Gripper system for blow molding machines scores with speed and high repeat accuracy

Gripper system for blow molding machines scores with speed and high repeat accuracy
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March 2017

 

The design of a gripper system for the Kautex Maschinenbau plant in Shunde, southern China depended on high precision and speed – there was also little time for development.

There are various ways to manufacture hollow plastic articles such as bottles, canisters and other containers. Extrusion blow molding is one economical option. In this method, a hot plastic tube is inserted into a mold and blown up with compressed air until it fills the mold. After a brief cooling period, the product is then removed from the mold and can be processed further. Kautex Maschinenbau is an international company with roots in Germany and that has already commercialized this process in 1949 with the first extrusion blow molding machines.

Double the output

The multi-purpose machines by Kautex include the KCC series produced at the company’s site in Shunde. KCC machines are used by customers in sectors such as packaging or for special applications. Kautex offers single-station and dual-station machines. Dual-station machines have an extrusion head with multiple nozzles that insert the hot plastic into two molds in an alternating fashion. These then go to the blowing stations to the left and right of the extrusion head, which blow up the article with compressed air. Two other machine sections then prepare the finished products for removal. Depending on the size and shape of the desired product, the extrusion head, blowing station and molds have between 1 and 12 nozzles or cavities.

When Shunde Kautex Plastics Technology Co. Ltd., a subsidiary founded in 1995, was developing the KCC20 MK3, or the third generation of the KCC series, they turned to Bosch Rexroth with a challenging task: The mechanical engineering firm needed a handling system consisting of two gripper arms and a corresponding linear guide, and all as soon as possible. The system needed to remove the finished items and place them on a conveyor belt running behind the machine. This Shunde Kautex solution, intended to be an optional add-on, saves space on either side, since the finished articles are not placed on the conveyor belt from the left and right of the machine and then have to be conveyed around it, as is usual.

Optimal design

Ulrich Dreizler, a sales representative with Bosch Rexroth in Lohr, Germany, wasted no time after receiving the request and immediately turned to his colleagues in Schweinfurt. The two German facilities worked closely with their colleagues and the customer in China to quickly design the handling system. “The challenge with this project was that we were pressed for time to dimension the gripper system correctly on the first try so we could work efficiently,” Dreizler reminisced. When dimensioning, the team had to keep two things in mind above all: the weight of the finished items that the grabbers would transport and the dynamics of the motors. The latter plays an important role, since the machine produces finished products for the gripper arm to pick up every eight seconds. This is why it was critical for the gripper arm to reliably place the finished items on the belt and return to pick up new articles within this time frame.

After only a few days, Bosch Rexroth presented Shunde Kautex a design proposal for the handling system, which was immediately accepted by those responsible there. Once approval had been received, the gripper system was pre-assembled at the Bosch Rexroth plant in Schweinfurt. It consists of two interchangeable elements that remove the finished articles from the left and right of the blowing stations. Compact modules with ball screw assemblies are responsible for moving the gripper system up and down. They have a very low installation height and, thanks to a zero-play nut system, high-precision repeatable positioning. Linear modules with ball rail systems and a geared belt drive move the system forward and back. They are designed to move even heavy loads at great speed with high precision.

Rapid commissioning

Once it was pre-assembled in Schweinfurt, Bosch Rexroth sent the handling system to China. Although it took far longer than planned for the components to clear customs, the tight schedule was still maintained. One important reason for this was the fact that the included energy chains were pre-assembled in the system, allowing Kautex Maschinenbau to complete the final assembly at the Shunde plant in a short time. On-site commissioning was able to be carried out within half a day with the help of Bosch Rexroth associates. Those in charge at Kautex in Shunde were extremely satisfied with the initial tests, and the company was able to present the machine, including the gripper system, at the Chinaplas 2016 trade fair in Shanghai.

Kautex’s customers demand high precision and high repeat accuracy. As Dreizler explained, “In this industry, it isn’t rare for these machines to run 24 hours a day throughout the entire year. And they have to produce the exact same items during this time. This naturally places high demands on the precision and durability of components.” This is why Shunde Kautex entrusted not only the handling system to Bosch Rexroth: The company also provides a large portion of the hydraulics, from valves to pumps, to hydraulic cylinders. These are responsible for moving all of the primary axes, for the vertical movement of the blowing mandrels, and for opening and closing the molds. The machine is also installed with linear guides from Bosch Rexroth that allow the closing units to move left and right. Even the striker plates themselves run on these guides.

KCC series machines are used by customers in sectors such as packaging, for example, or for special applications.

KCC series machines are used by customers in sectors such as packaging, for example, or for special applications.

 

Successful premiere

Following the successful trade show exhibition of the new KCC20, the partners analyzed the extensive data from the demo runs and developed further tweaks for mass production that now benefit the end customers of the series. “With this optional gripper system in particular, it was important to work together with Shunde Kautex to achieve our absolute best so this addition would be worthwhile for customers,” Dreizler said. The demand and initial sales of the machines with the optional handling system after the trade show is proof that this mission has been a success.