DD103183B1 - Process for the surface treatment of sewing machine needles - Google Patents

Description

Process for the surface treatment of sewing machine needles

The invention relates to a chemical and mechanical process for the surface treatment of sewing machine needles.

It is known to achieve smooth, polished or highly polished surfaces and deburred or rounded edges in the processing of needles:

Scouring and polishing with the aid of grinding or impactors of different materials, shapes and sizes in different media in vibratory sliding grinders, bells, drums and special equipment

- Kr etching, Bür st s and S _c hwabbeln means of rotating or moving in translation when using tools of polishing agents verschiedenster type and design.

In principle, a smoothing of the surface as well as a deburring and rounding of edges by mechanical removal of macroscopic and microscopic fine elevations is achieved in all the above-mentioned methods. The abrasion is due to the effect of pressure caused by the friction between the parts to be machined or between the parts and additional grinding, impactors or tools. The friction can be suitably varied by using grinding and polishing agents in a suitable composition and bonding.

In the manufacture of needles for sewing machines, rounded edges of the thread guide grooves and the eyelet as well as highly smoothed surfaces of the needles play the dominant role, especially in the ear and shaft area.

This is the prerequisite for a high reliability of the needles in the sewing process and to avoid missing stitches and thread breaks.

The technological effort with the help of mechanical methods to achieve these quality parameters is disproportionately high compared to the total cost of producing the needles.

By embossing and punching the tube, by milling the thread channels and the grinding of the embossing burr and the sharp vision of the needle tips creates a rough surface that must be smoothed in further work operations. In known manner, the smoothing of the ears by means of cotton threads or the like, which are coated with polishing paste, made on devices. For this, the needles are to be tied in the ear. The cording takes place due to the specific nature of the needles mainly by hand. The sewing machine needles are pushed over a cotton thread or the like, which is provided with a lacing needle. In order to achieve the highest possible economic effect, it is necessary to tighten the same number of sewing machine needles on each thread. This technology requires a high work intensity and is due to the necessary Öhrausrichteas before pushing on the constricting needle extremely cumbersome, time-consuming and highly dependent on the skill of each worker.

In general, electrochemical processes for polishing and deburring small parts are also known.

In such methods, the parts to be machined are clamped when using high current densities to ensure a secure electrical contact.

When using low current densities, preferably in small and mass parts, using suitable electrolytes, the processing is known as bulk material in hollow bodies.

In all these methods, the following disadvantages occur in particular:

- more or less severe uneven erosion,

- insufficient smoothing effect of macroscopic unevenness,

- relatively high asset value and energy consumption.

In mass processing often occur as a result of labile contact or when removing the parts of the electrolyte oxide or salt layers, which must be removed before a subsequent galvanic processing. On the other hand, especially suitable for the mass processing are suitable Überchlorsäure electrolytes explosive, which is why they are rarely used in industry.

Furthermore, it is known that smooth surfaces are achieved in steel parts by chemical processes. The most diverse acids and acid mixtures are used at different temperatures. It is also known that a common acid for pickling, e.g. Oxalic acid, hydrogen peroxide is added. The oxide layer formed in such processes forms a good protection against further oxidation. However, it has no decorative appearance and is therefore almost always undesirable. In a subsequent galvanic treatment, it is even disturbing and must therefore be removed. This can e.g. by addition of ammonium hydrogen fluoride in the aforementioned solution. Purely high requirements, however, the achieved gloss effect is not enough ·

The purpose of the invention is the elimination of the deficiencies of the known methods.

The invention has for its object to provide a combination of methods using the known method, which achieves smooth and shiny surfaces in sewing machine needles.

According to the invention this is by applying the following rfahrensschritte a known V _e

- Pretreatment of the sewing machine needles in a rotating hollow body in aqueous solution with the addition of oxalic acid and hydrogen peroxide

- then rounding and polishing by means of vibrating track lifters

- Then high gloss polishing in a centrifugal drum with the addition of Mikropolierkörperη and methanol or isopropanol

achieved ·

The inventive solution of the combination of methods to achieve smooth, shiny surfaces and rounded edges in the production of needles several deficiencies and especially costly, conventional processing methods are eliminated. This relates to the mechanical processing deburring, scraping, brushing and buffing and in particular the necking of the needle tube on polishing threads and the complex smoothing and polishing of the entire Öhrkonturen ·

Due to these operating operations, a uniform processing of the entire partial surface is not guaranteed, so that in addition to the reduction of the processing costs and the processing time, a substantial improvement in the overall surface quality is achieved.

