JPH0138437B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a lubricating method for stainless steel bolts and nuts that prevents seizing and electrolytic corrosion during tightening by setting the torque coefficient to 0.12 to 0.22. Conventionally, bolts and nuts made of mild steel or cast iron used in joints often suffer from abnormal corrosion (electrolytic corrosion) even though the objects to be fastened are almost sound. Therefore,
In order to avoid this phenomenon, the shift to stainless steel, which has excellent corrosion resistance and durability, has attracted attention and has become extremely popular. In general, it is well known that oxalate film is widely used as a film lubricant during cold plastic working of stainless steel materials. Usually, after degreasing and pickling stainless steel, treatment at a temperature of 70 to 95°C is performed. A method of immersing it in a liquid for 5 to 15 minutes is used. The treatment solution at this time is oxalic acid with nitrates and thiosulfates added as oxidizing agents, and halides such as fluoride and chloride as substrate dissolving agents. A grayish-brown film containing iron oxalate (2) as a main component and weighing 5 to 20 g/m ² is formed on the surface of the stainless steel. Furthermore, oil and fat, soda soap aqueous solution, etc. are applied on this film,
The material is reacted, water is removed by drying, and the material is subjected to cold processing. On the other hand, most conventional stainless steel bolts and nuts are made of SUS304, which has a high coefficient of friction.As a result, the sliding resistance on the thread engagement surface is large, and the thermal conductivity is lower than that of carbon steel or alloy. Because it is about one-third as small as steel, etc., it is difficult for the frictional heat generated on the engagement surfaces of screws to dissipate, resulting in localized high temperatures.Furthermore, the coefficient of thermal expansion is approximately 1.5 times larger than that of ordinary steel. , with the above properties added,
The expansion of the screw thread increases, making it more likely that "galling" will occur. Therefore, lubrication treatment is essential, but even if the lubrication treatment method described above for cold plastic working of stainless steel materials is applied to stainless steel bolts and nuts, good lubrication will not be achieved. Because it's too much, it becomes too tight, which causes problems. For example, as a result of surface processing a stainless steel bolt (SUS304) and a stainless steel nut (SUS304) with a diameter of 16 mm and a length of 75 mm using a lubrication treatment method for cold plastic forming, the standard tightening torque was 11 Kgf- m, the tightening force will be 6900-7300Kgf, and the torque will be 8Kgf-m.
Plastic deformation occurs depending on the degree. Since the tightening force at that time is approximately 6000Kgf, the yield point of this 16mm diameter bolt is 6000Kgf.
There is a danger that the tightening force will easily exceed this yield point, and on the other hand, this also leads to the disadvantage that it is easy to loosen, so that completely satisfactory results have not been obtained. Therefore, if the lubrication is too good, it will become too tight.
There is a risk of exceeding the yield point of the bolt, and on the other hand, this also leads to the disadvantage that it is easy to loosen, making it impossible to obtain a fully satisfactory result. This invention was made in view of the current situation, and after forming an oxalate film on the surface of at least one of stainless steel bolts and nuts by ordinary oxalate treatment, A method for lubricating stainless steel bolts and nuts, which comprises forming a lubricating film thereon with an aqueous emulsion containing waxes, mineral oil, and an amine salt of a _C12 to _C22 fatty acid as essential components. It provides: The details will be explained below. Stainless steel bolts and nuts are subjected to oxalate treatment, but the method of this oxalate treatment is not particularly limited, and may be any of the usual methods widely used in the cold plastic working of stainless steel materials mentioned above. It does not cause any trouble. For example, after degreasing with an aqueous solution of chemical detergent and washing with water, an accelerator is added to Agents A-1 and A-2 of the oxalate treatment agent FELBOND (registered trademark of Nippon Parkerizing Co., Ltd.) to form a film. All you have to do is wash it with water and dry it. Through such treatment, a film containing ferrous oxalate as a main component is formed on the surface of the substrate. Conventionally, there is a method using phosphate as a metal surface treatment method, but this phosphate treatment does not cause the reaction of oxalate as in the present invention and cannot be expected to be effective. After the oxalate treatment, the base material is further treated with a lubricant, and the lubricant used in this invention is as follows. That is, it is a mixture of waxes and mineral oil with an amine salt of a C ₁₂ -C ₂₂ fatty acid added as an essential component, and if used in the form of an aqueous emulsion, handling is extremely convenient. Here, as waxes,
Examples of the mineral oil include paraffin wax, carnaubau wax, polyethylene wax, paraffin wax, etc. Paraffin wax is preferable, and mineral oils include paraffin and naphthene mineral oils, and paraffin wax is preferable. Mineral oil is best. On the other hand, examples of amine salts of _{C12 to C22} fatty acids include lauric acid _, palmitic acid, stearic acid, and oleic acid, and examples of amines include monoethanolamine, Diethanolamine, triethanolamine, etc. can be mentioned, and amine salts of fatty acids of stearic acid and monoethanolamine are preferred. The lubricant to which this fatty acid amine salt is added has a composition as described below and is in the form of a grease, but it can be easily converted into an aqueous emulsion by adding water. The composition of the aqueous emulsion lubricant of this invention is as follows. In addition, % is weight %. Waxes 10-40% preferably 20-35% High viscosity mineral oil 5-30% preferably 15-25% Amine salts of fatty acids 5-20% preferably 7-15% Water 30-70% preferably 40-60% This lubricant, for example, is a 10% aqueous emulsion liquid that exhibits alkalinity with a pH value of 9.0±1.0 at 20°C, so in addition to improving lubricity, it also neutralizes the acid content associated with oxalate treatment. It has a sexualizing or alkalinizing effect. Even though it is called stainless steel, it does not mean that it will never corrode when acidified, so a lubricant converted to alkaline by adding amine salts of fatty acids can be used to fill the gaps that occur when tightening bolts and nuts. Corrosion can be completely prevented. In actual use of the lubricant of this invention, the lubricant is further uniformly dispersed in water to a concentration of about 10 to 50 g/distance, and the oxalate-treated base material is added to this liquid. Just soak it. Here, adjust the lubricant concentration to 10 to 50 g/
The reason for this is that if it is lower than 10g/
Naturally, an excellent lubrication effect cannot be obtained,
For example, 30, 20, 15, 10 and 5 for Natsu only.
The torque coefficient value when processing the concentration of g/ is
0.212, 0.211, 0.267, 0.296 and respectively.
0.351, and if the concentration exceeds 50g/, for example, 20g/
Even if only the g/concentration is processed, the torque coefficient value may be 0.133, 0.128, or 0.112 depending on the way the bolt and nut are engaged (the size of the gap), how they fit in, etc., so the lubrication This is because there is a risk of being too effective, and at the same time, this is undesirable as it increases costs. There is no particular need to heat the liquid at this time; a normal room temperature is sufficient, and the immersion time may be about 1 to 5 minutes. Finally, the desired product is obtained by drying the lubricated bolts and nuts. Although it is of course most preferable to perform the lubricant treatment on both the bolt and the nut in this invention, substantially the same effect can be obtained by treating either the bolt or the nut.
Therefore, the stainless steel bolts and nuts obtained by this invention are excellent bolts and nuts that cannot be obtained by conventional methods, and can be easily tightened with a smaller tightening torque than conventional stainless steel bolts and nuts. By using an alkaline lubricant, the purpose of crevice corrosion prevention can be fully achieved, so the service life can be extended by at least several times. Since the oxalate film in the metal is a poor conductor of electricity, it was found that it prevents corrosion at the contact surface with metals with different potential series.
It can be said that the significance of this invention is extremely large. Examples and comparative examples are shown below. Stainless steel hex bolt/nut (SUS304,
40 sets of M16×75) were prepared, subjected to oxalate coating treatment as shown in Table 1, and tested in Examples 1 and 2 and Comparative Examples 1 and 2 shown in the table. The tightening torque, axial force, and loosening torque of stainless steel hexagonal bolts and nuts after lubrication treatment were measured. The measurement conditions are as follows. That is, the object to be tightened is set on the sample, the bolt is fixed with a three-jaw scroll chuck, and the box thread is tightened.

