US3337668A - Process of producing spark plug insulators by dry pressing - Google Patents

Description

g- 1967 K. MdHLE: 3,337,668

PROCESS OF PRODUCING SPARK PLUG INSULATORS BY DRY PRESSING Filed Feb. 15, 1965 4 Sheets-Sheet 1 Fig. 8

INVEIYTOR. KARL MOHLE BY @wd h ATTORNEY.

Aug. 22, 1967 RS BY DRY PRESSING Filed Feb. 15, 1965 4 Sheets-Sheet 2 Fig.4-

' INVENTOR.

KARL MHLE BY g 2 (M ATTORNEY.

Aug. 22, 1967 K. MHLE 3,337,668

PROCESS OF PRODUCING SPARK PLUG INSULATORS BY DRY PRESSING Filed Feb. 15, 1965 1 4 Sheets-Sheet INVENTOR. KARL MOHLE ATTORNEY.

Aug. 22, 1967 K. MC DHLE 3,337,668

PROCESS OF PRODUCING SPARK PLUG INSULATORS BY DRY PRESSI Filed Feb. 15, 1965 4 Sheets-Sheet 4 mvErgToR. KARL MOHLE ATTORNEY.

United States Patent 3,337,668 PROCESS OF PRODUCING SPARK PLUG INSULATORS BY DRY PRESSIING Karl Miihle, Lndwigsburg, Germany, assignor to Eel-u- Werk Albert Ruprecht, Ludwigsburg, Germany Filed Feb. 15, 1965, Ser. No. 432,683 Claims priority, application Germany, Feb. 13, 1964, R 75,410 1 Claim. ((Il. 264-120) This invention relates to a process for the preparation of blanks for spark plug insulators by dry pressing compositions mainly comprising metal oxides, such as alumina or mixtures of various metal oxidese.g., Al O +Cr O These oxide ceramics, which are known per se, can have admixtures of fluxes, parting compounds and binders in conventional proportions. The dimensional tolerances of the insulator, since they affect the heat value of the spark plug, must be very close, and dry pressing, in which there is no shrinkage during drying, has seemed to be an ideal technique for meeting this requirement; there have therefore been many endeavours to produce spark plug insulators by such dry pressing. The term dry pressing in this context refers to the processing of compositions having moisture contents of preferably below 0.8%%a value which is too low for the applied pressure to be spread evenly by hydraulic propagation. It is therefore difficult to press such compositions, even with an addition of conventional parting compounds, binders and the like. 1

Another difficulty with spark plug insulators is that the insulator cross-section varies at the base, at the collar and at the stem or shank; also, there is a continuous and, as a rule, stepped bore extending lengthwise of the insulator. Previous endeavours have therefore been limited merely to pressing a blank of simple shape which is then turned or ground to the finished shape of the unfired insulator.

Such conventional process, however, is complicated and expensive and leads unavoidably to large wastage by breakage. The machining leads to a considerable waste of material which must be given complicated and costly further preparation before being suitable for re-use.

To obviate these disadvantages, it is an object of the invention to teach ways and means for producing readyto-fire pressed blanks of spark plug insulators from difficult-to-press oxide ceramics of the kind specified to which conventional parting compounds and binders have been added, with the use of a simple tool and commercially available automatic presses for making dry pressings.

My early endeavours to relate the procedure normally used with dry powder automatic presses to the preparation of spark plug insulators were unsatisfactory. For improved charging of the mould, it is conventional to boost charging by suction resulting from the relative movement between the pressing sleeve and the bottom ram. To use this feature in the case of long blanks formed with a continuous bore, such as spark plug insulators, a pressing needle used to pierce the bore in the blank had to be withdrawn downwardly through the bottom ram, in order that the prepared blank could be removed and the filling shoe could be moved over the charging aperture in the pressing sleeve. The pressing needles and bottom rams required for this purpose are long and diflicult to manufacture; also, elaborate actuation must be provided. To simplify manufacture of the pressing sleeve, the same is, conventionally, subdivided into an outer sleeve part, which determines collar diameter, and an inner sleeve part, which is pushed into the outer sleeve part and determines the diameter of the stem or shank of the insulator. The disadvantage of this design is that the inner sleeve part has too slight a wall thickness to be made of a metal faced with a sintered metal carbide, as would be desirable to ensure ready removal from the mould, reduced tool wear and reduced wall friction. The step, conventional with forming blanks of this kind for purposes of making the compression more uniform, comprising subdividing the top ram into a number of component rams, disposed like sleeves, one in another, makes it necessary to use complicated and easily disturbed actuating elements and precludes the use of such metal for the various component ram-s.

