Chrome steel alloy

Details Chrome steel alloy Chrome steel alloy

2002-07-17

2004-08-03

Yee, Deborah (Department: 1742)

Alloys or metallic compositions

Ferrous

Nine percent or more chromium containing

C420S069000, C148S325000

Reexamination Certificate

active

06770243

ABSTRACT:

Recent developments in sewing machines have also decisively changed the profile of demands imposed on industrial (sewing) needles. Hitherto, industrial needles for sewing machines have been produced from a carbon steel containing approximately 0.8 to 1.1% of carbon. In humid air, needles of this type tend to form rust spots, which very greatly limits their use. Therefore, to improve the resistance to corrosion and to avoid the formation of rust, the needles are coated by electrodeposition, for example in rotating drums. Nickel and/or chromium is applied as coating by cathode deposition. The layer thicknesses often differ very considerably, and critical areas, for example in the region of the eye, the point or the thread groove, can often only be provided with a very thin coating. However, it is in these very regions that, in operation, high levels of wear occur. Abrasion of the coating is also undesirable, since it is known that nickel is a highly allergenic metal even in very small concentrations.
A further drawback of the coating by electrodeposition is that during cathode deposition of metal in electrodeposition baths, hydrogen can be incorporated in the needle material. This hydrogen causes the brittleness to increase very considerably, with the result that there is a risk of needles breaking, with possible damage to the machine.
For economic production of the needles, the workability is a parameter of crucial importance. This applies in particular to the production of thin needles. The carbon steels containing up to 1.1% of carbon which have been used hitherto are just able to satisfy these conditions, but in the annealed state with carbon contents of over 1% there may already be difficulties with working the thread groove and the eye. With these carbon steels, it is possible to achieve a hardness of at most 800 to 840 HV1 after a special heat treatment.
However, the temperature stability, i.e. the maintenance of the hardness after heating, is insufficient. Even in the case of heating to 300° C., a drop in hardness of more than 200 HV1 units (10 HRC units) is possible. Furthermore, at full hardness, there is a considerable susceptibility to uptake of hydrogen, for example during coating by electrodeposition. Even low hydrogen contents may embrittle the martensitic microstructure, which is stabilized only by carbon, and cause an increased risk of fractures. This is particularly critical in the case of thin needles. Because of difficulties in the micromachining and precision machining of the eye and the thread groove and because of insufficient matching of the alloying elements, it has hitherto been impossible to utilize the advantages of relatively high-alloy steels.
The demands imposed on new needle materials are determined primarily by the increases in performance in sewing machines. Developments are toward an increase in the economic viability of the production of seams combined, at the same time, with simple operation and a longer service life of the sewing machines. The following measures serve this purpose:
increasing the sewing speed,
improving the thread guidance,
optimizing the sewing foot pressure,
continuous adjustability of the stitch width,
highest possible stitching force of the needles
combined with lowest possible friction.
The desire for higher sewing speeds results solely from economic considerations, in order to reduce costs and increase production. For example, industrial sewing machines are currently already driven at more than 7000 rpm. The high sewing speeds (i.e. the high stitch numbers) lead to particular loads on the needles and require adjustment of the materials and of the materials properties.
The high sewing speeds and the associated particular loads on the needles therefore require improved materials properties. These relate to the heat resistance of the needle point, the wear resistance as a sum property of corrosion and abrasion resistance, the hardness, the rigidity, the maximum bending force and the maximum bending.
Recent tests have shown that when thick materials are being sewn at high sewing speeds, temperatures of up to 300° C. occur at the needle point. Under these conditions, the wear resistance is significantly reduced after even a short period of use, a fact which is also attributable to insufficient protection by coatings applied by electrodeposition.
A major drawback of needles made from carbon steel is in particular the drop in the core hardness and the insufficient mechanical properties under extreme loads. The matrix, which is only stabilized by carbon, is often unable to resist deformation at elevated temperatures. As a result, the service life of the needle is reduced considerably. The deformation in turn significantly increases the risk of damage to the sewing machine.
An industrial needle should have a high core hardness and a high heat resistance, if possible to over 300° C.
The wear resistance as a sum property of abrasion resistance and corrosion resistance should be good and as far as possible should not be adversely affected by the action of air and moisture and by contact with abraded fabric and fibers (finishing agents, dyes, chemicals, bleach residues and other substances).
The risk of a needle breaking should also be low when different materials are being sewn, in particular during sewing in the transition region between different materials and when sewing padding and reinforcements.
The numerical value of the rigidity S, expressed as a quotient F
max
/S
max
(maximum bending force/maximum bending) should be high and have a scatter which is as low as possible. The bending of a needle until it breaks should be between 1.5 and 2.5 mm and should not exceed 3.0 mm.
The production of needles should be inexpensive, environmentally friendly and simple. The shaping and heat treatment should be possible with conventional installations. In the case of needles made from sintered carbide (German laid-open specification 38 19 481), this condition is not satisfied, since shaping requires diamond grinding tools and the eye has to be manufactured by means of spark erosion.
Needles for medium sewing speeds are produced from wire, which has a simple alloy structure and is easy to process. Inexpensive production is a crucial aspect in the selection of the materials. Carbon steels containing approx. 0.8 to 1.1% of carbon, approximately corresponding to a steel with materials number 1.1545, are customary. For high demands on the needles, wire from the upper carbon range is currently used. However, the limits of processability are encountered in this range.
To produce an industrial needle, a wire is processed predominantly by means of chipless shaping. In this case, first of all the needle stem and neck are processed and extruded by means of presses, and the eye is flattened and shaped out. Then, the needles are straightened and the thread groove is introduced by means of roll stamping. Precision machining of the eye and sharpening of the needle point follow as further processing stages. There then follows a hardening step with a subsequent tempering treatment, if appropriate also in combination with a deep cooling treatment. The sewing needles then achieve a hardness of approx. 60 HRC. This is followed by precision grinding of the needle points, cleaning and coating with nickel and/or chromium by electrodeposition. The coating by electrodeposition takes place in rotating plastic vessels with direct current being supplied, the negative supply conductor being introduced into the interior of the plastic vessel, where it makes contact with the needles. The electrolyte used is often the acid solution of a chromate (Cr
6+
) salt. From this solution, a thin film of chromium or hard chromium is deposited on a nickel layer which has often been deposited beforehand.
During the coating operation, it is very easy for hydrogen to diffuse into the lattice of the needle material, with the result that the hardened carbon steel can suffer considerable embrittlement. This in turn leads to a high susceptibility to breaking on the part of the need

Affiliated with

Also associated with

Rating

Chrome steel alloy does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Chrome steel alloy, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chrome steel alloy will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3357642