Threaded – headed fastener – or washer making: process and apparat – Process – Making externally threaded fastener – e.g. – screw or bolt
Patent
1995-02-22
1997-08-26
Larson, Lowell A.
Threaded, headed fastener, or washer making: process and apparat
Process
Making externally threaded fastener, e.g., screw or bolt
B21K 156
Patent
active
056605943
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a procedure for making a screw thread on a corrugated bar.
The corrugated bar used as raw material in the procedure of the invention for making a screw thread is produced from round section by a special forming method which produces the ribs of the corrugaged bar and simultaneously increases the strength of the steel during the manufacture. This manufacturing method increases the strength of the corrugated bar, and in addition the ribs produced become hardened, being of a considerably harder material.
Normal screw threads for a nut on a corrugated bar are made using known techniques either by rolling or by cutting. In these cases, the cross-section of the bar is reduced in the threaded portion and the tensile capacity of the bar is completely determined by the cross-section of the thread. The reduction in tensile capacity of the cross-section of the thread as compared to a solid bar is of the order of 20-30%. Thus, the tensile capacity of a threaded bar is exclusively determined by the cross-section of the thread, leaving the capacity of the rest of the bar unused, which means uneconomic use of steel. An economic target is to produce a thread whose tensional area is larger than or as large as the nominal area of the corrugated bar.
For the manufacture of a screw thread having the full tensile capacity of the corrugated bar, several methods have been patented. These are based on expanding the end of the corrugated bar by the cold upsetting method in room temperature. For example, patent application GB 2 227 802 presents a bar joint for use in the reinforcement of concrete, in which the cross-section of the bar ends to be joined is enlarged by cold upsetting and the ends are provided with a conical thread. FI-application 890509 presents a procedure for making mechanical joints between round reinforcement bars, in which the bars are joined together by means of a threaded sleeve placed at the juncture. According to this application, one or both ends of the bars to be joined are cold upset before threading. The upsetting is performed over the length of the part to be threaded and is so implemented that the root diameter of the threaded portion is at least equal to or larger than the normal diameter of the bars to be joined.
Cold upsetting causes no changes in the material or strength properties of corrugated bars. After the cold upsetting, the thread is produced on the upset area by cutting. This method preserves the strength properties of the steel bar unchanged, but it also removes material from the surface of the bar. By the cold upsetting method, the end of the corrugated bar can only be enlarged over a short length because the material structure of steel does not withstand cold upsetting well enough to allow a corrugated bar to be provided with a thread longer than that required for a nut. For joints requiring a long thread, the cold upsetting method is inadequate.
The object of the present invention is to eliminate the drawbacks of previously known techniques and to achieve a procedure for making a thread on a corrugated bar which preserves the increased strength of steel achieved during the manufacturing of the corrugated bar as well as the hardness of the steel surface and the toughness of the interior parts of the bar even during the threading process, allowing a thread with a full tensile capacity to be made on the corrugated bar.
In the procedure of the invention, the end of the corrugated bar is machined by removing the corrugation ribs and flank fillets of the bar. Next, the bar end is heated and then hot upset, thereby increasing its cross-sectional area. After the hot upsetting, the upset end of the corrugated bar is cooled. The bar end is threaded by rolling. The details of the features characteristic of the procedure of the invention are presented in the attached claims.
This procedure allows one to produce a thread with a tensional cross-section as large as or larger than the net cross-sectional area of a solid corrugated bar, which is decisive in respect of th
REFERENCES:
patent: 3415552 (1968-12-01), Howlett
patent: 3850535 (1974-11-01), Howlett et al.
patent: 4500224 (1985-02-01), Ewing
patent: 4594020 (1986-06-01), Hughes
Larson Lowell A.
Schoeffler Thomas C.
Tartuntamarkkinointi Oy
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