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Innovative and progressive research and development is part of our DNA. Spring specialists in Sweden have recently made prototypes and tests of springs in a new, cost effective material that can withstand high temperatures. Test results are very positive.

One of the requests of firm compression springs for high temperature applications origins from the Lesjöfors sales office in the Netherlands, where the customer wanted to replace disc springs with compression springs in an actuator application for large valves. The compression springs would have to work in an environment of around 200-250 degrees Celsius with high demands of strength and relaxation resistance. Furthermore, the springs would have to be ATEX certified which means no explosion risk.

Internal discussions among group companies
To discuss challenges and possible solutions, the Dutch sales manager André Boskemper contacted Stefan Musslinder, the group’s technical manager and Per Davidsson, technical manager at the factory in Lesjöfors, specialized in the manufacture of large, industrial springs. They came up with the idea of producing springs in tool steel, which had never been done before. Tool steel is mainly used for industrial tools and the world-leading manufacturer is Uddeholm, a company located in the neighboring municipality Hagfors.

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Testing and measurements
The traditional materials used for springs working in high temperature applications are made either in stainless steel or super alloys such as Inconel or Nimonic. The disadvantage is that these materials are very costly compared to the tool steel and the strength is fairly low in larger dimensions. The great advantages the team anticipated with tool steel led to a decision of starting prototype manufacturing and tests.

Stefan Musslinder comments on the development process:
“We manufactured ten springs in tool steel with a weight of about ten kilos each who we then hardened to 50 Rockwell C. We tested the springs’ heat resistance by a setting test to solid length at temperatures between 200 and 300 degrees Celsius. By doing so, we can measure how well the springs’ characteristics withstand high temperatures. The test results are very positive and we look forward to extended tests in longer time-series to investigate long-time relaxation resistance.”

Cost-effective and high quality springs
The potential for tool steel springs is rising and Lesjöfors in Åminnefors, Finland have received similar requests from Asian companies.
“Regularly, we get requests from customers who need springs working close to a furnace or in flow valve for steam for example. Compression springs in tool steel could be a great cost effective alternative in many high temperature applications”, says Per Davidsson.

Lesjöfors is one of the leading spring suppliers with internationally well known customers. The products are demanded in many markets, in diverse industries. The assortment of springs, stampings and pressings has a unique range, where one of the largest selections of standard springs are combined with high-tech, customized solutions. Lesjöfors has both manufacturing and sales offices in several European countries, Asia, United States and Mexico.

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Material. Manufacturing. Process. Design. How these three factors interact is crucial for the characteristics of a spring. There is no relevant academic research in this field in Sweden so at Lesjöfors, we develop the knowledge needed to design springs for the harshest environments.

Lesjöfors Industrifjädrar in Hudene, Västergötland, manufacture springs for a wide range of segments. One specialty is customized valve springs for tuned engines. Another customer in the racing and automotive industry is Öhlins Racing, a well-known customer to whom Lesjöfors has delivered front fork springs, shock absorber springs and many other springs for more than 20 years. For a customer base with extreme demands on the springs - regarding both tolerances, finish and performance - it is fundamental to stay at the technological forefront in order to maintain and develop the business.

Hans Andersson och Christian Olsson, Lesjöfors i Herrljunga. Hans Andersson och Christian Olsson, Lesjöfors i Herrljunga.

Stefan Musslinder is technical manager of the Lesjöfors group and reveals the success factors behind an optimal spring:
“The characteristics of a spring depends on three factors; material, manufacturing process and design. Thanks to deep knowledge in all three areas, we can fulfill the specifications from our customer.”

The desired function determines construction and materials

Knowing the nature of a material and from that calculate wire diameter and number of windings is fundamental for the design of an optimal spring. There is a large variety of materials for different applications. Spring steel is among the hardest steel materials available, which is necessary to withstand the high mechanical stresses that occur in the springs of a vehicle. The ever-increasing demands on low weight and small built-in space mean that the springs must endure enormous stresses.

