US2058841A - Method of treating metal-coated screws - Google Patents

Description

Oct. 27, 1936. R. THOMSON 2,058,841

METHOD OF TREATING METAL-COATED SCREWS Filed June 8, 1934 2 Sheets-Sheet 1 IL I T 25" 5 16 iv 16 INVENTOR ROE ERT THOMSON ATTORNEYS Oct. 27, 1936. R. THOMSON I 2,058,841

METHOD OF TREATING METAL-COATED SCREWS Filed June 8, 1934 2 Sheets-Sheet 2 WTHH:

. INVENTOR ROBERT THOMSQN ATTORNEYS Patented Oct. 27, 1936 I METHOD OF TREATING METAL-COATED SCREWS Robert Thomson, Arlington, N. J., assignor to Dardelet Threadlock Corporation, New York, N. Y., a corporation of Delaware Application June 8, 1934, Serial No. 729,563

14 Claims. (01. 10-1) v The present invention relates more particularly to the galvanization of screw threaded articles. When such an article is galvanized by the usual dipping process the distribution of the galvanizing material over the screw-thread is quite uneven. The galvanizing coating is too thick at some places and too thin at others. Deposits of excess material form tears or globules on the thread and fillets in the thread groove.

deposits materially distort the .prpfile of the thread and obstruct the screwing of the thread along a complementary thread.

Important objects of the invention are, to provide an improved method of treating a galvanized screw threaded article to remove irregularities from the galvanizing coating and produce a smooth, uniform, accurately gauged galvanized screw thread.

Other objects of the invention will appear hereinafter.

In the drawings, Fig. 1 is a sectional view showing the galvanized thread of a nut being operated upon by a mandrel designed to carry out the method;

Fig. 2 an enlarged longitudinal sectional view of a portion of the nut thread and a portion of the mandrel and showing an early stage of the operation of the mandrel on the galvanizing coati Fig. 3 a view similar to Fig. 2 showing an ad'- vanced stage of the mandrel operation;

Fig. 4 a longitudinal sectional View of a galvanized nut thread prior to treatment to remove the irregularities on the thread coating;

Fig. 5 a view similar to Fig. 4 showing the galvanizing coating smoothed over the thread surfaces to a proper uniform thickness;

Fig. 6 a face view of an internally screw threaded die for operating on the galvanizing 4o coating of an external screw thread to smooth the coating over the thread surfaces and accurately shape and size the thread; v

- Fig. 7 a sectional view of said die, showing the screw thread thereof before it is completely shaped for its purpose;

Fig. 8 an enlarged longitudinal sectional view of the incompletely shaped thread of the die and showing the manner in which the thread is operated on to shape it;

Fig. 9 an enlarged longitudinal sectional view of the completely shaped die thread;

Fig. 10 a longitudinal sectional view showing the die thread operating on the galvanizing coating of an external screw thread; and

Fig. 11 an enlarged longitudinal sectional view These of two interfitted Dardelet screw threads with galvanizing coatings that have been smoothed to accurate gauge for proper cooperation of the thrwds.

The invention is illustrated as. employed for 5 treating the galvanizing coatings. of the wellknown Dardelet self-locking screw threads. In Fig. 11, i5 designates a Dardelet externalthread, or bolt thread, and i5 designates a complementary Dardelet internal thread, or nut thread. 10 These threads are formed to interwedge for mutual frictional self-locking. Each thread has a groove materially wider than its rib, and its rib has steep abutment side faces. The bolt thread i5 has a thread-locking surface ll extending 15 along its root and sloping slightly, in' cross section, with reference to the axial line of the thread. Preferably the angle of slope is about six degrees' The nut thread if has a thread-locking surface it along its crest and inclined similarly 20 to the surface ll of the bolt thread. In cross section the ribs of both threads taper outward slightly. The nut may be freely screwed on the bolt, with the rib of the nut thread displaced to the left with reference to Fig. 11 and with the 25 inclined locking surface l8 backed away from the inclined locking surface l'l. When the nut engages an abutment however and its axial advance is arrested, further rotation of the nut causes axial displacement of its thread It to the 30 right, with reference to Fig. 11, to force the crest surface I8 into locking engagement with the surface H and to bring an abutment face of the nut thread against the opposed abutment face of the bOlt thread. 35

In the case of galvanized Dardelet threads, in order to prevent obstruction of said relative axial shift of one thread on the other for locking and unlocking the threads, the galvanizing coating should be smooth and of properly gauged thick- 40 ness over the thread surfaces. The present invention enables such a coating to be easily obtained. While the invention is of especial utility in treating galvanized Dardelet threads it may be employed very advantageously for treating 45 other types of threads also. l

