Lubricant for thread rolling and thread rolling method

Abstract

A thread rolling lubricant of a nonchlorine species, in which a lubricant base oil is blended with 25 through 35 weight % of (A) a sulfur species extreme pressure agent, 6 through 16 weight % of (B) an organic zinc compound, 2 through 12 weight % of (C) a calcium species additive, and 2 through 13 weight % of (D) an oiliness agent for carrying out thread rolling.

Description

[0001]This application claims priority to Japanese patent application serial number 2007-324549, the contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to a lubricant blended preferably for thread rolling and a thread rolling method using the same.[0004]2. Description of Related Art[0005]A screw thread can be formed by machining on a comparatively large-sized metal material of an insert nut arranged at, for example, an oil filter of an automobile or the like. However, in machining, a cutting chip is produced, and a step of removing the chip is complicated. In contrast thereto, in a case of thread rolling, a fabrication cost is low in comparison with that of machining and also the cutting chip is not produced. A strength of a rolled thread is higher than that of a cut screw. Therefore, a member forming a screw thread by machining is desired to shift to thread rolling.[0006]When a metal m...

AI Technical Summary

Benefits of technology

[0028]The lubricant may be added with additives of rust preventive agent, antioxidant, anticorrosives, colorant, antifoamer, perfume and the like as necessary within a range of not hampering an effect of the invention while constituting indispensable components by additives (A) through (D). These can be blended by themselves or in mixtures thereof. However, in a case of blending the additives, when a complicated composition is constituted by adding a number of the additives, although a quality of a screw and a condition of a lubricant per se can be promoted, conversely, there is a danger of increasing the recess of the ridge top portion. Hence, it is preferable to constitute a composition to a degree capable of minimally promoting a quality of a product. Specifically, these are constituted by 2 weight % or less, preferably, 1.5 weight % or less by the lubricant total amount reference within the range of not hampering ratios of the blending additives (A) through (D). Particularly, the degree of adding the rust preventive agent is preferable. When the rust preventive agent is added, rust of a product after having been worked can be prevented from being brought about.

[0029]When a rust preventive agent is blended, a kind thereof is not particularly limited but, for example, respective sulfonates of Ba, Na, Mg and the like and sulfonic acid compounds, ester compound of wax oxide and wax oxide compounds respective salts of Ba, Na thereof, polyhydric alcohol ester such as sorbitan monolate, lanolin and metal soap of lanolin and the like can be used. Among them, Ba species rust preventive agent is preferable. According to the invention, one kind of the rust preventive agent may be used by itself or two kinds or more may be mixed. Further, the rust preventive agent are mixed with mineral oil or synthetic oil, ester or the like to facilitate to dissolve to oils.[Thread Rolling]

[0030]In thread rolling, an inner peripheral face or an outer peripheral face of a work material is plastically deformed by using a thread rolling tool (tap or die) and raised such that a surrounding material gathers together along a shape of the rolling tool by a folding operation. When a female screw is cut at an inner peripheral face of a hole (bored previously by a drill or the like), a tap is used, and when a male screw is cut at an outer peripheral face of a rod member in a circular pillar shape, a die is used. In a case of working a female screw by a tap, the tap is rotated. In a case of working a male screw by a die, a work material is rotated. Normally, working is carried out in cold (at normal temperature). A variety of products of meter screw (M), a trapezoidal screw (TM, TW), and a taper screw (PT, PS) as well as a specially formed screw or the like can be fabricated. A principle of forming a screw thread and a recess of a top portion thereof by thread screwing has previously been explained.

[0031]A screw material constituting a work is not particularly limited so far as the screw material is basically a metal material capable of being plastically deformed such as, for example, a cold rolled steel plate or the like. A material having a high hardness and a low elongation (such as cast iron or the like) may not so suitable for rolling. When a steel material is worked, it is preferable to constitute the steel material by low carbon steel having carbon content of about 0.3 mass % or smaller. Because although when there is an increase in a carbon content of carbon steel, the hardness is increased, the carbon steel tends to be brittle. When the carbon content is low, elongation or a reduction of area is excellent. On top of that, a recess of a screw top portion can be reduced by using the lubricant precisely blended in accordance with a revolution number in thread rolling.