A-ll early endeavours to use conventional tools in the preparation of mouldings of the kind specified led to a very high fault rate, to heavy wear of the pressing tool and to a high rejection rate.

The invention obviates the disadvantages of the procedures hereinbefore described. According to the invention, a ceramic composition is introduced into a filling chamber of a pressing tool comprising a bottom ram, a pressing needle rigidly connected thereto, a pressing sleeve, and a top ram which can be unitary or may comprise a number of coacting parts not adapted for movement one in another, wherewith the ceramic composition is pressed to form the finished blank, whereafter the same is removed from the pressing tool by being pulled off the stationary pressing needle.

For a better understanding of the invention and to show how the same may be carried into effect, reference may now be made to the accompanying drawings wherein:

FIG. 1 is a sectioned view of an embodiment of a spark plug insulator blank prepared in accordance with the invention, and

FIGS. 2-9 diagrammatically show the various steps and motions performed by the pressing tool and associated means-Le, the means for introducing the composition and for removing the finish pressed blank-during the preparation of the blank shown in FIG. 1.

FIG. 1 shows a blank 10 which will subsequently form an insulator. The blank 10 comprises a base or foot 1, a collar 2 and a stem or shank 3. The blank 10 may be formed with a stepped bore 4 which, after the insulator has been fired, will receive a central electrode of a spark plug.

FIG. 2 shows a ceramic composition being introduced into a mould. A filling shoe 8 is moved from the right upon a table 7 which is flush with a pressing sleeve 6 when the same is in its top position, the shoe being disposed between the sleeve 6 and a top ram 5 which is also shown in its top position. Simultaneously, a take-up or receiving element 9, connected to the shoe 8, has placed the blank 10 last produced on a conveyor belt 11 for conveyance thereon to the left. A granular ceramic composition drops by free fall into filling chamber 14 of the sleeve 6 from the shoe 8, the same communicating via a flexible line 12 with some form of supply (not shown).

(not shown) of a surfaced metal; a pressing needle 16 which pierces the bore or passage 4 in the blank is rigidly secured to the bottom ram 15. As indicated by hatching 17, the bottom ram is secured to an automatic press and does not normally move. The filling chamber 14 of the sleeve 6 is of a size and design such as to receive, when the shoe 8 is moved over it, the quantity of granular ceramic required to produce the blank 10. A cylindrical portion of diameter D corresponds to the diameter of the collar 2 of the blank 10 in FIG. 1, and a step 18 corresponds to a shoulder 2 of the collar 2. The top ram 5 is formed with a hollow interior 19 which in shape matches the base 1 of the blank 10.

FIG. 3 shows the position of the tool shortly before the start of pressing. Upon termination of the charging step described with reference to FIG. 2, the shoe 8 and element 9 move to the right into the position shown in FIG. 3. As is conventional in the movement cycle of automatic presses, the sleeve initially stays in its top position while the top ram 5 descends, as indicated by an arrow A. In the position shown, the top ram 5 has come close enough to the sleeve as just to start to enter the cylindrical zone of diameter D. As the ram 5 penetrates farther into the latter zone, some of the ceramic therein is displaced into the hollow interior 19 of the top ram 5; a pin 21 biased by a spring prevents granular material from entering a passage 22 which serves to guide the pin 21.

When the top ram 5 has penetrated so far into the sleeve 6 as to be at a distance corresponding to the length or height of the collar 2 (FIG. 1) from the step 18 (as indicated by chain-dotted lines in FIG. 3), compression of the trapped ceramic continues because the sleeve 6 as well as the top ram 5 descend towards the rigid bottom ram 15, as indicated by arrows B and C in FIG. 4. The sleeve 6 can lead on the top ram 5 during this descent in manner known per se, so that more particularly the base part and collar part of the blank are given an extra or subsequent pressing by the top ram 5 near the end of the pressing step. Near the end of the descent, apex 23 of the needle 16 abuts the pin 21, the needle 16 engaging in a conical central passage (not shown) in the pin 21 and forcing the same back against the spring 20 into a position which is shown in FIG. 4 and which represents the termination of the pressing step.

In order that the finish pressed blank 10 may be removed, the top ram 5 disengages from the blank 10 and, as indicated by an arrow D in FIG. 5, returns to its top position, and the sleeve 6 descends, in the direction indicated by an arrow C in FIG. 5, at least far enough for a shoulder 24 of the bottom ram 15 to be disposed a little above the table 7. Then, and as FIG. 6 shows, the element 9 moves to the right, as indicated by an arrow B, and its two padded edges 25 engage below the shoulder 2 of the blank 10. The plan view forming FIG. 7 shows this position of the element 9, the same being articulated to the shoe 8.