As indicated inFi'g. 4, the Dardelet thread surfaces of a nut N which has been galvanized by dipping have the zinc distributed very unevenly. The zinc coating is too thick at some 5 places and too thin at others, and globular deposits and fillets distort the profile of the thread. To smooth this irregular coating, reduce it to a desired uniform thickness and accurately shape and size the thread for coaction with a comple- 55 mentary thread, a mandrel I9 is provided. Said mandrel has a. reduced cylindrical entering end portion 20, a forwardly tapering portion extending throughout a length, a, a non-tapering following portion 2| extending throughout the length I), and a shank 2| squared at its outer end to fit in a driving chuck or holder. An external screw thread 22 is formed on the mandrel and extends preferably continuously throughout the tapered and non-tapered lengths or and b. Said thread has a constant pitch corresponding to that of the nut thread to be operated on. The width-of the rib of the thread materially exceeds the width of the groove so that the rib will fill the wide groove of the Dardelet nut thread H5. The helico-idal groove bottom 23 of the mandrel thread slopes in cross section similarly to the slope of the crest surface l8 of the Dardelet nut thread, and the side faces 24 of the mandrel thread are correspondingly steep and converge slightly, to a corresponding degree. The crest surface 25 of the mandrel thread is straight in cross section. Throughout the length a it lies on a cone and throughout the length b it lies on a cylinder. The depth of the thread 22 is substantially uniform throughout its length.

In preparation for receiving its galvanized coat-v ing the nut thread I6 is cut by a tool slightly oversize and designed to cut back all of the thread surfaces to a certain degree below normal corresponding to the ideal thickness of the coating. A satisfactory thickness for example is one and one-half thousandths of an inch. Therefore when the thread surfaces have a coating ofthe calculated thickness the thread will be brought up to normal size and proportions for cooperation with a complementary thread. The convolutions of the mandrel thread 22 lying within the length I) are accurately and uniformly profiled and gauged to conform to the ideal of the thread [6 when the latter is galvanized. Assuming therefore that the thread I6 has been accurately formed and is screwed on said convolutions of the mandrel thread, there should be a uniform space between each thread surface of the mandrel thread and the opposed basic surface of the thread l6 beneath the galvanizing coating.

The galvanizing coating is applied to the nut thread by dipping or otherwise and it may be allowed to harden. The entering end of the mandrel is then passed through the galvanized nut, and relative rotation and axial advance at the proper pitch rate is caused to relatively advance the nut thread along the'mandrel thread. At first the leading end portion of the mandrel thread, due to the taper, has its thread surfaces rather widely spaced from the opposed surfaces of the nut thread, as shown in Fig. 2 axial advance continues along the taper the thread surfaces of the mandrel gradually. approach those of the nut. Consequently the excess deposits of galvanizing material are scraped, crushed and mangled to progressively increasing depth. This action causes considerable friction and suificient heat is thereby generated to soften or melt the galvanizing material. The softened material is distributed by the mandrel over the surfaces of the nut thread and compacted thereagainst. There is thus first a crushing action which breaks down and mangles the excess deposits and softens thematerial of the coating, and a following ironing action which distributes, compacts and smoothes the softened material. By means of the non-tapered portion of the As the 'mandrel thread, included in the length b, the

material is ironed out and burnished to render the coating smooth, dense, continuous, and of the desired uniform thickness. The coating will then effectually protect the underlying thread surfaces from corrosion. The non-tapered portion of the mandrel thread serves as a master gauge for the galvanized thread. The finished galvanized thread is shown in Fig. 5 with the coating C evenly distributed and the thread profile cleancut and correct, for proper cooperation with a complementary external screw thread.

For, operating on the galvanizing coating ofthe bolt thread l5 there is provided'a die in the form of a fiat plate or block 26 having a central bore in which a screw thread 21 is cut. The pitch of said thread is uniform, and the same as that of the bolt thread I5. The profile of the thread, however varies along the thread length. Throughout its length the groove bottom 28 of the thread is straight in cross section and lies on a cylinder. the length of the bore, the depth of the thread, from the groove bottom to the highest point of the crest, is uniform and the profile of the thread is uniform and shaped to conform accurately to an ideal of the galvanized thread l5.

Its side faces 29 are steep and inclined similarly to the side faces of the thread 15. The crest surface 30 is inclined similarly to the root surface ll of the thread l5.

Along the end portions 0 and e of its length the bore of the die is oppositely flared toward the adjacent faces of the die so that the crest of the thread along said lengths c and e lies on cones and the depth of the thread rib increases gradually from each face inward to the length d. Also, the rib along each of said end lengths c and e is pared off at its opposite faces so that the rib gradually decreases in width from the medial length d to the opposite faces of the die. This cutting down of the rib of the thread may be performed by a tool'T with a single cutting tooth which is screw-advanced relatively to the thread 21 and on a different pitch, to pare off the rib to a progressively greater depth as the tool recedes axially from the medial portion of the thread. The tool is operated first on one side of the thread rib and then on the other side. In Fig. 9 the die thread is shown with several tapered convolutions within the length 0, several non-tapered convolutions within the length d, and one and one-half tapered convolutions within the length e.