Further, soiling works for removing the emery, polishing agent and oil residues on the small parts are saved according to the respective mechanical working methods, and an increase of the corrosion resistance as well as the adhesion of galvanic precipitates is achieved.

The invention will be explained below using an exemplary embodiment.

The chemical treatment as the first stage of the process combination takes place in known rotating or vibrating hollow bodies. The speed or vibration frequency and the shape and size of the hollow body depends on the amount, shape, size of the small parts to be treated. By the movement of the small parts ensures that the parts are constantly washed around evenly through the aqueous solution and a partial Sisenanreicherung, especially in grooves, recesses and openings of the parts, is avoided and thus takes place on all sides uniform removal.

The aqueous solution is prepared at room temperature, being dissolved in one liter of fresh water 2o to 3 ° gr technical oxalic acid in crystalline form. To this prepared solution is added 40 to 100 ml of 35% technical grade hydrogen peroxide.

The exposure time of the needles is about 2o ° C for 3 to 3o minutes, depending on the shape, size and surface finish and required Einbnungseffekt the parts. The amount of the aqueous solution should preferably be used for the TCarenoberfläche

a ratio of

1 Ь aqueous solution: Io to 2o d m have product surface.

The resulting erosion is up to o, o2 mm. The described chemical treatment of steel needles can be carried out both in the uncured and in any other tempering condition. During the chemical treatment, the oxygen is constantly oxidized by the oxidizer peroxide. The added oxalic acid complexes the bis (III) oxide, thereby removing it and keeping it in solution. The solution used is unusable for reuse due to iron ion enrichment. A regeneration is complex and therefore uneconomical.

When removing the treated needles from the aqueous solution, the partial surface is covered with a ferric oxide layer. The oxide layer does not bear a decorative character and for this reason was measured before a subsequent surface treatment can be removed.

For this reason, in the second stage of the process combination, the vibratory sliding grinding of the needles takes place. As a result, once the oxide layer is removed at the outer contours of the needles and further a rounding of the edges and the further leveling of the surface is achieved.

For this purpose, all suitable Vibrationsgleitschleifmaschinen with trough-shaped working containers, which allow a sufficient circulation of the grinding wheels and the abrasive good, can be used. The choice of suitable gluing machines depends on the shape, size and volume of the small parts to be treated.

Of crucial importance for the processing effect to be achieved is the use of suitable grinding wheels and sole additives as well as the volume ratio of abrasive particles to abrasive material.

Based on the geometric shape and the size of the needles to be processed, the most suitable abrasives in their shape, size and their material are usually determined empirically. The same applies to the choice of sole ifzusätze and the volume ratio of abrasive body to Sohleifgut.

The removal of the oxide layer in grooves, breakthroughs u.a. Recesses and the high-gloss polishing of the entire surface of the needles takes place in the third stage of the process combination with the aid of centrifugal force. The known centrifugal drum method causes up to 2oo min "due to the high number of revolutions and the counter-rotating movement at a vertically arranged / rotating one Plate attached polishing drums that the polish to be treated does not overturn, but along the walls of the drums along. It can here finest polishing bodies, such as micro balls and pins from Qlas, ceramic or steel warden be used, which can penetrate into the most inaccessible recesses. The force of the Mikropolierkörper is increased by the centrifugal force by a multiple, thus achieving a high polishing and gloss effect on the entire surface of the needles. An essential prerequisite for the effect to be achieved and for a subsequent stain-free and residue-free drying of the needles is the use of a suitable polishing liquid, which in most cases should also act as a solvent.

Particularly suitable for this purpose are solvents, such as methanol, isopropanol and petroleum, and polishing chemicals for steel.

The highest gloss effect and the best stain- and residue-free surface is achieved when using methanol.

The needles and the polishing bodies are dried in a centrifuge and then separated by means of a combined longitudinal vibration conveyor.

Claims (1)

Bringing in on Method for smoothing sewing machine nadine, characterized by the use of the following method steps known per se: - Pretreatment of the sewing machine needles in a rotating hollow body in aqueous solution with the addition of oxalic acid and hydrogen peroxide - subsequent rounding and polishing by means of vibration sliding loops - Then high gloss polishing in a centrifugal drum with the addition of Mikropoiierkörpern as methanol or isopropanol.