US2193357A - Investment ring - Google Patents

Description

March 12, 1940. s, H.

. INVESTMENT [RING Filed April 8, 1938 Patented Mar. 12, 1940 UNiTED STATE OFEQE 2 Claims.

This invention, an expansible investment ring, is primarily designed for casting removable bridges for artificial dentures, and the improvement in this invention resides in the expansible feature which obviates breakage of the ring through the medium of contraction caused by sudden cooling of the ring relative to the investment, when removed from the furnace.

In the usual process of casting removable W bridges, the working model of the denture has the bridge formed in wax thereon together with necessary gates, and is placed in a non-expansible ring and invested in the ring, after which the assembly is placed in a furnace and heated to about 1600 C., which burns out all of the wax, leaving a mold of the bridge with its gates and vents.

When this type of investment ring is removed from the furnace and placed in the centrifugal 20 casting machine and centrifuged, the investment ring cools very quickly while the investment remains at a very high temperature, therefore the ring contracts about the substantially non-contracting investment. The result is that the ring I 25 usually breaks and is then unfit for further use.

This invention provides an investment ring which can be used repeatedly, since the ring may be eased up as soon as the investment has set, or when it is taken from the furnace; and after easing up, contraction due to cooling will not cause the ring to break, since the allowance for expansion compensates fully for the difference in contraction between the ring and its investment.

Although this ring is specifically designed for 3.3 dental casting processes, it can be used to advantage for other casting processes.

The main object of the invention therefore, is to provide an investment ring with means to compensate for unlike contraction between the ring and its investment.

Another object of the invention is to provide an investment ring with an eccentric connecting pin or pintle which may be removed at will for removing the investment, or eased up to com- 45 pensate for thermal contraction about an investment which has not contracted, whereby the breaking of the investment ring under tensional stresses is obviated.

In describing the invention, reference will be 50 had to the accompanying drawing of which:

Fig. l is a plan view of the invention showing in dotted lines a built-up Working model in position for investing.

Fig. 2 is a front elevation of Fig. l.

55 Fig. 3 is a section taken on line 3-3 of Fig. 1.

Fig. 4 is a fragmentary view taken on line 4-4 of Fig. 1.

The investment ring in its usual form consists of a ring Hl terminating at its ends II and I2 7 in a suitable releasable connection, using a pin, 5* sleeve, or other means to connect the ends, the

ring having a clasp is for attachment to a cen,

trifugal casting machine arm, (not shown).

This invention incorporates the structure just described, but is modified in the connecting means 10' by the provision of means for positively releasing the tension to an exact degree after the investment has set, to prevent breaking of the ring due to unequal expansion and'contraction between the ring and its invesement during heating and cooling of the assembly, while maintaining a diameter suitably supporting the investment.

This improvement is illustrated as consisting of the pintle sleeves it and iii formed on one terminal end of the ring indicated at l2, and an interposed pintle sleeve Ni formed on the other terminal H, the portions ll and [8 of the terminal end ll interlapping within the terminal end l2 as shown.

The pintle sleeves M, 15 and It all have the same inside diameter, although they could be made to vary and still produce the same result so long as the pintle could be removed at will.

The pintle consists of a straight rod bent at right angles to form a combined grip and lever arm i9, and this pin is eoc-entrically turned to a smaller diameter at 2! where it acts within the pintle sleeve l6, whereby, when the arm 19 is in one position, the eccentric 2| permits the ring to be expanded to an exact predetermined degree as shown in Fig. 2, and when turned to its other position, it retains the ring against expansion from its normal investing diameter.

Since the sleeves all have the same diameter, and no part of the eccentric projects diametri- 40 cally beyond the main portion of the rod, the pintle may be readily removed for opening the ring for removing the investment in the usual manner.

It is well known that eccentrics have been used for many purposes, however, this eccentric functions in a new way and provides a different result and one which has not been previously applied to investment rings. It limits the physical expansion of the ring to a degree only sufficient to compensate for difierence in thermal contraction between the ring and its investment, while still locking the ring to provide supporting means for the investment.

In the process of making the investment and casting the bridge, the pintle is inserted through the pintle sleeves and turned to the position shown dotted at 22, retaining the ring in its normal investing position.

The model 23, suitably built up with wax for bridge, gates and vents, is placed Within the ring and the ring filled with investing material, which is allowed to suitably set, after which the ring with its investment is placed in a furnace and heated to a temperature of about 1600 centigrade.

The pintle arm 19 may be turned to position l9 before placing the investment with its ring in the furnace, or, immediately upon removal from the furnace. This adjustment through eccentric 2| eases up the connection and permits the ring to open an amount equal to the eccentricity of the pintle, and prevents excess opening of the ring to maintain support for the investment.

After the ring with its investment has been removed from the furnace, the ring obviously cools very quickly while the investment cools slowly, therefore there is unequal contraction creating a tension on the ring when not eased up as just outlined.

Since the ring has been eased up through the agency of the eccentric sufficiently to allow contraction of the ring without acting on the investment, no strain is set up in the ring while all of the element of support is maintained, the amount of easing being fixed and non-variable.

The ring with its investment is placed in the centrifugal casting machine, (not shown), the metal poured and centrifuged, after which the pintle is removed through the medium of the grip 19, the ring manually expanded, and the investment removed and broken away from the casting.

It will be noted that the rivet heads 24 and the intermediary space between the interlapping members I! and i8 secure the investment in the ring during centrifuging while the connection is eased up.

Thus, a releasable, contraction-compensating joint is provided for an investment ring.

Having described an operative device and method of casting removable bridges and other types of castings, it will be understood that variations in construction and arrangement of parts, which variations are consistent with the appended claims may be resorted to without detracting from the spirit or scope of the invention, or sacrificing any of the advantages thereof.

I claim:

1. An investment ring having inter-lapping and terminal ends forming anchorage means for an investment and pintle sleeves of equal diameter formed on the respective terminal ends, and a pintle removable at will and adjustable to two positions and having a main body diameter rotatably fitting within the sleeves of one terminal end, and an eccentric portion of lesser diameter and entirely confined within the diametral limits of the body portion and operating within the sleeve of the other terminal end, and a lever arm integral with said pintle for adjustment and removal thereof at will.

2. An investment ring having interlapping terminal ends forming investment retaining means, and, pintle sleeves of equal diameter; rivet heads diametrically located relative to said terminal ends and forming additional retaining means; a pintle having a main portion fitting the pintle sleeves for one terminal end, and an intermediate portion of smaller diameter operating in the pintle sleeves for the other terminal end and having a clearance therein substantially equal to the contractual difference between the investment and the ring while maintaining association between the retaining means and the investment; said pintle being completely removable at will to permit excessive expansion of the ring to facilitate removal of the ring from the investment.

AUGUST S. GRETH.

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