called a “slug”. An ideal slug is cylindrical, semi-solid, uniform, and flat on top and bottom. A consistent slug promotes accurate fill weight and clean transfer into the capsule body at high speeds. 

To achieve the slug at the desired fill weight, you must answer two questions: 

  1. Can the product form a slug at 30 – 75 Newtons of force? 
  2. Is the correct thickness of dosing disk being used? 

If the product cannot form a slug at 30 – 75 Newtons of force, it will run dirty, causing a host of problems. Additionally, disk thickness and fill weight are somewhat proportional. If the disk creating the “die” for the slug is too thick, fill weight will be too heavy; if the “die” is too thin, fill weight will be too light. 

Selecting the Correct Dosage Thickness 

You can select the correct dosing disk thickness two ways: with a slug tester or real-time data. A slug-tester is a spring rate tester that is tooled with dies and punches that match the dosing bore and tamper nose diameters. The desired fi ll weight of product is measured on a gram scale and poured into the die. The product is then compressed with a punch. The slug tester has a readout for force (30 – 75 Newtons) and height (thickness of dosing disk). 

Real-time data requires the machine to be completely tooled up and running with enough powder to replicate an actual production run. Often, real-time data is collected during a troublesome production run. In this approach, chase the slug and disregard the capsule’s weight. A slug needs to be formed for accurate data collection. Once a good slug is achieved, note the dosing disk’s thickness and the capsule’s weight. Below is an example: 

Using a 24mm thick dosing disk, a weight of 850mg forms a good slug. Target weight is 750mg.

What thickness of dosing disk (D) is required to achieve a good slug? 

D/750mg = 24mm/850mg 

850 × D =24 × 750 

850 × D =18,000 

D = 18,000/850 

D =21.2mm 

Proper Settings 

There are many approaches to setting the tamping station heights. These approaches reference the thickness of the dosing disk. My preferred initial approach is the “Equal Steps” method (Figure 1). The first station to tamp after the slug is transferred is considered Station #1. The final tamp just before slug transfer is considered Station #5. For a 20mm thick dosing disk, Station #1 is adjusted to leave a 4mm step of powder. Station #2 is adjusted to leave another 4mm step, or a total of 8mm step of powder. Stations #3 and #4 are adjusted to 12mm and 16mm respectively. Finally, Station #5 is adjusted so the tamper pins are flush with the top of the dosing disk, or 20mm.

Figure 1

Slight Weight Adjustments 

Adjust Stations #3 and #4 down to increase weight. Adjust them up to decrease weight. Adjust Station #5 below the top of the dosing disk by no more than 1mm to increase weight. It is not recommended to adjust Station #5 above the top of the dosing disk, as the powder has no “die” to form this portion of the slug. 

Fluffy Powders 

For fluffy powders, use a lighter spring in place of the standard tamper compression springs. Try using only Stations #3, #4, and #5 for tamping. For a 21mm disk, set Station #3 at 7mm, Station #4 at 14mm, and Station #5 at 21mm. 

Heavy Fill 

For heavier fills, use heavy tamper compression springs on Stations #4 and #5 only. These springs must be used with caution. Using them on the other stations can cause damage to the machines. 


For more ideas or training on encapsulation, contact Natoli Engineering by phone at +1 636-926-8900, or email encap@ natoli.com.

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