In preparation for receiving its galvanizing coating the bolt thread l5 also is formed by a tool or tools designed to form the thread surfaces so that they will occupy positions slightly depressed below normal to a certain degree corresponding to the ideal thickness of the coating. Therefore when the thread surfaces have a coating of the calculated thickness the thread will attain normal size and proportions for cooperation with a complementary thread. The convolutions of the die thread lying within the length d are accurately and uniformly profiled to conform to the ideal of the thread l5 when the latter is galvanized. Assuming that the thread I5 has been accurately formed and is screwed on said convolutions of the die thread, there should be a uniform space between each thread surface of the die thread and the opposed basic surface of the thread l5, beneath the galvanizing coating.

The galvanizing coating is applied to the bolt Along the medial portion (1 of vanced through the die.

thread l by dipping or otherwise and it may be allowed to harden. The bolt and die are thenaxially centered and the end of the bolt is in-' serted into the threaded end portion 0 of the bore of the die. By relative rotation and axial advance at the proper pitch rate the bolt, is ad- 'The tapering portion of the die thread rib penetrates the excess deposits of galvanizing material on the bolt thread to gradually increasing depth as the axial advance continues, the rib filling the groove of the bolt thread more and more. Thereby the excess deposits of galvanizing material are scraped, crushed and mangled. This action causes considerable friction and sufficient heat is thereby generated to soften or melt the galvanizing material; The softened material is distributed over the surfaces of the bolt thread and compacted coating C smooth, dense, continuous and of the desired uniform thickness. The coating will then effectually protect the underlying thread surface from corrosion. The action of the nontapered portion of the die thread renders the profile of the galvanized bolt thread clean-cut and reduces the galvanized thread to proper dimensions for cooperation with a complementary nut thread. Said non-tapered portion of the die thread serves as a master gauge for the galvanized thread. The taper of the die thread within the length e provides a suitable run-out for the thread and facilitates retraction of the bolt from the die with-safety to thefinished coating.

The treatment of the metallic coatings on the external and internal Dardelet screw threads as described shapes and sizes the profiles of the threads to ideal shape and dimensions so that complementary threads will have proper working clearance for screwing and unscrewing cooperation and so that the threads will. coact properly for mutual self-locking. Any unevenness in the basic thread surfaces underlying the coating will be corrected by the treatment of the coating. The coating is compacted, shaped, sized and burnished to produce a thread profile of high precision accuracy over the underlying basic thread surfaces. The treatment of the coating. renders it hard, dense and permanent and gives it a close, fine skin texture and great wear resistance.

What I claim is:

l. The method of treating a galvanized screw-- threaded article to shape and size the galvanized thread, comprising displacing irregularities and reducing excess thickness of the galvanizing coating by a crushing action advanced helically along the thread and thereby softening the material of the coating by heat generated by friction, and fol lowing said crushing action with an ironing action advanced helically along the screw thread and gauged with reference to an ideal of the thread to smooth and compact the softened material over the surfaces of the thread and accurately shape and size the galvanized thread for cooperation with a complementary thread.

2. The method of treating a galvanized screwthreaded article to shape and size the galvanized thread, comprising displacing irregularities of the galvanizing coating by a crushing action advanced helically along the thread and thereby softening the material of the coating by heat generated by friction, and following said crushing action with an ironing action advanced helically along the screw thread and continuous with the crushing action and gauged with reference to an ideal of the thread, to. smooth and compact the softened material over the surfaces of the thread and accurately shape and size the galvanized thread for cooperation with a complementary thread.

3. The method of treating a galvanized screwthreaded article to shape and size the galvanized thread, comprising displacing irregularities .of the galvanizing coating by a crushing action advanced helically along the thread and increasing progressively and gradually in depth toward the thread, to thereby soften the material of the coating by heat generated by friction, and following said crushing action with an ironing action advanced helically along the screw thread and continuous with the crushing action and gauged with reference to an ideal of the thread, to smooth and compact the softened 'material over the surfaces of the thread and accurately shape and size the galvanized thread for cooperation with a' complementary thread.

4-. The method of treating a galvanized screwthreaded article to shape and size the galvanized thread, comprising displacing irregularities and reducing excess thickness of the coating by relatively advancing another screw thread helically.

along the galvanized thread with gradual advance of the walls of .said second thread transversely toward the basic walls of the galvanized thread as said helical advance progresses, to thereby crush excess deposits of the coating material between said walls of the threads and to heat and soften said material by heat generated by consequent friction and to smooth the softened material over the galvanized thread.

