JPS5948334B2 - load cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load cell used for load measurement, and more particularly to an improvement in a welded structure between a load cell body and a protective cover.

A load cell is a load detector or pressure detector that converts and measures load or pressure electrically.In the case of large load cells, it is used to measure thermal and load pressure, such as detecting roll rolling force of a rolling mill. It is often used in places with severe usage conditions, and while it is important to have excellent sensitivity to load and pressure and output characteristics, it is also important that large loads, fluctuating loads, or shocking loads are applied. Because of this, it is required to be reliable in terms of strength as well.

Further, load cells, especially large ones, are often used in harsh environments such as rolling mills, which are hot and humid.

Therefore, in addition to high strength, the performance required for a load cell is watertightness and rust resistance in order to protect the electronic circuit components built into the load cell body that convert pressure into electrical signals from such environments. , corrosion resistance, etc. are also required.

Generally, load cells employ welded structures to protect electronic circuit components, but as mentioned above, the load is severe and welded structures are often prone to defects, so the structure of the welded parts does not meet the required conditions. Failure to do so may result in fatigue failure.

Here, the structure of a conventional load cell will be explained using a round capacitive load cell as an example.

Figures a and t) show the configuration of a conventional round load cell.

The load cell main body 1 is formed of a disc-shaped steel block, and receives a load via an upper jaw pressure plate 6 and a lower jaw pressure plate γ arranged in the pressing direction.

Further, on the side surface of the load cell body 1, pressure receiving holes 2a, 2b, .
As shown in detail in FIG. 2, each pressure receiving hole 2 has a structure in which a pair of electrode plates 3 are attached to the inner surface of the pressure receiving hole 2 facing each other by adhesive or the like.

Then, the change in electric capacitance due to the displacement of the gap A of the electrode plates 3 due to pressure is detected by the electronic circuit component 4 stored in the electronic circuit component storage section 4a formed in the center of the main body 1, and It is designed to measure.

A protective cover 5 for protecting the electronic circuit component 4 from cooling water of the rolling line, radiant heat, etc. is fixed to the load cell body 1 by welding.

However, when a load is applied to the pressure plate 6 and the pressure surface of γ that are in contact with the load cell body 1, each portion of the load cell body 1 deforms in the radial direction and the thickness direction.

Due to the deformation, the protective cover 5 is pulled and bending force is also applied, and stress is generated at the welded portion between the protective cover 5 and the load cell body 1.

In particular, radial deformation directly affects the failure of the weld, and large deformations generate proportionally large stresses.

If the magnitude of the stress generated at this time exceeds the fatigue strength value inherent to the welded part, the welded part will suffer fatigue failure during long-term use.

Therefore, in order to obtain a strong load cell that can withstand fatigue failure, it is necessary to use a material or a welded structure with high fatigue strength at the welded portion.

The load cell body 1 is made of high-strength steel because it is subjected to high pressure, but since high-strength steel is a material that is prone to weld cracking, it is usually preheated to around 300°C before welding. , and to prevent cracks from occurring due to rapid cooling even after welding is completed, the temperature is still 300°C.
It is necessary to perform a so-called post-heat treatment in which the material is heated to a temperature around the same temperature and then slowly cooled.

On the other hand, electronic circuit components 4 housed within the load cell body 1
The heat-resistant temperature is much lower than the temperature of preheating and post-heat treatment performed during welding.

For this reason, a protective cover 5 is provided after storing the electronic circuit components 4.
When welding, preheating and post-heat treatment cannot be performed.

The third method that has traditionally been taken to solve this problem is
This will be explained with reference to the figures.

As shown in FIG. 3, the structure of the welded portion of a conventional load cell is composed of a load cell main body 1, a protective cover 5, and an intermediate welding member 8.

Regarding the materials used, the load cell body 1 is made of high-strength steel, and the protective cover 5 and intermediate welding member 8 are made of mild steel with good weldability.

As for the welding order, first, the joints 9a and 9b of only the end portions of the load cell body 1 and the intermediate welding member 8 are carefully welded while performing preheating 1 and post heat treatment.

After that, the electronic circuit components are installed in the electronic circuit component storage section 4a, and then the joint 9 between the intermediate welding member 8 and the protective cover 5 is
In this case, since both materials are made of mild steel with good weldability, there is no need for preheating or post-heat treatment, and electronic circuit components can be welded without exposing them to high temperatures.

This method is a clever method for welding high-strength materials, but on the other hand, a non-welded portion 10 remains at the boundary between the load cell body 1 and the intermediate welding member 8, and this portion becomes a notch and causes stress concentration. This is a drawback in terms of strength, as it can cause fatigue failure.

In view of these demands, it is an object of the present invention to provide a load cell having a welded structure with excellent strength and workability.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 4 shows the configuration of a load cell according to the present invention.

A step 11 is formed at the periphery of the opening of the electronic circuit component storage section 4a on the upper surface of the load cell body 1, and overlay welding is performed there using a low carbon steel welding rod to create an overlay weld layer 1.
2.

The overlay welding layer 12 is a means of welding the protective cover 5 at room temperature without preheating or post-heat treatment, similar to the intermediate welding member 8 shown in FIG. 3, but unlike the conventional welding structure, Since it is completely welded to the load cell body 1, there are no internal notches that could cause fatigue failure.

After overlay welding in this way, the main body is processed,
After the electronic circuit components are stored in the electronic circuit component storage section 4a, the joint portion 9c between the protective cover 5 and the overlay weld layer 12 is welded and fixed without preheating or post-heat treatment.

In this way, electronic components with low heat resistance can be stored inside the load cell without being thermally damaged, and there is no notch near the weld that can be a source of stress concentration, resulting in high strength and being used in conventional products. It is no longer necessary to process the intermediate welding member, as was previously done, and the overlay welding can be processed with rough processing accuracy, making it possible to provide a load cell with low manufacturing costs.

In the above embodiment, the overlay welding layer 12 is attached to the load cell body 1.
Although the 0 step portion 11 is formed, the overlay weld layer 12 may be formed without forming the step portion, or a continuous sloped portion may be formed on the load cell body 1 and the overlay weld layer 12 may be formed there. You may also do so.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of a conventional round capacitive load cell, where a is a plan view, b is a sectional view, Figure 2 is a front view showing details of the pressure receiving hole and electrodes, and Figure 3 is a conventional round capacitive load cell. FIG. 4 is a sectional view showing the structure of a welded portion of a load cell. FIG. 4 is a sectional view showing the structure of a load cell according to an embodiment of the present invention. 1...Load cell, 4...Electronic circuit component, 4a...
・Electronic circuit component storage section, 5...Protective cover, 12...
・Overlay weld layer.

Claims (1)

[Claims] 1. In a load cell equipped with a load cell body made of high-strength steel that forms an electronic circuit component storage portion, and a protective cover made of a mild steel material with good weldability that is welded to the load cell body and closes the electronic circuit component storage portion. , a load cell characterized in that an overlay welding layer made of low carbon steel is formed on the periphery of the opening of the electronic circuit component storage portion of the load cell main body, and the protective cover is welded to this overlay welding layer. .