Processes for reducing fatigue

The manufacturing process is just as important as the material, since different treatments can add specific properties. After coiling, the springs are heat treated at 200-450 degrees Celsius depending on the material and type of spring application. In this so-called stress relieving, the internal stresses emit from the coiled spring. Following is the grinding process if the end surfaces are to be flat. This is actually a basic requirement for all compression springs, but is sometimes excluded for cost reasons in less complex spring applications.

For springs that must withstand a large number of load cycles during their lifetime – e.g. the valve springs in a combustion engine – shot peening is an important and critical process. By bombarding the surface with small, hard steel shots, stresses are implemented into the surface of the material. Shot peening can increase the spring’s strength by up to 50 times.

Developing calculation models
The last step - before any surface treatment, marking etc - is presetting, when the spring is fully compressed two or three times. If the spring is correctly designed, internal stresses are created in the wire that work against the load stresses from the spring’s normal use. Since the spring becomes shorter when compressed, the designer must calculate the right length of the spring wire at coiling.
“In order to manufacture optimal springs, we must develop the technology we need to be the market leader. Therefore we have developed the calculation model ourselves, since there are no academic spring research in Sweden today”, says Stefan Musslinder.

Enormous stresses on valve springs
For the particularly exposed valve spring that is subjected to rigorous stress, especially in trimmed motors, additional measures are sometimes required for it to withstand fatigue. Spring kits of two or three valve springs mounted concentrically in each other are often used. This reduces the load on the individual spring and is a well-functioning solution in the limited space where the spring works.

“The requirements are tough straight through, from processes that keep the steel clean, to surface treatment, tempering, grinding and shot peening. The last step is to hot preset the valve spring for it to cope with the extreme heat environment where it will work”, Stefan Musslinder concludes.

Lesjöfors is one of the leading spring suppliers with internationally well known customers. The products are demanded in many markets, in diverse industries. The assortment of springs, stampings and pressings has a unique range, where one of the largest selections of standard springs are combined with high-tech, customized solutions. Lesjöfors has both manufacturing and sales offices in several European countries, Asia, United States and Mexico.

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Lesjöfors, one of Europe’s leading manufacturer of springs, pressings and wire parts acquires Spirbelt Beheer B.V., which includes its two subsidiaries Tribelt and De Spiraal in the Netherlands.

De Spiraal is a manufacturer of technical springs and industrial wire products with a diversified customer base, serving various markets such as the food, pharmaceutical and energy industries. Tribelt manufactures a broad mix of conveyor belts for customers within the food, processing and pharmaceutical industries. The companies are well established in the market and have long-lasting, stable customer relationships.

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The company’s revenues amount to MEUR 14 primarily in the European market with favourable profitability.

Lesjöfors’s President, Kjell-Arne Lindbäck, comments on the transaction: “De Spiraal and Tribelt are companies that fit well into Lesjöfors’s European platform, with a diversified customer base and opportunities for cross sales with our existing businesses. In addition, Tribelt will open up a new market for Lesjöfors with conveyor belt applications.”

The sellers and Managing Directors, René Spoelder and René Frielink, commented on the transaction: “We are happy for the company to become a part of a group specialized in springs and pressings. We also appreciate the decentralized structure of Lesjöfors and are looking forward to staying on and continuing to develop the company further.”

The Lesjöfors Group continues to grow
Over the years, Lesjöfors, owned by Beijer Alma, has conducted a number of acquisitions and established strong platforms in the Nordic region, other areas of Europe, North America and Asia. Following the latest acquisition of Tribelt and De Spiraal, Lesjöfors strengthens its position in Central Europe and broaden the wide product range further with conveyor belt applications. The Lesjöfors Group now consists of 26 production units in 13 countries. 

For further information, please contact: 
Kjell-Arne Lindbäck, CEO Lesjöfors AB
telefon: +46 (0) 705 74 99 94

Lesjöfors is one of the leading spring suppliers with internationally well known customers. The products are demanded in many markets, in diverse industries. The assortment of springs, stampings and pressings has a unique range, where one of the largest selections of standard springs are combined with high-tech, customized solutions. Lesjöfors has both manufacturing and sales offices in several European countries, Asia, United States and Mexico.

Published in Production
Tagged under

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