5. The method of treating a galvanized screw thread to shape and size the galvanized thread, comprising displacing irregularities and reducing excess thickness of the coating by relatively advancing helically along the galvanized thread a length of another screw thread tapered for gradual advance of its walls toward the basic walls of the galvanized thread as said helical advance progresses, to crush excess deposits of the galvanizing material between the said walls and heat and soften said material by consequent friction and then relatively advancing helically along the galvanized thread another length of thread with its walls in a definite uniformly spaced relation to the basic walls of the galvanized thread to smooth the softened material over said basic thread walls and accurately govern the thickness of the coating for proper cooperation of the galvanized thread with a complementary thread.

6. The method of treating a galvanized internal screw thread to smooth the material of the galvanizing coating over the thread, comprising relatively screw-advancing along said thread a core having a screw thread to interflt said galvanized thread and shaped and gauged with relation thereto to crush excess deposits of the galvanizing material and heat and soften said mate'- rial by consequent friction and distribute and galvanizing coating over the thread, comprising relatively screw-advancing along said thread an internal thread to interfit said external thread and shaped and gauged with relation thereto to crush excess deposits of the galvanizing material and heat and soften said material by consequent friction and distribute and smooth the softened material to a desired predetermined uniform thickness over the external thread.

8. The method of treating a galvanized screw thread to produce a continuous permanent wearresisting and corrosion-preventing coating over the thread, comprising subjecting the galvanizing coating on the thread to pressure directed and gauged to remove irregularities therefrom and to compact and smooth the coating and accurately shape and size the galvanized thread to an ideal for proper working clearance and screwing and unscrewing cooperation with a complementary thread.

9. The method of treating a metal coated screw thread to produce a continuous permanent wearresisting and moisture-excluding coating over the thread, comprising subjecting the metallic coating on the thread to wiping pressure advanced along the thread and progressively advanced depthwise of the thread to remove irregularities from the coating and render it smoothand dense, and gauging the advance of said pressure depthwise of the coating to accurately shape and size the coated thread to an ideal for proper working clearance and screwing and unscrewing cooperation with a complementary thread.

10. The method of treating a galvanized screw threaded article to produce a continuous permanent wear-resisting and corrosion-preventing coating over the thread surfaces, comprising subjccting the coating on the thread surfaces to a wiping pressure advanced along the helical path of the thread and progressively advanced depthwise of the coating to remove irregularities from the coating and smooth and burnish it, and gauging the advance of said pressure depthwise of the coating to shape and size the galvanized thread to an ideal for proper working clearance and screwing and unscrewing cooperation with a complementary thread.

11. The method of producing a galvanized screw thread, comprising forming a basic screw thread with its surfaces set back below normal a depth. corresponding to an ideal thickness of a galvanizing coating, applying a coating of galvanizing material to said thread surfaces, and treating said coating to produce a continuous permanent wear-resisting and corrosion-preventing surface over the screw thread by subjecting the coating to pressure directed and gauged to remove irregularities and to smooth and compress the coating and shape and size the galvanized thread to an ideal for Working clearance and screwing and unscrewing cooperation with a complementary thread.

12. The method of producing a galvanized screw thread shaped and sized to an ideal for working clearance and screwing and unscrewing cooperation with a complementary thread, comprising providing a basic screw thread with its surfaces set back below normal a depth corresponding to an ideal thickness of a galvanizing coating and with a coating of galvanizing material on said surfaces, and treating said coating on the basic thread surfaces by subjecting the coating to pressure directed and gauged to remove irregularities from the coating and smooth and compress it to an even continuous permanent wear-resisting and corrosion-preventing condition and shape and size the galvanized thread to said ideal for working cooperation with a complementary thread.

13. The method of producing a galvanized screw thread shaped and sized to an ideal for working clearance and screwing and unscrewing cooperation with a complementary thread, comprising providing a basic thread with its surfaces set back below normal a depth corresponding to an ideal thickness for a galvanizing coating and with a coating of galvanizing material over said surfaces, and treating said coating on the basic thread surfaces by subjecting the coating to wiping pressure advanced helically along the thread and advanced progressively depthwise of the thread to remove irregularities from the coating and smooth compress and burnish the coating to an even continuous permanent wear-resisting and corrosion-preventing condition, and gauging the advance of said pressure depthwise of the coating to shape and size the galvanized thread to said ideal for cooperation with a complementary thread.

14. The method of treating a galvanized screw thread to produce a continuous permanent wearresisting and corrosion-preventing coating over the thread, comprising displacing irregularities and reducing excess thickness of the galvanizing coating by relatively advancing helically along the galvanized thread a length of another screw thread with its thread rib tapered helically in the direction of said advance to gradually reduce

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