NAKANO SPRING Co.,Ltd.

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Leaf Spring

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What is a Leaf Spring?

A Leaf Spring is an important suspension part which supports not only the vertical movement of the vehicle body, but also movement in various directions. It consists of mutilayered steel boards which, by optimizing the thickness and number of leaves, allows for stable, smooth driving and a comfortable ride, so is used in many vehicles such as trucks, trailers and buses.

The features of Leaf Springs made by Nakano Spring

Our leaf springs are made from high quality, fully tempered spring steel and manufactured in our own factory, being strictly monitored from form working, heat treatment, assembly, coating and up to final quality inspection. Visual inspection at each process is undertaken to maintain our high level of quality. Consistent high quality and level of engineering built up over the years is behind our ability to supply many OEM products as well as manufacture various types of leaf springs.

Types and features of leaf springs

Leaf Spring Types by Structure

Multi Leaf Spring
（MLS）

A leaf spring is made by placing steel boards of different lengths one above the other. The required load rate and strength of the leaf spring is achieved by optimizing the thickness and length of the steel leaves. The ends may be tapered so that energy absorption efficiency is enhanced.

Long Taper Leaf Spring
（TLS）

A leaf spring with leaves rolled through most of its length so the thickness distribution throughout the leaf will result in a constant distortion rate when load is applied. This improves energy absorption rate which makes it possible to reduce the number of leaves resulting in lighter weight (compared to MLS). It also makes possible to create gaps between the leaves which helps prevent corrosion.

Difference Between Front and Rear Springs

Front Spring
(for front wheels)

On the front wheel, there are many directional forces at work, not only vertical but braking, stopping, steering, etc. and the multi-functional leaf spring supports it utilising the characteristics of the spring.

Rear Spring
(Double Leaf Spring, Rear Single Axle)

In a commercial vehicle, when comparing between an empty and fully loaded condition there is a significant difference in the load which the rear axle has to support, which affects the vehicle posture, cargo vibration, and steering stability. The leaf spring reduces the fluctuation this poses on the performance of the vehicle. The two springs are placed vertically and when the truck is empty only the lower spring is working and when load is added both springs work, with each load rate corresponding to the difference in load condition.

Rear Spring
(Trunnion Type, Rear Double Axle)

This is a trunnion suspension type of rear spring which is mainly used in large trucks with double rear axle. The center of the spring is connected to the truck body by a revolving support mechanism and load is transferred to the spring from both axles at the ends of the spring. When both rear axles are the drive axles, front/rear symmetrical springs are used so the load facter is the same for both axles. When only one of the rear axles is the drive axle, in order to secure ground grip and power on the drive axle side the spring is designed asymetrical to optimize load balance between the axles.

Product Line Up

Repair Parts for Trucks
Leaf Spring

We handle a wide range of repair leaf springs from those for small trucks to large trucks and trailers, from single leaf to spring assemblies, even manufacturer’s discontinued leaf springs. We can find them from our supply record of over 40,000 parts.

Repair Parts for Trailers
Leaf Spring

Our main items are for domestic trailers, but we also handle leaf springs for ocean container trailers and heavy equipment trailers. We sell single leaf springs as well as spring assemblies.

Simple Reinforcement Leaf Spring
(Extra Leaf – Additional Leaf)

Reduces front-up and unstable driving when fully loaded. Simple reinforcement spring with long history of usage, also available purpose made item which requires no cutting when attaching.

Springs for Land Cruiser

Land Cruiser, still very popular world wide. We have produced many types, in both domestic and overseas specifications.

Vibration Isolating Springs for Forging Machines

Springs placed under factory and office buildings which conduct forging. Absorbs vibration and reduces shaking of buildings. Leaf width of 70mm to 150mm available. Details can be discussed.

Springs for Railroad Trains

Springs produced for specialized railroad cars. Used in rail inspection cars and snowplow cars. Bolster springs have long been used in trams and cargo trains which face heavy vibration.

Reason Behind High Quality and Good Reputation

The know-how and experience which we have accumulated over the years making products for many kinds of vehicles and for various uses at our safe and reliable, centrally controlled factory enables us to offer quality products which meets our customers’ high expectations.

FAQ

Products
What kind of materials are leaf springs made of?
It is made from a kind of steel called Spring Steel. Spring steel differes slightly from pure iron as it contains about 0.5% of Carbon and trace amounts of other elements such as Maganese, Chromium and Silicon, called low-alloy steel.
What is the important factor in spring steel?
If the steel material contains impurities such as Phosphorus or Sulphur or non-metallic items like brick particles, it means bad quality. Material which has not been properly tempered is also low quality. It is like sword steel which has not been properly forged by hammer. NSK uses only high quality materials which have been fully tempered.
What other points are important regarding the material?
Material with scratched surface or which has been exposed to high temperature for too long during the manufacturing process causing Carbon loss at the surface (decarbonization) also means low quality. Material which has been over-decarbonized will not harden when quenched and so cannot be made into high quality spring. NSK materials are visually inspected at every step of the production process to maintain high quality.
Service
The leaf broke at the center bolt hole?
If the U-bolt is properly tightened, the area between the U-bolt does not function as a spring. Which means pressure is not applied repeatedly in the area between the U-bolts. When the U-bolt becomes loose while running and load is applied between the U-bolts where it shouldn’t, and as the center bolt hole is the weakest point it breaks at that spot. This is not the fault of the leaf spring itself, and checking the U-bolt whether it is properly tightened should be done regularly. If the U-bolt does not tighten properly even when power is applied, it could be that the U-bolt has stretched. Bolts which have been properly heat treated should be used.
Should the whole assembly be replaced in case of leaf springs?
Yes. Leaf springs last longer when whole assembly is replaced. Of course, when considering the cost you may want to replace only one leaf, but even in such case we recommend to replace at least three leaves, the one broken and those above and below it. The reason is these leaves may be scratched when the leaf between them is broken, which makes them weaker and prone to damage. Scratches increase surface fatigue considerably, so although assembly replacement may seem expensive, in the long run the total cost may not be so much.
Purchased just one leaf for replacement but the camber doesn’t fit properly?
When manufacturing the leaf spring at the factory, NSK makes sure the product is quality controlled with all measurements within the margins allowed in the drawing. Of course some margin is allowed, so those completed with minimum limit of allowance and those finished with maximum limit of allowance could end up with a small difference. This might cause a slight difference in camber. NSK is sensitive to such problems and does its best to avoid interchangeability problems before products are shipped out from the factory.

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