[Table] Turn the nut with a punch to the specified torque (1100Kgf
-cm). The torque or axial force was monitored by the deflection of the electromagnetic oscilloscope, and after tightening, the nut was loosened with a box wrench, and the required loosening torque was read from the deflection of the electromagnetic oscilloscope. The measurements were carried out on three sets of bolts and nuts, and the results are summarized in Table 2. Table 2 shows that the tightening torque is constant (1100Kgf
-cm) and the axial force and loosening torque when

【table】

[Table] The torque coefficient values calculated from these values are also listed. Note that the torque coefficient value K is obtained using the following calculation formula. In other words, K=T/d・F×10 ^-1 (where, T is the tightening torque, d is the bolt thread diameter, and F is the axial force) The preferable torque coefficient value K changes depending on the material. For stainless steel materials, values around 30% around 0.17, that is, 0.12 to 0.22, are considered to be practically desirable values. This means that when tightened to the standard tightening torque, the axial force with the minimum torque coefficient value of 0.12 will not exceed 96% of the yield point of stainless steel bolts, and even in the case of the maximum value of 0.22, the axial force of the conventional The axial force of stainless steel bolts and nuts lubricated with machine oil is approximately 15 to 20% higher than the standard tightening torque, so when tightening with a hand tool such as a spanner, the tightening force is equal to the standard tightening torque. 85% of the standard tightening torque is appropriate for the lubricated bolts and nuts of this invention when tightening with torque control using an electric torque wrench or the like. Therefore, when the tightening torque is kept constant, the axial force is appropriate, and the loosening torque is relatively large and has little variation. Since the most desirable torque coefficient is within the range of 0.12 to 0.22 with stable lubrication, from the results in Table 2, the torque coefficient obtained by Examples 1 and 2 is the most desirable. It became clear that the bolts and nuts that were used were extremely superior. On the other hand, both Comparative Examples 1 and 2 were judged to be unacceptable. This is because Comparative Example 1 has a torque coefficient value of
Since it is less than 0.12, there is a risk of tightening the bolt beyond its yield point, and in Comparative Example 2, there is a large variation in torque coefficient values within the same production lot.

Claims (1)

[Claims] 1. After forming an oxalate film on the surface of at least one of the stainless steel bolts and nuts by ordinary oxalate treatment, 10 to 40% by weight of wax, 5 to 30% by weight of mineral oil, _C12 ～ _C22
5-20% by weight of amine salts of fatty acids and water 30-70%
A method for lubricating stainless steel bolts and nuts, characterized by forming a lubricating film using an aqueous emulsion containing % by weight as an essential component.