Selection of the means of production is not left to chance at electrical plug and socket specialist Mennekes. The company uses particularly compact design granulation machines for direct granulation in close proximity to its production machinery. Probably the best-known product of the medium-sized group is the robust, red and durable “industrial power plug”.

This plug and a large family of such plugs and sockets form today part of a comprehensive range of plug and socket systems for different industries. With headquarters in the German Saar region town of Kirchhundem, the Mennekes company has grown into an internationally successful producer with several production locations and a high degree of vertical integration in production.

Sophisticated production with 40 injection moulding machines

A significant part of the production is taken up with injection moulding; this is where components and products are created, sometimes with tight dimensional and colour tolerances. 2,300 tonnes of plastics are processed annually in the Kirchhundem headquarters plant, mainly PA6 with or without flame retardants, but also PBT, PC and TPE. Part weight amounts mainly to between 2 grams and 2 kilograms. Almost 40 injection moulding machines with clamping forces between 500 and 6000 kN cover a wide product spectrum.

High flexibility and efficient processing

The production is characterised by frequent changeovers on most of the machines. “And these have tended to increase, not only since the difficult year in 2009”, states Dirk Gehle, production planer for the moulding shop at Mennekes.
This has had repercussions on, for example, material logistics, as well as disposal of injection moulding waste such as sprues, faulty parts and start-up lumps. Mennekes completely redesigned and rebuilt large parts of the already “mature” production facilities in 1999 and 2000. In connection with this, the concept that had been used up to that time of a central granulator was called into question. Cost reduction and environmental protection had gained more weight by that time. Around 1,000 tonnes per year were being ground, of which 10 percent or 100 tonnes was being disposed of as waste. A significant cost factor.

Machine-side granulators meet users’ requirements

Granulation directly at the injection moulding machines was also taken into consideration as an alternative to central granulation. Different machine-side granulator designs from several producers were systematically checked and some of them were then brought into the plant for testing. “We haven’t had the tests made in some laboratory, but got the employees to run tests in daily operation, on live objects, so to speak. Aspects such cleaning and robustness then receive recognition for their important contribution to efficiency that they really deserve in practice“, say Dirk Gehle in justification of this approach.

After all, the granulators are cleaned once daily on average; time saved and the degree of cleaning needed therefore have a direct affect on costs. Except for one old piece of equipment, only Hellweg granulators are in use throughout the entire injection moulding operation at Mennekes. They have been successively introduced since 2000 – and all of them are still in use today. As the result of interaction between the user and granulator producer, a number of small but practically relevant design improvements have been made and introduced into serial production at Hellweg.

There are presently 35 machine-side granulators performing their service at Mennekes. They process an estimated 5 tonnes per year of rejects, sprues and start-up waste. According to Dirk Gehle, there is hardly any more “waste” arising for disposal. A central granulator is still used, but only to granulate large housing enclosure parts. The relatively restricted space between the machines in the Mennekes production area did not initially favour use of machine-side granulators, as they would have restricted the available space even more. Despite high performance capability, the MDS240/200 granulators used have however a very compact design, being particularly narrow. They easily process heavy injection moulded parts, as well as small start-up lumps. The stabile design of the housing design ensures here high dampening of noise down to a low level.

Tailor-made for the user

Each granulator is cleaned once a day on average on account of production changeovers. It is here that the maintenance friendly design has an impact, also in gaining acceptance by the operator. A cleaning process takes, for example, only several minutes. Both the grinding chamber, produced with use of computer numerical control (CNC), as well as the closed rotor (without welding seams and without open chambers), are lightweight and can be rapidly accessed. The requirement for durability is illustrated by a figure given by Dirk Gehle: “Based on our experience, the blades can be re-sharpened round 30 times, keeping replacement part costs within reasonable limits”.

Aside from investment cost, granulator operation costs play a decisive role in selection of a granulator. “Apart from the blades that need to be re-sharpened, there are no other parts contained in the granulators that are subject to wear. And as the first granulators have now been in operation already for more than ten years, it is possible to make a reliable statement about robustness and life cycle costs”, Dirk Gehle summarises.

Mennekes Elektrotechnik

Founded in 1935, Mennekes Elektrotechnik GmbH & Co. KG (www.mennekes.de) still operates today as an entirely family owned company. Of more than 800 employees worldwide, more than two thirds are in Germany. The company’s range of products consists of 11,000 different standard series and special products. Production takes place in Germany at the headquarters in Kirchhundem and Neudorf in respectively the Saar and Erzgebirge (Ore Mountains) regions, as well as in China in Nanjing for the Chinese market. Consolidated turnover amounts to around 100 million Euro, more than half of which achieved in export. A current and future-oriented product developed by Mennekes and approved by leading car manufacturers are standard plug-in charging equipment for electric vehicles, for which the company was recently awarded the ÖkoGlobe environmental award.

Hellweg Maschinenbau

Hellweg Maschinenbau GmbH & Co. KG (www.hellweg-maschinenbau.de) is equally a family owned company, which has been designing and producing itself machines and equipment for the past 13 years, particularly for specific customer tasks for customers in the plastics and recycling industries throughout the world. The production programme includes machine-side and other granulators, edge strip shredders, feeding equipment for edge strips, film cutters, extraction and dust removal equipment, including accessories.

(Text and image: M.Droege / PR WORKS)