The blank 10 is then disengaged from the bottom ram 15 and pressing needle because the sleeve 6 and element 9 rise, as indicated by an arrow F in FIG. 8., into the top position visible therein.

Once the blank has left the needle 16, the shoe 8 starts to return to the left into the filling position, Also, the blank 10 removed from the pressing tool is placed on the conveyor belt 11 in the manner visible in FIG. 2, which shows the same position as FIG. 9.

The main difference between the pressing process according to the invention and the prior art procedures for comparable hollow objects prepared in automatic presses is that the pressing needle does not, in the process according to the invention, have to be withdrawn downwardly through a moving bottom ram; instead, the blank 10 is withdrawn upwardly and off the stationary bottom 15 and stationary pressing needle 16. The movement cycle of automatic presses permits this difference because, in the process according to the invention, no use is made, during filling, of the suction effect associated with the descent, in conventional processes, of the bottom ram; as already stated, filling is by the free fall of the ceramic material. For a given size of filling chamber 14, filling takes longer than in conventional processes-Le, the automatic must run slower-but the other disadvantages mentioned are obviated. The bottom ram need not be hollow in order to receive and guide the moving pressing needle, which is long and tends to jam. When the bottom ram 15 is a stationary element, the pressing needle 16 rigidly connected thereto is not much longer than the blank 10 and can be made of a surfaced metal without the likelihood of being damaged by buckling or other forces.

Indeed, the bottom ram 15 and the pressing needle 16 can be a unitary member made of a surfaced metal. Since the sleeve 6 and top ram 5 are not delicate sleeves disposed one in another, they too can be made of a surfaced metal, and the granular charge contacts only a surfaced metal during pressing. Being so very hard, a surfaced metal wears very well and can be machined so smooth that the ceramic-Le, the blankdoes not stick to the surfaces of the pressing tool and wall friction is reduced very considerably. Consequently, the pressure applied by the pressing tool is dissipated less than previously by wall friction and performs more useful work in compressing the ceramic filling.

The combined effect of the various steps hereinbefore described is to provide a manufacturing process Which has a very reduced likelihood of disturbances and which leads to satisfactorily pressed blanks having smooth surfaces and very close dimensional tolerances. In contrast to inulator blanks in which thermoplastics or other plastics are used as binders, there is no risk with the blank according to the invention of unwanted changes in shape occurring during firing or of cracks occurring due to an intense evolution of gas in the heat of firing.

The omission of the complex system required in conventional apparatuses for pressing needle actuation greatly reduces the space required and thus enables the pressing automatic to receive more pressing tools than previously, with the result, despite the speed reduction caused by the filling operation, of increased output.

I claim:

A process for preparing a spark plug insulator blank by .dry pressing a powdered ceramic composition mainly comprising metal oxides, comprising the steps of:

introducing suflicient powdered ceramic composition into a filling chamber to fill said chamber of a pressing tool comprising a stationary bottom ram having a pressing needle rigidly secured thereto and extending upwardly into said filling chamber and,

a movable pressing sleeve having upper and lower portions;

a movable table,

and a movable upper ram having a recessed chamber therein and a movable spring-loaded plunger mounted centrally within said recessed chamber within the upper ram, and a removal means for taking otf the prepared blank; moving the upper ram downwardly from an upper position into the upper portion of the pressing sleeve located in an upper position relative to the bottom ram, 7 r

and with the pressing needle positioned in the lower portion of said pressing sleeve;

movement of said upper ram into said sleeve causing compaction of the powder composition to fill the recessed chamber of the upper ram,

while the spring load on said plunger therein resists movement thereof from the force of the compacted powder within;

continued downward movement of said upper ram in fixed relationship with said sleeve and said table in unison to cause the pressing needle to centrally pierce the compacted powder composition to form a central aperture within the blank in the relative movement of the pressing needle from the lower position of the sleeve to the upper position of the sleeve and thereafter cause the needle to contact and displace the upper ram plunger against the force of the spring therein,

the upper ram shaping an upper part of the blank and the pressing sleeve shaping the lower portion with a shoulder on the blank, disengaging the upper ram from the blank raising the upper ram and moving the pressing sleeve and movable table further downwardly with respect to the bottom ram for bringing the pressed blank above the movable table,

introducing the removal means to seize the blank, raising the pressing sleeve and table and removal means and blank clear of the bottom ram and needle,

and removing the blank by the removal means.

References Cited UNITED STATES PATENTS 15 ROBERT F. WHITE, Primary Examiner.

.T. R. HALL, Assistant Examiner.

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