New pressure casting technologies are fully automating the production of even difficult-shaped cup bodies and handles.



Traditional cup manufacturing methods-such as the solid casting of difficult-shaped cups in a multi-part mold and the subsequent joining of individual cup parts-require a significant amount of manual labor for the production, finishing and handling steps, particularly where the cup handles are concerned. However, over the past few years, new technologies have been introduced that fully automate the production of special-shaped cups, including handle forming and attachment. The first fully automated cup production line* was installed three years ago and has successfully streamlined what was previously a very labor-intensive process. Today, an increasing number of cup manufacturers are realizing the benefits of automated cup production.

*Developed and supplied by SAMA Maschinenbau GmbH, Weissenstadt, Germany.

Roller-Shaped Round Cups

The traditional process of jiggering cups in plaster molds is the most efficient way to manufacture cup bodies, especially regularly shaped cups. However, producing and attaching the handle is a labor-intensive process that can comprise as much as 80% of a cup's manufacturing costs.

A new production technology enables the handle to be pressure cast and attached to a conventional jiggered cup body in a fully automatic process. The system can be used with the cup-shaping machines found in most tableware plants.

The system is composed of two handle pressure casting (PCH) units with a common handling unit in between. Each PCH unit consists of five handle pressure casting molds, and these are alternately supplied with slip. While the handling unit attaches a set of handles from the first PCH unit, the second PCH unit casts another set of handles.

Each handle is formed in a three-part mold. During the casting process-which occurs at up to 20 bars slip pressure-the mold is horizontally and vertically tightened with pneumatic cylinder units. After the entire casting process is complete (the five pressure casting devices are synchronized), the vertical axis is released, and the top mold part is lifted to expose the handle tips.

Meanwhile, the handling unit, which is equipped with specially designed holders, picks up the five centered cups and rotates them into a precise position above the handle molds in the corresponding PCH unit. To connect the handle with the cup body, the system vibrates the cup holder to a specific frequency and touches the cup body to the protruding handle tips (see Figure 1). The vibration softens the contact points through a thixotropy effect and virtually melts the cup body and handle together. This creates a strong bond between the handle and cup body without requiring excess slip, while also considerably reducing waste due to dropped handles and eliminating the finishing steps that were previously required around the attaching surfaces.

After a set number of seconds required for handle attachment, the side parts of the handle pressure casting mold are opened and the handle is released (see Figure 2). The completed cup-with the handle attached-is then placed on the conveyor belt and transported to the dryer (see Figure 3).

In addition to streamlining production, the system provides another important benefit-rapid mold changeover. Molds can be changed from one type of handle to the next in less than two minutes. Even a large system with 20 molds can be changed over in less than 20 minutes, providing a high level of production flexibility.

Thin-Walled, Non-Round Cups with Recessed Feet

Thin-walled, non-round cups with recessed feet are typically produced through a number of different production steps that require a considerable amount of manual labor. Either the entire article is solid-cast in multi-part plaster molds, or various individual components manufactured by jiggering and/or casting are joined together to create the finished cup. In addition to the labor required to produce the cups, the continuous abrasion of the plaster molds often causes deformations in the cup body, and the extensive fettling that is required unavoidably influences both the cup quality and yield.

Another new automated production plant was designed specifically for manufacturing cups that cannot be produced by the traditional plaster shaping method (i.e., roller machines) due to their inside and outside contours. The system comprises pressure casting units with four-part, fully porous resin molds to form the cup bodies, and PCH units with three-part resin molds to produce the handles (as described previously). The production sequence occurs in four distinct steps-pressure casting of the cup bodies, leather-hard drying, fettling and finishing, and applying the cup handles (see Figure 4).

Six body pressure casting units operate simultaneously and are supplied by a single slip system. The cup bodies are positioned upside down; two pairs of short-stroke air cushions close the sides of the body mold horizontally, while a hydraulic piston simultaneously closes the top and bottom parts of the body mold. The top part is firmly fixed to the closing frame, while the bottom/core mold is fixed on a turntable. A second bottom/core mold is also fixed on the turntable, so that when one bottom/core part is in the casting process, the second core part can be in a demolding position (see Figure 5).

After the cup has been demolded, a transfer device places it on a conveyor belt, which moves the cup through the leather-hard dryer for further strengthening/hardening (see Figure 6). At the exit end of the leather-hard dryer, the cup body is transferred to a robotic fettling unit. The robot holds the cup body by the foot and places it against a roller sponge unit to finish the mouth rim. Next, the spruce (a nub created by the injection of the slip into the mold) is cut off with a fixed blade, and the cup body is rotated so that a laser can detect the precise positions of the casting seams on the sidewalls.

The first robot then transfers the cup body to a second robot, which fettles the seams using a rigid elastic wired lathe (see Figure 7). The cup foot is fettled using the same process as on the mouth rim, and the cup body is conveyed to the PCH unit for handle attachment.

Complete Cup Casting

For non-round, footed cups with an almost homogenous wall thickness between the cup body and handle, a production unit for pressure casting the complete cup and handle in a single mold can be used (see Figure 8). The mold dimensions are identical to the molds that would otherwise be used for the cup bodies (see Figure 9). A patented "blind cast" inside the handle contour (see Figure 10) ensures the safe demolding of the cast cup without deformations. After being demolded, the cups are transferred to a leather-hard dryer and then to robots for fettling and finishing, including cutting out the blind cast in the handle.

Advantages of Automation

With all of these systems, cup handles are produced and applied in a fully automatic process. As a result, it is no longer necessary to continuously produce plaster molds for handles (which also eliminates the need for handle carousels and other casting equipment), cut and finish the handles, prepare handle sticking slip, manually place the handles into an attaching unit, manually apply the handles to the cups, finish the handle attaching points, or transport and store the handles in humid containers. As a result, significant savings in labor costs can be achieved.

The automated systems also increase quality and reduce rejects by ensuring that the handle shape and seam, the position of the handles on the cup body, and the connection between the handle and cup body are all consistently optimized. And because the system can produce cups in just about any shape (including cornered, recessed and foot cups, etc.)-and even different cup shapes at the same time-production flexibility can be greatly enhanced. The systems' rapid mold clamping and aligning capabilities increase this flexibility even further.

Such advantages are crucial to remaining competitive in today's global markets.

For more information about automated cup production, contact SAMA Maschinenbau GmbH, Schillerstr. 21, D - 95163 Weissenstadt, Germany; (49) 9253-8890; fax (49) 9253-1079; e-mail info@sama-online.com; or visit http://www.sama-online.com.