Calibration Station Components

The calibration station is designed with adjustable mechanisms and interchangeable parts that allow desired neck dimensions to be moulded. Let’s look at the components of the station and how they work.

The blow pin assemblies do the neck finishing. They are held in place by the mounting blocks, which are secured to the moving plate in the station’s die setting. The system of plates and guide rods moves the blow pins as the calibration cylinder’s piston rod extends and retracts.

The frame or stanchion mounts the extension to the blowmoulder. The stanchion has adjustments to help set the position of the calibration equipment relative to the position of the moulds.
Here is a blow pin assembly. The stem is a precisely machined metal part. One end is made to accept the cutting sleeve and the blow pin tip. The cutting sleeve is a hardened steel ring with sharp edges. During blow pin insertion, it cuts through the plastic and finishes the very top of the container’s neck. Its inside diameter should be very close to the stem’s outside diameter so it can slide on but fit snugly. Its outside diameter approximately corresponds with the diameter of the neck finish.

The Calibration Station
The blow pin assembly is designed so that the cutter can be replaced easily. It eventually dulls and leaves a ragged edge on the top of the neck or stops cutting the plastic altogether. In either case, the cutter needs to be changed on a regular basis.

The Cutter Needs to be Changed on a Regular Basis
The blow pin tip screws onto the stem and holds the cutter in place. A hex slot is usually provided in the end of the tip. Moderate torque is applied with a hex wrench. These parts are designed so that there is no gap between them once they are tightened.
The tip is designed with the container’s eye dimension in mind. Its size and shape largely determine the finished dimensions inside the bottle neck. A larger diameter on the tip will increase the eye dimension, while a smaller diameter on the tip will decrease it. The tips are always made slightly larger than the desired eye dimension because the plastic shrinks slightly as cooling continues after calibration.

Certain caps require the necks have special shapes forming their eye dimensions. Liner less caps do not have the cardboard inserts to act as a seal; but have a ridge of plastic that forms a seal against the special radius moulded inside the neck. This radius is formed by a specially shaped tip.

Caps with Necks that have Special Shapes Forming
Besides shaping the inside of the neck, the tip also plays a part in forming the wall and threads on the outside. As the tip inserts, it forces hot plastic outward and into the threads. The ‘E’ dimension is the outside dimension of the container neck. It’s measured from the root of the thread on one side to the root of the thread on the opposite side.

“E” Dimension Refers to Outside Dimension of the Containers Neck
The ‘T’ dimension is the overall thread diameter. The dimension to which the metal is cut into the mould’s thread insert largely determines the containers ‘T’ and ‘E’. Both dimensions however can be varied by changing the blow pin tip’s diameter. Increasing the diameter may create larger dimensions, while decreasing it may make them smaller. Remember that any change in the blow pin tip’s size will have a definite effect on the eye dimension.

‘T’ Dimension is the Overall Thread Diameter
The pressure at which the blow air is set may also have an effect on the outside neck dimensions, especially on thin-walled necks. In these cases an adjustment to the blow air pressure can increase or decrease outside dimensions. Be careful never to adjust the pressure so high that it overcomes the clamp pressure. This can show up as a heavy seam at the next parting line.

Centring Blow Pin
Good cooling is critical in forming good necks. If cooling is poor, necks can wrap as they continue to cool on their own. A separate supply hose and a separate drain hose should be connected to each blow pin. The other end of the stem is machined to fit into the mounting blocks. The mounting design can vary with different blow pin designs.
Here the pin is held in place by tightening the two spanner nuts. The mounting blocks have two or more adjusting screws for positioning the pin precisely in the centre of the cavity.

Centering of the Blow Pin is Critical
Positioning must be exact, front to back and side to side, or the pin will enter the parison ‘off centre’. This may cause the plastic to be stuffed into the neck. In the case of extreme misalignment, the wall and threads may be left incomplete.

The blow pin is centred visually using a combination of adjustments to the mounting block adjustment screws. The best method for doing this begins by inverting the striker plates in the top of the mould. Then close the moulds and lower the pins very slowly and carefully until they are right above the mould.

Blow Pin is Centred Visually
Visually check and assure that they can insert without interference. If one or more pins can’t, then adjust the screws appropriately. Then lower the tips until they are half way in the strikers.
Adjust the blow pin until the space between each tip and its striker seems even all the way around. Finally, snug down all the adjustment screws and complete the procedure by putting the strikers back in the right way. Lastly, tighten down all the bolts.

Let’s go over the procedures for centring the blow pin. First, invert the strikers and slowly and carefully lower the pin. Adjust the screws so that they can insert without interference and lower them half way into the strikers. Adjust the screws so that the space is even, snug down all the screws and turn the strikers.

The mounting blocks also provide the adjustment for setting the initial height of the pins.