Threaded – headed fastener – or washer making: process and apparat – Process – Making externally threaded fastener – e.g. – screw or bolt
Patent
1996-10-03
1998-07-07
Larson, Lowell A.
Threaded, headed fastener, or washer making: process and apparat
Process
Making externally threaded fastener, e.g., screw or bolt
470 12, 72318, 72358, 29446, B21H 302
Patent
active
057760012
DESCRIPTION:
BRIEF SUMMARY
The invention relates to thread formation. Particularly the invention relates to the formation of threads on deformed steel reinforcing rods for reinforced concrete structures.
According to an aspect of the invention, the invention provides a method of forming a thread on at least one end region of a deformed steel reinforcing rod, the method comprising: increase the diameter of the end region to a new, upset, diameter greater than the nominal diameter; and having a thread major diameter, which is greater than the nominal diameter and a thread minor diameter which is less than the nominal diameter.
The formation of such a thread enables the production of mechanical connections between pairs of rods, the connections having a strength greater than that of the rods being connected to one another.
Preferably, upsetting the end region produces an upset end region having a length which is typically 110% of the thread diameter (taken from peak to peak).
Preferably, the method further comprises a step of skimming the end region of the rod.
Preferably, said step of skimming the end region of the rod is carried out intermediate said cold upsetting and thread rolling steps.
Preferably, the thread minor diameter is no greater than 90% of the nominal diameter of the rod.
Preferably, rolling the thread onto the end region produces a thread having an effective diameter larger than the nominal diameter.
Preferably, the upset diameter of the end region of the rod is no greater than 110% of the nominal diameter D.
Preferably, the thread is of a formation having enlarged major and minor root radii.
Preferably, the thread is of a relatively coarse pitch, to enable a greater speed of assembly when forming a connection to the end of the rod.
The thread is preferably a parallel thread.
The upsetting operation as specified above produces full formed rolled threads. The effective diameter of such threads is typically around 5% greater than the nominal diameter of the bar.
Such "minimal" upsetting reduces the volume of upset material by up to 70% compared with prior systems, yet rod strength is not compromised by the reduced upsetting.
A further benefit of cold minimal upsetting is that this gives an important advantage of enabling transportable equipment to be used. In addition, minimal upsetting may be carried out during a much shorter time period than is required by prior art systems. Typically, the time saving over previous cold upsetting systems is in the order of 60%.
Other prior systems using hot forging methods to produce threaded rods have substantially higher energy requirements than that of the present invention due to their need to preheat the end regions of the rod.
Whenever any type of upsetting is utilized to increase the diameter of a region of a rod, rod length is always reduced. By minimizing the amount of upset, a further beneficial effect is that rod length is only reduced by a very small amount.
A yet further advantage of the combination of providing a minimal upset and thread rolling is that a smaller diameter and shorter connecting sleeve (coupler) than was previously possible may be utilized to connect two threaded ends together, and this has the beneficial effect of ensuring that rods joined in this manner have the least stiffening effect caused by a full strength mechanical joint.
Furthermore, if a coupler of smaller diameter is used then less concrete is required to cover the rods.
The invention includes threaded rods produced in accordance with the abovementioned method.
An embodiment of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:
FIGS. 1A to 1D schematically show a method of thread formation in accordance with the present invention;
FIG. 2 is an enlarged cross-sectional view showing a region "X" of the rod shown in FIG. 1D; and
FIGS. 3(I) to 3(VII) illustrate a method for connecting together a pair of deformed steel reinforcing rods, by means of a coupler.
Referring initially to FIGS. 1A to 1D, a method of thread for
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Degarmo et al, Materials and Processes in Manffacturing, 1994, pp. 353-356.
International Publication No. WO 93/24257 published Dec. 9, 1993.
WO,A,93 24257 Dec. 1993.
CCL Systems Limited
Larson Lowell A.
Tolan Ed
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