[0032]When a width dimension of a recess is large, a height dimension of a screw thread formed tends to be low, and therefore, an increase in a width dimension of a recess amounts to a low accuracy (quality) of a screw product. Thus, it is preferable that the recess of the screw thread portion is as small as possible to constitute a screw product having a good quality. For example, although when the width dimension of the recess is near to 0.5 mm, a significant inconvenience is not brought about basically in using the screw, but there is a case in which a failure in fastening is brought about occasionally. Although the fact does not pose a serious problem when used in a general household, but when used as a part requesting a high accuracy of (for example, an automobile part or the like), a reliability is low. In contrast thereto, when the width dimension of the recess of the screw thread top portion can be constituted by about 0.3 mm, a possibility of a failure in fastening can further be reduced.ExamplesLubricity Test

[0033]Lubricities (seizure loads) of respective lubricants and comparative examples comprising compositions shown in Table 1 through Table 4 are measured and evaluated by a four ball test. Comparative examples differ in kinds per se of additives blended. Although according to lubricant X-1, lubricant Y-1, and lubricant Z-1, respective kinds of additives blended are the same, blending rates thereof differ. Specific compositions (numerals in the table designate weight %) and a test result are shown in Table 1. Further, lubricants X-2 through X-11, lubricants Y-2 through Y-11, and lubricants Z-2 through Z-11 blending ratios of respective additives of which are variously changed are prepared by respectively constituting references by lubricant X-1, lubricant Y-1, and lubricant Z-1 and respective seizure loads are similarly measured. Compositions (numerals in table designate weight %) of lubricant X group and a test result are shown in Table 2. Compositions (numerals in table designate weight %) of lubricant Y group and a test result are shown in Table 3. Compositions (numerals in table designate weight %) of lubricant Z group and a test result are shown in Table 4. Further, although details will be described alter, as a result, lubricant Z group corresponds to the example of the invention. Dynamic viscosities of lubricant X group, lubricant Y group, and lubricant Z group in this case are respectively constituted as 20 mm2 / s. The four ball test is measured based on the standard of JIS K2519. A measured material is constituted by SUJ2 both in upper balls and lower balls.TABLE 1ComparativeComparativeComparativeLubricant

Problems solved by technology

However, in machining, a cutting chip is produced, and a step of removing the chip is complicated.

However, when the chlorine species lubricant is used, a chlorine species additive component is decomposed in working or ageing which can rust a material or a tool.

Also, in incinerating, a harmful substance of dioxin or the like is generated, which is adverse to an environment.

Further, an incinerator is corroded or damaged to shorten a service life thereof.

Furthermore, when a debris by chipping off the top portion 2 in fastening is bit by a fitting portion of the screw (between a flank of the male screw and a flank 4 of the female screw), the following problem is posed.

Further, a removing operation by a seizure is difficult.

However, when the recess 3 of the top portion 2 is large, there is also a danger of bringing about an error in the flank angle or a height dimension of the screw thread.

Therefore, as in the four references, a lubricant is not suitable for thread rolling since the lubricant is excellent simply in the lubricity.

Because when the lubricant is simply excellent in the lubricity, the folding operation becomes rather difficult to be produced, and also the recess of the screw thread portion tends to be enlarged.

Although when the lubricity of the lubricant is reduced, the recess of the screw thread portion can be reduced, thereby, a goal of surface roughness or shape of the screw thread is failed, and therefore, a quality of a product is deteriorated.

However, even when the productivity is intended to increase, the revolution number cannot simply be increased.

Because with an increase in the revolution number, a work material and a rolling tool are exposed to more severe working condition.

Further, also a size of a recess of a screw thread top portion is not particularly investigated.

Therefore, a problem remains in the lubricant of the background art for working a screw thread also in this respect.

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