Jon Carlisle, encapsulation technical service manager, Natoli Encapsulation Division, examines the function and optimal set-up of tamper-style encapulsation machines to increase product yield.
Key insights:
- There are four styles of encapsulation machines, which all use different methods to achieve filling an empty, hard, two-piece capsule at a desired weight.
- Tamper-style encapsulators use a tamping pin, forcing the powder into the dosing disk bore. This process is repeated several times in order to form a “slug,” prior to being transferred into the capsule body.
- The “slug” is necessary for accurate fill weight and clean transfer into the empty capsule when running at high speeds.
There are basically four styles of encapsulation machines: Tamper, Dosator, Semi-Automatic and Hand-filling. These styles of machines all use different methods to achieve filling an empty, hard, two-piece capsule at a desired weight.
Dosator-style encapsulators use light tamping force and vacuum to retain powder in a tube before transferring the powder into the capsule body. This style of machine is ideal for encapsulating sticky product.
Semi-automatic and Hand filling-style machines are best for encapsulating smaller batches, and coarse products (typically herbal blends). These encapsulators rely on powder being poured into the capsule body then scraped clean to achieve a proper fill.
How does tamping work?
Tamper-style encapsulators use tamper pins and a dosing disk. The tamping pin tamps the powder, forcing the powder into the dosing disk bore. This process is repeated several times in order to form a “slug,” prior to being transferred into the capsule body. An ideal slug will maintain structure, is a semi-solid, uniform, and flat on top and bottom. The “slug” is necessary for accurate fill weight and clean transfer into the empty capsule when running at high speeds.
To achieve the slug at the desired fill weight, two questions must be answered:
- Can the product form a slug at 30 – 75 Newtons of force?
- Is the correct thickness of the dosing disk being used the achieve the given weight?
If the product cannot form a slug at 30 – 75 Newtons of force, the powder can be lost and cause the encapsulator to operate dirty which will lead to a host of other problems. Additionally, disk thickness and fill weight are somewhat proportional. If the disk creating the slug is too thick, fill weight will be too heavy; if the disk is too thin, fill weight will be too light.
How to select the correct dosing disk thickness
Selecting the correct dosing disk thickness can be determined in two ways: 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 fill weight of the product is measured on a gram scale and poured into the die. The product is then compressed with the punch. The slug tester has a readout for force (30 – 75 Newtons) and height which will be related to the desired thickness of the 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 for products experiencing issues during a production run. In this approach, focus on the slug formation and disregard the capsule’s weight. A slug needs to be formed for accurate data collection. Once a good slug is achieved, notate the thickness of the dosing disk 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 the 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 different approaches to setting the tamping station heights. All these approaches reference the thickness of the dosing disk. My preferred initial approach is the “Equal Steps” approach (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 machine.
Increased product yield
By applying these techniques to achieve fill weight while forming a slug, product yield is increased several percent. Along with an increased yield, the encapsulator runs cleaner, so maintenance costs and change over time is reduced as well.