Strategic Modernization Drives Growth at Fritz Wohlenberg

Fritz Wohlenberg GmbH (FriWo) in Hanover, a company with 34 employees and a turnover of around three million euros, specializes in the small series production of technical rubber goods. Each day, up to thirty different products are manufactured, with all rubber compounds being produced in-house. The press department, which includes six vulcanization systems and one injection molding machine, has emerged as a significant growth driver, particularly due to consistent modernization efforts that began in the mid-1990s. A major milestone in this modernization was the 2007 acquisition of a new frame press equipped with magnetic clamping technology from Hilma-ROEMHELD, enabling up to twenty mold changes daily in minimal time.

The move for this latest modernization came in 2003, following an order from a manufacturer of engine block testing equipment that required rapid production of rubber seals. “In some cases, the courier who brought the molds to the site waited for the finished products,” recalls plant manager Martin Mehlau. The seals were vulcanized under high pressure, and at the time, the molds with various geometries had to be manually screwed onto the clamping surfaces of the presses. This process, combined with the time required for the molds to heat up to the appropriate production temperature, took around thirty minutes each for installation and heating.

Recognizing the severe time constraints, FriWo concluded that their success as a contract manufacturer specializing in customized solutions depended on upgrading their equipment. “At that time, it became clear to us that as a contract manufacturer specializing in individual customer solutions, we would only have a chance if we retrofit here,” states the FriWo plant manager, summarizing the company's strategic decision.

Diverse Production Capabilities and Custom Solutions

Wohlenberg GmbH maintains an inventory of approximately two thousand different press molds of various shapes and sizes for recurring orders, along with around twelve thousand extrusion dies. The production quantities vary significantly, as Mehlau explains: “In the case of custom-made products, we sometimes produce only a few copies from one mold, of other articles it is several hundred at a time.” Their standard repertoire includes profile cords, hose rings and cylindrical buffers, profile cord rings, molded articles, and coupling packages. As a craftsman's business, Fritz Wohlenberg GmbH can also fulfill special requests, such as seals for vintage cars or specialized rubber parts.

While exotic small orders add variety, standard products dominate daily production. These are primarily ordered by technical traders who supply the chemical and petroleum industries, mechanical engineering, and the food industry. Despite the focus on standard products, buyers appreciate the handcrafted quality from the Hanover-based producer. Wohlenberg excels particularly in its development and mixing department, a service that, according to Mehlau, is offered by only a few companies of comparable size in the industry today.

Elastomer Formulation and Rubber Press Investment

At FriWo, technicians formulate elastomer recipes to meet customer specifications, regulations, and standards. These recipes incorporate up to twenty different components to achieve the desired hardness, heat resistance, elasticity, extensibility, and resistance to weather, petrol, oils, alkalis, and acids. Annually, the company processes about 15 tons of natural rubber, primarily sourced from Vietnam and Malaysia, and nearly twice that amount of synthetic rubber. Before further processing, each batch undergoes rigorous quality assurance checks to ensure it meets all requirements for production.

Founded in 1891, the purchase of two new rubber presses was a significant financial undertaking for the company. Nonetheless, managing director Theodor Knäbe recognized the necessity and approved the investment. FriWo selected vulcanizing presses from Rucks Maschinenfabrik in Glauchau, Germany, equipped with magnetic clamping technology from Hilma-ROEMHELD, due to their longstanding cooperation. “Hilma was already known to us and Ruck also recommended this supplier,” recalls Mehlau.

Hilma, based in Siegerland, Germany, is a leading expert in die and mold clamping and effective die or mold change in mechanical engineering, forming technology, and the plastics and rubber industry. Hilma develops and produces individual clamping systems and standard fixtures exclusively at its Hilchenbach site, with magnetic clamping technology playing a crucial role. The company sells its products worldwide and is represented by the ROEMHELD Group with sales and service companies in 39 countries across all continents.

New Vulcanizing Presses with Magnetic Clamping Technology

In 2007, FriWo received two vulcanizing presses, each equipped with a pair of Hilma magnetic clamping plates. These presses feature clamping surfaces of 600 x 600 millimeters, ample for vulcanizing molds of the same height in a single process. They are networked with the three existing frame presses and the injection molding machine acquired in 2002, allowing for centralized control. Control programs for each mold are managed from a computer, and when a mold is inserted, only the corresponding data needs to be loaded. Mehlau highlights the advantage: “This ensures that recurring orders can be reproduced to one hundred percent at any time without any problems.”

Wohlenberg employees appreciate the new clamping technology not only for the ease of repeating orders but also for the significant time savings during mold changes. The plant manager notes: “If today we have to quickly produce five or six different small series in a row, this is only possible thanks to the fast magnetic clamping technology.” The time required for clamping and releasing a mold has been reduced from half an hour to five minutes. With six tool changes, the company saves three hours of setup time daily, and the new clamping technology enables them to meet tight deadlines for specific jobs.

Reduced Set-Up Times and Less Scrap

Mehlau also appreciates the quality improvement. “Since the pressing forces are higher than on our old machines and are evenly transferred to the mold via the magnetic clamping plates, extremely homogeneous rubber products are produced. This has significantly reduced the number of rejects.”

Magnetic clamping technology allows for quick, precise, and easy clamping of a wide variety of molds. The magnetic clamping plates are suitable for both horizontal and vertical use. Once the mold is positioned, a two to three-second electrical power supply magnetizes the mold on the magnetic clamping plate. During production, current-independent permanent magnets provide the necessary force to hold even mold halves weighing several tons without deformation, accurately positioned, parallel, and reliably, ensuring high precision in production and minimizing mold wear. The magnetic field penetrates only a few millimeters into the mold, so it does not affect production. Even in the event of a power failure, the molds remain securely clamped thanks to electro-permanent magnet technology; power is only needed for demagnetization and release.

The FriWo presses vulcanize at a pressure of approximately 200 bar and temperatures between 300°F and 350°F. After the initial pressing, the mold opens completely, cold rubber is added, and the mold is closed again for about one second. The press briefly ventilates to allow the last air inclusions to escape, then closes completely. Five to six minutes later, the article is vulcanized and ready for finishing.

Satisfaction with Hilma-ROEMHELD Magnetic Clamping Technology

Mehlau summarizes, “We are very satisfied with Hilma-ROEMHELD's service and customer support right from the start, and reliability is particularly evident when problems arise.” Today, the magnetic clamping technology operates without any issues and employees are highly satisfied with its performance.